# Thread: Is the speed of light really a constant?

1. Originally Posted by Dywyddyr
Originally Posted by ScienceNoob
Positrons and Electrons are far form virtual, so I will just ignore that you even said that.
You don't even know what a virtual particle is?
You're dumber than I thought.

Yes I made a large mistake, in referring to Noether as a man, but like I said I don't know what she said, or want to speak for her so I didn't make any false claims.
And you were so arrogant (and willing to hang on to your ignorance) that you didn't bother to look.
And you "didn't want to speak for her (or make any false claims)" but you had no hesitation at all in flatly declaring that "what [s]he said then he is WRONG".

Also we measure the distance to galaxies by brightness not with a measuring stick.
This is how we can calculate the difference in values between what used to be expected for that distance.
Hope this helped.
And we see that brightness because of...?
Oh wait. It wouldn't be the arrival of photons, would it?
So, we know how far away it is before it explodes.
How do we get a time of explosion?
By seeing the photons of that explosion arrive where we are.
So no, it didn't help. (Except to further illustrate your cluelessness).
I now know more about virtual particles thanks for clarification.

You bring up a good point about the time of explosion.

Perhaps a method would be if gravitational waves don't receive this same effect yet travel at the speed of light.

We could measure the change in gravity at the speed of light and when we see the explosion the delta will be the delay due to vacuum polarization.

Although I am sure there are better methods of measuring this.

2. You've now had to admit your very limited knowledge/understanding in a number of threads where you have arrogantly posted bullshit from a position of ignorance and been called on it. Here's a tip, you'll get much more out of the forums if you admit your ignorance to yourself and ask questions rather than posting the bullshit. Just saying...

3. Seems to me that if one has a radicle opinion regarding a core concept like the speed of light, then one needs to be presenting experimental evidence to invalidate the currently held opinion. Or at the very least detailing how such an experiment might be preformed. This is a serious area for study. We would all love to have someone start work toward a Faster than Light space drive.

4. Originally Posted by ScienceNoob
I now know more about virtual particles thanks for clarification.
Yet the fact that you wrote
Originally Posted by ScienceNoob
Positrons and Electrons are far form virtual, so I will just ignore that you even said that.
shows the depths of your ignorance.
(And saying you "now know more" implies - falsely - that you knew something about them in the first place. This is shown to be a lie by the quoted statement).

You bring up a good point about the time of explosion.
Perhaps a method would be if gravitational waves don't receive this same effect yet travel at the speed of light.
Uh what?
A) Gravity travels at the speed of light but it arrives faster than light?
B) As of early 2014, no direct detection of gravitational waves has been accomplished. (So feel free to make up more bullcrap).
C) A spherical mass explodes into a spherical "burst" of the same mass. How's that affect gravity?

We could measure the change in gravity at the speed of light and when we see the explosion the delta will be the delay due to vacuum polarization.
Or, gravity somehow moves faster, or elves did it. YOU DON'T KNOW.
You have ZERO support (you still haven't responded to my points about the original paper - it's not taken seriously by science as far as I can tell).

Although I am sure there are better methods of measuring this.
Yeah.
The thing is, the less you know about anything the more sure you are.
And then you have to spend time backtracking when someone gives you a link to basic sh*t that you should already know like the back of your hand if you expect to be taken seriously.

5. Originally Posted by tk421
Originally Posted by bangstrom
That is, unfortunately, all too evident. It's preventing you from learning.
I take criticism such as this seriously because it is a frequent occurrence for someone to be so sure of their own convictions that they are blind to any contrary evidence no matter how convincing the evidence may be. Take the evolution controversy for example.

If I fall into that category, then this is something I need to work on, so could you or anyone else give me an example of some understanding that I have failed to grasp. This may be a dangerous question.

On the the other hand, there is such as "the cat calling the kettle black." You said you joined in late so I wrote a brief outline of some of the major points that were discussed earlier but, in this post, you have failed to demonstrate any understanding of what I wrote or what has transpired earlier in the thread. You may know your stuff and, from what you have written, I would guess we are on the same page as far as the physics is concerned but you appear to be confused about about who said what earlier in the thread, what claims were made, or what the discussions were about.

I can give you a pass on this because this thread has involved too much confusion and more heat than light (at any speed) to expect expect anyone to keep up. My summary of the thread included both my views as a minority and my summary of the more popular views contrary to mine. You appear to have totally confused the two and begin to claim I was wrong when the "wrong" views were not mine at all.

Here is one example that causes me to question you judgment. Much earlier in the thread there was a debate about whether or not one could count cycles and convert cycles into seconds. There is a Catch 22 here because, how can you count seconds before you have determined the duration of a second? Some claimed that can't simply be done and the definition is flawed because it uses seconds to define seconds.

My position is that you can convert cycles to seconds because we have a conversion factor. Just divide cycles by 9,192,631,770 Hz and we are done. We have a workable definition of a second that is complete and there is no need contemplate the apparent paradoxes because there are none.

How can you claim that this a complication or that I am rejecting the definition of a second. That is not my position and I have stated my position several times in the thread and in my summary that you have apparently failed to understand.

RedPanda" offered to demonstrate how I was "wrong" in my counting of cycles and determining seconds before we knew the duration of a second and I appreciate his effort because this is a good way to resolve a debate

The debate continued as a long series of back and forth Q and A's that occupied a good length of the thread and this was the point you joined. Our debate continued a while longer and appeared to be progressing but it had not yet been resolved.

I mentioned that the debate about the conversion factor was continuing and I knew for sure it would because that was to be the topic of my next post.

Now here is where your initial impression appears to have clouded your view to the point where you got everything totally backward and you even missed the point that the debate about the conversion factor was in the thread. No wonder you can't make sense of it.

Originally Posted by tk421
The debate over the conversion factor continues.
Only in your mind, apparently. I'm sorry that I cannot help you. You are stuck on a trivial point, apparently because you have some other agenda that somehow requires the fabrication of this complication. But it is solely of your own making.

The second is defined as it is. Its definition could hardly be more clear. That you refuse -- not merely fail -- to grasp it is not something that I or anyone else can fix, apparently. The problem is entirely in your head. You will have to make a choice to get unstuck. Until then, I'm done. I'm happy to educate anyone who is interested in it, but I have learned to avoid those who actively reject knowledge for one reason or another. That seems to be the case here, regrettably.

6. Originally Posted by bangstrom
If I fall into that category
You do.
It's been pointed out numerous times.

so could you or anyone else give me an example of some understanding that I have failed to grasp
This too has been done numerous times.

There is a Catch 22 here because, how can you count seconds before you have determined the duration of a second?
Because, as has ALSO been pointed out: we don't count cycles per second. We count cycles and THEN define that count to have taken a second.

My position is that you can convert cycles to seconds because we have a conversion factor. Just divide cycles by 9,192,631,770 Hz and we are done. We have a workable definition of a second that is complete and there is no need contemplate the apparent paradoxes because there are none.
Crap.
Your "workable definition" is entirely self-referential and therefore useless as a definition.

How can you claim that this a complication or that I am rejecting the definition of a second.
And this is exactly what you're failing to understand.

Ignore list for the crackpot.

7. Originally Posted by bangstrom
If I fall into that category, then this is something I need to work on, so could you or anyone else give me an example of some understanding that I have failed to grasp.
I have suspected that your inability to answer simple questions is indication of some kind of cognitive dissonance.

If I was to ask a simple question e.g.
"If I have an apple and someone gives me another apple - how many apples do I have?"
you would answer with something like
"If I ate the apples I'd have none."

And if I said
"Wouldn't it be 2 apples?"
you would reply with something like
"It wouldn't be two apples if someone gave you an orange instead."

It is not that avoid the question, per se.
It is more like you avoid the answer.

8. Originally Posted by Dywyddyr
Because, as has ALSO been pointed out: we don't count cycles per second. We count cycles and THEN define that count to have taken a second.
I asked if anyone could give me an example of where my stubbornness about conversion factors has prevented me from understanding the issue and you have just given me one. It is a good example because, if this could be understood, it would clear up about half of the confusion prior to this point.

You said, "Because, as has ALSO been pointed out: we don't count cycles per second. We count cycles and THEN define that count to have taken a second."

I admit I don't understand this so could you explain how counting cycles is any different from counting in fractions of a second with each cycle being a fraction of a second?

I don't understand why we must define a second before we can count seconds because the duration of a second has already been defined by international convention and we have a conversion factor to convert cycles to seconds or seconds to cycles. So there is no need to do redefine a second. It has already been done.

Here is the issue as I see it.

Every cycle in a uniform signal has an interval of time called a "period" and the period lies on a greater continuum time intervals. So starting with the period of a cycle, it works like this.

Period, second, minute, hour, day, year, and on and on. The continuum can be added to or extended in either direction to fit our needs.

We also have conversion factors for each step of the continuum so, when we count any one of the intervals, we are simultaneously counting them all. When we count in seconds we are also counting in units of 1/60 minutes. We know there are 60 seconds in a minute, and 9,192,631,770 cycles in one second of a caesium gismo.

I don't know why I even have to explain this.

9. Originally Posted by RedPanda
I have suspected that your inability to answer simple questions is indication of some kind of cognitive dissonance.

If I was to ask a simple question e.g.
"If I have an apple and someone gives me another apple - how many apples do I have?"
you would answer with something like
"If I ate the apples I'd have none."

It is not that avoid the question, per se.
It is more like you avoid the answer.
If you have a problem with any of my answers, run the question by me again and I will answer it straight up.

10. Originally Posted by bangstrom
Originally Posted by RedPanda
It is not that avoid the question, per se.
It is more like you avoid the answer.
If you have a problem with any of my answers, run the question by me again and I will answer it straight up.
Firstly, I was pointing out that I repeatedly have problems with your answers because I have had to run the same questions by you multiple times.
Telling me to ask the questions again does not solve the problem of me having to ask the same questions repeatedly - it makes it worse.

Do you not believe me? Are you not able to recognise that behaviour in your postings? I expect not.

(It's the one where I have had to repeat the same question a 3rd time.)

11. Originally Posted by RedPanda
Originally Posted by bangstrom
Originally Posted by RedPanda
It is not that avoid the question, per se.
It is more like you avoid the answer.
If you have a problem with any of my answers, run the question by me again and I will answer it straight up.
Firstly, I was pointing out that I repeatedly have problems with your answers because I have had to run the same questions by you multiple times.
Telling me to ask the questions again does not solve the problem of me having to ask the same questions repeatedly - it makes it worse.

Do you not believe me? Are you not able to recognise that behaviour in your postings? I expect not.

(It's the one where I have had to repeat the same question a 3rd time.)
If you don't like my answers then explain why not and I will deal with that. You are right that if you keep asking the same question you can expect the same answer. You keep asking the same questions so which third timer do you have in mind.

12. Originally Posted by bangstrom
You are right that if you keep asking the same question you can expect the same answer.
Where did I say that?
You don't give the same answers - you wriggle and squirm to avoid answering them.
Much like you are doing now.

13. Originally Posted by RedPanda
Originally Posted by bangstrom
You are right that if you keep asking the same question you can expect the same answer.
Where did I say that?
You don't give the same answers - you wriggle and squirm to avoid answering them.
Much like you are doing now.
I didn't say you said that but you keep asking the same questions and I give you the same answer or a slight rephrasing of the same.
Do you have a question or not?

14. Dftft

15. Originally Posted by bangstrom
Originally Posted by RedPanda
Originally Posted by bangstrom
You are right that if you keep asking the same question you can expect the same answer.
Where did I say that?
You don't give the same answers - you wriggle and squirm to avoid answering them.
Much like you are doing now.
I didn't say you said that
Is English not your first language?
"You are right": for you to agree with me, I would have had to have said what you are agreeing with.
It is no wonder that you can't understand scientific definitions, since even basic English is beyond your grasp.

Originally Posted by bangstrom
but you keep asking the same questions and I give you the same answer or a slight rephrasing of the same.
Yes - but if you had bothered to read what I wrote you would know that you weren't answering the questions I asked.
You were making up your own questions because they were easier to answer.

Originally Posted by bangstrom
Do you have a question or not?
And now you are avoiding answering my questions by pretending you don't know what my questions are.
The questions are still there. They haven't disappeared.

The only reason I can think of for you not to answer them is because they show your claim is wrong.

Clearly, you would much rather look stupid than admit you are wrong.
Cognitive dissonance rules your world and no-one here will ever be able to get through your self-inflicted wall of ignorance and denial.
But you probably think you look like a really deep thinker, sitting there with your eyes closed, your fingers in your ears and repeating your "LA LA LA LA LA LA LA LA!! I CAN'T HEAR YOU!!!" mantra.

16. Originally Posted by RedPanda
You don't give the same answers - you wriggle and squirm to avoid answering them.

Is English not your first language?
"You are right": for you to agree with me, I would have had to have said what you are agreeing with.
It is no wonder that you can't understand scientific definitions, since even basic English is beyond your grasp.
Forgive my English.

I found a couple un-re-re-answered questions in post #90. The same post also contained my evasions of the original questions and, since they were evasive, I didn't find them worth repeating.

Q. "I'll repeat the question:I have just counted 9,192,631,770 cycles over an unknown length of time.
How many seconds did it take?"

A. The seconds are unknown because the number is only in cycles.

Q. "Do you agree that the number of seconds is unknown?"

A. Certainly. Does the Pope wear little red shoes?

I will be away from my yurk for a few days while I take my yak to the Kazakhstan fair. Here are some things you can consider before you reply to "my" answers.

If you look at your definition for a standard second it should be apparent that this can't be the only definition for a second. The definition is literally a microwave recipe for how to determine the duration of a second with a caesium gadget. That means there must be more than one definition for a second and more than one standard second because people had standard seconds long before they had caesium gadgets emitting microwaves.

There is nothing circular about using seconds to define seconds. Think of it as using old pre-microwave seconds to define caesium seconds. Caesium gadgets emit a radio frequency of 9,192,631,770 Hz. This is in cycles per second so to convert cycles to seconds you divide the number of cycles by the frequency. This is what the definition instructs you to do.

The duration of seconds in a single cycle of a caesium transition is one 1 / 9,192,631,770 seconds. This is the period of a caesium cycle in seconds. So, by counting cycles of caesium transitions, you are simultaneously counting seconds.

The value for c is defined as 299,792,458 m/s. This is a physical constant, giving us the distance an EM signal travels in one second. The length of a meter is defined as the distance light travels in 1/c seconds and the duration of a second is the time it takes light to travel 299,792,458 m. This last value is the more universal definition of a standard second and it is the principle behind the method for determining the duration of a second in cycles of caesium transitions.

17. Originally Posted by KJW
Originally Posted by RedPanda
Originally Posted by bangstrom
The length of a second is also pegged to the speed of light which makes the difficulty complete.
The length of a second is defined as:
"The duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom. This definition refers to a caesium atom at rest at a temperature of 0 K."
I am not sure where the speed of light comes into it.

Ask Farsight. It is something he has been saying recently on The Physics Forum.
I wish "Like" worked :-)

18. Originally Posted by ultimatesceptic
The speed of light was fixed in 1972, and the length of a metre was pegged to the speed of light. Therefore the speed of light (in metric) cannot vary, even though it does in fact fluctuate over time.

Is this true? I believe it is.
This is an interesting question. When one pays attention to your phrasing "fluctuate OVER TIME", one has to thing about the theory of "varying speed of light" of Moffat and Magueijo. Both of them are mainstream physicists (so this is not a crackpot theory) and Moffat is a larger than life one (Magueijo, less so).
Best I know, their theory has been refuted.

19. Originally Posted by bangstrom

Here is one example that causes me to question you judgment. Much earlier in the thread there was a debate about whether or not one could count cycles and convert cycles into seconds. There is a Catch 22 here because, how can you count seconds before you have determined the duration of a second? Some claimed that can't simply be done and the definition is flawed because it uses seconds to define seconds.

My position is that you can convert cycles to seconds because we have a conversion factor. Just divide cycles by 9,192,631,770 Hz and we are done. We have a workable definition of a second that is complete and there is no need contemplate the apparent paradoxes because there are none.

How can you claim that this a complication or that I am rejecting the definition of a second. That is not my position and I have stated my position several times in the thread and in my summary that you have apparently failed to understand.

The problem here is that you're ignoring the whole concept of "relativity". You're looking for an absolute definition of "a second" instead of a relative one.

In relativity, nothing is ever absolute. There is no "absolute second" nor can there ever be.

What we have instead is an established relationship between the time required for one event and another. We can, for example, compare the time it takes light to travel a certain distance (such as a "light year") against the time it takes the Earth to make one orbit around the Sun. Or we can measure the number of oscillations made by a subatomic or atomic particle. Stuff like that.

We don't expect to be able to notice it if all events were to uniformly slow down, though. If the time required for the Earth to make one orbit around the Sun were to get longer at the same time as the time required for a beam of light to travel one light year got longer - we couldn't detect that. But we know we couldn't detect that, so we don't bother with it.

If you are suggesting that we should bother with it, then you're throwing out Relativity. Relativity, simply stated, says there is no such thing as absolute speed, distance, or absolute time. It's not merely a matter that we don't what number to assign to those things. We don't think there is anything to know. They don't exist.

20. Originally Posted by bangstrom
there must be more than one definition for a second and more than one standard second because people had standard seconds long before they had caesium gadgets emitting microwaves.
There is only one definition of the second operating at any given time. Later definitions replace earlier definitions. It is true that the later definitions are based on the earlier definitions so that earlier work using the older definitions remain as valid as they once were, but once implemented, it is the new definition that is the definition, and the old definition is no longer the definition.

Originally Posted by bangstrom
There is nothing circular about using seconds to define seconds. Think of it as using old pre-microwave seconds to define caesium seconds.
I think you need to better consider what it means to be a definition (of anything).

Originally Posted by bangstrom
duration of a second is the time it takes light to travel 299,792,458 m. This last value is the more universal definition of a standard second
No. This is in no way the definition of the second.

21. Originally Posted by bangstrom
I found a couple un-re-re-answered questions in post #90. The same post also contained my evasions of the original questions and, since they were evasive, I didn't find them worth repeating.
Why be so evasive?

It is not my fault if you are unable to answer simply questions truthfully without undermining your own argument.
In fact, it should have made you realise you are doing something wrong when your argument requires you to be disingenuous.

But you still managed to avoid 2 of the questions:
Originally Posted by RedPanda
So, do you agree that the number of cycles provides no information about how long it took?
Simply counting the number of cycles provides no clue as to how long it takes, correct?

22. Originally Posted by kojax

The problem here is that you're ignoring the whole concept of "relativity". You're looking for an absolute definition of "a second" instead of a relative one.

In relativity, nothing is ever absolute. There is no "absolute second" nor can there ever be.

What we have instead is an established relationship between the time required for one event and another. We can, for example, compare the time it takes light to travel a certain distance (such as a "light year") against the time it takes the Earth to make one orbit around the Sun. Or we can measure the number of oscillations made by a subatomic or atomic particle. Stuff like that.

We don't expect to be able to notice it if all events were to uniformly slow down, though. If the time required for the Earth to make one orbit around the Sun were to get longer at the same time as the time required for a beam of light to travel one light year got longer - we couldn't detect that. But we know we couldn't detect that, so we don't bother with it.

If you are suggesting that we should bother with it, then you're throwing out Relativity. Relativity, simply stated, says there is no such thing as absolute speed, distance, or absolute time. It's not merely a matter that we don't what number to assign to those things. We don't think there is anything to know. They don't exist.
We have an absolute definition of a second and it is to be found in the value of c where c is in units of 299,792,458 m/s. Everything can then be measured relative to c.

The value of c may or may not be an absolute in the natural world but it is our absolute by definition and it serves as a starting point for defining units of measurement in terms of seconds and meters relative to the value of c.
If the speed of light were to slow, it would cause the Earth to orbit the sun more slowly by causing EVERYTHING to occur more slowly proportionate to the change in c so all of our clocks would also run slower.
Since everything would be changing uniformly, we would not be able to observe the change locally.

However, if the Earth were to orbit the sun more slowly while c remained the same, we would notice this change.

23. Originally Posted by RedPanda
Originally Posted by bangstrom
I found a couple un-re-re-answered questions in post #90. The same post also contained my evasions of the original questions and, since they were evasive, I didn't find them worth repeating.
Why be so evasive?

It is not my fault if you are unable to answer simply questions truthfully without undermining your own argument.
In fact, it should have made you realise you are doing something wrong when your argument requires you to be disingenuous.

But you still managed to avoid 2 of the questions:
Originally Posted by RedPanda
So, do you agree that the number of cycles provides no information about how long it took?
Simply counting the number of cycles provides no clue as to how long it takes, correct?
I was being sarcastic when I said my answers were evasive since you seemed so convinced that they were.

If we know the frequency of the cycles, we have all the info we need to deal with a count of cycles. We know the frequency of caesium transitions and it is 9,192,631,770 Hz.

Again and again, the answer to both of your questions is, NO.

24. Originally Posted by bangstrom
If we know the frequency of the cycles, we have all the info we need to deal with a count of cycles. We know the frequency of caesium transitions and it is 9,192,631,770 Hz.
And now we are back to where you went wrong.

The definition of a second is:
"The duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom."
(If you are using a different definition of a second, then you have moved away from the scientific consensus and are simply making up your own definitions that no-one else uses.)

That definition only requires that you count cycles, not seconds.
And each cycle is a single unit. They are not cycles per second but simply cycles.

Also, the length of time is unknown because the number is only in cycles.
Simply counting the number of cycles provides no clue as to how long it takes.

So, put simply, the definition of a second is 9,192,631,770 caesium cycles.
Cycles are just cycles: there is no mention of time or frequency.

At this point I would expect you to mention conversion factors.
You might say that you know that caesium transitions at 9,192,631,770 cycles per second.
You might say that caesium cycles have a frequency of 9,192,631,770 Hz giving you a conversion factor.
This conversion factor is needed to support your claim that the definition of a second is recursive and reliant on that frequency.

Q: But where did you get that conversion factor from?
A: You got it from the definition of a second.
The definition came first and your conversion factor is based upon it.
Without the definition, you have no conversion factor.

So, to claim that the definition of a second uses the frequency of caesium is putting the cart before the horse.
You do not have a frequency until after the definition of a second exists.

If you disagree, then please show how you established the conversion factor without using that pre-existing definition of a second.

25. Originally Posted by bangstrom
Originally Posted by RedPanda
Originally Posted by bangstrom
I found a couple un-re-re-answered questions in post #90. The same post also contained my evasions of the original questions and, since they were evasive, I didn't find them worth repeating.
Why be so evasive?

It is not my fault if you are unable to answer simply questions truthfully without undermining your own argument.
In fact, it should have made you realise you are doing something wrong when your argument requires you to be disingenuous.

But you still managed to avoid 2 of the questions:
Originally Posted by RedPanda
So, do you agree that the number of cycles provides no information about how long it took?
Simply counting the number of cycles provides no clue as to how long it takes, correct?
I was being sarcastic when I said my answers were evasive since you seemed so convinced that they were.

If we know the frequency of the cycles, we have all the info we need to deal with a count of cycles. We know the frequency of caesium transitions and it is 9,192,631,770 Hz.

Again and again, the answer to both of your questions is, NO.
This is silly. Counting the cycles is like counting the beats on a metronome that somebody else has set going, in the dark. All you need to do is count and then you can define for yourself a unit of time, as a certain number of beats of that metronome.

You do not need to see or measure anything at all - just count.

26. Originally Posted by bangstrom
Originally Posted by RedPanda
So, do you agree that the number of cycles provides no information about how long it took?
Simply counting the number of cycles provides no clue as to how long it takes, correct?
Again and again, the answer to both of your questions is, NO.
Are you saying that the number of cycles provides information about how long it took?
Are you saying that simply counting the number of cycles does tell you how long it takes?

This contradicts your earlier statements that the time taken for a particular number of cycles is unknown.

27. Originally Posted by bangstrom
Originally Posted by kojax

The problem here is that you're ignoring the whole concept of "relativity". You're looking for an absolute definition of "a second" instead of a relative one.

In relativity, nothing is ever absolute. There is no "absolute second" nor can there ever be.

What we have instead is an established relationship between the time required for one event and another. We can, for example, compare the time it takes light to travel a certain distance (such as a "light year") against the time it takes the Earth to make one orbit around the Sun. Or we can measure the number of oscillations made by a subatomic or atomic particle. Stuff like that.

We don't expect to be able to notice it if all events were to uniformly slow down, though. If the time required for the Earth to make one orbit around the Sun were to get longer at the same time as the time required for a beam of light to travel one light year got longer - we couldn't detect that. But we know we couldn't detect that, so we don't bother with it.

If you are suggesting that we should bother with it, then you're throwing out Relativity. Relativity, simply stated, says there is no such thing as absolute speed, distance, or absolute time. It's not merely a matter that we don't what number to assign to those things. We don't think there is anything to know. They don't exist.
We have an absolute definition of a second and it is to be found in the value of c where c is in units of 299,792,458 m/s. Everything can then be measured relative to c.

The value of c may or may not be an absolute in the natural world but it is our absolute by definition and it serves as a starting point for defining units of measurement in terms of seconds and meters relative to the value of c.
If the speed of light were to slow, it would cause the Earth to orbit the sun more slowly by causing EVERYTHING to occur more slowly proportionate to the change in c so all of our clocks would also run slower.
Since everything would be changing uniformly, we would not be able to observe the change locally.

However, if the Earth were to orbit the sun more slowly while c remained the same, we would notice this change.

Earlier in this thread you argued that if the speed of light did change, the time requirements for all other natural phenomena would change with it.

So the time it takes a Cesium atom to complete 9,192,631,770 cycles would still remain equal to the time it takes a photon of light to travel 299,792,458 meters.

Using a Cesium atom as a "second" allows us to establish a relative second, instead of an absolute one. That was probably the goal of using it.

And that, in turn, means that no, we do not have an "absolute" definition of a second. If you continue to insist that we have one, then you are just trying to set up a straw man.

28. Originally Posted by RedPanda
Q: But where did you get that conversion factor from?
A: You got it from the definition of a second.
The definition came first and your conversion factor is based upon it.
Without the definition, you have no conversion factor.

So, to claim that the definition of a second uses the frequency of caesium is putting the cart before the horse.
You do not have a frequency until after the definition of a second exists.

If you disagree, then please show how you established the conversion factor without using that pre-existing definition of a second.
The conversion factor is the frequency of the microwave signal emitted by a caesium clock (and it is a clock ). Do I need to show you the math... again?

If you know the frequency of a caesium clock, you know the value of the conversion factor and it works with any EM emission. Do I need to show you the math...again?

The "second" was defined years ago and people have been measuring EM frequencies in meters per second since the early days of radio in the time of Hertz, Armstrong, and Marconi.
The values we need to convert cycles of a caesium clock to seconds are given in the definition of a standard second or they can be found in reference books.
The whole purpose for the definition of a "standard" second is to enable someone with the proper equipment to determine the duration of a second locally without reference to a remote standard clock. It is for those who need a level of accuracy far beyond that which is normally required for scientific work.

29. Originally Posted by RedPanda
Originally Posted by bangstrom
Originally Posted by RedPanda
So, do you agree that the number of cycles provides no information about how long it took?
Simply counting the number of cycles provides no clue as to how long it takes, correct?
Again and again, the answer to both of your questions is, NO.
Are you saying that the number of cycles provides information about how long it took?
Are you saying that simply counting the number of cycles does tell you how long it takes?

This contradicts your earlier statements that the time taken for a particular number of cycles is unknown.
Which part of , "No." is unclear?

Counting cycles does provide information about how long it took. So, yes. Counting cycles gives us information about time.

Yes, counting cycles does tell you how long it takes but it may not be in units of seconds.

My statements about counting cycles not giving you the time were in response to questions asking if counting cycles gives you the time in "seconds."

The answer is, NO. Counting cycles of an unknown period does not give you time in seconds. But, you are still counting time in beats of a metronome or whatever form of cycles you are counting.

30. Originally Posted by kojax

Earlier in this thread you argued that if the speed of light did change, the time requirements for all other natural phenomena would change with it.

So the time it takes a Cesium atom to complete 9,192,631,770 cycles would still remain equal to the time it takes a photon of light to travel 299,792,458 meters.

Using a Cesium atom as a "second" allows us to establish a relative second, instead of an absolute one. That was probably the goal of using it.

And that, in turn, means that no, we do not have an "absolute" definition of a second. If you continue to insist that we have one, then you are just trying to set up a straw man.
A change in the speed of light would also change the rate of caesium transitions. The rate of a caesium clock is relative to c which is our "absolute" for the definition of a second. Just solve for seconds.

For practical purposes, a caesium clock is a convenient gadget for measuring the duration of a standard second with a high degree of accuracy. The "standard second" is as close as we can get to the "absolute" second which is found in the value of c.

31. An insistent crank.

32. Originally Posted by bangstrom
Counting cycles does provide information about how long it took. So, yes. Counting cycles gives us information about time.

Yes, counting cycles does tell you how long it takes but it may not be in units of seconds.
Ok - so how long would it take to count 36 beats and what unit of time are you using?

Originally Posted by bangstrom
The answer is, NO. Counting cycles of an unknown period does not give you time in seconds.
I agree.
Counting 9,192,631,770 cycles over an unknown period of time does not give you the time in seconds.
But that contradicts your earlier claim that the definition of a second is circular.

33. Originally Posted by bangstrom
Originally Posted by RedPanda
If you disagree, then please show how you established the conversion factor without using that pre-existing definition of a second.
The conversion factor is the frequency of the microwave signal emitted by a caesium clock (and it is a clock ). Do I need to show you the math... again?
That frequency is based on a pre-existing definition of a second.
I asked you to show me how you established the conversion factor without using that pre-existing definition of a second.
You have never provided that information - so you would not be showing me "the math" again.

Originally Posted by bangstrom
If you know the frequency of a caesium clock, you know the value of the conversion factor and it works with any EM emission. Do I need to show you the math...again?
That frequency is based on a pre-existing definition of a second.
I asked you to show me how you established the conversion factor without using that pre-existing definition of a second.

Originally Posted by bangstrom
The "second" was defined years ago and people have been measuring EM frequencies in meters per second since the early days of radio in the time of Hertz, Armstrong, and Marconi.
I asked you to show me how you established the conversion factor without using that pre-existing definition of a second.

Originally Posted by bangstrom
The values we need to convert cycles of a caesium clock to seconds are given in the definition of a standard second or they can be found in reference books.
I asked you to show me how you established the conversion factor without using that pre-existing definition of a second.

To summarise: I asked you to show me how you established the conversion factor without using that pre-existing definition of a second.

34. Originally Posted by bangstrom
Originally Posted by kojax

Earlier in this thread you argued that if the speed of light did change, the time requirements for all other natural phenomena would change with it.

So the time it takes a Cesium atom to complete 9,192,631,770 cycles would still remain equal to the time it takes a photon of light to travel 299,792,458 meters.

Using a Cesium atom as a "second" allows us to establish a relative second, instead of an absolute one. That was probably the goal of using it.

And that, in turn, means that no, we do not have an "absolute" definition of a second. If you continue to insist that we have one, then you are just trying to set up a straw man.
A change in the speed of light would also change the rate of caesium transitions. The rate of a caesium clock is relative to c which is our "absolute" for the definition of a second. Just solve for seconds.

For practical purposes, a caesium clock is a convenient gadget for measuring the duration of a standard second with a high degree of accuracy. The "standard second" is as close as we can get to the "absolute" second which is found in the value of c.
Except is is not absolute, nor considered to be absolute. It's relative. All frames of motion agree that, relative to the rate at which a local cesium atom makes its cycles, the rate of travel for a beam of light is always measured to be a cedrtain, fixed, amount.

Nobody is attempting to measure it against an absolute refernce point, and without an absolute reference point to measure against, there is no way to know whether C matches it. Consequently C is not understood to be an absolute reference point. Just a point of common agreement between frames

At best, you are splitting hairs. At worst, you are putting words into someone else' mouth and then pointing out that they were wrong to say the things they'd idn't say.

35. Originally Posted by RedPanda
To summarise: I asked you to show me how you established the conversion factor without using that pre-existing definition of a second.
It would be next to impossible to to establish a conversion factor without using a pre-existing definition of a second because that would involve starting from scratch and re-inventing the second all over again. And more importantly, it would be totally unnecessary. Why even try?

We have a conversion factor for converting cycles to seconds and that is ALL we need.

The frequency of a caesium clock is based on a pre-existing definition of a second which is only natural because we had seconds before we had atomic clocks. What is the problem with that?

36. Das ist nicht nur nicht richtig, es ist nicht einmal falsch!"

37. Originally Posted by bangstrom
Originally Posted by RedPanda
To summarise: I asked you to show me how you established the conversion factor without using that pre-existing definition of a second.
It would be next to impossible to to establish a conversion factor without using a pre-existing definition of a second because that would involve starting from scratch and re-inventing the second all over again.
Which contradicts your earlier claim that the definition of a second is circular.

Using the number of cycles of caesium does not provide any information about how long those cycles take.
And there is no conversion factor when using those cycles to define how long a second is because "It would be next to impossible to to establish a conversion factor without using a pre-existing definition of a second".
And no, the earlier definitions of a second can't be used as a conversion factor, because they are not 9,192,631,770 cycles long.

Originally Posted by bangstrom
And more importantly, it would be totally unnecessary. Why even try?
Because that it what is needed to support your claim that the definition of a second is circular.

Originally Posted by bangstrom
We have a conversion factor for converting cycles to seconds and that is ALL we need.
But you don't have a conversion factor unless you define how long a second is.

Originally Posted by bangstrom
The frequency of a caesium clock is based on a pre-existing definition of a second which is only natural because we had seconds before we had atomic clocks. What is the problem with that?
The main problem is that the length of a second used to calculate the frequency of caesium is a different length to the second we had "before we had atomic clocks".
If you use the older definitions of a second to calculate the frequency of caesium's cycles, you will not get the number 9,192,631,770.

Originally Posted by bangstrom
We have a conversion factor for converting cycles to seconds and that is ALL we need.
Originally Posted by bangstrom
You: "It would be next to impossible to establish a conversion factor without using a pre-existing definition of a second because that would involve starting from scratch and re-inventing the second all over again.
Those two sentences pretty much sum up the contradictory nature of your argument.
You say that the definition of a second uses a conversion factor - but when asked to provide that conversion factor you say that it is impossible to provide one.

"The number 9,192,631,770 is in Hz or cycles per second of EM radiation."
"Someone had to calculate the values of the frequency and wavelength of a caesium clock to determine the number of cycles you need to count."
"The number 9,192,631,770 is not just a number. It has a unitary value of cycles per second (Hz)."
"There are 9,192,631,770 cycles in a second so the number is in cycles per second."
et al...

Originally Posted by bangstrom
I figure that, if a second is defined as 9,192,631,770 cycles of the hyperfine structure transition frequency of caesium-133, atoms, then the number 9,192,631,770 must be in units of Hz or cycles per second. Where did I go wrong?
Your mistake is in thinking that the definition of a second is measured in cycles per second when, as you have now stated, the conversion factor that would give you Hz is "next to impossible to to establish...without using a pre-existing definition of a second".
There is no pre-existing definition (i.e. prior to the current definition) of a second that matches 9,192,631,770 caesium cycles - therefore, any conversion factor based on previous definitions of a second would not produce the number 9,192,631,770.

38. Originally Posted by RedPanda
Originally Posted by bangstrom
Counting cycles does provide information about how long it took. So, yes. Counting cycles gives us information about time.

Yes, counting cycles does tell you how long it takes but it may not be in units of seconds.
Ok - so how long would it take to count 36 beats and what unit of time are you using?
It would take 36 beats of time to count 36 beats. The time would be measured in beats.

Originally Posted by RedPanda
Originally Posted by bangstrom
The answer is, NO. Counting cycles of an unknown period does not give you time in seconds.
I agree.
Counting 9,192,631,770 cycles over an unknown period of time does not give you the time in seconds.
But that contradicts your earlier claim that the definition of a second is circular.
You read my statement wrong so here is a clarification. Remember that cycles occur in units of time called a "period" and I said, "Counting cycles of an unknown period does not give you time in seconds.

I did not say, "Counting 9,192,631,770 cycles over an unknown period of time does not give you the time in seconds."

Counting cycles gives you an indication of time and the definition of a second gives us all the information we need to convert cycles to seconds.

I never claimed the definition of a second is circular. My claim is that there is nothing circular about using seconds to define seconds. We can think of it as using old seconds to define new seconds.

The standard length of a second has been determined and agreed upon by international convention to be 9,192,631,770 cycles of caesium transitions. The definition of a second tells us that one second is equal to the time interval of 9,192,631,770 cycles so anyone who counts 9,192,631,770 cycles has measured an interval of time equal to one second. And that interval should be equal to the agreed upon duration of a standard second as well as equal to the duration of a second measured by anyone else in the world who has counted 9,192,631,770 cycles.

39. Originally Posted by bangstrom
Originally Posted by RedPanda
To summarise: I asked you to show me how you established the conversion factor without using that pre-existing definition of a second.
It would be next to impossible to to establish a conversion factor without using a pre-existing definition of a second because that would involve starting from scratch and re-inventing the second all over again. And more importantly, it would be totally unnecessary. Why even try?

We have a conversion factor for converting cycles to seconds and that is ALL we need.
Yes. That is quite true. A "second" was once thought to be absolute, because the concept of Relativity hadn't been thought up yet.

After relativity was thought up, we then realized that we don't actually need an absolute frame of reference. We can simply relate all of the non-absolute frames and that is good enough. I think we agree on this matter.

Now I'm hoping we'll be able to agree about one other thing: The speed of light is also a relative speed, not an absolute speed. Nobody knows light's "absolute" speed, and indeed there may be no such thing. It's not a matter that the absolute speed of light changes. The absolute speed of light is simply a gibberish concept.

Since experiments have shown that there is no "aether", or background frame of reference that underlies all other frames of reference (and space is therefore not exactly a medium), light can't have an absolute speed when measured against the Aether. If we try to measure it against anything other than an Aether, we are forced to accept that our observations are relative observations, and not absolute observations.

40. Originally Posted by RedPanda
Because that it what is needed to support your claim that the definition of a second is circular.
That is not my claim.
Originally Posted by RedPanda
But you don't have a conversion factor unless you define how long a second is.
We know how long a second is. It is the length of time it takes light to travel 299,792,458 meters. This is derived directly from the value of c.
Originally Posted by RedPanda
The main problem is that the length of a second used to calculate the frequency of caesium is a different length to the second we had "before we had atomic clocks".
If you use the older definitions of a second to calculate the frequency of caesium's cycles, you will not get the number 9,192,631,770.
There is no difference in the length of an old second verses the new and when you use the old second to calculate the value of a caesium emission, you get the value of 9,192,631,770 Hz.

A caesium clock emits 9,192,631,770 cycles in the one second of time it takes light to travel 299,792458 meters. This is the origin of the number 9,192,631,770.

Originally Posted by RedPanda
You say that the definition of a second uses a conversion factor - but when asked to provide that conversion factor you say that it is impossible to provide one.
It is possible to provide a conversion factor and that conversion factor is, "The duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom."

To convert cycles to seconds you divide the total number of cycles by 9,192,631,770.

But the conversion factor you are asking for is both unnecessary and an exercise in futility. You appear to be asking for a conversion factor that begins with the new rather than the old definition of a second.

Working backwards from the "new" definition of a second we get: One cycle of a caesium clock has a wavelength of 3.356409519815204 m ( 1 sec/ c ) and 9,192,631,770 cycles of that wavelength amounts to 299,792,458 meters traveled by a light ( EM) signal in one second.

This is the value of c and the distance light travels in one second which is back to the old definition of a second and the point from which we derived the new definition.

The new definition of a second is simply a "bench top" set of instructions for how to measure the duration of a second so anyone in the world who has need for a highly accurate measurement of time in seconds can count 9,192,631,770 cycles of a caesium clock and have a "second" that exactly matches the standard established for the length of a second. It is not really a new second any different from the old.

Originally Posted by RedPanda
Your mistake is in thinking that the definition of a second is measured in cycles per second when, as you have now stated, the conversion factor that would give you Hz is "next to impossible to to establish...without using a pre-existing definition of a second".
There is no pre-existing definition (i.e. prior to the current definition) of a second that matches 9,192,631,770 caesium cycles - therefore, any conversion factor based on previous definitions of a second would not produce the number 9,192,631,770.
The 9,192,631,770 number is in units of cycles per second. That is why 9,192,631,770 cycles is the duration of one second.
And it is the old definition of a second that gives us the value of 9,192,631,770 Hz in the new. There are 9,192,631,770 cycles in a one second interval of a caesium microwave emission.

41. Originally Posted by kojax
[
Now I'm hoping we'll be able to agree about one other thing: The speed of light is also a relative speed, not an absolute speed. Nobody knows light's "absolute" speed, and indeed there may be no such thing. It's not a matter that the absolute speed of light changes. The absolute speed of light is simply a gibberish concept.
I can agree that the absolute speed of light is a gibberish concept. Even if c is a variable it would still look like a constant from anyone's point of view so we really don't know. The speed of light is designated as an absolute to give us a common reference point for our units of distance and time. It is defined as a "relativistic invariant." It may not be an absolute speed but it looks like one so we can measure all speeds relative to c.

42. Originally Posted by bangstrom
Originally Posted by RedPanda
Originally Posted by bangstrom
Counting cycles does provide information about how long it took. So, yes. Counting cycles gives us information about time.
Yes, counting cycles does tell you how long it takes but it may not be in units of seconds.
Ok - so how long would it take to count 36 beats and what unit of time are you using?
It would take 36 beats of time to count 36 beats. The time would be measured in beats.
But 'Beats' is not a unit of time and there is no definition for how long a beat is.

Your statement is circular and is therefore useless.
You criticised the current definition of a second for being circular - but then you happily promote your own circular definitions.

Originally Posted by bangstrom
Originally Posted by RedPanda
Originally Posted by bangstrom
The answer is, NO. Counting cycles of an unknown period does not give you time in seconds.
I agree.
Counting 9,192,631,770 cycles over an unknown period of time does not give you the time in seconds.
But that contradicts your earlier claim that the definition of a second is circular.
You read my statement wrong so here is a clarification. Remember that cycles occur in units of time called a "period" and I said, "Counting cycles of an unknown period does not give you time in seconds.
No.
Cycles occur in units of 'cycles'.
As you said: "Each cycle was a single unit. They were not cycles per second but simply cycles."

Originally Posted by bangstrom
I did not say, "Counting 9,192,631,770 cycles over an unknown period of time does not give you the time in seconds."
A period is "a length or portion of time."
So, yes, you did say that counting 9,192,631,770 cycles over an unknown period of time does not give you the time in seconds.
Unless you are also redefining what a period is as well?

Originally Posted by bangstrom
Counting cycles gives you an indication of time and the definition of a second gives us all the information we need to convert cycles to seconds.
Ok.
Then using the current definition of a second, how long would it take to count 36 cycles?
No, not caesium cycles. Or are caesium cycles in some way different to other cycles?
I suspect that you are relying on circular reasoning - again.

Originally Posted by bangstrom
I never claimed the definition of a second is circular.
Yes you did.
"The number 9,192,631,770 is in Hz or cycles per second of EM radiation."
You clearly stated that the definition of a second is dependant on knowing how long a second is.
That is circular and therefore useless.

Originally Posted by bangstrom
My claim is that there is nothing circular about using seconds to define seconds.
We can think of it as using old seconds to define new seconds.
Why would we want to think something that is wrong?
We do not use old seconds to define new seconds - they are of different lengths.

Originally Posted by bangstrom
The standard length of a second has been determined and agreed upon by international convention to be 9,192,631,770 cycles of caesium transitions.
...which contradicts your earlier claim that "The number 9,192,631,770 is in Hz or cycles per second of EM radiation."

It would be a lot easier if you could get your argument straight and stop contradicting yourself.

43. Originally Posted by bangstrom
Originally Posted by RedPanda
But you don't have a conversion factor unless you define how long a second is.
We know how long a second is. It is the length of time it takes light to travel 299,792,458 meters. This is derived directly from the value of c.
How many times will you keep making that same incorrect statement.
I'll post it AGAIN:
"One second is now defined to be exactly 9,192,631,770 cycles of the hyperfine structure transition frequency of caesium-133 atoms."
As you can see, there is no mention of c or light or 299,792,458 meters in that definition.

Originally Posted by bangstrom
Originally Posted by RedPanda
The main problem is that the length of a second used to calculate the frequency of caesium is a different length to the second we had "before we had atomic clocks".
If you use the older definitions of a second to calculate the frequency of caesium's cycles, you will not get the number 9,192,631,770.
...
And it is the old definition of a second that gives us the value of 9,192,631,770 Hz in the new.
There is no difference in the length of an old second verses the new and when you use the old second to calculate the value of a caesium emission, you get the value of 9,192,631,770 Hz.
LOL.
No.
Why would they bother making up a new definition of a second if it matched the existing definition of a second.
Not only is your claim wrong, but it doesn't even make sense.

Seriously - where are you getting your faulty information from?
There can't be a website with that many errors.
You are just making this shit up, aren't you.

44. Originally Posted by RedPanda
Seriously - where are you getting your faulty information from?
There can't be a website with that many errors.
You are just making this shit up, aren't you.
My suspicion is that he is a firm anti-relativist. He needs to deal with the sticky problem of all the evidence in support of relativity, however, so he starts with the notion that there is some fundamental circularity in the definition of standards that somehow allows him to disregard all that evidence. He's running into trouble, though, because you and others keep making it difficult for him to get past that first step. But he's firmly convinced that he's right, so 'round and 'round he goes, hoping against hope that he actually has a logical argument.

It's very, very sad. If he were to exert that much effort learning real science, he might actually accomplish something other than contribute to global warming.

45. Originally Posted by tk421
My suspicion is that he is a firm anti-relativist. He needs to deal with the sticky problem of all the evidence in support of relativity, however, so he starts with the notion that there is some fundamental circularity in the definition of standards that somehow allows him to disregard all that evidence. He's running into trouble, though, because you and others keep making it difficult for him to get past that first step. But he's firmly convinced that he's right, so 'round and 'round he goes, hoping against hope that he actually has a logical argument.
I don't think I can understand being so committed to a position that I would need to make up stuff to support it.

If I am unsure about a claim, I double check that it is correct.
If someone disagrees with my claim, I double check that it is correct.
For example, even though it makes sense that the previous definition of a second would produce a different length of a second, I still checked what the length of the previous second was before saying that they were different.

I don't understand why some people cling so desperately to being wrong.

46. Originally Posted by RedPanda;587124}
I'll post it AGAIN:
[I
"One second is now defined to be exactly 9,192,631,770 cycles of the hyperfine structure transition frequency of caesium-133 atoms."[/I]
As you can see, there is no mention of c or light or 299,792,458 meters in that definition.
The definition was derived from, and is consistent with, the value of c. The definition is a simple "how to measure" instruction, not a detailed explanation that includes an explanation of how it was derived.

Originally Posted by RedPanda
The main problem is that the length of a second used to calculate the frequency of caesium is a different length to the second we had "before we had atomic clocks".
If you use the older definitions of a second to calculate the frequency of caesium's cycles, you will not get the number 9,192,631,770.
There is no difference in the length of a second by either definition. Only the wording is different. The number 9,192,631,770, times the wavelength of a 9,192,631,770 Hz caesium emission equals 299,792,458 meters which is the distance light travels in one second. The length of a second in either case is identical and consistent with the value of both meters and seconds in the constant c.

Originally Posted by RedPanda
Why would they bother making up a new definition of a second if it matched the existing definition of a second.
Not only is your claim wrong, but it doesn't even make sense.
There is no difference in the value of a second either way but, in actual practice, we could expect to find differences in the determination of a second from laboratory to laboratory because of the usual material and method errors.

By the old definition, a laboratory would first have to determine the length of a standard meter before they could time the speed of light over a distance of meters to get the length of a second. This is not easy and it is a major source of experimental error. All this experimental work has been done previously and it has been agreed upon by international convention that a second is equal to 9,192,631,770 cycles on a caesium clock. This simplifies the determination of a standard second enormously because a laboratory only needs to count cycles on a caesium clock and it specifies the material and method for the sake of uniformity.

47. Originally Posted by bangstrom
The definition was derived from, and is consistent with, the value of c.
Wrong.

Originally Posted by bangstrom
There is no difference in the length of a second by either definition.
Wrong.

Originally Posted by bangstrom
There is no difference in the value of a second either way
Wrong.

Originally Posted by bangstrom
By the old definition, a laboratory would first have to determine the length of a standard meter before they could time the speed of light over a distance of meters to get the length of a second.
Wrong.

Seriously - where are you getting this bullshit from?
There can't be a website with that many errors.
You are just making this shit up, aren't you.

48. Originally Posted by RedPanda
Originally Posted by tk421
My suspicion is that he is a firm anti-relativist. He needs to deal with the sticky problem of all the evidence in support of relativity, however, so he starts with the notion that there is some fundamental circularity in the definition of standards that somehow allows him to disregard all that evidence. He's running into trouble, though, because you and others keep making it difficult for him to get past that first step. But he's firmly convinced that he's right, so 'round and 'round he goes, hoping against hope that he actually has a logical argument.
I don't think I can understand being so committed to a position that I would need to make up stuff to support it.

If I am unsure about a claim, I double check that it is correct.
If someone disagrees with my claim, I double check that it is correct.
For example, even though it makes sense that the previous definition of a second would produce a different length of a second, I still checked what the length of the previous second was before saying that they were different.

I don't understand why some people cling so desperately to being wrong.
You said, "For example, even though it makes sense that the previous definition of a second would produce a different length of a second, I still checked what the length of the previous second was before saying that they were different."

An an unsupported opinion is useless as teats on a bull. When you checked the lenght of a previous second, what was it and how does it compare with the new?

49. Originally Posted by bangstrom
An an unsupported opinion is useless as teats on a bull.
But you continue to make them, don't you.
(See my previous post for 4 examples of your unsupported opinions.)

Originally Posted by bangstrom
When you checked the lenght of a previous second, what was it and how does it compare with the new?
Do you not know what the two values are?
Then I suggest that you find out before making any more stupid statements about them being the same.

What you have done there is typical crank behaviour.
You have resorted to the often heard cry of the crazy theorist: "Prove me wrong!"

"That which can be asserted without evidence, can be dismissed without evidence."
Therefore I dismiss your unsupported assertions.

50. Originally Posted by RedPanda
Originally Posted by bangstrom
An an unsupported opinion is useless as teats on a bull.
But you continue to make them, don't you.
(See my previous post for 4 examples of your unsupported opinions.)

Originally Posted by bangstrom
When you checked the lenght of a previous second, what was it and how does it compare with the new?
Do you not know what the two values are?
Then I suggest that you find out before making any more stupid statements about them being the same.

What you have done there is typical crank behaviour.
You have resorted to the often heard cry of the crazy theorist: "Prove me wrong!"

"That which can be asserted without evidence, can be dismissed without evidence."
Therefore I dismiss your unsupported assertions.
In other words, you have never compared the value of the two seconds as you claim to have.

I have compared them and found them to be the same and explained more than once why they are the same.

I am not asking you to prove me wrong so much as I am calling you on your own bull. You have demonstrated almost no knowledge about the topic and can't even explain the meaning of the 9,192,631,770 number which is central to the issue.

51. Originally Posted by bangstrom
In other words, you have never compared the value of the two seconds as you claim to have.
Wrong.

Originally Posted by bangstrom
I am not asking you to prove me wrong so much as I am calling you on your own bull.
Wrong.

Originally Posted by bangstrom
You have demonstrated almost no knowledge about the topic and can't even explain the meaning of the 9,192,631,770 number which is central to the issue.
Wrong.
(I see a pattern forming...)

Originally Posted by bangstrom
I have compared them and found them to be the same and explained more than once why they are the same.
Then provide a link to a site showing these two identical values, quoting the relevant parts.
Or just leave it as just another one of your many unsupported assertions.

52. Time to move this to the trash.

53. Originally Posted by RedPanda
Originally Posted by bangstrom
I have compared them and found them to be the same and explained more than once why they are the same.
Then provide a link to a site showing these two identical values, quoting the relevant parts.
Or just leave it as just another one of your many unsupported assertions.
The claims I have been making are based on common knowledge information and some simple math. The only part that is obscure is the meaning of the 9,192,631,770 number used to convert cycles of a caesium clock to intervals of a standard second.

Here is a quote explaining its significance.

"A "cesium(-beam) atomic clock" (or "cesium-beam frequency standard") is a device that uses as a reference the exact frequency of the microwave spectral line emitted by atoms of the metallic element cesium, in particular its isotope of atomic weight 133 ("Cs-133"). The integral of frequency is time, so this frequency, 9,192,631,770 hertz (Hz = cycles/second), provides the fundamental unit of time, which may thus be measured by cesium clocks."
tycho.usno.navy.mil/cesium.html

Light (EM) radiation is measured in cycles per second so a one second interval of a 9,192,631,770 Hz microwave signal contains 9,192,631,770 cycles. Dividing the total number of cycles by 9,192,631,770 gives us the time of the signal in seconds or we could count 9,192,631,770 cycles and that would be the value of one standard second. This is our conversion factor for converting cycles to seconds. N seconds = N cycles per second / N cycles.

Since light is said to travel 299,792,458 meters in one second, a one second interval of a 9,192,631,770 Hz signal should be 299,792,458 m long, if allowed to continue, and contain 9,192,631,770 cycles.

It makes no difference if you measure the duration of a second by dividing a caesium clock signal by 9,192,631,770 Hz or if you measure a second by the time it takes a light signal to travel 299,792,458 meters. The latter is the older version of a standard second from which the newer version is derived but the seconds in both are identical.

54. Originally Posted by bangstrom
Originally Posted by RedPanda
Originally Posted by bangstrom
I have compared them and found them to be the same and explained more than once why they are the same.
Then provide a link to a site showing these two identical values, quoting the relevant parts.
Or just leave it as just another one of your many unsupported assertions.
"A "cesium(-beam) atomic clock" (or "cesium-beam frequency standard") is a device that uses as a reference the exact frequency of the microwave spectral line emitted by atoms of the metallic element cesium, in particular its isotope of atomic weight 133 ("Cs-133"). The integral of frequency is time, so this frequency, 9,192,631,770 hertz (Hz = cycles/second), provides the fundamental unit of time, which may thus be measured by cesium clocks."
So you don't have anything supporting your claim that the current second and the previously defined second are the same length?
I didn't think so.
It is rather dishonest of you to pretend that you did.
But, since your claims are complete bollocks, I guess you had no other choice but to lie.

55. Originally Posted by RedPanda
So you don't have anything supporting your claim that the current second and the previously defined second are the same length?
I didn't think so.
It is rather dishonest of you to pretend that you did.
But, since your claims are complete bollocks, I guess you had no other choice but to lie.
I'm sorry that you can't check the math to see if it is correct.

56. Originally Posted by bangstrom
Originally Posted by RedPanda
So you don't have anything supporting your claim that the current second and the previously defined second are the same length?
I didn't think so.
It is rather dishonest of you to pretend that you did.
But, since your claims are complete bollocks, I guess you had no other choice but to lie.
I'm sorry that you can't check the math to see if it is correct.
Well, at least you admit that you have no links that support your claim that the new and the old seconds are the same.
Admitting you have a problem is the first step.

But, since all you have are baseless assertions, there is no reason to think you are doing anything more than pulling numbers from your arse.

Your abject failure to find any external links to support your claims should have indicated to you that you are wrong.
But it appears your denial is too ingrained for you to be able to see that.

To summarise: Put up or shut up.
If you have nothing to support your claims then stop making them.

57. Originally Posted by bangstrom
Originally Posted by kojax
[
Now I'm hoping we'll be able to agree about one other thing: The speed of light is also a relative speed, not an absolute speed. Nobody knows light's "absolute" speed, and indeed there may be no such thing. It's not a matter that the absolute speed of light changes. The absolute speed of light is simply a gibberish concept.
I can agree that the absolute speed of light is a gibberish concept. Even if c is a variable it would still look like a constant from anyone's point of view so we really don't know. The speed of light is designated as an absolute to give us a common reference point for our units of distance and time. It is defined as a "relativistic invariant." It may not be an absolute speed but it looks like one so we can measure all speeds relative to c.
If this is your perspective, then there is really no contradiction with mainstream science. I don't get what the other posters are even bickering about now. ...?

Since there is no absolute frame of reference against which the duration of a second can be measured (only relative frames), it is impossible to say how long a second is in absolute terms. And since the absolute value of a second is un-defined, there is no way to know whether it changes or not.

However, the relative value of a second, as measured in any inertial frame, is 9,192,631,770 Hz of a cesium atom in the observer's frame.

Maybe you and Panda are just talking past each other? Maybe Panda thinks you're trying to say that the relative value of second is changing, but really you're only suggesting that the absolute value of a second is changing (or never had a definite value to begin with - which is what mainstream science claims.)

Originally Posted by AlexG
Time to move this to the trash.
Fine. As soon as you agree with Bangstrom that he is correct. The speed of light does not have a defined absolute value. (Although it does have a defined relative value which is the same for all inertial frames.)

It's weird to see a thread on this forum where the majority of posters take the view that is opposed to mainstream science, instead of the view that agrees with it.

58. Originally Posted by kojax
Maybe you and Panda are just talking past each other? Maybe Panda thinks you're trying to say that the relative value of second is changing, but really you're only suggesting that the absolute value of a second is changing (or never had a definite value to begin with - which is what mainstream science claims.)
He thinks the definition of a second is circular and is based on the speed of light.
He is wrong.

There are also other claims he makes (e.g. the currently defined second is the same length as the previously defined second) which are also wrong.
He also compounds his erroneous claims by making further erroneous claims.

59. Originally Posted by RedPanda
Originally Posted by kojax
Maybe you and Panda are just talking past each other? Maybe Panda thinks you're trying to say that the relative value of second is changing, but really you're only suggesting that the absolute value of a second is changing (or never had a definite value to begin with - which is what mainstream science claims.)
He thinks the definition of a second is circular and is based on the speed of light.
He is wrong.
The definition of a second is based on other phenomena that have fixed relationships with the speed of light. That's just about as good as being based on the speed of light.

He has been kind enough to specify that it is only the absolute duration of a second that is unclear, and not its relative duration when compared with other phenomena occurring in the same frame of motion

And that is correct. The absolute (non-relative) duration of a second is undefined. There is no such thing as an Aether, and therefore no such thing as an absolute speed or duration for any phenomena. Only relative durations are possible to determine.

There are also other claims he makes (e.g. the currently defined second is the same length as the previously defined second) which are also wrong.
He also compounds his erroneous claims by making further erroneous claims.
He made clear that the previous definition of an "emphemeris" second, which is based on the Earth's rotation, was also indirectly based on the speed of light (and may yield a slightly different value than the Cesium clock second), because if the speed of light changes, then the speed of all other phenomena would change also.

That last part is a bit of conjecture, but not far off base. It is likely that the speed of light determines all other speeds.

If your problem with Bangstrom is that he's being wordy and arrogant, but not rejecting established physics, then I guess I'll need you to show me where in the forum rules it states that wordiness and arrogance are not permitted on this forum.

Until then, this is an interesting discussion, because one poster has managed to annoy a number of other posters to the point of opening their minds a little bit, and the rest of the posters who understand Relativity now have the opportunity to fill those minds with useful information.

60. Originally Posted by kojax
The definition of a second is based on other phenomena that have fixed relationships with the speed of light. That's just about as good as being based on the speed of light.
[Citation needed]

Originally Posted by kojax
He has been kind enough to specify that it is only the absolute duration of a second that is unclear, and not its relative duration when compared with other phenomena occurring in the same frame of motion
And that is correct. The absolute (non-relative) duration of a second is undefined. There is no such thing as an Aether, and therefore no such thing as an absolute speed or duration for any phenomena. Only relative durations are possible to determine.
He may have been talking about that with you, but that it not what he was talking about with me.
In fact, he has said many times that the second he is talking about with me is defined.

Originally Posted by kojax
He made clear that the previous definition of an "emphemeris" second, which is based on the Earth's rotation, was also indirectly based on the speed of light (and may yield a slightly different value than the Cesium clock second)
No. He has explicitly stated that the emphemeris second and the current second are exactly the same.
And regardless of how the emphemeris second is defined, he has explicitly stated the current second is based on the speed of light - which it is not.

Originally Posted by kojax
If your problem with Bangstrom is that he's being wordy and arrogant, but not rejecting established physics, then I guess I'll need you to show me where in the forum rules it states that wordiness and arrogance are not permitted on this forum.
Nope.
My problem with him is that he repeatedly makes claims that are patently wrong and then gets upset when asked to support his assertions.

If you want to provide support for his claims (e.g. that the ephemeris second is exactly the same as the current second) then please go ahead.
So far, bangstrom has been unable to do so, so it would be nice to have someone who can.

61. Originally Posted by RedPanda
No. He has explicitly stated that the emphemeris second and the current second are exactly the same.
And regardless of how the emphemeris second is defined, he has explicitly stated the current second is based on the speed of light - which it is not.
I would be glad to discuss the connection between the standard second and the speed of light or the historical connection between the Ephemeris second and the SI second or how we are unable to measure the the speed of light as anything other than the defined value of c... with anyone who cares.

62. Originally Posted by bangstrom
Originally Posted by RedPanda
No. He has explicitly stated that the emphemeris second and the current second are exactly the same.
And regardless of how the emphemeris second is defined, he has explicitly stated the current second is based on the speed of light - which it is not.
I would be glad to discuss the connection between the standard second and the speed of light or the historical connection between the Ephemeris second and the SI second or how we are unable to measure the the speed of light as anything other than the defined value of c... with anyone who cares.
Why would anyone be interested in more of your senseless conjectures?
You clearly are unable to support your claims; you just pluck random sentences from your butt and throw them at the forum to see if any of them stick.

63. Red Panda, you are becoming the pot that calls the kettle black.

Bangstrom may have used a round-about method, but he ultimately ended up saying exactly what modern physics says. All measurements of time, distance, or speed are relative. Because they are relative there is no way to know the "absolute" value of C, or of a second, or of a meter, or of anything else for that matter.

He has admitted that C is always the same for observers in all inertial frames of motion - which is all he needs to admit.

The rest of the discussion has focused on the "absolute" value of C, which is really a nonsense concept. C has no absolute value, because nothing has an absolute velocity.

You've just got to quit thinking with your heart and start using your brain.

64. Originally Posted by kojax
Red Panda, you are becoming the pot that calls the kettle black.
Bangstrom may have used a round-about method, but he ultimately ended up saying exactly what modern physics says. All measurements of time, distance, or speed are relative. Because they are relative there is no way to know the "absolute" value of C, or of a second, or of a meter, or of anything else for that matter.
He has admitted that C is always the same for observers in all inertial frames of motion - which is all he needs to admit.
The rest of the discussion has focused on the "absolute" value of C, which is really a nonsense concept. C has no absolute value, because nothing has an absolute velocity.
You've just got to quit thinking with your heart and start using your brain.
So, you aren't able to support his claim that the ephemeris second is the same length as the current definition of a second either?
I didn't think so.

Just because he's your new best friend doesn't make him right.
Perhaps you should quit thinking with your heart and start using your brain.

Originally Posted by kojax
The rest of the discussion has focused on the "absolute" value of C, which is really a nonsense concept. C has no absolute value, because nothing has an absolute velocity.
And no, that is not the rest of the discussion.
That is just the discussion you've been having.

65. Originally Posted by RedPanda
Originally Posted by kojax
Red Panda, you are becoming the pot that calls the kettle black.
Bangstrom may have used a round-about method, but he ultimately ended up saying exactly what modern physics says. All measurements of time, distance, or speed are relative. Because they are relative there is no way to know the "absolute" value of C, or of a second, or of a meter, or of anything else for that matter.
He has admitted that C is always the same for observers in all inertial frames of motion - which is all he needs to admit.
The rest of the discussion has focused on the "absolute" value of C, which is really a nonsense concept. C has no absolute value, because nothing has an absolute velocity.
You've just got to quit thinking with your heart and start using your brain.
So, you aren't able to support his claim that the ephemeris second is the same length as the current definition of a second either?
I didn't think so.
This is Bangstrom's quote from post #23 of this discussion:

Originally Posted by Bangstrom
The Ephemeris second is not easily determined, it is inexact, and it varies with time. To avoid confusion, its value is standardized by comparison with the SI second as measured with a cesium clock and the date on which the Ephemeris second was measured is also a part of the standard definition.
The speed of light would be a variable if the second in m/s were an Ephemeris second because the Ephemeris second varies randomly over short periods of time and it is growing longer over long periods of time. The last big earthquake and tsunami in Japan slowed the rate of Ephemeris time but the SI second and the standard speed of light remain unchanged.
You and I may have varying rates of reading comprehension, but I'm pretty sure he's saying that he believes the Ephemeris Second, and the SI second often end up having slightly different values.

Just because he's your new best friend doesn't make him right.
Perhaps you should quit thinking with your heart and start using your brain.
He's probably a crank most of the time, and just happens to be right this once.

However the reason I am taking his side on this matter is because I see it as a valuable opportunity to discuss special relativity. It seems that possibly some posters on this discussion don't understand relativity as well as they could, or this discussion would not have become so uncivil as it has in the first place.

Light is not a privileged frame of reference. It's just as relative as anything else. Different observers in different frames of motion in Special Relativity may not disagree about its speed, but they certainly disagree about its frequency, and they may disagree about how far it is traveling, and about when it arrives at its destination.

Originally Posted by kojax
The rest of the discussion has focused on the "absolute" value of C, which is really a nonsense concept. C has no absolute value, because nothing has an absolute velocity.
And no, that is not the rest of the discussion.
That is just the discussion you've been having.
That might be because I've been staying on topic.

66. Originally Posted by kojax
This is Bangstrom's quote from post #23 of this discussion:
Originally Posted by Bangstrom
The Ephemeris second is not easily determined, it is inexact, and it varies with time. To avoid confusion, its value is standardized by comparison with the SI second as measured with a cesium clock and the date on which the Ephemeris second was measured is also a part of the standard definition.
And this is what bangstrom said in post #150:
Originally Posted by bangstrom
I have compared them and found them to be the same and explained more than once why they are the same.
So - not only wrong on several counts but inconsistent.

Are you going to support his claim that "the date on which the Ephemeris second was measured is also a part of the standard definition."?
Or perhaps claim that his sentences don't contradict each other?

tbh: I expect you will just repeat what you've done previously and simply gloss over the complete shite he's been talking.

Originally Posted by kojax
He's probably a crank most of the time, and just happens to be right this once.
The amount of blind support you are giving makes me suspect 'crankness' is contagious.

Originally Posted by kojax
That might be because I've been staying on topic.
Is this new discussion you started 'on topic' then, hmm?

I seriously question the wisdom of supporting bangstrom - but your mistakes are yours to make.

67. Originally Posted by RedPanda
Originally Posted by kojax
This is Bangstrom's quote from post #23 of this discussion:
Originally Posted by Bangstrom
The Ephemeris second is not easily determined, it is inexact, and it varies with time. To avoid confusion, its value is standardized by comparison with the SI second as measured with a cesium clock and the date on which the Ephemeris second was measured is also a part of the standard definition.
And this is what bangstrom said in post #150:
Originally Posted by bangstrom
I have compared them and found them to be the same and explained more than once why they are the same.
So - not only wrong on several counts but inconsistent.

Are you going to support his claim that "the date on which the Ephemeris second was measured is also a part of the standard definition."?
Or perhaps claim that his sentences don't contradict each other?

tbh: I expect you will just repeat what you've done previously and simply gloss over the complete shite he's been talking.
The statements above exemplify the confused and fact-free nature of your views. The two seconds I was comparing and were, on one hand, the "second" defined as the time it takes light to travel the distance of 299,792,458 m, and on the other hand, the second determined by counting cycles of caesium transitions. The two are exactly the same if you crunch the numbers which I did.

Neither of these seconds are the Ephemeris second which is based on the rotation of the Earth and its determination is strictly a matter of observational astronomy. It varies over time and therefore it is necessary to designate the time when it was measured. The E second of 1952 was the designated as the standard second and this is the length of a second upon which the SI second is based.

From Wilipedia:
"The ephemeris time of the 1952 standard leaves a continuing legacy, through its ephemeris second which became closely duplicated in the length of the current standard SI second."
en.wikipedia.org/wiki/Ephemeris_second

68. Originally Posted by bangstrom
The two seconds I was comparing and were, on one hand, the "second" defined as the time it takes light to travel the distance of 299,792,458 m, and on the other hand, the second determined by counting cycles of caesium transitions.
Again, you are wrong.
Are you actually able to post something - anything - not untrue?

Here is a summary of the conversation:

RP: "For example, even though it makes sense that the previous definition of a second would produce a different length of a second, I still checked what the length of the previous second was before saying that they were different."

BS: "When you checked the lenght of a previous second, what was it and how does it compare with the new?"

RP: "Do you not know what the two values are?"

BS: "I have compared them and found them to be the same and explained more than once why they are the same."

Originally Posted by bangstrom
The statements above exemplify the confused and fact-free nature of your views.
Pot, kettle, noir.

69. Redpanda, I think you're not even trying to communicate. Go back to post #146. There Bangstrom clearly was comparing the second defined by C and the second defined by a Cesium atom. If you were referring to the Ephemeris second in your own posts, you didn't say so.

Doing a quick search of this page, starting at post #101, the first time "ephemeris" appears on this page is post #160. That means that when Bangstrom posted what he said in #146, the word "ephemeris" hadn't been used for 45 posts. Where, then, do you get the impression that he meant to speak of it?

70. Originally Posted by kojax
Redpanda, I think you're not even trying to communicate.
kojax, I don't think you're even trying to understand.

Originally Posted by kojax
If you were referring to the Ephemeris second in your own posts, you didn't say so.
I was - as is clear from my post - comparing the current definition of a second with the previous definition of a second.
You can even see it in bangstrom's post: "the lenght of a previous second, what was it and how does it compare with the new?"
What is the previous definition of a second if not the ephemeris second?

Originally Posted by kojax
Doing a quick search of this page, starting at post #101, the first time "ephemeris" appears on this page is post #160. That means that when Bangstrom posted what he said in #146, the word "ephemeris" hadn't been used for 45 posts. Where, then, do you get the impression that he meant to speak of it?
RP: "For example, even though it makes sense that the previous definition of a second would produce a different length of a second, I still checked what the length of the previous second was before saying that they were different."
BS: "When you checked the lenght of a previous second, what was it and how does it compare with the new?"
(And "the previous definition of a second" was first referred to in post #137.)

He asked a question regarding a post I made to someone else.
I know exactly which subject matter I was talking about.
And his use of the words 'previous' and 'new' indicated he knew what I was talking about, too.

But no, go ahead - please tell me what I was actually thinking.

71. Originally Posted by Markus Hanke
There are 2 choices, one is the speed of light is a constant, the other one is the speed of light is not a constant.
The speed of light in vacuum is neither constant nor varying, it is a relativistic invariant. The distinction is very subtle and is irrelevant in flat space-time, but it is very important in curved space-times, such as extended regions around massive bodies, because then we have to account for the differences in coordinate speed and proper speed. Coordinate speed of light actually does vary ( in fact it drops to zero at the event horizon of a black hole ), but the speed of light being relativistically invariant means that proper speed - which is what is physically measured in a local rest frame - is the same everywhere. Only the latter is physically meaningful since in curved space-times there is no global notion of time. Proper speed to be everywhere locally exactly c just means that all observers experience the same laws of physics, regardless of where they are and how they move. This leads to the very counter-intuitive result that no stationary far-away observer ever sees anything reach the event horizon of a black hole, while at the same time someone in free fall will cross it in finite and well-defined proper time as measured on his own watch; this is not a contradiction, but a simple manifestation of the nature of gravity.
Markus, can you explain this to me in more step by step simpler terms? I think starting with relativistic invariant? I only have high school and some tech training in electronics. You seem smart to me - maybe overly smart - but are you smart enough to teach me? Teaching others is not always possible for really smart people. I see you as someone who enjoys a mental challenge though - I ask this more because of your interest in that Chinese poet "cold mountain" than in your Einsteinian relativity theories, but I am sure they can tie together.

72. Originally Posted by Mayflow
Originally Posted by Markus Hanke
There are 2 choices, one is the speed of light is a constant, the other one is the speed of light is not a constant.
The speed of light in vacuum is neither constant nor varying, it is a relativistic invariant. The distinction is very subtle and is irrelevant in flat space-time, but it is very important in curved space-times, such as extended regions around massive bodies, because then we have to account for the differences in coordinate speed and proper speed. Coordinate speed of light actually does vary ( in fact it drops to zero at the event horizon of a black hole ), but the speed of light being relativistically invariant means that proper speed - which is what is physically measured in a local rest frame - is the same everywhere. Only the latter is physically meaningful since in curved space-times there is no global notion of time. Proper speed to be everywhere locally exactly c just means that all observers experience the same laws of physics, regardless of where they are and how they move. This leads to the very counter-intuitive result that no stationary far-away observer ever sees anything reach the event horizon of a black hole, while at the same time someone in free fall will cross it in finite and well-defined proper time as measured on his own watch; this is not a contradiction, but a simple manifestation of the nature of gravity.
Marcus explained the issue quite nicely and any attempt to elaborate on it would likely make it sound more complicated than it is but I could offer a crude explanation of some of the terms.

The "global notion of time" is what I like to call a "god's view of time." This would be how time might appear to an observer beyond our universe with a time-frame independent of ours. Such an observer would see time in our universe passing at different rates in different parts of the universe.

From a global perspective, the speed of light can vary but there is no such thing as a gods eye view of the universe to tell us which is the "preferred" or "absolute" speed of light.

A local rest frame is the point of view of an observer that is inertially at rest. (Not accelerated in any direction.) A rest frame can be in motion as with passengers on a plane who may be moving but they feel no motion.

Flat space-time is the familiar 3-D space of Euclid, Newton, and Special Relativity where time and space are uniform in all locations and parallel lines never meet. This is our intuitive view of the world.

Curved space-time is the space-time of General Relativity where parallel lines meet at a great distance and cross like the longitude lines on the curved surface of a globe. This is described by the 4-D geometry of Riemann.

The amount of curvature in curved space-time can vary something like a sheet of graph paper made of rubber only the curvature is in four dimensions of space. 4-D space is impossible to imagine and it is hard to think of either space or time as curving but the curvature is what we observe as gravity. The greater curvature about a massive body, the greater its gravity.

I prefer to think of curved space-time as "shorter space and slower time" because that is the effect we observe as space-time becomes more curved. Time slows and distances shorten and these differences cause ponderous bodies to move together in curved paths- gravity.

"Coordinate" speed is the speed of objects observed at a distance and the coordinate speed of light can vary. We can observe the speed of light slowing in the presence of of massive bodies because of gravity.

"Proper" speed is the speed of an object as it is measured from the location of the object itself. Passengers on a plane observe motions inside the plane in proper speed.

It is contrary to ordinary experience to find rate of coordinate speed to be any different from proper speed. A person walking on the ground appears to move just as fast as a person walking on a plane. But, at relativistic speeds close to c or in a gravitational field far from ones own, the two speeds begin to part company.

Even though the coordinate speed of light (that of a remote observer) may vary because of changes in speed or gravity, the proper speed of light (locally observed) never changes because local variations in space and time are always proportional to c.

The speed of light is a constant when measured relative to ones local environment so c is said to be relativistically invariant. This makes c a physical constant.

73. Originally Posted by bangstrom
Originally Posted by Mayflow
Originally Posted by Markus Hanke
There are 2 choices, one is the speed of light is a constant, the other one is the speed of light is not a constant.
The speed of light in vacuum is neither constant nor varying, it is a relativistic invariant. The distinction is very subtle and is irrelevant in flat space-time, but it is very important in curved space-times, such as extended regions around massive bodies, because then we have to account for the differences in coordinate speed and proper speed. Coordinate speed of light actually does vary ( in fact it drops to zero at the event horizon of a black hole ), but the speed of light being relativistically invariant means that proper speed - which is what is physically measured in a local rest frame - is the same everywhere. Only the latter is physically meaningful since in curved space-times there is no global notion of time. Proper speed to be everywhere locally exactly c just means that all observers experience the same laws of physics, regardless of where they are and how they move. This leads to the very counter-intuitive result that no stationary far-away observer ever sees anything reach the event horizon of a black hole, while at the same time someone in free fall will cross it in finite and well-defined proper time as measured on his own watch; this is not a contradiction, but a simple manifestation of the nature of gravity.
Marcus explained the issue quite nicely and any attempt to elaborate on it would likely make it sound more complicated than it is but I could offer a crude explanation of some of the terms.

The "global notion of time" is what I like to call a "god's view of time." This would be how time might appear to an observer beyond our universe with a time-frame independent of ours. Such an observer would see time in our universe passing at different rates in different parts of the universe.

From a global perspective, the speed of light can vary but there is no such thing as a gods eye view of the universe to tell us which is the "preferred" or "absolute" speed of light.

A local rest frame is the point of view of an observer that is inertially at rest. (Not accelerated in any direction.) A rest frame can be in motion as with passengers on a plane who may be moving but they feel no motion.

Flat space-time is the familiar 3-D space of Euclid, Newton, and Special Relativity where time and space are uniform in all locations and parallel lines never meet. This is our intuitive view of the world.

Curved space-time is the space-time of General Relativity where parallel lines meet at a great distance and cross like the longitude lines on the curved surface of a globe. This is described by the 4-D geometry of Riemann.

The amount of curvature in curved space-time can vary something like a sheet of graph paper made of rubber only the curvature is in four dimensions of space. 4-D space is impossible to imagine and it is hard to think of either space or time as curving but the curvature is what we observe as gravity. The greater curvature about a massive body, the greater its gravity.

I prefer to think of curved space-time as "shorter space and slower time" because that is the effect we observe as space-time becomes more curved. Time slows and distances shorten and these differences cause ponderous bodies to move together in curved paths- gravity.

"Coordinate" speed is the speed of objects observed at a distance and the coordinate speed of light can vary. We can observe the speed of light slowing in the presence of of massive bodies because of gravity.

"Proper" speed is the speed of an object as it is measured from the location of the object itself. Passengers on a plane observe motions inside the plane in proper speed.

It is contrary to ordinary experience to find rate of coordinate speed to be any different from proper speed. A person walking on the ground appears to move just as fast as a person walking on a plane. But, at relativistic speeds close to c or in a gravitational field far from ones own, the two speeds begin to part company.

Even though the coordinate speed of light (that of a remote observer) may vary because of changes in speed or gravity, the proper speed of light (locally observed) never changes because local variations in space and time are always proportional to c.

The speed of light is a constant when measured relative to ones local environment so c is said to be relativistically invariant. This makes c a physical constant.
Thanks. I will try to think about the relative speeds sometime, but my mind got caught up in a sort of wonderment as I was reading your answer. OK, I think I get that thing about the parallel lines never meeting in flat space in 3D because 3D does not recognize that time can be a factor and that beacause of that space can warp. I don't really fully grok it, but it seems to make some sense.

What I got hung up on, is why we see space in 3D? There is vertical and we see that as one dimension such as height. There is horizontal and we see that as 2 dimensions (width and length) - what if we turn a pencil sideways, does it now become shorter and wider? Also why divide what we see from a horizonal perspective into 2 dimensions and what we percieve as vertical into only one dimension?

74. Originally Posted by Mayflow
Thanks. I will try to think about the relative speeds sometime, but my mind got caught up in a sort of wonderment as I was reading your answer. OK, I think I get that thing about the parallel lines never meeting in flat space in 3D because 3D does not recognize that time can be a factor and that beacause of that space can warp. I don't really fully grok it, but it seems to make some sense.
In an attempt to add another dimension to their work, some 19th century artists discovered an easy way to visualize Riemann's 4-D curved space where parallel lines meet at infinity but there is no way to grok the whole thing because time is distorted as well as space so seeing in 4-D is only half the picture. Here is a selfie of M. C. Escher demonstrating the technique for visualizing 4-D space.

M.C. Escher – Hand with Reflecting Sphere

Picasso and Dali used 4-D space and time in their work but nobody does 4-D space-time better than Escher.
Originally Posted by Mayflow
What I got hung up on, is why we see space in 3D? There is vertical and we see that as one dimension such as height. There is horizontal and we see that as 2 dimensions (width and length) - what if we turn a pencil sideways, does it now become shorter and wider? Also why divide what we see from a horizonal perspective into 2 dimensions and what we percieve as vertical into only one dimension?
Length isn't a dimension by itself and it can be applied to any of the four dimensions so your horizontal view is still one dimensional. I like to divide the dimensions into height, width, depth, and duration.

A common explanation for why we can only see in 3-D is that 4-D vision would be too confusing for animals so we have evolved to see in only three dimensions but I suspect it works the other way around. If an organism could occasionally move in 4-D space, that would be a great evolutionary advantage but an equal freedom of motion through all four dimensions may be physically impossible in our universe.

A universe where objects or even particles can move with equal freedom through four dimensions would be too chaotic for biological evolution to occur in the first place.

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