Thread: Symmetry of Special Relativity

In the threads Special Relativity Primer and Special Relativity Primer discussion the twins paradox was raised. It was a long time ago so I apologise if others have already covered this issue.
Back in 2011 the discussion seems to have faded. The moderator said:

Originally Posted by Janus

The rest of the posts in this thread have been split off to pseudoscience. Please keep in mind that the intent of this thread is to aid in the understanding of SR, and not to serve as a soapbox for those who wish to dispute it.

I guess that means that anyone who disputes SR is automatically talking pseudoscience.
So I am unsure whether this is the right forum for these discussions.

Anyway - here is my view of the twins paradox.

Ground control and Astronaut each has a clock and they synchronise their clocks to midday.
They agree to meet at 1 pm to check clocks.
Ground control sees the Astronaut recede further and further.
The astronaut sees Ground Control recede.
Then Ground Control sees the Astronaut approaching. The Astronaut sees Ground Control approaching.
They meet and check their clocks. Ground Control clocks shows 1 pm. The Astronaut's clock shows 1 pm.

Which is, of course, what we would expect.

Originally Posted by Farad

They meet and check their clocks. Ground Control clocks shows 1 pm. The Astronaut's clock shows 1 pm.

How did you calculate this result? It appears to be incorrect. Obviously I can't calculate what the correct result should be because you don't provide sufficient information.

I guess that means that anyone who disputes SR is automatically talking pseudoscience.

Well, if someone who understood it thoroughly disputed it with real evidence then perhaps not. But most people tackle it with an impressive mixture of ignorance and argument from incredulity.

Originally Posted by Farad

Ground control sees the Astronaut recede further and further.

Because he drove home for lunch?

Your "premise" is far too vague to make any serious comment on.

Originally Posted by Farad

Ground control and Astronaut each has a clock and they synchronise their clocks to midday.
They agree to meet at 1 pm to check clocks.
Ground control sees the Astronaut recede further and further.
The astronaut sees Ground Control recede.
Then Ground Control sees the Astronaut approaching. The Astronaut sees Ground Control approaching.
They meet and check their clocks. Ground Control clocks shows 1 pm. The Astronaut's clock shows 1 pm.

Which is, of course, what we would expect.

Ground control does indeed see the astronaut receding, and the astronaut sees ground control receding.
Ground control sees the astronaut approaching, and the astronaut sees ground control approaching.

But something else happened, before, between, and after these two scenarios. It had to. Something had to cause the first scenario, to change the first scenario into the second scenario, and to stop the second scenario turning back into the first scenario! (Answer - someone had to accelerate or decelerate)

Who changed the scenario? The astronaut, or ground control? (Answer - it was the astronaut)

This is where the asymmetry is found and this is the reason for the asymmetric result. (Result - an asymmetry between their clocks when the astronaut and ground control are once again in the same place)

Time dilation under Special Relativity is 'caused by' one observer at rest seeing another observer move. The result is the first observer sees the moving observer's clock slow down. Each observer must see the other observer as moving,

Originally Posted by Farad

Each observer must see the other observer as moving,

But only one of them will experience acceleration.

Originally Posted by Farad

They meet and check their clocks. Ground Control clocks shows 1 pm. The Astronaut's clock shows 1 pm.

How did you calculate this result?

Originally Posted by Farad

Time dilation under Special Relativity is 'caused by' one observer at rest seeing another observer move. The result is the first observer sees the moving observer's clock slow down. Each observer must see the other observer as moving,

But who did the moving? Did ground control do any moving?

In Special Relativity, time-dilation is symmetrical only between inertial frames of reference in relative motion. An accelerating frame is not inertial, and that is how the asymmetric result occurs.

For a more in-depth explanation, you need to understand the relativity of simultaneity.

Originally Posted by Strange

Originally Posted by Farad

Each observer must see the other observer as moving,

But only one of them will experience acceleration.

So you agree that according to Special Relativity, if both Ground Control and Astronaut are in inertial frames the results must be symmetrical?

Originally Posted by Farad

They meet and check their clocks. Ground Control clocks shows 1 pm. The Astronaut's clock shows 1 pm.

How did you calculate this result?

The results must be symmetrical according to Special Relativity. .

How can they meet, whilst remaining in inertial frames? (clue - they can't)

Originally Posted by SpeedFreek

Originally Posted by Farad

Time dilation under Special Relativity is 'caused by' one observer at rest seeing another observer move. The result is the first observer sees the moving observer's clock slow down. Each observer must see the other observer as moving,

But who did the moving? Did ground control do any moving?

In Special Relativity, time-dilation is symmetrical only between inertial frames of reference in relative motion. An accelerating frame is not inertial, and that is how the asymmetric result occurs.

For a more in-depth explanation, you need to understand the relativity of simultaneity.

A thing can only be moving if it is observed. In your own frame you are always at rest - not moving.
In my example there is no mention of acceleration. If you are saying 'There must always be acceleration' I quite agree. In which case there are no inertial frames, hence no Special Relativity. In which case the asymmetrical twins paradox is not a paradox of Special Relativity.

There is no paradox of the twins. The apparent paradox is due to a failure to take into account the history of the accelerations involved.

But there are inertial frames - you are in an inertial frame if you are not accelerating.

BUT... there is also the relativity of simultaneity, how you define a common "now" between two frames in relative motion. And guess what - simultaneity is shifting during acceleration!

I don't know why you are arguing against SR. It has been experimentally proven, repeatedly, in many different kinds of experiment.

I am guessing you are arguing against the symmetry of time-dilation between inertial frames in relative motion, which is impossible to falsify in practice.

Originally Posted by Farad

In my example there is no mention of acceleration.

Wasn't mentioned: correct.
However if there actually was no acceleration how did the astronaut return?

Originally Posted by Farad

Originally Posted by Strange

But only one of them will experience acceleration.

So you agree that according to Special Relativity, if both Ground Control and Astronaut are in inertial frames the results must be symmetrical?

If one of them experiences acceleration are they both in inertial frames?

The results must be symmetrical according to Special Relativity.

You think?

Originally Posted by Dywyddyr

Originally Posted by Farad

In my example there is no mention of acceleration.

Wasn't mentioned: correct.
However if there actually was no acceleration how did the astronaut return?

How did he even start moving away?

I gave him the benefit of the doubt and allowed that he was already moving and the 12 o'clock watch synchronisation was done in passing.

Yup, you can do the first clock synchronisation in passing before moving away, and the final clock readings in passing too, when returning. But the bit in between (turnaround) definitely requires an acceleration.

Please correct me if I'm wrong on this: If they both accelerated, and by equal amounts, there would be no paradox, then? They'd both age by exactly the same amounts?

I mean suppose ground control gets in a space ship also, and accelerates away from point zero (the point where they were in the same frame so they could synchronize their watches). The astronaut also accelerates away from point zero at the same rate, for the same duration (so both are moving at the same speed relative to point zero.) Then later they both turn around and come back. They'd both have aged by the same amount?

The only way one can age more than the other is if one of them accelerates more, right? Even if they accelerate away, and then accelerate back, the second acceleration doesn't "cancel out" the first?

Originally Posted by kojax

Please correct me if I'm wrong on this: If they both accelerated, and by equal amounts, there would be no paradox, then? They'd both age by exactly the same amounts?

Correct, they would both age by exactly the same amount.

There are no paradoxes in SR. The only paradoxes arise when SR is incorrectly applied.

Originally Posted by kojax

I mean suppose ground control gets in a space ship also, and accelerates away from point zero (the point where they were in the same frame so they could synchronize their watches). The astronaut also accelerates away from point zero at the same rate, for the same duration (so both are moving at the same speed relative to point zero.) Then later they both turn around and come back. They'd both have aged by the same amount?

Correct.

Originally Posted by kojax

The only way one can age more than the other is if one of them accelerates more, right?

Correct.

Originally Posted by kojax

Even if they accelerate away, and then accelerate back, the second acceleration doesn't "cancel out" the first?

I'm not quite sure what you mean, here.

How does acceleration affect Special Relativity time dilation?
Let's say Observer A measures that he (A) is accelerating and Observer B measures that he (B) is not accelerating . (This is impossible but let's leave that aside for now.)
Observer A sees Observer B moving, hence Observer A sees Observer B's clock slowing down.
But Observer B will see Observer A moving . Are we to conclude that Observer B will , for some strange reason, not see Observer A's clock slow down?

Originally Posted by Farad

How does acceleration affect Special Relativity time dilation?

NEGLECTING the acceleration is why there's a "paradox". As Speedfreek has pointed out.

Let's say Observer A measures that he (A) is accelerating and Observer B measures that he (B) is not accelerating . (This is impossible but let's leave that aside for now.)

Really? It's impossible for one party to accelerate while the other doesn't? Why is that?
I wonder why people bother to wave goodbye to friends departing in a car?

Observer A sees Observer B moving, hence Observer A sees Observer B's clock slowing down.
But Observer B will see Observer A moving . Are we to conclude that Observer B will , for some strange reason, not see Observer A's clock slow down?

Huh?

Originally Posted by Farad

How does acceleration affect Special Relativity time dilation?
Let's say Observer A measures that he (A) is accelerating and Observer B measures that he (B) is not accelerating . (This is impossible but let's leave that aside for now.)
Observer A sees Observer B moving, hence Observer A sees Observer B's clock slowing down.
But Observer B will see Observer A moving . Are we to conclude that Observer B will , for some strange reason, not see Observer A's clock slow down?

First you have to distinguish between what each visually sees and what they determine is happening to the other clock.

If we are talking about what they see, then each sees the following:

Observer B will Observer A's clock run slow as they recede, then after he accelerates to return, he will see A's clock run fast. This ends up with him seeing A's clock accumulate more time than his own.

Observer A will see B's clock run slow as he recedes, but does not see B's clock speed up when B turn around, because he has to wait for the light from B carrying that information to reach him. He ends up seeing B's clock running slow for a much longer time than he sees it running fast and ends up seeing B's clock accumulating less time than his own.

As fars as what each determines what is happening to the other clock.

According to A, B's clock runs slow on both the outbound and inbound legs and ends up accumulating less time then his own.
According to B, A's clock also run slow on both legs, however when he accelerates to return and he goes from being outbound to being inbound, A's clock jumps ahead of his own (Relativity of Simultaneity). The jump forward in time more than compensates for the periods that A's clock ran slow and A's clock ends up accumulating more time than his own.

In Both cases A and B end up agreeing as to Who's clock ended up accumulating the least time.

From the example in Post 1, at 1 pm both Ground Control and the Astronaut measure all clocks and all measurements agree. It is 1 pm for both parties. Therefore one observer cannot have measured time dilation.

This symmetry of Special Relativity is acknowledged in Special Relativity: What Time is it? Michael Fowler, Physics Department, UVa. where the author talks about Jack and Jill both having light clocks.
According to Jack ' Jill is aging more slowly because she’s moving! ' But the author then goes on to agree that the situation is symmetrical:

we must now turn everything around and look at it from Jill’s point of view. Her inertial frame of reference is just as good as Jack’s. She sees his light clock to be moving at speed v (backwards) so from her point of view his light blip takes the longer zigzag path, which means his clock runs slower than hers. That is to say, each of them will see the other to have slower clocks, and be aging more slowly. This phenomenon is called time dilation.

So there is a problem: IF both of their measurements of time agree then it does not make sense to say there is time dilation.

So what about the experimental 'proof' of Special Relativity?

The author in the Virginia.edu lecture goes on to talk about the Dying Muons experiment but he strangely forgets what he has just said about the symmetry of Special Relativity. If lab observers measure Muon time as slowed down, then Lab time has slowed down from the Muon frame of reference. In other words measurements of time from all frames must agree so there can be no basis for saying 'time seems to have slowed'.

Originally Posted by Farad

From the example in Post 1, at 1 pm both Ground Control and the Astronaut measure all clocks and all measurements agree. It is 1 pm for both parties. Therefore one observer cannot have measured time dilation.

The highlighted portion is an assumption on your part.
Not supported by the facts.
As Strange pointed out in post #2.

Originally Posted by Farad

From the example in Post 1, at 1 pm both Ground Control and the Astronaut measure all clocks and all measurements agree. It is 1 pm for both parties. Therefore one observer cannot have measured time dilation.

This is the logical fallacy of "begging the question"; you have assumed that the clocks agree and concluded that therefore there was no time dilation. However, your initial assumption is wrong.

This symmetry of Special Relativity is acknowledged in Special Relativity: What Time is it?

Michael Fowler, Physics Department, UVa. [SIZE=3][FONT=arial] where the author talks about Jack and Jill both having light clocks.
According to Jack ' Jill is aging more slowly because she’s moving! '[COLOR=#000000] But the author then goes on to agree that the situation is symmetrical:

There is no acceleration in this case. They are both inertial frames of reference and so the situation is symmetrical.

So what about the experimental 'proof' of Special Relativity?

There is lots.

The author in the Virginia.edu lecture goes on to talk about the Dying Muons experiment but he strangely forgets what he has just said about the symmetry of Special Relativity. If lab observers measure Muon time as slowed down, then Lab time has slowed down from the Muon frame of reference.

What makes you think he has forgotten? Muons can't tell us what they see (although we can calculate what they would see) so there is nothing to mention.

In other words measurements of time from all frames must agree so there can be no basis for saying 'time seems to have slowed'.

Nonsense. If A sees B's clock running slower than his and B sees A's clock running slower than hers then they will both conclude that time has slowed for the other.

I will do what I usually do here and bring up GPS. Yes, I know: boring.

GPS has to take these (and other) relativistic effects into account or it wouldn't work.

Originally Posted by Dywyddyr

Originally Posted by Farad

From the example in Post 1, at 1 pm both Ground Control and the Astronaut measure all clocks and all measurements agree. It is 1 pm for both parties. Therefore one observer cannot have measured time dilation.

The highlighted portion is an assumption on your part.
Not supported by the facts.
As Strange pointed out in post #2.

and from Strange, a similar objection:

Originally Posted by Strange

This is the logical fallacy of "begging the question"; you have assumed that the clocks agree and concluded that therefore there was no time dilation. However, your initial assumption is wrong.

I have not made any assumption. What I said is a necessary consequence of Relativity.

Take two people , A and B, in motion relative to each other. It would be nonsense to claim 'A measured B as having moved 1 mile whereas B measured A as having moved three quarters of a mile.' They both must obtain the same result. That is a consequence of relativity.

In the same way , if A and B have clocks then their measurements must agree. If they set their clocks at midday , watch each other move then compare their clocks at say A's 1 pm then that must also be B's 1 pm. Therefore we cannot say 'A observes B's clock as running slow.' That is impossible.They both have the same measurement of time for all clocks.

Originally Posted by Farad

I have not made any assumption. What I said is a necessary consequence of Relativity.

If you claim that the fact their clocks both show the same time is not an assumption (despite the fact you have provided no calculations or evidence to support his) then the assumption is that the situation is symmetrical.

It is OBVIOUSLY not symmetrical as one of the people accelerates and the other doesn't.

This is not even an argument from ignorance, this is an argument from "la-la-la, I can't hear you I've got my fingers in my ears".

This is utterly pointless. Relativity works. It has been proved to work. It is the basis of technology in use everyday. You know that computer you are using? It contains "semiconductors". You know that semiconductor feature sizes are now so small we have to take quantum effects into account. If relativity was wrong, your computer wouldn't work.

Just go and learn the basics and come back with some intelligent questions.

p.s. using a bigger font doesn't make your assertions any more plausible. It just makes you look cranky.

Originally Posted by Farad

Take two people , A and B, in motion relative to each other. It would be nonsense to claim 'A measured B as having moved 1 mile whereas B measured A as having moved three quarters of a mile.' They both must obtain the same result. That is a consequence of relativity.

Wrong.

In the same way , if A and B have clocks then their measurements must agree. If they set their clocks at midday , watch each other move then compare their clocks at say A's 1 pm then that must also be B's 1 pm. Therefore we cannot say 'A observes B's clock as running slow.' That is impossible.They both have the same measurement of time for all clocks.

Wrong. Just saying it is impossible is not exactly a rational argument. When A's clock says 1 pm they will see B's clock read 12:59 (or whatever - again you haven't provided any information). When B's clock says 1 pm they will see A's clock read 12:59.

That is why it is called "relativity".

Originally Posted by Farad

Originally Posted by Dywyddyr

Originally Posted by Farad

From the example in Post 1, at 1 pm both Ground Control and the Astronaut measure all clocks and all measurements agree. It is 1 pm for both parties. Therefore one observer cannot have measured time dilation.

The highlighted portion is an assumption on your part.
Not supported by the facts.
As Strange pointed out in post #2.

and from Strange, a similar objection:

Originally Posted by Strange

This is the logical fallacy of "begging the question"; you have assumed that the clocks agree and concluded that therefore there was no time dilation. However, your initial assumption is wrong.

I have not made any assumption. What I said is a necessary consequence of Relativity.

No, That conclusion is a consequence of your not understanding the consequences of Relativity.

Take two people , A and B, in motion relative to each other. It would be nonsense to claim 'A measured B as having moved 1 mile whereas B measured A as having moved three quarters of a mile.' They both must obtain the same result. That is a consequence of relativity.

But Relativity say that the two people will disagree as to the distance, this is a consequence of Length contraction and the Relativity of Simultaneity. Saying that something is nonsense because it conflicts with how you think it should be is not an argument.

Originally Posted by Farad

I have not made any assumption. What I said is a necessary consequence of Relativity.

Please answer me one question: how can you justify the comment "it is a necessary consequence of relativity" when you obviously have no idea what relativity is or how it works?

Originally Posted by Farad

I guess that means that anyone who disputes SR is automatically talking pseudoscience.

Well, not exactly "automatically," but given the mountain of experimental evidence in support of SR, the complete lack of evidence in contradiction with SR, and the proven logical self-consistency of SR, any dispute would have to be incredibly well supported. We never see this; the claimant always suffers from some combination of ignorance, stupidity, and adherence to some dogmatic belief. That's why, for all practical purposes, anyone who disputes SR is talking pseudoscience.

So I am unsure whether this is the right forum for these discussions. Anyway - here is my view of the twins paradox...

Your view is simply wrong, as Strange and others have pointed out to you repeatedly. The situation is not symmetrical. One twin undergoes an acceleration, while the other does not. If you understand SR, you would know why that difference is not a triviality. Continuing to insist that there is symmetry is to demonstrate that you do not know what you are talking about. To persist in your assertions -- presented ultimately in standard boldface CrankFont(tm), no less -- simply marks you as yet another ignorant, arrogant fool. If you're here to understand SR better, you're doing a craptastic job of it. If you're here to push an agenda, you're still doing a craptastic job of it. Step away from the "increase font to ludicrous size" menu option, turn on your brain and re-read with an open mind the explanations you have been given. Concentrate on why an acceleration makes a huge difference. Concentrate also on why this acceleration (experienced by only one twin, not both) fundamentally breaks the symmetry. Once you've grown intellectually enough to understand that, you'll be one step closer to understanding the resolution to the so-called Twins Paradox.

Originally Posted by Farad

So what about the experimental 'proof' of Special Relativity?

The author in the Virginia.edu lecture goes on to talk about the Dying Muons experiment but he strangely forgets what he has just said about the symmetry of Special Relativity. If lab observers measure Muon time as slowed down, then Lab time has slowed down from the Muon frame of reference. In other words measurements of time from all frames must agree so there can be no basis for saying 'time seems to have slowed'.

If you want to examine things from the Muon frame, you also have to take Length contraction and the Relativity of Simultaneity into account. The height of the Atmosphere is less due to length contraction, which allows the Muon to cross it in its limited lifetime, and the clock on the surface reads later at the moment the muon hits the atmosphere according to the Muon than it does according to the ground observer. The Author did not forget anything, He just didn't bother with explaining how things appears for the Muon. Not because he couldn't, but because he really didn't have to.

Originally Posted by Strange

It is OBVIOUSLY not symmetrical as one of the people accelerates and the other doesn't.

Acceleration has nothing to do with the effects of Special Relativity.
'Two people are moving relative to one another.'
In the 'Light clock' experiment from the Virginia Uni site I linked to, acceleration does not come into it. Jack and Jill obtain the same measurements.

It is worthwhile mentioning acceleration because that is the 'noise' people usually introduce into the Twins Paradox to explain away a fatal flaw in reasoning. There are thousands of 'experts' each with their own take on how acceleration accounts for the paradox but as someone said, their is no paradox. If both twins age at the same rate (which they must) then there is no basis for saying 'The other twin seemed to age slowly'.

Originally Posted by Farad

Acceleration has nothing to do with the effects of Special Relativity.
'Two people are moving relative to one another.'
In the 'Light clock' experiment from the Virginia Uni site I linked to, acceleration does not come into it. Jack and Jill obtain the same measurements.

If there is no acceleration then the twins CANNOT meet again and their clocks will always agree.

It is worthwhile mentioning acceleration because that is the 'noise' people usually introduce into the Twins Paradox to explain away a fatal flaw in reasoning. There are thousands of 'experts' each with their own take on how acceleration accounts for the paradox but as someone said, their is no paradox. If both twins age at the same rate (which they must) then there is no basis for saying 'The other twin seemed to age slowly'.

Is it worthwhile pointing out (probably not) that the only "fatal flaw in reasoning" here is yours?

Originally Posted by Janus

But Relativity say that the two people will disagree as to the distance, this is a consequence of Length contraction and the Relativity of Simultaneity. Saying that something is nonsense because it conflicts with how you think it should be is not an argument.

Take the situation where A and B are moving relative to one another.
Say A measures B as moving 1 mile.
Please tell me what B will measure: 1. A moved 1 mile 2. A moved more than one mile 3. A moved less than one mile.

We are told that the laws at operation in A's frame also operate in B's frame.

Originally Posted by Farad

Take the situation where A and B are moving relative to one another.
Say A measures B as moving 1 mile.
Please tell me what B will measure: 1. A moved 1 mile 2. A moved more than one mile 3. A moved less than one mile.

Assuming there is no acceleration involved then, as you are fond of saying, the situation is symmetrical. Therefore B will measure A as also travelling 1 mile.

But: A will measure themselves as moving more than 1 mile. And, of course, B will measure themselves as moving more than 1 mile.

Originally Posted by Farad

Originally Posted by Janus

But Relativity say that the two people will disagree as to the distance, this is a consequence of Length contraction and the Relativity of Simultaneity. Saying that something is nonsense because it conflicts with how you think it should be is not an argument.

Take the situation where A and B are moving relative to one another.
Say A measures B as moving 1 mile.
Please tell me what B will measure: 1. A moved 1 mile 2. A moved more than one mile 3. A moved less than one mile.

We are told that the laws at operation in A's frame also operate in B's frame.

Your question is too vague. It all depends on how the measurements are made.

For example if A determines that after 1 hr on by his clock B is 1 mile away and you are asking how for A is from B when B says 1 has passed, then the distance according to B will be 1 mile.

On the other hand, if we put a marker 1 mile from A as measured by A, and then ask how far A is away from B when B passes the marker according to B, B will say that A is closer than 1 Mile away because length contraction shortens the distance between A and the marker.

But then again, if we say that after 1 hr according to A, B is 1 mile away and ask B how far A is when 1 hr has passed on A's clock, B will say that A is farther than 1 mile away. This is because according to B, A's clock runs slow, so by the time 1 hr passes on it, more than an hour has passed for B, and the distance between A and B has increased to more than 1 mile.

All the law's of operation are the same in both frames, but do have to apply all the laws.

Originally Posted by Strange

Originally Posted by Farad

Take the situation where A and B are moving relative to one another.
Say A measures B as moving 1 mile.
Please tell me what B will measure: 1. A moved 1 mile 2. A moved more than one mile 3. A moved less than one mile.

Assuming there is no acceleration involved then, as you are fond of saying, the situation is symmetrical. Therefore B will measure A as also travelling 1 mile.

But: A will measure themselves as moving more than 1 mile. And, of course, B will measure themselves as moving more than 1 mile.

That's impossible. A and B are moving relative to one another. IF A measures B as moving then A must measure A as being at rest.

Originally Posted by Farad

That's impossible. A and B are moving relative to one another. IF A measures B as moving then A must measure A as being at rest.

Doh. You're right. I wrote that too quickly.

But the principle applies: both will see the others distances shortened relative their own.

And I realise now that your question is poorly worded (as is often the case with people who don't understand relativity).

For example, you say: "Say A measures B as moving 1 mile." And this is meaningless unless you say 1 mile according to who; is it a mile in A's frame of reference or B's frame of reference.

Originally Posted by Strange

Originally Posted by Farad

That's impossible. A and B are moving relative to one another. IF A measures B as moving then A must measure A as being at rest.

Doh. You're right. I wrote that too quickly.

But the principle applies: both will see the others distances shortened relative their own.

And I realise now that your question is poorly worded (as is often the case with people who don't understand relativity).

For example, you say: "Say A measures B as moving 1 mile." And this is meaningless unless you say 1 mile according to who; is it a mile in A's frame of reference or B's frame of reference.

Just a couple of questions that you most likely covered already. If there is no acceleration by A or B wouldn't their frames stay the same no matter how fast they were moving or what directions? Shouldn't their measurements all be the same including time?

This article is rather long, but is a fascinating insight into the mind of a very intelligent relativity denier. Exactly the same characteristics as people we get here: failing to understand the basic principles, thinking they are the first to spot "the fatal flaw", being accused of pulling everyone's leg ("trolling" as we would put it now).

What Happened to Dingle?

Originally Posted by bill alsept

[Just a couple of questions that you most likely covered already. If there is no acceleration by A or B wouldn't their frames stay the same no matter how fast they were moving or what directions? Shouldn't their measurements all be the same including time?

If they are in relative motion, then they will both see the other's lengths (in the direction of motion) contracted relative to their own, and the other's clocks running slow relative to their own.

Originally Posted by Strange

Originally Posted by Farad

That's impossible. A and B are moving relative to one another. IF A measures B as moving then A must measure A as being at rest.

Doh. You're right. I wrote that too quickly.

But the principle applies: both will see the others distances shortened relative their own.

And I realise now that your question is poorly worded (as is often the case with people who don't understand relativity).

For example, you say: "Say A measures B as moving 1 mile." And this is meaningless unless you say 1 mile according to who; is it a mile in A's frame of reference or B's frame of reference.

We are only dealing with 2 frames of reference. Either A's frame is at rest or B's frame is at rest. A cannot be moving relative to A's frame. B cannot be moving relative to B's frame.
This is not hard. If you measure someone as having travelled 1 mile then they will have measured you as travelling 1 mile. It's called relativity.

It therefore follows that neither A nor B could have measured each other as not having travelled 1 mile. In other words the nonsense comes in when people say things like 'To A, B's distances appear lengthened. ' They are not measured as lengthened. They cannot be measured as lengthened if both A and B arrive at the same measurements. It's easy!

Originally Posted by Strange

Originally Posted by bill alsept

[Just a couple of questions that you most likely covered already. If there is no acceleration by A or B wouldn't their frames stay the same no matter how fast they were moving or what directions? Shouldn't their measurements all be the same including time?

If they are in relative motion, then they will both see the other's lengths (in the direction of motion) contracted relative to their own, and the other's clocks running slow relative to their own.

Even if there is no acceleration involved?

Originally Posted by Farad

Acceleration has nothing to do with the effects of Special Relativity.

Feel free to use general relativity, which includes gravity and equivalently acceleration, to calculate the result. Not surprisingly you will find that this produces exactly the same result (i.e. one twin ages more than the other).

Originally Posted by bill alsept

Even if there is no acceleration involved?

Yes. Special relativity is all about inertial (non-accelerating) motion.

Originally Posted by Farad

We are only dealing with 2 frames of reference. Either A's frame is at rest or B's frame is at rest. A cannot be moving relative to A's frame. B cannot be moving relative to B's frame.
This is not hard. If you measure someone as having travelled 1 mile then they will have measured you as travelling 1 mile. It's called relativity.

Probably true. Although you still haven't said whose mile.

In other words the nonsense comes in when people say things like 'To A, B's distances appear lengthened. '

Well, that would be nonsense. The lengths of a moving object are reduced relative to the observer.

They are not measured as lengthened. They cannot be measured as lengthened if both A and B arrive at the same measurements. It's easy!

They are measured as shortened. Again: GPS. It works. The relative changes in time and length due to relative velocity and differences in gravitational potential have to be taken into account when calculating a position or you get the wrong answer.

And every single experiment has confirmed the theory works. No experiment is in conflict with it.

So just repeatedly saying, "it's wrong" is of zero value.

Originally Posted by Strange

They are measured as shortened. Again: GPS. It works. The relative changes in time and length due to relative velocity and differences in gravitational potential have to be taken into account when calculating a position or you get the wrong answer.

And every single experiment has confirmed the theory works. No experiment is in conflict with it.
.

But that involves acceleration from g. Are there any experiments that confirm time dilations when there is no acceleration involved?

Originally Posted by bill alsept

But that involves acceleration from g. Are there any experiments that confirm time dilations when there is no acceleration involved?

Well, special relativity is just a special case of general relativity, so it is impossible for GR to be correct and SR not. But, for example
Trouton-Rankine experiment
Kennedy-Thorndike experiment
Michelson-Morley experiment
Time dilation of moving particles - Wikipedia, the free encyclopedia

And so on.

And, of course, as I said earlier: your computer works.

Originally Posted by Strange

Originally Posted by bill alsept

But that involves acceleration from g. Are there any experiments that confirm time dilations when there is no acceleration involved?

Well, special relativity is just a special case of general relativity, so it is impossible for GR to be correct and SR not. But, for example
Trouton-Rankine experiment
Kennedy-Thorndike experiment
Michelson-Morley experiment
Time dilation of moving particles - Wikipedia, the free encyclopedia

.

But all of these experiments were performed in a gravitational field where everything including light is being accelerated constantly. Wouldn't that make a difference?

But all of these experiments were performed in a gravitational field where everything including light is being accelerated constantly. Wouldn't that make a difference?

Gravitational time dilation is fairly simple to account for in experimental setups.

Originally Posted by AlexG

But all of these experiments were performed in a gravitational field where everything including light is being accelerated constantly. Wouldn't that make a difference?

Gravitational time dilation is fairly simple to account for in experimental setups.

Yes but is the acceleration accounted for?

Light is accelerated only in the sense that it is following a curved geodesic. c is a vector quantity, and so has a directional component, so one could say that by following a curved path (even though it is the shortest distance) light changes directions and so undergoes accelerated movement. The speed of light doesn't change however.

And yes, this factor is accounted for. Do you really think that experimental physicists would overlook gravitational effects?

Originally Posted by AlexG

Light is accelerated only in the sense that it is following a curved geodesic. c is a vector quantity, and so has a directional component, so one could say that by following a curved path (even though it is the shortest distance) light changes directions and so undergoes accelerated movement. The speed of light doesn't change however.

And yes, this factor is accounted for. Do you really think that experimental physicists would overlook gravitational effects?

So it is being accelerated?

Originally Posted by bill alsept

Originally Posted by AlexG

Light is accelerated only in the sense that it is following a curved geodesic. c is a vector quantity, and so has a directional component, so one could say that by following a curved path (even though it is the shortest distance) light changes directions and so undergoes accelerated movement. The speed of light doesn't change however.

And yes, this factor is accounted for. Do you really think that experimental physicists would overlook gravitational effects?

So it is being accelerated?

\

Yes, and the acceleration shifts it's frequency. Speed is unchanged.

Originally Posted by AlexG

Originally Posted by bill alsept

Originally Posted by AlexG

Light is accelerated only in the sense that it is following a curved geodesic. c is a vector quantity, and so has a directional component, so one could say that by following a curved path (even though it is the shortest distance) light changes directions and so undergoes accelerated movement. The speed of light doesn't change however.

And yes, this factor is accounted for. Do you really think that experimental physicists would overlook gravitational effects?

So it is being accelerated?

\

Yes, and the acceleration shifts it's frequency. Speed is unchanged.

I thought so and that is why in post 47 I asked "Are there any experiments that confirm time dilations when there is no acceleration involved?"

Originally Posted by bill alsept

Originally Posted by AlexG

Originally Posted by bill alsept

Originally Posted by AlexG

Light is accelerated only in the sense that it is following a curved geodesic. c is a vector quantity, and so has a directional component, so one could say that by following a curved path (even though it is the shortest distance) light changes directions and so undergoes accelerated movement. The speed of light doesn't change however.

And yes, this factor is accounted for. Do you really think that experimental physicists would overlook gravitational effects?

So it is being accelerated?

\

Yes, and the acceleration shifts it's frequency. Speed is unchanged.

I thought so and that is why in post 47 I asked "Are there any experiments that confirm time dilations when there is no acceleration involved?"

Do you mean are there any experiments which have taken place in a gravitational field so weak that it can effectively be ignored?

Originally Posted by AlexG

Do you mean are there any experiments which have taken place in a gravitational field so weak that it can effectively be ignored?

Yes, someplace that everything isn't being accelerated constantly (so much). I know there is no place in the universe but why do the experiments on a planet right in the middle of a gravitational field? I wonder how much different it would be out between galaxies. It just seems to me that if everything your measuring and everything your measuring with is constantly being accelerated by gravity then there is nothing special about it.

I don't need to go where there is no rain to measure rain. I only need to measure the difference between rains.

It does apply that sometimes you must avoid an influence that can skew your results. Take WMAP, for example, where the satellite needed to be very carefully aligned and positioned in order to prevent influences from giving poor data on CMB.
But that is influence, not the object you are measuring.

Originally Posted by Neverfly

I don't need to go where there is no rain to measure rain. I only need to measure the difference between rains.

It does apply that sometimes you must avoid an influence that can skew your results. Take WMAP, for example, where the satellite needed to be very carefully aligned and positioned in order to prevent influences from giving poor data on CMB.
But that is influence, not the object you are measuring.

My question at post 47 was "Are there any experiments that confirm time dilations when there is no acceleration involved?" I was told "Yes. Special relativity is all about inertial (non-accelerating) motion." Where are these non accelerating experiments?

Any object, or space station or geosynchronous satellite in free fall is in a non accelerating environment.

Originally Posted by bill alsept

My question at post 47 was "Are there any experiments that confirm time dilations when there is no acceleration involved?" I was told "Yes. Special relativity is all about inertial (non-accelerating) motion." Where are these non accelerating experiments?

No, it wasn't your question.
You asked, "even if no acceleration is involved" which is very different from, "Are there any experiments that confirm time dilations when there is no acceleration involved?"

And to answer the second question, I refer you back to the post I just made above: Accelerations do not need to be removed in order to measure the difference in accelerations.

Originally Posted by Neverfly

Originally Posted by bill alsept

My question at post 47 was "Are there any experiments that confirm time dilations when there is no acceleration involved?" I was told "Yes. Special relativity is all about inertial (non-accelerating) motion." Where are these non accelerating experiments?

No, it wasn't your question.
You asked, "even if no acceleration is involved" which is very different from, "Are there any experiments that confirm time dilations when there is no acceleration involved?"

And to answer the second question, I refer you back to the post I just made above: Accelerations do not need to be removed in order to measure the difference in accelerations.

I said post 47, that was my question in post 43. Anyway I am not asking about the difference in acceleration I want to know why there would be time dilation if there were NO acceleration.

Originally Posted by AlexG

Any object, or space station or geosynchronous satellite in free fall is in a non accelerating environment.

I agree it is far less than here on the surface but it is still constantly being accelerated.

Originally Posted by Janus

Originally Posted by Farad

Originally Posted by Janus

But Relativity say that the two people will disagree as to the distance, this is a consequence of Length contraction and the Relativity of Simultaneity. Saying that something is nonsense because it conflicts with how you think it should be is not an argument.

Take the situation where A and B are moving relative to one another.
Say A measures B as moving 1 mile.
Please tell me what B will measure: 1. A moved 1 mile 2. A moved more than one mile 3. A moved less than one mile.

We are told that the laws at operation in A's frame also operate in B's frame.

Your question is too vague. It all depends on how the measurements are made.

For example if A determines that after 1 hr on by his clock B is 1 mile away and you are asking how for A is from B when B says 1 has passed, then the distance according to B will be 1 mile.

On the other hand, if we put a marker 1 mile from A as measured by A, and then ask how far A is away from B when B passes the marker according to B, B will say that A is closer than 1 Mile away because length contraction shortens the distance between A and the marker.

But then again, if we say that after 1 hr according to A, B is 1 mile away and ask B how far A is when 1 hr has passed on A's clock, B will say that A is farther than 1 mile away. This is because according to B, A's clock runs slow, so by the time 1 hr passes on it, more than an hour has passed for B, and the distance between A and B has increased to more than 1 mile.

All the law's of operation are the same in both frames, but do have to apply all the laws.

I suggest you are not thinking about who is moving. The observer never moves.
'For example if A determines that after 1 hr on by his clock B is 1 mile away and you are asking how for A is from B when B says 1 has passed, then the distance according to B will be 1 mile. '
Translate - A determines that after an hour B has moved 1 mile away. For B , A is moving. A has moved 1 mile in 1 hour so they both agree and there is no time dilation or length contraction . So I agree with your point.

'On the other hand, if we put a marker 1 mile from A as measured by A, and then ask how far A is away from B when B passes the marker according to B, B will say that A is closer than 1 Mile away because length contraction shortens the distance between A and the marker.'
'If we ask B how far A is away' - remember A is moving according to B. B cannot pass the marker. B sees A moving 1 mile in one hour. A sees B moving 1 mile in one hour. Their clocks and rulers agree.

Let me put this to you: Let's say two Olympic officials have synchronised watches before a race. After the race they have both agreed on the length of the track. After the race they compare stop clocks and both show 1 minute for the race. Could one official say to the other 'Your clock was running slow.' ? Does it make any more sense for them both to say to each other 'Your clock was running slow'? (This is different to the two frames of reference examples but I mention it because it highlights a faulty conclusion.

Originally Posted by bill alsept

I said post 47, that was my question in post 43. Anyway I am not asking about the difference in acceleration I want to know why there would be time dilation if there were NO acceleration.

You're right- my mistake.
Foot- meet mouth.
As per your question: I must be in total stupid mode today because I am not following you- at all. Time Dilation is an effect.
A gravity well will cause time dilation. As well as inertia. If you are asking how it can happen when there is no acceleration, then you might also say, "I need to learn a lot more on this topic..."

Some further reading here on testing:

Today, special relativity's predictions are routinely confirmed in particle accelerators such as the Relativistic Heavy Ion Collider. For example, the increase of relativistic momentum and energy is not only precisely measured but also necessary to understand the behavior of cyclotrons and synchrotrons etc., by which particles are accelerated near to the speed of light.

Tests of special relativity - Wikipedia, the free encyclopedia

Although I give a focused direction in the link, I still think you should scroll up and read it from the beginning once you've been satisfied that there are tests of time dilation:
Time dilation - Wikipedia, the free encyclopedia

Originally Posted by Neverfly

I still think you should scroll up and read it from the beginning once you've been satisfied that there are tests of time dilation:

I have no problem with time dilation. I find it to be the most insteresting of all phenomena. My questions have more to do with what the Farad and Strange were discussing. When A or B are observing and measuring each other I think the constant acceleration of gravity would make a difference to the readings. I would think that no two objects could ever be in a non accelerating frame compared to each other.

Originally Posted by bill alsept

I would think that no two objects could ever be in a non accelerating frame compared to each other.

Why?

Originally Posted by bill alsept

But all of these experiments were performed in a gravitational field where everything including light is being accelerated constantly. Wouldn't that make a difference?

It would. And by doing a full analysis using general relativity, you can calculate exactly how much difference. It is usually insignificant.

But, as I say, SR is just an approximation of GR. So ...

Originally Posted by bill alsept

I have no problem with time dilation. I find it to be the most insteresting of all phenomena. My questions have more to do with what the Farad and Strange were discussing. When A or B are observing and measuring each other I think the constant acceleration of gravity would make a difference to the readings. I would think that no two objects could ever be in a non accelerating frame compared to each other.

Time dilation and length contraction are results of the same effect. They both obey the same laws and are both affected by (realtive) velocity, acceleration and gravity.

In the case of inertial frames, they are both symmetrical. A will see B's clock running slow and B will see A's clock running slow

Originally Posted by Farad

repeated ignorant nonsense

Farad, theory shows you wrong. Experiment shows you are wrong. Practical technology shows you are wrong.

You have had your errors explained to you.

Are you going to do anything other than repeat your misunderstandings?

Originally Posted by Neverfly

Originally Posted by bill alsept

I would think that no two objects could ever be in a non accelerating frame compared to each other.

Why?

Because there is always acceleration. All object effect all other object in the universe.

if " they are both symmetrical. A will see B's clock running slow and B will see A's clock running slow" thay are in parallel worlds

Originally Posted by Water Nosfim

if " they are both symmetrical. A will see B's clock running slow and B will see A's clock running slow" thay are in parallel worlds

Or maybe their both slow clocks

Originally Posted by Water Nosfim

if " they are both symmetrical. A will see B's clock running slow and B will see A's clock running slow" thay are in parallel worlds

Stop posting nonsense. Farad is doing enough of that already, he doesn't need your help.

Originally Posted by Strange

Originally Posted by Water Nosfim

if " they are both symmetrical. A will see B's clock running slow and B will see A's clock running slow" thay are in parallel worlds

Stop posting nonsense. Farad is doing enough of that already, he doesn't need your help.

For two frames of reference . if A sees B moving and measures distance and speed then we can be assured by relativity that B sees A moving with the same measurements.

Special Relativity demands symmetry. If we observe , from the lab frame of reference , muons travelling at X , then rest assured that in the muon frame , the lab is travelling at X.

I'll say this once. I have met your type: Insults, plea to 'They have done it'. The classic 'You don't understand.'

I am here to think issues through.

If you insult again I shall ignore you.

Originally Posted by Farad

Special Relativity demands symmetry. If we observe , from the lab frame of reference , muons travelling at X , then rest assured that in the muon frame , the lab is travelling at X.

The lab sees the muons time dilated and length contracted (relative to the lab).

The muons "see" the lab time dilated and length contracted (relative to them).

This can be easily calculated and has been confirmed in many different situations.

I'm going to give Water Nosfim 3 days off for posting nonsense in the Physics section after being requested not to. Also, sending this to pseudoscience as it is just another garden variety relativity denial thread.

I had set out my argument clearly and unemotionally. I gave reasons and I answered counter points.
Megalomaniac Harold handwaves away the thread, chopping it in half and sends it to the kookey bin. No reasons given because he doesn't have to give reasons. He acts against people with a dissenting view - judge jury and executioner - all that is bad in power.

The pattern is familiar - the power hungry encourage foot soldiers such as Strange to wage debate through insult, ridicule and humiliation. No matter how whacky the foot soldiers are , they are OK because they are on the right team. They are defending 'science' from the unwashed hordes.

Above all - protect the megalomaniacs' ears from voices of dissent.

Originally Posted by Farad

I had set out my argument clearly and unemotionally. I gave reasons and I answered counter points.

You have not addressed the basic problem here. How do you propose to falsify the symmetrical time-dilation between inertial frames in relative motion?

In order to falsify it, you need to present a scenario without any accelerations involved (as acceleration is non-inertial), using purely inertial frames, and show how the results are asymmetrical. Go ahead...

Originally Posted by Farad

I had set out my argument clearly and unemotionally. I gave reasons and I answered counter points.

No. You replied, but did not answer. Your replies were often mere repetitions of assertions.

Megalomaniac Harold handwaves away the thread, chopping it in half and sends it to the kookey bin.

You are acting like an infant. Your errors have been shown to you patiently and repeatedly. You obviously did not come here to learn. Instead you are on a crusade of some sort. We have met your kind before.

No reasons given because he doesn't have to give reasons. He acts against people with a dissenting view - judge jury and executioner - all that is bad in power.

The reasons are obvious to anyone paying attention. Since you don't seem to be among that group, allow me to provide some education. Your stubborn denials of logic and experiment show you to be a crank. Is that clear enough?

The pattern is familiar - the power hungry encourage foot soldiers such as Strange to wage debate through insult, ridicule and humiliation. No matter how whacky the foot soldiers are , they are OK because they are on the right team. They are defending 'science' from the unwashed hordes.

The pattern is familiar -- the would-be new-Einstein has his bubble burst by the prickly pin of reality, and lashes out at those with actual knowledge. Unable to accept his sub-genius status (hi, Bob!), he accuses everyone else of being part of a power elite.

Wah wah wahhhhhhhh!

Above all - protect the megalomaniacs' ears from voices of dissent.

If you're an idiot, don't expect to be treated as a genius. If you're a megalomaniacal idiot, don't expect to be treated gently.

Farad, so far all you have done is:

Present a scenario with a departing and returning astronaut and claimed the time-dilation should be symmetrical, whilst ignoring the fact that in order to return the astronaut has to accelerate and thus is not in inertial motion and thus the result is not expected to be symmetrical.

And

Failed to show how the time-dilation/length contraction in the muon example is not symmetrical.

So far, there is no substance to your objections. Please try to provide some.

Originally Posted by Farad

For two frames of reference . if A sees B moving and measures distance and speed then we can be assured by relativity that B sees A moving with the same measurements.

Special Relativity demands symmetry. If we observe , from the lab frame of reference , muons travelling at X , then rest assured that in the muon frame , the lab is travelling at X.

You don't seem to understand that this true only for inertial frames. In the twin experiment, the travelling twin is not in an inertial frame.

Originally Posted by Farad

No reasons given because he doesn't have to give reasons.

The thread remained in the physics section, or maybe it was cosmology, for two days. In all that time you never addressed the point about acceleration. It became obvious that you were not open to discussion.

Originally Posted by Farad

Megalomaniac Harold handwaves away the thread, chopping it in half and sends it to the kookey bin. No reasons given because he doesn't have to give reasons. He acts against people with a dissenting view - judge jury and executioner - all that is bad in power.

The pattern is familiar - the power hungry encourage foot soldiers such as Strange to wage debate through insult, ridicule and humiliation. No matter how whacky the foot soldiers are , they are OK because they are on the right team. They are defending 'science' from the unwashed hordes.

Above all - protect the megalomaniacs' ears from voices of dissent.

Oh come off it. It is a discussion forum. On the Internet.

Not exactly something important.

duty_calls.jpg
"What do you want me to do? LEAVE? Then they'll keep being wrong!"

Originally Posted by bill alsept

Originally Posted by Neverfly

Originally Posted by bill alsept

I would think that no two objects could ever be in a non accelerating frame compared to each other.

Why?

Because there is always acceleration. All object effect all other object in the universe.

Experiments have been performed that rule out any significant effect on clocks by acceleration. I know you keep stressing the idea of testing where there is no acceleration, but going the other way is just as effective and much easier to do. Here's the set up. You place a radioisotope sample in a centrifuge and spin it so that it experiences very high g forces. The beauty of this experiment is that, by varying the radius of the centrifuge you can get different combinations of the speed of the sample and g force. You can have it experience the same g force at different speeds or different g forces at different speeds. If acceleration has any effect on the sample decay rate, higher accelerations would have a larger effect.

Such experiments have been performed at accelerations up to 10^18 g and no additional variation in the decay rate due to acceleration has shown up; the difference in decay rate always matches that for what you would predict for the speed of the sample alone.

Originally Posted by Janus

Originally Posted by bill alsept

Originally Posted by Neverfly

Originally Posted by bill alsept

I would think that no two objects could ever be in a non accelerating frame compared to each other.

Why?

Because there is always acceleration. All object effect all other object in the universe.

Experiments have been performed that rule out any significant effect on clocks by acceleration. I know you keep stressing the idea of testing where there is no acceleration, but going the other way is just as effective and much easier to do. Here's the set up. You place a radioisotope sample in a centrifuge and spin it so that it experiences very high g forces. The beauty of this experiment is that, by varying the radius of the centrifuge you can get different combinations of the speed of the sample and g force. You can have it experience the same g force at different speeds or different g forces at different speeds. If acceleration has any effect on the sample decay rate, higher accelerations would have a larger effect. Such experiments have been performed at accelerations up to 10^18 g and no additional variation in the decay rate due to acceleration has shown up; the difference in decay rate always matches that for what you would predict for the speed of the sample alone.

Good point but maybe a centrifuge is not equivalent to an inertial or gravitational mass. Could the spinning somehow cancel out the effect leaving only the original frame of inertial or gravitational depending on where the centrifuge experiment was taking place?

Originally Posted by bill alsept

Good point but maybe a centrifuge is not equivalent to an inertial or gravitational mass. Could the spinning somehow cancel out the effect leaving only the original frame of inertial or gravitational depending on where the centrifuge experiment was taking place?

There is a principle at the base of GR that acceleration and gravity are effectively the same thing. This has been tested to pretty high levels of accuracy (a few parts per billion, I believe).

But I still don't really understand your question. You seem to be asking if the special case of (general) relativity, i.e. dealing with inertial frames, could somehow be wrong. I don't see how this could be wrong without the rest of GR being wrong.

So, the answers to your question seem to be:

1. Special relativity has been tested in dozens of ways (and also demonstrated by the fact that the electronic equipment we are using to communicate works). In these tests the effects of gravity are very small but can be taken into account anyway. All these tests have matched the predictions of SR and GR.

2. General relativity has also been tested in very many ways. All these tests have matched the predictions of GR.

3. Special relativity is just a simplified special case of general relativity.

Can you be a bit more explicit about where you see a problem?

Originally Posted by Strange

Originally Posted by bill alsept

Good point but maybe a centrifuge is not equivalent to an inertial or gravitational mass. Could the spinning somehow cancel out the effect leaving only the original frame of inertial or gravitational depending on where the centrifuge experiment was taking place?

There is a principle at the base of GR that acceleration and gravity are effectively the same thing. This has been tested to pretty high levels of accuracy (a few parts per billion, I believe).

Of course being interested in push gravity I totaly agree with that and have always assumed that.

Originally Posted by Strange

But I still don't really understand your question. You seem to be asking if the special case of (general) relativity, i.e. dealing with inertial frames, could somehow be wrong. I don't see how this could be wrong without the rest of GR being wrong.

The only problem I have with GR is that it doesn't explain anything physically. I am sure the math is correct and considered beautiful but thats all it is to me is a tool or a glorified calculator. There is nothing about it that I can say is wrong because it doesn't stake any specific claims that can be countered. It is just complicated math applied to what we already see. I have no problem with GR, only with the very vaige descriptions it backs. It has no accountibility. Its a force but its not a force. Its curved space time we guess but we don't know how or why it can bend space. The list goes on and on but I don't have it in front of me right now. I have no problem with GR because it is probably right if you consider the math only but what does it represent? How does it really explain HOW gravity works? How does it explain quantum mechanics, singularities etc. I know, it doesn't have to.

Originally Posted by Strange

Can you be a bit more explicit about where you see a problem?

If your saying that every question has to conflict with GR then I guess I do have a problem with GR but my questions had to do with what you and Farad were talking about earlier with A and B, time dilation and observers point of view etc. Sometimes that subject gets confusing and I was trying to get clarification on inertia, free fall and acceleration, etc. so I could try to work the situation out for myself. Along the way one question lead to another. At this point I still have some questions on this but I've got to learn how to better ask them.

Originally Posted by bill alsept

The only problem I have with GR is that it doesn't explain anything physically.

But it does. Mass (and energy, etc.) has an effect on the geometry of space (and time). That is the physical mechanism.

In another thread someone asked, but "why" does mass alter the geometry of space-time? There are various possible answers to that. But they are really just philosophy. "Because it does" is good enough for me.

If someone comes up with a deeper explanation (or you get a push gravity model to work) that will just expose another layer of "but why" questions.

Sometimes that subject gets confusing and I was trying to get clarification on inertia, free fall and acceleration, etc. so I could try to work the situation out for myself. Along the way one question lead to another. At this point I still have some questions on this but I've got to learn how to better ask them.

It is very simply to work it out for yourself in the case of inertial motion. You just need to apply the Lorentz transform in the right way (being careful about whose frame of reference you are dealing with). It gets a little more complicated if you want to deal with simple acceleration where people jump between frames of references, such as in the Twin "Paradox". but it is still doable by someone with minimal math background. (That is why it is a little frustrating when people like Farad just say it is wrong with no apparent effort to understand it. No doubt he will accuse me of throwing insults around again, now. Ho hum.)

You really can ignore gravity and acceleration because the effects are tiny on Earth. If you do want to deal with that then you are into the full "horrors" of GR! (GPS receivers use a much simplified approximation.)

Originally Posted by bill alsept

The only problem I have with GR is that it doesn't explain anything physically. I am sure the math is correct and considered beautiful but thats all it is to me is a tool or a glorified calculator. There is nothing about it that I can say is wrong because it doesn't stake any specific claims that can be countered.

You misunderstand what it means to explain something. If one theory tells me to many significant digits the outcome of an experiment, it is a better theory than one that feels good, but which cannot provide a quantitatively correct answer. From the point of view of scientists, the first theory has in fact explained what nature does, even if that explanation is emotionally unsatisfying. Again, nature has no obligation to behave according to your wishes.

How does it really explain HOW gravity works? How does it explain quantum mechanics, singularities etc. I know, it doesn't have to.

These why and how questions really have no ultimate answer, no matter what theory you propose, whether GR or push gravity. There is always a point where you have to throw up your hands and say, well, that's just the way it is. If you've ever had an extended discourse with a young child, you'd know what I mean. So the mere absence of an ultimate answer that is also emotionally satisfying to you personally is not a valid reason to reject a theory. If it were, we'd actually have to reject all theories. If you think about it carefully, you'll realise the truth of that statement.

Originally Posted by Strange

Originally Posted by bill alsept

The only problem I have with GR is that it doesn't explain anything physically.

But it does. Mass (and energy, etc.) has an effect on the geometry of space (and time). That is the physical mechanism.

I believe mass indirectly causes gravitybecause of shielding. The shadow causes an imbalance in the gravitationalconstant leaving an unequal push we call g. When we have the capability to findthings like dark matter and dark energy you will be able to test my idea. GRjust says space and time are curved and offers no physical explanation as I didabove. Physically It can’t be proved right or wrong because it makes no claims.

Originally Posted by Strange

In another thread someone asked, but "why" does mass alter the geometry of space-time? There are various possible answers to that. But they are really just philosophy. "Because it does" is good enough for me.

But not for me and many others.

Originally Posted by Strange

If someone comes up with a deeper explanation (or you get a push gravity model to work) that will just expose another layer of "but why" questions.

That is OK. What If Copernicus had thought why bother sharing his idea because it will just expose another layer of "but why" questions?

Sometimes that subject gets confusing and I was trying to get clarification on inertia, free fall and acceleration, etc. so I could try to work the situation out for myself. Along the way one question lead to another. At this point I still have some questions on this but I've got to learn how to better ask them.

Originally Posted by Strange

You really can ignore gravity and acceleration because the effects are tiny on Earth. If you do want to deal with that then you are into the full "horrors" of GR! (GPS receivers use a much simplified approximation.)

I think as long as long as they have an effect at all the question will still be nagging.

Originally Posted by tk421

Originally Posted by bill alsept

The only problem I have with GR is that it doesn't explain anything physically. I am sure the math is correct and considered beautiful but thats all it is to me is a tool or a glorified calculator. There is nothing about it that I can say is wrong because it doesn't stake any specific claims that can be countered.

You misunderstand what it means to explain something. If one theory tells me to many significant digits the outcome of an experiment, it is a better theory than one that feels good, but which cannot provide a quantitatively correct answer. From the point of view of scientists, the first theory has in fact explained what nature does, even if that explanation is emotionally unsatisfying. Again, nature has no obligation to behave according to your wishes.

How does it really explain HOW gravity works? How does it explain quantum mechanics, singularities etc. I know, it doesn't have to.

These why and how questions really have no ultimate answer, no matter what theory you propose, whether GR or push gravity. There is always a point where you have to throw up your hands and say, well, that's just the way it is. If you've ever had an extended discourse with a young child, you'd know what I mean. So the mere absence of an ultimate answer that is also emotionally satisfying to you personally is not a valid reason to reject a theory. If it were, we'd actually have to reject all theories. If you think about it carefully, you'll realise the truth of that statement.

My clock shows me when the sun will come up. There are programs that calculate exactly when and where but none of this tells me why. That is a seperate issue and thanks to others before us they where interested in finding out why the sun does what it does. And their theory was testible because we can see what's happening and measure it. GR only has math (like calculating when the sun will come up) that could be applied to many other ideas as well. Maybe Ideas that could actually be measures or seen.

Originally Posted by bill alsept

[I believe mass indirectly causes gravitybecause of shielding.

OK. But why does mass shield gravity. What is the physical explanation?

I don't want you to answer that. I am just pointing out that whatever explanation you have, there will always be another "yes, but why" question.

If you say, "it is because the gravity particles are absorbed by protons" I will just say, "why are they absorbed" and so we carry on down the rabbit hole.

Eventually you will have to say, "that's just the way it is."

Originally Posted by bill alsept

My clock shows me when the sun will come up. There are programs that calculate exactly when and where but none of this tells me why. That is a seperate issue and thanks to others before us they where interested in finding out why the sun does what it does. And their theory was testible because we can see what's happening and measure it. GR only has math (like calculating when the sun will come up) that could be applied to many other ideas as well. Maybe Ideas that could actually be measures or seen.

You still completely miss the point. I can still ask why questions of your "theory" until you reach a point where there's nothing you can do but say, "that's just the way it is." This is true of all theories. You are still so centered on yourself that you think that, once you yourself are satisfied with a reply, you have the answer. But if you open your mind a bit and allow all others to enjoy the same privilege, then you cannot legitimately claim that I don't have an answer. I am perfectly fine with what GR says, especially since I can compute accurately what nature will do. You cannot. You say that GR doesn't provide "an answer" as to why spacetime curves. Yet, I look at the energy-stress-momentum tensor and that tells me why. That satisfies me just fine. Who are you to declare that it doesn't?

Now let's shine some light on your approach. You say you favor push gravity because it "explains" something in a way that you like. But saying that particles push on something else and makes them move just begs the questions of how and why? You might say "because touching things makes them move."

Why?

"Because of momentum conservation."

Why does the universe obey that conservation law?

"Umm...because Emmy Noether said so."

Can you explain what she said?

"Well, it involves lots of math."

Remind me, again, what's wrong with GR?

"It involves lots of math."

Ah, I see. So, why do you favor push gravity?

Bill wants classical, mechanical answers in a relativistic, geometric universe.

Originally Posted by Strange

Originally Posted by bill alsept

[I believe mass indirectly causes gravitybecause of shielding.

OK. But why does mass shield gravity. What is the physical explanation? I don't want you to answer that. I am just pointing out that whatever explanation you have, there will always be another "yes, but why" question. If you say, "it is because the gravity particles are absorbed by protons" I will just say, "why are they absorbed" and so we carry on down the rabbit hole. Eventually you will have to say, "that's just the way it is."

Mass does not shield gravity, it shields the particles that make up the gravitational constant. Someday this will be a testable which is better than curved space time that can never be. Why not bent waffles as you might say.Your idea than questions should not be asked because they will never end is silly. First of all how boring is that and second it's just wrong. For instance everything we know about science is mostly because someone asked. Besides if a push particle is found it would answer the question. Curved space is like the emperors new clothes and can,t even be looked for let alone be found.

Originally Posted by bill alsept

[Your idea than questions should not be asked because they will never end is silly. First of all how boring is that and second it's just wrong.

Boring? That's a matter of taste. As to wrong, then let's have you back up that assertion with an example.

For instance everything we know about science is mostly because someone asked.

Oh good grief. That has NOTHING to do with whether or not one may ask questions ad infinitum. Once again, there seems to be a deep logical lapse.

Besides if a push particle is found it would answer the question.

Again, that's an unsupported assertion. Since you're so certain of its correctness, please demonstrate that it is true, even in principle. We'll then proceed to ask you a sequence of "why" questions that you will eventually fail to answer.

Curved space is like the emperors new clothes and can,t even be looked for let alone be found.

Yes, so you have said, many times, ad nauseam. But scientists differ from you on this point. We can take up the matter of epistemology somewhat later (you seem to have an arbitrarily limited idea of what it means to know or to find something). First, I'd like to get past this block of yours regarding "why" questions.

Curved space is like the emperors new clothes and can,t even be looked for let alone be found.

Of course it can be looked for, has been looked for, has been found. As early as the 1919 Eddington observations, and as recently as Gravity Probe B: Testing Einstein's Universe

Originally Posted by AlexG

Curved space is like the emperors new clothes and can,t even be looked for let alone be found.

Of course it can be looked for, has been looked for, has been found. As early as the 1919 Eddington observations, and as recently as Gravity Probe B: Testing Einstein's Universe

Good link thanks. Interesting though that the first paragraph says:

"Nevertheless there are at least four good reasons to think that the theory is incomplete and will eventually need to be overthrown in just the same way that Newton's was. Firstly, general relativity predicts its own demise; it breaks down in singularities, regions where the curvature of spacetime becomes infinite and the field equations can no longer be applied. These cannot be dismissed as mere academic curiosities, because they do apparently occur in the real universe if general relativity holds. Theoretical work by Stephen Hawking and others has proven that singularities must form within a finite time (the universe is necessarily "geodesically incomplete"), given only very generic assumptions such as the positivity of energy. Two places where we expect to find them are at the big bang, and inside black holes like the one at the center of the Milky Way. If we are to fully understand these phenomena, then general relativity must be modified or extended in some way."

How come I can't question GR if everyone else does? Who wouldn't want to? Thats the part I don't get.

Originally Posted by tk421

Originally Posted by bill alsept

[Your idea that questions should not be asked because they will never end is silly. First of all how boring is that and second it's just wrong.

Boring? That's a matter of taste. As to wrong, then let's have you back up that assertion with an example.

I can't think of any reason to not ask a question if your interested in something.

Originally Posted by tk421

Since you're so certain of its correctness, please demonstrate that it is true, even in principle. We'll then proceed to ask you a sequence of "why" questions that you will eventually fail to answer.

And that is what I am doing. You just don't like to think about those "why" questions because for over 100 years there are still seems to be no answers. I am not the only one saying that and you know it.