# Thread: constant speed of light

1. The Theory of Relativity states that the speed of light is the same for all observers. No matter what a person's velocity is, light always goes at c faster than them. Sorry, but that doesn't make a bit of sense to me.

Suppose a cop is stationed at a spot on the road to watch out for speeders, and he uses his laser-guided speedometer to measure a car going 60mph. However, another car is measured at going 70 mph. If the 60mph car has his own laser speedometer, then the other car is measured by that person as 10mph. So therefore, an object's velocity changes with reference to the observer.

But light doesn't do that. It seems as if the first car speeds up by 10mph, the light also speeds up by 10mph just to keep a velocity of c greater than what the reference point is going. No other object will do that just to keep up with its reference like that, at least not on its own, not even other forms of energy like sound or heat; that's why its possible to travel faster than sound, because sound's speed changes as your speed changes.

Why doesn't light do the same? Again, it can't be the fact that its pure energy, otherwise sound and heat would be constant for all observers. What am I missing?

2.

3. Most probably the fact that nobody has a conclusive answer, yet it is true all the same.

4. From what I understand, neither sound nor heat are pure energy. They are interactions between particles that have mass. Photons are massless. Also, the speed of light does change depending on the material it's passing through. The real constant is the speed of light in a vacuum.

5. The constancy of the speed of light as measured by observers in different inertial frames is one of the postulates on which special relativity was devised. It is not a consequence of theory, but one of the things assumed at the outset. There were good reasons for assuming it, such as the Michelson-Morley experiment although, interestingly, Einstein claimed that he was unaware of this experiment when he wrote his 1905 paper on Special Relativity. *

Essentially, the theory comes up with a scheme whereby observers in relative uniform motion arrive at different values for the same distance and time intervals in such a way that the speed of light appears to be the same to both observers. Incidentally, a consequence of this is that if an object is moving at a speed v' with respect to an observer who is himself moving at v" in the same direction with respect to an observer who is considered to be stationary, the observer who is considered to be stationary would not measure the speed of the object to be v' + v". It would be less than this. Resultant velocities cannot be obtained simply by adding together relative velocities.

* Why Einstein denied knowledge of the Michelson-Morley experiment is a puzzle discussed at length in the book by Abraham Pais (The Science and the life of Albert Einstein). However, no definite answer seems to be arrived at.

6. the reason the speed of light is the ultimate constant, is because it'd take an infinite amount of energy to reach it.
the reason it would take an infinite amount of energy to reach the speed of light, is because the object would become infinitely heavy if it ever reached the speed of light.
it helps to think exponentially.
it'd basically take more energy to accellerate less and less, the faster you go.

7. Originally Posted by Hazz
Most probably the fact that nobody has a conclusive answer, yet it is true all the same.
Well, Einstein had to have a conclusive answer, otherwise his theory wouldn't hold water.

And how was this concept a backbone for relativity? How does light's constant speed eventually result in the theory of relativity? Shouldn't it be the other way around?

8. Originally Posted by davidstebbins
Originally Posted by Hazz
Most probably the fact that nobody has a conclusive answer, yet it is true all the same.
Well, Einstein had to have a conclusive answer, otherwise his theory wouldn't hold water.
No, it was a postulate; something taken as being true. You didn't need to know why was true. The reason the theory holds water is that starting from that postulate, the theory makes predictions of how the universe behaves assuming that postulate is true, and and every real physical experiment we have performed to date confirms those predictions as being correct. This, in turn, suports the original postulate.

And how was this concept a backbone for relativity? How does light's constant speed eventually result in the theory of relativity? Shouldn't it be the other way around?
Because, starting from the initial postulates:

1. The laws of physics are the same for all interial frames of reference.
2. The speed of light is a constant as measured in all inertial frames of reference.

You can deduce all of the particulars of the theory of Special Relativity:
Time dilation
Length contraction
The relativity of simultaneity
E=mcÂ²
etc.

They all fall out as natural consequences of the validity of the first two postulates.

9. Originally Posted by Janus
Originally Posted by davidstebbins
Originally Posted by Hazz
Most probably the fact that nobody has a conclusive answer, yet it is true all the same.
Well, Einstein had to have a conclusive answer, otherwise his theory wouldn't hold water.
No, it was a postulate; something taken as being true. You didn't need to know why was true. The reason the theory holds water is that starting from that postulate, the theory makes predictions of how the universe behaves assuming that postulate is true, and and every real physical experiment we have performed to date confirms those predictions as being correct. This, in turn, suports the original postulate.

And how was this concept a backbone for relativity? How does light's constant speed eventually result in the theory of relativity? Shouldn't it be the other way around?
Because, starting from the initial postulates:

1. The laws of physics are the same for all interial frames of reference.
2. The speed of light is a constant as measured in all inertial frames of reference.

You can deduce all of the particulars of the theory of Special Relativity:
Time dilation
Length contraction
The relativity of simultaneity
E=mcÂ²
etc.

They all fall out as natural consequences of the validity of the first two postulates.
So we don't know why light speeds up for all observers, we just know that if it didn't, Relativity wouldn't hold water, yet it does?

So tell me: Relativity has been around for well over a century. Why is it that people have just been content with "Just because," to explain light's consistency, and why, in turn, should I be content with it?

10. It's not just because. That's not how science works. The theory of relativity makes predictions. Thos predictions have turned out to be true to a high degree of accuracy (i.e., the limit of our ability to test them), therefore, relativity is most likely true. Nothing in science can ever be proven though.

The thing is, relativity accurately predicts the result of all of these experiments. If you have another idea that doesn't depend on a constant speed of light, it'll still have to give the same predictions for time dilation experiments, etc. Those experiments will never be invalidated by a new theory. If two theories make the exact same predictions, we'd tend to favor the simpler theory (but only in that case). (That's Occam's Razor.)

Edit: Oh yeah. I think that the constancy of light can be deduced from the assumption that the laws of physics are constant for all inertial frames of reference. So there is only one assumption underlying relativity and everything else is a deduction.

11. Let me put it this way: "Gravity pulls you toward the earth" is a postulate, right? It was this concept that explained many phenomena involving free fall experiments. That doesn't mean, however, that it doesn't have its own scientific explanation. The phenomenon is explained mathematically in Newton's Law of Universal Gravitation.

So why does the constant speed of light lack such an explanation, especially a mathematical one? Yes, I understand now that the constant speed of light is a necessary postulate for the highly-accurate theory of relativity to make sense mathematically, but that doesn't mean we can shun the need for a mathematical explanation of the constant speed of light, so why have we for over a century?

12. David, Newton didn't explain why the gravitational constant G = 6.67428 x 10^-11 m^3 kg^-1 s^-2. It just is what it is. So how is the speed of light different than that?

13. actually, what newton did, was build on previous knowledge,
then he took that knowledge, and knotted it together in a neat package,
and added some ideas of his own. just like einstein did.

newtons chief idea, was that it wasn't 1 object pulling at the other.
it was that multiple objects pulled towards eachother.
even the tiniest space rock has some nano-sized pull at earth.
and earth, even though being a dustspeck, has a tiny pull at the sun.

anyways, the next 2 borders of science is gravity and light.

14. thinking about light, since it takes an infinite amount of energy to reach the speed, it might be more than just a speed. also because its got the same speed ratio regardless of the frame of reference.. hmm.. some sort of logarithmic curve. i'm wondering if actually attaining the speeds close to light might bend some of einsteins rules.
maybe you'll create a spacial negative gravity well that tries to pull you back into the universe, making the light sort of the "atmosphere" of the universe,
and lightspeed being the escape velocity of the universe.
maybe thats why your mass increases as you speed up. it might be the universe exerting a pull on you, to keep you from escaping space-time.
like earths gravity exerts a pull on you to keep you from escaping its field of gravity.

well, this is just wild speculation.

15. Originally Posted by dejawolf
actually, what newton did, was build on previous knowledge,
then he took that knowledge, and knotted it together in a neat package,
and added some ideas of his own. just like einstein did.

newtons chief idea, was that it wasn't 1 object pulling at the other.
it was that multiple objects pulled towards eachother.
even the tiniest space rock has some nano-sized pull at earth.
and earth, even though being a dustspeck, has a tiny pull at the sun.

anyways, the next 2 borders of science is gravity and light.
Whatever. So it wasn't Newton, but a group of other people. That doesn't mean it isn't an explained phenomenon rather than an assumed postulate. Man wasn't content to say "If gravity didn't exist like this, then x wouldn't happen, so it must be that way," and leave it at that. Man has explained gravity, so it went from postulate to theory.

Why hasn't light's consistency done the same?

16. It is of some interest to consider what people thought about the propagation of light prior to Einstein's Special Relativity. Amongst physicists, there was widespread belief in an "aether" - an elusive medium which supported the propagation of light in the way that an atmosphere supports the propagation of sound and, furthermore, which could define a state of absolute rest. An object at absolute rest would not be moving with respect to the aether. Maxwell believed in an aether and so did Lorentz, after whom the "Lorentz transformations" are named. Even Einstein himself once believed in an aether.

Michelson and Morley attempted to discover how the earth moved with respect to the aether by comparing the speed of light beams moving in different directions (relative to the earth's motion through space) and famously came up with a null result. It didn't seem to matter how light was moving with respect to the aether, its speed was always the same. This was an empirical result. Various attempts were made to explain why the speed of light did not appear to change with respect to its motion through the aether. However, by far the simplest approach is that provided by Einstein - there isn't an aether, there is no such thing as absolute rest, the speed of light is the same in all inertial frames of reference.

If one were to assume that an observer moving in the same direction as a light beam measures the speed of light to be not c but, let's say, (c -100) km/sec, this would imply that the observer is moving at 100 km/sec in absolute terms. That is, it would be evidence of an absolute state of rest relative to which the observer is moving. We would then be back in the nineteenth century trying to find out what this thing at absolute rest is.

17. Okay, I get it that light is the same for all observers, for whatever reason, and this postulate has been tested and verified experimentally. That's not what I'm asking, either now or at the beginning. I'm asking HOW! How can light speed up when an observer speeds up without any force applied to it, but won't speed up for an observer in constant speed? Those experiments you mention merely state that light is the same for all observers, by hook or crook. It doesn't explain this phenomenon, and to this day, over a century later, people have just been content with this lack of explanation.

18. Light doesn't "speed up" when an observer moves. The value measured by the moving observer remains the same as that for an observer who has not started to move. However, to measure the speed of light, one must measure a distance and also the time taken for light to travel that distance. It is these measures of distance and time that the two observers would disagree on. One of observer might consider that the light has moved 1 km whilst the other thinks that it has moved only 0.8 km. It was by making distances and time intervals relative to the motion of the observer, rather than being fixed, that Einstein managed to explain why the speed of light would be the same to both observers.

Quantitatively, if the light moves from the origin to the point (x,y,z) in the time t in one frame of reference, and if in the other frame (moving with respect to the first) it moves from the origin to (x',y,'z') in a time t', then

x<sup>2</sup> + y<sup>2</sup> + z<sup>2</sup> - c<sup>2</sup>t<sup>2</sup> = 0

x'<sup>2</sup> + y'<sup>2</sup> + z'<sup>2</sup> - c<sup>2</sup>t'<sup>2</sup> = 0

The situation envisaged is one in which observers in two frames of reference cause the light to be emitted from their origins at the instant when the origins coincide. The above equations describe the spherical wavefronts that would be seen by each observer.

It is the measures of distance and time which change, not the value of c.

The relationships between, x',y',z' and t' and x,y,z and t are the Lorentz transformations which Einstein presented in his paper of 1905.

19. Have you read the Wikipedia article on the speed of light? It says that the speed of light through a medium is 1/sqrt(permittivity * permeability). The permittivity and permeability of free space and the equations of electromagnetism are properties of the universe which, under relativity, will be the same for any inertial reference frame. Thus, the speed of light must be the same for any inertial reference frame.

Another thing is, light doesn't speed up when you speed up. It's a lot wierder than that. Something like, length contraction plus time dialation causes you to measure a beam of light at the same speed at any time (although correct me if I'm wrong).

Edit: Old Fool beat me to the second part there.

20. ^^^Wikipedia is literally so non-credible that Universities and high schools the world over are rapidly forbidding it to be used in bibliographies in any way, shape, or form. So no, I haven't read it, but I have good reason not to. Wikipedia can't be trusted for shit.

21. I really have no idea what you mean. Wikipedia is very reliable when it comes to math and science topics. I'm not sure I'd trust current event pages, or biographical pages too much, but I've never had any trouble with anything related to math or science (at least none that I couldn't rule out under common sense, such as graffiti).

Anyway, ignore the article then, but check out the reference section. Regardless of the quality of the article, the references can speak for themselves. The same goes for a University paper. (BTW, my University has no policy against Wikipedia.)

Edit: BTW, I thought you might be interested in this quote:
"Although Middleburyâ€™s history department has banned Wikipedia in citations, it has not banned its use. Don Wyatt, the chairman of the department, said a total ban on Wikipedia would have been impractical, not to mention close-minded, because Wikipedia is simply too handy to expect students never to consult it." from here. This site agrees. Universities may be banning the citation of Wikipedia, but that doesn't make it worthless.

22. Originally Posted by MagiMaster
Anyway, ignore the article then, but check out the reference section. Regardless of the quality of the article, the references can speak for themselves. The same goes for a University paper. (BTW, my University has no policy against Wikipedia.)
Fine. I checked out the references (and I did more than scan over them, btw). I didn't find a single reference that even looked like it would explain my confusion. The closest thing I found was that it was the value of c, not light itself, that was important in relativity, which is why light being slowed in a medium didn't affect relativity. Nothing, however, explaining why c was constant for all observers.

23. I think that you will have to resort to the time-honoured method of reductio ad absurdum - assume that light as observed by observers in relative motion does travel at different speeds and then see where that leads you. These different observers are supposed to be moving relative to one another - let's say that one is at rest and the other is moving at 1 km/sec. This leads to the question, "What do you mean by saying that one is at rest"? Can you define absolute rest? You run into the same problem no matter what their speeds are - you somehow have to define what you mean by zero speed (or rest). In short, you are right back to the problems that people wrestled with in the nineteenth century. Your belief in different speeds of light for observers moving relative to each other requires a specification of absolute rest in order that you can say how fast they are moving - perhaps some entity (like the aether) which is assumed to be at absolute rest. Unfortunately, there is no evidence that any such entity exists. We would have a similar problem with sound waves if it were not known that sound moves relative to a medium through which it propagates - air. However, there is no such medium for light.

24. Originally Posted by Old Fool
I think that you will have to resort to the time-honoured method of reductio ad absurdum - assume that light as observed by observers in relative motion does travel at different speeds and then see where that leads you. These different observers are supposed to be moving relative to one another - let's say that one is at rest and the other is moving at 1 km/sec. This leads to the question, "What do you mean by saying that one is at rest"? Can you define absolute rest? You run into the same problem no matter what their speeds are - you somehow have to define what you mean by zero speed (or rest). In short, you are right back to the problems that people wrestled with in the nineteenth century. Your belief in different speeds of light for observers moving relative to each other requires a specification of absolute rest in order that you can say how fast they are moving - perhaps some entity (like the aether) which is assumed to be at absolute rest. Unfortunately, there is no evidence that any such entity exists. We would have a similar problem with sound waves if it were not known that sound moves relative to a medium through which it propagates - air. However, there is no such medium for light.
My confusion has nothing to do with absolute rest. In fact, I don't think I ever uttered the word "absolute" in any sense of the word anywhere in this thread. Relativity specifically states that there is no such thing as absolute anything, that everything is relative to another frame, hence the name.

My confusion involves the changing of relative speeds. Again, suppose one car is stationed at rest on the side of the highway as another car goes down the highway at 50mph. Then, all of a sudden, the stationary car starts going at 30mph. Is the first car speeding up to 30mph, or is the second car slowing down to 20mph? You have no way of knowing unless you factor in the earth, but one car, take your pick which, is still remaining at constant speed relative to the earth one way or another.

But light isn't like that. It speeds up for an accelerating reference, but those same photons stay at the same speed for an inertial reference. It's almost as if light is traveling at two speeds at once.

25. Ok. Try this then. Two spacecraft are out in deep space (no nearby references). From one's point of view, the other is going .5*c. You blink and now it seems to be going .2*c. Which sped up and which slowed down. The answer is, it doesn't really matter. (Actually, the acceleration matters, but not for this problem.)

Or how about this one. You're sitting in a spacecraft. Another passes you by at .5*c. It has a mirror parallel to it, 1 light-second away. As it passes it fires a beam of light towards the mirror. From it's point of view, the light travels 2 light-seconds (to the mirror and back) in 2 seconds. So it's speed is 2/2 * c.

From your point of view, the ship will have moved forward 1 light-second during those two seconds, so the light beam will have to travel a total of sqrt(5) light-seconds. But by your clock, it also takes it sqrt(5) seconds to travel that distance. So it's speed is sqrt(5)/sqrt(5) * c.

So neither of you can agree on how far the light beam went, or how long it took to get there, but you both agree that it was travelling at the same speed. So who's right about the distance? Both of you are.

26.

27. 8)

There must be more postulates for Special Relativity: the axioms of Lorentz Transformations, restrictions of the Lorentz Group.

And that 1/sqrt(-1) has no physical significance, because you can imagine
the following (theoretical) possibility:

take your speed to close to that of light and emit infinite energy in an infinitesimal time. Then you would never have attained light speed but would have jumped discontinually beyond lightspeed. This must lead to
consideration of 1/sqrt(-1) if the formula stays valid.

For General Relativity that timespace forms a union and can be warped by gravity.

28. Originally Posted by davidstebbins
....Suppose a cop is stationed at a spot on the road to watch out for speeders, and he uses his laser-guided speedometer to measure a car going 60mph. However, another car is measured at going 70 mph. If the 60mph car has his own laser speedometer, then the other car is measured by that person as 10mph. So therefore, an object's velocity changes with reference to the observer....

Actually, what is happening is that the reflected speed of light changes so the rate of number of photons per seconds hitting the speedometer changes but some how entire humanity believes that its not the speed but rather its the frequency thats changing.

This is actually limitation of human imagination, simply put humans should not try to venture these area of intellect. They simply cannot comprehend these simple facts. The other problem is that only those who digest these wrong ideas get into Phd. programs; Thats the eligible criteria, hence science has got struck in 19 century.

29. Human imagination? Reflected light? Struck?
All with a half meter optic cable and a cup of coffee has the potential of destroying the earth, why should we worry about what a smart robot thinks?

30. Originally Posted by MagiMaster
Ok. Try this then. Two spacecraft are out in deep space (no nearby references). From one's point of view, the other is going .5*c. You blink and now it seems to be going .2*c. Which sped up and which slowed down. The answer is, it doesn't really matter. (Actually, the acceleration matters, but not for this problem.)

Or how about this one. You're sitting in a spacecraft. Another passes you by at .5*c. It has a mirror parallel to it, 1 light-second away. As it passes it fires a beam of light towards the mirror. From it's point of view, the light travels 2 light-seconds (to the mirror and back) in 2 seconds. So it's speed is 2/2 * c.

From your point of view, the ship will have moved forward 1 light-second during those two seconds, so the light beam will have to travel a total of sqrt(5) light-seconds. But by your clock, it also takes it sqrt(5) seconds to travel that distance. So it's speed is sqrt(5)/sqrt(5) * c.

So neither of you can agree on how far the light beam went, or how long it took to get there, but you both agree that it was travelling at the same speed. So who's right about the distance? Both of you are.
Where the heck did you get sqrt(5)? That is the most random thing I've seen in this thread yet.

31. sqrt(2^2 + 1^2) Simple, euclidean geometry. From your point of view, the laser moves two light-seconds out and back, and one light second forward. So it's total distance would be sqrt(5). (Correct me if I'm wrong of course.)

32. How. How light has an ending speed.

Photons are spinwaves, the medium is higgsbosons, the higgsbosons has a compareable size to the size of what caused the photon, so the photon moves to a compareable speed to the reaction which caused it.

33. Originally Posted by MagiMaster
sqrt(2^2 + 1^2) Simple, euclidean geometry. From your point of view, the laser moves two light-seconds out and back, and one light second forward. So it's total distance would be sqrt(5). (Correct me if I'm wrong of course.)
You lost me there as well, MagiMaster. Which leg of the triangle is 2 light-seconds? I thought they were 1 light-second apart.

34. Right you are Harold. Though I believe he is talking about spin speed. And naturally the spin is the frequency, wouldn't you say? and a higgs boson's mass is unknown, yet we know how mediums alter the frequency, so all we need to examin is how massive any particle medium is and examin how fast it allows the photon spin and thereafter examin how much less massive (though gravitonless) the higgs particle must be, to cause the faster spin.

Everyone okay with that?

35. No.

The speed of light in a vacuum is always measured to be the same because light defines our time and our distance. Whenever there's time dilation, such as that programmed into GPS, it's because the speed of light varies. You can never measure this locally, because it affects your local clocks.

Such a gradient in c is more commonly known as gravity.

36. If I could go off topic for a minute, I feel the need to point out one thing: What about quantum mechanics? I believe it was Stephen Hawking himself who said, and I quote "These theories [GR and QM] are known to be inconsistent with each other. They cannot both be correct."

So therefore, there is that slight possibility that the constant speed of light is just a bunch of bull and that we're wasting our time with it, eh?

37. That's maybe a bit strong. Einstein started off with his Special Relativity with the "postulate" that the speed of light was always measured to be the same. The postulate holds. It is always measured to be the same. But that's not quite the same thing as saying it is the same, and it doesn't explain why. Later, he said this:

"In the second place our result shows that, according to the general theory of relativity, the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity and to which we have already frequently referred, cannot claim any unlimited validity. A curvature of rays of light can only take place when the velocity of propagation of light varies with position. Now we might think that as a consequence of this, the special theory of relativity and with it the whole theory of relativity would be laid in the dust. But in reality this is not the case. We can only conclude that the special theory of relativity cannot claim an unlimited domain of validity; its results hold only so long as we are able to disregard the influences of gravitational fields on the phenomena (eg of light)..."

Thatâ€™s from The General Theory of Relativity: Chapter 22 - A Few Inferences from the General Principle of Relativity. He meant what it looks like. He was talking about a constant velocity for Special Relativity. We take that to be constant speed. Then when he says the velocity isnâ€™t constant for General Relativity, people say he wasnâ€™t talking about speed. But he wasnâ€™t talking about velocity as a vector quantity. He didnâ€™t mean the curvature of light was there because the light changed direction. That would be saying the curvature is there because the curvature is there. He meant that the curvature was there because the speed changes. He meant c varies. Itâ€™s there in black and white from the man himself. I think Einstein had things pretty much worked out by 1955, but physicists then rather judged him to be a crazy old buffoon, and he never got it out. Nowadays people get taught that Einstein said something different to what he actually said.

All very interesting.

38. Originally Posted by Harold14370
Originally Posted by MagiMaster
sqrt(2^2 + 1^2) Simple, euclidean geometry. From your point of view, the laser moves two light-seconds out and back, and one light second forward. So it's total distance would be sqrt(5). (Correct me if I'm wrong of course.)
You lost me there as well, MagiMaster. Which leg of the triangle is 2 light-seconds? I thought they were 1 light-second apart.
Sorry if I lost you. I was doing a bit of simplifying. If you look at it drom above, the beam of light makes an isosceles triangle as it travels 1 light-second out and 0.5 light-seconds forward, hits the mirror and then travels 1 light-second back and another light-second forward. So the actual distance would be 2*sqrt(1^2 + 0.5^2) = 2*sqrt(1.25) = 2*sqrt(5/4) = 2*sqrt(5)/2 = sqrt(5)

39. Originally Posted by Farsight
That's maybe a bit strong. Einstein started off with his Special Relativity with the "postulate" that the speed of light was always measured to be the same. The postulate holds. It is always measured to be the same. But that's not quite the same thing as saying it is the same, and it doesn't explain why. Later, he said this:

"In the second place our result shows that, according to the general theory of relativity, the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity and to which we have already frequently referred, cannot claim any unlimited validity. A curvature of rays of light can only take place when the velocity of propagation of light varies with position. Now we might think that as a consequence of this, the special theory of relativity and with it the whole theory of relativity would be laid in the dust. But in reality this is not the case. We can only conclude that the special theory of relativity cannot claim an unlimited domain of validity; its results hold only so long as we are able to disregard the influences of gravitational fields on the phenomena (eg of light)..."

Thatâ€™s from The General Theory of Relativity: Chapter 22 - A Few Inferences from the General Principle of Relativity. He meant what it looks like. He was talking about a constant velocity for Special Relativity. We take that to be constant speed. Then when he says the velocity isnâ€™t constant for General Relativity, people say he wasnâ€™t talking about speed. But he wasnâ€™t talking about velocity as a vector quantity. He didnâ€™t mean the curvature of light was there because the light changed direction. That would be saying the curvature is there because the curvature is there. He meant that the curvature was there because the speed changes. He meant c varies. Itâ€™s there in black and white from the man himself. I think Einstein had things pretty much worked out by 1955, but physicists then rather judged him to be a crazy old buffoon, and he never got it out. Nowadays people get taught that Einstein said something different to what he actually said.

All very interesting.
It does sound like he's taking back what he said about Special Relativity. Einstein is saying, in no uncertain words, that the speed of light, even in a vacuum, changes as gravity increases, e.g. a black hole. What else could "The results hold only so long as we are able to disregard the influences of gravitational fields on the phenomena (eg of light)" possibly mean? Einstein wasn't much one for ambiguity, so he obviously meant one thing, and one thing only, and he wasn't one for making people put two and two together, either. If he had a thought, especially a scientific one, he'd state it clearly and bluntly.

40. without being too "psuedo-science", is it possible for any scientist to be in two places at once?

Seriously.

A theory of everything: can the same scientist EXIST in the same place elsewhere?

Is that not relativity?

You are all trying to EXPLAIN relativity, yet you cannot agree with one another: look at the forest (for the trees).

You are all passionate about science.......finding that great theory will "eclipse" you...........if you could explain it to anyone, it will eclipse them, but technically you cannot exist somewhere else as someone else.

............Einstein............wow, I hope he is watching this.

41. I despise doing this (replying to myself), but, but, but, if you seriously think Einstein was Jesus, as well understood, you're pushing shit up a hill.

I mean, Jesus gave himself to everyone...........and you are all trying to make Einstein's mind as though it were Jesus's.

You need someone who does that sort of thing (xxxx up a hill) well.

Someone taught to register something astrophysicists themselves have yet to feel suddenly enraptured with.

42. I mean, Einstein was right...........BUT, is it possible for anyone to understand Einstein.......for anyone to BE Einstein, like that was his life's work........and so profoundly?

Why not look for a NEW SCIENCE to explain the same damn reality?

43. Streamsystems, you obviously do not understand what I'm trying to do anymore than you understand Einstein.

We aren't trying to understand Einstein. We're trying to understand his theories, which, may I remind you, are meant to be understood. That's why they're science.

44. I understand what you are trying to understand, "Einstein". But answer me this, can two minds exist in the same place at once?

My point is, "is not relativity about space-time and how it works, and if so, is understanding space-time and how it works actually allowed to exist in A and B where A and B are actually in two different space and time locations"?

Basically, what if understanding space-time requires a certain "reference" of the observor that must be acted as a reference of the observor, as a concept of "perception", to understand space-time.

Or, are you suggesting that a theory of space-time incorporates the "universal observor", like God?

45. Originally Posted by MagiMaster

Or how about this one. You're sitting in a spacecraft. Another passes you by at .5*c. It has a mirror parallel to it, 1 light-second away. As it passes it fires a beam of light towards the mirror. From it's point of view, the light travels 2 light-seconds (to the mirror and back) in 2 seconds. So it's speed is 2/2 * c.

From your point of view, the ship will have moved forward 1 light-second during those two seconds, so the light beam will have to travel a total of sqrt(5) light-seconds. But by your clock, it also takes it sqrt(5) seconds to travel that distance. So it's speed is sqrt(5)/sqrt(5) * c.

So neither of you can agree on how far the light beam went, or how long it took to get there, but you both agree that it was travelling at the same speed. So who's right about the distance? Both of you are.
Hmm, it seems like your mixng frames here quite a bit. For example, in one hand, your saying that the spacecraft has moved 1 light-sec by your point of view, but later say that it traveled for sqrt(5) seconds. This is a contradiction. If the spaceship is traveling at 0.5c, it can either, from your perspective, travel sqrt(5)/2 light-sec in sqrt(5) sec , or travel 1 light sec in 2 sec. It cannot travel 1 light-sec in sqrt(5) secs.

46. Originally Posted by streamSystems
I understand what you are trying to understand, "Einstein". But answer me this, can two minds exist in the same place at once?

My point is, "is not relativity about space-time and how it works, and if so, is understanding space-time and how it works actually allowed to exist in A and B where A and B are actually in two different space and time locations"?

Basically, what if understanding space-time requires a certain "reference" of the observor that must be acted as a reference of the observor, as a concept of "perception", to understand space-time.

Or, are you suggesting that a theory of space-time incorporates the "universal observor", like God?
Well, by that logic, no one except Isaac Newton can fully understand why an mass times acceleration equals force, and only Galileo Galilee can fully understand why two free-falling objects in a vacuum hit the ground at exactly the same time. By your logic, no one can fully understand anything scientists say except the scientist who originally says them, yet they do.

47. Originally Posted by Janus
Originally Posted by MagiMaster

Or how about this one. You're sitting in a spacecraft. Another passes you by at .5*c. It has a mirror parallel to it, 1 light-second away. As it passes it fires a beam of light towards the mirror. From it's point of view, the light travels 2 light-seconds (to the mirror and back) in 2 seconds. So it's speed is 2/2 * c.

From your point of view, the ship will have moved forward 1 light-second during those two seconds, so the light beam will have to travel a total of sqrt(5) light-seconds. But by your clock, it also takes it sqrt(5) seconds to travel that distance. So it's speed is sqrt(5)/sqrt(5) * c.

So neither of you can agree on how far the light beam went, or how long it took to get there, but you both agree that it was travelling at the same speed. So who's right about the distance? Both of you are.
Hmm, it seems like your mixng frames here quite a bit. For example, in one hand, your saying that the spacecraft has moved 1 light-sec by your point of view, but later say that it traveled for sqrt(5) seconds. This is a contradiction. If the spaceship is traveling at 0.5c, it can either, from your perspective, travel sqrt(5)/2 light-sec in sqrt(5) sec , or travel 1 light sec in 2 sec. It cannot travel 1 light-sec in sqrt(5) secs.
Good point. I've obviously got something wrong. Can anyone rewrite that with some better math? The basic idea works, but I didn't work it out carefully enough.

Oh yeah. I had a question about SR. (Feel free to answer in a new thread if this isn't the place.) If you're travelling to a destination 10 ly away at 0.5*c, you should time your arrival at 5*sqrt(5) years, right? And people back home would time your arrival... when? Would it be 20 years, or 10*sqrt(5) years?

48. Originally Posted by davidstebbins
Well, by that logic, no one except Isaac Newton can fully understand why an mass times acceleration equals force, and only Galileo Galilee can fully understand why two free-falling objects in a vacuum hit the ground at exactly the same time. By your logic, no one can fully understand anything scientists say except the scientist who originally says them, yet they do.
well, you can never fully understand what a person meant when he wrote something down, even when he did his best to make himself clear,
because words are limited. only a direct mind-link would ever give a full understanding of what a person is saying.

about 1 mind existing in 2 places.. relativity is about the point of view.
is looking at a house from the outside, vs the inside being 2 different minds?

49. ...Light cannot be constant if it were you could not measure it.

50. Input into your postulations using light a a quantum variable in algebraic nomenclature and see what happens. I would make a wager on it.

[Duplicate post deleted, Ophiolite]

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