Is relativity self-contradictory??

Overdoze,

True, but how will B know if it is accelerating or decellerating?

Tom

 

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That's irrelevant, as previously explained, due to the symmetry of B's trajectory. IOW, at some point in its trajectory it may be accelerating; if so, it will have to be decelerating at some other point so as to return to A. (Note: here I'm using "accelerating" in the sense of a positive change in speed, rather than the more proper mathematical sense of changing velocity.)

 

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Overdoze,

Do you agree that the time dilation a clock experiences is based on it's speed relative to the absolute frame of reference?

If so, wouldn't you be able to take two clocks travelling at different speeds, and determine their absolute speeds by using their time dilations and their relative speeds to one another??

Tom

 

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Prosoothus

If so, wouldn't you be able to take two clocks travelling at different speeds, and determine their absolute speeds by using their time dilations and their relative speeds to one another??

You are soooo close to proving to yourself there is no absolute frame of reference.

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That's correct, with the qualification that we're talking about the so-called proper time of the clock (as opposed to its time as observed by some other inertial observer.)

No, because their observations of each other would be mutually symmetrical. This is a property of the Lorentz transformations. That is, if an object X is Lorentz-transformed with respect to you as the observer, then you will appear identically Lorentz-transformed to object X with X as the observer.

 

Overdoze,

Let me try to prove my point:

Experiment 2:

You have three clocks on Earth. One is stationairy, while the other two (A and B) travel away from Earth at .45c in opposite directions (A and B are travelling at .90c away from each other). After a long trip, they turn around and come back to Earth. When the observer on Earth reads them, what will the result be:

1) Clock A is slower than clock B
2) Clock B is slower than clock A
3) Clocks A and B are still synchronized.

Tom

 

The answer is 3) -- assuming both clocks turn back after the same time interval as individually measured by each of them. Again, symmetry comes into play.

 

Overdoze,

I see your point. Your claiming that the time dilation averages out due to the roundtrip of the clock(s). I assume that if it was a one-way trip, the absolute motions can be derived from the clocks readings.

Tom

 

Except the irony is, there is no way for the clocks to see each other's reading without a roundtrip being involved. If the clocks themselves don't turn around and meet up, then the signals they send to each other will serve as their proxies to complete the "roundtrip". In either case, information is making roundtrips, and it's at this more abstract and universal level that most relativists think. IOW, the statement about speed of light ends up being translated into a statement about information propagation and everything else gets recast accordingly in terms of information transfers.

 

overdoze:

They wouldn’t have to exceed c. If it can be accepted that the universe is infinite in extent, it is only a step further to see that the universe might be infinite in a (special) relativistic way, where the furthest galaxy is moving at .9(infinite number of 9’s)c. Just like no galaxy need be the last galaxy in an infinite universe, no galaxy need exceed c--an approachable not attainable limit just like infinity--in a relativistic universe. Such a universe adheres to the cosmological principle and seems simpler and more consistent to me than the models cosmologists propose today. It also more closely matches what we observe (namely a flat universe).

Remember that when you add velocities in relativity, you get less than their sum. In a relativistic universe, if the galaxies were equally spaced and every galaxy was receding from its closest neighbor at v, the furthest galaxies from you would not exceed c relative to you. Every galaxy would observe the universe as fairly uniform in structure at each successive radius in every direction, just like we do.

That is actually what cosmologists propose. But it need not be that way. It could be that 15 billion light years away the galaxies are receding at .9(millions of 9’s)c and 30 billion light years they are receding at .9(billions of 9’s)c. And so on and true for every observer in the universe. This would make the entire universe--even if infinite in extent—theoretically observable at ages ranging from the first observable moments (background radiation) to the present, which is you.

There’s no incompatibility with big bang theory. The age of the universe is calculated by us, we who are the oldest beings in it as we observe it. Most everything else, because it is receding from us, is aging slower to be younger. Everything could still have been simultaneously born. In the twin paradox, the twins can agree both that the traveling twin is years younger and that they were born on the same day.

Regarding the twin paradox:

Many books will tell you that the traveling twin is younger because he accelerated and leave it at that. Or they might elaborate to say that the traveling twin feels the equivalent of a gravitational field during acceleration and gravity slows clocks. Or they might erroneously say that all the time distortion occurred during the traveling twin’s acceleration. There is an intuitive way to view the paradox, no tensor calculus required. Here is the step-by-step:

Treat each twin as moving, relative to the other twin taken as stationary. Ask yourself, what is each twin moving relative to? The stay-at-home twin is moving relative only to the traveling twin. The traveling twin, on the other hand, is moving relative to both the stay-at-home twin and the space between the twins.

Both twins are accelerating, relative to each other. That only the traveling twin feels the acceleration is important only to discern who is moving relative to the space between the twins. He who feels the acceleration, accelerates relative to all of space along his axis of motion, this axis including his twin. He who doesn’t, accelerates relative only to his twin.

Special relativity tells us that moving objects contract along their axis of motion. That applies to the twins. The stay-at-home twin observes that the traveling twin is contracted along his axis of motion. The traveling twin, by virtue of moving relative to all of space along his axis of motion, observes this entire axis including the stay-at-home twin contracted.

Ask yourself, what proper distance is each twin traversing? (“Proper” means “as measured by an observer in his own reference frame.”) If the stay-at-home twin observes that the traveling twin made a 1-unit round trip, the traveling twin observes himself traversing less than that distance, because proper distance is contracted along his axis of motion, and the twins' trips are otherwise symmetrical. The traveling twin moves through a contracted version of the stay-at-home twin’s space. That is how the twins' trips are asymmetrical. Both twins have accurate clocks that measure the elapsed proper time away from each other. The traveling twin’s clock shows less elapsed proper time upon reuniting, for the simple reason that the traveling twin traverses less distance than the stay-at-home twin. The clock is like an odometer.

 

I agree with you, yet consider Relitivity (E=mc2) being applied to light its-self. Then what happens.

 

Uh-oh, I feel a "does light have mass" thread coming up

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Yes, that’s right. The difference between us is that I know how to correctly implement that into a mathematical analysis, whereas you do not.

I don’t know whether to laugh or scream.

Your statement above is incorrect. The speed of light postulate does not say that the distance traveled by a light pulse is the same in all frames of reference! It says that the speed (gasp!) of the light pulse is the same for all frames of reference (duh!).

If our observer is watching the mirrors move past him at speed ‘v’, and he determines that the mirrors are separated by a distance ‘d’, then there is no way he could possibly determine that the light traveled a distance ‘d’, because the top mirror moves from its original position while the pulse is in transit. More precisely, the top mirror moves a distance vt2, and so the light pulse must move that additional distance to catch it.

Your mistake is that you made an assumption that is not implied by relativity, namely invariance of the spatial interval traversed by the light pulse. This is such an elementary point that I am really quite shocked that you haven’t gotten it by now. It seems clear that relativity is a subject that you not only do not know, but also do not want to learn. That really is too bad for you, because you’re going to continue to look like a jackass every time you misrepresent it—especially because I linked you to Einstein’s paper 2 or 3 times already. You really have no excuse.

I don’t need you to tell me what relativity is. I could teach you a great deal about this subject, but you are so dead-set against learning anything that disagrees with your preconceived notions that you won’t have it. I recently read through the “Unrelative Relativity I and II” threads. Your attitude towards education is very childish, as it seems to be “Don’t confuse me with the facts, because I’ve already made up my mind.”

If you could just get beyond this ridiculous “relativity is illogical” mantra that you keep repeating, you would start making some progress in your understanding.

And you would be funny, if you weren’t such a sad case. You seem to really enjoy your total ignorance of math, physics and logic. That is the only reasonable explanation of why you consistently and categorically reject one valid post after another by people who are only trying to correct your misunderstanding. At least you appear to be listening to overdoze--there may be hope for you yet.

Try to at least learn Algebra I and Physics I. Your Reign of Error has gone on for far too long.

Tom

 

Re: My my, how things have changed

I disagree with that. The mathematics must be looked at, because Prosoothus is trying to compare special relativity to Galilean relativity. Also, he got both of them wrong, which further warrants a closer look at the math, because his argument flows from his mis-derivation.

No, the principal point in question is: "Is relativity internally consistent or not?"

Again, you need the mathematics to settle it.

I'm not sure that that is correct. Prosoothus made it clear that he espouses Galilean relativity. The frame of absolute rest in that scheme is the frame in which Maxwell's equations take on their textbook form. Is that necessarily the "vacuum frame"? If so, it is not obvious to me.

I definitely don't agree with this. The predictions of the Lorentz transformation are not predictions on what an observer sees, they are predictions of what actually happens in that observer's frame.

A simple example will serve to prove the point. Two events occur simultaneously in frame S. Event 1 is a red flash 3E8m to the right of the origin, and Event 2 is a blue flash 6E8m to the left. Light from Event 1 reaches the origin in 1s, and light from Event 2 reaches the origin in 2s. Thus, the observer sees the events 1s apart, when they are actually simultaneous in his frame.

Tom

 

Tom2:

Along those lines, do you see anything wrong in the following story?:

If I am passing by the Earth towards the Andromeda galaxy--some 3 million light years away as measured from the Earth--at a velocity < c relative to the galaxy that will get me there in 1 proper year, my proper distance to the galaxy must be < 1 light year. If I then decelerate in 10 proper years to a full stop relative to the Earth and galaxy by the halfway point between them, my proper distance to the galaxy increases from < 1 light year to 1.5 million light years during the deceleration. Although the galaxy is measurably receding from me at far > c, I continue to receive light from the galaxy, although the light is extremely redshifted.

 

I don't recall having had a discussion about that

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prosoothus, overdoze etc. don't you get a headache of this stuff? this seems to be the never ending story on this board
I still think, to say it oversimplistic and short, that relativity discussions is a problem of interpretation of experiments. It's also a discussion about philosophy. I think all relativists are positivists to the bone.

 

Tom2,

You are comparing the movement of the mirrors to a stationairy observer. Unfortunately, the stationairy observer you are referring to is the absolute frame of reference. Just because you are calling the "absolute frame of reference" an observer, doesn't make your equations relativistic.

You know it's funny, when you first came to sciforums you where actually a person that someone could talk to. Unfortunately, over time, you became a stuck-snob that specializes in personal attacks instead of logical arguments. No, I don't have a PHD in theoretical physics, but I didn't think it was required on sciforums.

I consider it real funny how you claim that my equations and logic are wrong, even though these are the very same equations that overdoze has shown me a few months earlier. Yet I see no personal attacks on overdoze.

I hate to disappoint you, but relativity is not brain surgery. The reason I find relativity so hard to understand is because it's illogical. Sure, relativity can give a nice and cute result when dealing with the round-trip of light. But relativity breaks down when you attempt to apply it to a one-way trip of light.

Finally, let me say that if your convinced that I can't or won't learn, then just disregard my posts. I will disregard your posts, and we will both be happy. After all, I'm sure that you won't lose your job if you can't teach me relativity.

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Tom

 

c'est moi,

Welcome back!!! Where have you been???

Well, I started this thread to continue a discussion I was having with Tom2 (a new poster) an another thread. I also wanted to bring the fact into the open that time dilation and/or length contraction compensate for the variance created by the absolute model. Overdoze was the first to explain this to me, but since his explaination has in the middle of a large thread, I felt it necessary to start a new thread that was exclusively dedicated to the topic.

Tom

 

Prosoothus

The reason I find relativity so hard to understand is because it's illogical.

Illogical, no. Counter-intuitive, yes. But the fact that you think it's hard to understand is no reason to believe it's wrong.

Sure, relativity can give a nice and cute result when dealing with the round-trip of light. But relativity breaks down when you attempt to apply it to a one-way trip of light.

No, because if it breaks down on a one-way trip, it would always break down. That's not the case.

Finally, let me say that if your convinced that I can't or won't learn, then just disregard my posts.

Where is the fun in that ?

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Q,

Let me be more specific:

Let's say you are in a frame of reference moving at .90c. If you shine a light in your frame of reference towards a mirror so that the light reflects and comes back to you, you will find that you only need one time dilation and length contraction to convert the speed of light from c in your frame of reference to c in another frame of reference.

In other words, the Gamma factor (time dilation and length contraction) is required to convert the roundtrip of light from c in one frame of reference to c in another frame of reference in order to preserve the principle of invariance of light.

However, if you don't have a roundtrip of light, but have a one way trip of light in your frame of reference, a single Gamma factor is insuficient for the conversion. If you have your flashlight pointing in multiple directions in your moving frame of reference, you will need to apply a different Gamma factor for every beam of light in order for the conversion to be correct.

I expressed this problem to James in a previous thread, and the only way he found to convert the one-way beams of light shining in multiple directions in a moving frame of reference to another frame of reference, while preserving the principle of invariance of light, was to apply MULTIPLE time dilations to each beam of light in the SAME frame of reference. Unfortunately, as you know, you can't have multiple time dilations in the same frame of reference.

So, as you can see, relativity was meant to compensate for the round-trip of light in a moving frame of reference. It was never meant to compensate for the one-way trip of light in the same frame.

Tom