Understanding the Validity of Relativity: Questioning and Learning

[Joanna Dark]

OK

If you were sitting at the station and I was on a train traveling along a perfectly flat track, it appears to me that it is you who is moving. Remember that?

So I'm moving away from you in a straight line and you are stationary, regardles of velocity it appears we are traveling at the same velocity. You are moving at a 1000 mps and to you I am moving at 1000mps. If I were to slow down and reverse the train back to you it would still appear that for me it is you who are reversing back to me. So this situation is completely symmetrical. Now If I traveled to Pluto and back at a 1000 mps when I got back my clock would have traveled slower for the entire journey evidenced by the fact our clocks don't match.

So on a single journey to Pluto (with no return fare) regardless of velocity didn't my clock travel slower than yours? So how is it possible in this symetrical situation that we see each others clocks traveling at the same speed?

I'm not sure I could make my point of view any clearer than that, regardless of whether I am right or wrong?

 

[Doc Al]

If you were sitting at the station and I was on a train traveling along a perfectly flat track, it appears to me that it is you who is moving. Remember that?

Got it! You say you are at rest (speed = 0) and you say I am moving at some speed (speed = v). And vice versa.

So I'm moving away from you in a straight line and you are stationary, regardles of velocity it appears we are traveling at the same velocity. You are moving at a 1000 mps and to you I am moving at 1000mps.

OK. Our relative speed is the same.

If I were to slow down and reverse the train back to you it would still appear that for me it is you who are reversing back to me. So this situation is completely symmetrical.

It would be symmetrical if you swapped coordinates. But some things change: In one case I'm moving towards you; in the other I'm moving away from you. The big change is that you have moved from one inertial frame to another.

Now If I traveled to Pluto and back at a 1000 mps when I got back my clock would have traveled slower for the entire journey evidenced by the fact our clocks don't match.

That happens to be true. But the analysis of that situation is more complicated. Since you change directions, the situation is not symmetric. I, on earth, stayed in a single inertial frame throughout your trip; you did not. Relativistic effects between inertial frames are symmetric; acceleration breaks the symmetry.

So on a single journey to Pluto (with no return fare) regardless of velocity didn't my clock travel slower than yours? So how is it possible in this symetrical situation that we see each others clocks traveling at the same speed?

Edit: On a single journey in which both observers stay in a single inertial frame, we both see each other's clock run slow.

I'm not sure I could make my point of view any clearer than that, regardless of whether I am right or wrong?

I recommend that you first understand why relativistic effects (time dilation, length contraction, clock desynchronization) are symmetric as long as both sets of observers remain in single inertial frames.

 

[chroot]

So on a single journey to Pluto (with no return fare) regardless of velocity didn't my clock travel slower than yours?

Another grand misconception. It is meaningless to compare the time on two clocks unless you are able to bring them back together at the same place and time. The reason? Such a comparison would require some standard of absolute time. How could you tell travelers exactly when to report the reading on their clocks? You can't. That conclusion isn't a failing of technology or imagination, it's an unusual consequence of the real nature of time.

The classical view of time is that time marches on at the same rate, lockstep, everywhere in the universe. It's as if you could snap your fingers, say "now!" and take a snapshot photograph of the entire universe, showing exactly where everything is and what every clock reads. This is a naive concept of time, though one which is very adequate for use on Earth, where velocities are so small compared to c.

A more accurate view is that time is experienced locally. Every clock moves on a different path through spacetime, and objects moving along one path experience a different duration of time than do objects moving on other paths. It's impossible to synchronize two clocks unless they are at the same spot in spacetime because the very concept of simultaneity is relative.

If you attempt to synchronize two distant clocks in one frame of reference, they will not be synchronized in any other frame of reference. Even if you build an apparatus using light signals or what not to synchronize the clocks from one observer's perspective, every other observer in the universe will claim that you failed. The entire concept of comparing elapsed time on clocks is flawed, unless you can bring those clocks back together. If they are brought back to (effectively) the same point in spacetime, every observer in the universe will agree that they have been synchronized, and the times elapsed on each will then have universal validity.

That's the resolution of the twin paradox: clocks moving on unique paths through spacetime experience unique durations of time. The only way to universally compare their readings is to bring them back together. When you do so, you are actually comparing the proper times elapsed over their unique paths through spacetime, and they need not be the same.

- Warren

 

[Joanna Dark]

So we are almost there.

The similarities as I see it are that if we are stationary to one another our clocks match. Naturally. Or say we were traveling at the same speed in the same direction or opposite directions our clocks would match. I believe we have full agreement on that. Both our clocks slow down at the same rate.

You agree that if I am moving and you are stationary, it appears that you are moving. So in all appearances neither one of us believes we moved. Hence the reason it would be easy to believe the sun revolves around the Earth without knowing any better. My point was to show our perspective is exactly the same. Only difference being clock speed. So it would be impossible for us both to see the exact same clock speed. You appear to understand.

If I were to accelerate or decelerate my way to pluto, and you were stationary, we would observe each others clocks traveling at different times. Perhaps when I arrived my clock is a year to 10 years behind yours. Agreed.

We don't seem to agree that if I traveled to pluto at a constant speed, and you were stationary, that there would be any time difference in our clocks.

That is confusing to me because if we go back to the original Einstein eg. I used of the moving train observer and the train station observer (who are timing the same light traveling between the ceiling and the floor of the train) they observe the light traveling at the speed of light despite the light having traveled at two different distances. Even if the train was at a constant speed this would require time dilation. i.e. their clocks couldn't possibly match. So we have a problem. What I am getting from you does not match my basic understanding in this case.

If you mean you actually do agree on this then we have agreed on everything so far and I lost as to what the actual problem is.

If by the same inertial frame you mean traveling at the same constant speed in a straight line, then I'm lost aswell, as that is like saying if I paint a white wall white it will still be white. I am getting a sense that we are close to the crux of the problem but not quite there.

 

[Joanna Dark]

Wait I think I have it. So you are saying that If we are traveling at the same speed then our clock times match. So therefore reciprocation does occur. Is that it?

 

[RandallB]

Joanna your still presenting a confusing description that is not allowing you yourself to maintain a constant reference to understanding what is being seen by anyone observer: example:

If you were sitting at the station and I was on a train traveling along a perfectly flat track, it appears to me that it is you who is moving. Remember that?

A good start especial the part about remembering the perspective your taking; that while on the train you are not in fact moving but Dr Al is (presumably back on earth) But in the very next sentence you say;

So I'm moving away from you in a straight line and you are stationary, regardles of velocity it appears we are traveling at the same velocity.

What you forgot already?
You’re not moving, Dr Al is! If you were both moving at the same velocity the two of you would be stationary with respect to each other.

You are moving at a 1000 mps and to you I am moving at 1000mps.

Same problem pick a perspective and complete all your measurements before taking on the other view.

If I were to slow down and reverse the train back to you it would still appear that for me it is you who are reversing back to me. ….. … Now If I traveled to Pluto and back at a 1000 mps when I got back my clock would have traveled slower for the entire journey evidenced by the fact our clocks don't match.

NO remember you said you were not moving!
Pluto is coming toward you! at the same speed that Dr Al in moving away from you. Use a speed of 0.5c for both of them putting them in the same reference frame. (just two frames here yours & Dr Al’s ok). That means YOU DO NOT SLOW DOWN! No reverse the train and go back to AL! You take off from your stationary position at a new speed (and reference frame) designed to chase down Dr Al who has been getting away from you. I’d suggest twice his original separation speed (0.5c + 0.5c = 0.8c, for now you have to trust the addition used here) from your starting stationary position on the train. That way he will see you coming at a speed of 0.5c. [assume you instantly jump off the ‘stationary train’ and onto one following Dr Al to overtake him at a speed of 0.5c]

So this situation is completely symmetrical.

Well not yet,
Only now are you ready to just begin to look at the other view of Dr Al (and Pluto) being stationary watching you go towards Pluto at 0.5c and then turn around and come back at 0.5c. Now it is “completely symmetrical” IF you starting in a stationary position on the train and completely working out the problem should get the same answer as Dr Al does when he assumes he remains stationary.
PS. If you crunch these numbers and do not get the same result – trust me check for an error.

But do not say:

So on a single journey to Pluto (with no return fare) regardless of velocity didn't my clock travel slower than yours? So how is it possible in this symetrical situation that we see each others clocks traveling at the same speed?

I'm not sure I could make my point of view any clearer than that, regardless of whether I am right or wrong?

Frankly there was no point of view there to get a fix on. The way to make your view clearer is work through a problem completely for just one reference view before debating how it must look to someone else.
Then work out the other reference frame view – completely.

Only then can Dr Al or others help you out in how you are evaluating the results in each frame of view.

 

[chroot]

The similarities as I see it are that if we are stationary to one another our clocks match. Naturally. Or say we were traveling at the same speed in the same direction or opposite directions our clocks would match. I believe we have full agreement on that. Both our clocks slow down at the same rate.

You need to be careful with your language, as it's the cause of many of your misconceptions. "Both our clocks slow down at the same rate" should be expressed as "both clocks appear to the other observer to be running slowly." You cannot ever make a statement about a measurement without expressing who is making that measurement.

My point was to show our perspective is exactly the same. Only difference being clock speed. So it would be impossible for us both to see the exact same clock speed. You appear to understand.

Again, this is the same problem. "Clock speed" means nothing. You must specify who is measuring which clock for this statement to have any meaning. It sounds like you're still unwilling or unable to grasp that if two people are in relative motion then they will each measure the others' clock as running slow. If that's true, I give up, and I will lock this thread. You can take your questions elsewhere, as they have been thoroughly answered here, several times over.

If I were to accelerate or decelerate my way to pluto, and you were stationary, we would observe each others clocks traveling at different times. Perhaps when I arrived my clock is a year to 10 years behind yours. Agreed.

This statement contains more gross misunderstandings:

1) You cannot compare distant clocks.
2) Once you involve acceleration you're not really dealing with special relativity anymore.

We don't seem to agree that if I traveled to pluto at a constant speed, and you were stationary, that there would be any time difference in our clocks.

Again, this is a meaningless statement. You can't compare the clocks until you bring them back together.

That is confusing to me because if we go back to the original Einstein eg. I used of the moving train observer and the train station observer (who are timing the same light traveling between the ceiling and the floor of the train) they observe the light traveling at the speed of light despite the light having traveled at two different distances. Even if the train was at a constant speed this would require time dilation. i.e. their clocks couldn't possibly match. So we have a problem. What I am getting from you does not match my basic understanding in this case.

Time dilation occurs for objects in relative motion. Constant relative motion included.

- Warren

 

[Doc Al]

So we are almost there.

The similarities as I see it are that if we are stationary to one another our clocks match. Naturally. Or say we were traveling at the same speed in the same direction or opposite directions our clocks would match. I believe we have full agreement on that. Both our clocks slow down at the same rate.

There's no need to drag a third reference frame in. If we both move together, our relative speed is zero--we are in the same frame. That's all that counts. Our clocks run at the same rate.

When you say we are both moving together, you mean with respect to some third party. Don't think in terms our clocks running slow in that third frame. (It's true, but irrelevant for determining how we see each other.) Because there could be a fourth frame in which we are moving together at some different speed--do our clocks slow down twice?

You agree that if I am moving and you are stationary, it appears that you are moving. So in all appearances neither one of us believes we moved. Hence the reason it would be easy to believe the sun revolves around the Earth without knowing any better. My point was to show our perspective is exactly the same. Only difference being clock speed. So it would be impossible for us both to see the exact same clock speed. You appear to understand.

Bad example of Earth about the sun--the Earth is accelerating. Yet again, if we travel in two different inertial frame, we would measure each other's clock as running slow. (Key: How do you measure the rate of a moving clock?)

If I were to accelerate or decelerate my way to pluto, and you were stationary, we would observe each others clocks traveling at different times. Perhaps when I arrived my clock is a year to 10 years behind yours. Agreed.

If our clocks read the same time on earth, then you went to pluto and back, our clocks will no longer read the same time when we compare them side by side after your trip. Your clock (and you) will show less elapsed time.

We don't seem to agree that if I traveled to pluto at a constant speed, and you were stationary, that there would be any time difference in our clocks.

I don't like the term "time difference in our clocks". Again, we would each measure the other's clock as running slowly. As far as whether the times on our clocks match--that brings in the question of how do you define simultaneity. If we happen to pass by each other (only once, since we agree not to change frames), we can just look at each other's clock as we passed each other. But other than that, we'd have to agree on how to compare clocks--and that involves the question of simultaneity. As Warren stated, there's no universal definition of simultaneity--that too depends on relative motion. (Again I suggest you learn how one would go about measuring the rate of a moving clock.)

That is confusing to me because if we go back to the original Einstein eg. I used of the moving train observer and the train station observer (who are timing the same light traveling between the ceiling and the floor of the train) they observe the light traveling at the speed of light despite the light having traveled at two different distances. Even if the train was at a constant speed this would require time dilation. i.e. their clocks couldn't possibly match. So we have a problem. What I am getting from you does not match my basic understanding in this case.

Again, all we've talked about is the observed rate at which moving clocks run. We both observe "time dilation": moving clocks run slow.

If you mean you actually do agree on this then we have agreed on everything so far and I lost as to what the actual problem is.

If by the same inertial frame you mean traveling at the same constant speed in a straight line, then I'm lost aswell, as that is like saying if I paint a white wall white it will still be white. I am getting a sense that we are close to the crux of the problem but not quite there.

Not sure what you're saying here.

Wait I think I have it. So you are saying that If we are traveling at the same speed then our clock times match. So therefore reciprocation does occur. Is that it?

I don't know what you mean by "our clock times match". At what instant? According to who? What I am saying (yet again) is that I see your clock run slow by the exact factor that you see my clock run slow--that's what I mean by saying that time dilation is symmetric.

The only time you can have agreement about what time is showing on two different clocks is if they are at the same place at the same time. In that case EVERYONE, regardless of their motion, will agree as to what each clock read at the moment they intersected. But if the clocks are moving with respect to each other and they are not at the same spot, then what they read when depends on who's definition of "when" is being used.

I strongly suggest that you answer my question: How can you measure the rate of a moving clock?

 

[Joanna Dark]

Right I got the problem. I can understand what you are saying theoretically, but I can't grasp an understanding of how your explanation works in any practical application.

My understanding is that If *I* (v=?) were moving away from a *stationary* observer (v=0) that my clock speed while seeming normal to me will be in a slower time frame than the stationary observers.

Why do I think that? Because if that were true then logically the speed of light would be equal for both observers. It is the whole basis for this theory.

If the stationary observer sees my clock as experiencing time-dilation and I calculate his clock as experiencing time-dilation then it would appear both of our clocks are running slower simultaneously and at the same time they are running faster than each others. That appears grossly absurd to me and completely contradictory. What do I logically do with that? Not meaning to be offensive, but it is honestly useless to me. If I don't imagine the two clocks to be simutaneously running in two different time frames then they can't possibly observe the same ray of light simultaneously traveling two separate distances and still maintain the speed of light on both clocks.

This is basis for my third reference frame, which allows me to know the simultaneous events taking place. Noone wants to let me offer me that luxury as there is no way I can know what each clock is doing at the same time.

Let's give this a tangible quality. Say I am recreating this event in a 3d computer environment (I'll call it "I Am God-a-vision"), which is practically how my mind is observing the experiment. Why couldn't I set it up so I can observe the speed of each clock simultaneously for example? I'll put four timers on my screen. Two timers represent the speed of the stationary and moving clocks and the other two represent their observation of each other's clock. Now according to you, the first two clocks would be traveling at normal speed in their own frame of reference and the second two would be experiencing equal time dilation. Effectively this cancels one another out and both clocks are actually traveling at the same speed. Err, um, yah?

My version appears accurate in that the two clocks are not running the same speed and their observations of each other's clock are not equal. This way I can put a light traveling between two points (moving or stationary) anywhere in the 3d environment and both observers will see the light beam travel at c. I can place ten observers traveling at ten different velocities and directions and they will all see the same thing... c.

But if I base my model on your explanation no one sees light travel at c, except for any observer traveling at the same velocity as the the two points my light is traveling between. Why is that? My understanding is based on visually understanding what is happening at each frame of reference simultaneously so it makes intuitive sense. It seems to work fine. Add reciprocation and it doesn't.

This is the same problem I have with my teacher and no one seems to understand the difficulty I have in accepting reciprocation.

 

[chroot]

If the stationary observer sees my clock as experiencing time-dilation and I calculate his clock as experiencing time-dilation then it would appear both of our clocks are running slower simultaneously and at the same time they are running faster than each others. That appears grossly absurd to me and completely contradictory.

Stop thinking about what the clocks are "actually" doing. You seem to have this idea that if one observer sees your clock running normally, yet another sees your clock running slow, then there is some kind of contradiction.

Stop thinking that your clock has some "correct" speed. It doesn't. One observer can see it running at one speed, and another observer can see it running at a different speed. There's nothing wrong with this. Similarly, one observer can look at a nearby tree and have it appear very large, while a distant observer sees the same tree as being quite small. It's the same tree, but each observer has a different view of it. There's nothing wrong or contradictory about this.

Repeat this to yourself five times: Every unique observer has a unique view of every clock.

This is basis for my third reference frame, which allows me to know the simultaneous events taking place. Noone wants to let me offer me that luxury as there is no way I can know what each clock is doing at the same time.

This is exactly the mistake you keep making. You keep wanting to move from a physically realistic frame of some real, human observer into some kind of mystical omniscient "God frame" in which you know what's really simultaneous and what's really on the face of the clocks. There is no God frame. The only information an observer has is that which he sees.

Why couldn't I set it up so I can observe the speed of each clock simultaneously for example?

You're welcome to make such a model, but it is not a model of special relativity. It is some kind of bastardization of relativity which will predict results which are incompatible with experiment, and thus provably wrong.

You cannot simply pick and choose which bits of relativity theory you want to examine and then toss out the rest. Doing so necessarily destroys the consistency of the theory.

the first two clocks would be traveling at normal speed in their own frame of reference and the second two would be experiencing equal time dilation.

CLOCKS DO NOT EXPERIENCE TIME DILATION. Time dilation is an effect that occurs when an observer in one reference frame views a clock in another reference frame. No matter how you move or where you go, you personally will never "experience" time dilation. You may look back at your buddies on Earth and see their clocks running slowly, though.

But if I base my model on your explanation no one sees light travel at c, except for any observer traveling at the same velocity as the the two points my light is traveling between.

The only things you need to accept ab initio are these postulates:

1) All observers measure the speed of light to be the same.
2) The laws of physics are identical in every inertial reference frame.

The entirety of special relativity (time dilation, length contraction, relativity of simultaneity, etc.) are all derived directly from these two postulates. You need not suppose or assume anything else.

Why is that? My understanding is based on visually understanding what is happening at each frame of reference simultaneously so it makes intuitive sense. It seems to work fine. Add reciprocation and it doesn't.

Your intuition is WRONG. The theory you're describing (and attacking!) is a strawman theory which is not special relativity.

This is the same problem I have with my teacher and no one seems to understand the difficulty I have in accepting reciprocation.

It's as if you were claiming the Earth were a cube, and then complaining that no one seems to understand the difficulty you have in accepting that the Earth has no corners.

- Warren

 

[Joanna Dark]

I don't actually think any of these things you are suggesting.

I like God vision? All I am doing is thinking that the only absolutely necessary element for Special Relativity to work is that the speed of light is the same for all observers. Each observer's time can be calculated relative to their velocity and direction based on an "absolute" constant speed of light.

If I know my velocity and direction and yours then I can work out both our time frames an punch that into my model. I could observe them simultaneously.

At v=0 then time is, let's say, "normal speed". At v=c time freezes. Time works on a sliding scale for anyone traveling at any velocity between the two. Speed of light is thus equal to c for all observers.

I know it is not as simple as this, but it's a rough explanation for how my model would work. The only thing I can't grasp is why two people traveling at different velocities would observe each others clocks traveling slow. And still no one has given me a reason for this. That's all I asked. The only difference really as far as I can gather is that in my version one observer would see the other's clock slow and one would see the other's clock traveling fast.

Otherwise it sounds really simple to me actually. I don't see where the confusion arises, between what I have trouble with and what others think I have trouble with. It's only one point. The best any of you have given me is that it is a fact. Not why.

 

[chroot]

So... you're really looking for someone to give you a reason to believe your own personal theory, which is not self-consistent and is demonstrably wrong? You're not actually trying to learn relativity at all, eh?

If you express your "theory" mathematically, you'll discover it contains absurdities. If you try to test it empirically, you'll predict incorrect results. It's wrong. Enough said.

- Warren