A personal recap, and maybe you correcting me.

[Menoman]

Like many people I assume, special relativity, in particular time dilation and the lightbox example, are two hangups on my common sense.

 

I'm under the impression that the lightbox example does not truly 'explain' why time travels slower in the lightbox moving relative to me (and the lightbox stationary relative to me)

 

It's more of a tool that help you understand that time dilation actually exists, not a tool to help you understand WHY, just a 'description' per se. Would that be accurate?

 

Secondly, the "Twin Example" of time dilation, something I don't particularly understand, and boggles my head quite a bit to be honest, is that we all know what relativity is, and means. So since no specific frame of reference is preferred over any other frame of reference. Why can't we put the frame of reference to the twin in the spaceship? If he was the frame of reference, then the twin on earth would move away from him at .8c, or whatever you want to make it, and then come back at him. This seems like a contradiction that no frame of reference is special doesn't it?

 

It makes my mind think the special frame of reference is being the earth twin, because the opposites do not hold true if you switch the frame of reference to the spaceship twin... because he will not come back and the earth twin actually be younger than him... yet the frame of reference shouldnt matter?

[jedaisoul]

There are plenty of people better equipped to answer these questions than I am, but here goes. I'm sure someone will correct me if necessary...

 

I'm under the impression that the lightbox example does not truly 'explain' why time travels slower in the lightbox moving relative to me (and the lightbox stationary relative to me)

 

It's more of a tool that help you understand that time dilation actually exists, not a tool to help you understand WHY, just a 'description' per se. Would that be accurate?

 

In a sense, yes. Science generally attempts to describe WHAT happens, not WHY. Why is often a philosophic or theological question.

 

Secondly, the "Twin Example" of time dilation, something I don't particularly understand, and boggles my head quite a bit to be honest, is that we all know what relativity is, and means. So since no specific frame of reference is preferred over any other frame of reference. Why can't we put the frame of reference to the twin in the spaceship? If he was the frame of reference, then the twin on earth would move away from him at .8c, or whatever you want to make it, and then come back at him. This seems like a contradiction that no frame of reference is special doesn't it?

 

It makes my mind think the special frame of reference is being the earth twin, because the opposites do not hold true if you switch the frame of reference to the spaceship twin... because he will not come back and the earth twin actually be younger than him... yet the frame of reference shouldnt matter?

Einstein's theories have moved on a lot from 1905 when he asserted that all frames of reference are equal. That was Special Relativity. There are two answers to your query in SR terms:

• Special relativity, as originally expressed, did not take acceleration into account, therefore it could not answer your query. It was, apparently, a paradox.
  
• However, it is not correct to say that SR cannot deal with accelerated frames. When you do take acceleration into account, the body that has undergone acceleration is the "moving" body. So not all frames of reference are equal.

 

In 1916, Einstein's General Theory included gravity, and that changes the answers again. Firstly, it is often said that SR is just a special case of GR (in which the gravitational field is uniform). IMHO, this is not true. SR and GR have different conceptual frameworks. So SR is analogous (in it's conceptual framework) to the special case of GR. Analogous is not the same. In GR, the gravitational field is a physical entity. The interpretation of what that means vary. I would suggest that makes the gravitational field the de facto preferred frame of reference. Now I'm sure that idea will be hotly disputed, so I'll leave it there and let others take up the discussion. My main point is that the interpretation of the equality of fames of reference has changed...

[swansont]

The light-clock is an example that demonstrates time dilation. They "why" is that the speed of light is constant in all frames. However, the consequences of that are not generally obvious, and many find them to be counterintuitive.

 

 

Einstein's theories have moved on a lot from 1905 when he asserted that all frames of reference are equal. That was Special Relativity. There are two answers to your query in SR terms:

• Special relativity, as originally expressed, did not take acceleration into account, therefore it could not answer your query. It was, apparently, a paradox.
  
• However, it is not correct to say that SR cannot deal with accelerated frames. When you do take acceleration into account, the body that has undergone acceleration is the "moving" body. So not all frames of reference are equal.

 

 

The problem of the twin is actually mentioned in a general sense at the end of section 4 of Einstein's 1905 paper; he comes to the proper conclusion, but does not mention that it is the acceleration that allows the identification of the slow clock — that came later. And he does define the reference frames to which special relativity applies.

[NYSportsGuy]

Okay here it goes again. Special relativity is nothing more than a perception. IT basic fundamental idea is that if two things are moving away from each other in constant speed.....they can be said to be either standing still or one is moving relavtive to the other no matter which is is ACTUALLY moving or NOT. But this is only for a constant speed. Now the effects of this motion is that an oberserver from earth observing his twin moving at .8c lets say, sees the clock on the ship of his twin moving slower than his own clock oN Earth. This is ONLY because the angle and the distance at which he can record the clock on the spaceship is growing farther and wider all the time. It doesnt mean neccesarily that the twon on the spaceship is ACTUALLY moving slower....it is just a perception and vice versa.

 

The General Theory of Relativity explains why this phenomena happens even further by adding the fact that accelerating object cause the same effects that gravity does...in essence because acceleration = gravity. As of now, Einstein says four things: time, space, gravity and acceleration are ALL RELATIVE. And as an object accelerates towards you it will appear to move faster, as it acclerates away from you it appears to be slower because the rays of light which allow you to see it (which are ALWAYS constant) will take either longer or faster to reach your senses or your eyes in this case.

 

Thus gravity, accleration and moving uniformly really really fast (ie- .3c or faster) all cause time to slow down.And if time slows down, according to the formula space must shorten or be faster. Time can change, space can change....but timespace together MUST ALWAYS BE CONSTANT!

[Menoman]

 

Einstein's theories have moved on a lot from 1905 when he asserted that all frames of reference are equal. That was Special Relativity. There are two answers to your query in SR terms:

• Special relativity, as originally expressed, did not take acceleration into account, therefore it could not answer your query. It was, apparently, a paradox.
  
• However, it is not correct to say that SR cannot deal with accelerated frames. When you do take acceleration into account, the body that has undergone acceleration is the "moving" body. So not all frames of reference are equal.

 

This makes the most sense to me, I haven't gotten into much gravity and such yet in my lectures, so I'm trying to stay away from that for now. But this puts it into a framework I can understand I believe.

 

As my lectures go on and on further I'll probably be back, and I'll peruse a bit to see if there's any questions people throw up that I can be of help to as well...

 

Anyway in essence, this is a Hello everyone, and thanks for the explanations

[iNow]

Special relativity is nothing more than a perception.

You can keep repeating yourself on this site all you want. You are still wrong and you have still failed to support your contention with anything more than a bunch of hand-waving.

[Janus]

Okay here it goes again. Special relativity is nothing more than a perception. IT basic fundamental idea is that if two things are moving away from each other in constant speed.....they can be said to be either standing still or one is moving relavtive to the other no matter which is is ACTUALLY moving or NOT. But this is only for a constant speed. Now the effects of this motion is that an oberserver from earth observing his twin moving at .8c lets say, sees the clock on the ship of his twin moving slower than his own clock oN Earth. This is ONLY because the angle and the distance at which he can record the clock on the spaceship is growing farther and wider all the time. It doesnt mean neccesarily that the twon on the spaceship is ACTUALLY moving slower....it is just a perception and vice versa.

 

The General Theory of Relativity explains why this phenomena happens even further by adding the fact that accelerating object cause the same effects that gravity does...in essence because acceleration = gravity. As of now, Einstein says four things: time, space, gravity and acceleration are ALL RELATIVE. And as an object accelerates towards you it will appear to move faster, as it acclerates away from you it appears to be slower because the rays of light which allow you to see it (which are ALWAYS constant) will take either longer or faster to reach your senses or your eyes in this case.

 

 

Why do keep saying this when you have been repeatedly told that it is WRONG!

 

Time dilation has nothing to do with increasing distance between you and another object or the time it takes light to travel between you.

 

This is easily seen by just looking at the equation for time dilation:

[math]t = \frac{t`}{\sqrt{1- \frac{v^2}{c^2}}}[/math]

 

There is no difference in the answer when v is negative (a velocity towards you) or positive(a velocity away from you). The time dilation remains the same, the clock moving relative to you runs slow.

 

Compare this with the equation for Doppler effect:

 

[math] f = \left( \frac{c}{c + v} \right) f` \,[/math]

 

Where you do get a different answer for postive and negative velocities.

 

The Doppler effect is due to the increasing distance and the time it takes light to travel between the two objects. But it is a completely different mechanisim from that which results in time dilation.

 

In fact, when dealing with higher veloicites, the Doppler effect equation is modified to take the separate effects of Relativity into account and one gets the Relativistic Doppler shift equation:

 

[math] f_o = \sqrt{\frac{1-v/c}{1+v/c}}\,f_e, [/math]

[jedaisoul]

Special relativity is nothing more than a perception...

I don't think it is appropriate to present alternative theories in an answer to someone who is trying to understand the mainstream theory. Now I happen to think that the evidence for SR is open to different interpretations, but I just gave the best understanding that I have of the mainstream explanation.

 

So it's not just a matter of whether your interpretation is correct, it is irrelevant in this thread.