Why are the effects of Time Dilation permanent but Length Contraction is Not?

[Dale]

Do you have any mainstream scientific references to support your interpretation?

Where do you disagree?
1. The photons minimum and maximum speed are the same in every frame and that = invariant speed of light.
2. Our visual perspective depends on where we observe an object.

I agree here.

3. The photon perspective is the only reality of its own position in space.

I disagree here. A photon doesn't have a valid perspective. See:

https://www.physicsforums.com/showthread.php?t=511170

And even if it did no reference frame represents the "only reality" of anything. Your claim that one inertial frame is more valid than another is a direct contradiction of the principle of relativity.

 

[Janus]

Hi DaleSpam,
Let's see you are saying the photon physically hits the back of the ship before the one in front hits in the Earth frame. Then they physically hit at the same time in the ships frame. Do you understand how absurd that sounds? The photon has to be in two places at the same time.

The point is that "at the same time" means something different for the Earth frame than it does for the Ship frame. Events that the two frames can agree happen at the same time are those that happen at the same point (for example, the light hitting one end of the ship and the reading on the clock at that end of the ship at that instant.)

For demonstration here is the classic train example for the Relativity of Simultaneity.

First, events according to the embankment frame:

Here the lightning flashes originate when the ends of the train are adjacent to the red dots on the embankment and the embankment observer is at the midpoint between the two.

The embankment observer sees both flashes at the same time, and being halfway between the lightning strikes concludes that they occurred at the same time. Notice how the flashes reach the train observer at different times.

Now the thing to keep in mind is that in this frame, the train is length contracted, and it it this length contraction that allows it to just fit in between the two dots on the embankment.

Now the same scenario according to the Train frame. In this frame, the train is its proper length and it is the embankment which is length contracted. Now the train is longer than the distance between the two dots. The front of the train hits the right red dot before the rear reaches the left dot. The lightning strikes must originate when the ends of the trains are aligned with the dots, otherwise you will have a contradiction between the frames.

This means that in a very real sense, the lightning strikes occur at different times in the train frame. If the light from those flashes expand outward at c relative to the train, the train observer will see each flash at different times (just as he did according to the embankment frame. ). The reverse argument is that since he sees the flashes at different times, is halfway between the ends of the train(where the lightning strikes occurred) and the light from the strikes approaches him at the same speed from both ends (the speed of light is invariant), then the lightning strikes occurred at different times.

You will also note that in the train frame, the flashes also reach the embankment observer at the same time. Further, if you compare the two animations, you will note that the train observers position with respect to the embankment when each flash reaches him is the same in both as is the embankment observer's position with respect to the train when the flashes reach him.

Thus there are no true contradictions between the frames, only a disagreement as to what is simultaneous when it come to events that are separated by some distance. Note that this is not just a matter of one observer being further from the source and seeing it later, because each observer accounts for his distance from the source to determine when the flash really occurred. It is a very real difference in the simultaneity of events separated by distance.

This is length contraction and the Relativity of Simultaneity working together. If you were to place clocks at the red dots, the ends of the trains and with each observer (with the clocks in each frame synchronized in that frame), you could include time dilation into the mix, and find that everyone will agree as to what times were on any two clocks when those clocks passed each other, or when the light from either strike hit them. They will not agree as to the synchronization of clocks between frames (each frame claiming their own clocks as being in sync while the other frame's clocks are not), nor as to the relative clock rate between frames. (each will consider the clocks in the other frame as running slow.)

This is what Special Relativity is about, there are real differences in time and space between inertial frames.

 

[Qzit]

DaleSpam.

Janus has a depth of understanding that comes from his thinking about Relativity and not just a surface interpretation of what he read. To truly understand Relativity you have to think about what is happening from the different perspectives. Once Janus said in the Earth frame the photon will hit the back of the ship first we no longer had a disagreement in our understanding. He agrees the distance traversed in the forward direction is different than the distance traversed in the rear of the ship for the one way path of a photon. When we find out new information we have to challenge old conclusions with the new information. I agree that the observer in the middle of the ship will measure the distance to be the same for the forward and backward photons return trips. Were they reflected at the same time? NO! You were arguing that each photon hit the ends of the ship twice because of your belief that contraction is physical. Janus understands Relativity of simultaneity correctly.

Now the second issue we disagree on. Time dilation for the speeding spaceship is an increase in volume and decrease in density. This once again takes thinking it out for understanding. You say time dilation is contraction and I say dilation is expansion. This can be proven by photons invariance to a frame. The speed of light can be used as an anchor because it travels through all frames like they were not there the photons speed does not vary from frame to frame. If you contract the distance in a frame you have to speed a clock up to match the shorter distance. If you expand the distance you have to slow the clock down to give the photon enough time to traverse the same distance. Only this way does the clock match the distance in the rest frame of all frames. If your clock is faster in a frame your measuring stick is shorter. If your clock is slower than your measuring stick is longer. This way you measure the speed of light in every frame to be invariant although it does take longer to traverse a dilated frame.

 

[Dale]

Janus has a depth of understanding that comes from his thinking about Relativity and not just a surface interpretation of what he read. To truly understand Relativity you have to think about what is happening from the different perspectives.

I agree on both counts. Janus is quite knowledgeable, and to understand relativity you do have to think about what is happening in different reference frames and recognize that each is equally valid.

Once Janus said in the Earth frame the photon will hit the back of the ship first we no longer had a disagreement in our understanding. He agrees the distance traversed in the forward direction is different than the distance traversed in the rear of the ship for the one way path of a photon. When we find out new information we have to challenge old conclusions with the new information.

I am glad you have changed your mind and now agree with me, on this point at least.

You were arguing that each photon hit the ends of the ship twice because of your belief that contraction is physical.

I certainly never said any such nonsense.

Time dilation for the speeding spaceship is an increase in volume and decrease in density.

Please provide a mainstream reference to support this assertion.

This once again takes thinking it out for understanding. You say time dilation is contraction and I say dilation is expansion. This can be proven by photons invariance to a frame. The speed of light can be used as an anchor because it travels through all frames like they were not there the photons speed does not vary from frame to frame. If you contract the distance in a frame you have to speed a clock up to match the shorter distance. If you expand the distance you have to slow the clock down to give the photon enough time to traverse the same distance. Only this way does the clock match the distance in the rest frame of all frames. If your clock is faster in a frame your measuring stick is shorter. If your clock is slower than your measuring stick is longer. This way you measure the speed of light in every frame to be invariant although it does take longer to traverse a dilated frame.

You claim that you believe that relativity is correct. If so, then you believe that the Lorentz transform is correct (even if you disagree with my interpretation of it). However, what you are saying is incompatible with the Lorentz transform itself.

I challenge you once again to actually do the math. Unfortunately, it looks like you will have to do so on your own now.

 

[nitsuj]

I have never seen the first postulate written that way. It is always written in terms of reference frames, not observers.

Opps.

I always thought of an observer as being the same as a FoR.

Pretty clear there can be more then one observer in a FoR.

An important distinction.

 

[dfaullin]

Wow! I wish I would have kept following up on my post. I just thought it was kind of over. I learned a lot from reading through the posts. Thank you for having the conversation. I wanted to especially thank George for performing that calculation for me on page 2 (post 25 or so).

Amazing that after 105 years of the existence of Special Relativity, it is still a mind warp and debatable as to the true nature and effects implied by the theory.

 

[ghwellsjr]

Wow! I wish I would have kept following up on my post. I just thought it was kind of over. I learned a lot from reading through the posts. Thank you for having the conversation. I wanted to especially thank George for performing that calculation for me on page 2 (post 25 or so).

Amazing that after 105 years of the existence of Special Relativity, it is still a mind warp and debatable as to the true nature and effects implied by the theory.

You're welcome, Dylan. (It was post #26.)