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

[Qzit]

One way to look at it is that we measure time and space we are only measuring "slices" of a larger reality, and that different frames are looking at different slices.

On this we agree but it still does not explain why the Earth observer sees the photon hit the back of the ship first and the front second while the ship observer sees them hit simultaneously. If the Earth frame sees a difference in the relative time (to hit the back and front of the ship) than inside of the spaceship there has to be a difference in the one way speed of light. There is no way to get around that. From an observer in the center of the ship the one way speed of light is different. Not that the spaceship frame could measure it but the reality is the speed within the ship is c+v and c-v. The round trip is “C” in both directions. The Earth observer is the only one that can measure the one way direction of light. That measurement is c+v and c-v for closing and departing distances. So in a moving frame light can cover a different distance in the same amount of time. This would explain why atomic clocks lose Nano seconds going from east to west.

 

[Dale]

On this we agree but it still does not explain why the Earth observer sees the photon hit the back of the ship first and the front second while the ship observer sees them hit simultaneously. If the Earth frame sees a difference in the relative time (to hit the back and front of the ship) than inside of the spaceship there has to be a difference in the one way speed of light. There is no way to get around that.

This is incorrect. The distance traveled by the light is different for the forward and backward paths in the Earth frame, and that distance is different than the distance traveled by both paths in the ship frame. The speed of light is the same, and the various distances are different. Again, you should work out the math to convince yourself of this. If you need help there are many on this form who will be willing.

The Earth observer is the only one that can measure the one way direction of light.

What makes the Earth observer so special?

 

[Qzit]

Hi DaleSpam,

This is incorrect. The distance traveled by the light is different for the forward and backward paths in the Earth frame, and that distance is different than the distance traveled by both paths in the ship frame. The speed of light is the same, and the various distances are different. Again, you should work out the math to convince yourself of this. If you need help there are many on this form who will be willing.

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.

Math is no guarantee that you are correct. While the math does contract the visual object the same as your view. You actually believe the contraction is physical. Does the math prove it’s physical?

 

[Dale]

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?

Yes, I do. That is why the relativity of simultaneity is the single most difficult concept for students to grasp in learning special relativity. It goes very strongly against our non-relativistic intuition.

Math is no guarantee that you are correct ... Does the math prove it’s physical?

The math is a guarantee that what I am saying is consistent with SR and that what you are saying is not consistent with SR. Then experiments prove that SR is correct in the domain where it is tested. The math is necessary, but not sufficient, which is why we do experiments too.

In any case, my repeated suggestions that you do the math are not for the purpose of proving my point, they are simply to help you learn. If I were only interested in proving my point then I would do the math myself. But you will learn more and faster if you do it.

 

[nitsuj]

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.

Math is no guarantee that you are correct. While the math does contract the visual object the same as your view. You actually believe the contraction is physical. Does the math prove it’s physical?

The first postulate is the laws of physics are always the same no matter the observer, as long as they're inertial. Consider that time is merely a measurement, like length is a measurement. Your intuition is right, just got to tune it a bit more physicsy. It would be absurd for someone right next to (inertial with) the experiment to believe the photons didn't hit simultaneously. (im assuming this is the scenario) That observer is in the "same" spacetime, specifically frame of reference as the experiment.

Said differently, considering another observers FoR doesn't make it "reality". Only your own observation does. I think causality is the final nail in that.

In another, more crude way, conscious observers are special in that we can in-vision what would happen in the other FoR. That cannot "physically" be considered a/the "reality". I know nothing of LET but this conscious observer reasoning would be getting off on the wrong foot (with either theory).

I couldn't think of an equation for that.

 

[Dale]

The first postulate is the laws of physics are always the same no matter the observer, as long as they're inertial.

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

 

[Dmytry]

This question is in regard to special relativity.

From my rudimentary understanding, concerning the twin paradox, if one twin leaves traveling near the speed of light and returns, he will find himself younger than his twin who stayed behind. Hence, the effect of time dilation is permanent.

However, I have never read anywhere that the traveling twin's length will also be permanently adjusted due to length contraction.

How is it that one Lorentz transformed aspect remains while the other one vanishes upon the traveling twin's return?

I apologize if this question has been asked before. If so, and you know where to find the responses, please point me in the right direction.

Thank you!

~Dylan

The twin that returns, however, will - upon return - be aging at the same rate as the twin that stayed home. The clock that the twin took with him in a voyage will be counting off time length of 1 second, in a second, when he's back home. The length of the traveling twin's sleep, or the length of his heartbeat (ignoring the senile insomnia, ha ha, and other effects of aging on the staying twin) will not be affected permanently, just as the length of his body was not.

The age is like a position, not like length interval.

 

[Qzit]

Hi nitsuj,

The first postulate is the laws of physics are always the same no matter the observer, as long as they're inertial.

Thank you. That is what I am trying to get across. Relativity of simultaneity is just the distance light travels for each observer. When you say the photon hits the back of the ship first for the Earth observer that is the reality and proves that the one way distance in the spaceship frame that light travels is different than the return trip distance light travels. There does not need to be an observer for reality of physical position in space. The reality is the photon hits the back of the ship in both frames by the same physical position in space. The problem is the MMX experiments was the two way distance light travels. No matter what frame you are in the two way distance will make it appear light travels the same distance/time. If the math you use takes the distance traveled and divided by ½ for the one way speed you will be wrong because the travel out is always adjusted by the return travel. An orthogonal way to prove my point would be with Atomic clocks. You are on the equator and have three atomic clocks synchronized. One stays stationary one is taken in a plane to the west and one to the east around the world. When they return the clock that flew west loses time compared to the stationary one and the one that flew east gains time compared to the stationary one. Einstein said atomic clocks can be used to measure the speed of light. This experiment proves the distance light traverses a moving frame is different than a frame at rest. There was a second experiment I remember reading about using four atomic clocks. Four clocks were synchronized in New York three were taken to the North Pole. One was brought back to New York and the other two were taken to San Francisco. The one brought back to New York stayed synchronized. Out of the two that went to San Francisco one went to New York and the one in New York went to San Francisco. New York to San Francisco lost 14 Nano seconds San Francisco to New York gained 14 Nano seconds. This also proves the one way distance traversed/time interval is different. Wake up the MMX experiments were flawed that Einstein used for Relativity. That does not negate Relativity or simultaneity of relativity. It only proves that simultaneity of Relativity is visual and not physical.

The MMX experiments were not flawed just the math used for the one way distance of traversed light that was assumed.

If you took either clock back to their origin they would be synchronized again.

 

[Dale]

Qzit, pleas learn to use paragraphs to separate your thoughts. A little bit of organization will help communication a great deal.

When you say the photon hits the back of the ship first for the Earth observer that is the reality

I have asked this before, but why? What is it about the Earth observer that makes them so special that their reference frame represents "reality"? Do you believe like Copernicus' detractors that the Earth is at the center of the universe or otherwise occupies some priviledged position?

The reality is the photon hits the back of the ship in both frames by the same physical position in space.

Again, this is not true in any frame, we have already discussed this.

Wake up the MMX experiments were flawed that Einstein used for Relativity. That does not negate Relativity or simultaneity of relativity. It only proves that simultaneity of Relativity is visual and not physical.

Can you provide any mainstream scientific reference which supports your claim?

I would like to remind you that this forum is not for anti-relativity rants, it is for learning mainstream physics. When you signed up for your account you agreed to the rules that prohibit overly speculative posts. If you have an anti-relativity agenda you had best look elsewhere.

 

[Qzit]

Hi DaleSpam,

You and I agree on Relativity being correct but we disagree on what that means. In order to stop getting confused let’s look at everything from the photons perspective. 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.
3. The photon perspective is the only reality of its own position in space.
If we can agree on that we made progress. Now before you read with a challenging attitude try and follow your logic with the three things we agree on not where we disagree.
You are riding a photon and you can know the exact position of another photon instantaneously. This removes relativity of simultaneity.
Lets go through this thought experiment again because the math is different from the reality of the photon.
A spaceship is traveling ½ the speed of light. Two photons side by side are traveling an intersect course with the space ship. When the two photons reach the front of the spaceship one reflects back to an observer at rest in line with the traveling photons and the ship. The second photon reaches the back of the spaceship and reflects back to the same observer at rest. While the photon was moving from the front to the back the ship moved ½ the speed of light forward intersecting a contracted position relative to the length of the ship. We visualize the photon covering 75% and the ship 25%. This is a contraction of the returned photons measurement from the front to the back that the observer at rest sees. (1-v^2/C^2)=1-25=75 just what the observer at rest sees for the returned photon distance. Now because we think light travels the same speed relative to the ships frame we take the square root and get a contraction of 0.866 just about half + the time dilation increase of the ships length by gamma. Once again the MMX experiments are affecting reality of position. The MMX experiment was not wrong but the conclusions of the experiment were incorrect.

The Earth frame is the only place you can measure the one way speed of light in a space ship. The returned light from the front and back of the ship will be the same and if you incorrectly divide that by 1/2 you are mistaken when the photon actually hit the back and front of the ship.

 

[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.)