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

[dfaullin]

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

 

[russ_watters]

Time and distance aren't the same type of dimensions and they work differently. You can walk down the street and come back to where you started, but you can't move forward in time, then go back to the time you started at. So time dilation's effects are cumulative.

 

[PAllen]

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

Welcome to Physicsforums.

This question has been asked, but it is a good question. I don't know of an FAQ to point you to, but I am happy to answer this.

Note that accumulated time for one twin is less, but that once the twins are together, the rate of their clocks is immediately the same. Similarly, the twins height is immediately the same when they re-unite. Age is the sum of moment to moment 'passage of time'. What would be needed for distance would be a measure of moment to moment 'passage of space'. There is nothing as convenient as a clock to measure this. However, if the non-inertial twin measured the integrated distance traveled by the inertial twin, and vice versa, the non-inertial twin would conclude the inertial twin had traveled less distance (compared to what the inertial twin measures for the non-inertial twin). In this sense, there is an analogous 'permanent' length contraction effect for the twin scenario.

 

[dfaullin]

Ah, very interesting. The traveling twin will have measured a smaller distance relative to the Earth-bound twin's measurement. That helps me feel better about it.

Because of this, will they both measure the same velocity for the traveling twin (since v=d/t)? In other words, does the smaller distance measured by the traveling twin occur in the same proportion as the smaller time measured by the traveling twin?

Also, thinking of time as accumulating (whereas length does not) helps me visualize the situation better too, so thank you for the prompt replies on the matter. I've been racking my brain on day on this stuff and it feels good to finally feel like I've accomplished something (a better understanding).

One last question: While the amount of time that passes for the traveling twin will be smaller than what is measured by the Earth-bound twin, each twin in his/her own frame does not feel time pass any differently. I guess I'm having trouble understanding how the clocks will show different times whereas the twins feel time pass at the same, normal rate in their own frames.

 

[PAllen]

Because of this, will they both measure the same velocity for the traveling twin (since v=d/t)? In other words, does the smaller distance measured by the traveling twin occur in the same proportion as the smaller time measured by the traveling twin?

Yes.

One last question: While the amount of time that passes for the traveling twin will be smaller than what is measured by the Earth-bound twin, each twin in his/her own frame does not feel time pass any differently. I guess I'm having trouble understanding how the clocks will show different times whereas the twins feel time pass at the same, normal rate in their own frames.

If all processes (clocks, biological aging, chemical processes etc.) are all 'slower' by the same amount, everything seems normal. How can you detect anything out of the ordinary?

 

[ThomasT]

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?

Because it applies to different velocities (speeds). An oscillator's frequency is, apparently, dependent on its speed. So, when the traveling twin is reunited with the earthbound twin, then their clocks (and their biological oscillators) are 'keeping time' at the same rate. But while the traveling twin was traveling at a rate of speed exceeding the earthbound twin, then the periods of his clock and biological oscillators were increased. And that increase was cumulatively, and irreversibly, recorded as a slowing of time and aging.

 

[dfaullin]

It just seems like 1 second for Twin A is the same as 1 second for Twin B. What is different is the time that Twin A sees passing for Twin B.

I think I just need to think some more about it. I need to reconsider how I view the situation in light of thinking about the distance of the traveling twin being literally less than what Earth-bound twin measures.

Thanks again for your responses.

 

[Dale]

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?

Actually, time dilation and length contraction are the same in this regard. A pair of ticks on a clock measures a uniform duration between the ticks. A pair of ticks on a rod measures a uniform distance between the ticks. While the twins are traveling both kinds of ticks are distorted. When they return to rest both kinds of ticks are undistorted.

The difference is simply that we typically keep a running total of the ticks for a clock but not for a ruler. The device which we use to keep a running total of ticks for a ruler is called an odometer. The device which we use to measure ticks of a clock without keeping a running total is called a metronome. So, the proper comparison is between clocks and odometers or between rulers and metronomes.

 

[harrylin]

Actually, time dilation and length contraction are the same in this regard. A pair of ticks on a clock measures a uniform duration between the ticks. A pair of ticks on a rod measures a uniform distance between the ticks. While the twins are traveling both kinds of ticks are distorted. When they return to rest both kinds of ticks are undistorted.

The difference is simply that we typically keep a running total of the ticks for a clock but not for a ruler. The device which we use to keep a running total of ticks for a ruler is called an odometer. The device which we use to measure ticks of a clock without keeping a running total is called a metronome. So, the proper comparison is between clocks and odometers or between rulers and metronomes.

Actually a metronome produces a beat; we measure it with a frequency meter. But indeed, the comparison is between clocks and odometers as well as between rulers and frequency meters.

 

[dacruick]

The difference is simply that we typically keep a running total of the ticks for a clock but not for a ruler. The device which we use to keep a running total of ticks for a ruler is called an odometer. The device which we use to measure ticks of a clock without keeping a running total is called a metronome. So, the proper comparison is between clocks and odometers or between rulers and metronomes.

I like this explanation. I think it is useful to make a direct comparison from length contraction to time dilation. If we look at age as the sum of all of the ticks on a clock, then for our length contraction to show its effects in the same way, we would have to define height as the sum of the individual's length over time. It sounds absurd right? I agree...

It is useful to treat time in this way (cumulatively), and it is not useful to treat height like this. Yet I do not think that they intrinsically differ. Hmm...well, those are just my thoughts.

 

[Elroch]

There's another way to look at it, as well. With time dilation what happens is that two people keep a record of time and their record differs in the end. The same would happen with distance if it was performed in a certain way. Suppose A goes to Alpha Centauri and back, and B stays on Earth. Both measure the apparent distance they travel relative to each other.

When they compare distances at the end, B says the total distance was just over 8 light years, but A says it was actually a lot less. Of course we know the reason that for A the distance to his destination was contracted when he was going fast.

 

[dacruick]

When they compare distances at the end, B says the total distance was just over 8 light years, but A says it was actually a lot less. Of course we know the reason that for A the distance to his destination was contracted when he was going fast.

I have a question about this. Is it the distance between the planets that is contracted or the length of the spaceship that's contracted? I always assumed that both were possible, it just depended on the frame of reference. In the case that the distance between the planets is contracted, that then implies that the spaceship was stationary, and that both Earth and Alpha Centauri were moving with respect to the spaceship. This then also implies that the observer on Earth was experiencing time dilation to a greater degree than the observer on the spaceship.

Is my recollection of the events accurate?

 

[ghwellsjr]

I like this explanation. I think it is useful to make a direct comparison from length contraction to time dilation. If we look at age as the sum of all of the ticks on a clock, then for our length contraction to show its effects in the same way, we would have to define height as the sum of the individual's length over time. It sounds absurd right? I agree...

It is useful to treat time in this way (cumulatively), and it is not useful to treat height like this. Yet I do not think that they intrinsically differ. Hmm...well, those are just my thoughts.

Remember, length contraction occurs only along the direction of motion, so unless the traveler is laying down, it's not his height that is contracted but his thickness front to back.

 

[ghwellsjr]

I have a question about this. Is it the distance between the planets that is contracted or the length of the spaceship that's contracted? I always assumed that both were possible, it just depended on the frame of reference. In the case that the distance between the planets is contracted, that then implies that the spaceship was stationary, and that both Earth and Alpha Centauri were moving with respect to the spaceship. This then also implies that the observer on Earth was experiencing time dilation to a greater degree than the observer on the spaceship.

Is my recollection of the events accurate?

Yes.

Just remember that in any Frame of Reference, nothing is unusual for stationary observers/objects/clocks--it's only those things that are moving in that FoR.

So in the spaceship's FoR, the spaceship is normal but the distance between planets is contracted. In the planet's RoR, the spaceship is contracted.

Also, remember that two observers in constant relative motion directly towards or away from each other will always measure that relative speed to be the same, independent of any FoR and independent of any means by which they make the measurement.

 

[dfaullin]

Ah, I just made a connection (in my mind)!

Light takes the shortest path through space-time. Thus, the closer you are traveling at the speed of light, the shorter your distance will be.

But now I don't understand this: You say that the distance measured by Earth-bound twin will be greater than the distance measured by traveling twin. How does Earth-bound twin measure that distance? Using a photon? Then shouldn't that measurement give the shortest possible distance, since light is taking the shortest path to the star and back?

Thanks for the great responses.

It also helps to think that the stationary observers will notice nothing unusual ever, only those things which are moving that will exhibit strange behavior. I wish I would have used this forum sooner. I bet I would have done better in Physics when I was in college. :)

 

[dacruick]

Also, remember that two observers in constant relative motion directly towards or away from each other will always measure that relative speed to be the same, independent of any FoR and independent of any means by which they make the measurement.

So if the person traveling to the other planet measures the distance to be quite small due to length contraction, and the person on Earth measures that distance to be large, how can they both measure the same speed relative to each other? Is this reconciled using time dilation?

I can understand how the spaceship traveling at let's say 0.9c has it's length contraction balanced out by the time dilation, but in what way does the spaceship observe a person standing on earth.

 

[ghwellsjr]

Ah, I just made a connection (in my mind)!

Light takes the shortest path through space-time. Thus, the closer you are traveling at the speed of light, the shorter your distance will be.

But now I don't understand this: You say that the distance measured by Earth-bound twin will be greater than the distance measured by traveling twin. How does Earth-bound twin measure that distance? Using a photon? Then shouldn't that measurement give the shortest possible distance, since light is taking the shortest path to the star and back?

Thanks for the great responses.

It also helps to think that the stationary observers will notice nothing unusual ever, only those things which are moving that will exhibit strange behavior. I wish I would have used this forum sooner. I bet I would have done better in Physics when I was in college. :)

The Earth-bound twin can use light to measure the distance to the planet. He starts a timer when he sends a flash of light (it might actually be a radio signal as used in radar) which reflects off the planet and stops the timer when he receives the return signal. The distance is one half of the time interval times the speed of light. Even though the light take the shortest path, it still takes time for it to make the trip.

 

[ghwellsjr]

So if the person traveling to the other planet measures the distance to be quite small due to length contraction, and the person on Earth measures that distance to be large, how can they both measure the same speed relative to each other? Is this reconciled using time dilation?

I can understand how the spaceship traveling at let's say 0.9c has it's length contraction balanced out by the time dilation, but in what way does the spaceship observe a person standing on earth.

The spaceship can measure the speed that the person standing on Earth is traveling away from him by observing the Relativistic Doppler of a signal coming from Earth and calculating the speed. It will be the same Doppler and therefor the same speed that the Earth observer will measure of the spaceship.

 

[dfaullin]

Okay, imagine this scenario.

An observer on Earth is going to measure the distance to Alpha Centauri in two ways. First, he will send a photon and calculate the distance as 1/2 ct.

Then, he will send an odometer to Alpha Centauri traveling near the speed of light (say .9c) and have it return and will take 1/2 of the odometer reading.

Which distance will be shorter?

~Dylan

 

[PAllen]

Okay, imagine this scenario.

An observer on Earth is going to measure the distance to Alpha Centauri in two ways. First, he will send a photon and calculate the distance as 1/2 ct.

Then, he will send an odometer to Alpha Centauri traveling near the speed of light (say .9c) and have it return and will take 1/2 of the odometer reading.

Which distance will be shorter?

~Dylan

Well, there really is no such thing as an odometer to measure travel through empty space. This is why, in my initial answer, what I posed for each twin to measure is the travel distance of the other, as they measure it. So let's say the twin A remains on Earth and measures B traveling 4 lightyears away (to some star) and back - total distance 8 ly. Assume B has traveled there at .9c. B measures A traveling away and back to B. The distance B measures for A's trip will be approx 3.5 light years (assuming 'instant turnaround'). However, as soon as B stops at Earth again and measures the distance to the star, they get 4 light years. So they say 'whoa, this relativity can be really strange'. Yes, it can.

As to how B can measure A (and the sun) distance as A travel's away and back (per B), any valid method will do (in our situation of constant speed). For example, they could use parallax with the aid of companion traveling along with them at some distance away. This modest distance (to the companion) could also be measured any convenient way (rulers, light travel time, it doesn't matter).

 

[dfaullin]

Mind blown!

 

[Elroch]

I have a question about this. Is it the distance between the planets that is contracted or the length of the spaceship that's contracted? I always assumed that both were possible, it just depended on the frame of reference. In the case that the distance between the planets is contracted, that then implies that the spaceship was stationary, and that both Earth and Alpha Centauri were moving with respect to the spaceship. This then also implies that the observer on Earth was experiencing time dilation to a greater degree than the observer on the spaceship.

Is my recollection of the events accurate?

To an observer on the spaceship, the rest of the Universe appears to be squashed in the direction of flight. For example, when a spaceship slows down, in the (non-inertial) decelerating frame, things in front of it can appear to be receding (and things behind it can appear to be receding as well). Of course, it is also true that, to someone observing a spaceship, it appears to be squashed along the direction of (relative) motion.

 

[Elroch]

Well, there really is no such thing as an odometer to measure travel through empty space.

True. There can be no such thing since there is no aether. But measuring position and speed relative to the midpoint of source and destination seems a natural choice for this problem.

 

[PAllen]

True. There can be no such thing since there is no aether. But measuring position and speed relative to the midpoint of source and destination seems a natural choice for this problem.

In a generic twin problem, there is not necessarily a well defined destination, certainly not necessarily an obvious mid point (if you consider arbitrary trajectories). The thing that seems natural and completely general for me - best stand in for an odometer - is for each twin to measure the apparent travel distance of the other twin; as I have suggested in post #3 and again in #20.

 

[Qzit]

WOW, this is a fun thread. What would be the difference between your brain synapsis firing at 16 frames/second, 16 frames / day or 16 frames/year? If everything is relative in your FoR absolutely nothing. Your synapsis is your internal clock for judging time. So the traveling twin’s synapsis is slowed compared to the twin on Earth. Well I suspect so are your relative metabolism and the relative cycles of all the electrons in your body. In fact they can be so slowed that if you had a magic telescope to watch your twin on Earth he would seem to move so fast you would think of him as the comic book hero the Flash. Is the distance contracted? No. Your sense of time is contracted. If you were traveling at 0.9C and a photon closing the distance towards you would be 1.9C. A photon traveling parallel with your ship would have a relative departing speed of 0.1C. Now what is physically happening and what you observe to be happening are two different things because of the speed of your synapsis and the cycling electrons in your FoR.

 

[ghwellsjr]

Okay, imagine this scenario.

An observer on Earth is going to measure the distance to Alpha Centauri in two ways. First, he will send a photon and calculate the distance as 1/2 ct.

Then, he will send an odometer to Alpha Centauri traveling near the speed of light (say .9c) and have it return and will take 1/2 of the odometer reading.

Which distance will be shorter?

~Dylan

Assuming that Alpha Centauri is 4 light years away from Earth, the observer on Earth will measure 8 years for a signal to get there and back and so will calculate its distance to be 4 light years.

He can send an odometer there and back at .9c and measure the distance that way. He can make an odometer by observing the spectrum of light coming from Alpha Centauri and from the Sun prior to sending away the odometer. Then, as the odometer is traveling, it continuously measures the Relativistic Doppler coming from both stars. One will be the reciprocal of the other. (Only one is required for the measurement but I'm showing that either one or both can be used.) Assuming that one of these ratios is R, the speed of the odometer is:

β = |(1-R²)/(1+R²)

Integrating the speed over time yields distance traveled as a function of time. To make the calculation easier, we will assume that the speed is constant throughout the entire roundtrip which means that we only have to multiply the speed by the total time to get the total distance.

Now let's work out the details for our example:

At .9c, the values of R will be √[(1-β)/(1+β)] and its reciprocal. So R for Earth will be 0.2294 and for Alpha Centari will be 4.359 during the outbound portion of the trip. For the inbound portion of the trip, these numbers are exchanged.

The odometer will use the equation above to determine that β is indeed 0.9c.

Now at 0.9c, the clock on the odometer will be running slow by a factor of 1/γ. We calculate γ as 1/√(1-β²), so 1/γ = √(1-β²) which equals 0.4359. Now we need to calculate how long the trip will take. We do this first in the Earth frame as distance divided by speed which is 8 light years (round trip) divided by 0.9c which equals 8.8889 years. Now we multiply this by 1/γ to figure out what the time will be in the odometer's frame. This will be 8.8889 years times 0.4359 or 3.8747 years. This means that the total distance traveled is 3.8747 times 0.9 c or 3.4872 light years for the round trip or 1.7436 light years for the distance between Earth and Alpha Centauri. As a sanity check, this should be the distance in the Earth frame divided by γ or multiplied by 1/γ which we calculated as 0.4359. Indeed, 4 times 0.4359 is 1.7436 light years.

So to answer your question, the distance measured by the odometer is shorter.

 

[ghwellsjr]

Well, there really is no such thing as an odometer to measure travel through empty space.

True. There can be no such thing since there is no aether. But measuring position and speed relative to the midpoint of source and destination seems a natural choice for this problem.

Well, I just showed how to make an odometer to measure travel through empty space.

And I don't understand why you base your conclusion on the idea that "there is no aether". I don't see the connection.

I also don't understand your comments about "the midpoint of the source and destination".

 

[ghwellsjr]

WOW, this is a fun thread. What would be the difference between your brain synapsis firing at 16 frames/second, 16 frames / day or 16 frames/year? If everything is relative in your FoR absolutely nothing. Your synapsis is your internal clock for judging time. So the traveling twin’s synapsis is slowed compared to the twin on Earth. Well I suspect so are your relative metabolism and the relative cycles of all the electrons in your body. In fact they can be so slowed that if you had a magic telescope to watch your twin on Earth he would seem to move so fast you would think of him as the comic book hero the Flash. Is the distance contracted? No. Your sense of time is contracted. If you were traveling at 0.9C and a photon closing the distance towards you would be 1.9C. A photon traveling parallel with your ship would have a relative departing speed of 0.1C. Now what is physically happening and what you observe to be happening are two different things because of the speed of your synapsis and the cycling electrons in your FoR.

WOW, I think you're having too much fun. A lot of erroneous ideas here.

What do you mean that there is no difference between 16 frames per second, day or year? It is true that all processes, including biological will be slowed down for the traveling twin, as determined by the rest frame of the Earth, but the traveling twin will also determine that the Earth twin is the one that is experiencing time dilation according to his own rest frame. And you're also mixed up on the speed of a photon being 1.9c or 0.1c according to the traveling twin. I suggest that you do a lot of reading or asking questions instead of trying to answer them until you get yourself up on the learning curve.

 

[harrylin]

Well, I just showed how to make an odometer to measure travel through empty space.

And I don't understand why you base your conclusion on the idea that "there is no aether". I don't see the connection.

I also don't understand your comments about "the midpoint of the source and destination".

I also wondered about that... My 2 cts: There are no mechanical odometers; I suppose that what was meant, is that there is no material ether on which we could let an odometer roll. Note also that if we could, then any odometer would measure "absolute" lengths, for the wheel is at rest wrt the road at the point of contact!

And I think that the midpoint of source and destination depends on the reference system for two twins in arbitrary motion.

 

[Qzit]

ghwellsjr
I think you were reading with your mind and not your eyes. You would not perceive a difference in time out in space if your relative synapsis fired 16 times a second, a day or a year. My other question to you is what is the closing speed between two photons traveling on a collision course? This was not in reference to the traveling twin. Of course the traveling twin would see it differently with his clock slowed.

 

[nitsuj]

WOW, I think you're having too much fun. A lot of erroneous ideas here.What do you mean that there is no difference between 16 frames per second, day or year? It is true that all processes, including biological will be slowed down for the traveling twin, as determined by the rest frame of the Earth, but the traveling twin will also determine that the Earth twin is the one that is experiencing time dilation according to his own rest frame. And you're also mixed up on the speed of a photon being 1.9c or 0.1c according to the traveling twin. I suggest that you do a lot of reading or asking questions instead of trying to answer them until you get yourself up on the learning curve.

I can't see one in his/her post. Could you be more specific since your are being so bold.

The closing distance comment is fairly accurate (#'s aren't). The concept is definately right (excluding the "distance" contraction / "time contraction" comment).

Of course the 16 seconds, days, year comment is referring to time dilation. I am pretty sure you understand that. It means there is no difference in the traveling observers perception of time passing (tick tock / proper time ect) to that of an observer who is at "rest".

I suggest that you do a lot of reading or asking questions instead of trying to answer them until you get yourself up on the learning curve.

Nice ain't it?

You've helped me improve my understanding of SR on a number of occasions ghwellsjr, it is a shame to see you post a reply like that. When I know you are capable of getting Qzit's interpretations on a more defined track / train of thought.

 

[Dale]

I can't see one in his/her post.

I don't know which ones ghwellsjr noticed, but I saw a few that were either wrong or only conditionally right:

WOW, this is a fun thread. What would be the difference between your brain synapsis firing at 16 frames/second, 16 frames / day or 16 frames/year? If everything is relative in your FoR absolutely nothing. Your synapsis is your internal clock for judging time. So the traveling twin’s synapsis is slowed compared to the twin on Earth. Well I suspect so are your relative metabolism and the relative cycles of all the electrons in your body.

So far everything is fine.

In fact they can be so slowed that if you had a magic telescope to watch your twin on Earth he would seem to move so fast you would think of him as the comic book hero the Flash.

This would be true on the return journey, but false on the outward journey.

Is the distance contracted? No.

False. Distance is contracted too.

Your sense of time is contracted. If you were traveling at 0.9C and a photon closing the distance towards you would be 1.9C. A photon traveling parallel with your ship would have a relative departing speed of 0.1C.

True only in the Earth frame.

Now what is physically happening and what you observe to be happening are two different things because of the speed of your synapsis and the cycling electrons in your FoR.

This is a LET interpretation, not a SR interpretation. However, interpretations cannot be experimentally proven one way or the other, so I have no objection other than a kind of general distaste for LET as a pet theory of crackpots.

 

[nitsuj]

Yes Dalespam I understand your point and even ghwellsjr's point. This forum like's to be techincaly right, which is awsome and separates a poor quality physics forum from a great one. Leaving out discussions about biology, conciousness and the sorts is important to point out because of the add difficulty of interpretation among other things.

But do you understand my point?

Qzit's interpretations are not flat out wrong, they are poorly defined. This is a big difference if someone is going to call those interpretations as erroneous. Said differently a lot of Qzits interpretations are correct, ghwellsjr implied most were wrong. In a sense, possibly pushing Qzit further down the learning curve.

I wouldn't have an issue if ghwellsjr replied pointing out the technicalities, like you did.

And yes, as I noticed too (a layman of SR) the "distance" contraction isn't right. Big deal, point it out and say good for you in noticing the impact of closing distances. So one wrong comment.

Your last comment, if I understand right, yes if Qzit wants to stay "true" to SR (or physics in general), the "reality" is the observation (measurement +calculation). But it is merely a prefference, and not crackpottery.

 

[Dale]

Do you understand mine?

Qzit's interpretations are not flat out wrong, they are poorly defined.

Yes, I understand your point. Only the one comment was flat out wrong, the rest could be either wrong or right depending on the "poorly defined" details.

 

[Dale]

Your last comment, if I understand right, yes if Qzit wants to stay "true" to SR (or physics in general), the "reality" is the observation (measurement +calculation). But it is merely a prefference, and not crackpottery.

Let me clarify my intention.

Now what is physically happening and what you observe to be happening are two different things because of the speed of your synapsis and the cycling electrons in your FoR.

This is a LET interpretation, not a SR interpretation. However, interpretations cannot be experimentally proven one way or the other, so I have no objection other than a kind of general distaste for LET as a pet theory of crackpots.

In LET it is true that what is physically happening and what you observe to be happening are two different things. In LET as you move relative to the aether your lengths contract and times dilate such that the measurements you make are incorrect. Specifically, your coordinate time is an incorrect measure of the aether coordinate time, and so forth. Only the physics in the aether frame are "physically happening".

On the other hand, in SR every reference frame is equally valid. So both of our observations are equally valid observations of what is physically happening. The disagreements between our observations are not because one of us "distorted" and the other is not but rather simply because we are each observing the same physics from different but valid perspectives. In this view, your coordinate time is a correct measure of the proper time, and so forth.

Both of the above interpertations are valid, and in principle I have no problem with the LET interpretation. However, most of the proponents of LET that I have encountered are crackpots and my interactions with them are usually fairly unpleasant. So I have a certain "guilt by association" distaste for LET. I was not calling Qzit a crackpot nor even implying it, merely expressing the source of my distaste for LET.

 

[nitsuj]

Understood Dalespam.

I appreciate what you are saying.

You've been patient with me in that past with such things & George too to a lesser extent. It's really really helped me in trying to grasp the concepts of SR intuitively.

So it kinda burns me to see a post like I've been commenting on. Where a poster is on the cusp of being correct, but is instead "written off" as being not worthy (the interpretations) of a helpfull reply.

 

[Qzit]

I did not know my thoughts were LET or crackpot ideas Sorry. Please help me understand a little better.

False. Distance is contracted too.

I thought it was only the view that was contracted and not the distance. If your synapsis is slowed than distance would appear contracted but the physical distance remains the same for a photon to travel. How does a spaceship actually contract space in front of it? Please help I am confused. I did not understand that a spaceship could do anything to the space in front of it. If I were mid-point to a destination would I be in a physical contraction?

Your sense of time is contracted. If you were traveling at 0.9C and a photon closing the distance towards you would be 1.9C. A photon traveling parallel with your ship would have a relative departing speed of 0.1C.

True only in the Earth frame.

"C" I thought was a constant. What does not matter where you observe? If there is no observer "C" is always "C". What you observe is an accurate mathematical difference based on relativity. Why do you see it more than an optical affect?

This would be true on the return journey, but false on the outward journey.

If you had a magical telescope (which is impossible to begin with) say your Synapsis on the ship is firing at 16 frames an hour and your twin is firing at16 frames per second on Earth. The Earth twin would always be moving much faster to my way of thinking. This would be real and not just observed I would suspect. If I am wrong please explain.

 

[ghwellsjr]

I still maintain that Qzit has a lot of erroneous ideas. Most basically is his concept expressed in his last sentence that it's only because of your sluggish neurons in your For that explains why observations differ from reality:

Now what is physically happening and what you observe to be happening are two different things because of the speed of your synapsis and the cycling electrons in your FoR.​

In your FoR, your synapses and cycling electrons are perfectly normal. It's the other person's synapses and cycling electrons that are experiencing time dilation. He's got this backwards.

How about this comment:

In fact they can be so slowed that if you had a magic telescope to watch your twin on Earth he would seem to move so fast you would think of him as the comic book hero the Flash. Is the distance contracted? No. Your sense of time is contracted.

He's thinking that because your processes are running slowly, you would see your Earth twin's processes as running fast which is not correct. He's not talking about Relativistic Doppler which is observable with a real telescope, he's talking about a magic telescope that eliminates the Doppler to let you see what's really going on. And he has it wrong, the traveling twin would see the Earth twin's processes as going slow, not fast.

And what do you make of his last comment: "Your sense of time is contracted."? Time is not contracted, it's dilated, but either way, your sense of time is always normal, never contracted or dilated.

Now as to his comments regarding the closing speed of photons which he said is not related to the Twin Paradox:

If you were traveling at 0.9C and a photon closing the distance towards you would be 1.9C. A photon traveling parallel with your ship would have a relative departing speed of 0.1C.

I don't think he understands that the speed of a photon, like the propagation speed of all light, AKA the one-way speed of light, is never observable, it is assigned a speed by a theory, in this case the Theory of Special Relativity, and that speed is always c, not 1.9c or 0.1c. In his later post, he asked:

My other question to you is what is the closing speed between two photons traveling on a collision course?

The answer to that is 2c but it should not be regarded as any measurable or physically real speed, it's just the difference between two speeds in a given FoR. There is nothing traveling at 2c with respect to any FoR or to any other object.

I really want to help Qzit learn SR and if I have misdiagnosed his comments, then I apologize, and he can help me by providing relevant feedback.

 

[nitsuj]

I did not know my thoughts were LET or crackpot ideas Sorry. Please help me understand a little better.
I thought it was only the view that was contracted and not the distance. If your synapsis is slowed than distance would appear contracted but the physical distance remains the same for a photon to travel. How does a spaceship actually contract space in front of it? Please help I am confused. I did not understand that a spaceship could do anything to the space in front of it. If I were mid-point to a destination would I be in a physical contraction?

"C" I thought was a constant. What does not matter where you observe? If there is no observer "C" is always "C". What you observe is an accurate mathematical difference based on relativity. Why do you see it more than an optical affect?

If you had a magical telescope (which is impossible to begin with) say your Synapsis on the ship is firing at 16 frames an hour and your twin is firing at16 frames per second on Earth. The Earth twin would always be moving much faster to my way of thinking. This would be real and not just observed I would suspect. If I am wrong please explain.

I am not skilled enough in SR to debate certain SR concepts.

But I can tell you forget about including biology if you plan on learning SR concepts here. Not supprisingly it shouldn't come up.

Understand that time and length are measurements. It is these measurements that are comparatively different with relative motion. You can as easily works backwards by considering c is constant. c is two measurements, time and length. Simmer that...

For me an easy way to understand this "which perspective (FoR) is "real"" is to consider the simple idea that motion is relative. If you can subscribe to that, the rest of observations made of course have that same principal.

that's about as well as I can explain the concept.

 

[nitsuj]

ghwellsjr, I think I may have taken your post a little differently then your intent.

You made me realize something; I take back my comment the poster was on the cusp of being correct. That, as I found out myself with SR concepts, is far different from understanding.

 

[Qzit]

WOW I see my English is very poor. You are correct to gig me for that. Let’s look at contraction a different way. If you had a spaceship coming towards at ½ the speed of light and there was a mirror on the front and on the back of the spaceship to bounce returning photons we can see contraction as an optical effect of the finite speed of light. Now we shoot a signal to the ship. Half of the signal hits the first mirror and heads back. The second ½ of the signal moves towards the back of the ship. While the second half of signal is moving towards the back the ship has closed the distance towards the signal by 1/3 of the ships length when the second half of the signal bounces off. On return of the signal to the stationary observer the ship appears to be 2/3 its actual size. Moving away it would appear to be 1 and 1/3 its actual size. This is because of the finite speed of lights optical effect not a physical effect to my way of thinking. Am I wrong?

Put a strobe on in the dark to mimic a slowed synapsis firing. You sit down and watch others move. They appear to be moving faster.

 

[Janus]

"C" I thought was a constant. What does not matter where you observe? If there is no observer "C" is always "C". What you observe is an accurate mathematical difference based on relativity. Why do you see it more than an optical affect?

It would be more correct to say that c is invariant. c has the same value relative to any inertial frame as measured from that frame.

So in your ship you will measure the light as traveling at c relative to the ship. In other words, the light coming from in front of you will take the same time to travel from the front of the ship to the back of the ship as the light traveling from the back of you will take to travel from back of the ship to the front.

However, the same light as measured from the Earth travels at 0.1c relative to you going in one direction and 1.9c going in the other. This means that according to the Earth, the light passing you from behind takes longer to pass from back to front of your ship than that light you are meeting takes to pass from front to back of your ship.

 

[ghwellsjr]

WOW I see my English is very poor. You are correct to gig me for that. Let’s look at contraction a different way. If you had a spaceship coming towards at ½ the speed of light and there was a mirror on the front and on the back of the spaceship to bounce returning photons we can see contraction as an optical effect of the finite speed of light. Now we shoot a signal to the ship. Half of the signal hits the first mirror and heads back. The second ½ of the signal moves towards the back of the ship. While the second half of signal is moving towards the back the ship has closed the distance towards the signal by 1/3 of the ships length when the second half of the signal bounces off. On return of the signal to the stationary observer the ship appears to be 2/3 its actual size. Moving away it would appear to be 1 and 1/3 its actual size. This is because of the finite speed of lights optical effect not a physical effect to my way of thinking. Am I wrong?

Let's put it this way, you are half wrong. What you are describing is Doppler but it's not like normal Doppler for sound in air where there is in fact no length contraction. With Relativistic Doppler involving light, there is the effect caused by the finite speed of light which is what you are talking about, but when you subtract that out, there remains an effect caused by the contraction of the length of the spaceship.

 

[Qzit]

Hi ghwellsjr
After you subtract the Doppler how much more contraction is there?

Hi Janus,
How do you measure the one way speed of light in a single direction or is it assumed that inside the ship the speed of light is measured to be the same in both directions?

 

[Dale]

I did not know my thoughts were LET or crackpot ideas

I tried to make it clear. I never said that you were a crackpot, nor did I intend to imply it. I was only mentioning the reason for my aversion to LET.

I thought it was only the view that was contracted and not the distance. If your synapsis is slowed than distance would appear contracted but the physical distance remains the same for a photon to travel. How does a spaceship actually contract space in front of it? Please help I am confused. I did not understand that a spaceship could do anything to the space in front of it. If I were mid-point to a destination would I be in a physical contraction?

Spaceships don't do anything to space. Length contraction is an aspect of the mathematical relationship between different inertial reference frames, just like time dilation. This relationship is called the Lorentz transform. In different reference frames the physical distance is different, even after you correct for all of the view-related and finite-speed-of-light-related effects. You cannot have time dilation without length contraction, they are two sides of the same "coin" (the Lorentz transform).

"C" I thought was a constant. What does not matter where you observe? If there is no observer "C" is always "C". What you observe is an accurate mathematical difference based on relativity. Why do you see it more than an optical affect?

If I am traveling at .9 c in Earth's frame heading towards a pulse of light then in the Earth's frame the distance between the pulse of light and me is closing at 1.9 c. In my frame I am traveling at 0 c by definition, so in my frame the distance between the pulse of light and me is closing at c. So your statement above is only true in the Earth's frame, not in my frame.

If you had a magical telescope (which is impossible to begin with) say your Synapsis on the ship is firing at 16 frames an hour and your twin is firing at16 frames per second on Earth. The Earth twin would always be moving much faster to my way of thinking. This would be real and not just observed I would suspect. If I am wrong please explain.

It is impossible to start from a false premise like a magical telescope and obtain any valid conclusions. Can you think about your real question and ask it without any impossible premises?

 

[Qzit]

Hi DaleSpam,

I am beginning to think I think more in line with LET but I do not know the meaning. Between my use of the English language and your replies about LET I am sorry if I was unpleasant. I thought the Lorentz transformations were the same as the optical effect. I did not realize there is a different Lorentz contraction then the one I described with the mirrors. What is the mathematical Lorentz contraction for measuring the length of a ship going ½ “C” to a stationary observer?

 

[Dale]

The Lorentz transform is given here:
http://en.wikipedia.org/wiki/Lorent...ormation_for_frames_in_standard_configuration

All of the usual relativistic features like time dilation, length contraction, and the relativity of simultaneity are contained in it. The Lorentz transformations are not optical effects. They are what remain after all of the optical effects are accounted for. They are not due to the fact that the speed of light is finite, but rather they are due to the fact that the speed of light is invariant.

 

[Qzit]

Hi DaleSpam,

All of the usual relativistic features like time dilation, length contraction, and the relativity of simultaneity are contained in it. The Lorentz transformations are not optical effects. They are what remain after all of the optical effects are accounted for. They are not due to the fact that the speed of light is finite, but rather they are due to the fact that the speed of light is invariant.

Relativity of simultaneity is an explanation of visual contraction not physical contraction. The Lorentz contraction says close to the speed of light the contraction is close to 100%. If a ship could go “C” it would have no length. I can explain relativity of simultaneity that shows it to be a visual effect of the finite speed of light. You are in a ship going near the speed of light. You are in the front of the ship and hit the switch that simultaneously turns on the front and back of a pulse emitter. The front goes off first and the signal travels down the ship at the speed of light. When the signal reaches the back of the ship the back reaches the position the first pulse fired. There is your contraction due to the finite speed of a photon. If you set off the signal in the center of the ship there would be no issue with the simultaneity of relativity and no contraction. Instantaneous and simultaneity of relativity are two different things.


Time dilation on the other hand should be a physical issue. Time slowing down suggests that mass dilates, gets larger and less dense. This is definitely an issue of invariance of “C”. If mass dilates and the path of the electron increases the cycles tick slower to match the longer distance a photon has to travel to maintain its invariance. Every other frame uses their own measuring stick and tick of their clock for measurement. If there measuring stick is shorter like in outer space away from mass there clock ticks faster. In this way the speed of light is measured in every frame to be invariant.

 

[Dale]

Relativity of simultaneity is an explanation of visual contraction not physical contraction.

This is incorrect. The relativity of simultaneity is not an explanation of any kind of contraction.

You are in the front of the ship and hit the switch that simultaneously turns on the front and back of a pulse emitter. The front goes off first

You are contradicting yourself.

When the signal reaches the back of the ship the back reaches the position the first pulse fired.

This is incorrect in every reference frame. There is some time, dt, between when the first pulse is fired and when the signal reaches the back of the ship. In that time the light has moved a distance c dt.

If you set off the signal in the center of the ship there would be no issue with the simultaneity of relativity and no contraction.

This is also incorrect. Length contraction depends on the relative velocity between two frames, not on the location of some light source.

Time slowing down suggests that mass dilates, gets larger and less dense.

Also incorrect. As v->c time slows down, and lengths contract making objects smaller and more dense.

Every other frame uses their own measuring stick and tick of their clock for measurement. ... In this way the speed of light is measured in every frame to be invariant.

At least you got something right.

Qzit. You should stop making assertions and start asking questions. You have some very strangely confused ideas about relativity. I am not sure what the source is. I would like to help, but I can't tell where to start yet.

 

[Qzit]

Hi DaleSpam,

Relativity of simultaneity is an explanation of visual contraction not physical contraction.

This is incorrect. The relativity of simultaneity is not an explanation of any kind of contraction.

You did not understand my thought experiment.

You are in the front of the ship and hit the switch that simultaneously turns on the front and back of a pulse emitter. The front goes off first

You are contradicting yourself.

I am not contradicting myself if you understand the concept of Relativity of Simultaneity. That is why I mentioned instantaneous as different from simultaneity. You have to understand the inherent relativity of the finite speed of light.

When the signal reaches the back of the ship the back reaches the position the first pulse fired.

This is incorrect in every reference frame. There is some time, dt, between when the first pulse is fired and when the signal reaches the back of the ship. In that time the light has moved a distance c dt.

Of course from a observer at rest the ship and the distance light traveled is the same so the observer at rest sees the two pulses at the same place. The result is the observer at rest sees no length to the ship.

If you set off the signal in the center of the ship there would be no issue with the simultaneity of relativity and no contraction.

This is also incorrect. Length contraction depends on the relative velocity between two frames, not on the location of some light source.

This merely changes the pulse to instantaneous rather than simultaneous of relativity.

Time slowing down suggests that mass dilates, gets larger and less dense.

Also incorrect. As v->c time slows down, and lengths contract making objects smaller and more dense

If your assertion were true than we would not have an invariant speed of light in every frame. A clock that slows down has a longer length measuring stick. The slowed clock has to have enough time for the photon to cover the increased distance of the dilation. If it were smaller the slowed clock would allow the photon to wiz past the measuring stick early destroying the invariant speed of light.

Do you want me to learn from others that are also mistaken?