functionally faster than light.

[md65536]

That reminds me an episode of looney tunes (was it the coyote and the road runner or bugs bunny?) where the main character is in a house falling from a cliff and steps out at the last moment before reaching the ground as if nothing happened, next to the crumbles of his house.

Edit: removed a misunderstanding of your analogy.

 

Besides integration, you can also "neglect" acceleration time by making it happen during a time that you can ignore. Imagine the house is falling and you cut to a scene where the character is safely on the ground. What happens next doesn't depend on how the character escaped, by analogy.

OK forget acceleration.

So at the starting point and time T=0 you have an observer A on Earth (standing still) and an observer B traveliing at 0,99c. They both observe an object that for the observer A is 7 LY away and for observer B I guess is not.

Right from the beginning they will disagree on observations.

They don't disagree. Their measurements are different because they're measuring properties that are *relative*. They agree because the measurements are mutually consistent. Edited February 23, 2013 by md65536

[swansont]

They don't disagree. Their measurements are different because they're measuring properties that are *relative*. They agree because the measurements are mutually consistent.

 

They disagree on any length and time measurement, but not on a consistent picture that agrees with the laws of physics.

[michel123456]

yes.

 

The puzzling thing is that (between others) when you erase acceleration, observer B believes that observer A moves at 0.99C in the opposite direction. Only when acceleration is there one can discern who is moving related to whom.

Also, acceleration is the necessary staircase that goes from one FOR to another. I know calculations become complicated but without acceleration there is no possible passageway.

 

Imagine that observer B is orbiting the Earth at 0,99C, can you jump into his spaceship just like that?

[Didymus]

ACG, I'm not intending to do anything dishonest. But, to describe one's flow of time as dependant on it's speed relative to another object mandates that each object be experiencing an infinite number of frames of time (and spacial distortion) simultaneously as there are virtually infinite objects in our universe traveling at all sorts of speeds and trajectories.

The biggest reason I bring up the "going .99c for 1 year and ending up 7 lightyears away" thing... is because einstein pointed out that there is no preferred frame of reference. It would be equally logical to state that... from the frame of reference of the ship, they are standing still and it is the planet moving toward them at that speed. Thus, to whatever extent the ship experiences time dilation in it's frame of reference, so must the planet it's traveling toward. Thus, this planet systems away would suddenly experience time and space dilation because of some object coming toward it, lightyears away.

And, if this is the case, it must also experience time dilation based on every other rock in the universe moving relative to it, completely oblivious of this planet's existence. Some would say that this is reductio ad absurdum, but ... when two objects begin moving relative to each other... how do you define which is to experience time dilation? Unless you assume this is attributed to inertial changes due to acceleration, rather than consistent speed... but that opens an even uglier can of worms.

another endlessly more complicated consideration of this illustration.... what if a second passenger is boarding this ship, intending to catch up to a meteor that should pass this point 7 lightyears away... but this meteor is traveling at, say .1C... Depending on which direction a meteor so far away is traveling, the ship's speed relative to his target would change wildly... I'm not doing the actual math at 2 AM (Yes, I am losing sleep over this)... but with the whole (v+u)/(1+((vu)/(c^2)) bit... somewhere between .89c(ish) and a dilation factor well below 7... to adding a few digits behind .99c and making this factor significantly higher. Thus, two people on the same ship would have a different intended targets and thus different relative speed, and thus experience time and space SIGNIFICANTLY differently based on what theoretical point they're thinking of.

 

... thus the problem mixing objective absolutes with subjective reference frames.

[swansont]

ACG, I'm not intending to do anything dishonest. But, to describe one's flow of time as dependant on it's speed relative to another object mandates that each object be experiencing an infinite number of frames of time (and spacial distortion) simultaneously as there are virtually infinite objects in our universe traveling at all sorts of speeds and trajectories.

 

 

One's flow of time is measured in one's own frame. There is only one time that you experience — you do not experience an infinite number. The time of your frame, as measured by someone else, will be different.

 

 

The biggest reason I bring up the "going .99c for 1 year and ending up 7 lightyears away" thing... is because einstein pointed out that there is no preferred frame of reference. It would be equally logical to state that... from the frame of reference of the ship, they are standing still and it is the planet moving toward them at that speed. Thus, to whatever extent the ship experiences time dilation in it's frame of reference, so must the planet it's traveling toward. Thus, this planet systems away would suddenly experience time and space dilation because of some object coming toward it, lightyears away.

 

If the planets are in the same frame there is no dilation relative to each other. It's only relative to the spacecraft, and each will see the other's clock as running slow, and will see length contraction of the other frame.

 

 

And, if this is the case, it must also experience time dilation based on every other rock in the universe moving relative to it, completely oblivious of this planet's existence. Some would say that this is reductio ad absurdum, but ... when two objects begin moving relative to each other... how do you define which is to experience time dilation? Unless you assume this is attributed to inertial changes due to acceleration, rather than consistent speed... but that opens an even uglier can of worms.

 

If they are in inertial frames, the other frame is always experiencing the dilation. It's only when you shift frames by accelerating that you can say one experienced dilation while the other didn't.

 

 

[michel123456]

I understand that nobody ever "experiences" time dilation.

Time dilation is what one observes about someone else.

[phyti]

Didymus

...The biggest reason I bring up the "going .99c for 1 year and ending up 7 lightyears away" thing... is because einstein pointed out that there is no preferred frame of reference. It would be equally logical to state that... from the frame of reference of the ship, they are standing still and it is the planet moving toward them at that speed. Thus, to whatever extent the ship experiences time dilation in it's frame of reference, so must the planet it's traveling toward. Thus, this planet systems away would suddenly experience time and space dilation because of some object coming toward it, lightyears away.

...

this factor significantly higher. Thus, two people on the same ship would have a different intended targets and thus different relative speed, and thus experience time and space SIGNIFICANTLY differently based on what theoretical point they're thinking of.

 

 

Lets simplify the calculations with v/c = .8 and target 10 ly distant.

A-naut Al blasts off from earth, accelerates in orbit to speed, and sets his clock to zero as he passes Ed on the earth setting his clock to zero. Al and Ed have never read anything pertaining to SR (they spend all their time conducting experiments in an underground bunker) They calculate time to target = 10/.8 = 12.5 yr. Later, as Al passes the target, he records his clock reading of 7.5 yr. He has arrived earlier than calculated. SR predicts as a result of the motion, Als ship and all its contents will function at a slower rate due to time dilation, and be length contracted, but Al will not be able to detect either of the effects. To reconcile the time difference, Al interprets his time dilation as a contraction of the universe outside his ship by a factor of 7.5/12.5 = (.6).

The contraction of the ship is a physical phenomenon resulting from altered em fields. The contraction of the universe is perception, i.e. physical phenomenon confined to and conditioned by the mind.

When the observer moves, no one else shares his experience unless they move with him.

 

The supposed symmetry between moving objects is only true comparing motion in isolation. If examined within the context of all physical phenomena within the universe:

1. the momentum of the earth -Mv is not equal to the momentum of the ship mv,

2. the energy to move the ship would not move the earth, and

3. the pilot can control the ship at will, but not the earth.

 

Hope this provides some clarity.

[Didymus]

I understand that nobody ever "experiences" time dilation.

Time dilation is what one observes about someone else.

If this.is the case, is time dilation not just a sort of optical illusion? If no clock experiences change itself, but only appears to change from other points of view?

[md65536]

The supposed symmetry between moving objects is only true comparing motion in isolation. If examined within the context of all physical phenomena within the universe:

1. the momentum of the earth -Mv is not equal to the momentum of the ship mv,

2. the energy to move the ship would not move the earth, and

3. the pilot can control the ship at will, but not the earth.

I think this part is misleading because it doesn't matter if the traveler and "stationary" observer have different momentum. It works out exactly the same if it's two twins in identical ships in space. It can work even if the first leg of a journey is symmetrical.

 

If this.is the case, is time dilation not just a sort of optical illusion? If no clock experiences change itself, but only appears to change from other points of view?

An illusion would be if some observations were inconsistent with other observations. All observers measure a change in rate of moving clocks relative to local clocks, consistently as described by SR. Bring any two clocks together and all observers will agree on how the two times compare to each other. No one will think they observed incorrectly.

[michel123456]

(...)

 

An illusion would be if some observations were inconsistent with other observations. All observers measure a change in rate of moving clocks relative to local clocks, consistently as described by SR. Bring any two clocks together and all observers will agree on how the two times compare to each other. No one will think they observed incorrectly.

Many illusions if not all are perfectly consistent with the laws of physics.

 

If this.is the case, is time dilation not just a sort of optical illusion? If no clock experiences change itself, but only appears to change from other points of view?

That's my understanding although I have read so many scientists arguing that time dilation is actually happening. Truly I don't want to enter this debate again.

[elfmotat]

Many illusions if not all are perfectly consistent with the laws of physics.

 

That's my understanding although I have read so many scientists arguing that time dilation is actually happening. Truly I don't want to enter this debate again.

 

It's not an illusion. (The word "illusion" in this context is rather ill-defined anyway.) Time dilation is a phenomenon with measurable consequences.

[michel123456]

It's not an illusion. (The word "illusion" in this context is rather ill-defined anyway.) Time dilation is a phenomenon with measurable consequences.

I agree that the word 'illusion" is ill=defined.

Let's resume the question (again): does the one who "experiences" time dilation has any clue that he actually "experiences" time dilation? Is it possible that one 'experiences" different time dilations at the same time because he is observed by different observers?

Of course not.

[elfmotat]

I agree that the word 'illusion" is ill=defined.

Let's resume the question (again): does the one who "experiences" time dilation has any clue that he actually "experiences" time dilation? Is it possible that one 'experiences" different time dilations at the same time because he is observed by different observers?

Of course not.

 

Nobody "experiences" time dilation. Observer's clocks run at different rates, and everyone agrees how much time is ticked off on each observer's clock.

[michel123456]

Nobody "experiences" time dilation. Observer's clocks run at different rates, and everyone agrees how much time is ticked off on each observer's clock.

Wonderful!

We agree on something.

That must be a first.

[Arnaud Antoine ANDRIEU]

(...) , and everyone agrees how much time is ticked off on each observer's clock.

 

We should call it "the spin of the time"

 

[swansont]

I agree that the word 'illusion" is ill=defined.

Let's resume the question (again): does the one who "experiences" time dilation has any clue that he actually "experiences" time dilation? Is it possible that one 'experiences" different time dilations at the same time because he is observed by different observers?

Of course not.

 

Of course not. Correct. It is not a prediction of the theory that this will happen.

[md65536]

Nobody "experiences" time dilation. Observer's clocks run at different rates, and everyone agrees how much time is ticked off on each observer's clock.

Okay it's wonderful we all agree... but... but...

 

As long as we all agree on what "experience" means. Here we're talking about effects that can be measured locally (an observer doesn't experience time dilation locally), and specifically we're excluding any observations of distant objects.

 

If on the other hand you include observations as part of what you experience, then time dilation IS experienced, and yes you can experience multiple different amounts of time dilation relative to multiple differently moving objects: Each object's clock can be observed (ie. experienced) ticking at a different rate. In this way, time dilation is "experienced" in the observations of the moving objects as Doppler shifts in the rate of an observed clock's tick rate.* In SR, the observed Doppler shift is a combined effect of the moving clock actually (not illusory) ticking slow relative to you, and the appearance (can be considered illusory) of the clock ticking faster or slower due to a changing distance to the observed object, which means a changing travel time of incoming photons.

 

elfmotat, I know you understand this better than I do, so this attempt at clarification is aimed at people like me who usually have misconceptions about something or other.

 

 

* So... yes, a local clock's time dilation is not experienced except by other observers, but other clocks' time dilation is measured (experienced?) by the observer.

Edited February 27, 2013 by md65536

[phyti]

"michel123456" post="732023" timestamp="1361952850"

I agree that the word 'illusion" is ill=defined.

Let's resume the question (again): does the one who "experiences" time dilation has any clue that he actually "experiences" time dilation? Is it possible that one 'experiences" different time dilations at the same time because he is observed by different observers?

Of course not.

The moving observer is AFFECTED by time dilation, but so is his clock, and everything that moves with him. By using the capitalized word, I can say he does not experience it, nor detect it.

The moving observer is AFFECTED by length contraction, but so is his ruler, and everything that moves with him. By using the capitalized word, I can say he does not experience it, nor detect it.

Anyone NOT moving with him will observe the effects to varying degrees, depending on their relative motion.

It's the observers own motion that causes the effects, not the motion of the rest of the universe.

[Didymus]

But it can be measurable from a single reference frame, according to the theory. If you set up markers every "lightday" away, and began traveling at .99c, as soon as you reached this speed, the space between them would seem to shrink and you would pass them round very 3 hours (and a few minutes) or so, instead of every 24 hours.

 

Because you know you havn't really shrunk the universe, you would be able to adjust for that illusion and know that you are traveling at about 7C from your perspective.

 

...unless you believe the rubber pencil trick actually transmitters the pencil just because it appears wobbly.

[michel123456]

The moving observer is AFFECTED by time dilation, but so is his clock, and everything that moves with him. By using the capitalized word, I can say he does not experience it, nor detect it.

The moving observer is AFFECTED by length contraction, but so is his ruler, and everything that moves with him. By using the capitalized word, I can say he does not experience it, nor detect it.

Anyone NOT moving with him will observe the effects to varying degrees, depending on their relative motion.

It's the observers own motion that causes the effects, not the motion of the rest of the universe.

The moving observer believes that the Earth is moving, not him. He observes that the Earth is time dilated and length contracted.

It is absolutely symmetric.

Relativity describes what an observer observes.

Edited March 1, 2013 by michel123456

[Delta1212]

But it can be measurable from a single reference frame, according to the theory. If you set up markers every "lightday" away, and began traveling at .99c, as soon as you reached this speed, the space between them would seem to shrink and you would pass them round very 3 hours (and a few minutes) or so, instead of every 24 hours.

 

Because you know you havn't really shrunk the universe, you would be able to adjust for that illusion and know that you are traveling at about 7C from your perspective.

 

...unless you believe the rubber pencil trick actually transmitters the pencil just because it appears wobbly.

Let's say you fire off markers from Earth. You fire them in the same direction, at close to the speed of light such that they are traveling away from Earth spaced out at intervals of one "lightday" each.

 

If you took a spaceship, caught up with the markers and matched speeds with them, you would find that they are actually much farther apart but the space between them appeared contracted from the moving frame of Earth.

 

From the perspective of Earth, the markers are each 1 lightday apart. From the perspective of the markers, they are each perhaps 2 lightdays apart. You cannot say that one is "really" how far apart they are and the other is an illusion. You could decide that Earth's frame is real so something that appears to be 7 lightyears from Earth is actually 7 lightyears, even if you see it as 1 lightyear, but that's just defining "real" as "measured from Earth's frame" and illusion as "measured from a frame other than Earth's."

 

There's no reason to select Earth's frame as representing the most accurate picture of reality except that we happen to be living on it at the moment. Someone living on a different planet may measure the distances we see very differently because their planet is not at rest with respect to Earth, and there is no reason why our measurements are real while theirs are an illusion.

[Didymus]

If there is no physical change, but only a way to describe what the observer observes... Then the whole thing is a trivial optical illusion. However, if there's a physical change as you describe, that would mean every time a photon travels toward the earth, the earth's speed relative to that photon is C, thus as long as the sun shines, time can not exist and space must be infinitely compressed in any direction from which light travels toward us.

 

One could change the subject to saying that it only explains how we observe the object in relative motion, not any other part of space... Yet light's frequency is readily observable... If any frame of reference between us and photons, as predicted, we should observe all functions of light as instantaneous.

[md65536]

If there is no physical change, but only a way to describe what the observer observes... Then the whole thing is a trivial optical illusion. However, if there's a physical change as you describe, that would mean every time a photon travels toward the earth, the earth's speed relative to that photon is C, thus as long as the sun shines, time can not exist and space must be infinitely compressed in any direction from which light travels toward us.

 

One could change the subject to saying that it only explains how we observe the object in relative motion, not any other part of space... Yet light's frequency is readily observable... If any frame of reference between us and photons, as predicted, we should observe all functions of light as instantaneous.

There *is* a physical change in measurements, but only per observer. The observed object doesn't change in any absolute way. You're trying to take the "relative" out of relativity, but then you end up with nonsense. A contracted length is contracted depending on the observer, it doesn't change the object in a universal way---because there is no such universal measurement in SR. There is no absolute time or distance.

 

It is only a trivial illusion as much as all of time and distance is. But they are consistently measurable, so it is meaningless to call them illusions. You might as well say "reality isn't real". No, SR can describe what observers see, experience, observe, measure, and know from observation, even if you distinguish between those.

 

Light doesn't have a frame of reference, so your "photon from the sun" example doesn't apply even with relative measurements. The Earth's speed relative to a photon is c for no time at all, over a distance that is contracted to zero length, so it doesn't make sense to speak of speeds relative to a photon.

 

Imagining light experiencing things as instantaneous---strictly abstractly---doesn't change how we experience light, acting at a constant rate of c, using measurements that are relative to the particular measurer (observer).

Edited March 2, 2013 by md65536

[elfmotat]

There *is* a physical change in measurements, but only per observer. The observed object doesn't change in any absolute way. You're trying to take the "relative" out of relativity, but then you end up with nonsense. A contracted length is contracted depending on the observer, it doesn't change the object in a universal way---because there is no such universal measurement in SR. There is no absolute time or distance.

 

It's important to note, however, that there are invariant quantities that every observer agrees on. Namely, proper time (the time a clock will actually tick off) and proper length (the length of something as measured in its own rest frame).

Edited March 2, 2013 by elfmotat

[Didymus]

Photons have no frame of reference now? Then, how exactly can they be a constant? Take the Doppler effect... We move relative to a source of light and see a redshift. Intuitively, we think "we're moving relative to the wave, duh.". However, this violates SR. So, instead of our motion relative to the source adding or subtracting from our speed relative to that light (as would make perfect sense), Einstein states that our additional speed is diluting the space through which light travels and the change in frequency is caused by a change in wavelength rather than relative speed.

 

But, if the photon has no frame of reference how do you suppose it's affected by spacial dilation?

 

...either way... Fine, photons are cheating. What about galaxies?

 

Hubble's constant. Put dots on a balloon and blow it up. The larger the balloon, the more the dots will accelerate away from one another. This is how we explain the universe expansion accelerating.

 

Larger it gets, the greater the red shift and we can already observe objects that have been shifted WELL out of the visible spectrum, indicating that those rocks with nothing but inertia to propel them are approaching the speed of light relative to us. Once the universe passes the 13.7 billion LY (iirc) mark, objects at that distance will have a rest frame of greater than C relative to us.

 

Even if we assume that both objects will see the other forever frozen in time where they passed that point... All this suggests is that we won't be able to observe them... Not that time or space is being altered in any way for either object... Just because there happens to be another object billions of lightyears away moving at a certain speed relative to it.

 

... In fact, it stands to reason that the universe may well already exceed this size... But because of the rate of expansion past that point, it can't be detected because light will never reach us because we're already outpacing it.

 

 

The Doppler effect and Hubble's constant conclusively disprove the idea of SR causing time dilation. The math on a small scale works for GPS... But on a large scale, it's observably wrong.

 

There's a difference between physical changes and changes in how one observer would measure the other. When I close my eyes, I can't observe my phone at ALL! That doesn't mean my phone has stopped existing.

 

If the only changes being made is a change in observation.... That's as useful as closing your eyes and noting that you can't observe things visually at the moment.