functionally faster than light.

[elfmotat]

By definition, if the speed of light is c in all inertial frames then there is no inertial frame where the speed of light is zero. Photons do not have rest frames by definition.

[Delta1212]

Motion due to the expansion of the universe is different than motion due to normal acceleration because the objects themselves aren't actually accelerating, space is just increasing between them. Beyond the distance at which space is expanding at a rate greater than one lightyear per year, objects do not appear frozen in time, they simply cannot be observed because the light will never reach us. It's like a train that can't reach the end of a track because track is being laid down in front of it faster than it can move.

 

Part of the problem with labeling length contraction and time dilation as illusory is that there is no absolute rest frame from which you can measure things to determine what the "real" distance and timing of objects and events is. From Earth, I can say that a certain galaxy is 7 ly away, but Earth is moving around the sun, and the sun is moving around the Milky Way. Because the Earth is moving, it experiences time dilation and length contraction, so how do I know what the "real" distance is?

 

You could launch a spaceship away from Earth and sync its motion with the galactic core, but the galaxy is hurtling through space as well. Measurements of the distances to other galaxies will be contracted, so you have to adjust again. You could sync up with the average of the galactic cluster, but that's moving with respect to other things.

 

No matter what you sync with, you're always moving with respect to something else. There's no way to reach a point where you can say, "Ok, I am now not moving, and am therefore experiencing no length contraction or time dilation."

 

Anything that you see moving will be length contracted and will appear to expand if you match velocities with it, and it will also see you as being time dilated and you will find that you agree that your clock was previously running slow when you match velocities with it.

[IM Egdall]

Ok, my understanding was that time was distorted by speeds close to the speed of light not the actual distance...

There is no "actual distance." All distances are relative. The distance you measure, as Swansont said, depends on your frame of reference. And distance is affected by any speed. Its just that the amount of length contraction is extremely small at relative speeds which are small compared to the speed of light.

 

The same is true for time.

[Didymus]

And, therefore if there is no such thing as a constant space or time, then by definition, there can be no constant speeds (light). The more hoops people jump through to protect light's status as a constant, the more it disproves itself.

 

You can't have a constant measurement of two things that are, each, unconstant (change in position in space over a period of time).

[Delta1212]

You can if those things vary proportionately.

 

2/1=2

4/2=2

10/5=2

 

The numerator and denominator both vary but the quotient is constantly 2.

[michel123456]

That should ring a bell.

 

Meaning that time & space are basically 2 different measurements of the same thing.

[IM Egdall]

And, therefore if there is no such thing as a constant space or time, then by definition, there can be no constant speeds (light). The more hoops people jump through to protect light's status as a constant, the more it disproves itself.

 

You can't have a constant measurement of two things that are, each, unconstant (change in position in space over a period of time).

Huh? The fact that the speed of light is absolute, that it is unaffected by the speed of its source or the observer, is what leads to the relativity of time and space. Google "relativity light clock" and you'll find lots of explanations of this.

 

To your last sentence: Relative (uniform) motion reduces both distance and time by the same factor, the Lorentz factor. This factor cancels out when you divide distance by time to get speed.

 

[Didymus]

To delta: logical correlation, but not proportional to this conversation. If time expansion and space contraction were proportional, we would see no time dilation because the two would cancel eachother out. If time dilation were to be a viable explanation for the results of the "atomic clocks on a plane" test, when the aircraft landed, the clocks would be synchronized again.

 

To IM... If you're going to use the light clock idea as proof... When/where/how was it actually tested? As a thought experiment, it's no more valuable than "imagine a photon traveling toward a pair of objects a lightyear away at the point of emission. For C to be a constant, that light must hit both simultaneously regardless of where in the universe each object travels during that year."

 

The light clock idea misses a number of obvious variables.... First off, the path that the light will take isn't longer or shorter based on how the observer is moving... If the train is moving, light bouncing 90 degrees to each mirror (for the W path) will fall off track as the train moves the length between the point of emission and the edge of the mirror. Light that continues bouncing along that perceived "straight path" will in fact be traveling at an angle relative to the speed of the train as is described for how the observer on the ground sees the light.

 

Second.... There have been "real experiments" to "prove a constant speed of light from moving sources... Guess what the first step is.... Taking that incoming, redshifted light.... And bouncing it off of a mirror stationary relative to the rest of the set up.

 

... And guess how light bounces. It's absorbed and reemitted... Thus completely nullifying the experiment because as soon as the light hits that first mirror, the mirror is now the source of that light, so of course it will travel at a constant speed.... Because they're using stationary sources.

 

Please... If anyone knows of an evidence where these variables were taken into account... Please tell me. I'be read a lot of studies and so far the best explanation I've got is ".... Well... These people are scientists... I'm sure they thought of that."

 

And that is the faith of religion. Not science.

[Delta1212]

To delta: logical correlation, but not proportional to this conversation. If time expansion and space contraction were proportional, we would see no time dilation because the two would cancel eachother out. If time dilation were to be a viable explanation for the results of the "atomic clocks on a plane" test, when the aircraft landed, the clocks would be synchronized again.

They are functionally the same phenomenon viewed from different frames.

 

A very fast plane might see itself traveling 1 mile in x amount of time. An observer on the ground might see the same distance as being 2 miles, which the plane takes 2x amount of time to cover, but the observer will see the plane's clock ticking at half speed. When the plane lands, it will come to rest with respect to the observer, and they will both agree that the clock on the plane ticked off half as many seconds as the clock on the ground.

[elfmotat]

What started off as a good question has now devolved into crank nonsense. If you want to learn SR then go buy a textbook. If you don't, then stop wasting our time.

[swansont]

Didymus, on 08 Mar 2013 - 18:21, said:

To delta: logical correlation, but not proportional to this conversation. If time expansion and space contraction were proportional, we would see no time dilation because the two would cancel eachother out. If time dilation were to be a viable explanation for the results of the "atomic clocks on a plane" test, when the aircraft landed, the clocks would be synchronized again.

 

 

Theories are not wrong simply because you don't understand them. Both of these claims are straw men.

[Didymus]

"What scientific evidence is there that takes into account the following variables...."

"This is nonsense, Buy a textbook, don't waste our time"

 

"You don't understand."

Very insightful answers. Keep in mind, though, that this is a science forum. If you don't want to waste your time actually digging in and questioning things, why are you here? If your mind is already made up and you have no interest in considering other possibilities, and seem to be offended when others offer alternative explanations... what are you doing here?

Science is not about reaffirming your unquestioning loyalty to the accepted theory... einstein was the one who described such a thing as a sign of great intellectual weakness. That the single greatest failure in how americans view education is how we preach the doctrine that will be accepted and any sign of questioning this doctrine is looked down upon. Science is the art of seeking better/simpler explanations for how the universe works.

... I'm rather disappointed.

[ACG52]

Keep in mind, though, that this is a science forum. If you don't want to waste your time actually digging in and questioning learning things, why are you here?

[elfmotat]

The forum is meant for legitimate science questions, not to entertain the delusional fantasies of crackpots. If you want to learn Relativity then go out and buy a textbook. If you have a specific question that comes up in your study, ask here and I'd be more than willing to help. What you're doing now I have very little patience for.

[swansont]

"What scientific evidence is there that takes into account the following variables...."

 

"This is nonsense, Buy a textbook, don't waste our time"

 

"You don't understand."

 

Very insightful answers. Keep in mind, though, that this is a science forum. If you don't want to waste your time actually digging in and questioning things, why are you here? If your mind is already made up and you have no interest in considering other possibilities, and seem to be offended when others offer alternative explanations... what are you doing here?

 

Science is not about reaffirming your unquestioning loyalty to the accepted theory... einstein was the one who described such a thing as a sign of great intellectual weakness. That the single greatest failure in how americans view education is how we preach the doctrine that will be accepted and any sign of questioning this doctrine is looked down upon. Science is the art of seeking better/simpler explanations for how the universe works.

 

There is no preaching, there is no doctrine. It's a theory that has quite a lot of experimental confirmation. You might want to consider that people here have already asked the questions and learned about the evidence in support of the theory, before arriving here. Also that alternative explanations have been tried and discarded because they don't work.

 

... I'm rather disappointed.

 

We'll have to learn to live with that.

…

Done.

[Didymus]

Elfmotat, your absence will not be missed. Not everyone who disagrees does so out of ignorance. I've pointed out legitimate inconsistencies and missed variables in the popularly accepted experiments. If you have nothing of value to add beyond "but this book says I must stay strong in my faith" ... please, feel free to move on.

 

Some of those questions being: People are using the "lightclock tests" as proof... everywhere I've seen, this has been a poorly thought out idea rather than anything functionally tested. If this is to remain "proof" ... specifically when was this functionally tested?

 

In what way has anyone tested the uniformity of the speed of light from actual moving sources? i.e. without beginning the experiment by causing the light to be re-emitted from an object stationary relative to the rest of the experiment (such as bouncing the light off of a mirror)?

 

I agree people have done many experiments and supported their theory with quite a bit of pretty math... I propose that nearly every such experiment is inherently flawed because they're only measuring light with each mirror as a source, only showing that this light is moving at a constant speed relative to it's source rather than in "every frame of reference."

 

It's a theory that has quite a lot of experimental confirmation.

 

Cool story. I've read through the list of aether wind experiments you provided. None of them conclusively prove anything about time dilation or light's speed being constant from moving reference frames.

Sometimes, it's acceptable to combine frames of reference (i.e. atomic clocks on jets) where the clocks (adjusted by the formula being tested) happen to exactly match the formula being tested after they've flown around the world. Other times, you yourself have said that it's inappropriate to combine frames of reference, when we realize that, based on this math, a person traveling .99c for one year will end up 7 light years away.

 

Perhaps I can be more specific... you claim that it has "quite a lot of experimental confirmation." ... Can you cite/explain a single experiment supporting any aspect of relativity that can actually stand up to basic critical thinking. Something that doesn't have glaring inherent flaws that corrupt the whole experiment... like all of the aether wind ones you listed previously?

Edited March 10, 2013 by Didymus

[swansont]

Perhaps I can be more specific... you claim that it has "quite a lot of experimental confirmation." ... Can you cite/explain a single experiment supporting any aspect of relativity that can actually stand up to basic critical thinking. Something that doesn't have glaring inherent flaws that corrupt the whole experiment... like all of the aether wind ones you listed previously?

 

Can you list an actual "inherent flaw" in the experiments, e.g. Hafele-Keating or GPS?

[Delta1212]

Sometimes, it's acceptable to combine frames of reference (i.e. atomic clocks on jets) where the clocks (adjusted by the formula being tested) happen to exactly match the formula being tested after they've flown around the world. Other times, you yourself have said that it's inappropriate to combine frames of reference, when we realize that, based on this math, a person traveling .99c for one year will end up 7 light years away.

 

You seem to be confusing combining frames with observing relativistic effects.

 

A person traveling at .99c (as observed from Eartg) will not cover 7 light years (as observed from Earth) in one year (as observed from Earth).

 

From Earth, he will be observed to have taken about 7 years to travel 7 lightyears. He will have experienced about 1 year during which time he will have traveled a distance that he measures to be 1 lightyear. If he then "stops" (I.e syncs velocity with Earth again) he will see that distance as being 7 lightyears and agree that he spent 7 years traveling that distance during which he experienced time at a slower rate.

 

Mixing frames would be taking the time measured by the traveler and the distance measured by the non-traveler and saying that the traveler moved at FTL speeds. Experiencing the effects of relativity involves syncing observers from different frames back up to the same frame at which point the measurements of that frame will be held to be valid by all parties with time dilation and length contraction being the phenomena that explain the difference in the subjective experience of each while they were in different frames.

[Didymus]

You seem to be confusing combining frames with observing relativistic effects.

 

A person traveling at .99c (as observed from Eartg) will not cover 7 light years (as observed from Earth) in one year (as observed from Earth).

 

From Earth, he will be observed to have taken about 7 years to travel 7 lightyears. He will have experienced about 1 year during which time he will have traveled a distance that he measures to be 1 lightyear. If he then "stops" (I.e syncs velocity with Earth again) he will see that distance as being 7 lightyears and agree that he spent 7 years traveling that distance during which he experienced time at a slower rate.

 

Hafele-Keating is the most common experiment people I've talked to have brought up. Definitive evidence of time dilation. Essentially Atomic clock on the ground vs. atomic clocks on a jet, flies around the world... clock reads different (and by the predicted amount). We know that these clocks can not be made inaccurate, therefore after traveling, the fact that this clock has a few missing nanoseconds is hard evidence of SR. It's assumed that these clocks have legitimately experienced the entire flight through a shorter period of time.

 

Hense, the example in the first post of this thread... same situation, except with a longer distance and higher speed. Pick a point 7 light years away. Travel toward that point at .99C. According to your clock, you can stop after 1 year, look behind you and have traveled 7 light years. If time dilation is correct, the speed of light can not be a limit. To dismiss the above illustration is to dismiss Hafele-Keating by the same logic.

 

Of course, for swanson, the thought experiment is a bit like Schrodinger's cat... the whole intention is to illustrate the illogical implications of the Hafele-Keating experiment. You asked what inherent flaws are in the test so many people have put their faith into:

 

1: it has the implications of the illustration in the original post of this thread.

2: The plane was flying along an unspecified path at an unspecified average altitude at an unspecified speed... The only thing documented about the altitude is that the aircraft's altitude was considered negligible and not included in the predicting formula. True, the GR implication of a few miles is only a fraction of a percent... but consider the scale of their results! less than 180 billionths of a second over a period of a quarter million seconds. The negligible amount is larger than their results.

3: In order to get the math right, GR had to be taken into consideration, thus the distance of the ground clock from center of gravity. They wanted to test this ratio.... and in order to prove the math they were testing... the used that same formula to adjust the results... to prove the formula. This circular reasoning doesn't jump out at anyone? The fact that the clocks had to be adjusted by this expected amount indicates that, after the trip, these clocks were still in sync... and were only out of sync by the expected amount BECAUSE they were artificially adjusted to "simulate the clock being at the center of the earth" in order to account for GR.

 

4: (This one, I admit can be taken a number of ways. This one has so many variables, I very well may be missing something simple) For the SR calculations, the rotational speed of the earth was taken into account... but not the orbital speed. One could say "but the plane is moving with the earth, so the orbital speed doesn't change anything." ... However, to the same extent, the plane was traveling with earth's rotation. The only SR change relative to the ground clock would be actual ground speed. I've seen some attempt to explain it as an object on a marry-go-round... Objects farther from the center will be traveling faster because they're traveling a larger circumference during each revolution. However, this is only relative to an outside, preferred frame of reference... which we were trying to -disprove- ... not rely upon. On any marry-go-round, put screws in at any distance from the center, and spin it at any speed... even though each will have a different ground speed, none of these screws will have a speed relative to each other. If we're to accept a preferred frame of reference that would account for rotational speed, then there's no real reason not to account for orbital speed as well.

 

 

5.... then, even if everything was done appropriately and the readings weren't adjusted assuming the formula's correctness to prove itself correct... All we have is a reading no way to isolate the variable to conclude that "the relative speed of one clock to the other" is what caused the discrepancy .. let alone that it was an alteration of time as opposed to an alteration of some function of the clock itself. If I want to set a bigfoot trap... and set meat outside my backdoor, postulating that if an adult, male bigfoot is in the area, he'll eat it... and it turns up gone the next day... I still have to prove it wasn't because of a dog or cat or bird or raccoon or any other simple explanation. Likewise, a result like this doesn't conclusively show that it was relative speed (as opposed to any other variable) that caused time (as opposed to any physical property of the clock) to alter by this amount.

[michel123456]

You seem to be confusing combining frames with observing relativistic effects.

 

A person traveling at .99c (as observed from Eartg) will not cover 7 light years (as observed from Earth) in one year (as observed from Earth).

 

From Earth, he will be observed to have taken about 7 years to travel 7 lightyears. He will have experienced about 1 year during which time he will have traveled a distance that he measures to be 1 lightyear. If he then "stops" (I.e syncs velocity with Earth again) he will see that distance as being 7 lightyears and agree that he spent 7 years traveling that distance during which he experienced time at a slower rate.

 

Mixing frames would be taking the time measured by the traveler and the distance measured by the non-traveler and saying that the traveler moved at FTL speeds. Experiencing the effects of relativity involves syncing observers from different frames back up to the same frame at which point the measurements of that frame will be held to be valid by all parties with time dilation and length contraction being the phenomena that explain the difference in the subjective experience of each while they were in different frames.

??? the bold part.

 

You seem to argue that the Earth is correct while the traveler is wrong when you say "and agree that he spent 7 years (...)"

 

And also you said:

traveling at 0,99 c he observes the Earth 1 LY away

traveling at 0 c he observes the Earth at 7 LY away

 

So if he makes a u-turn and travels at minus 0,99 c, what will be his observation?

[Didymus]

For this one, I will agree with the orthodox interpretation of things:

There is no "negative speed." Direction is irrelevant. Whatever effects relative speed has, it's the same moving toward or away from an object.

... where this gets interesting is under the theory that time dilation may be activated by a given object's acceleration as opposed to relative velocity. Both have their faults, of course... but the problem with claiming that "acceleration" is what starts to slow time down is that when that object decelerates... this would simply be acceleration in the opposite direction.

To your question, per the theory: He sees an object 7 lightyears away. When he starts moving between these two objects at a speed of .99c, the entire universe will seem to contract (in the direction of travel) by a factor of 7, and thus, the distance between these two objects (while moving at this speed) will seem to only be 1 LY. If he stops at any point in the process... the universe will seem to stretch back into it's former state, increasing the gap between the two points to 7 LY. If he resumes travel in either direction... it shrinks again.

Of course, that's when the second part of the above illustration kicks in. What if a second person is traveling in this same craft... but is interested in some meteor or second ship that should be near that spot in 7 years. Say this object is moving at .1C either toward or away from you. Depending on what you're measuring your relative speed against, the entire universe may be contracted by significantly different factors... for two people on the same ship, depending on what object they're thinking of.

... hence, the problem with the claim that relative speed causes spacial contraction in the first place. But, without it, the Doppler effect would have to be acknowledged as evidence against the constant of C.

[swansont]

 

Hafele-Keating is the most common experiment people I've talked to have brought up. Definitive evidence of time dilation. Essentially Atomic clock on the ground vs. atomic clocks on a jet, flies around the world... clock reads different (and by the predicted amount). We know that these clocks can not be made inaccurate, therefore after traveling, the fact that this clock has a few missing nanoseconds is hard evidence of SR. It's assumed that these clocks have legitimately experienced the entire flight through a shorter period of time.

 

Hense, the example in the first post of this thread... same situation, except with a longer distance and higher speed. Pick a point 7 light years away. Travel toward that point at .99C. According to your clock, you can stop after 1 year, look behind you and have traveled 7 light years. If time dilation is correct, the speed of light can not be a limit. To dismiss the above illustration is to dismiss Hafele-Keating by the same logic.

 

You are mixing frames, as has been pointed out before. When you stop, you are not in the same frame of reference as when you are moving. Meaning you can't take an elapsed time from one frame and use a distance measured in another. The invariance (and speed limit) of c is defined for measurements made in a single frame of reference.

 

It shouldn't be a shock that when you violate the rules for finding the result that you get the wrong answer.

 

 

Of course, for swanson, the thought experiment is a bit like Schrodinger's cat... the whole intention is to illustrate the illogical implications of the Hafele-Keating experiment.

 

To be a good thought experiment you have to apply the theory in a correct and valid way. Which is missing when you mix frames.

 

You asked what inherent flaws are in the test so many people have put their faith into:

 

1: it has the implications of the illustration in the original post of this thread.

2: The plane was flying along an unspecified path at an unspecified average altitude at an unspecified speed... The only thing documented about the altitude is that the aircraft's altitude was considered negligible and not included in the predicting formula. True, the GR implication of a few miles is only a fraction of a percent... but consider the scale of their results! less than 180 billionths of a second over a period of a quarter million seconds. The negligible amount is larger than their results.

3: In order to get the math right, GR had to be taken into consideration, thus the distance of the ground clock from center of gravity. They wanted to test this ratio.... and in order to prove the math they were testing... the used that same formula to adjust the results... to prove the formula. This circular reasoning doesn't jump out at anyone? The fact that the clocks had to be adjusted by this expected amount indicates that, after the trip, these clocks were still in sync... and were only out of sync by the expected amount BECAUSE they were artificially adjusted to "simulate the clock being at the center of the earth" in order to account for GR.

 

No circular reasoning. Have you actually read their papers on the experiment?

 

The claim about "unspecified average altitude at an unspecified speed" is wrong. I've seen the worksheet that they handed to the pilot to fill out (it's something we have in the library; a perk of working where I work) and average speed is easy anyway since v = d/t

 

4: (This one, I admit can be taken a number of ways. This one has so many variables, I very well may be missing something simple) For the SR calculations, the rotational speed of the earth was taken into account... but not the orbital speed. One could say "but the plane is moving with the earth, so the orbital speed doesn't change anything." ... However, to the same extent, the plane was traveling with earth's rotation. The only SR change relative to the ground clock would be actual ground speed.

 

No, because the earth is not an inertial frame — it's rotating, and when you circumnavigate the globe, and do so in both directions, the rotation is a very important term. You could include the effects of the orbit, but they will be much smaller, since you are only sampling of order 1% of it, it's approximately linear motion. The effect is well wit

 

I've seen some attempt to explain it as an object on a marry-go-round... Objects farther from the center will be traveling faster because they're traveling a larger circumference during each revolution. However, this is only relative to an outside, preferred frame of reference... which we were trying to -disprove- ... not rely upon. On any marry-go-round, put screws in at any distance from the center, and spin it at any speed... even though each will have a different ground speed, none of these screws will have a speed relative to each other. If we're to accept a preferred frame of reference that would account for rotational speed, then there's no real reason not to account for orbital speed as well.

 

 

You are confusing inertial with preferred.

 

5.... then, even if everything was done appropriately and the readings weren't adjusted assuming the formula's correctness to prove itself correct... All we have is a reading no way to isolate the variable to conclude that "the relative speed of one clock to the other" is what caused the discrepancy .. let alone that it was an alteration of time as opposed to an alteration of some function of the clock itself. If I want to set a bigfoot trap... and set meat outside my backdoor, postulating that if an adult, male bigfoot is in the area, he'll eat it... and it turns up gone the next day... I still have to prove it wasn't because of a dog or cat or bird or raccoon or any other simple explanation. Likewise, a result like this doesn't conclusively show that it was relative speed (as opposed to any other variable) that caused time (as opposed to any physical property of the clock) to alter by this amount.

 

The Pound-Rebka experiment had confirmed the general relativistic effect a decade earlier, so the only additional variable is speed.

[Moontanman]

I've been trying to follow this and I think i understand to some extent but I have to say that from the frame of the guy on the space ship he has traveled 7 ly in one year of his life... correct? Isn't this from his stand point faster than light? I may be confused i admit..

[md65536]

I've been trying to follow this and I think i understand to some extent but I have to say that from the frame of the guy on the space ship he has traveled 7 ly in one year of his life... correct? Isn't this from his stand point faster than light? I may be confused i admit..

He's traveled 7 LY of distance measured from Earth's frame, in 1 year measured from the ship's frame.

 

How is that faster than light? How long did it take light to make the same journey? (Example answer: It took 7 years according to a clock on Earth, but the ship took over 7 years according to the same clock. Is there any clock which records the ship traveling faster than light? Or do you have to switch between clocks and frames in order to measure the ship differently than you measure light?)

 

 

He's traveled less than 1 LY in 1 year, both measured from the ship. Light is faster according to the traveler. He's traveled 7 LY in a little over 7 years, according to Earth. Light is faster. According to anyone else's measurement: Light is faster.

Edited March 10, 2013 by md65536

[Moontanman]

He's traveled 7 LY of distance measured from Earth's frame, in 1 year measured from the ship's frame.

 

How is that faster than light? How long did it take light to make the same journey? (Example answer: It took 7 years according to a clock on Earth, but the ship took over 7 years according to the same clock. Is there any clock which records the ship traveling faster than light? Or do you have to switch between clocks and frames in order to measure the ship differently than you measure light?)

 

 

No, I am not suggesting he physically traveled faster than a photon in any time frame but from his point of view he has made a 7 ly journey in less than one year.

 

This reminds me of a novel where society develops two branches, one of which travels back and forth between stars at very high fractions of c and they are separated out as different because the home worlds all experience time much faster than the constant travelers and so both evolve into different societies and it is hinted they speciate as well due to this...