How does the Twins Paradox challenge our understanding of ageing?

[Dale]

I mean that the periods of oscillators (the tick rates of clocks) change during intervals when their (the oscillators, the clocks, etc.) velocities are changing. I don't think this is an ambiguous statement, and it's supported by the outputs of accelerometers and accelerated clocks.

How is it supported by the experimental results? You have not given an equation yet that we can compare to experimental results.

I repeat my earlier request for the equation describing this relationship between acceleration and tick rate. The SR formula has been given, is well supported by the evidence, and depends only on velocity and not on higher derivatives of position.

 

[jadgerz]

Uh well, if he does it won't be coming from you...


Do you have an alternate explanation? The actual lag experienced by these jets is exactly in accordance with GR.


It is one of the most demonstrated phenomena in physics. Every particle fired through an accelerator exhibits this effect; every airplane with a clock in it, and every GPS satellite. Much of our modern navigation technology is built upon it. If the technology did not compensate for this effect, it would not work.


And yeah. That Mt. Rainer experiment is awesomely awesome.

[ EDIT: Ah. I see Sylas has already dealt with you. And more diplomatically than I, especially considering he was the one you were being so condescending to.]

I am amazed at how people are (still) such slaves to dogma. And how "nasty" they get when you "dare" disturb their locked minds. The experiment done back in 1971... if my memory serves me right... the Hafele and Keating experiment (?) was later torn to shreds after a review, one being the inventor of atomic clocks themselves (or some important association) if I recall. I neither deny or accept the theory of time dilation. I read it myself and although I don't proclaim to be an expert my response would be: "I wouldn't pay money for it". My point is that there is some reasonable doubt, or at least serious unanswered questions in regards to time dilation and for those who say: "This is how it is" are a total bore. I was hoping for an intelligent discussion on the matter but I find myself confronted with people possessed with a conditon known as "Doctrinaire Loyale". This condition usually afflicts religious zealots who still believe the world is flat, or the Earth was created in October 6006 BC. or that the Earth is the center of the universe. They flinch in pain when you say something contrary to their beloved dogma. Do I risk being burned at the stake for daring to question the validity of "time dilation"? (Oh, the ghost of Bruno!). Some greeting this is to "the new kid on the block". Please, I am a degreed person, well studied in physics, science and engineering. I'm seriously looking for people who can discuss this matter with an open, logical mind. May I start afresh and ask you "learned" folks again my questions?

 

[russ_watters]

Sylas,

You are a bit condescending in your response, however, I need to take issue with your statements. You made one statement which tells me that maybe you'd need a bit more education in physics...

I'll pause here and let you ponder my statements. I don't claim to have an answer to the universe but I know one thing for sure, no one else does either.

[separate post]May I start afresh and ask you "learned" folks again my questions?

Sure, you may start again. We don't hold grudges here. However, we also recognize when we're pumping a dry well: Sylas's response to your first post was not in the least bit condescending, but your posts are dripping with attitude. Your ability to learn - and our willingness to teach you - will require that you drop your attitude and really start trying to understand what people are explaining to you. Please understand, we're not here for the fun of arguing with crackpots or beating down people who know less: this forum is here to help teach people physics and the people who make significant contributions are sincere in their desire to teach people. So you can decide which you are - someone who wants to learn or a crackpot who just wants to berate the dogmatic establishment - and choose to start fresh... or not.

 

[atyy]

Things to ponder:
1. If velocity is relative then, between two moving objects, there is no faster or slower and thus time is not slower or faster for either one, i.e. the Twins Paradox is nada.
2. If an object were entirely alone in the universe it could never possesses "velocity".
3. Velocity cannot be measured internally but acceleration can thus, if between two objects that are accelerating from each other, it would be possible to determine which one is doing the accelerating and how much.
4. From the above, if there really is such as thing as time dilation, then I would put my money on acceleration as the "culprit". Anything that goes in a circle is accelerating even if it keeps a constant velocity. Anything circling the Earth or not going in an absolutely straight line such as shuttles and airplanes at a constant velocity are accelerating.

Not exactly, but close. Velocity is frame dependent, acceleration is absolute - in loose language, there is no such thing as velocity, whereas acceleration really exists. In that sense, time dilation thought of as clocks running slow or fast is relative, since the rate of a clock would have the form dT1/dT2, where one of the Ts is a coordinate time, which is frame dependent. So in that sense, there is not really such a thing as time dilation - we think of differences in clock readings as differences in integrals, not derivatives. Since there is not really such a thing as time dilation, the rest of your argument is moot.

 

[atyy]

My guess is that when more science is done, it will be found that accelerations do affect tick rates.

But we already know that acceleration affects the "rates" of some clocks, such as pendulum clocks.

Acceleration does not affect the rate of an ideal clock, by definition. So we will never find that acceleration affects the rate of an ideal clock, since if acceleration affects the rate of a clock, then the clock is not ideal.

BTW, what do you mean by the rate of a clock? To define the rate of a clock, don't you need some other clock or clocks to compare it with?

 

[matheinste]

I am amazed at how people are (still) such slaves to dogma. And how "nasty" they get when you "dare" disturb their locked minds. The experiment done back in 1971... if my memory serves me right... the Hafele and Keating experiment (?) was later torn to shreds after a review, one being the inventor of atomic clocks themselves (or some important association) if I recall. I neither deny or accept the theory of time dilation. I read it myself and although I don't proclaim to be an expert my response would be: "I wouldn't pay money for it". My point is that there is some reasonable doubt, or at least serious unanswered questions in regards to time dilation and for those who say: "This is how it is" are a total bore. I was hoping for an intelligent discussion on the matter but I find myself confronted with people possessed with a conditon known as "Doctrinaire Loyale". This condition usually afflicts religious zealots who still believe the world is flat, or the Earth was created in October 6006 BC. or that the Earth is the center of the universe. They flinch in pain when you say something contrary to their beloved dogma. Do I risk being burned at the stake for daring to question the validity of "time dilation"? (Oh, the ghost of Bruno!). Some greeting this is to "the new kid on the block". Please, I am a degreed person, well studied in physics, science and engineering. I'm seriously looking for people who can discuss this matter with an open, logical mind. May I start afresh and ask you "learned" folks again my questions?

The problem with accusations of dogma is that those accused are allowed no argument in reply as any arguments they use will also be labelled as dogmatic.

You say you are looking to discuss issues with an open and logical mind, that's what we all want to do. But when people have looked at the evidence with "open and logical minds" and have come to conclusions other than those you want, you label them as dogmatic. Mistaken maybe, (though I do not believe so) but dogmatic no.

Matheinste.

 

[jadgerz]

The problem with accusations of dogma is that those accused are allowed no argument in reply as any arguments they use will also be labelled as dogmatic.

You say you are looking to discuss issues with an open and logical mind, that's what we all want to do. But when people have looked at the evidence with "open and logical minds" and have come to conclusions other than those you want, you label them as dogmatic. Mistaken maybe, (though I do not believe so) but dogmatic no.

Matheinste.

I agree. Let's just say that "ruffled feathers have been smoothed" and let's start afresh. Good, that done, let's continue our discussions in a civilized manner.

The one honorable and learned gentlemen earlier implied that the tests done by Hafele & Keating in 1971 gave results that were "exactly" what would be predicted by GR. Well, that is not so. For the eastbound flight the predicted (calculated) time dilation was (-40 +/- 23) nanoseconds. The H&K experiment had an observed time dilation of (-59 +/- 10) nanoseconds. Hardly exact. An interesting read on this experiment is by Dr. Kelly (PhD), which I suggest you read, and another critique by the inventor of the atomic clock. Quite frankly, if the H&K experiment was introduced as evidence in a court of law I believe it would be summarily rejected.

What does such a variance in the predicted and the "observed" results of the H&K experiment imply? It implies doubt. Look at the range of the predicted dilation. It could be from 17 to 63 nanoseconds. Not quite the accuracy mentioned by the other honorable and learned gentlemen. If it were as precise as mentioned then it would be "exact"

 

[jadgerz]

But we already know that acceleration affects the "rates" of some clocks, such as pendulum clocks.

Acceleration does not affect the rate of an ideal clock, by definition. So we will never find that acceleration affects the rate of an ideal clock, since if acceleration affects the rate of a clock, then the clock is not ideal.

BTW, what do you mean by the rate of a clock? To define the rate of a clock, don't you need some other clock or clocks to compare it with?

At the risk of appearing to take sides, let me make a comment in support of ThomasT's assertion. If you study the Hafele & Keating's experiment from 1971 you will see it was necessary to predict the time dilation effect of both Special and General Relativity. Special Relativity being the Kinematic Relativity and General being the Gravitional. Now, correct me if I'm wrong but Gravity, to my understanding, is a Force, correct? Well, to invoke the name of Newton, he said that Force (F) is equal to mass times acceleration (ma). F = ma. Of course you know all this and I don't mean to suggest you don't. Just a reminder of the point for the argument at hand. The presence of gravity implies acceleration and since gravity (so it is said) affects the rate of an ideal clock in General Relativity then so does acceleration.

If Thomas T is asserting that acceleration affects the rate of the clock as opposed to an actual dilation of time then he has my vote for now. May I suggest (as have others more knowledgeable than myself) that this time dilation phenomena in a gravitational field (accelerration) is analoguous (spelling?), but not exactly, to a chemical rate of reaction in varying temperature regimes.

I hope I haven't offended either of you in bringing this up. God Bless all of you.

 

[Dale]

For the eastbound flight the predicted (calculated) time dilation was (-40 +/- 23) nanoseconds. The H&K experiment had an observed time dilation of (-59 +/- 10) nanoseconds. Hardly exact.

True, the H&K experiment had a relatively low precision, as you would expect at such low velocities. But despite the low precision the result does agree with SR and does not agree with Newtonian physics.

However, time dilation is well established to very high precision in a wide variety of experiments at many laboratories using many different techniques. The data is overwhelmingly in support of time dilation. All of the reputable scientific data points to the correctness of the SR prediction, some to within several percent, and some to within a few parts per million. Here is a sampling:

G. Gwinner, Mod. Phys. Lett. 1, 20, no. 11 (2005), pg 791.
H.E. Ives and G.R. Stilwell, J. Opt. Soc. Am. 28 pg 215–226 (1938);
H.E. Ives and G.R. Stilwell, JOSA 31 pg 369–374 (1941).
Otting, Physik. Zeitschr. 40, 681 (1939).
Hasselkamp et al., Z. Physik A289 (1989), pg 151.
Rossi and Hoag, Physical Review 57, pg 461 (1940).
Rossi and Hall, Physical Review 59, pg 223 (1941).
Rasetti, Physical Review 60, pg 198 (1941).
Redei, Phys. Rev. 162 no. 5 (1967), pg 1299.
Durbin, Loar and Havens, Physical Review 88, pg 179 (1952).
D. Frisch and J. Smith, Am. J. Phys. 31 (1963) 342.
Terell, Nuovo Cimento 16 (1960) pg 457.
Greenberg et al., Phys. Rev. Lett. 23 no. 21 (1969), pg 1267.
Ayres et al., Phys. Rev. D3 no. 5 (1971), pg 1051.
Burrowes et al., Phys. Rev. Lett. 2 (1959), pg 117.
Kaivola et al., Phys. Rev. Lett. 54 no. 4 (1985), pg 255.
McGowan et al., Phys. Rev. Lett. 70 no. 3 (1993), pg 251.
Hay et al., Phys. Rev. Lett. 4 (1960), pg 165.
Kuendig, Phys. Rev. 129 no. 6 (1963), pg 2371.
Olin et al., Phys. Rev. D8 no. 6 (1973), pg 1633.
Mandelberg and Witten, Journal Opt. Soc. Amer. 52, pg 529 (1962).

 

[sylas]

The one honorable and learned gentlemen earlier implied that the tests done by Hafele & Keating in 1971 gave results that were "exactly" what would be predicted by SR. Well, that is not so. For the eastbound flight the predicted (calculated) time dilation was (-40 +/- 23) nanoseconds. The H&K experiment had an observed time dilation of (-59 +/- 10) nanoseconds. Hardly exact.

Certainly there were measurement errors; there always are in this and any other experiment. You should not read that remark as saying the experimental result was exact, but rather that the experiment was completely consistent with relativity, and that it falsified the Newtonian view of an absolute time.

The actual comment was by DaveC426913, and in his own words it is as follows:

The fact that these clocks on airplanes, etc. show a variance with the average of the 45 atomic clocks is no proof of "time dilation".

Do you have an alternate explanation? The actual lag experienced by these jets is exactly in accordance with GR.

Dave is correct, and it is a rather strange reading of his words to think he means that the lag was actually measured exactly. A more natural understanding of this phrase is that the actual lag -- which we can measure only to a limited precision, of course -- is completely consistent with the exact value given by relativity. But if it is confusing, no doubt he would rephrase.

What is definitely INCORRECT, however, is to say that measurements of clocks on jets can be explained as a natural variance analogous to the variance between the multiple clocks (45?) used to keep track of a reference time for Earth's surface.

The consideration of measurement uncertainties is enough to show that time dilation exists, and that it matches the relativistic exact solution within measurement precisions. The evidence proves that time dilation is real, and lends strong experimental support to the relativistic formulae.

Some details that may be of interest.

• The original 1971 experiment used four clocks on the jet flights, to give a check on natural variations between clocks.
• In 1971, there was already no credible doubt of the result. It would have been a stunning upset had the result been anything else, but give that the clocks of sufficient accuracy were available, and also the technology to fly them around the world, it was inevitable that some scientist was going to make this test.
• Since then the experiment has been repeated with more and more accurate clocks; and always the results are consistent with relativity in the sense used by Dave. I wouldn't use the qualifier "exact" myself, since the measurement itself is obviously not exact, but Dave's wording is still okay because the correspondence itself is exact up to allowed precision.
• Now, the corrections for relativity are routinely used not as something to check with experiment, but as a necessary correction that must be applied because time dilation is real, and the relativistic equations do tell you with complete accuracy what correction factor is required for it. (There's a difference between accuracy and precision.)

This is more than enough to prove that the idea of no time dilation is wrong. Science never gives final proof of a new theory; that's why the notion of "falsification" is used so widely. The relativistic formulae for time dilation have been consistent with all attempts to test them, even as tests of greater and greater precision are applied.

Cheers -- sylas

 

[Dale]

The presence of gravity implies acceleration and since gravity (so it is said) affects the rate of an ideal clock in General Relativity then so does acceleration.

This is a common misconception. Gravitational acceleration is not what affects ideal clocks in GR, it is the gravitational potential.

"http://en.wikipedia.org/wiki/Gravitational_time_dilation" is the effect of time passing at different rates in regions of different gravitational potential; the lower the gravitational potential (closer to the center of a massive object), the more slowly clocks run."

This distinction becomes important e.g. in determining the gravitational time dilation at the center of a spherical mass where the gravitational acceleration is 0 but the gravitational time dilation is maximum because the gravitational potential is minimum.

 

[jadgerz]

Certainly there were measurement errors; there always are in this and any other experiment. You should not read that remark as saying the experimental result was exact, but rather that the experiment was completely consistent with relativity, and that it falsified the Newtonian view of an absolute time.

The actual comment was by DaveC426913, and in his own words it is as follows:


Dave is correct, and it is a rather strange reading of his words to think he means that the lag was actually measured exactly. A more natural understanding of this phrase is that the actual lag -- which we can measure only to a limited precision, of course -- is completely consistent with the exact value given by relativity. But if it is confusing, no doubt he would rephrase.

What is definitely INCORRECT, however, is to say that measurements of clocks on jets can be explained as a natural variance analogous to the variance between the multiple clocks (45?) used to keep track of a reference time for Earth's surface.

The consideration of measurement uncertainties is enough to show that time dilation exists, and that it matches the relativistic exact solution within measurement precisions. The evidence proves that time dilation is real, and lends strong experimental support to the relativistic formulae.

Some details that may be of interest.

• The original 1971 experiment used four clocks on the jet flights, to give a check on natural variations between clocks.
• In 1971, there was already no credible doubt of the result. It would have been a stunning upset had the result been anything else, but give that the clocks of sufficient accuracy were available, and also the technology to fly them around the world, it was inevitable that some scientist was going to make this test.
• Since then the experiment has been repeated with more and more accurate clocks; and always the results are consistent with relativity in the sense used by Dave. I wouldn't use the qualifier "exact" myself, since the measurement itself is obviously not exact, but Dave's wording is still okay because the correspondence itself is exact up to allowed precision.
• Now, the corrections for relativity are routinely used not as something to check with experiment, but as a necessary correction that must be applied because time dilation is real, and the relativistic equations do tell you with complete accuracy what correction factor is required for it. (There's a difference between accuracy and precision.)

This is more than enough to prove that the idea of no time dilation is wrong. Science never gives final proof of a new theory; that's why the notion of "falsification" is used so widely. The relativistic formulae for time dilation have been consistent with all attempts to test them, even as tests of greater and greater precision are applied.

Cheers -- sylas

Keeping our focus with the H&K experiment in 1971 I recommend you read Dr. A. Kelly's critique of the test. The "errors" weren't just a result of usual experimental errors but bad science. I'll let the work speak for itself. Atomic clocks are always drifting, falling out of time, etc. etc. and have to constantly be updated, pulled from service, etc. due to these reasons. I'm not crying "conspiracy" but due to the fact the GPS system is run through a military organization we can not investigate or corroborate the topic as we can in a civilian environment. Their explanations, motivation, information, etc. that the military gives out to the public on these matters are, by the very nature of a military establishment, done so for reasons which must always be taken as suspect whether true or not. As Winston Churchill called it: "A bodyguard of lies". Your "details of interest" are more rhetorical than factual. I would respond to them in detail but that would be a bit lengthy. Dr. Kelly's critique did not claim falsification, just a critique of technique. Have you read it? Please do. He doesn't deny time dilation, he simply states the particular experiment by H&K proves nothing and after reading it I find the critique very plausible. Of course some snide-*** out there will say so what or something worse but hey, that's their problem, not mine.

 

[Dmitry67]

I'm not crying "conspiracy" but

Yes, you are :)

 

[ThomasT]

Yes, but your statements indicate that a resulting change in tick rate is caused by 1, even though we would get the same exact resulting tick rate without 1. That indicates the resulting tick rate wasn't caused by 1.

Note that 1 = accelerating the traveling clock.

There's an invariant relationship between accelerating the traveling clock and the difference between the two clocks when they're reunited back on earth.

I'm not sure what you're saying above.

In Earth's frame, the ship's clock ticks at the same (slow) rate after acceleration as it did before the acceleration.

So the Earth twin will see no change in the tick rate of the traveling clock during the trip?

A change in v may or may not coincide with acceleration of the clock, but will affect its tick rate equally either way.

I thought that "change in v" = "acceleration".

 

[Janus]

At the risk of appearing to take sides, let me make a comment in support of ThomasT's assertion. If you study the Hafele & Keating's experiment from 1971 you will see it was necessary to predict the time dilation effect of both Special and General Relativity. Special Relativity being the Kinematic Relativity and General being the Gravitional. Now, correct me if I'm wrong but Gravity, to my understanding, is a Force, correct? Well, to invoke the name of Newton, he said that Force (F) is equal to mass times acceleration (ma). F = ma. Of course you know all this and I don't mean to suggest you don't. Just a reminder of the point for the argument at hand. The presence of gravity implies acceleration and since gravity (so it is said) affects the rate of an ideal clock in General Relativity then so does acceleration.

If Thomas T is asserting that acceleration affects the rate of the clock as opposed to an actual dilation of time then he has my vote for now. May I suggest (as have others more knowledgeable than myself) that this time dilation phenomena in a gravitational field (accelerration) is analoguous (spelling?), but not exactly, to a chemical rate of reaction in varying temperature regimes.

I hope I haven't offended either of you in bringing this up. God Bless all of you.

Just to add a little to what DaleSpam has already noted about GR time dilation being due to potential not acceleration. One example would be a uniform gravitational field (one that does not change strength with height). In such a field two clocks at different heights would run at different speeds even though they experience the same acceleration.
While it would be difficult to find a perfectly uniform field, the argument can still be used to examine fields generated by different masses. For example, the while the surface gravity of Uranus is slightly less than that of the Earth, the depth of the of the field is greater, and a clock on Uranus would run slower than a clock on the Earth.

A more practical example would be GPS satellites. In order to remain accurate, they have to have their clocks pre-adjusted to account for both SR and GR time dilation, the higher the orbit, the greater the GR adjustment. If GR time dilation were due to experienced acceleration, then a clock in a free fall orbit experiences none, and it wouldn't matter what the altitude of the satellite was in terms of the GR part of the dilation.

You just can't make "time dilation by acceleration" match up with the time dilation factors we actually see under real circumstances.

 

[ThomasT]

How is it supported by the experimental results? You have not given an equation yet that we can compare to experimental results. I repeat my earlier request for the equation describing this relationship between acceleration and tick rate.

What about this:

The tick rate is r(1-(v/c)2)0.5, where v is the relative velocity of the clock and the observer determining a tick rate, and r is the tick rate of the clock at rest.

When the velocity of the traveling clock changes (when it's accelerated), then its tick rate (wrt the stationary earthbound observer) changes.

 

[jadgerz]

Yes, you are :)

You must be that snide-*** I was referring to. Disinformation is part and parcel for military. They, and with good reason, never give out the truth. Never, never, always remember that.

Forgive me if I can't respond to everyone's comebacks on the topic. Some of your responses simply don't make sense by the grammar used and I simply can't respond. Here's an example which I hope sylas will forgive me for using but it typifies what I am saying:

•In 1971, there was already no credible doubt of the result.

Now what does this mean? Before or after the test? What does "...already no credible doubt" mean? What's "credible"? Does he mean "already" in 1971? Of course not, that's when the test was performed. If you read Dr. A. Kelly's critique he shows H&K were doubtful of their own results. Does the sentence really mean that in 1971 there were already no credible doubt as to what the result would be? "Credible" is one of the most subjective words in the English language.

Forgive me sylas but many of your comments are "ambigious" but I do appreciate your responses. Anyways, here's a question for you learned folks. Simple answer please and I'll be your best friend if you do.

If time dilation is a fact, which many here say it is, then is it "Time Travel"? In other words does an object leave the present (relative present of course) and travel into the future or past?

 

[jadgerz]

If GR time dilation were due to experienced acceleration, then a clock in a free fall orbit experiences none, and it wouldn't matter what the altitude of the satellite was in terms of the GR part of the dilation.

Janus, you really need to rethink this statement. Are you saying a clock in a free fall orbit does not experience acceleration? I'll give you the opportunity to reconsider this one. See what I nice guy I am?

 

[Dmitry67]

If time dilation is a fact, which many here say it is, then is it "Time Travel"? In other words does an object leave the present (relative present of course) and travel into the future or past?

Time dilation does not help to time travel

But thank you, I've never heard of such conspiracy before. Americans never landed on the Moon - yes, alien corpses - yes, but military hiding the correct equations from physics - that made my day :)

 

[edpell]

This is a common misconception. Gravitational acceleration is not what affects ideal clocks in GR, it is the gravitational potential.

Yes, and since gravitational potential goes as 1/r and the amount of matter "out there" goes as r^2 my local gravitational potential is mostly set by "the distant stars". Yes, we must take into account the finite speed of propagation of the gravitational potential, it is not instantaneous action at a distance.

 

[Dale]

What about this:

The tick rate is r(1-(v/c)2)0.5, where v is the relative velocity of the clock and the observer determining a tick rate, and r is the tick rate of the clock at rest.

When the velocity of the traveling clock changes (when it's accelerated), then its tick rate (wrt the stationary earthbound observer) changes.

That is the same as the equation I gave in https://www.physicsforums.com/showpost.php?p=2531754&postcount=160". So if that is what you mean, then we are obviously in agreement. I am glad we straightened that out.

 

[Janus]

If GR time dilation were due to experienced acceleration, then a clock in a free fall orbit experiences none, and it wouldn't matter what the altitude of the satellite was in terms of the GR part of the dilation.

Janus, you really need to rethink this statement. Are you saying a clock in a free fall orbit does not experience acceleration? I'll give you the opportunity to reconsider this one. See what I nice guy I am?

We are not talking coordinate acceleration. We are talking proper acceleration, or the acceleration measured by an accelerometer. An accelerometer attached to a clock in orbit would read zero no matter the altitude of the orbit.

 

[jadgerz]

Time dilation does not help to time travel

But thank you, I've never heard of such conspiracy before. Americans never landed on the Moon - yes, alien corpses - yes, but military hiding the correct equations from physics - that made my day :)

Did I say that? Not me!

 

[jadgerz]

We are not talking coordinate acceleration. We are talking proper acceleration, or the acceleration measured by an accelerometer. An accelerometer attached to a clock in orbit would read zero no matter the altitude of the orbit.

Try again Janus. Are you saying all those inertial guidance systems carried on all those spacecraft (mercury, gemini, apollo, etc.) were just for looks?

 

[DaveC426913]

Did I say that? Not me!

You did conclude that time travel exists. You equated time dilation with time travel. Since we see time dliation every day, your logic tells you that time traveling is indeed occurring.

Which it is - if you accept that as a definition of time travelling. That family on the top of Mt. Rainer experienced a few more microseconds than we did. If you want to look at that as time travel, so be it.

 

[jadgerz]

You did conclude that time travel exists. You equated time dilation with time travel. Since we see time dliation every day, your logic tells you that time traveling is indeed occurring.

Which it is - if you accept that as a definition of time travelling. That family on the top of Mt. Rainer experienced a few more microseconds than we did. If you want to look at that as time travel, so be it.

I ASKED the question as to whether other people in the forum consider time dilation as time travel. And did not say that it was. What do you think it is?

 

[edpell]

I ASKED the question as to whether other people in the forum consider time dilation as time travel. And did not say that it was. What do you think it is?

I consider time dilation to be time travel but not a vary useful form of time travel as the gammas involved for interesting FORWARD movement in time say 1000 seem impractical to me.

 

[jadgerz]

A person on Earth "observes" the flashes [let us say the clock on the ship emits a light flash every one second ship time] at a lower frequency due to the, distortion caused by the, finite speed of propagation of light. Versus if we have [this is a thought experiment] a signal that propagates at say 10^100 times c would the observer on Earth see the flashes at a rate of one per Earth clock second?

Edpell, please forgive me. In a later blog I suggested your very same experiment as an experiment to test time dilation. With the exception I proposed trying to speed up a space probe at a "significant" percentage of light speed so there would be no doubt as there are at these nano and micro second variances that any possible change in "flash time" could be attributed to time dilation. I was unaware of this blog on your part and forgive me if I have made it seem it was my proposal. Credit where credit is due. It is yours.

 

[edpell]

In the sense that I here in 2010 can go to the year 3010 while aging only 1 year (with a gamma of 1000) I would call it time travel. There is no jump, no discontinuity of time. The time in the two frames are stretched one with respect to the other.

In changing frames time and space are no longer orthogonal. I do not know how we wish to word this in English. In the still frame the moving person seems to spend more of their effort in motion in the spatial dimensions and less in the time dimension. Note I said "seems to" so do not throw stones instead let us hear your alternative wording. Thanks.

 

[edpell]

Edpell, please forgive me. In a later blog I suggested your very same experiment as an experiment to test time dilation. With the exception I proposed trying to speed up a space probe at a "significant" percentage of light speed so there would be no doubt as there are at these nano and micro second variances that any possible change in "flash time" could be attributed to time dilation. I was unaware of this blog on your part and forgive me if I have made it seem it was my proposal. Credit where credit is due. It is yours.

My memory is that no one responded to my thought experiment. I still think it is a interesting question.

 

[jadgerz]

My memory is that no one responded to my thought experiment. I still think it is a interesting question.

It is a good one. I would be better as a "real" experiment rather than a thought experiment however. I have to admit I'm a skeptic when it comes to time dilation even though many on this thread claim otherwise. My "variant" of the experiment would be to get a space probe speed up to a "significant" percentage of the speed of light. A speed which would put to rest all doubts as to whether any observed time dilation phenomena was truly a result of velocity. On board would be a beacon pre-set to give a "flash" at a known precise interval. Let's say that flash interval was exactly one second as you suggested. If an observer on Earth saw the flash as every 1.01 second he would know that an observer on the probe would be seeing the flash at 1.00 second, because it was pre-set thus, and the Earth observer could conclude there is something to the time dilation theory. I hope I made sense with that. I just don't believe the round the world airplane trips with atomic clocks puts the matter to rest.

 

[Dale]

We are not talking coordinate acceleration. We are talking proper acceleration, or the acceleration measured by an accelerometer. An accelerometer attached to a clock in orbit would read zero no matter the altitude of the orbit.

Try again Janus. Are you saying all those inertial guidance systems carried on all those spacecraft (mercury, gemini, apollo, etc.) were just for looks?

Janus is correct. An accelerometer detects proper acceleration, not coordinate acceleration. So an accelerometer in orbit (or any free fall) reads 0. A spacecraft is not always in free fall, so the fact that it reads 0 in orbit doesn't prevent it from being useful.

 

[edpell]

Let's say that flash interval was exactly one second as you suggested. If an observer on Earth saw the flash as every 1.01 second he would know that an observer on the probe would be seeing the flash at 1.00 second, because it was pre-set thus, and the Earth observer could conclude there is something to the time dilation theory. I hope I made sense with that. I just don't believe the round the world airplane trips with atomic clocks puts the matter to rest.

I think the airplane experiment has been discussed earlier (not sure which thread) and we concluded the time change effect was not a SR effect but a GR effect.

Yes, I too would find a simple experiment with a noticeable gamma most satisfying.

Yes, physics friends, muon decay in accelerator labs is probably that simple experiment but it would be so much cooler with an on-board human made clock.

 

[edpell]

What about lateral red shift? That is if an light emitting object in space is moving toward us we see a blue shift and if it is moving away from us we see a red shift. If an object is moving laterally we should also see a red shift due to the time dilation effect slowing the frequency of the particular transition observed. This may have already been done? If not this seems like a great experiment waiting to be done. How exactly you determine the motion of the object by means other than red shift is the question. I would think jets emitted from things that have jets (i.e. neutron stars with accreting matter?) would work.

 

[jtbell]

What about lateral red shift?

This is called the transverse Doppler effect and has been observed:

http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html#Tests_of_time_dilation