Has Time Dilation been tested?

[Rasori]

Honestly, has it? At 17,000 mph in orbit, I'd think it'd be at least partially possible, especially over an extended period of time.

 

Maybe they're planning on doing tests on the ISS when they finish it, I don't know. But I'm really curious if any tests have been done/planned for something other than a clock--a clock is just a measurement of time, and I'm not saying it's not accurate, but I'd be more willing to rely on something like the following:

 

a crew of astronauts is supposed to serve on the ISS for one month. With them, they bring many materials, including 1 kg of Th-234. After their 30-day trip, less than 500g of Th-234 should be left. However, if time dilation has taken effect, about 500g, maybe more, should still be left.

 

Now, I'm sure we can get more accurate measurements than "less than 500g." I don't know the formula, but I'd bet it's possible to predict how much time should have been dilated and so how much of the radioactive material is left. I'm not sure if time dilation can act well enough in that amount of time--it might need to be a larger sample of it that's in motion for longer, or a different material. But I think it could be done, and I also think it would be quicker proof than leaving someone up in space for 40 years and seeing if he's wrinkled or not, and more definitive than just comparing clocks.

 

Tell me what you think, if you care enough to.

[5614]

I know that it certainly has been prooven on many occasions. Though I cannot tell you them off by heart (try a google search, or even within SFN here). Swansont can tell you if you wait!

[bascule]

At 17,000 mph in orbit, I'd think it'd be at least partially possible, especially over an extended period of time.

 

The atomic clocks aboard the GPS satellites have to compensate for relativistic effects. See this page for more information:

 

http://www-astronomy.mps.ohio-state.edu/~pogge/Ast162/Unit5/gps.html

[timo]

I was hoping to find a more detailed explanation but in the end I didn´t want to keep looking any longer and this short text has all the information needed: http://hands-on-cern.physto.se/hoc_v21en/page_text/sm_paty5.html

 

To sum it up: Considering radioactive decays as a test for time dilatation is not only a very good but also a very old idea.

[Rasori]

Aha. Well, that makes me feel better. I don't know why, but I just don't think clocks are foolproof. Nice to know that something as easy as this has been done.

[sergey500]

Yes it has, two atomic clock on two different jets, flying at different high speeds, caused .00000001 dilation (or more zeros)

[Severian]

Time dilation is directly seen by the decay of particles in the upper atmosphere. Muons are produced by cosmic rays hitting the upper atmosphere, but since muons decay very very fast, you might expect them to decay before reaching the Earth. However, they do reach the Earth: they are travelling so fast that they suffer time dilation, making them live long enough to reach us before decaying. Without SR, they would decay long before they reach us.

[slur]

It should be noted that "time dilation" is relativistic. From the POV of the earth Muons evolve slower, but from the POV of the Muon it evolves in normal time. It is not that the Muons are moving fast, but that they are moving fast relative to us. So you would expect to detect fewer Muons on the trailing side of the Earth's orbit than you would on the leading side, for example.

[reyam200]

since they reach the earth. can they cause cancer? prolonged exposure to any radiation is harmful. i guess it would depend on the strength of the radiation.

[swansont]

since they reach the earth. can they cause cancer? prolonged exposure to any radiation is harmful. i guess it would depend on the strength of the radiation.

 

Probably. But it's part of the natural background, and you can't do all that much about it.

[Klaynos]

We're all being hit by radiation all the time, not much you can do about it...

[the tree]

prolonged exposure to any radiation is harmful.

Are you including light and heat in that? Because we sorta need them to live.

We're all being hit by radiation all the time, not much you can do about it...

Sure there is, just get a lot of tin foil, some lead paint and an industrial freezer or two, that ought to cut out a fair amount.

[Klaynos]

Are you including light and heat in that? Because we sorta need them to live.

Sure there is' date=' just get a lot of tin foil, some lead paint and an industrial freezer or two, that ought to cut out a fair amount.[/quote']

 

 

Ok, nothing sensible!

[J.C.MacSwell]

Originally Posted by Klaynos

We're all being hit by radiation all the time' date=' not much you can do about it... [/quote']

 

 

 

Ok, nothing sensible!

 

 

 

Sunscreen?

[CPL.Luke]

sunscreen won't block out the x-rays and gamma-rays and various oter particles that strike you every day.

 

 

beside the statistacal probability that you would get cancer from the background radiation is so low that you shouldn't think about it.

[J.C.MacSwell]

sunscreen won't block out the x-rays and gamma-rays and various oter particles that strike you every day.

 

 

beside the statistacal probability that you would get cancer from the background radiation is so low that you shouldn't think about it.

 

Still a sensible thing you can do about some radiation.

[Saint]

Time dilation is directly seen by the decay of particles in the upper atmosphere. Muons are produced by cosmic rays hitting the upper atmosphere, but since muons decay very very fast, you might expect them to decay before reaching the Earth. However, they do reach the Earth: they are travelling so fast that they suffer time dilation, making them live long enough to reach us before decaying. Without SR, they would decay long before they reach us.

 

What is the mechanism that drives radioactive decay? I assume you know what the mechanism is, and that that mechanism could never be influenced by acceleration or velocity. I assume that based on the fact that you jumped all the way to "time dilation" in order to show why muons reach the Earth. Or, by "time" do you simply mean the physical mechanism internal to the muon? If "time" is simply based on physical rates of vibration, then wouldn't it be more accurate, and less confusing to simply call it that?

[CPL.Luke]

What is the mechanism that drives radioactive decay? I assume you know what the mechanism is, and that that mechanism could never be influenced by acceleration or velocity. I assume that based on the fact that you jumped all the way to "time dilation" in order to show why muons reach the Earth. Or, by "time" do you simply mean the physical mechanism internal to the muon? If "time" is simply based on physical rates of vibration, then wouldn't it be more accurate, and less confusing to simply call it that?

 

radioactive decay occurs because of the weak nuclear force. When particles decay they averagely do it in a certain period of time (its somewhat based on a probability), the probability that a muon would last long enough to reach the surface of the earth is so low that it would be impossible to see them in the numbers that we do (sattelites have measured the amount of radiation that hits the atmosphere).

 

The reason why the particles do in fact reach us is because there extreme velocity relative to us causes there time to be dilated according to special relativity, so from the particles perspective very little time has ellapsed between its entering the atmosphere and it hitting the ground.

[Saint]

radioactive decay occurs because of the weak nuclear force. When particles decay they averagely do it in a certain period of time (its somewhat based on a probability)' date=' the probability that a muon would last long enough to reach the surface of the earth is so low that it would be impossible to see them in the numbers that we do (sattelites have measured the amount of radiation that hits the atmosphere).

 

The reason why the particles do in fact reach us is because there extreme velocity relative to us causes there time to be dilated according to special relativity, so from the particles perspective very little time has ellapsed between its entering the atmosphere and it hitting the ground.[/quote']

 

So the answer to my question about the mechanism for radioactive decay is that you don't know. Yes, we know it happens, but do we know what actually casues an individual instance of decay? Nope. Do we know how extreme velocities will alter this unknown mechanism? Nope. Until we understand this mechanism, I suggest taking the muon example off the "proof" list for time dilation, unless, as I stated earlier, we are taking "time" to simply mean the physical rate of vibration.

[CPL.Luke]

yes we do know, its through the weak interaction mediated by the W and Z bosons, severian could do a much better job explaining it than I could, but YOU could also just pop over to wikipedia and read the relevant article on the weak interaction and radioactive decay.

 

as for time, your idea of it is not quite accurate. Time is just a dimension in which we measure the intervals between events, when a muon is moving far slower relative to us (they are created in particle accelerators all the time) the time of decay (in our reference frame) is lower.

 

if you want more proof of time dilation look at the GPS system. The computers aboard those sattelites have to compensate for time dilation in order to give the user an accurate reading. If they did not do this your GPS reciever would alter your position by 10km every day.

[timo]

So the answer to my question about the mechanism for radioactive decay is that you don't know. Yes, we know it happens, but do we know what actually casues an individual instance of decay?

The interaction terms in the lagrangian.

Nope.

What do you call "know"? A physicists "know" is "have a mathematical description".

Do we know how extreme velocities will alter this unknown mechanism?

Yes. Due to relativity you know how to transfrom back and forth between the system of rest and a moving system. Do the calc in the system of rest and transform.

Nope.

Unless one knows the basics of relativity.

 

unless, as I stated earlier, we are taking "time" to simply mean the physical rate of vibration.

Severian mixed up his times a bit. That´s not uncommon since physicists tend to talk to and write for people who can tell out of context which time is meant. The "they decay very fast"-part was about eigentime, the "live long enough to reach us"-part was about coordinate time.

Sadly, I do not understand what you want to vibrate.

[swansont]

radioactive decay occurs because of the weak nuclear force.

 

Beta decay is driven by the weak force, but AFAIK alpha decay isn't.

[Severian]

So the answer to my question about the mechanism for radioactive decay is that you don't know. Yes, we know it happens, but do we know what actually casues an individual instance of decay? Nope. Do we know how extreme velocities will alter this unknown mechanism? Nope. Until we understand this mechanism, I suggest taking the muon example off the "proof" list for time dilation, unless, as I stated earlier, we are taking "time" to simply mean the physical rate of vibration.

 

We can predict the lifetime of the muon in its rest frame using our models of particle physics. Then we can ask what its lifetime in the laboratory (ie. the Earth's rest frame) would be if time dilation were true. Then we can test this prediction with observations and do indeed find it to be correct.

 

This is pretty good evidence for time dilation.

[swansont]

So the answer to my question about the mechanism for radioactive decay is that you don't know. Yes, we know it happens, but do we know what actually casues an individual instance of decay? Nope. Do we know how extreme velocities will alter this unknown mechanism? Nope. Until we understand this mechanism, I suggest taking the muon example off the "proof" list for time dilation, unless, as I stated earlier, we are taking "time" to simply mean the physical rate of vibration.

 

Under the assumptions of relativity, the speed of an object, relative to another, does not change the laws of physics. So the mechanism of the decay is unchanged - as far as the muon is concerned, it is at rest. And from this point of view, the decay rate is affected just as relativity predicts when viewed from another frame of reference. So there is absolutely no reason to exclude this observation from the list of things that confirm time dilation.

 

And, As CPL Luke has mentioned, there is GPS. And there is also the Hafele-Keating experiment of clocks on airplanes. And the Vessot experiment of a Hydrogen maser on a rocket (that's mostly GR, though). Atomic fine structure has relativistic terms in it, that's confirmed by spectroscopy. And so on and so forth.

[YT2095]

Sure there is, just get a lot of tin foil, some lead paint and an industrial freezer or two, that ought to cut out a fair amount.

 

it would cut SOME sure, but when you consider there are particles that can pass clean through the entire planet and come out the other side "unaware" that it`s even passed through anything, lead`s not going to help much