Time dilation argument

1. Sep 21, 2010

bhsmith

I am interested in a reason as to why time dilation is not possible. I have done some sloppy google research and have found few people that think it is false.
Is there anyone that could give me a basic explanation of why it might not be true? other than the fact there is no proof of it.

2. Sep 21, 2010

George Jones

Staff Emeritus
I am not sure what you mean; time dilation is observed routinely everyday.

3. Sep 21, 2010

bhsmith

But is there any reason why it would not be true? whether you believe it to be or not.

4. Sep 21, 2010

George Jones

Staff Emeritus
It is not a matter of belief, it is a matter of scientific observation.

5. Sep 21, 2010

bhsmith

ok i'm asking the wrong question i think.

What is an example of experimental evidence that has proved time dilation?

6. Sep 21, 2010

starthaus

g-p-s

7. Sep 21, 2010

DaveC426913

As starthaus cryptically points out, both SR and GR have to be factored in to GPS coordinates because if they were not, they would not work.

i.e. NASA guys send up some satellites, use them to range stuff on Earth. Numbers come up short. NASA figures in time dilation. Numbers work perfectly. (Not really but essentially.)

Last edited: Sep 21, 2010
8. Sep 21, 2010

Rebound

If I recall correctly, one of the first empirical observations was done using 2 synchronized atomic clocks, one of which stayed on the ground and the other taken up in a plane. Although the actual difference in the time measured was very small the clocks were accurate enough to measure it.

9. Sep 21, 2010

DaveC426913

And nowadays, time dilation measurements are http://leapsecond.com/great2005/" [Broken]. << awesomeness

Last edited by a moderator: May 4, 2017
10. Sep 21, 2010

starthaus

Yes, the Haefele-Keating experiment, a poor cousin to GPS.

11. Sep 21, 2010

Passionflower

I think this experiment together with the Eddington experiment at Principe are rather poor as the positive outcomes seem to have been caused by experimenter bias.

With contemporary precision both experiments are now unquestionably indicative of the validity of GR but with the available precision at the time a positive result could not have been derived.

There is no excuse for experimenter bias.

12. Sep 21, 2010

Staff: Mentor

You can find some in the sticky post at the top of this forum, titled "FAQ: Experimental Basis of Special Relativity".

13. Sep 21, 2010

JesseM

What's your source for that claim? The Hafele-Keating experiment has been criticized by some anti-relativity types in non-peer-reviewed publications, but I get the impression that mainstream scientists think the criticisms are basically misguided. For example, the Experimental Basis of Special Relativity page from John Baez's site has this to say:

14. Sep 21, 2010

starthaus

You must have missed my first answer. :-)

15. Sep 21, 2010

Passionflower

This is not about proving relativity wrong, I do not believe Kelly and Louis Essen, the inventor of the atomic clock, are anti relativists. I think they are simply people who like to be honest about what an experiment can show and what not and who abhor experimenter bias.

For anyone who wants to check for themselves, here are the results from the experiment and the way the adjustments where done: http://tycho.usno.navy.mil/ptti/1971/Vol%2003_17.pdf [Broken]

I would assume you agree with me that if experimenter bias is shown in any experiment, even if later, with higher accuracy, a theory is proven right, it is still unacceptable and inexcusable and is something that should not be brushed away?

I take it you have the same attitude about the Principe experiment, it was all perfectly derivable?

Last edited by a moderator: May 4, 2017
16. Sep 21, 2010

JesseM

You're misinformed, A G Kelly certainly is an anti-relativist, just look at http://www.worldnpa.org/pdf/ebooks/Kelly%20-%20New%20Theory%20of%20the%20Behavior%20of%20Light.pdf [Broken] section says:
Sure, but if a few anti-relativity types argue for experimental bias in non-peer-reviewed publications but no one in the mainstream physics community seems to think their criticisms have any merit, then short of making a detailed study of the experimental issues myself I'm inclined to bet it's very unlikely that the criticisms really do have merit and that the mainstream physicists are all misguided or involved in a cover-up.
No, I didn't mention that one because I hadn't looked into it, I'm certainly open to the possibility that some famous experiments may have been flawed if at least some mainstream scientists hold this view. This Scientific American article suggests some respected science historians feel that Eddington did make a mistake in throwing out some data, although others feel he had legitimate reason for doing so since the data was collected from an instrument that had lost focus during the eclipse.

Last edited by a moderator: May 4, 2017
17. Sep 21, 2010

Passionflower

Well that certainly changes things. I made some updates just before you posted this so my quote is now a bit different, but in any case, then we obviously have to question Kelly and Essen's argument for the same reason, namely bias. Again this is not about proving relativity wrong, but about the validity of the particular experiment.

But promoting questionable experiments is a breading ground for anti-relativists. Instead of the HK experiment there are many much better and certainly unquestionable experiments. So I prefer we quote those than this piece of 'relative antiquity'.

Yes, that seems to be the case, and if it was intentional there is no excuse for that IMHO. Again, here later experiments show clearly the predicted effect.

And good for Scientific American! While in western culture truth is generally thought to be more important than 'saving face' there are cases in science where 'saving face' seems more important, from, to stay with relativity, math errors by Einstein or Hilbert to Eddington's experiment in Principe and perhaps also the HK experiment.

Last edited by a moderator: May 4, 2017
18. Sep 21, 2010

JesseM

Of course anytime you bring up the HK experiment you can mention that more accurate experiments (including GPS) have been done since, but there's no reason to make the concession to anti-relativists that the HK experiment is "questionable" just because some anti-relativists have raised questions about it in non-peer-reviewed publications whose arguments have not been accepted by any mainstream scientists. That would be a bit like a biologist agreeing not to mention Archaeopteryx as evidence for evolution because some creationists have made unfounded speculations that it's a hoax or that it has no real reptile-like characteristics.
If they knew the instrument had lost focus doing the crucial period when the data was being collected it seems to me there would be a reasonable case for throwing out that data.
I haven't seen any attempt to "save face" on the Eddington experiment, there seems to be thoughtful debate about whether Eddington's experimental procedure was reasonable or not. And what "math errors" do you think scientists tried to sweep under the rug?

19. Sep 22, 2010

starthaus

Agreed, this is why my first answer was "GPS". Such that there is no discussion about validity.

20. Sep 22, 2010

bcrowell

Staff Emeritus
FAQ: Was the famous Hafele-Keating experiment bogus?

No. Certain internet kooks, including someone named A.G. Kelly, have produced reanalyses of the Hafele-Keating data in an attempt to disprove relativity. This is just silly, because the experiment was reproduced four years later to better precision, and again, to much higher precision, in a 25th-anniversary reenactment. The GPS system depends on general relativity, so any time you use a GPS receiver, you're reproducing relativistic time dilations of the type seen by Hafele and Keating.

Hafele and Keating, "Around the world atomic clocks:predicted relativistic time gains," Science 177 (1972) 166.

Hafele and Keating, "Around the world atomic clocksbserved relativistic time gains". Science 177 (1972) 168.

Ashby, "Relativity in the Global Positioning System," http://www.livingreviews.org/lrr-2003-1