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Einstein's Theory To Go Beta Testing
pinqkandi writes: "This article over at CNN looks into the relativity of Einstein's theory of relativity (pun intended) as equipment becomes more and more precise. Soon atomic clocks will be placed in the International Space Station to analyze the accuracy of Einstein's theories. One of the lead researchers says that if Einstein's theory is not right, it will only need minor adjustments to account for changes in space-time, due to its deadly accurate precision."
If you don't understand either one, take a look
here:
is here, with a little more information on Lorentz and CPT violation.
AFAIK the current GPS satelite system makek adjustments for relativity in the signals it is sending around and they have been adjusting for this for years. See the articles at Metaresearch and lsu.edu for more info.
It hasn't been proved, it just hasn't been disproved. That's why it's a theory.
-Tolerate my intolerance
The tests that Kostelecky is proposing are somewhat different than the earlier tests. In the previous tests researchers looked for changes in the frequency difference between two clocks when they were moving at different velocities or when they were at different heights in the earth's gravitational field. These tests looked at standard relativity theory (either special or general) and checked that the predictions it made were correct. In the new tests, one looks for changes in the frequency of a clock as it points in different directions (which would be akin to an ether, picking out a prefered direction in space) or a similar effect as the velocity of the clock changes.
These tests have been performed on the ground recently by measuring the frequency of a clock as its direction relative to the stars changes due to the rotation of the earth. (For example, see Phillips, et al., Physical Review D 63, 111101 (2001) or Physical Review Letters 85, 5038 (2000)- showing off is always good.) In space, one could use the faster rotation of the space station as the atomic clocks in space which may substantially outperform ground based clocks.
Technically, you're never going to get zero gravity. And yes, you're right, ISS isn't anywhere near that -- it's in orbit, and uses gravity to stay that way. ISS and the like are weightless (or near weightless) because they are effectually in a free fall; this state is termed "microgravity".
Atomic clocks on ISS are a trivial test of relativity compared to Gravity Probe B, hopefully to be launched soon after DECADES of development. A one-pager "GPB for Dummies" is here. GPB tests not for alterations in time but another phenomenon known as "frame dragging" which has never been directly measured. There's been lots of criticism about GPB as being too ambitious, so there's been lots of independent reviews.
An article (membership requires) in May Physics Today details the extensive corrections GPS must make for both special relativity (velocity corrections) and general relativity (gravity corrections). This has tested Einstein every day of the past 20 years, and he has held up.
They already have quite accurate measurements on the effect of relativity on reference frames moving at different speeds and at different potentials in a gravity well. They are dead on, so far. For example, the GPS system (which uses atomic clocks generating signals to locate where you are) needs to have its clocks reset periodically because they get out of sync with ground clocks. I'm sure there is more than enough literature on this part of the theory for anyone to be happy. The only place where i would begin to question it is when you are dealing with an extreme difference in gravity (not on the velocity side, that has already been tested). I suppose (since it is a MODEL after all, just an extremely good one) that when gravity is very large other terms might begin to show themselves, if they do exist.
Have a look
here if you want to read more regarding GPS birds and relativity
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whereas the general theory is concerned with bodys that are accelerating ( In general relativity acceleration and gravity are equivalent).
Common misconception. Acceleration and gravity are not equivalent in General Relativity. They are *locally* (that word is extremely significant here) indistinguishable. The fact of the matter is that Special Relativity can handle acceleration just fine by using calculus. General Relativity is only needed where spacetime is not flat (i.e. in the presence of gravity), since the two postulates of Special Relativity only hold in regions of flat spacetime.
As coauthor of the Lorentz-violation paper being discussed, I'd like to reply to a few comments that have been made. This comment seems like a good starting point.
_Special_ relativity and quantum mechanics have no trouble getting along. In fact, the so-called Standard Model of particle physics, based on relativistic quantum physics, is an enormously successful theory. The trouble lies in getting relativistic gravity (i.e., _general_ relativity) to play nice with quantum mechanics. This is where string theory comes in.
The good thing about string theory is that it allows gravity and quantum mechanics to get along. The bad thing about string theory is that there is absolutely _no_ experimental evidence for it, and there are almost no possible tests of it that could be conducted in the near future. Lorentz violation is a major exception:
The afore-mentioned Standard Model obeys a certain symmetry called ``Lorentz symmetry'', which lies at the heart of special relativity. However, string theory allows Lorentz symmetry to be broken. Thus, any experimental detection of Lorentz violation could be a great signature of string theory, and, maybe, quantum gravity. Moreover, there exist current experiments that are capable of detecting Lorentz violation to a very high precision.
To summarize: We are studying Lorentz violation because (1) It is a possible signature of quantum gravity, and (2) It can presently be studied to very high precision.
Chuck
Actually, GPS knows about this and takes advantage of it. It is the only consumer relativity application I know of.
The GPS SV's are going about 3900 m/s which is a sufficient percentage of the speed of light for relativity to come into play. If relativity weren't taken into account and Einstein obeyed, you'd be off by ~100 meters.
The correction could be done in the receiver or the signal could be biased in the SV. Following the Principle of Alice's Restaurant:
Factoring this correction into the SV, the onboard clocks use a frequency of 10.22999999543 MHz and your GPS receiver uses 10.23 MHz. This simplifies the GPS receiver software immensely.
GPS was designed during the 1970's by some really smart forward thinking guys.