# A problem with the theory of relativity? **URL:** \ **Category:** Factual Questions\ **Created:** [July 21, 2000, 2:12am UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310 "2000-07-21T02:12:29Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Diceman](https://avatars.discourse-cdn.com/v4/letter/d/22d042/32.png) [@Diceman](https://boards.straightdope.com/u/Diceman)\ **Post date:** [July 21, 2000, 2:12am UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310/1 "2000-07-21T02:12:29Z")
This is a question inspired by the ‘faster than light’ thread. IIRC, it’s the Special Theory of Relativity that theorizes that time should slow down for a body as it approaches the speed of light. Recently, I heard an interesting argument challenging the validity of this effect. The argument goes as follows: Global Positioning System (GPS) satellites all have internal clocks. They orbit the earth at thousands of miles per hour, a much greater velocity than we on earth move at. Therefore, shouldn’t they be constantly going out of synch because time passes slower for them than it does for us? The difference in time would be very, very small, but over the course of a few years wouldn’t it become enough to cause a problem? What do the rest of you Einsteinien Dopes think of this argument? ---
**Author:** ![Bear\_Nenno](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bear_nenno/32/3358_2.png) [@Bear\_Nenno](https://boards.straightdope.com/u/Bear_Nenno)\ **Post date:** [July 21, 2000, 2:20am UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310/2 "2000-07-21T02:20:10Z")
I do not know how the satelites work, but your assumption that time is different for them is correct. Maybe they a program that adds an additional millasecond every year or whatever it is. Maybe the correct time is always beamed to the satelite like the way the atomic clock in Colorado sends a signal that sets clocks automatically every minute or so. They actually sell wrist watches that will pick up the signal. That way you will always have THE correct time. Scientists really did an experiment with two identical atomic clocks. One was put on a plane and flown around… the other stayed on the ground. After the plane landed, the two clocks showed different times. I think it was off by a few microseconds or something like that. I guess I could whipe the dust off the ole Physics book and give you the formula for Time Dilation (sp?) but someone like TC will be here soon enough with it anyway… -Bear ---
**Author:** ![JimOfAllTrades](https://avatars.discourse-cdn.com/v4/letter/j/ba8739/32.png) [@JimOfAllTrades](https://boards.straightdope.com/u/JimOfAllTrades)\ **Post date:** [July 21, 2000, 3:10am UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310/3 "2000-07-21T03:10:57Z")
> [@](#): > > Recently, I heard an interesting argument challenging the validity of this effect. The argument goes as follows: > > Global Positioning System (GPS) satellites all have internal clocks. They orbit the earth at thousands of miles per hour, a much greater velocity than we on earth move at. Therefore, shouldn’t they be constantly going out of synch because time passes slower for them than it does for us? The difference in time would be very, very small, but over the course of a few years wouldn’t it become enough to cause a problem? Actually, GPS satellites prove the theory, not challenge it. The reason is that they _are_ affected by the time dilation, the people who designed them knew they would be, and put in corrective measures (i.e. they screwed with the clocks enough to offset the expected error), and the fix is working. If the theory were wrong, the correction factor put in by the engineers would itself be a source of error, not a correction. Ugly ---
**Author:** ![Balance](https://avatars.discourse-cdn.com/v4/letter/b/ccd318/32.png) [@Balance](https://boards.straightdope.com/u/Balance)\ **Post date:** [July 21, 2000, 3:16am UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310/4 "2000-07-21T03:16:58Z")
IIRC, GPS satellite clocks are stratum-2 clocks–which means they are regularly updated from the stratum-1 clock at the Bureau of Standards to prevent time dilation (and other oddities) from desynchronizing them significantly. The clock in a GPS handset is a stratum-3 clock, and so forth. ---
**Author:** ![RickG](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rickg/32/5174_2.png) [@RickG](https://boards.straightdope.com/u/RickG)\ **Post date:** [July 21, 2000, 3:28am UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310/5 "2000-07-21T03:28:11Z")
Note that the GPS satellites do not only correct for Special Relativistic effects (velocity induced time dilation), but **General** Relativistic effects. For example, our clocks move slightly slower relative to the satellites because we are deeper in the Earth’s gravity well. Also, there are GR corrections due to the non-uniformity of the gravitational field. Suffice it to say that SR and GR are among the most precisely tested physical theories out there (and when I say theory, I mean ‘established as a correct model for all our observations,’ not just a wild guess). It’s been some time since I looked at it, but you might try finding a copy of Clifford Will’s book, Was Einstein Right? It contains extensive discussions of the experimental proof of GR, IIRC. (I audited Cliff Will’s graduate GR course, and took undergrad stat. mech. with him, when I was in college at Wash. U. in St. Louis–he’s a terrific teacher). Rick ---
**Author:** ![dorkbro](https://avatars.discourse-cdn.com/v4/letter/d/ed8c4c/32.png) [@dorkbro](https://boards.straightdope.com/u/dorkbro)\ **Post date:** [July 21, 2000, 3:28am UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310/6 "2000-07-21T03:28:22Z")
Just to pick a small nit … The theory of **Special** relativity dealt only with inertial reference frames - i.e. those in which there was no acceleration. In the case you are describing, we would also need to account for the difference in acceleration of us here on earth and the satellites orbiting above us. This is what Einstein deals with in the **General** theory of relativity. In fact, under general relativity, objects in regions of high gravitational potential (like the satellites) will experience time more rapidly than those in areas of low potential (like us on Earth). I am not going to pretend to be able to do the math well enough to figure out whether the effects of special or of general relativity will have the greater impact - but it is possible that the clocks on the satellites have to be adjusted because time is passing FASTER for them. Can someone with a little bit more recent instruction help me out here? (Or explain why I am completely wrong.) ---
**Author:** ![Bear\_Nenno](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bear_nenno/32/3358_2.png) [@Bear\_Nenno](https://boards.straightdope.com/u/Bear_Nenno)\ **Post date:** [July 21, 2000, 3:29am UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310/7 "2000-07-21T03:29:44Z")
Looks like my guess about the clock signal was right. And Balance does recall correctly > [@](#): > > The Master Control facility is located at Schriever Air Force Base (formerly Falcon AFB) in Colorado. These monitor stations measure signals from the SVs which are incorporated into orbital models for each satellites. The models compute precise orbital data (ephemeris) and SV clock corrections for each satellite. The Master Control station uploads ephemeris and clock data to the SVs. The SVs then send subsets of the orbital ephemeris data to GPS receivers over radio signals. - from [http://www.colorado.edu/geography/gcraft/notes/gps/gps\_f.html](http://www.colorado.edu/geography/gcraft/notes/gps/gps_f.html) ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [July 21, 2000, 5:48am UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310/8 "2000-07-21T05:48:50Z")
The time dilation formula is as follows: T = t(1 - (v/c)[sup]2[/sup])[sup]1/2[/sup] where t is the time that a clock on the ground ticks off, v is the speed of a plane zooming by, and T is the time that a clock on the plane ticks off. Since, for someone in motion, time slows down, T will be less than t. Quoth **Bear\_Nenno** : > [@](#): > > Scientists really did an experiment with two identical atomic clocks. One was put on a plane and flown around… the other stayed on the ground. After the plane landed, the two clocks showed different times. I think it was off by a few microseconds or something like that. I’ve heard that too, but does anyone have any specs on this experiment? The figures I’ve heard always seemed a little suspect to me. Just to confirm my suspicions, I worked out the Math for a plane going 1 km/s, generously faster than an [SR-71A](http://www.fortunecity.com/silverstone/toyota/47/fast_plane.html). At this speed, the time dilation would account for about one part in 1.8×10[sup]11[/sup]. That is, for the clocks to differ by one microsecond, the plane would have to fly for 50 hours. Of course, this is ignoring the afforementioned GR effects. At least it’s more believable than my friend who told me that high-speed pilots tend to live longer because they spend so long in a difference reference frame. :rolleyes: ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 21, 2000, 5:50am UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310/9 "2000-07-21T05:50:17Z")
If you want to get _really_ weird about it, the clocks on the GPS satellites _aren’t_ affected by relativity… But the clocks here on Earth are, so we have to correct for that. This is because while we’re being constantly accelerated here on Earth to the tune of 9.8 m/s/s, the satellites are in free-fall, not accelerating at all. Note an important point here: Under General Relativity, gravity is a fictitious force, in every way equivalent to the force you feel pushing you against the back of the seat in an accelerating car, for instance, or pressing you against the wall of the Rotor at the amusement park. It takes some getting used to, but it really does make sense. Oh, and just a minor quibble: It’s not a matter of “also” considering GR; when you’re working with GR, the SR comes automatically. Makes things a lot simpler. ---
**Author:** ![Bear\_Nenno](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bear_nenno/32/3358_2.png) [@Bear\_Nenno](https://boards.straightdope.com/u/Bear_Nenno)\ **Post date:** [July 21, 2000, 6:20am UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310/10 "2000-07-21T06:20:50Z")
Achernar, Haefele and Keating did the experiment I think. I could not give much more info without looking around for it. ---
**Author:** ![JonF](https://avatars.discourse-cdn.com/v4/letter/j/cab0a1/32.png) [@JonF](https://boards.straightdope.com/u/JonF)\ **Post date:** [July 21, 2000, 11:05am UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310/11 "2000-07-21T11:05:23Z")
> [@](#): > > Maybe the correct time is always beamed to the satelite like the way the atomic clock in Colorado sends a signal that sets clocks automatically every minute or so The GPS clocks are “steered”, but not that often. They are purposely set to run slow by by about 38,700 nanoseconds per day when sitting on the surface of the Earth so they don’t drift unacceptably (relative to our clocks when they are in orbit) between corrections. [What the Global Positioning System Tells Us about Relativity](http://www.metaresearch.org/mrb/gps-relativity.htm) [General relativity in the global positioning system](http://vishnu.nirvana.phys.psu.edu/mog/mog9/node9.html) > [@](#): > > the satellites are in free-fall, not accelerating at all Erk? GR says that acceleration is indistinguishable from gravitation, so I think you are formally correct; but in the sense of acceleration being the second time derivative of position, they’re constantly accelerating. They are also in a gravitational field. ---
**Author:** ![C\_K\_Dexter\_Haven](https://avatars.discourse-cdn.com/v4/letter/c/b2d939/32.png) [@C\_K\_Dexter\_Haven](https://boards.straightdope.com/u/C_K_Dexter_Haven)\ **Post date:** [July 21, 2000, 11:54am UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310/12 "2000-07-21T11:54:40Z")
All of my relatives are special, so my family is probably an example of Special Relativity, and they live in 3-dimension space, so they may also be an example of Spacial Relativity. Although I had an uncle who was a very high position in the army, he was a General Relativity. Can I have another vodka and orange juice? ---
**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\ **Post date:** [July 21, 2000, 12:57pm UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310/13 "2000-07-21T12:57:15Z")
> [@](#): > > In October 1977, Joseph Hafele and Richard Keating carried out what must have been a grueling experiment. They flew four portable atomic clocks twice around the world on commercial airlines, once in each direction. Their purpose was “… to test Einstein’s theory of relativity with macroscopic clocks.” Such measurements became possible only because of the very high precision of modern atomic clocks. [They] verified the predictions of the theory to within 5-10%. A few years later, physicists at the University of Maryland carried out a similar experiment with improved precision. They flew an atomic clock round and round over Chesapeake Bay for flights of 15-h duration and succeeded in checking the time dilation prediction to better than 1%. Today, when atomic clocks are transported from one placed to another for calibration or other purposes, the effect of time dilation caused by their motion must always be taken into account. source: **Fundamentals of Physics** Halliday and Resnick ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [July 21, 2000, 2:03pm UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310/14 "2000-07-21T14:03:53Z")
There’s more than one way to test relativity than flying clocks around in a plane. In Stephen Hawking’s book _A Brief History of Time_ he mentioned an experiment where hyper-accurate clocks were placed at the top and the base of a watertower. The clock at the base is deeper in earth’s gravity well so it is in a different reference frame. The effect is small so you leave them there for awhile to let the effect add up. Guess what? It worked. Relativity survives as a theory yet again. As to satellites moving in a different time frame they do. I can find a cite for this if annyone wants but basically the Soviet Cosmonauts who spent 6 months aboard the Mir spacestation were about 3 seconds behind everyone on earth when they returned. > [@](#): > > At least it’s more believable than my friend who told me that high-speed pilots tend to live longer because they spend so long in a difference reference frame. They do not live longer. Let’s say a person has exactly 500,000 hours to live in their life. Whether you speed around at 99.999999% light speed or stay on earth YOU will still perceive your life as exactly 500,000 hours long. A guy who stays on earth will seem to age faster (actually he won’t _age_ faster…he’ll just look sped up like he’s in fast forward) from the prespective of the guy flying around but as far as each is concerned both had the same amount of time to live. > [@](#): > > Erk? GR says that acceleration is indistinguishable from gravitation, so I think you are formally correct; but in the sense of acceleration being the second time derivative of position, they’re constantly accelerating. They are also in a gravitational field. IIRC the force felt by gravity and the force felt by acceleration are _indistinguishable_…in effect they are exactly the same thing. There’s no ‘formally’ correct about it. They are equivalent…they are the same…no matter how you slice it. Picture a person in a box in deep outer space accelerating at 1g. Now put that box on earth. The person inside will feel 1g. The person in the box has no way to look outside and see what is going on so he has no way to know whether the 1g he feels is because we’re accelerating him or have him sitting on a planet. Chronos (as usual in these types of threads) is right on the money. ---
**Author:** ![handy](https://avatars.discourse-cdn.com/v4/letter/h/b5a626/32.png) [@handy](https://boards.straightdope.com/u/handy)\ **Post date:** [July 21, 2000, 3:41pm UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310/15 "2000-07-21T15:41:06Z")
'Furthermore, contrary to normal intuition, the Theory of Relativity tells us that light always travels at the same speed relative to some observer, no matter what the relative motion of the observer. Thus, light emitted from a moving airplane does not travel with the speed of light plus the speed of the airplane, it travels with the “speed of light”, no matter what the speed of the airplane! In a vacuum, light always travels at a speed of 299,792,458 meters per second, no matter how its speed is measured. Although this seems strange, it has been confirmed in many experiments. These experiments show that it is our “common sense” that is wrong in this case! ’ From: [http://csep10.phys.utk.edu/guidry/violence/lightspeed.html](http://csep10.phys.utk.edu/guidry/violence/lightspeed.html) ---
**Author:** ![Phobos](https://avatars.discourse-cdn.com/v4/letter/p/3d9bf3/32.png) [@Phobos](https://boards.straightdope.com/u/Phobos)\ **Post date:** [July 21, 2000, 3:49pm UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310/16 "2000-07-21T15:49:29Z")
[QUOTE] \*Originally posted by JonF \* \*\* > [@](#): > > Erk? GR says that acceleration is indistinguishable from gravitation, so I think you are formally correct; but in the sense of acceleration being the second time derivative of position, they’re constantly accelerating. They are also in a gravitational field. > \*\* I’m curious about the distinction too. Seems like there is constant acceleration of the satellite toward the Earth due to gravity, but it’s counteracted/balanced by the momentum(?) of its orbital velocity. Another case where I need to dust off my physics textbooks. ---
**Author:** ![\_Tim](https://avatars.discourse-cdn.com/v4/letter/_/e47c2d/32.png) [@\_Tim](https://boards.straightdope.com/u/_Tim)\ **Post date:** [July 21, 2000, 8:06pm UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310/17 "2000-07-21T20:06:19Z")
In reference to JonF’s van Flandern link, I’d like to point out that the Lorentzian Relativity parts of that page are highly questionable science at best. (I don’t immediately see a problem with the GPS data, which admittedly is what is JonF was using the reference for) See [Refutations of Some Incorrect/Erroneous/Vacuous Claims about Cosmology and Relativity](http://www.math.washington.edu/~hillman/Relativity/wrong.html), which, among other things, discusses van Flandern’s ideas. Note in particular [this link](http://xxx.lanl.gov/abs/gr-qc/9909087) to Steve Carlip’s published van Flandern rebuttal. I’m not really an expert, any real physicists care to comment? I find it ironic that this link was referenced apparently in support of General Relativity… ---
**Author:** ![voguevixen](https://avatars.discourse-cdn.com/v4/letter/v/b5ac83/32.png) [@voguevixen](https://boards.straightdope.com/u/voguevixen)\ **Post date:** [July 21, 2000, 8:31pm UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310/18 "2000-07-21T20:31:44Z")
[http://einstein.stanford.edu/index.html](http://einstein.stanford.edu/index.html) For the latest “testing” of the theory. (Using gyroscopes in space.) ---
**Author:** ![JonF](https://avatars.discourse-cdn.com/v4/letter/j/cab0a1/32.png) [@JonF](https://boards.straightdope.com/u/JonF)\ **Post date:** [July 21, 2000, 10:00pm UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310/19 "2000-07-21T22:00:14Z")
> [@](#): > > In reference to JonF’s van Flandern link… Yeah, van Flandern writes soem good stufr some questionable stuff and some just plain wacko stuff. I don’t understand why. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 22, 2000, 2:15am UTC](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310/20 "2000-07-22T02:15:54Z")
Well, you can define acceleration as second derivative of position, but position in what reference frame? In GR, you can define a reference frame in which everything on the surface of the Earth is accelerating up, and the satellites aren’t accelerating, and everything’ll be perfectly valid, and you won’t even have to worry about this mysterious “gravity” force. If you really want, you can do all of your calculations considering gravity and acceleration to be two different phenomena which just happen to be identical, but since they are identical, it’s a lot easier just to call them the same thing and be done with it. [Next page](https://boards.straightdope.com/t/a-problem-with-the-theory-of-relativity/26310.md?page=2)