# Time Dialation in Uniform Motion [duplicate]

Is there EVIDENCE (proof) that time dilation actually occurs in the case of relative UNIFORM mottion (i.e., where no acceleration or decelleration occurs)? By proof, I don't mean mathematically but, instead, in observerable reality. No one answered this simple question. I raise this because to say in such a case that, from BOTH reference frames, the "moving" cliock is ticking slower than the "stationary" clock is a LOGICAL CONTRADICTION . Even invoking relativity of simultaneity where one clock begins ahead of the other, the period of supposed dilation is overlapped by both frames.

• Possible duplicate of Is time dilation an illusion? – DilithiumMatrix Apr 7 '17 at 15:45
• Duplicate by same user? physics.stackexchange.com/q/323441 – RenatoRenatoRenato Apr 7 '17 at 15:47
• physics.stackexchange.com/q/54717 – dmckee --- ex-moderator kitten Apr 7 '17 at 15:54
• Still waiting. The "proof" given involves gravity/acceleration (absolute motion), not relative UNIFORM motion. Since both reference frames are in the same Universe (reality), what is ACTUALLY occuring in each reference frame can't be a CONTRADICTION (i.e., the absurdity that each clock is REALLY ticking slower than the other). A plausible explanation is that such is what merely APPEARS to the respective observer. Even invoking relativity of simultaneity where one clock begins ahead of the other, there is still a period when the supposed time dialation is overlapping in both reference frames. – Rob Apr 13 '17 at 5:42

## 1 Answer

We are constantly in communication with GPS satellites, which only work because they take into account time dilation due both to special relativity and general relativity. It turns out that special relativity is the larger effect, so I think this would count as hard evidence.

Edit: GPS devices communicate with GPS satellites via microwave signals. The signals are sent from the GPS satellites with a time stamp, and by knowing how fast the speed of light is along with the current time, the device can determine how far it is from each satellite and thus triangulate its location. In order for this to work, the clocks on the GPS satellites obviously need to be synched with clocks here on earth. Thus, the clocks on the satellites were set to run slightly faster when they were built and launched so that when they got into high speed orbit the satellite clocks would run at the same speed as our own clocks.

• Can you be more specific. Precisely in what way do you say GPS satellites rely on time dialation to occur in uniform motion? – Rob Apr 7 '17 at 17:54
• Rob, see the edit – Travis Apr 7 '17 at 18:06
• I must ask you: Are you CERTAIN that the satellite clocks are adjusted to run faster, as opposed to slower, than the clocks on the ground? This is important because the clocks on the ground are not only experiencing the Earth's gravitational acceleration (in curved space which we can't "see") as the satellites are but a GREATER acceleration at that due to their closer proximity to Earth, slowing Earth clocks MORE than the satellite clocks and, thus, requiring their adjustment the other way, i.e., slowing them down (assuming acceleration the ONLY cause). – Rob Apr 8 '17 at 17:44
• So, if you're correct in that we speed up the satellite clocks, then this would indicate they are subject to additional time dilation to offset the amount affecting Earth's clocks. We might be tempted to invoke time dilation as an explanation due to the satellites' uniform motion, but uniform motion is relative. So, Earth's clocks would ALSO be slowed further. BTW, back to the nonsense that each clock runs slower than the other! – Rob Apr 8 '17 at 17:48