Science Forums 2

[CraigD]

Originally Posted by arkain101

… This means one of two things.

1)
-There is an actual time delay and difference in world lines between the two reference frames; S and E.

This is what the theory of relativity predicts, and a very large body of precise experimental data confirms.

Though the agreement between predicted and actual clock data from GPS satellites is one of the best known and most often mentioned confirmations of relativity, it’s not an example of the “twin paradox” scenario described in this thread, because the clocks on the satellites actually run faster, not slower, than identical clocks on the ground at the equator. This is because gravitational time dilation decrease with the satellite’s altitude, and velocity time dilation, which depends of orbital speed, which also decreases with altitude, decreases also. The result is that, at an altitude up to about 3280 km, satellite clocks run slower than surface clocks, then faster than them above that altitude. GPS satellites orbit at about 20200 km.

Originally Posted by arkain101

-Person E is observing Person S with 5 minutes of delay. For example, If person S stops orbiting earth and flies down to earth and lands next to person E and shakes his hand, during this, person E must observe the events of person S in such a way as to make up the 5 minutes of delay, which would be fast forward, in order for their world lines to merge so that they may shake hands.

This idea the world lines of person E and S must “merge” in order for them to be able to shake hands, etc, isn’t a prediction of relativity, nor suggested by any experimental evidence. If such a thing were true, none of us would be able to shake hands, as we’ve all moved at slightly different relative speeds and at slightly different altitudes, so all have followed slightly different world lines, and experienced slightly different durations of proper time between events.

In short, the idea of people getting “out of sync” in such a way that they can occupy nearby positions in spacetime, yet not interact, though it appears in various popular SF stories, isn’t a real scientific idea.

Originally Posted by arkain101

… It must be clarified which type of "clock" (mechanical or atomic ie: light clock) we are talking about in a Real or Hypothetical Special Relativity experiment.

According to relativity, and well-supported by experiments and other theories, it doesn’t matter what kind of clock is used to measure proper time.

Because time dilation effects for nearly all phenomena involving what we usually call “clocks”, such as the compact atomic clock on GPS satellites and large one in ground stations, these clocks must be very accurate and precise to detect them. If we had large, high-speed spacecraft, nearly any kind of clock could.