Jacques' question and JaKiri's answer

[Severian]

Bob is in a constant situation. Let's say you doubled the duration of the test (Bob's time) he would be twice as old. Bill would be closer to light speed (Bob's perspective) through the "middle half" of the longer test than in the first and last quarters (the "other half" which is identical to the original test) of the longer test. So for Bill the "middle half" would be of less duration than the "other half" whereas for Bob it would be the same duration.

 

But how can you distinguish them? You can't - every physical observable that both Bob and Bill can measure will give the same result (assuming they are in a box, or a lift or somesuch) so you cannot distinguish which one is in a gravitational field and which one is being 'slowed down'. Therefore there can be no difference in age.

 

Of course, as I described it, it isn't a well defined experiment, because I should be comparing their ages in a particular frame - while that is OK at the end (where they are at rest relative to one another) it is not OK at the beginning (when they are not at rest relative to one another). Instead, we would have to have Bob on Earth and Bill somewhere far away (outside Earth's gravity well) but at rest in Bob's frame. Then Bill would accelerate away with 1g for a time T, and then decelerate at 1g (but still heading in the same direction) until he came to rest in Bob's frame again at time 2T. Then compare their ages in Bob's (and now Bill's) frame, and they wil be the same.

[J.C.MacSwell]

But how can you distinguish them? You can't - every physical observable that both Bob and Bill can measure will give the same result (assuming they are in a box' date=' or a lift or somesuch) so you cannot distinguish which one is in a gravitational field and which one is being 'slowed down'. Therefore there can be no difference in age.

 

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Let's have the twins meet in outer space, Bob at rest and Bill 1/2 light speed with respect to Bob and they synchronize their watches on the "fly by". Both are then blindfolded. Bob "stays put" and feels nothing. Bill gets deflected around a series of gravitational objects without getting captured in their orbits until he again meets Bob again and they again check their watches on the second "fly by". Bill has felt nothing except possibly some slight tidal effects.

 

Would you say their watches still agree?

[Newtonian]

Sorry for interrupting,but i feel the twin paradox will always appear to me invalid.Because the twin accelerating at C always stops and accelerates back.Which gives us a frame of ref for each simultaneous.I think laws of physics would be violated.

As an example i offer this.

The universe is approx 14.5 billion years old,so if we had a telescope capable of allowing us to see say 14.49 by then we must calculate the light we see has taken 14.49by to reach us.Therefore we assume a correct age,however IF a person travelled at LS from secs after the big bang upon reaching earth his time frame would be a younger universe.Which is invalid because then we would say depending on ones Frame of reference the universe has no calcuble age.

A thought ,from our own frame of reference we acknowledge we are not at the edges of the expanding universe,and whichever direction we care to view,the universe expands before us.So how can we give a definitive age for an infinite universe.

I presume i may not have this correct,but unless we can pinpoint our exact location in space time,our physics will always fail when calculating such.Im comfortable it being our best guess but not our arrogant affirmation.

Please help me out here if im wrong.