Equivalence, not identity. Gravity curves space-time and has effects.johanfprins wrote:Well in this case a free falling accelerating reference frame cannot be an inertial reference frame as Einstein has postulated and used to develop his theory of gravity.tomclarke wrote: The equivalence is between different FORs. Therefore velocity is relative. Not acceleration is relative.
It is meaningless to talk about time slowing down in an FOR because time is relative. I think that is the source of your difference from me here. For example you talk above about measuring the age of the universe, as though there were some absolute measure of timeI agree that when you are within a gravitational field in space you will accelerate; but this acceleration does NOT cause time to slow down within your reference frame.Gravitation is equivalent to acceleration,
Although the effect of gravity is equivalent to curved space-time (as GR says) it is not true that the effect of all acceleration is so equivalent. The accelerated spacecraft is (clearly) not an inertial FOR because objects inside it experience a force.Well if you free-fall past another object and you are of the opinion that you are stationary as you must within an inertial reference frame, then you must conclude that it is the other object that is accelerating past you.but that does not mean that only relative acceleration matters.How do you measure it? One can measure a force on an object which is enclosed whthin another object that is accelerating. And although the enclosed object will not be able to discern whether this force is caused by a gravity field outside, this force is NOT the same as gravity within the universe. Time does not actually slow down merely because the clock suffers acceleration. It does slow down within a gravitational field owing to the fact that matter consists purely of waves and not of "particles".Absolute acceleration is phyically measurable (though not distinguishable from a gravitational field if GR is correct).
[/quote]I know this has been the belief for nearly 100 years by now: But it is wrong. I have given you the example of the two spaceships accelerating and decelerating symmetrically, and you just ignored it. Do you agree that the twins must, at least in this case, have the same age when they meet up?Thus the two cases are different in acceleration experienced by the two spaceships, and not equivalent.
If you look above at one of my early posts I do not ignore this case, and give it as example. If they accelerate & decelerate symmetrically then there is no change, as you would expect. So we agree here. It is the assymetrical acceleration that causes the difference.
You argue that assymetrical acceleration is physically equivalemnt to symmetrical acceleration. But that cannot be true, since I can distinguish the two cases easily with accelerometers!