RE: Travelling at the speed of light?[Question]
October 22, 2015 at 2:14 am
(This post was last modified: October 22, 2015 at 3:18 am by Alex K.)
(October 21, 2015 at 8:38 pm)heatiosrs Wrote:(October 21, 2015 at 7:52 pm)vorlon13 Wrote: From his perspective, realizing at launch Andromeda is 2 million light years away, and then arriving there 40 years later, he can do the math and calculate how fast he was going, and the number is 50,000X.Yeah but that does not mean that he was in fact going 50,000 times the speed of light during his trip that's just the illusion given because of our choice to accept general relativity.
As for us pudgy stay at homes, we've seen multiple ice ages come and go, and probably forgot all about our wayward traveler pretty early on.
It only appears to be 50,000X if we don't do the math, if we were(as in us observing him) we would still get the same conclusion that he got if we factored in the same events he experienced.
Well, I don't think accepting (special) relativity has much to do with it. Ok, so time dilation is a real thing that has been observed empirically. But even if your intergalactic traveller had never heard of relativity - if she would travel the 2 million light years to the outskirts of the Andromeda galaxy at 99.99999999% the speed of light, roughly 28 years would pass on her spaceship while 2 million years pass on Earth and Andromeda. If she then naively divides the 2 million light years distance by the time she has experienced on her ship, she would find that she went 70000 times the speed of light (*). The point is that to get the number, you mix quantities from two different reference frames - the distance as seen by a resting (wrt Earth and Andromeda) observer, and the time measured by a moving observer, and it is therefore not the usual definition of a velocity but some kind of strange mathematical chimera.
(*) to put matters into perspective - in order to reach this velocity, she has to put 70000 times her rest mass in energy into the propulsion. This means that if she and her ship weigh a metric ton, she has to annihilate 70000 tons of matter and antimatter to just get up to speed. Alternatively, fusing 70 megatonnes of hydrogen to helium (not burning TNT!) would do the trick.
The fool hath said in his heart, There is a God. They are corrupt, they have done abominable works, there is none that doeth good.
Psalm 14, KJV revised edition
