Wednesday, December 16, 2015

spacetime - Where in Universe does time move faster than it moves on Earth?


I know that around black holes and areas with dense gravitational fields, time is supposed to move a lot slower, meaning that for example, a year in Earth might be just a second around a Black Hole.


Is there a place where the gravitational field is so low (perhaps there is an anti-gravitational field), that a second of Earth might seem like an entire year there? In other words, is it possible that time would move a lot faster there than it moves on Earth?



Answer



See the wiki article on time measured at GPS satellites. It's at http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html


To have time go slower just climb up the earth's gravitational well. Go up to the GPS satellite orbits and general relativity has it that time will go faster, I.e., the GPS clocks go faster than the ones at the earth. It is a small effect, 45 microseconds per day difference. Actually, because the satellites are moving with respect to us, Special Relativity says time is slower by 7 microseconds per day. Subtract the two and the bottom line effect is 45-7 = 38 microseconds per day faster than clock on earth. Yes, austronauts, if high enough, age more than we do on earth. The GPS system adjusts the time to take this into account and give us time on earth.


Go further out, not towards the Sun, and it'll be a bit faster. But not that much more, another small effect.


The effects are pretty small, our gravity is just not much, from a relativistic or cosmological point of view. Or even including the Sun, where we are. There are some large regions of the universe with (for maybe random reasons or maybe not yet clear reasons) a lower density of matter, by more than is expected. Called voids or supervoids. Gravity will be less there, and time will tick faster also. Still by a small amount, nothing big.


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