Science Forums 2

[CraigD]

Originally Posted by Agen

If we send a ship to another galaxy, lets not forget that other galaxies are moving away from is (the expanding universe) and may of them are doing so at great velocities in reference to us. Wouldn't this cause time dilation between the ship and home and as a result one would age more than the other or something to that regard?

For travel within our Milky Way galaxies and its neighbors, the time dilation would be slight.

Within a typical galaxy, the maximum relative velocity of stars is on the order of , or 0.0003 c. The fastest moving stars, known as hypervelocity stars, have speeds on the order of 10 times as fast, 0.003 c. Our neighboring galaxies, the Local Group, are within about 1.5 Mpc of us, so, per Hubble’s law, have velocities away from us on the order of , about the same as for stars within a galaxy. Per special relativity, this means that the maximum time dilation “tau” factor is about


Were we to travel between stars, or even just between planets in our solar system, time dilation factors of similar size can be had by changing ones distance from massive bodies such as galactic centers, stars, or giant planets, via gravitational time dilation. For example, moving from the Solar system to a star 1 parsec from galactic center dilates time by about 0.99999975, from Earth to Mercury about 0.999999978, to the atmosphere top of Jupiter, about .999999988.

Though significant in terms such as synchronizing clocks – a time dilation factor of 0.99999975 equates to about 8 sec/year – it wouldn’t be very noticeable in terms of ordinary human experience.

Getting near actual black holes, on the other hand can produce time dilation factors of nearly zero, effectively freezing time. Various folk, from SF authors to physicists, have suggested that, if you’re able to build traversable wormholes with movable mouths, parking a mouth near the event horizon of a black hole is a good way to make a practical time machine.

Sources: wikipedia articles “stellar kinematics”, “Hubble’s law”, “Local Group”, “supermassive black hole”, “time dilation”, and “time travel”.