Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Time flow on other planets or galaxies

  1. Feb 23, 2012 #1
    First excuse my grammar english is not my first language

    My question is does the speed at which the planet is revolving on itself, the speed at which the earth is rotating around the sun and the speed at which the milky way is travelling throught space is affecting the rate at which time flows ?

    Let's say that to someone not moving at all on earth time flows at a rate=1

    Relative to someone in the vacuum of space but still in our galaxie does time goes slower because he is travelling slower through space since you substract the revolving and rotating speed of the earth.

    And let's say someone is in another galaxy that travels through the universe twice as fast as the milky way so while 1 year passes over there 2 years have gone here in the milky way ?

    My last question is someone in a plane is aging slower because he is going faster relative to someone standing still on the ground, if the plane is rotating on itself while going the same speed forward will that change anything for the flow of time ?

    I hope that somehow makes sense
  2. jcsd
  3. Feb 23, 2012 #2


    User Avatar
    Science Advisor
    Gold Member

    All your questions are about how speed effects the rate of time which would imply that you want to ignore the effects of gravity. If so, your questions could be answered in the context of Special Relativity (which ignores gravity) rather than the more complex answers you would get from General Relativity.

    So, according to Special Relativity, each state of unaccelerated motion can be considered a state of rest in which time flows normally and for which any object in motion time slows down the faster the speed but it's not a linear relationship. In other words, going twice the speed doesn't make time flow at half the rate.

    Thus, an observer on the surface of the earth can consider himself at any moment to be at rest and the other observers that you mentioned are all traveling at different rates relative to him. It doesn't matter which direction they are traveling or whether they are rotating, their instantaneous speed controls their rate of time.

    Now, this is an oversimplified answer because the observer on the surface of the earth is also changing his own speed due to the rotation of the earth and the earth's motion around the sun and the sun's motion in the rotating galaxy, etc, etc, etc, plus gravity is involved but that leads to very complicated answers which you are better off ignoring until you get Special Relativity clear in your mind.
  4. Feb 23, 2012 #3


    User Avatar
    Gold Member

    It is important to keep this in perspective. The effects of SR and GR are vanishingly small under these circumstances.

    Best case - and a ridiculously contrived one - you've got a rogue star system rocketing through the galaxy relative to us at an outrageous 1/10th the speed of light. Its time is dilated as observed by us by no more than 1 part in 1000. i.e after a year for us, it's been 364 days and 16 hours for them.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook