# Now on Earth and Mars

*Most recent answer: 05/14/2018*

- Neil (age 50)

uk

I think what he means is this. There are a variety of ways of dividing up space-time events into sheets of "now". Each of these ways is physically ok in the sense that each such coordinate system ("reference frame") uses the same laws of physics. Now here can correspond to a range of different now-moments somewhere else, depending on which reference frame is chosen. In Special Relativity, the set of now-sheets that include this time here on Earth cover a range of moments on Mars. The time range of those Mars-now moments, measured by a clock on Mars, is 2d/c, where d is the distance to Mars and c is the speed of light. Depending on the distance, which varies a lot, that can come out to be 15 minutes.

Mike W.

*(published on 05/14/2018)*