Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: xRyanx on 17/08/2009 02:32:11

Title: sundials and the relativity of time
Post by: xRyanx on 17/08/2009 02:32:11

My friend brought this issue to me like a week ago and I can't figure it out.  He asked how clocks could run at different speeds closer to bodies of mass if a sundial wouldn't.
A sundial somehow supported several miles from the surface of the earth will always tell the same time as one directly beneath it, at the earth's surface, won't it?  Will a clock that is accurate on earth disagree with the sundial several miles from the surface?

Title: sundials and the relativity of time
Post by: Nizzle on 18/08/2009 09:48:22

Yes, they will be arguing about a few seconds per century perhaps..

Title: sundials and the relativity of time
Post by: LeeE on 18/08/2009 16:08:44

This is quite a fiendish post and took some time to figure out  [;D]

I think the explanation is that sundials don't really measure time but actually measure the amount of rotation of the Earth.  If one sundial is fixed in place above the other then they will both measure the same degree of rotation, as they will have both rotated by the same amount even though they are in different gravitational potentials.  Two clocks though, which do measure time, and with one placed beside each sundial, will show different times (time elapsed since the clocks separated from each other) for the two sundials.

Title: sundials and the relativity of time
Post by: xRyanx on 18/08/2009 18:00:20

I GET IT!

thanks