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View Full Version : Is There a Layman's Definition of Spacetime?

Fiery Phoenix
2009-Aug-29, 02:21 PM
I'm only asking this because every time I want to explain the basic difference between Newtonian mechanics and Einstein's relativity to someone, I am compelled to say the word spacetime, and whoever is listening to me tends to get a bunch of question marks over their head. :lol:

My question is simply, if someone asks me what spacetime is, what should I say? It really isn't something that can be explained nor understood easily. Or am I wrong?

I just want a definition of spacetime in layman's terms is all -- assuming there is even one.

Thanks.

Argos
2009-Aug-29, 02:25 PM
Wiki´s definition (http://en.wikipedia.org/wiki/Spacetime) is pretty simple. It hardly gets any simpler. Live with that.

Incomplete
2009-Aug-29, 02:33 PM
I'm only asking this because every time I want to explain the basic difference between Newtonian mechanics and Einstein's relativity to someone, I am compelled to say the word spacetime, and whoever is listening to me tends to get a bunch of question marks over their head.

Even Newton had a spacetime of sorts, but it was a boring one because time and space had no connection to each other. In other words there was a universal time shared by everybody everywhere, and a universal space everywhen. So there was no reason to combine space and time conceptually.

One spatial direction can always be turned into another by a rotation. That's why we don't try to separate them; we just refer to "space". Einstein showed that time can be turned into space too, and space into time, except that its hard to rotate more than a tiny amount (it requires a very high speed), and impossible to rotate completely (since speed is limited by c).

GoneToPlaid
2009-Aug-29, 03:06 PM
Another good example to expand in the Wiki definition is to research the orbit of Mercury, how a century or two ago astronomers thought that there had to be another planet on the other side of the sun in order to account for Mercury's orbit not exactly matching predictions using classical Newtonian methods, and how Einstein's theory of special relativity instantly provided the solution to the problem.