Trying to make sense of the time in spacetime

[WarrickF]

trying to make sense of the "time" in spacetime

Hi All,

I'm trying to make sense of the "time" in spacetime. I understand that Einstein chaned the way of thinking to object following a path in space time, and that matter bends space time but I really don't unserstand where the time part in space time comes from. Can someone please help me out here?

Thanks
Warrick

 

[jdavel]

WarrickF,

The notion of spacetime was not new with Einstein's theory of relativity. It is perfectly consistent with the classical relativity postulated by Galileo, incoroporated by Newton into his laws of motion, and generally believed until 1905. But in classical relativity, it's optional; in Einstein's relativity it's essential; at high relative speedsyou can't consider location and time independently.

That said, however, the idea of spacetime isn't at all complicated. Imagine (or draw) a graph with position along the horizontal axis and time along the vertical axis. Every point on this graph is associated with a unique time and a unique location, right? These points represent events, which are occurences (like a flash of light or a snap of your fingers) at some place and at some time. This graph represents spacetime. Everything that's ever happened, is happening, or ever will happen is somewhere on this graph.

There's a great little book that develops the theory of relativity with almost no math by using the notion of events in spacetime. It's by Robert Geroch, and I believe the title is "General Relativity from A to B" or something like that. It's a great read, and you'll definitely come away understanding spacetime.