MadSci Network: Astronomy
Query:

Re: Does gravity pull us through time?

Date: Thu Oct 6 09:13:57 2005
Posted By: Suzanne Willis, Acting Associate Dean
Area of science: Astronomy
ID: 1126133088.As
Message:

Well, the short answer is no. Let me see if I can explain a bit.

First, the three spatial dimensions and the one time dimension merge (to some extent) in both special and general relativity, so that we refer to four-dimensional space-time. Mass causes a warping of space-time in its neighborhood, the effects of which we observe as gravity.

The time dimension, however, is always treated differently from the spatial dimensions, even in relativity (it is usually given an imaginary number for its coordinate, which makes mathematical sense in a way I won't go into here). And clearly our experience of it is very different.

The time dimension has caused a good deal of thinking, head-scratching, writing, theorizing, and so on in the physics community. Do we in fact "travel through" it similarly to the way we travel through the spatial dimensions? If so, how "fast"? One second per .... what?

There are situations both in special and in general relativity where an observer may see your clock running slowly, but, and this is a big but, as far as you are concerned, your clock is always fine. For example, if you are traveling at a high rate of speed relative to someone, and they see that you have traveled some distance in a very short time, to you it looks like it was a much shorter distance (and your clock is fine). The rest frame of a clock, and anything that keeps time in any way is a clock, including you, is the home of the "proper time," and it never varies.

The consensus is that time does not "flow" in the usual sense. Events exist in space-time, and that's where and when they are. The passage of time is something of which we are aware, even if we can't really define it very well, but the notion of "moving" through time does not appear to be useful to our understanding of the universe.

There is a very good article on time in the Internet Encyclopedia of Philosophy. You can also find public lectures on the theory of time and space on Stephen Hawking's Web site.


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