MadSci Network: Physics

Re: What is the shape of time?

Date: Fri Feb 16 18:44:19 2001
Posted By: Ken Wharton, Post-doc, Laser/Plasma Physics
Area of science: Physics
ID: 980098198.Ph

Good ideas!

First off, it's important to think of time as a dimension. Step outside of time and try to imagine the whole 4-D universe... Time is just an axis, just like space. We experience time "flowing", but that's just because we're inside of it. Time doesn't really flow forward any more than space flows to the left.

You seem to have come up with the concept of a light-cone. An event that is 1-light minute away, and 1 minute in the future is on our future light cone. (It's called a cone rather than a sphere because normally these things are drawn on paper, with one dimension of space and one of time; the resulting shape makes a cone.) You seem to be wondering if it's possible to redefine the concept "now" to mean "events on our light cone". Similarly, you note that what you were doing 1 minute ago has a different light-cone, which appears to be "propagating" away from you. (If you step outside of time, though, you'll see it's not really moving in any particular direction.)

I think this is a perfectly valid way of looking at the universe... after all, when a photon travels at light-speed, from the photon's perspective the journey seems to take no time at all. In a sense, a photon is everywhere on the light cone at once -- so the perspective you suggest is simply that of a photon. Also, this makes it obvious why faster-than-light travel would necessarily imply time-travel -- you'd be able to travel into past light-cones. This important point isn't always obvious when you think about time in the "normal" manner.

This picture does have its limitations, however. First of all, it's not energy that's expanding out... Energy is well-defined; think of it more like information accessiblity. Also, "interference" is probably a bad analogy... that implies constructive and destructive wave-mixing, which is certainly not happening. Finally, the picture violates our common-sense notion of "now", so if you're not extremely careful with it you can likely reach all sorts of incorrect conclusions.

Here are some relativity links.

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