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plant
2010-Apr-07, 02:19 PM
I read somewhere that implied that everything is always travelling at "c" (speed of light) through space-time. The faster you go through space, the slower you go through time and vice-versa. But if you're travelling through space at c - like a photon, then presumably you're 'stationary' with respect to time. So would this mean that the photon would experience the flow of time in the rest of the universe to be infinitely fast? What i'm trying to get at is: what would the experience of the universe be like if you were a photon?

Tensor
2010-Apr-07, 04:02 PM
I read somewhere that implied that everything is always travelling at "c" (speed of light) through space-time. The faster you go through space, the slower you go through time and vice-versa.

We had a thread about this a couple of months ago. With the recent transfer to the new version of vbulletin, we don't currently have the ability to link to that discussion and why that's not quite the right way to look at it.

But if you're travelling through space at c - like a photon, then presumably you're 'stationary' with respect to time. So would this mean that the photon would experience the flow of time in the rest of the universe to be infinitely fast? What i'm trying to get at is: what would the experience of the universe be like if you were a photon?

The correct answer is:We don't know. A photon's frame of reference isn't a valid frame of reference(you end up with division by zero), so we can't really say. If, however, you take the photon's experience as a limit and extrapolate, then the photon experiences zero time and the photon's path contracts to zero length. See why it kinda, sorta doesn't make any sense? And why it's considered not valid?

tdvance
2010-Apr-07, 07:04 PM
No---you don't "travel" through spacetime really. Your speed is distance through space divided by time (which of course depends on frame of reference, which determines which directions are space and which one is time) and is generally much less than c.

astromark
2010-Apr-07, 07:34 PM
It has been the popular standard that in the vacuum of space a light photon has a velocity, c.
That at c. time does not move forward from that frame of reference.. Other sub atomic particles with 0 rest mass may also attain this velocity. Transversing a opaque substance can and does slow light. As does hitting some thing... Ouch !

plant
2010-Apr-08, 07:44 AM
ok.. but i thought that space and time weren't 'real'... just 'shadows' of space-time.... if you know what i mean...

plant
2010-Apr-08, 07:46 AM
so.. it can't go anywhere because time stands still- but it doesn't have to because it's there already!

loglo
2010-Apr-09, 02:50 AM
so.. it can't go anywhere because time stands still- but it doesn't have to because it's there already!

Yes, which is why it is called a null geodesic.

Ken G
2010-Apr-09, 03:36 AM