Does time exist for photons?

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James Marciniak

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Does time exist for photons?
« on: 07/02/2011 01:30:07 »
James Marciniak  asked the Naked Scientists:
Dear Naked Scientists,

First, I am a great fan of Naked Scientists and Naked Astronomy.

Unlike shows here in the US, they're not afraid of complicated explanations or knowledge for the sake of knowledge.

Question 1: I believe that the general theory of relativity indicates that time passes more slowly for an object approaching the speed of light. If that is true, then don't photons traveling from, say, a distant galaxy make the trip in no time at all from the photons' point of view, since they are (duh!) traveling at the speed of light?

Question 2: If the answer to Question 1 is yes, then doesn't that suggest that time does not exist for photons and, consequently, that it may not actually exist at all, because it is not present in all frames of reference?

Jim Marciniak

What do you think?
« Last Edit: 07/02/2011 01:30:07 by _system »


Offline JP

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Does time exist for photons?
« Reply #1 on: 07/02/2011 02:20:31 »
This gets asked a lot, and it's very confusing, so prepare yourself for a long answer.  :)

First, you're pretty much right that if you synchronize two clocks on two objects, and set one moving at near the speed of light, it's clock will appear to run much slower than the clock on the stationary object.  That's special relativity (not general). 

However, that only holds true for objects that have an inertial reference frame.  Such a frame is one in which the object is stationary.  The special theory of relativity assumes from the start that light is always moving at the same speed in all inertial reference frames.  Therefore there is no frame in which light is stationary!  What this means is that you can't, in this theory, talk about the point of view of light, including how time looks from it's point of view.  We just don't know how to describe it's point of view with the theory.  Since there's no known way to measure it's point of view either, we really can't answer this question at all. 

But coming to your second question, time certainly exists in all inertial reference frames, which exist for objects with mass that can never quite move at the speed of light.  Even though the theory doesn't address the point of view of photons, it certainly does address the point of view of massive objects and seems to be quite accurate when checked with experiments.

Check out this thread for a lengthy discussion on the topic:
« Last Edit: 07/02/2011 02:23:39 by JP »


Offline Soul Surfer

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Does time exist for photons?
« Reply #2 on: 07/02/2011 09:04:09 »
Why post this question when there is a big discussion on it already going on.
this was only two topics away  when I posted this.

The big thing everyone forgets is that these time changes only apply to looking at another frame of reference from your own.  Whatever speed you are going at and whatever gravitational field you are in (neglecting extreme tidal (gravity gradient) conditions that would destroy objects as big as a human body)  time, space and the laws of physics in your own frame of reference always look perfectly normal.  That is precisely what relativity is all about!
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