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sardeans
2008-Apr-10, 02:55 AM
If light beams always travel away from each other (and everything else) at the speed of light, then is it not possible for two photons to be traveling parallel to each other and appear stationary. For example, if you had two flashlights and pointed them in a parallel position and turned them on at the exact same time, then would the light beams appear stationary to each other rather than one moving away from the other at the speed of light?

Steve Limpus
2008-Apr-10, 03:28 AM
If light beams always travel away from each other (and everything else) at the speed of light, then is it not possible for two photons to be traveling parallel to each other and appear stationary. For example, if you had two flashlights and pointed them in a parallel position and turned them on at the exact same time, then would the light beams appear stationary to each other rather than one moving away from the other at the speed of light?

Hey Sardeans

If you were somehow able to ride that photon you would not experience any motion through the dimension of time, rather, all your 'motion' would be through dimension(s) of space. No time will pass for you, you'll 'instantly' be at your destination, so you won't experience being stationary with respect to the other photon, and vice-versa.

*pzzzt* <------ Steve's brain short circuits

alainprice
2008-Apr-11, 05:05 PM
The problem is this: What does a photon perceive? Nothing!

Your question is invalid with current knowledge.

Disinfo Agent
2008-Apr-11, 05:28 PM
Hello, Sardeans, welcome to the forum. I think your question is interesting and may have an illuminating answer, but I suspect that it is not easy to answer. You see, relativity theory makes it very difficult to put oneself in a photon's place, so to speak. The quote below, from John Baez's Usenet Physics FAQ (http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/headlights.html), should give you an idea of the difficulties.

Sometimes people persist: What would the world look like in the reference frame of a photon? What does a photon experience? Does space contract to two dimensions at the speed of light? Does time stop for a photon?. . . It is really not possible to make sense of such questions and any attempt to do so is bound to lead to paradoxes. There are no inertial reference frames in which the photon is at rest so it is hopeless to try to imagine what it would be like in one.

Ken G
2008-Apr-11, 07:59 PM
There is one way to make progress on that question, the only way really, and this instead of being in the frame of a photon (which is impossible for anything with rest mass, like us), is to take a limit of being at speeds closer and closer to c. So imagine two identical rockets blasting off at speeds like 0.999c or 0.99999999999c, whatever you like, and ask what happens as you add more and more "9s". The distance of their travel shrinks, as suggested by Steve Limpus' limiting case, and the amount of time for them to complete any particular finite journey gets shorter and shorter on their clocks (though being always about the same for stationary clocks left behind). But the two rockets are always side by side, always apparently stationary at the same distance away. I think it is reasonable to look at Steve Limpus' limit where the photons are also always side by side at that same distance, but no time passes and the direction of travel is squished into a single point, turning the universe into a plane at one instant. That explains how the photons can be perceived as not moving-- no time passes.

Disinfo Agent
2008-Apr-11, 08:21 PM
What a coincidence, Fraser has just written about photons!

Shortest Single-Photon Pulse Generated: Implications for Quantum Communications (http://www.bautforum.com/universe-today-story-comments/72744-shortest-single-photon-pulse-generated-implications-quantum-communications.html)

We should probably not forget, when we talk about photons, that they are "really" quantum mechanical beasts.