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DanielLC comments on Stupid Questions Thread - January 2014 - Less Wrong
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On the Neil Degrasse Tyson Q&A on reddit, someone asked: "Since time slows relative to the speed of light, does this mean that photons are essentially not moving through time at all?"
Tyson responded "yes. Precisely. Which means ----- are you seated?Photons have no ticking time at all, which means, as far as they are concerned, they are absorbed the instant they are emitted, even if the distance traveled is across the universe itself."
Is this true? I find it confusing. Does this mean that a photon emitted at location A at t0 is absorbed at location B at t0, such that it's at two places at once? In what sense does the photon 'travel' then? Or is the thought that the distance traveled, as well as the time, goes to zero?
You can't build a clock with a photon.
You can't build a clock with an electron either. You can build one with a muon though, since it will decay after some interval. It's not very accurate, but it's something.
In general, you cannot build a clock moving at light speed. You could build a clock with two photons. Measure the time by how close they are together. But if you look at the center of mass of this clock, it moves slower than light. If it didn't, the photons would have to move parallel to each other, but then they can't be moving away from each other, so you can't measure time.
I'm not sure what the significance of building a clock is...but then, I'm not sure I understand what clocks are. Anyway, isn't 'you can't build a clock on a photon' just what Tyson meant by 'Photons have no ticking time at all'?
Yes. I meant that he meant that.