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Comment by yequalsx | Hacker News Reader

I'm not a philosopher and may be misinterpreting the quote in question. The philosopher is not claiming that infinite sequences can't have a distinct start. He is claiming that an infinite amount of time could not have elapsed before the present time, t. If it did then it would have taken an infinite amount of time to get to time t-1 and thus we'd never have gotten to time t since it'd require an eternity to get to t-1.

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I'm no philosopher nor a physicist either, but I don't see why that would even be a problem. We know by now that time is relative. To a photon, all of our infinite time, if it is infinite, "happens" all at once, so why would it matter if it took an infinite amount of it to get here. If you could stop a photon and ask it, it would reply that we were always here.

Here we are having philosophical debates about it, but I suspect if we just stuck with the math -- regardless of our intuitions -- most of these kinds of arguments would turn out to be a distraction rather than a solution to the problem. That's kind of the point many empiricists like Krauss are trying to make.

I think the rub is in the, "if we could stop a photon...". We can't. From the photon's perspective there is no time elapse. The photon doesn't believe time has lasted forever. I imagine it would not even understand the concept.

I believe that it is not possible for an infinite amount of time to have elapsed before this moment in time. I think that is what the quote in question is attempting to state.

> I think the rub is in the, "if we could stop a photon...". We can't.

Scientists "freeze" light inside a crystal for one minute. [0]

Stopping single photons in one-dimensional circuit quantum electrodynamics systems [1]

[0] http://www.gizmag.com/stopping-light-inside-crystal/28610/

[1] http://www.ese.wustl.edu/~jushen/Papers/Stopping_Single_Phot...

I mean stop it in the sense of the perspective of the photon. I don't know enough physics but I suspect that from the photon's perspective it hasn't stopped. This is because there is no time elapse from the photon's perspective. The other points in my previous post remain valid. I think!

Those experiments always use variations on the word "stop". The speed of light does not vary.

In those experiments, "stop" usually means absorbed and later re-emitted.

Further reading: http://en.wikipedia.org/wiki/The_Unreality_of_Time

Yes, but why would you need an infinite amount of elapsed time to get infinity time?

Think of the real number line. We are at some point t that represents our current time. If time goes back forever, that is had no beginning then it means (-∞, t] represents all the time up to t. How did we get to t? I would take an eternity to get to t-1. Indeed, for each moment in time it took an eternity to get there. Hence time must have had a beginning.

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