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inunsure's avatar

Understanding time travel?

Asked by inunsure (423 points ) September 1st, 2012

So jumping right into it.
If we observe someone traveling close to the speed of light, the time passing for them seems slower and the faster they get the slower time should seem to us. So how is it when they go faster than light to us they dont look like they back in time so the people start to look younger, etc?

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4 Answers

gasman's avatar

They don’t go faster than light – that’s impossible by the laws of physics. Relativity taught us that the passage of time depends on relative speed.

Even at walking speed each of us “travels into the future” (which really just means we age more slowly) by a few picoseconds or so relative to stationary observers. The so-called twin paradox has been confirmed by experiment.

Relativity does not provide for time travel into the past.

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Pazza's avatar

Interestingly, I work for a company that does nuclear cleanup now, and was looking at stuff relating to the inside of reactors, as from an engineering point of view I was very interested (I still think its the most expensive way ever conceived to boil water!) anyway, I stumbled across this: http://www.fstdt.com/QuoteComment.aspx?QID=70003 there’s a picture near the bottom of the page.

I believe its known as ’Čerenkov radiation’

May be worth a google.

Just found this when I googled ’Čerenkov radiation’:
http://en.wikipedia.org/wiki/Cherenkov_radiation

Also google it with an image search. Some good pictures.

I think its an ‘em’ pressure wave traveling through a medium, as apposed to light, in anycase, I’m assuming it means information can travel faster than light through a medium.

Jack79's avatar

@Pazza basically what it says is that, while light only travels at ¾ speed in water, due to Cerenkov radiation the electrons can go faster than their light, but only faster than their “phase velocity”, ie 0.75c, which is still less than 1c (ie the speed of light in a vacuum). Still not faster than the speed of light.

Though I’m sure there’s some theoretical possibility to go beyond that.

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