Speed of light

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Speed of light

Postby Brightonian » Thu Dec 15, 2011 4:42 pm

Something I read in Scientific American is bothering me (Dec 2011, Letters, p5). A reader had asked how astronomers can see out to "42 billion light years" as stated in a previous article, given that light could not have travelled further than 13.7 bn years since the formation of the universe. The reply was that since space is expanding, "an object that emitted light 13.7 bn years ago is now 42 bn light years away". So space is expanding faster than the speed of light?
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Re: Speed of light

Postby admin » Fri Dec 16, 2011 8:14 am

Good question, and something I've been trying to make sense out of for a long time. As best I can tell the speed of light is itself relative to the fabric of space. And since space is not matter, it can stretch any way it likes. I picture it as a piece of graph paper. If the horizontal scale is in years and the vertical scale is in light years, then "you can't travel faster than light" means that a graph of your motion can't rise more rapidly than the diagonal of that square. But the squares themselves can stretch, as if the graph were drawn on a rubber sheet.

Keep in mind that this is not my area of expertise, just something I've read about and tried to understand.
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Re: Speed of light

Postby slaven41 » Fri Dec 16, 2011 4:57 pm

I think that's a pretty good description of it, or at least as good as anything I could muster, anyway. It's not really my area either.
"It's only Neutron. We call him that because he's so positive." --from This Island Earth
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