Thursday, October 29, 2009
FAR, FAR AWAY & LONG, LONG AGO
At 3:55 a.m. EDT on April 23, a NASA satellite ("Swift") detected a gamma ray emission from an object believed to be about 13 billion light years from Earth. The event is believed to have taken place about 600 million years after the Big Bang when the universe was created.
Light takes 13 billion years to go 13 billion light years. If the object was 13 billion light years away from Earth when it exploded, it had to have travelled those 13 billion light years since the Big Bang (when "Earth" and the object, and everything else were all together in one tiny little space): that is, the object travelled 13 billion light years away from "Earth"in only 600 million years.
To get 13 billion light years away from "Earth" travelling at the speed of light would take 13 billion years, not 600 million years.
a -- it was (way!) closer to "Earth" when it omitted the gamma ray pulse than 13 billion light years (ie distance estimate is wrong)
b -- it emitted the light (way!) longer than 600 million years after the Big Bang (ie time estimate is wrong)
c -- "Earth" & the object were not in proximity at the time of the Big Bang (ie Big Bang assumptions are wrong)
d -- The object separated from "Earth" (way!) faster than the speed of light.
e -- something else (for example, light does not travel at "the speed of light").
Note that our Earth did not exist 13 billion years ago; "Earth" (in quotes) designates a sort of virtual place that would later be occupied by our Earth. Since the idea of the Big Bang is that all matter in our universe occupied a very small space, exactly what space "Earth" occupied is not relevant -- unless of course that is where the solution lies...
Right now, the leading explanation for how something could get 13 billion light years away from "Earth" in 600 million years may be something like this... (a) the whole universe expanded / inflated at a rapid rate shortly after the Big Bang; and (b) this is allowed by General Relativity: space itself can expand, separating objects faster than the speed of light; it's not that the objects are moving, it's that the space between object is expanding.
So d (carefully using the word "separated") may be the leading explanation...
WIKIPEDIA ON THE EXPANSION OF SPACE