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Name: Stuart
Status: other
Grade: other
Location: NV
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Question:
If the speed of light is a constant and not relative. Then assuming the universe is expanding, how come we can see an event that took place 13.1 billion years ago when the universe was only 650 million years old. Surely the object wasn't 13.1 billion light years away from us at the time of the event? If we can see the event now, then the light must have been traveling for 13.1 billion years. How can this be?

http://news.bbc.co.uk/1/hi/sci/tech/8329865.stm


Replies:
You are right, the object would not need to have been 13.1 billion light years away from us at the time of the event. Between then and now, the spatial fabric of the universe has expanded. Such expansion adds more distance for the light to travel while its en route. Think of an ant trying to walk around a balloon while somebody is blowing it up.

Of course, between 650 million years and now, the universe did not expand by a huge amount. So, the object must have been quite far away (sorry to be vague, I do not know the exact numbers). That is fine, though. The universe was still VERY large at age 650 million years. It is possible (some would say likely) that the universe was, and is, INFINITE in spatial extent, so there would have been objects at arbitrarily large distances.

Douglas Stanford


This is a very interesting and important question. In a theory of the creation of the universe there is an extremely rapid expansion of the universe that takes place before the slower Big Bang expansion. The expansion is really fast and is in fact faster than light. There is however the problem that you address in that there has not been sufficient time since the Big Bang for light to travel across the universe and back again. This dilemma is resolved by understanding the enormous rate of initial expansion of the universe.

David Kupperman



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