

Is earth travelling at 0.88 speed of light - ifran

Hi,<p>I am confused by the article on http://www.bbc.co.uk/news/science-environment-13964767. If light left the black hole 0.77 billon years after the big band how can it take 12.9 billon years for the light to get to the earth?<p>Unless I have misunderstood the article. A quick response will stop me pulling all my hair out. Are we saying at that time or as the light is near a black hole the laws of physics were different. Otherwise we would need to be travelling at about 0.88 speed of light for it to be true. Cheers guys.
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JohnLBevan
It could be due to Inflation
(<http://en.wikipedia.org/wiki/Inflation_(cosmology)>). This is where the
universe expands faster than the speed of light, since it's not the matter
moving, but the space between it that's expanding. Not my area though, so
would welcome thoughts from someone intelligent in that area. JB

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JohnLBevan
Hey Miahi, good point, but if the light set off at .77bn years, and we assume
it's on the edge of the far side of the universe to us, we'd be at most 1.54bn
light years apart (were it not for Inflation) when the light left. We'd be
moving away from the light, but it's taken 12.9bn years to cover the initial
1.54bn light years and subsequently catch up with us. JB

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miahi
Found this note here:
[http://www.science20.com/news_articles/ulas_j11200641_most_d...](http://www.science20.com/news_articles/ulas_j11200641_most_distant_quasar_yet-80376)

[2] Because light travels at a finite speed, astronomers look back in time as
they look further away into the Universe. It took 12.9 billion years for the
light from ULAS J1120+0641 to travel to telescopes on Earth so the quasar is
seen as it was when the Universe was only 770 million years old. In those 12.9
billion years, the Universe expanded and the light from the object stretched
as a result. The cosmological redshift, or simply redshift, is a measure of
the total stretching the Universe underwent between the moment when the light
was emitted and the time when it was received.

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JohnLBevan
Hey Miahi, I agree with what you, but I think Ifran's question is about why
the light had to travel so far in the first place.

If you assume(?) that the maximum speed anything can travel is the speed of
light, and ignore factors such as space expanding (redshift / inflation) then
at .77bn years the radius of the universe would be .77bn ly, so the maximum
distance between two objects (A & B) is 1.54bn ly. Now if light leaves A it
has to travel that 1.54bn ly to point B; it shouldn't take 12.9bn ly to do
this. However, A and B aren't fixed points - so though the light from A is
heading towards B, B is trying to run away (albeit at a slower pace). Here,
Ifran's calculated the minimum average speed at which B would be running from
A as .88c (if we assume that light from B is moving at c and not influenced by
any interference, and that both A and B moved at c for the first .77bn years).
That seems to be moving too fast, given at this stage in the universe's life
the known/current laws of physics apply. Redshift can account for some of
this, and Inflation means that the starting distance can also be much larger
than the assumed 1.54bn ly, which hopefully explains the rest?

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miahi
If that black hole is 12.9 billion light-years away, it takes 12.9 billion
years for the light to travel to us. Considering the age of the Universe 13.75
billion years, what they actually presume in the article is that we don't move
at all: 12.9 (the time of the travel) + 0.77 (the age of the light) = 13.67,
in the error margin of the age of the Universe (± 0.11).

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billpg
From it's point of view, we are travelling away from it really fast.

