4 ms·

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 lig

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

miahi 15y ago
Found this note here: http://www.science20.com/news_articles/ulas_j11200641_most_distant_quasar_yet-80376 http://www.science20.com/news_articles/ulas_j11200641_most_d... [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.
- JohnLBevan 15y ago
  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?

miahi 15y ago

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

JohnLBevan 15y ago
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?