Re: The universe expands ...
Posted: Thu Jun 20, 2013 9:03 am
SpheresOfBalance wrote:I don't buy the background radiation, being anything more than from current and past stars. It has nothing to do with a bang, other than its where the stars supposedly come from.
From what I understand, the view we have of the cosmic background radiation is essentially the inner surface of a sphere. In every direction we look, we can see photons that have been travelling towards us for over 13 billion years. We cannot see beyond that, because the photons involved were the very first to escape the seething heat and density of the early universe, I think the term is decoupling. It happened at a fairly specific temperature, which is why the photons all look the same/have the same energy. There may be plenty more universe beyond that shell and the thinking is that anyone at the extreme of our vision could look out and see the same as us. The reason being that if you can imagine the universe the size of a golf ball, the bit we can see may have been only a millimetre across and it has spent the last 13.7 billion years getting bigger. Next to our millimetre was another one that has also spent the last 13.7 billion years getting bigger. Whether what we can see is all of the universe, as far as I can tell, depends on whether there is enough mass to make all the photons go round in circles, more or less.Godfree wrote:I agree , the most ridiculous statement I heard about the CBR was
we see it whatever direction we look , it's all around us the same image ,???
thats pathetic , if it was real and the image of the early universe ,
it would be in one spot , you would have to look in the right direction ,
the fact that the image can be generated pointing your telescope anywhere you like ,
makes it obvious that the effect is something else entirely,
In other words, we can only see 13 odd billion light years away, because any light from further away hasn't had time to get here. Our picture of the universe will grow with time, but the most distant thing we will ever be able to see is the cosmic microwave background radiation and that will always be as far away as the universe is old.
There is an element of truth in Godfree's tired photon hypothesis in that the energy of the radiation does decrease as the wavelength increases. Suppose photons were ping-pong balls being thrown at you, if suddenly twice as many are being thrown you will absorb twice as much energy, even though the individual ping-pong balls aren't going any faster. Thanks to Newton, we know that a moving ping-pong ball will not stop unless something gets in the way; on Earth they have to contend with air resistance and a strong gravitational field. In space it would carry on forever, so too photons. They don't get tired.