How is it possible for cosmic background radiation to still be detected?

Question

This is probably a really dumb question based on completely misunderstanding the whole idea ... but I'll ask it anyway.

There is a cosmic background radiation which is is pretty uniform in all directions but with a few ripples in it.

As far as I understand it this uniform scattering of photons started to propagate out shortly (in cosmological terms) after the big bang.

What I don't get is this. The solar system (and our galaxy) did not exist at the time, and the matter/energy from which it was formed came from matter 'condensed' from the big bang. Since that matter could travel no faster than the background radiation and would generally be travelling less quickly, how can any of the radiation be still passing us or coming towards us. I get that what we are detecting is like looking back in time but I don't see how any of this energy could be effectively behind us the race away from the big bang, even if space and time themselves are being inflated in the big bang.

Answer 1

i think your confusing lies in the area that you believe that the universe has a center and an edge, therefore if we are expanding away from the center, how come we are still reading cosmic microwave background radiation from the 'time of last scattering' when protons and electrons couple to make the first atoms about 400000 after the hot big bang.

The Big Bang was not an explosion from a single point, with a center and an edge. Most of the photons are cosmic microwave background photons that were present since the Big Bang but which have been traveling freely only since 400000 years after the Big Bang. These photons always travel at the speed of light relative to the galaxies near them. As the Universe gets older, the galaxies do not expand but the distance between the galaxies gets larger. The photons emitted by one galaxy do indeed spread out through the Universe, but photons from other galaxies can still be seen.

summary: cosmic microwaves background radiation are everywhere no matter where you are in the universe

this link below explains it better than i can.

very interesting question

Answer 2

About 300 000 years after the big bang, the universe was dense enough to let circulate freely within it. This is not so important, what's important is that this light was there initially. Now, to answer a bit more precisely, this light is sort of the ambient light of the universe. This background radiation is everywhere, in every direction relatively equally and will be until the end of time. The initial light of the big bang is still moving around in the same container it was initially except the container got much bigger. The fact that we can "look" at this light is completely irrelevant, it would be there without us and it is everywhere in the universe.

I hope that's clear...

Answer 3

Not too sure on this one. Very shortly after the Big Bang the universe experienced a period of 'super inflation'. This is to account for phenomena like the observed lack of curvature or flatness of our current universe. There is also evidence for this in the observed ratio of Helium/Hydrogen atoms in space. Obviously the super-expansion took place before a certain % of Hydrogen fusions took place in the primaeval fireball. The upshot is, with super-expansion, different regions could not possibly be in contact for thermodynamic equilibrium, so there would be variations in temperature between them.This was indeed observed by the COBE probe which observed fluctuations of millikelvins in the background temperature of about 4kelvin.

Answer 4

The radiation still lingers around because it hasn't dissipated yet.
Consider it like a room with all hard walls as the universe and the radiation as a rubber ball....and throwing the ball is the big bang

Answer 5

Sycamore got it right. There was no center to the big bang. *Every* place is a place where the big bang happened. The CBR is the glow we see from from those locations that are far enough away that light just got to us from there.

Answer 6

I have the National Geographic Channels TV special on MPEG if you want it. It's called Birth of The Universe. Really nice special and will answer all those questions.

[e-mail]

Answer 7

One really easy way to detect it is to listen for radio waves where there should be empty space. No matter where you look for truly empty space, you'll find very low frequency radio waves staring back at you.

Actually, while matter can't travel faster than light, as you suggest, space itself CAN travel faster than light.

Answer 8

radiation takes a long time to disapate - especially that sort of amount, and plus it had no where to escape to!!

Answer 9

I belive so, Steven Hawkings said it exsisted, and I belive him.