Motion of the Primordial Universe Revealed

neutron_p writes "New results from an instrument located high in the Chilean Andes (the Cosmic Background Imager) are giving researchers a clearer view of what the universe looked like in the first moments following the Big Bang. Cosmologists observe a time in the universe's distant past when atoms were first forming. The findings reveal the first movements between these "seeds" that ultimately led to clusters of early galaxies."

Comments

Re:This has always confused me

[TMB]

Don't microwaves move in a straigth line?

Yes (well, technically it doesn't in a curved space-time, but since the universe is globally flat, any deviations are extremely small on average).

In which case, shouldn't any radiation created by the big bang be at least 13 billion light years away from it's point of origin by now?

Yes.

So, unless they are reflecting off something or the universe wraps around at the edges, why can we still detect them?

Uh... here's where you've lost me. They're going in straight lines - that's why we can see them. When you look straight up and detect CMB photons, they were emitted from a point 13 billion light years away in that direction. When you look straight down, those photons were emitted from a point 13 billion light years away in that direction.

[TMB]

Re:This has always confused me - me too

[TMB]

Presumably the universe and the matter in it could not expand more rapidly than light.

Those two statements are different... matter cannot move faster than the speed of light, but the expansion of the universe can.

In fact, the expansion of the universe doesn't have a physical velocity associated with it - it's a fractional rate of change. So if the universe expands at "0.1 Gyr^-1", then proper distances increase by 10% per gigayear (*). If the distance you're interested in is larger than 10 billion light years, then it increases at faster than the speed of light. But that same rate of expansion corresponds to a much smaller velocity if you're dealing with a much smaller distance.

A photon's important length is its wavelength, lambda. This wavelength increases because of universal expansions at a rate of lambda * H_0... or about 10^-24 m/s for an optical photon (wavelength of 500nm). But this isn't even a real velocity, it's just the rate of change of the wavelength - even if it were greater than the speed of light, it has nothing to do with causality.

(*) This rate of expansion (also known as the Hubble constant, H_0) is, for historical reasons, usually expressed in units of km/s/Mpc... but you'll notice that the km and Mpc cancel out, giving a fractional rate. If the Hubble constant is 70 km/s/Mpc (consistent with current measurements), that is equal to 0.072 Gyr^-1.

[TMB]

Re:This has always confused me

[Alsee]

Several others have tried to answer, but I don't think you got any clear and correct answer.

The thing that is confusing you is that you have the very common image of the big bang being like a hand grenade explosion in the vacuum of space. You are picturing there is some point in the middle of our universe that was the center, from which everything spread out. The big bang is is no normal explosion, it was an explosion of space not in space, and there is no center in our universe.

In order to explain a picture of what it *is* like we need to imaging the universe is 2D instead of 3D. Imagine we live in a 2D sheet of rubber rather than 3D space. Now lets curve that sheet of rubber around into a ballon. We live in the surface of that ballon. There is *nothing* inside or outside the skin of the ballon - not even a vacuum. Our universe *is* the skin. You, me, the sun, the stars, they are specs within that skin.

That ballon is expanding. In the past the was smaller. Imagine running backwards, srhinking that ballon down to a point. That point would be the big bang. It was in the past, sort of in the center of our current ballon. That point is not anywhere in our universe, it is not on the skin of the ballon.

Now to explain the microwaves we see from the big bang. When you run backwards all of the stars and dust and gas were closer together in the skin of that smaller ballon. Go back far enough and everything in our universe was squashed togther - everywhere. There was very little space itself for it all to fit in. All of the space in our universe was filled with a dense hot soup of glowing particles.

So that glow came from everywhere in our universe. No matter what direction we look, that point umpteen billion light years away was glowing umpteen billion years ago. The very spot we are at now was glowing umpteen billion years ago, and if someone billions of light years from here were to look at us they would see that old glow from here.

Did that make sense?

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