Is the CMB radiation that asronomers study the same heat that was released after the Big Bang?

Question

The website about WMAP says that since light travels at finite speed then the far-away objects we see are actually much older. So, am I understanding this correctly? Do the scientists study the CMB radiationbecause it is the oldest thing left from the Big Bang? And how does measuring the temperature fluctuations help scientists learn more about how long ago it happened, etc. ?
Thank you, if this is a stupid question, I apologize in advance.

Answer 1

These are EXCELLENT questions.

Clarification. The CMB is not radiation emitted during the period of "hyperinflation" in the early universe, more commonly known as the "Big Bang."

What we are actually seeing is the light emitted right as the universe went from being opaque to more or less transparent; all those ionized hydrogen and helium atoms recombined so instead of being able to absorb and scatter all wavelengths of light, the gas could now only absorb specific colors corresponding to specific absorption and emission lines. This event occurred when the universe was about 300-400k years old. This event is commonly called "deionization".

Question 1)
This radiation is the oldest thing left from the big bang, ***that we can easily observe and image with current technology***. Older artifacts would be the slew of neutrinos produced during primordial nucleo-synthesis at the age of about 1 second to 3 minutes. This is when all the protons and most of the helium, lithium, beryllium and boron formed. (Virtually ALL of the lithium around today is primordial. It only gets destroyed in stars, never created.) But, neutrinos are very difficult to observe and we sure as heck can't form images from them. They don't scatter off of anything, really.

Another relic would be gravitational waves that ought to have been generated during inflation, and maybe there is even a gravitational background from the Planck epoch prior to this. I don't really know that much about this, but there might be some hope of imaging these phenomomena someday, with gravitational telescopes on a far grander scale than anything we currently are even designing, but at least we can imagine such an instrument, which is better than the neutrinos.

Question 2)

The fluctuations tell us several things. These fluctuations correspond to areas of higher and lower density. These density variations are the "seeds" that eventually collapse into the structures of voids, walls and galaxy superclusters we see in the universe today. (Imagine a uniform density cloud of gas. Since the density is equal everywhere, it will tend to stay that way, since gravity is pulling equally in all directions. You need a little over density to start things collapsing) So, we can look at the statistical distribution of this density pattern, model the rate of curdling that would occur, and see if the result statistically matches the structure we see in the universe at different epochs of its history. (Statistical distribution in this context means quantifying how many lumps there are of different sizes and how they are spread around.)

Another piece of info is to compare those fluctuations to what we would expect to see from random variations at a quantum mechanical scale. The inflation hypothesis predicts that random density fluctuations that exist due to quantum mechanical uncertainties would be "frozen" into universe and tremendously expanded during inflation.

A statistical comparison of the observed CMB fluctuations to what our understanding of QM predicts is a crucial test of the inflation hypothesis.

Finally, the magnitude of those fluctuations is another test. The fact that in opposite directions the average temperature of the CMB is so close is strong evidence that these different parts of the universe that are not now in any kind of thermal contact(*), once were in thermal contact. One way to resolve this simple contradiction is to have some sort of superluminal expansion, where space expands such that different parts of the universe recede from one another effectively faster than the speed of light.

(*)Light from the part in one direction has barely had time to reach us, much less the parts of the universe in the far opposite direction


This post is already too long. If you have further questions about some of these details, post another question and let me know via my contact link here at answers.

Answer 2

Yes, the CBR is the afterglow of the Big Bang. The fluctuations in temperature and their correlations across the sky are related to the speed of expansion at the time that the universe became transparent (it was opaque before due to the high temperature). They are also suggestive of early stages of galaxy developement.

Answer 3

It was originally the first visible light that could travel freely when the universe was cool enough to be transparent. But the expansion of space in the 13 billion years since then has stretched it out so it now has much longer microwave wavelength.

Answer 4

No in my opinion. It's the temperature of space which depends on the density of stars. This was derived by Eddington long time ago.

Answer 5

Now, this is more like it!!!!. Katydid, your questions were excellent and shows that you've taken the time to get to know the subject matter. The answers....both of you, are good, damn good.

I was going to answer this question, but it's been done more than adequately enough:):).

Answer 6

See the answer I chose to my question. It's all nonsense, to varying degrees. They don't know, and are making up that they could know, by guessing.