3) There’s no evidence for the Big Bang
Sadly, yes, I have actually seen this one fairly often. I have no idea where people get the idea that scientists make things up without having good evidence behind it (oh wait… we’re out to disprove God because all scientists hate God or some crap like that).
The Big Bang theory does have a good amount of evidence behind it. So we’ll take a look at the three biggies.
a) Cosmological Redshift: As I explained in my earlier post, we can use spectroscopy to determine the rate at which galaxies are moving away from us. Additionally, since it takes light time to travel, the further away we look, the further back in time we are looking.
What we find, is that all galaxies in the universe are moving away from us. The further they are, the faster they’re moving away. So if we play the whole thing in reverse, all the galaxies will come back together at a single point in time. This point in time is what we call the Big Bang.
b) The Cosmic Microwave Background (CMB): Figuring that if you played everything back in time like this that all that energy would be crammed into a smaller space, that means the temperature would go up. And also since galaxies couldn’t have formed yet, we’d expect a gaseous sort of universe early on. As I discussed earlier, hot dense gasses emit photons at a peak wavelength corresponding to their temperature. Unfortunately, since things were so dense, photons couldn’t get very far.
However, with the available information, astronomers were able to determine at what density and time, photons would finally be able to get far enough that we could observe them. This is called the “surface of last scattering” and has a very specific temperature. So we should be able to look for photons with energy (wavelength) corresponding to that temperature.
But due to redshift, they will appear at a different wavelength. This radiation should appear from every direction. This was a prediction made by the Big Bang theory that was later confirmed by Penzias and Wilson who stumbled on it accidentally!
No other theory of the universe has ever been able to make such a profound prediction to the degree of accuracy the Big Bang did in this instance. Making such amazing predictions is one of the highlights of a good theory. None before or since have ever been able to pull off such a feat.
But the successes of the CMB prediction don’t stop there. Another important piece of the puzzle lies in that the CMB couldn’t be completely even. If it were, then galaxies couldn’t form since there would be no “seeds” with higher mass and thus a stronger gravitational pull to form around.
Thus, the Big Bang theory had to predict that the CMB would not be completely homogeneous. It should have some variations to it, and those variations would have to be of a specific size in order to get the universe we see today.
Early results for the Big Bang didn’t look too good for this prediction and threatened to sink the whole ship. However, the devices used were not actually sensitive enough to pick up these minute variations. But recently, with the Wilkinson Microwave Anisotropy Probe (WMAP), these perturbations have been discovered precisely as predicted.
Score two strong predictions for the Big Bang. Zero for any others.
c) Distribution of Elements: With the conceptual framework intact thanks to the first point, it was also possible to calculate how much of each element should be formed in the initial event. It should be obvious that, given a bunch of protons, electrons, and neutrons, hydrogen should be the easiest to form. Indeed, stick a proton and an electron in a room together and they’ll automatically hook up due to their magnetic attractions.
Additionally, with such high energies, it would be possible to fuse some of this hydrogen into helium and even a little bit of heavier elements. Since astronomers had a good handle on the energies, it was possible to calculate how much of each there should be. If that number didn’t match up with observations, the Big Bang theory would be shot.
Fortunately, the predictions do match up pretty closely. I stated a value earlier of 80% hydrogen, 20% helium, and neglected the rest since it would be statistically insignificant. In the universe today, we observe 75% hydrogen, 24% helium, and 1% everything else. This discrepancy is easily accounted for by nearly 14 billion years of stars cooking hydrogen into helium and other heavier elements.
So there’s three major pieces of evidence for the Big Bang, any one of which, if it had turned out any other way, would completely discredit the theory. Fortunately for the Big Bang, it has passed all of those tests, and not a single other theory has yet been able to adequately explain such things, or many anywhere near as profound of predictions (or any successful predictions for that matter). This is why the Big Bang stands alone as the premiere theory in cosmology today.
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