Entry 2094, on 2020-12-14 at 12:32:38 (Rating 1, Science)
My religious friends often like to take me on in a good old science versus religion debate. The most common form of this is probably evolution versus creation, but coming in a close second is the Big Bang versus Genesis.
From many people's perspective the debate is over and the evidence for the Big Bang cannot be denied, but those people should think again, because there is more nuance to the subject that that.
Never fear, I haven't become a Bible-bashing, science-denying, religious freak, because I still think the Big Bang is fundamentally correct and undeniable, but let's look at some of that nuance, especially in relation to various genuine science stories circulating in recent times which really do question the Big Bang in its current form.
Before I discuss these challenges, I would like to list the evidence which lead to the Big Bang becoming widely accepted - outside of fundamentalist religious communities, at least - in the first place.
First, there is the observation, which really got started with Edwin Hubble's incredibly skilfull and meticulous observations in the early part of the twentieth century, that galaxies (with a few exceptions) are all moving away from us, and that the further away they are, the faster they are moving. By the way, I discussed Hubble's work in a post titled "Favourite Things 3" from 2013-01-25, if you want details.
At this point, I should explain the "with a few exceptions" part above. The exceptions relate to very close galaxies (by close I mean just a few million quadrillion kilometers!), where the underlying trend of galaxies moving away from each other can be disguised by lesser movements at random, and which will sometimes be towards another galaxy, such as ours.
When the galaxies are close the relative underlying expansion is smaller and the random factor can be more prominent. More distant galaxies will be moving away too fast for the random component to override the expansion. Also, note that the "random" movement isn't totally random, because galaxies exist in clusters where the members interact with each other.
But the big point is that these observations show the universe is expanding. We know that because of the fact that all galaxies obey the relationship where the distance between galaxies and the speed they are receding from each other (minus any random movements as discussed above) is consistent with the universe itself expanding and taking the galaxies with it.
If the galaxies are moving apart they must have been closer in the past, and at one point they must have all overlapped. By extrapolating backwards in time that time is about 13.8 billion years ago. At that point the universe was compressed into a single point, and that's where we logically place the Big Bang.
Second, there is the Cosmic Microwave Background (CMB). This was discovered accidentally when some radio engineers were trying to remove some radio "noise" from their antenna. It was eventually discovered that this noise came from all directions and had the exact characteristics expected for the theoretical background "light" from the Big Bang. After almost 14 billion years the original extremely bright energetic light has been reduced to cool microwave radiation, but it is definitely there and supports the Big Bang model extremely well.
So the CMB also fits with an energetic event 13.8 billion years ago, and this is completely independent of the expansion observations. When we get two supporting, independent results, we should be confident we are onto something!
There is other supporting evidence for the BB but those are the two big ones, and the easiest to understand. If the Big Bang didn't happen, there was something that happened which gave very similar results. In fact, if there is something which differs slightly from the standard explanation, then it is still fair to call it a Big Bang, in my opinion.
Most of the alternative explanations concentrate on events which might have resulted in our universe originating through very similar processes to what we now accept. For example, a popular idea is that our universe is just a "bubble" of space-time which broke off from a greater universe which is probably infinite in space and time.
So in that case, the greater universe (or multiverse, if you prefer) existed before the Big Bang and just our universe began then. The big difference here is that space and time didn't begin in the Big Bang, just our particular part of it. But even then you could argue that a Big Bang still happened, just in a slightly different form.
So the Big Bang is a fact, by any reasonable interpretation of the data. There are undoubtedly mysteries which remain, especially in relation to inflation, dark matter, and dark energy, and how they relate to the bigger subject. But something happened 13.8 billion years ago and it was big. And it certainly looked like something went "bang", or the equivalent of that. Call it something else if you wish, but "Big Bang" (even though that name was originally created by an opponent to the theory in an attempt to trivialise it) is a good enough description for me!
Comment 1 by Anonymous on 2020-12-23 at 12:01:16:
This post lacks clarity. Was there a Big Bang or not? I cant tell from reading this.
Comment 2 by OJB on 2020-12-23 at 15:35:41:
Something happened which produced the universe. Maybe it was a Big Bang where the whole universe appeared from nothing, maybe it was a "Big Bounce" where a previous Universe collapsed and then re-expanded, or maybe it was a "Big Bubble" where a bubble of the bigger multiverse broke off and formed our universe. Whichever it is, a cosmological creation event of some sort happened. Maybe "Big Bang" is not the best name, but remember that was a name created by an opponent to the theory, not the official name which might have been chosen otherwise.
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