Entry 2145, on 2021-08-11 at 11:01:33 (Rating 1, Science)
I mentioned in a previous post how I intended to write some material about the origin of the universe. I have done a lot of political commentary recently, and after a while it all seems a bit trivial (although it isn't, really) so what could be less trivial, for a change, than the origin and nature of the entire universe?
There are two major ways to explain the universe: first, that it was always here and always will be; and second, that it had a specific origin at some point of time in the past.
Not that long ago, there were two theories which covered these two possibilities: the "eternal universe" idea was covered by the Steady State Model, and the universe with an origin at some point in time was covered by the Bang Bang Model.
In general, the Big Bang is by far the theory with the widest support today, but there are variations on that general theme which might either be thought of as completely different ideas or as major modifications to the traditional Big Bang.
First, let me say why the Big Bang is a good model. There are several observations which point towards a major event causing the origin of the universe some time in the past.
First, it has been known for about a hundred years now that almost all galaxies are moving away from each other, and the further apart they are the faster they are moving apart. This indicates the universe itself is expanding, and by playing this expansion back in time there is a point where all the galaxies occupied a single point. That is about 14 billion years ago, and that was when the Big Bang was theorised to have happened.
Second, there is a cool glow which is observed almost equally in all directions, which has been called the Cosmic Microwave background (CMB). This was discovered by accident by some radio engineers, but it fits in perfectly with what we would expect as the leftover radiation after the Big Bang.
There are also other, less critical observations, such as lithium abundance, but those first two are the major facts pointing to an origin about 14 billion years ago.
The Steady State theory did try to explain the first observation by proposing continuous creation of new matter in all space at a very low - almost unobservable - rate, which filled the gaps left by the expansion and allowed the universe to still be eternal and isotropic (looking about the same at all times and in all places). But observations of galaxies at great distances - and therefore also a long time in the past, because it takes a long time for light to travel from galaxies - shows that the past universe was more compact than it is today, so the Big Bang fits the facts much better.
But whatever theory you support, it should explain the CMB and the universal expansion, which point to an event 14 billion years ago. So whatever else you believe, your ideas must fit in with some sort of event like the Big Bang in the past.
So it seems like a simple conclusion to say that the Big Bang is right, but it's not quite that simple.
For example, if the universe was created 14 billion years ago, what happened before that, and what caused the expansion to be triggered? The common answers here are that there was nothing before the Big Bang because time itself was created then; and that there was nothing needed to trigger it because quantum theory tells us that some events happen with no cause.
Neither of those seem fully philosophically satisfactory though, so I would like to discuss a few alternative views.
First, maybe our universe is just a part of a much larger (probably infinite in space and time) entity which is usually called the "multiverse". The Big Bang might be just where our universe emerges as a "bubble" in the multiverse. Other universes might exist (probably an infinite number of them) which are either undetectable or difficult to detect from ours.
Second, maybe ours is the only universe in space but one of an infinite progression of them in time. In other words, maybe our universe was "born" after a previous one went into a "Big Crunch" which is the opposite of a Big Bang. Maybe universes expand for a time, then compact back to a single point and trigger a new cycle. Maybe this has always happened and always will happen. This is sometimes called the "oscillating universe".
Again, it is difficulty, but not impossible, to prove or disprove this hypothesis, but it does quite neatly explain what was before the Big Bang and what caused it.
There is one other factor which might be seen as more philosophical than scientific, but that I need to mention here. That is the anthropic principle. This notes that the universe seems to be fairly well set up for life to exist. If one of many constants was slightly different than it actually is, we would have no stars (so no planets, no energy, and no life) or the universe would collapse after a short time, not giving life time to develop; or various particles would be unstable and not allow atoms and molecules to form, also eliminating the possibility of life.
So why is the universe set up in such a way? Maybe God wanted it that way? This is actually used as an argument in favour of a creator, but that is unnecessary, because the two modifications of the Big Bang I mentioned above also explain the fine tuning without resorting to the supernatural.
If many - or an infinite number - of universes exist in either space (multiverse) or time (oscillating universe) then each different instance would have different properties. This universe has constants quite well tuned for the existence of life, but countless other universes don't. It is inevitable that some universe amongst a vast or infinite number would seem fine tuned for life, but that is just a matter of pure chance.
Some people might ask here: what is the chance that our universe was the one which is correctly fine tuned? Well, the answer is 100%. If this universe wasn't tuned for life then there would be no life, and we wouldn't be asking the question. The fact that we are here is the result, not the cause.
Some theories are elegant, and answer some difficult questions, but that doesn't mean they are true. I think we will discover some modification of the Big Bang which fills in some of the blanks we currently have. I like the multiverse theory, and there might be some way to prove it too. Some people think specific anomalies in the homogeneity of the CMB indicate interactions with another universe. Are they right? We don't know yet, but maybe we will in the near future.
I like multiverse theories because they explain what we see and answer some of the most difficult questions we have about the nature of reality. But we shouldn't be seduced by simplicity and elegance. Truth is more important, and that might be stranger than any theories we currently have!
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