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How Many Universes?

The consequences of the anthropic principle continue to worry me. More specifically I cannot understand how the universe seems to be so finely tuned that it allows life to exist. Its not the fact that planets exist, or even stars, although those are important. Its more the really basic stuff, like the universe existing for billions of years, or that the proton is stable, or that objects such as stars and planets can exist because the values of various forces are just right for that to happen.

The history of science, and of astronomy in particular, has been a continual progression of discoveries which make our place in the universe less and less important. We thought humans were a special creation but evolution showed we weren’t. We though the Earth was the center of the universe but the heliocentric theory showed it wasn’t. We though the Sun was the center of the universe but the discovery of the structure of the galaxy showed it wasn’t. We thought the galaxy was the whole universe but observations showed that there are billions of others.

So there seems to be nothing special about us, or our planet, or our star, or our galaxy. It just happens that out of the trillions of planets out there (although I admit we only know about a few hundred so far) that Earth is well suited for carbon based life to exist (and I think that’s the only type of life which can arise naturally – but that’s another story).

So what’s the chances of Earth being as good as it is for life? First, let’s just say that its not that great – the fact that 99% of species which ever existed have become extinct shows that! Major global disasters such as asteroid, meteor and comet collisions, huge volcanic eruption events, and major climate variations show that Earth is far from ideal for life. But it is good enough.

So let’s say the chances of a planet being “good enough” are one in a billion (a totally arbitrary number I admit, but it doesn’t matter too much as I hope you will see). If Earth was the only planet in the universe we would say we are very lucky that the right formula has arisen at all (the formula involves mass, orbit, axial tilt, temperature, composition, gravity, etc) but if there are trillions of planets then its inevitable that many will be “good enough” and there must be a huge number which are actually better than Earth!

So that explains the planet – and a similar argument applies to the star (our Sun) and galaxy. What about the universe? Why do the basic laws allow stars and planets to even exist? The tempting answer is to apply the same logic as I have for the planet and say that there are a large (maybe infinite) number of universes and ours just happens to be one with good (but not perfect) conditions for life to exist (just like the Earth provides good but not perfect conditions for life).

The only problem is that we know other stars and planets exist but we are a bit less certain (and that’s a real understatement) about other universes.

At this point we really get into the realm of philosophy more than science. It would certainly be nice if there was an infinite (in time and space) multiverse which our universe is only a small part of. Universes could form with arbitrary laws and sometimes those universes would allow life to exist. Ours does, but there would be others where life also exists (probably in better conditions than in this universe too).

Some people (who maybe haven’t thought this through too carefully) might ask at this stage: but what are the chances of us existing in just the right universe? I would say the answer to that is 100% because that’s where we are. Its like a lottery winner asking “what is the chance of me winning” after they already won. That would be 100% but if they asked before winning it might have been only 0.0001% Only people who already have won (or exist in a “friendly” universe ask the question so the answer can only be one thing!

The whole question I have dealt with here is so big that there are theological implications. Many people think the fine-tuned universe we live in proves a god exists because the chances of all the laws and constants being just right are just too tiny to contemplate otherwise. If this was the only universe they would have a good point (although there are other possible explanations) but I think the multiverse theory answers the question better.

I only have one nagging doubt. If the multiverse creates all of these universes and only some are good for life, why do the “meta-laws” of the multiverse allow the creation of universes at all? (in fact the same argument could apply to a god) But, at this point, I prefer not to even think about that!

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