Normal

a) How do we know that there isn't life in every single solar system? We don't

b) If we exist in a universe that supports life, how do we know that life is unlikely? We don't

c) If life only exists in a universe that supports life (this seems to be necessarily true), any universe that contains life will necessarily seem "lucky" to the life that exists to examine such a situation.

The multiverse is irrelevant.

Jesse

But if there is only one universe, and at least a few of the constants were set in a random way (perhaps by 'spontaneous symmetry breaking' after the Big Bang, as some physicists have speculated), then if there is only a very narrow range of values these constants could take in order to have a universe with life, then the universe would probably not contain any life. In a sufficiently large multiverse there might be a good chance that at least some universes would contain life, and naturally any life that existed would find that the universe they lived in contained a lot of anthropic coincidences.

Suppose you know that you are the product of an automatic in vitro fertilization machine that's supposed to randomly pick a frozen sperm and frozen egg, unfreeze them and allow them to fertilize, and then incubate the resulting embryo in an artificial womb for 9 months. Unfortunately the machine is malfunctioning, so on 99.999% of its runs it can be expected to do something which will prevent a baby from being created, like bring together two sperm cells instead of a sperm and an egg, or like keeping the artificial womb at 50 degrees instead of 98.6 degrees. You also know that at some point after it was turned on, it broke down completely. Armed only with the knowledge that you were a product of this machine, would you think it more likely that it had gone through many runs before breaking down, or only a small number, perhaps even one? Of course your answer to this question should depend somewhat on your a priori beliefs about the probability that such a machine would run X number of trials, but assuming you don't rate it as too unlikely a priori that it ran quite a few times before breaking down, the additional knowledge that you exist and were a product of one of those runs should lead you to conclude it's more likely that the number was large.

Normal

Again:

c) If life only exists in a universe that supports life (this seems to be necessarily true), any universe that contains life will necessarily seem "lucky" to the life that exists to examine such a situation.

You assume this universe is one of the first to exist, when this universe could of possibly existed in hunderds of thousands of billions of trillions of different forms before ours, and we are the only ones to notice how "lucky" we are because we are alive and in a universe that supports life. If there were that many prior universes (or infinitely many), any chance above 0 for life existing in a universe (which is clearly above 0 since we exist) will have a good chance of happening.

Jesse

Normal:
c) If life only exists in a universe that supports life (this seems to be necessarily true), any universe that contains life will necessarily seem "lucky" to the life that exists to examine such a situation.

But if there is only one universe, it may be extremely unlikely that there is any life to examine anything. Your statement is a bit like if the person who had been created by the baby-making machine I described above said "if adult minds can only be created on successful runs of the machine, then any intelligences able to comprehend their situation will observe they were the result of a very luck run." True, but I'd say it doesn't change the fact that such a person should say that their own existence makes it more likely that the machine ran many times than that it only ran once (assuming the a priori probability of running many times is not too fantastically low)--do you agree or disagree?

Normal:
You assume this universe is one of the first to exist, when this universe could of possibly existed in hunderds of thousands of billions of trillions of different forms before ours, and we are the only ones to notice how "lucky" we are because we are alive and in a universe that supports life.

What are you talking about? My whole argument was to support the idea that the observed anthropic coincidences make it more plausible that our universe is not the only one, and that there are a large number of other ones. I was responding to your claim that "the multiverse is irrelevant"--I think it is relevant, because observing anthropic coincidences makes it more likely that there are other universes or other regions of space with different, less "lucky" values of physical constants.

Normal

Agree, I think my problem is the term "multiverse", which I explain below.

My interpretation of the "multiverse" was that it entailed numerous universes existing simutaniously in parallels. I think this detail is extraneous and that the only universe that needs to exist is our own.

My point was that if our own universe is in a constant state of expansion-collapse, and has been so "timelessly", then the multiverse is irrelevant and all that needs to exist is our own universe. Any chance above 0 for life existing (it is clearly above 0), will mean life will eventually exist.

Corona688

There is a glaring problem with that, though - the same glaring problem that exists with many irreducible complexity arguments...

The probability calculated deals only with life as we know it. If the universal constants were different, yes, life as we know it might not exist - but that doesn't mean life would not.

Another way of looking at this is goldfish... I wish I knew who to accredit this parable to.. goldfish grow to suit their environment; the larger the bowl, the larger the goldfish. The goldfish looks at the bowl that it's grown to fit and says 'this bowl fits me too perfectly to be simply chance, it must have been designed JUST for ME.' Not so, it's just some plain ordinary goldfish bowl that it's grown to fit.

Life's like that, it adapts to it's environment; if there were a different environment, there might be different life.

So in summary, unless we can calculate every possible combination of universes and life within those universes, you and I are really not qualified to give anything but an 'I don't know' as to the odds of life occuring.

Jesse

Normal:
My interpretation of the "multiverse" was that it entailed numerous universes existing simutaniously in parallels. I think this detail is extraneous and that the only universe that needs to exist is our own.

My point was that if our own universe is in a constant state of expansion-collapse, and has been so "timelessly", then the multiverse is irrelevant and all that needs to exist is our own universe. Any chance above 0 for life existing (it is clearly above 0), will mean life will eventually exist.

OK, I gotcha. I'd consider expansion-collapse-expansion with different constants each time to be a sort of variation on the multiverse, just like the idea of a spatially infinite universe in which different regions (separated by domain walls) have different constants can also be considered a variation on it. I think the "bouncing universe" idea, where each collapse leads to a new big bang, has fallen out of favor among physicists, although chaotic inflation is similar in some ways.

Jesse

But as I said in my earlier post to GPLindsey, there do seem to be some minimal requirements for life, such as relatively stable complex molecules (or something similar to molecules) to be the units of heredity, like DNA. In our universe only Carbon and possibly Silicon could play that role, and I think at least a few of the anthropic coincidences are such that if the constants didn't fall within a particular narrow range, there would be no elements that could do so.

Normal

Do you know why the bouncing universe theory is no longer widely accepted? Or why the spatially inifinite universe is favored? The bouncing universe model always seemed to make the most sense to me (although we all know what makes sense has no actual influence on reality).

Jesse

Originally the bouncing universe theory was based on the notion that collapsing matter in the universe wouldn't necessarily lead to a singularity, but in 1970 Stephen Hawking and Roger Penrose used some new mathematical methods to show that expansion/collapse must lead to a singularity according to the theory of general relativity (it was also shown that beyond a certain point, a collapsing star must lead to a black hole with a singularity at the center). This doesn't necessarily rule out the bouncing universe idea since quantum gravity may do away with the notion of singularities, and I'm not really sure why other ideas like chaotic inflation are more popular--perhaps physicist's best guesses about how a theory of quantum gravity would apply to cosmology don't match with what would be needed for a bouncing universe to work. Also, I think I read somewhere that there was a problem with entropy in the bouncing universe scenario, where entropy would increase on each bounce and this would cause each successive bounce to last for less and less time before the universe recollapsed.