Life and the size of the universe

[Mazuz]

Thought I'd share a thought I had about a year or so ago while I was looking through a Hubble photos book in wonderment at the vast scale of the universe.

Suppose our universe is but one in let's say an infinite number of other universes all within a multiverse.

And let's say that the formation of life is extremely rare, which could be true for many reasons but let's just say that it is because life's formation relies on quantum luck, where a highly unlikely event needs to occurs just by chance to get it started. And let's suppose that a sufficient quantum event occurring in the right situation to start life is so uncommon that on average it would only occur once in a great number of universes.

Lets also assume that universes come in sizes.

It would seem to then be the case that those rare universes that contained instances of life would be larger on average than other universes, since a larger universe would offer more opportunities for the rare event of life to occur in.

Depending on what the odds of life forming are it could be the case that life nearly always finds itself alone in a universe that is seemingly incomprehensibly large.

And so as the thought goes maybe our own immense universe is a predictable likelihood based on our being here in the first place, maybe we have something like an intimate connection to this vastness as our existence may in large part be related to it.

Just an idea, all thoughts and comments etc are welcome.

 

[Chalnoth]

Lets also assume that universes come in sizes.

It would seem to then be the case that those rare universes that contained instances of life would be larger on average than other universes, since a larger universe would offer more opportunities for the rare event of life to occur in.

But that depends upon how likely various different sizes are. By most naive estimates of how easy it is to get a big universe, it turns out that you get more than enough small universes to make up for the loss of volume compared to the larger universes (e.g. you get more than twice as many universes with half the volume). There are proposed solutions to this, but nobody knows for sure what the right answer is. Yet.

 

[Chronos]

On a scale factor, the average between the Planck length and the size of the observable universe is only a few angstroms. In other words, the Planck length is unimaginably tiny.

 

[eloheim]

On a scale factor, the average between the Planck length and the size of the observable universe is only a few angstroms. In other words, the Planck length is unimaginably tiny.

That made me figure out that the 'scale factor average' between the Planck time and the age of the universe is something like 10^(-28) secs, if by some miracle, I did the math right. Anyone know a significant value thereabouts?

 

[Chalnoth]

On a scale factor, the average between the Planck length and the size of the observable universe is only a few angstroms. In other words, the Planck length is unimaginably tiny.

Actually, wouldn't the average of the Planck length and the size of the universe simply be half the size of the universe? :)

Presumably you meant the average in logarithmic space...

 

[Chronos]

It is the average based on the current apparent size of the observable universe. We do not know the current actual size of the universe.

 

[jobigoud]

On a scale factor, the average between the Planck length and the size of the observable universe is only a few angstroms. In other words, the Planck length is unimaginably tiny.

I too would like some elaboration on this sentence, as I feel there is something I am not understanding fully.

I believe Chalnoth above writes about "Half the size of the universe" because if you do the arithmetic mean between the size of the universe and any other length, even very small, you can't get a result lower than (size of the universe / 2).

So are we talking about the same kind of average?

Let's say S is the size of the universe as measured in Planck length units. How do we come to "a few angstroms" ?

Thanks!

 

[Kevin_Axion]

What he means is that if you find the midway point between the size of the Universe and the Planck Length, it will be a few ångströms or the size of 3 atoms. The Observable Universe is $$8.80\times 10^{26} m$$ and the Planck Length is $$\sqrt{\frac{\hbar G}{c^3}}\approx 1.6161252\times 10^{-35}m$$. The midway is approximately $$10^{-9}$$ which is the size of an atom. It's like saying you have a skyscraper and an ant, the midway is a clock tower.

 

[jobigoud]

Ah thanks!
So it is indeed the midway point between the orders of magnitude, not the distances themselves, thank you

(Which is kinda strange because if we were to express the exact same numbers using a different base for the exponentiation, I think we would get totally different results…)

 

[Naty1]

Mazuz: if there are an INFINITE number of universes, then there are an infinite number of small universes with life...so I don't buy your "predictable" hypothesis.

Also, it now seems life will spring up in the most unlikely places...that it's probable rather than rare ...as in deep sea plumes "poisoned" with sulfur gases, bacteria that live in arsenic, bacteria that eat the hydrocarbons from the Gulf Oil spill, and so forth...

So I think it likely there are forms of life in unknown environments beyond our wildest imagination in THIS universe.

 

[Chalnoth]

Ah thanks!
So it is indeed the midway point between the orders of magnitude, not the distances themselves, thank you

(Which is kinda strange because if we were to express the exact same numbers using a different base for the exponentiation, I think we would get totally different results…)

Nope! The base doesn't matter. The exponents with different bases are simply related to one another by the ratio of the logarithms of the base, so in averaging the exponents, you just have an overall factor sitting in front that doesn't impact the result (the average would still be roughly the size of an atom).

 

[DaveC426913]

Ah thanks!
So it is indeed the midway point between the orders of magnitude, not the distances themselves, thank you

(Which is kinda strange because if we were to express the exact same numbers using a different base for the exponentiation, I think we would get totally different results…)

At first I thought so too. But consider a simpler scale: mm to km. That's 10^-3 to 10³.

Halfway is 10⁰, or m. Is m halfway between mm and km? Yes. There are as many mm in a m as there are m in a km.

And it is unit-independent. There are as many [0.039 inches] in [39 inches] as there are inches in [39,000 inches].