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Author Topic: What's The Real Probability Of Life Existing Elsewhere In The Universe?  (Read 1001 times)

Offline Solium

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So the Milky Way has an estimate 100 billion stars and there's an estimate 100 billion galaxies. The Ingredients that make up life as we know it are abundant in the universe.

The numbers suggest there must be countless rocky planets in the goldilocks zone in other solar systems where life could possibly take root and evolve.

Theory has it microbes evolved very early after the formation of the Earth, and were the primary life form for billions of years. So it suggests simple life forms should exist elsewhere at that level.

This maybe expanding on the general question but we also know a lot of other factors were required for life on Earth. A Moon large enough to stabilize the Earth’s rotation. A planet that's tilted just enough to provide seasons. An iron core which protects the Earth from the solar winds and radiation.

What is missing from all of this is the “genesis” of life. Without knowing what was the spark of life on Earth, (assuming life started here and wasn’t transferred from someplace else) can we really surmise it ever happened a second time in the Universe?

How do we know the conditions that possibly created life on Earth wasn’t a one time event not to be repeated again?

If we found microbes or fossils on other worlds in our solar system, it would be a huge game changer. It would suggest life can come into being and flourish in many places in the universe.

What we do know about our own solar system, and space in general is it’s a self sterilizing environment. It doesn’t appear the universe as we know it is conducive for life.

Why would we think life on Earth is anything more than a fluke, when you consider all the factors mentioned above?
« Last Edit: 03/08/2016 21:41:26 by Solium »


 

Offline Atomic-S

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Science does not know enough about the possible ways life might create itself to calculate the probability with any accuracy, but it is evident that the probability per planet is very low.  That is clear from trying to calculate the probability for a one-celled organism to originate on Earth, where we at least have a fairly good acquaintance with the environment and the chemistry. What is clear is that such an organism is quite a complex system whose occurrence by chance is quite unlikely.  We would be assuming that life elsewhere in the universe would necessarily be, if not like that on  Earth, nonetheless chemically complex or we would not be justified in calling it "life", and because it must be such, we can say that the probability of its occurrence elsewhere is likewise very low.  But we really can't be more precise in the calculation in view of our extremely limited knowledge of the composition of environments elsewhere in the universe.
 
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Offline alancalverd

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It is almost certain that life (i.e. selfreplicating molecules) could evolve on any planet that has liquid water.
 
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Offline PmbPhy

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Quote from: Solium
So the Milky Way has an estimate 100 billion stars and there's an estimate 100 billion galaxies. The Ingredients that make up life as we know it are abundant in the universe.
The statement that there's an estimate of 100 billion galaxies is misleading because cosmologists have absolutely no idea how many galaxies there are in the universe. There's not even an estimate. Any estimate is not only misleading but also 100% inaccurate. It's quite possible, even likely, that there are an infinite number of galaxies in the universe. If its not infinite then its finite. Given that fact ask yourself what the difference is between an infinite number of galaxies and a finite number of galaxies. What do you get?

If there is an infinite number of galaxies in the universe then the probability that there's life elsewhere in the universe is 1. A probability of 1 means that its exactly 100% certain. If that's true then it follows from that that there's an infinite number of worlds which have intelligent life on them.

What determines all of this is the mass density and nature of matter in the universe. To be 100% precise it depends on the stress-energy-momentum tensor and the cosmological constant. That will determine the spatial geometry of the universe. If you're not familiar with the cosmological principle then it's stated as follows. From Wikipedia: https://en.wikipedia.org/wiki/Cosmological_principle
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In modern physical cosmology, the cosmological principle is the notion that the distribution of matter in the universe is homogeneous and isotropic when viewed on a large enough scale, since the forces are expected to act uniformly throughout the universe, and should, therefore, produce no observable irregularities in the large scale structuring over the course of evolution of the matter field that was initially laid down by the Big Bang.
This implies that the number of galaxies per unit volume is  a constant when that volume is viewed on a large enough scale. Under these conditions there are three possibilities for the spatial geometry of the universe.

1) Closed and spherical
2) Open and flat
3) Open and hyperbolic

If the universe is open, which it appears to be, then the universe is infinite in size and contains an infinite number of galaxies.
 
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Offline evan_au

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Quote from: Solium
Without knowing what was the spark of life on Earth, (assuming life started here and wasn’t transferred from someplace else) can we really surmise it ever happened a second time in the Universe?
Without knowing what was the spark of life on Earth, can we really surmise it didn't happen a second time in the Universe?

That is the problem with only knowing 1 solar system, which only has 1 planet in the Goldilocks zone. It doesn't give a basis to estimate the probability of it happening elsewhere.

But if we find water-soluble life outside the Goldilocks zone (eg Europa), that also changes the statistics.
 
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Offline Solium

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Thanks for all the feedback. Interesting to read! I'm always contemplating the variables of this question.

 

Offline Atomic-S

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If there is an infinite number of galaxies in the universe then the probability that there's life elsewhere in the universe is 1. A probability of 1 means that its exactly 100% certain. If that's true then it follows from that that there's an infinite number of worlds which have intelligent life on them.
We have no firm evidence that there are an infinite number of galaxies, so that this statement cannot be considered science but only speculation.

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It is almost certain that life (i.e. selfreplicating molecules) could evolve on any planet that has liquid water.
No doubt it could, if it were already present. A tougher question is whether on a planet that has liquid water, self-replicating molecules sufficiently advanced to become established as a viable species could spontaneously form if they did not pre-exist.

 

Offline clueless

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Why would we think life on Earth is anything more than a fluke, when you consider all the factors mentioned above?
Well, the anthropic principle suggests otherwise and is favoring the presence of God. In any case, life is a mystery, yet I don't mind because I like mystery novels, even though this particular novel won't be solved any time soon.
 

Offline Blame

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Breaks down to 3 sections.

1) If life gets going in a usable environment it will evolve and the universe is well big enough to provide plenty of those. Question is how difficult is that first step where a naturally occurring molecule started reproducing itself? Could be so unlikely it only happened once or alternately the universe could be positively crawling with bug eyed monsters.   

2) How big is the universe? I think it fair to assume a finite size for purposes of discussion because that is the prevailing consensus.

3) Is there a god? If there is and He/She/It created the universe for us then could you plausibly argue that it was made so big just for us?
 

Offline Solium

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This is old news but I just learned scientists found amino acids in asteroids that date back to the formation of the solar system.  This means the building blocks of life are not only abundant but existed at the time of planet formation. While we still don't know the "spark" that created life, if it can happen twice, then it must happen a lot in the universe. I prefer to leave supernatural explanations out of a science based discussion.
 

Offline Atomic-S

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There is presumably no way to calculate the probability that these amino acids will assemble themselves into a viable bacterial colony without assuming something about the environment.
 

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