Life in our universe

Recent estimates have put the number of galaxies in our known universe to be in the area of 100 billion. When you look at our own Milky Way galaxy, our sun is only one of 200 billion other stars within the galaxy (http://hypertextbook.com/facts/1999/TopazMurray.shtml). This being said, it is obvious that the universe is ungodly huge. How can anyone logically believe that there is no other life in our universe? How many other little rocks floating around one of trillions of stars in our universe have been lucky just like our planet to be able to foster life? People who preach intelligent design say that the liklihood of our existence on this planet is rediculously low, and that alone gives evidence for some sort of higher power. However when one considers the scope of the universe, how can anyone say that we are the only planet that is sustaining life? I just find it hard to believe that we should single our planet out from the trillions of others in our universe. Anyone agree or disagree?

Stephen Crane, the guy who wrote The Red Badge of Courage, wrote this poem:

A man said to the Universe:
"Sir, I exist!"
"However," replied the Universe,
"The fact has not created in me
A sense of obligation."

I highly recommend the following book:
http://www.amazon.com/gp/product/0387955...ks&v=glance
Fun and very informative.

Of the stars in our galaxy, the evolution of intelligent life would seem to require one of the relatively few that are far removed from the galactic center. Only there do stars avoid "close passes" with other stars for long enough periods of time that planetary orbits (and thus life-compatable conditions) can remain stable.

Of those relatively few stars -- we require one of an acceptable spectral class, with rocky planets, which may be relatively rare (they require a large number of "heavy" elements).

Now, of those rocky planets, how many will be in the very narrow "habitable zone" where liquid water can (and does!) exist? How many of those will have an orbit with sufficiently small eccentricity?

Of those, how many have a strong magnetic field to protect the atmosphere from being stripped by solar wind (and to protect against ionizing radiation)? A large moon is also important, as it tends to stabilize against precession of the axis of rotation.

This is just for favorable conditions... On how many of these worlds is life actually going to start? On how many of those worlds will life make critical (and seemingly difficult) leaps, such as the prokaryote-eukaryote transition?

And on how many of those will human-level intelligence actually evolve (it may not be particularly important for survival of a species)?

To top it off, the galaxy (and in particular, our solar system) do not show much evidence of colonization. It turns out that given any reasonable assuptions about technology and the period between colonization attempts, the time scale for colonization of the galaxy is far less than the timescale for evolution of intelligence. Thus, if intelligent life were relatively common, and even one species thought that colonization were a good idea -- the entire galaxy would likely have been colonized before we showed up on the scene.

The point is that it's easy to look at big numbers or look up at the night sky and be awed, but if you analyse the problem in some detail it does appear that we are pretty special... Whether you want to impart religious significance to that is, of course, up to you.

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To top it off, the galaxy (and in particular, our solar system) do not show much evidence of colonization. It turns out that given any reasonable assuptions about technology and the period between colonization attempts, the time scale for colonization of the galaxy is far less than the timescale for evolution of intelligence. Thus, if intelligent life were relatively common, and even one species thought that colonization were a good idea -- the entire galaxy would likely have been colonized before we showed up on the scene.


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If im reading this correctly, you are saying that there should be some sort of leftover remains showing signs of colonization. Do you really think that after the human race dies out on this planet that it will show any signs of our past existence? It will probably be like any other crater covered rock in the universe. Homosapiens have only been around for 100,000 years, while the universe itself has been around for 13,000,000,000 years (roughly). I would think it is safe to say that given that there are 100,000,000,000 galaxies in the universe, and the given the time frame, there is a very likely chance that life is out there or has been out there before us. As far as our own solar system, photographs of Mars show evidence of past oceans and river beds. Saturn's moon, Titan, is the closest planetary body in our solar system to being earth-like in that it has a nitrogen-rich atmosphere and lakes and rivers of liquid methane.

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If im reading this correctly, you are saying that there should be some sort of leftover remains showing signs of colonization. Do you really think that after the human race dies out on this planet that it will show any signs of our past existence? It will probably be like any other crater covered rock in the universe.

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Once a species has colonized the galaxy (and mapped its resources), I find little reason to expect that relatively rare planets meeting ideal conditions for life would be abandoned for long...

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Homosapiens have only been around for 100,000 years, while the universe itself has been around for 13,000,000,000 years (roughly). I would think it is safe to say that given that there are 100,000,000,000 galaxies in the universe, and the given the time frame, there is a very likely chance that life is out there or has been out there before us.

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Maybe, but that is a guess based purely on some awe-inspiring numbers. Keep in mind that that the early universe was filled with only hydrogen and helium -- no complex, life-supporting chemistry allowed! Heavy elements are created in stars -- thus you have to wait until later generations of stars form for any shot at life. And as was the point of my previous post -- the conditions required are pretty special...

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As far as our own solar system, photographs of Mars show evidence of past oceans and river beds. Saturn's moon, Titan, is the closest planetary body in our solar system to being earth-like in that it has a nitrogen-rich atmosphere and lakes and rivers of liquid methane.

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Yet they appear to be sterile, even in our fertile solar system...

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Once a species has colonized the galaxy (and mapped its resources), I find little reason to expect that relatively rare planets meeting ideal conditions for life would be abandoned for long

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Well considering that humans will eventually exhaust our planets resources and eventually die off without the universe even blinking, i dont see how you can say that. We already have the capacity to destroy our planet (thermonuclear weapons) and are destroying our ozone layer as well. On a universal scale, we have little impact and our planet will eventually end up as a dead rock, just like Mars etc.., a lot sooner than one thinks. Given that there are galaxies out there that were formed only one-billion years after the Big Bang, it is very likely that life has evolved elsewhere than our own planet.

Hubble Deep Field

This photo represents only a fraction of space the width of a dime 75 feet away. Tell me that there is no life in the universe besides us.

[Jbrochu]

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Now, of those rocky planets, how many will be in the very narrow "habitable zone" where liquid water can (and does!) exist?

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How do we know that every form of life requires water? I always wonder if I'm missing something when I see this argument about no water and no oxygen being used to support the conclusion that there is no life somewhere else.

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Well considering that humans will eventually exhaust our planets resources and eventually die off without the universe even blinking, i dont see how you can say that.

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It is based purely on experience with life. Once life can freely travel in a particular domain, it aggressively seeks out and takes advantage of resources. So, one might expect that once life begins traveling interstellar distances in search of premium planets, there is little chance of resources (such as our solar system) going to waste, even after one particular species goes extinct. Thus, once our solar system is colonized I would not expect alien life to simply leave and never return in the midst of a galaxy teeming with life. It would be roughly like leaving out raw chicken for 24 hours and expecting it to be germ-free.

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We already have the capacity to destroy our planet (thermonuclear weapons) and are destroying our ozone layer as well. On a universal scale, we have little impact and our planet will eventually end up as a dead rock, just like Mars etc.., a lot sooner than one thinks. Given that there are galaxies out there that were formed only one-billion years after the Big Bang, it is very likely that life has evolved elsewhere than our own planet.

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Maybe your definition of "life" is a lot looser than mine -- I'm mainly interested in intelligent life. I would agree that there is probably some kind of life out there -- but the power of its philosophical or religious implications may not be particularly great. Intelligent life might be another story, however.

An argument based on the fact that your mind is boggled doesn't carry too much weight. Of course I can't tell you that there's no life "out there." But I can say that certain facts are consistent with intelligent life being very rare, even on a galactic scale.