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astromark
2008-Oct-30, 10:22 AM
A / An infinitely large number.
B / Almost none.
C / Some other number between A and B
In order to answer this interesting question you first must set some boundaries.
Do you expect to see life like we know?
Microbic and biotic single cell life, or complex sentient beings ?
or some thing between these two.

Its far to early to say what might be the 'norm'... We do not have that information.
No. I can not throw out the Drake equation. It fits best what we now of as yet. Working logically through all the Galaxy we are in. As many as hundreds or as few as none.

I would suggest that life across the universe is common and will be found any place that can support it. But I can not know that.
The distances and time intervals involved in finding any life form are so big we must except that we might never find our nearest neighbors in space... and for the same reason 'they' will not find us. This is a good thing. Cos we are not ready.

cran
2008-Oct-30, 11:02 AM
Your initial question was about the number of civilisations in this galaxy -
phrases like "infinitely large number" seem to be more appropriate for conjectures about life in the universe ...

Whether maximum or minimum, to make any determination about the number of civilisations, you'd best begin with a general definition of a civilisation ...

Even using life on Earth as a guide, we can see that not all forms of life develop what we might recognise as intelligence ...

of those which arguably do, not all intelligent forms of life develop into civilisations ...

so, you immediately have three limiters to your "infinitely large" number ...

Grashtel
2008-Oct-30, 11:06 AM
I'm always hearing minimum figures but whats the max? Forget about the Drake equation. Its too limited. Assuming every habitable world has life and wet rocky planets are common then how many are there?

Earth and venus are similar in size. Mars once had oceans. I think it quite likely this is the norm. Every suitable star could have between one and three planets on average. Its impossible to say ofcourse. Our telescopes aren't good enough.

But hypothetically, how many could there be? Not counting colonies.
Expansive ones (or at least ones that would make themselves visible), not very many, a few hundred at most.

Non-expansive/hidden ones lots, assuming that every possible niche for life (including very speculative ones) not only has life but a civilization of some (mostly non-technological or at least with nothing we would recognize as technology) description there could potentially be dozens in the Solar System without our knowledge, including at least one other one on Earth in the ocean of molten iron that is the outer core.

Eroica
2008-Oct-30, 12:10 PM
There may be as many as 400 billion stars in the Galaxy. Some will be unsuitable for life and some - according to your criteria - will be capable of hosting a handful of life-bearing planets. So I guess you could start with a rough estimate of 400 billion and then find reasons to whittle it down. :think:

antoniseb
2008-Oct-30, 01:35 PM
Before I try to answer the OP title question, how many civilizations have there been on Earth?

astromark
2008-Oct-30, 06:19 PM
As interesting as it is to speculate all the 'what if's'... as has been said. We are the only life form we know of that has reached this level of technical ability that suggests intelligence. We could argue about that.
The events that have shaped the development of the human race is very complex. With some assured poignancy I can state that, that will not have happened any where else. Just a simple asteroid collision could, no. Did change the patterns of development here. What of the chances of us never being given the opportunity to rise to dominance. That could have easily happened.
The answer to your question is so complex we can only best guess the possibilities.
We could be one of the only places... or one of thousands. We can not be sure. Yet.

cran
2008-Oct-30, 10:06 PM
umm ... what happened to the OP?
someone called Australian Recession?

poor Astromark has been left holding the bag ...

mugaliens
2008-Oct-30, 10:21 PM
Need input:

A. How many stars in our galaxy?
B. What percentage of stars have class-M planets like our own?
C. What's the age of our galaxy?
D. How old is our planet?
E. How long has our planet supported life?
F. How long has our planet supported "civilizations?"

The answer will be:

A. The Milky Way contains at least 200 billion stars.
B. I said I needed input...
C. The Milky Way is estimated to be 13.2 billion years old.
D. Earth is 4.54 billion years old
E. Life on Earth has existed for approximately 3.8 billion years.
F. Earth has supported "civilizations" for approximately 14,000 years

Number < A*B*F/E*E/D*D/C

This reduces to:

Number < A*B*F/C, or 200 Billion * 14,000 / 13.2 Billion

Make it 212,121 * B, or roughly 200,000 * B.

So, if the percentage B is 1%, then the answer is 2,000 civilizations.

Now - I KNOW I'm doing the math wrong, here. Please help me out.

cran
2008-Oct-30, 10:51 PM
"class M planets" ... hmm ...

I remember there used to be talk of a "goldilocks" zone in a solar system -
a region where a planet should be able to retain liquid water, and therefore sustain life ...

Thinking about what might be required for evolution to allow for the rise of intelligent life, and then civilisations ... might such need the galactic equivalent of a "goldilocks" zone?

ie, would there be regions where the conditions are either "too hot" or "too cold" for the sort of complex evolution required?

Eroica
2008-Oct-31, 09:19 AM
Thinking about what might be required for evolution to allow for the rise of intelligent life, and then civilisations ... might such need the galactic equivalent of a "goldilocks" zone?

ie, would there be regions where the conditions are either "too hot" or "too cold" for the sort of complex evolution required?
Galactic Habitable Zone (http://en.wikipedia.org/wiki/Habitable_zone#Galactic_habitable_zone)

cran
2008-Oct-31, 11:22 AM
Thanks Eroica ...

I wanted our (now departed) OP to think about that in the light of the "infinitely large" viewpoint ... that the total of stars in the galaxy is probably quite different from the total of potentially habitable systems ...

plugging in a number like 200 billion, or 400 billion (any advance on 400 billion?) then also needs some consideration of stellar population densities - with an upper and lower limit ... likely, the potential hosts would number significantly less ...

JustAFriend
2008-Oct-31, 03:42 PM
Number of civilizations in the Milky Way Galaxy: 1 so far with data pending....

mugaliens
2008-Oct-31, 07:42 PM
Number of civilizations in the Milky Way Galaxy: 1 so far with data pending....

Well, let's keep our eyes peeled...

astromark
2008-Oct-31, 08:00 PM
Just like the vanishing OP... were did he go ?
It has been said that a advanced civilization may have happened just once.

ravens_cry
2008-Oct-31, 08:48 PM
One.
By one definition, a civilization is the most advanced culture. Therefore, since there can be only one winner, there is only one civilization.
I am not saying we are it or not, however.

mugaliens
2008-Oct-31, 10:08 PM
One.
By one definition, a civilization is the most advanced culture. Therefore, since there can be only one winner, there is only one civilization.
I am not saying we are it or not, however.

Now that, ravens_cry, is a rather interesting and unique perspective - quite nicely said.

I would have to qualify it by saying that it's only true if one is heads and shoulders above the rest.

The corollary is, "would the rest even be aware of how far advanced the advanced civilization is?" Are chimps aware that we humans built the skyscrapers, or do they just take it for granted like the three-year-old takes his first non-crib bed for granted?