I very strongly believe that aliens exist, especially the microbial type, but also the intelligent type. Just look at the [very large] numbers and you'll know what I mean. I use exponential form as it makes working with large numbers much easier.
Number of stars in an average galaxy: 1E11 (100 billion)
Number galaxies in the universe: 2E11 (200 billion)
Number of planets and fair-sized moons around a star on average: 2.5E01 (25)
Number of planets and fair-sized moons in the universe: 1.E11*2E11*2.5E01, (1*2*2.5)E(11+11+1), 5E23 (500 sextillion (aka 500 billion trillion))
That's for starters. There are conditions though:
The galaxy must be "new" enough for metals (elements beyond helium) to form. You can't have life without carbon, hydrogen, oxygen, and nitrogen (CHON as I remember it). This eliminates about 1 in 25 possibilities.
The galaxy must be stable. Colliding galaxies cause so much mayhem from things like star burst and the rare collision that life will be extremely difficult to develop even if other conditions are suitable. This removes about 1 in 5 galaxies.
Stars must fall within the galactic habitable zone. Too close to the galaxy center, it's dangerous due to stars more likely going supernova inhibiting. Too far out and metals are lacking. This is about 1 in every 10,000 stars as a rough estimate.
The star must be of the right type. There are 7 main star types (classes), in order from coolest to warmest: M, K, G, F, A, B, and O. Our own star is G2, near the upper (warmer) edge of the G-glass. The A, B, O, and upper 1/3 of the F classes have too short of a duration for intelligent life to develop but they are fairly rare. The M class and lower 1/3 end of the K class live long, but the planet risks being tidally locked (like our Moon is to Earth), but are very common. This, thus, covers about 1 in 20 stars (for intelligent life, 1 in 2 for microbial).
The planet or moon must fall within the habitable zone of a star. Too close to the star and the planet scorches. Too far and the planet is frozen. Even something as far out as 12 AU (between Saturn and Uranus; based on our Sun) could still have life, but must be tucked far under the surface of a planet or moon). Close-in planets could still be okay, mainly if tidally locked. This eliminates about half of the possibilities.
The star must be stable. A young star is quite unstable and fierceful. An old star is also unstable, from running out of fuel. Thus, the star needs to be of the right age. This eliminates about 1 in 20 stars.
The planet or moon must have a reasonable, fairly circular orbit. Planets with wild elliptical orbits will have short bursts of great heat followed by a long period of great cold making for an unstable environment. Many planets seem to have elliptical orbits. This eliminates about 1 in 10 planets I'd say.
The planet or moon must have some form of protection against hazards such as solar flares - an ocean, atmosphere, deep caves, and/or magnetic field of sufficient strength. This eliminates about 1 in 5 planets.
The gravity of the planet or moon must be just right. Too small of a planet means too little gravity to hold on to an atmosphere. Too large of a planet and getting around will be extremely difficult. This removes 1 in 10 planets.
Techtonic activity is necessary for recycling old material. Mars is practically dead and there hasn't been any known techtonic activity for billions of years. I would say that this eliminates 1 in 5 planets.
Finally, the planet or moon must have a solid surface not under an excessively thick atmosphere. Sure Jupiter or Neptune may have something solid far below, but this is going way too far. Venus is pushing it. This eliminates about 1 in 50 planets.
So, let's sum up the result:
5E23 / 2.5E01 / 5E00 / 1E04 / 2E01 / 2E00 / 2E01 / 1E01 / 5E00 / 1E01 / 5E00 / 5E01 =
(5/2.5/5/1/2/2/2/1/5/1/5/5)E(23-1-0-4-1-0-1-1-0-1-0-1) = 0.0004E13 = 4E09
That still 4 billion possibilities in the universe for intelligent life. I would still say that there's a few hundred in our galaxy alone (us being one of those)!
I am amazed at how stubborn programmers are. True, I am one myself. But most of you seem to think they know The Truth. Everybody who says something is a fact is plain wrong, except for the fact that there are really no possible facts.
I have read a lot about the universe and the general answer is: We don't have a friggin clue about how everything works. We don't know whether we can or can't travel in time. Wormholes probably exist. Can we travel through them? Not normally, they are too unstable, but that doesn't mean it's impossible.
But I have to be honest, I can't say I even remotely understand most of what I know about the universe.
It was asked in this thread what would happen if you would reach the end of the universe. One of the most interesting theories I've heard on this was that you would end up on the other side. Strange? No, you won't be teleported to the other side.
We can compare it with the world. The world's surface is 2D, but bend over a third dimension. If we get to the "end" of the world, we end up on the other side because it's round, not flat. The same may be true for the universe: 3D, bend of a 4th dimension (not considering time). The growing of the universe would be like blowing up a balloon.
And what about dimensions? It was already said before, but whoever says we have 3 (or 4, including time) dimensions... I can't say you're wrong, but you are ignorant. There may be a lot, lot more.
Ah, and minimum 4 lightyears away, the closest possible aliens? We still haven't ruled out Europa.
The fact (okay, can I really call this a fact?) is we know fairly little about the universe. And I doubt we'll ever know even a fraction of The Truth.
(insert remark about 42 here)
There are several facts, so you are wrong.
Peanut butter is hot.
Fire goes good with jelly.
If you don't belive me then I'll show you pictures of my ex-girlfriend and we can watch Napalm week on the history channel.
I think there are a few interstellar species, and a bunch of indusrial and tons of pre-industrial species. I think the ones that make it into space (real space not just interplanetary) tend to either wipe out he other species near them, or get wiped out by them.
That's a take on the Drake Equation (=hitler in three moves, but anyway...).
Originally Posted by ulillillia
However, you haven't yet taken into account the final, possibly very limiting and unpredicatable factor w/r/t to contacting extra-terrestrial life:
Percentage of intelligent species that destroy themselves/their environment too early, because of their intelligence/technology
So, depending on whether you actually count that as intelligence, those multipliers might have met the mother of all divisors. I would, but I would even include people who disagreed with this poll, making me kind of a wet carpet. Remember, the majority will kill us all.
That's why I finally decided go ahead and start making killer robots.
Originally Posted by MK27
Intelligence - Hitler one link BTW, thanks to yours truly, yes its a legitimate link as well.
And one thing noone likes to consider is that, some species has to be the first to achieve interstellar travel, maybe its going to be US. Maybe, and I shudder to even type these words, we are the most intelligent and advanced species in the Milky Way...
Then again, maybe we are the dumbest and the last.
>I am amazed at how stubborn programmers are. True, I am one myself. But most of you seem
>to think they know The Truth.
And I will talk about it loudly! Just like you can!
>I have read a lot about the universe and the general answer is: We don't have a friggin clue
>about how everything works.
That reminds me of something a religious zealot would say. If you're content figuring that you don't have a clue, fine, but we can't all be so pragmatic. :p It's not like we're having a good debate on weighty matters, anyway. I have to disagree about knowing nothing in particular about the universe... it's big... physical evidence and reasoned logic has helped us understand a lot about our solar system and our little blue planet, a small part of the universe though it may be.
This should settle it:
Weddell Seals Sounds
I cannot stop listening to this and I am now worried that I like cold water.
If you back up into the link, there are a few more clips with photographs. They are deceptively normal looking, for seals.
I haven't seen them, but that doesn't mean I am in disbelief of their existence. Same goes for most things in life.
I have a time machine on my wrist.
This got me thinking about whales, then about aliens that might be completely water-based.
Originally Posted by MK27
So if aliens land on earth, they might live at the bottom of the ocean and have zero need for interaction with humans.
Heck, aliens may have even be able to live in the mantle of the earth, or in the core, where no humans will ever go.
Who really knows. ;)
I think the question is really moot. The entire universe is actually alive, both on individual and collective levels. I mean, think about it. You are *a* being. Made up up trillions of *beings*. Which are, in turn, probably made up up smaller beings (there are components of indiviual cells that exhibit autonomous behaviour - some these even resemble bacterium!). Why should not indiviual atoms be capable of conciousness? Towards infinity in either direction, "beings" exist. We are not alone. :D