The universe is so big it is impossible to say, I would assume though with all those other galaxy's and planets that there would be some sort of life form.

Real: If people really think that we are the only living thing in this universe then there is something seriously wrong.

real they have to be bro there is so much proof its not even funny :p

i think there real, there just not like little green people in silver suits with laser and flying saucers.

I am going to say real... Simply because Quantum Physics cant even prove the size of the Universe

-Ace wrote What are you 7 there obviously fake.

They're* also they're real haven't you seen your mother.

(Warning: Long Post Ahead)

Much of the conversation regarding the search for life revolves around finding planets in the habitable or "Goldilocks" zone of a star. This zone is the area surrounding a star in which liquid water can form and exist on a planet. The estimated distances of the habitable zone of the Sun, for example, extend from about 0.95 AU to 1.37 AU.* (For reference, the Earth's semimajor axis of orbit is 1.00 AU from the Sun, whilst Venus is at 0.72 AU, and Mars is at 1.52 AU, respectively). But there are far more important stellar requirements than this...

First, it's of note that approximately 85% of stars are believed to exist in multiple-star systems, and we can just about rule out any of these stars as being "fit" for harboring life bearing planets due to the complex gravitational issues which occur when orbiting two or more stars. Because of this, then, it is very, very unlikely that a planet could sustain an orbit stable enough to allow life to form. (For what it's worth, it's also of note that this percentage has been disputed, but regardless, the gravitational issues still stand).

Next, we need to look at the size of the star as size definitely matters (just not how you may be thinking it does)! It should be obvious based on the fact that we are here, that our star is an ideally sized star; it will exist long enough (~10 billion years on main sequence) to not only allow life to occur, but to also allow life the necessary time to evolve. The Sun is in the top 10% of all stars in terms of mass, but this is mostly due to the fact that smaller stars like red dwarfs vastly outnumber it. As far as size goes, the Sun, which is a main sequence G-class star, is really somewhere in the middle of the pack. Now, let's take a look at stars larger than our Sun...

(Just in case of any of you went philosophical on me after that last statement, I'd like to bring you back by taking a moment to repeat my favorite version of the "weak" anthropic principle which states that, "Living observers will always find themselves in a universe whose physical properties are consistent with the existence of life.")

As we all should know, as the mass of an object increases, so, in turn, does its gravity. Using this simple fact, we can show why systems with stars much larger than our Sun are unideal places to look for life: A star just two times the mass of our Sun has its fusion increased tenfold to overcome the increase in gravity which, then, causes its lifespan to be decreased fivefold, which will be about two billion years on the main sequence. (It's important to note that it took a billion years for single-celled organisms to arise on Earth, and 2.5 billion more years for us to show up).

As is expected, the larger a star gets, the shorter its lifespan. A supergiant like Betelgeuse, for example, will only exist for a couple hundred million years. We're definitely not going to find life there or orbiting around any other supergiant star... (Go supernova already...!)

Now, let's take a quick look, as this post is getting really long, at why stars much smaller than the Sun are also not ideal places to look for life as we know it. Specifically, we'll be looking at red dwarfs since they are the most prevalent stars in the Milky Way:

Since red dwarfs are so much cooler than our Sun, the habitable zone is much further in. For a typical red dwarf, it has to be moved in to an area about 1/20th of Mercury's orbit. The chances of a planet forming in such an incredibly small region are very slim. However, if a planet were to form in this region, there is a serious problem in the form of intense tidal forces. The tidal force is inversely proportional to the distance cubed (F = 2GMmr/R^3), so the closer the planet is to the star, in this case 1/20th of Mercury's orbit, the more intense the tidal forces will be.

So, as the planet orbits around the star, the friction generated by the tides bleeds rotational energy away as heat, slowly slowing the rotation of the planet down. In only a few hundred million years, the planet would be tidally locked to the star, as the Moon is to the Earth.

In conclusion, it's estimated that only 5% of ALL stars are of the right mass in which they are small enough to have a lifespan long enough to allow life to arise and evolve yet large enough to have their habitable zones in an area where tidal locking is not an issue.

(Just to keep your hopes up, 5% of all the stars in the Milky Way is still 20 billion stars!)

Nice little thing I wrote awhile back

Kasting JF, Whitmire DP, Reynolds RT. Habitable zones around main sequence stars. [Internet]. 1993. [cited 23 May 2012]. Available from: [ Register or Signin to view external links. ]

Lada CJ. Stellar multiplicity and the IMF: most stars are single. Harvard. [Internet]. 2005. [Cited 23 May 2012]. Available from: [ Register or Signin to view external links. ]

Plaxco K, Gross M. Astrobiology: a brief introduction. Baltimore: The John Hopkins University Press; 2006, 2011. 330 p.

CSIRO. Main sequence stars. [Internet]. 2004. [cited 23 May 2012]. Avaible from: [ Register or Signin to view external links. ]

Barnes R, Raymond SN, Jackson B, Greenberg R. Tides and the evolution of planetary habitability. [Internet]. 2008. [cited 23 May 2012]. Available from: [ Register or Signin to view external links. ]

Ya I think they're real we can't be the only ones in the universe.

-Ace wrote What are you 7 there obviously fake.

1. Your a ******.. 2. Respect other people's opinions. 3. Your a ****** again.