# What is the probability of life in Universe?

1. Oct 1, 2007

### Viva-Diva

Hello to all scientists here,

I am not a physicist and am new to the forum.

Considering the Universe is so huge, isn't the probability of having life on other planets in the universe equally high?

Viva-Diva

2. Oct 1, 2007

### marcus

at least 99.999 % if you consider the entire observable universe (just an informal guess).

but we still might be the only life in our GALAXY, at least that has evolved to the point of being able to measure the speed of light and imagine inhabiting other planetary systems and stuff like that.

there are billions of galaxies, and each galaxy contains billions of stars (actually more in both cases, like hundreds of billions, but not to be overprecise)

so if life is extremely rare for some reason we don't understand, then it's conceivable that Earth might be the only planet with life in the Milkyway galaxy. (I can hardly see how life could be so rare, but let's pretend we are alone in the galaxy).

even then, you still have all those billions of other galaxies. but we may never interact with life in other galaxies because they are so far away. in some sense it seems almost not to matter.

what seems to matter to me is what other life and what other civilizations are there in the Milkyway. they are the ones we might someday (if they exist) talk with or learn about

======================
Viva, I almost wish you had asked a slightly different question (which would be a LOT harder to answer) namely
what do you estimate is the probablility of other life in the Milkyway galaxy?

for the universe as a whole, it is almost certainly 100 percent. it isn't even an interesting question, as I see it.

but if you just ask about other life in Milkyway, how prevalent is it? does it exist at all? if it exists are we talking like 5 other civilizations in the whole galaxy, or hundreds? because at this level, the level of galaxy, how you answer is constrained by the socalled Fermi question---this puts some nittygritty meaning into it and gives some traction to the mind. then you can't just say anything that comes into your head.

Last edited: Oct 1, 2007
3. Oct 1, 2007

### mgb_phys

This is known as the drake equation http://en.wikipedia.org/wiki/Drake_equation, basically the number of stars * the probablility that the star could have life on planets around it.

4. Oct 1, 2007

### cristo

Staff Emeritus
I agree with marcus: it is far more interesting to try and find out if life exists in our galaxy since we may, at some point in the future, be able to contact them.

The study of exoplanets (planets outside our own solar system) is somewhat of a new field of research, and one that there are a growing number of astronomers turning their expertise to. We are discovering more exoplanets within the Milky Way each month. In fact, I remember a talk I went to a couple of months ago where a project called DARWIN was mentioned. This is scheduled to start in the next decade and, I think, is something to do with what used to be called PPARC (the Particle Physics and Astronomy Research Council) here in the UK. The aim of this mission is to try and seek out earth-like planets orbiting nearby stars.

All in all, it's an exciting period for astronomy/cosmology at the moment.

Last edited: Oct 2, 2007
5. Oct 2, 2007

### Chronos

The vast majority of scientists would concede the probability of extraterrestrial life is 100% in the universe at large, and probably 90% that some form of life existed on Mars at some point in the past. Intelligient life is, however, a sticky wicket. It takes a very long time to arise and requires improbable events. Placing odds on these events is very difficult. I would guess it is very probable we are the only technologically accomplished species in this galaxy at this time. Civilization, as we know it, has only existed on earth for a handful of thousands of years. And civilizations capable of extraterrestrial communication has only existed here for about 50 years. This is an incredibly tiny slice of time in the life of a galaxy [or universe]. Furthermore, the window to detect our EM emissions by accident could easily close within the next 100 years. Assigning only slightly pessimistic values to the Drake equation yields a value of less than one comparably accomplished civilization to any given galaxy in the universe at such a tiny slice of time. The background noise of the universe yields long odds that any of them are detectable to us.

6. Oct 2, 2007

### Viva-Diva

Thank you all for your views and nice links that you all directed me to.

But Chronos, why did creation of Universe make a lot of people angry?:-)

7. Oct 2, 2007

### Feonix12

Personally i would think there is a 99.9% probability of life on another planet. Im assuming life has to have the right conditions and the right timing but so many chances in the universe you would think there would be more than one.

8. Oct 20, 2007

### zankaon

The possibility and near reality perhaps of detecting an oxygen signature of atmosphere of terrestrial exoplanets is quite amazing. The following is excerpt of previous post in astronomy:
How far away from earth might the oxygen signature of our atmosphere be spectographically detectable? The flip side is how far away might an exo-terrestrial planet's atmospheric oxygen signature be detectable? For example,Gliese 581 c,d are larger (5-7x earth) terrestrial planets at 20 lyrs distance.http://en.wikipedia.org/wiki/Gliese_581_c Hence a fast and easy extensive way of surveying for surface life; thus for our planet, over 2 billion years of significant oxygen signature exposure.

9. Oct 21, 2007

### Dan Tee

If there is intelligent life in our Galaxy, how could we communicate considering the distances likely to be involved ?? it could be a one sided communication

10. Oct 21, 2007

### marcus

one sided sounds good to me.

When I read Jonathan Swift book Gulliver's Travels, he is communicating oneway to me. from back around 1700s.
I'm happy, you have problems with it?

If there is other intelligent life in our Galaxy, I hope they thought to radio us a copy of their equivalent of Wikipedia, or the Encyclopedia Britannica. If they did, and we get it in a few thousand years, we'll have a ball with it.
Onewayness not withstanding!

Last edited: Oct 21, 2007
11. Oct 21, 2007

### Wallace

Interesting, I'd never thought about 'one-way' communication with ET's like this before. I guess the issue is that it's quite an investment in time and money to send the signal out if you have no idea where to send it or whether there is anyone to listen.

At least in writing a novel you know that people do read novels, and indeed that people exist!

I believe (though correct me if I'm wrong) that the sensitivity of SETI programs on Earth would not pick up the kind of signals that Earth sends out (TV, radio etc) if these signals where sent from even the closest stars to us. So for instance, ET could be watching telly on a planet orbiting Alpha Centauri and we wouldn't pick it up with SETI.

We don't actively send out high powered signals into space to try and send info to ET (though this has been done for small periods of time in the past) even though we do spend a fair bit of time listening. What if all the civilisations in the galaxy are waiting for the call, but no one has tried dialing yet, kind of like a post first date phone stand off

12. Oct 22, 2007

### Dan Tee

No, I do not have a problem with one way it is the only way for those distances and if we could actually communicate we would probably only argue. I do like your analogy to a novel, perhaps they would send a comprehensive history of themselves and a few usefull tips say some does and don’ts.

Re comments by Wallace concerning SETI, can I ask "Does SETI only pick up certain types of signal??"

Perhaps the huge distances that we are faced with are Natures way of keeping us out of trouble

13. Oct 23, 2007

### Chronos

SETI limits detection modes to the most probable wavelengths - like the neutral hydrogen 21 cm band. Other modes are less attractive because of detectability limits. We make the fairly reasonable assumption ET is aware of these limits.

14. Oct 25, 2007

### Zenparticle

I think it's just a quote that he finds amusing/interesting..But I can not answer for him just what my logic tells me.

15. Oct 25, 2007

### mgb_phys

From Restaurant at the end of the Universe ( 3rd hitch hikers book)

"The story so far:
In the beginning the Universe was created.
This has made a lot of people very angry and been widely regarded as a bad move"

16. Oct 26, 2007

### Chronos

mgb has me cornered. It is ironic humor. Douglas Adams is very good at this sort of thing. I loved the part where the cosmic octopus revealed the secret to the TOE - 42. Hard to argue with that kind of logic. The Drake equation is a very logical approach to estimating the abundance of life in the universe. The sun is a very common type of star [small, dim, invariant output, and long lived], planets are the rule, not exception, and planets occupying 'goldilocks' orbits are assuredly abundant throughout this galaxy and the universe. So the probability of ET life forms within the milky way is virtually 100%, and nearly 100% life forms do, or did, exist on other bodies within our own solar system.

The probability of intelligent [as in technologically capable of communicating with us] life forms has a very poor probability of existing. The chances of it having existed elsewhere at any time during the lifetime of our solar system is virtually zero. Our ability to even calculate the probability of it existing anywhere else in our galaxy is also close to zero. The fact the skies are not abounding with signals from alien civilizations - priceless. Fermi raised a very good argument. Not only do we lack irrefutable physical evidence of their visits to earth, we also lack radio evidence they exist. Granted detection of an alien TV station is a shot in the dark, we most certainly have the technology to detect such broadcasts emanating from anywhere in the galaxy, if our big 'ears' were pointed in the right direction. Obviously it will take centuries to scan the entire sky, but the evidence is clear. Civilizations like our own a rare. Statistically speaking, no more than five like our own currently exist within this galaxy. The absence of signals also has statistical significance and this the pure number crunching result.

17. Oct 26, 2007

### Chronos

The probability of intelligent [as in technologically capable of communicating with us] life forms has a very poor probability of existing. The chances of it having existed elsewhere at any time during the lifetime of our solar system is virtually zero. Our ability to even calculate the probability of it existing anywhere else in our galaxy is also close to zero. The fact the skies are not abounding with signals from alien civilizations - priceless. Fermi raised an excellent argument. Not only do we lack irrefutable physical evidence of alien visitors, we also lack radio evidence. Granted detection of an alien broadcast is a shot in the dark. But, we have the technology to detect such broadcasts emanating from almost anywhere in this galaxy - if our big 'ears' are pointed in the right direction. Obviously it will take centuries to scan the entire sky, but the evidence so far is clear. Civiliations technologically equivalent to our own are rare. Statistically speaking, no more than five such civiliations are likely to currently exist within this galaxy, and zero is still not excluded.[/QUOTE]

18. Jul 30, 2008

### baywax

[/QUOTE]

The stats are fine but if we're looking for radio signals we might be looking for the wrong thing. There's more than one way to send a signal... many of which we have not thought of, no doubt.

Its particularly heartening to hear that we have turned our search for exoplanets into our own galaxy. I wondered if that was happening.

19. Jul 30, 2008

### dilletante

Hi Chronos,

Do we actually have the technology to detect alien TV signals from anywhere in the galaxy, and have we made any attempt to do so? I am hoping you have more information on SETI than they provide on their website, which seems pretty meager. I have been unable to find how many stars they have looked at, for how long or at what frequencies. They did mention one study of 100 nearby stars. It is my impression that they are concentrating on the frequency of neutral hydrogen, which earthlings are not allowed to broadcast on. If aliens think like us, then they are listening to the same frequency and not broadcasting on it either :)

I have been unable to determine whether we actually have made an attempt to listen to normal broadcast channels, or if we are capable of hearing anything broadcast on those channels beyond our neighborhood. Certainly if we are restricted in the bandwidth we listen to and have covered only a small number of stars, it seems premature to conclude that intelligent life is rare or nonexistent. Sagan did not seem to think so, and he was involved with SETI. It would be great to have some additional factual information!

20. Jul 30, 2008

### keinve

Where do i begn? first, as others have stated, other civilizations might use different EM waves for the same purpose. Second, since all EM waves travel at the speed of light, they might simply be too far to reach us yet. Third, EM waves can be disrupted by large amounts of physical matter, or by extremly large gravity wells, such as black holes. I will give you one point. Civilizations like our own are rare. But you didn't specify the technology, which is why i agreed with you on that point. A civilizations technology could be high enough to go faster than the speed of light(just exaggerating for the purpose), yet have a completly, no joke intended, alien civilization. One other thing. By 'communication', do you mean they would be able to understand us, or anything we do? Or do you mean contact us, regardless of if we undersand it? Because, if you mean the second one, a civilization could have already threatened us to put down our arms, or be killed, we just might not have noticed. If it's the first one, then the chances are, litterally, next to none. An alien species might not even notice us, or we them.