Is there life in the universe, and if so has it visited Earth?

[Ivan Seeking]

You seem unable to wrap your head around the distances and timing involved. It would be like someone from Seattle, WA walking all the way to the African Savannahs to find a single blue ant. Even if that ant figured out how to click it's mandibles together rather loudly recently it still would only be a few fractions of a second ago and so far would not have done any good.

That's what the distances and duration of the universe turn the hunt for extraterrestial life into, we're the ant, the aliens would be the seattle resident, and the clicking would be our EM broadcast technology. Sure the odds of a more advanced lifeform existing somewhere are amazingly good but the sheer size and timescales involved make us finding each other amazingly bad.

How can one impose these limits on a race that we assume can travel the distances required in the time required? As I said, already we are figuring out how to identify other earth-like planets. What might we be able to do in a million years?

 

[CEL]

How can one impose these limits on a race that we assume can travel the distances required in the time required? As I said, already we are figuring out how to identify other earth-like planets. What might we be able to do in a million years?

Will we still be here in a million years? Nobody knows. It is clear that if we had the technology for interstellar travel, in a few million years we would be able to colonize the Galaxy, provided that we would last that long.
In that case, a civilization with our actual level of technology would probably be able to detect us in their vicinity. After decades of search we found zilch.
Is it probable that at this instant there exist other civilizations in our galaxy? In my opinion the answer is yes. Have they visited us? I don't think so.

 

[andrewj]

http://video.google.com/videoplay?docid=-5594744703753734741

Bearing in mind this post by Ivan in the UFO stickied thread.

10,000,000,000,000,000,000,000 stars in the universe, a very conservative estimate but let's assume it's correct.

And the Drake equation is possible given the criteria and confirms there must be intelligent life: maybe in the galaxy, but definitely in the universe by the laws of probability.

http://www.activemind.com/Mysterious/Topics/SETI/drake_equation.html

And apply this to the universe, in a sort of what if way assuming this is fairly typical.

My question is two fold, we're fairly certain that probability indicates there must be life elsewhere in the universe, and assuming evolution works in simiilar if not the same ways elsewhere: it's fair to claim that their is intelligent life, so we accept life is out there? Yes/no?

Now given the conclusion is yes, do you think the intelligent life has visited Earth?

c\onspiracy theorists would have you believe that were inundated with the feckers . but don't you really think intelligent beings would try and make contact
not just with the cia but with the populus

 

[Ivan Seeking]

This is not about conspiracy theories. It might be [if such things are possible] that we have been visited and the CIA is as clueless as everyone else.

 

[Ivan Seeking]

In that case, a civilization with our actual level of technology would probably be able to detect us in their vicinity. After decades of search we found zilch.

We may not be looking for the right thing. Either way, after thinking about this problem for about twenty years, I realized that we can't say that the odds of contact are astronomically small, as most people do. This is like saying saying that we know the odds that interstellar travel [IST] is possible. Well, either the laws of physics allow it or they don't. There really are no odds. If IST is not generally possible, then the odds of contact may be small or zero. But if IST is possible, contact could be a near certainty. There is simply no way to know. We can only guess at the odds of the odds. Based on our current understanding of physics, contact seems to be unlikely, and in most cases, impossible.

 

[DaveC426913]

We may not be looking for the right thing. Either way, after thinking about this problem for about twenty years, I realized that we can't say that the odds of contact are astronomically small, as most people do. This is like saying saying that we know the odds that interstellar travel [IST] is possible. Well, either the laws of physics allow it or they don't. There really are no odds. If IST is not generally possible, then the odds of contact may be small or zero. But if IST is possible, contact could be a near certainty. There is simply no way to know. We can only guess at the odds of the odds. Based on our current understanding of physics, contact seems to be unlikely, and in most cases, impossible.

IST is definitely possible. Now, it may not be practical, but it is achievable.

Thing about judging whether it's practical is that it then becomes a guess as to the motivation of the the minds doing the judging - and then we're back to guessing how aliens think.

Who knows, maybe they evolved on a planet that's 95% water, and generation ships or suspended animation are as natural to them as in-flight movies.

 

[Ivan Seeking]

IST is definitely possible. Now, it may not be practical, but it is achievable.

Sure, at this point we can only imagine it being possible for a few local stars, but that's where the "unlikely" chance of contact comes in - leaving the door cracked open just a bit. Even if we are ultimately bound by the technical limits that we understand now, there is always a chance that someone else lives in the immediate neighborhood.

 

[PlasmaSphere]

This seems relevant. Top 10: Controversial pieces of evidence for extraterrestrial life.

http://space.newscientist.com/article/dn9943

1. 1976, The Viking Mars landers detect chemical signatures indicative of life

2. 1977, The unexplained extraterrestrial "Wow!" signal is detected by an Ohio State University radio telescope

3. 1996, Martian "fossils" are discovered in meteorite ALH80041 from Antarctica

4. 2001, A more rigorous estimate of the "Drake equation" suggests that our galaxy may contain hundreds of thousands of life-bearing planets

5. 2001, The red tinge of Jupiter's moon Europa proposed to be due to frozen bits of bacteria, which also helps explain the mysterious infrared signal it gives off

6. 2002, Russian scientists argue that a mysterious radiation-proof microbe may have evolved on Mars

7. 2002, Chemical hints of life are found in old data from Venus probes and landers. Could microbes exist in Venusian clouds?

8. 2003, Sulphur traces on Jupiter's moon Europa may be the waste products of underground bacterial colonies

9. 2004, Methane in the Martian atmosphere hints at microbial metabolism

10. 2004, A mysterious radio signal is received by the SETI project on three occasions - from the same region of space

Also i remember the Red rain in Kerala incident where red rain sporadically fell on the southern Indian state of Kerala. I think most scientists now think it was likely terrestrial, but the possibility is still there.
http://en.wikipedia.org/wiki/Red_rain_in_Kerala

 

[Ivan Seeking]

Warp Drive: A New Approach
http://xxx.lanl.gov/PS_cache/arxiv/pdf/0712/0712.1649v2.pdf

To be published in JBIS in early 08, and co-authored by PF member robousy.
https://www.physicsforums.com/showthread.php?t=204637

 

[hubertg]

I think the odds for life are out there. However, the universe is incomprehensibly large. It would seem to me that distance and time would be a prohibitive factor that any given life form could possibly find us, let alone get here...it would be like some one looking for one particular grain of sand on/in all the beaches and oceans of earth. Beam me up scotty !..hg

 

[Pippo]

...it would be like some one looking for one particular grain of sand on/in all the beaches and oceans of earth....hg

I fully agree, it's impossible to find one particular grain of sand, but let me say that the grain of sand is surely there, it's in somewhere.

 

[Ivan Seeking]

A promising but labour-intensive technique to find alien worlds has netted its first multiple-planet system, a new study reveals. The technique, called microlensing, can find smaller planets than rival methods, and one day might be able to find distant counterparts to Earth. [continued]

http://space.newscientist.com/article/dn13322-first-multiple-planet-system-found-by-microlensing.html

 

[Schrodinger's Dog]

Well I'm glad this thread is still going. There are some more conventional forms of space travel, that whilst not achieving interstellar travel particularly readily might be worth while. Like Solar sails, that gradually increase speed. Also there are suggestions that if you could create a sufficient amount of gravity in front of a ship this would bend space enough to shorten the distance between two objects, which is pretty much the idea of warp drives, thus avoiding the problem of FTL.

For the moment though, conventional albeit cutting edge methods are being explored such as ion drives.

http://news.bbc.co.uk/1/hi/technology/4527696.stm

I remember a suggestion as well of them using the sun as a gravitational lens, and our solar system as a giant observatory. But this is well beyond our current means.

 

[mikelepore]

Does anyone know whether binary and triple stars are likely to have planets? Would those planets orbit one of those stars or orbit the system of stars? Would the mass distribution of those stars cause the orbits of the planets to be highly eccentric? The reason I ask is because too much eccentricity, giving anyone planet temperature swings from too hot to too cold, would strongly affect the term in the Drake equation that represents the percentage of "earth-like."

 

[CEL]

Does anyone know whether binary and triple stars are likely to have planets? Would those planets orbit one of those stars or orbit the system of stars? Would the mass distribution of those stars cause the orbits of the planets to be highly eccentric? The reason I ask is because too much eccentricity, giving anyone planet temperature swings from too hot to too cold, would strongly affect the term in the Drake equation that represents the percentage of "earth-like."

As a star collapses from a cloud of gas and dust, a quality called angular momentum causes formation of a central condensation surrounded by a thin disk of matter. At this point it seems the system then either evolves into a planetary system or a binary/multiple star.

If a planet could form, it would orbit the main star, but its orbit would be influenced by the other stars.

 

[mikelepore]

A highly eccentric orbit obeys conservation of angular momentum just as much as a circular one does. It could be rare to have a system with the planets close to being in concentric circles, which is important for making life possible in our own system. I was thinking about several ways in which too much eccentricity is bad for the probabilty of life. Temperatures may swing across hundreds of kelvins. Planets are more likely to exert tidal forces on one another, causing vulcanism or even crumbling whole worlds. Larger planets may eject smaller planets out of their orbits or collide with them. Not only is there the probability of those amino acids doing something interesting, but they also have to be left undisturbed for a long time. In the earliest posts in this topic, someone estimated the probability of a system having an "earth-like" planet to be around 1/3. That astonished me. I thinking that this one probability factor must be a very, very small.

 

[_Mayday_]

10,000,000,000,000,000,000,000 stars in the universe, a very conservative estimate but let's assume it's correct.

I know we are assuming it is correct. BUT how would someone go about making such a prediction if so much of the universe is out of our reach?

I'm going to say yes, there is life other than us, but that is just being optimistic maybe as it would be pretty cool :shy:

I don't think it has ever reached Earth though. No reason.

 

[Schrodinger's Dog]

I know we are assuming it is correct. BUT how would someone go about making such a prediction if so much of the universe is out of our reach?

I'm going to say yes, there is life other than us, but that is just being optimistic maybe as it would be pretty cool :shy:

I don't think it has ever reached Earth though. No reason.

As I said this is a speculatory thread asking you to make your own conclusions, based on your own experiences and knowledge. Of course we cannot know what is going on beyond our visible Universe. But it's not a huge jump to assume that given the sheer numbers of stars we are not alone. Even scientists admit this as a credible hypothesis, given the numbers, this is why SETI exists. Of course the whole point is to get people talking about the likelihood, even if it isn't grounded in scientific fact, it still makes an interesting topic of conversation.

Why is it optimistic though, to think given the absolutely huge expanse of the universe, and the recent knowledge that planets are far more common than we thought, why is it a jump to think life isn't out there, somewhere else?

 

[_Mayday_]

It would be nice to think there is something else out there, but I can't imagine it. Would other life live in totally different condition? If so then yes, I would agree that there is probably other life, I say this because it just means that the conditions for life are less specific so I would think there is a higher probability.

It would be very interesting to see how they differ from us though.

 

[CEL]

... In the earliest posts in this topic, someone estimated the probability of a system having an "earth-like" planet to be around 1/3. That astonished me. I thinking that this one probability factor must be a very, very small.

The only solar system we know that has an earth-like planet is ours. There is one planet out of nine with life, so a more reasonable assumption is that 10% of the planets have such property.

 

[Schrodinger's Dog]

The only solar system we know that has an earth-like planet is ours. There is one planet out of nine with life, so a more reasonable assumption is that 10% of the planets have such property.

I think 10% is a little optimistic and wouldn't it be about 11%. Assuming even there are 9 planets that one is Earth like 11% of the time is probably not quite right.

And of course the reason we only know Earth, is to do with being unable to detect planets of such insignificant mass with current methods.

 

[_Mayday_]

There are only 8 planets in our solar system, Pluto is now classified as a dwarf planet. So a 1 in 8 chance then.

 

[CEL]

I think 10% is a little optimistic and wouldn't it be about 11%. Assuming even there are 9 planets that one is Earth like 11% of the time is probably not quite right.

And of course the reason we only know Earth, is to do with being unable to detect planets of such insignificant mass with current methods.

I used 10% because it is a round number. We can only speculate about earth-like planets around other stars. Since Sol is a very ordinary star, there is no reason to think that other G2 class stars have planetary systems much different from ours.
Someday we will have the technology to detect small planets orbiting other stars and will be able to assign other values to Drake equation. Until then I think we should use as model the only system we know.

 

[Schrodinger's Dog]

I used 10% because it is a round number. We can only speculate about earth-like planets around other stars. Since Sol is a very ordinary star, there is no reason to think that other G2 class stars have planetary systems much different from ours.
Someday we will have the technology to detect small planets orbiting other stars and will be able to assign other values to Drake equation. Until then I think we should use as model the only system we know.

Indeed, I agree. Just being pedantic I suppose, and of course introducing a little doubt.

There are only 8 planets in our solar system, Pluto is now classified as a dwarf planet. So a 1 in 8 chance then.

Well that's another thread in itself hehe. Still it rounds down to 10%.

 

[mikelepore]

The ambiguity of the phrase "earth-like" needs some attention. Let's start with that range of orbital radii in which you can have liquid water. Suppose you do find another planet with the right temperature for liquid water. That is, it it had any water -- but there isn't any water there. Then you find another planet that has the right temperatures for liquid water. Unforunately its atmosphere is all ammonia gas. Now you find another planet with the right temperatures for liquid water. Unfortunately, it has no magnetic field to deflect the solar wind. You find another planet with the right temperature for liquid water, but it's more volcanic than Io, with much of the planet's surface being destroyed on a daily basis. You find another planet with the right temperatures for liquid water, but the planet has almost no carbon atoms. I believe this is more problematic than most people think. To be a place for life to develop, you have to "win the lottery" many times.

 

[cristo]

To be a place for life to develop, you have to "win the lottery" many times.

I think when a lot of people think of intelligent life elsewhere, they think of life forms very similar to our own. However, why would any intelligent life have to be even the slightest bit similar to ours? Why would it need to be carbon based and breathe oxygen? These implicit assumptions are always in the back of peoples' minds but, in my opinion, shouldn't be. I also agree with what Stephen Hawking once said (I think), namely that if we were visited by extra terrestrial beings it would not be the pleasant experience that many people fantasize about!

 

[_Mayday_]

I think when a lot of people think of intelligent life elsewhere, they think of life forms very similar to our own. However, why would any intelligent life have to be even the slightest bit similar to ours? Why would it need to be carbon based and breathe oxygen? These implicit assumptions are always in the back of peoples' minds but, in my opinion, shouldn't be. I also agree with what Stephen Hawking once said (I think), namely that if we were visited by extra terrestrial beings it would not be the pleasant experience that many people fantasize about!

That is an interesting point actually. And by life we may be talking about a tiny bacteria, not a green man with big eyes.

The other point made on Hawking is also a good one. The thought of other life forms similar to us popping in for a few days to say hi seems far fetched, then there are also problems like communication, though I can't imagine there is much to say to a single cell organsim.

 

[binzing]

Basically, just look at the odds. There has GOT TO BE life in this universe other than on Earth.

 

[CEL]

I think when a lot of people think of intelligent life elsewhere, they think of life forms very similar to our own. However, why would any intelligent life have to be even the slightest bit similar to ours? Why would it need to be carbon based and breathe oxygen? These implicit assumptions are always in the back of peoples' minds but, in my opinion, shouldn't be. I also agree with what Stephen Hawking once said (I think), namely that if we were visited by extra terrestrial beings it would not be the pleasant experience that many people fantasize about!

The only element capable of forming the long chains necessary to life is carbon. Although some scientists have speculated on the possibility of silicon based life, this element does not produce complex enough molecules.
In order to produce energy, life must use exothermic chemical reactions. We know of two of those reactions that work on Earth's lifeforms: fermentation and oxidation. Fermentation is used by some bacteria, in the absence of oxygen, but it is inefficient and works only with primitive lifeforms. Only after ocean algae produced enough oxygen in our atmosphere more complex lifeforms could develop.
Of course other oxidants, like chlorine, could be used in the reaction, but oxygen is much more abundant and life, specially complex forms, need abundance of useful elements and compounds.

 

[russ_watters]

Oxygen is helpful for complex life, but not required for life. One thing not mentioned (recently) is liquid water. It has some unique properties (such as floating when it freezes and being a good solvent) that make it somewhat unique.

 

[Schrodinger's Dog]

Very important in shallow waters where they'd freeze from bottom to top instead of top to bottom, thus hindering any chance of life in any but deep seas. In fact it's almost uncanny, that ice is less dense than water.

 

[CEL]

Oxygen is helpful for complex life, but not required for life. One thing not mentioned (recently) is liquid water. It has some unique properties (such as floating when it freezes and being a good solvent) that make it somewhat unique.

As I mentioned in my previous post, fermentation produces energy in the absence of oxygen, but is too inefficient to allow complex life. It is very possible that primitive life exists outside Earth, using fermentation, but the only way such life could visit us is attached to meteorites. By the way, this is one of the proposed mechanisms for the beginning of life in our planet.
You are right about the need of a liquid to allow interaction between the complex molecules necessary to life. This liquid must be abundant in order to life begin and develop. Since the most abundant element in the universe is hydrogen, we must search hydrogen compounds as necessary for life. Besides water, we can think of methane, ammonia and hydrogen fluoride as simple liquids. Those are really gaseous, as is water, unless the temperature is low enough or the pressure high enough. Since at very low temperatures chemical reactions are too slow to allow complex life forms to evolve, we need an atmosphere dense enough for one of those gases to exist in liquid form.
Earth has an atmospheric pressure high enough for water to exist in liquid form in a range of temperatures ideal for life.
That is why we must look for earth-like planets in our search for intelligent life.

 

[mikelepore]

that ice is less dense than water

I can't remember why that happens. Can you tell me? The polarity of the molecule?

 

[K.J.Healey]

ALL stars should have some orbital radii where liquid water could exist, correct? Its not just surface temp but gravity, other gaseous atmosphere to keep it non vaporous, etc.

 

[DaveC426913]

I can't remember why that happens. Can you tell me? The polarity of the molecule?

Yes. The polarity of the molecule causes it to crystalize as a lattice wherein the individual atoms are forced to line up farther apart as a crystal than they can get as an amorphous liquid. Same mass but greater volume = less dense.