Even if we send probes to every planet in the universe it is possible that they will all come up -ve.

this isn’t true, there’s at least one. Right?

It doesn’t matter.

Possibly true*, but that’s talking about multiple lottery draws, not a single draw (as I explained earlier).

(* it’d be a risky gamble. Say the pot was at 28 million and you had 14 million quid just sitting around. You could buy every ticket combination and be assured of winning the jackpot, plus all lower prizes – BUT you risk sharing it with other people and making a loss).

And also doesn’t take into account the near impossibility of writing out all the tickets in time for the next draw! (1,2,3,4,5,6. 1,2,3,4,5,7. 1,2,3,4,5,8……. :D)

What would anyone accept as evidence? So far we have had eyewitness reports,video footage,photos,radar returns,and physical traces left behind(high levels of radioactivity etc). If this evidence was used in any other kind of case there wouldnt be a question. It would be regarded as proven.

It doesn’t matter.

I’m struggling to see how the fact that life has definitely arisen once in the universe (something that I hope everyone can agree on 😉 ) is inadmissible as evidence for life in the universe.

Please continue your point rightplace.
I agree there are not infinite planets…. so..?

If you want some numbers to use, NASA astrobiologists reckon, based on our current experience of what “habitable” means, that there are 10,000,000,000 habitable “Earth-like” planets in our galaxy and around 1,000,000,000,000,000,000,000 in the observable universe.

Erm..

It does matter.

I’m a beleiver in Aliens, nope, I am, and am of the thought that we’ve already been visited way back. To get to where we are I think some beings visited here, populated the planet for a short period of time, found us lot on here, mated, we evolved into what we currently are.
I think that the reason so many breakthroughs in science and the apreciation of the Arts have been so profound in the last 160years or so is due to human evolvemnt and our Brains capacity to be used more effectively, like it should be.

On Girl who sits on a desk across from me looks like a Grey.

You are Erich von Daniken AICMFP.

OK, to take the point about a finite number of planets. If we agree on that then we are getting somewhere.

What we don’t know is what the chance of life spontaneously happening is. It could be vanishingly small.

What most of you seem to be concentrating on is the big number (of planets) but somehow you’re not too bothered about how small the chance of life starting is. If it is a vanishingly small chance, then overall chances of finding alien life will also be vanishingly small.

The point is, that we can’t know what that chance is because we’ve not observed it happening.

Chances are that in time, we may get a pretty good idea of what the big number is, but we have literally no idea what the small number might be.

What most of you seem to be concentrating on is the big number (of planets)

That’s because it’s kind of important.

I reckon most people would consider odds of, say, 1 in 1,000,000,000,000,000,000 to be “vanishingly small” but even that would give you 1,000 instances of extraterrestrial life in the observable universe. Obviously chances are they’d be too far away to ever contact, but that’s another issue 🙂

Intelligent life hasn’t got as far as Doncaster, so I doubt there will be any on planets in Galaxies Far, Far Away.

I reckon most people would consider odds of, say, 1 in 1,000,000,000,000,000,000 to be “vanishingly small”

It’s not really a question of “what most people reckon” though is it?

This isn’t the committee for the formation of alien lifeforms.

My point (still) is that no one knows, or can know, what the figure is. it is unknowable, and may be very, very, very small.

But really, my point about the planets is important – do you think there are an infinite number or not?

you sure as you originally said

The number of stars and galaxies is totally irrelevant

so its important and irrelevant.
I am liking your logic as much as your probabilities.

My point (still) is that no one knows, or can know, what the figure is. it is unknowable, and may be very, very, very small.

And mine is that even if it’s very, very, very small there’s probably still something out there because of the vast number of planets. Worst case: it’s 1 in 1,000,000,000,000,000,000,000. I find that somewhat implausible.

I’m not arguing for certainty here (and I don’t think anyone else is either), just for the balance of probabilities.

Junkyard,

When I said that the number of stars and galaxies was irrelevant I was kind of assuming that people would be thinking of a finite number – how large that number might be isn’t important, but it is important that it is finite.

Then you started talking about an infinite number of chimps, which gave me cause to check that we were all indeed thinking of this problem within a finite universe.

Simple really.

So do you, Junkyard, think that there are a finite number of planets?

the balance of probabilities

Aaaaaaarggghhhhhhhh!

I’m just slapping myself on the forehead.

That Hubble telescope has a lot to answer for.

What we don’t know is what the chance of life spontaneously happening is. It could be vanishingly small.

It could be, but we don’t have any reason to suspect that it is.

We have the estimate that there are 1,000,000,000,000,000,000,000 planets that pass the basic requirements of being habitable as we know it (e.g. orbiting a star at a distance that is not too hot/cold for liquid water). So we’ve already whittled down the field based on what prerequisites we know are required.

Now it could be that is all that is required, and that most of those planets have, or had, or will have, life on them. Or it could be that other prerequisites are needed that we don’t know about.

e.g. perhaps such planets need a seed event (such as being struck by a meteor containing bacteria or suitable amino acids, as suggested earlier) in which case time plays an important factor too: chances of getting hit by a meteor right this second are slim, but at any time in 13.7 billion years it is quite a bit higher!

At the end of the day I find it unlikely that life is a 1-in-sextillion (yes really) chance on planets that we know can support it.

So far we only have direct experience of one Earth-like planet, and that has plenty of life on it, so success rate is looking pretty good so far 😀

.
(to avoid confusion that last sentence is a joke)

It could be, but we don’t have any reason to suspect that it is.

Or that it isn’t.

Or that it isn’t.

This isn’t an argument it’s just contradiction!

So RPRT are you just arguing over the error bars and caveats that are applied to statements like “I think it’s very unlikely that the Earth is the only planet in the universe that is ever going to be capable of supporting life”?

Or that it isn’t.

Now you’re asking me to prove a negative.

Put it this way, so far we have no evidence that Earth is “special” or “unique” or that whatever mechanism created life on this planet wouldn’t also work on other planets.

Or indeed that there aren’t other forms of life possible that we are not even considering (i.e. non carbon-based) that are created in other ways.

thepurist,

Have you not read the thread?

About half way down the first page we had:

i think it would be both naive and arrogant to think in the near infinite expanse of space there wouldn’t be another planet, perhaps thousands of planets, with intelligent life on them.

Followed by various other comments along the same lines.

That’s not quite “arguing over the error bars”

I’m just slapping myself on the forehead.

Well, I did that when you said “infinitesimally small”, so now we’re even 😉

every smudge of light is a galaxy, each galaxy has billions of stars. It’s a terrible waste of space if there’s nothing else out there to enjoy it.

I can’t even begin to contemplate something like that without boggling my own mind. 🙂

Another way of looking at this…

Two people, one each end of a really long flat road. Given enough time they will probably see each other (assuming they don’t die before they reach the passing point).

The same two people at opposite edges of an equally massive flat circle (in terms of square metres) and the chances of them seeing each other becomes much less as the paths they can take are no longer linear.

Then imagine the same two people at opposite edges of an equally massive but mountainous circle and the chances of them seeing each other becomes even less than the previous situation.

mastiles_fanylion – Member
Another way of looking at this…

Two people, one each end of a really long flat road. Given enough time they will probably see each other (assuming they don’t die before they reach the passing point).

The same two people at opposite edges of an equally massive flat circle (in terms of square metres) and the chances of them seeing each other becomes much less as the paths they can take are no longer linear.

Then imagine the same two people at opposite edges of an equally massive but mountainous circle and the chances of them seeing each other becomes even less than the previous situation.

I was keeping up until this point. Now I’m just confused…. 😉

Put it this way, so far we have no evidence that Earth is “special” or “unique” or that whatever mechanism created life on this planet wouldn’t also work on other planets.

We do, i posted it earlier.
On earth, for complex animal life we need
– large moon (much larger than any other observed planets)
– plate tectonics (doesn’t exist on any other observed planets)
– spinning core providing a sheild from radiation
– to be in a habital zone not only of the solar system but of the galaxy, where there are very few supernova or other events emitting harmful particles
– to have relatively few extinction level events.
..
the list goes on…

Theres also the problem of timescales. Does all life evolve into complex life?? Life existed on earth for 4 billion years, yet complex life only evolved around 600 million years ago, and humans only 200,000 years ago, and we’ve only had the technology to get into space for 60 or so!

In 600 million more years the earth will be sterile and long before that humans will be cease to exist, and thats if we survive any future extinction events which happen once every 100 million years or so.

This creates quite a narrow window to communicate with any other aliens.

m_f: no argument there. The chances of us being able to communicate with any life out there is incredibly tiny, even if life was abundant.

Currently we’d just have to hope they had better comms tech than us that did something outside our current understanding of physics. Otherwise our conversation will suffer from a slight 100 light-year satellite delay 😀

My boss says that apparently having a massive planet like Jupiter nearby is really important as well, but he’s a bit vague, he saw a programme on the telly.

On earth, for complex animal life we need

For complex animal life perhaps, though even then I’m not sure all of those are undisputed prerequisites (see the earlier point about microbes found surviving inside nuclear reactors for how previous assumptions are changing).

Saw the same programme – they were suggesting that Jupiter basically takes the hits from NEOs so we don’t have to – basically Earth is hiding behind it’s big brother, and we have the Moon nearby to mop up a lot of the stuff that Jupiter lets by.

Amazing set of coincidences, all to give us a meaningless existence 😀

m_f: no argument there. The chances of us being able to communicate with any life out there is incredibly tiny, even if life was abundant.

You’ve missed the point again Graham.

He was talking about me and you.

Thanks Horatio,

It’s been very lonely out here in the endless void of the STW forum.

He was talking about me and you.

😀

Otherwise our conversation will suffer from a slight 100 light-year satellite delay

A bit like when I first used Skype on 56k dial-up…

Horatio: you said several times in your testimony that such features hadn’t been seen on “any other observed planets”?

Can you tell the court what percentage of the sextillion habitable planets we’ve been able to conclusively check for, say, “plate tectonics”?

I see. And would you consider that a statistically meaningful sample sir?

We do, i posted it earlier.
On earth, for complex animal life we need
– large moon (much larger than any other observed planets)
– plate tectonics (doesn’t exist on any other observed planets)
– spinning core providing a sheild from radiation
– to be in a habital zone not only of the solar system but of the galaxy, where there are very few supernova or other events emitting harmful particles
– to have relatively few extinction level events.

Why are there things needed? the point is you cannot tell what would affect the unknown. Life forms based on an nitrogen cycle rather than a carbon one? cycle ? perfectly possible

This creates quite a narrow window to communicate with any other aliens.

yes but the issue is whether there is life not whether we can have a chat about what tyres for their world 😉
RPRT Considering you think the number of planets is irrelevant you are very keen to know my view and yet incredibly unkeen to make any comment on why an increasing number does not alter the odds. You can use the lottery or chimps and shakespeare and planets if you like its just wrong.

When I said that the number of stars and galaxies was irrelevant I was kind of assuming that people would be thinking of a finite number – how large that number might be isn’t important, but it is important that it is finite.

The basic premise that the numbers do not affect the odds is flawed. I assume you accept that if I buy more lottery tickets [ with different numbers before you get smart] i increase my chances of winning. Therefore more planets increases the chances of their being life. Infinite would only guarantee it occurs so apparently the odds are unchanged till we reach infinity then?

In essence the more planets the more chance of the correct conditions. That seems undebatable tbh.

Junkyard: I think his killer point was that the chance of life on a “habitable” planet is unknown and could be less than 1 in sextillion (I love saying that number), or basically equal or less than 1-in-X where X is the number of planets.

So it’s not so much that X doesn’t matter, just that if you accept X is finite then the probability of life could be 1-in-X.

GrahamS – ah, but that *is* one possible outcome isn’t it? The sort of elegant quirk that the universe plays now and again, where fiendishly complex processes yield the simplest equations.

All we need to accept that is some reason to believe that the current scientific consensus resulting from many published and peer reviewed papers is somehow wrong. It’d be abso-blummin-lutely brilliant if someone could smack a curveball into some pillar of science because that’s the sort of thing that drives our understanding forward, but I can’t see it coming from this thread. (Or rather I believe there’s an infinitesimally small chance that it will 😉 )

GrahamS – ah, but that *is* one possible outcome isn’t it?

Yep. It is possible, which is why I said I don’t have absolute faith in alien life and that “nothing is certain”.

But… I don’t see any evidence that suggests the figure is that low, and far cleverer men with nice beards, pointy heads, multiple degrees and NASA coffee mugs seem to agree.

It’d be abso-blummin-lutely brilliant if someone could smack a curveball into some pillar of science

Yep, that would be fun, though personally speaking I would find a definitive revelation that we are absolutely alone in the universe to be incredibly depressing.

Our last remaining hope would be that when Earth finally explodes, bits of our planet eventually make it to other habitable planets and have enough amino acids and genetic material to start the whole thing again.

That may even be how we got here…

rprt.. I’m not sure HH was actually agreeing with you though. 😉

Anyway…

There is one thing we know for absolute certainty, unless, as suggested earlier, we are indeed in a simulation… but even if were are, would it matter?

Right, the one thing we know for certain is that the probability of life on this planet is 1. We exist, there can’t be much argument about that. (TJ? 😉 )

So, that means that the probability of life occuring at least somewhere in the universe is 1… (that’s us for the hard of thinking)

Given that, I’d say that the chances for there being life on any particular planet are not infinitesimally small, otherwise we wouldn’t be here.

So the question now is this, which of these is more likely:-

a) that the probability of life existing on a particular planet is exactly the right number for there to be only a single planet (ours) in the entire universe with life?

or

b) that the probability of life existing on a particular planet is any other number than the one above?

I know which I am putting my lottery money on this week!