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Aliens then, what do we all reckon? Given the vastness of the universe and the quantity of Earth-like planets that must exist, it seems almost inevitable that intelligent life would have evolved on a planet outside our Solar System.

Personally I think there are planets in other systems that will have developed life - possibly even a system comparable to Earth's ecosystem - but I don't think we'll ever know for certain for two main reasons:

1. The simple vastness of space; there may well be a million other "Earths" out there harbouring life, but it would take thousands of years to travel between any two of them, even at speeds approaching light, so the chances of two such civilisations ever encountering one another is extremely remote;

2. We might simply be at the wrong "time". Intelligent life on this planet has only been around for a few hundred million years and humans only a couple of million years, which is just a blip, given that the universe is at least 13 billion years old. So there might well have been an Earth-like planet, say one hundred light years away, which developed a civilisation and a technology capable of sending a probe to Earth, but if it was a billion years ago, there's no way we could possibly know. (Conversely such a civilisation may develop on another planet a billion years from now, but as intelligent life on Earth is unlikely to still be around by then, no-one's going to know).

Of course, you may take another view; perhaps you think there are no aliens: our civilisation is unique. Or just unique in its place in time. Or maybe you think the universe is teeming with aliens all about to invade us with their unknowable alien weaponry? Or maybe you think the universe is teeming with aliens, but they're all a great bunch of lads who want only to help us?

So, yeah. Aliens.

I agree. There are definitely aliens and we will definitely never meet them. Bit of an uncomfortable thought, really.

Aliens. Yep. Actually, I don't think it's inevitable that there are aliens elsewhere in the universe, although if I were forced to make an evens bet, I'd bet in favour of it.

Yes, there are billions of stars and galaxies out there, but really we have no idea what the probability of life starting is, given the right conditions. It could be tiny. But having said that, apparently life on Earth started quite soon after Earth became a stable enough environment (rather than waiting a few billion years), so that does suggest that it's a likely thing to happen. Multi-cellular life, on the other hand, is a different matter. I think that took quite a long time to emerge, and I think is considered by some to be more of a freak event. Maybe it's rare.

But then, while it's possible that we're the only planet with multi-cellular life (or "animal" life or human-level intelligent life), it would seem a bit odd if it just happened to exist on exactly one planet. Yes, I know we don't know the probabilities of these things, but it would still seem a bit odd if, given the vastness of time and space, they have exactly the right amount of vastness to make one a likely number of planets with life on (as opposed to 10, 100, or just plain 0).

But having said that, it could be that the probability of life (or intelligent life or whatever) evolving in this particular universe is tiny, but that there are actually many universes, so it's inevitable that life will exist in some of these universes, even if there are no cases of life in most of these universes.

There's quite a lot of interesting stuff that could be said about the anthropic principle, but maybe I'll save that for another time.

Don't see why not. Some interesting thoughts here (http://www.scientificamerican.com/artic ... -galaxies/) on why we've not yet spotted (or realised that) anyone else.

Ian Volante wrote:Don't see why not. Some interesting thoughts here (http://www.scientificamerican.com/artic ... -galaxies/) on why we've not yet spotted (or realised that) anyone else.

That was quite interesting but I think the whole SETI project, laudable though it is, is flawed for all kinds of reasons:

- Hypothetically, valid signals could be missed because the "correct" wavelength wasn't being monitored at the time;

- Similarly, such signals might arrive on a wavelength that is being monitored, but as no pattern can be detected, they are discarded as white noise;

- We're a few hundred or thousand years too early, or late. We've only had about 100 years to even attempt to monitor the universe beyond our own solar system; decipherable signals or messages may well have been sent towards Earth around a few million years ago, but in the form sent, there'd be no way that our ancient descendants would be able to detect them. And give it a couple of thousand years, there won't be any more intelligent life on Earth so any attempts by hypothetical alien civilisations to contact us will simply go unnoticed.

It's a tiny, tiny window really, and if the hypothetical civilisations in other systems are anything like this one, then their technological windows are likely to equally small. That two such intelligent civilisations would arise at the same time and actually be able to communicate with one another (over vast distances, so there'd be a lot of lag) is pretty remote.

So I'd say that just because we - within an insignificant period of time - haven't managed to pick up signs of other civilisations yet is a pretty poor argument for there being none.

JimBentley wrote:

Ian Volante wrote:Don't see why not. Some interesting thoughts here (http://www.scientificamerican.com/artic ... -galaxies/) on why we've not yet spotted (or realised that) anyone else.

That was quite interesting but I think the whole SETI project, laudable though it is, is flawed for all kinds of reasons:

- Hypothetically, valid signals could be missed because the "correct" wavelength wasn't being monitored at the time;

- Similarly, such signals might arrive on a wavelength that is being monitored, but as no pattern can be detected, they are discarded as white noise;

- We're a few hundred or thousand years too early, or late. We've only had about 100 years to even attempt to monitor the universe beyond our own solar system; decipherable signals or messages may well have been sent towards Earth around a few million years ago, but in the form sent, there'd be no way that our ancient descendants would be able to detect them. And give it a couple of thousand years, there won't be any more intelligent life on Earth so any attempts by hypothetical alien civilisations to contact us will simply go unnoticed.

It's a tiny, tiny window really, and if the hypothetical civilisations in other systems are anything like this one, then their technological windows are likely to equally small. That two such intelligent civilisations would arise at the same time and actually be able to communicate with one another (over vast distances, so there'd be a lot of lag) is pretty remote.

So I'd say that just because we - within an insignificant period of time - haven't managed to pick up signs of other civilisations yet is a pretty poor argument for there being none.

I don't see why any of this makes SETI flawed. Sure, stuff might get missed, but that doesn't mean they won't find a signal.

We also have no idea how long we're going to survive. You say "give it a couple of thousand years, there won't be any more intelligent life on Earth", but what are you basing this on? There's a chance we'll destroy ourselves, but if we don't within the next 100 years or so, we'll probably go on to bigger and better things. There's every chance that other intelligent life will have got over that threshold too. I can only guess that you're working on the assumption that all intelligent life ends up destroying itself shortly after becoming technologically capable. But I don't think it's valid. You also haven't explicitly come out with it for some reason.

Gavin Chipper wrote:I don't see why any of this makes SETI flawed. Sure, stuff might get missed, but that doesn't mean they won't find a signal.

I think I was just pointing out that for various reasons, it's incredibly unlikely. But not impossible.

Gavin Chipper wrote:I can only guess that you're working on the assumption that all intelligent life ends up destroying itself shortly after becoming technologically capable. But I don't think it's valid. You also haven't explicitly come out with it for some reason.

Well, that's because I don't know for sure, explicitly. There are other possibilities (maybe everyone will get on board generation starships and fuck off out of our solar system completely, for instance) but the whole "we'll just all kill each other on this planet" seems more likely.

Another possibility is that if an advanced civilisation wants to survive more than a few hundred years it may decide to conserve its resources, and so will avoid radiating a significant amount of energy into space, so SETI's efforts might be in vain. On the other hand, they could well take steps to capture more of their sun's output artificially - which our planet-hunters might detect by observing anomalous dips in a star's brightness (one such possibility has been seen already, though probably not).
http://www.iflscience.com/space/alien-m ... s-study-0/

Peter Mabey wrote:Another possibility is that if an advanced civilisation wants to survive more than a few hundred years it may decide to conserve its resources, and so will avoid radiating a significant amount of energy into space, so SETI's efforts might be in vain. On the other hand, they could well take steps to capture more of their sun's output artificially - which our planet-hunters might detect by observing anomalous dips in a star's brightness (one such possibility has been seen already, though probably not).
http://www.iflscience.com/space/alien-m ... s-study-0/

Either way, it's just another of the frustrating aspects of the whole thing, isn't it? We might think we've discovered a Dyson sphere by observing such anomalies in the outputs of stars, but a civilisation sophisticated enough to build such a thing may well not want to broadcast it to all and sundry. So they would simply re-route some of the star's captured energy to simulate the star's expected energy profile, I would think, and no observer would be any the wiser.

JimBentley wrote:

Gavin Chipper wrote:I don't see why any of this makes SETI flawed. Sure, stuff might get missed, but that doesn't mean they won't find a signal.

I think I was just pointing out that for various reasons, it's incredibly unlikely. But not impossible.

Gavin Chipper wrote:I can only guess that you're working on the assumption that all intelligent life ends up destroying itself shortly after becoming technologically capable. But I don't think it's valid. You also haven't explicitly come out with it for some reason.

Well, that's because I don't know for sure, explicitly. There are other possibilities (maybe everyone will get on board generation starships and fuck off out of our solar system completely, for instance) but the whole "we'll just all kill each other on this planet" seems more likely.

I'd say that if a civilisation reaches "technological level" then there's a certain probability that they will wipe themselves out before consolidating their position in the universe. But the probability that they won't wipe themselves out is probably not negligible, so I think it's perfectly likely that our search for other races won't fail simply because we're in the wrong time. I think a decent number of technological races will survive for millions or billions of years.

JimBentley wrote:

Peter Mabey wrote:Another possibility is that if an advanced civilisation wants to survive more than a few hundred years it may decide to conserve its resources, and so will avoid radiating a significant amount of energy into space, so SETI's efforts might be in vain. On the other hand, they could well take steps to capture more of their sun's output artificially - which our planet-hunters might detect by observing anomalous dips in a star's brightness (one such possibility has been seen already, though probably not).
http://www.iflscience.com/space/alien-m ... s-study-0/

Either way, it's just another of the frustrating aspects of the whole thing, isn't it? We might think we've discovered a Dyson sphere by observing such anomalies in the outputs of stars, but a civilisation sophisticated enough to build such a thing may well not want to broadcast it to all and sundry. So they would simply re-route some of the star's captured energy to simulate the star's expected energy profile, I would think, and no observer would be any the wiser.

I think people overstate the threat from aliens. An alien race that has built a Dyson sphere has nothing to worry about from anything other than a really technologically advanced race. And I think once they reach that level, things like war are going to be pretty antiquated ideas to these guys.

Still, if an alien race has let all the dirt in their galaxy build up over several millennia, a good once over with somebody else's Dyson sphere could be a pretty tempting idea.

Aliens floating in the clouds of Venus?

There was an interesting Sky at Night last night. Worth catching on the iPlayer.