h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

New entry on SETI came up in Peer Review and Mikey the HUmmingmouse put a link to here in the forum, so hopefully you can use the following - the entry there missed this stuff out, I don't see any mention here, so forgive me if you've already got stuff on this, but any discussion of SETI needs to cover the following two important concepts. (1) von Neumann machines. No need to build millions of probes to search the galaxy for life. Build just the one probe, but make it self replicating. Send it out (you don't even need a particularly exotic drive system), when it gets to the next system it builds a copy of itself, sends that out, refuels and moves on. So in the next stage there are two probes, four on the next, then eight, sixteen, thirty-two, etc. etc. Even if the probes move at only a fraction of lightspeed, before long (i.e. a couple of million years, say) the galaxy is full of the damn things. This brings us on to (2) The Fermi paradox. We've thought of the von Neumann machine concept. It won't be *that* long (i.e. < 1 million years) before we can build it. If there are other civilisations out there, it's reasonable to assume that at least some of them are more advanced than we are. So the question - the Fermi paradox - is, where are their von Neumann probes? Where are their generation starships? Where are their signals? Look on Ray Kurzweil's web page for info on why that influential thinker believes SETI will fail. It's depressing in some ways, but if you're going to be definitive, you really should include the well-defended viewpoint that, against literally astronomical odds, we appear, according to a reasonable set of assumptions, to be the sole intelligent life in this galaxy. Bummer.

Hi Hooloovoo,

I'm quite into SETI as well - in fact I was just checking this project for its current status, as I've now taken over the h2g2 University from Peta. (The Power! The Power!)

I think Kurzweil's argument is flawed, and here's why.

He fails to take into account the relative timescales and rates involved in the evolution of life. Consider these timescales:

The Universe has been around for something like 4.5 billion years. The Earth has been around for about 4 billion. Life's been on the Earth for about 3.5 billion years. Mankind has been here for about 5 million. We've been able to broadcast electronic information into space for about 100 years.

Now, it happens that our planet is comparatively old in the Galaxy - indeed in the Universe. We see everything moving away from us fairly uniformly in all directions (perhaps we smell, or something). That last 100 years, in which we've been transmitting ourselves across the Galaxy, is a tiny, tiny proportion of the amount of time that life's been on this planet.

Now, imagine another civilisation in another part of the Galaxy that's had their planet exactly as long as ours. Let's say they've also had life on that planet as long as we have, and also, if you like, that they've had human-like beings making their way steadily up the evolutionary ladder until they're ready to have electronics and dishes and suchlike. We'll assume they evolve as fast as we did as well - why not.

Let's say their planet is 20,000 light-years away - still well within our Galaxy. They could have become electronicised (i.e. able to beam messages into space) 19,000 years ago, and their emissions will only just be reaching us. There could, in fact, be thousands of civilisations that evolved quicker than us and have been at it for 100,000 years, but their messages might only just be reaching us from the other side of the Galaxy. Conversely, there might be a civilisation next door to us that just happens to be 1,000 years behind us in its evolution - it's a tiny amount of time compared to the age of planets and life on them. When you consider that some civilisations on Earth have been separated from others technologically speaking by at least 1500 years (take Mayans and Spanish in the year 1600 as an example) - it's much more likely that completely separated planets will have vastly differing states of evolution.

It's all perfectly possible, and is a perfectly good theory as to why we've not heard anything from them yet. FBI/CIA cover-ups aside.

There's a flaw in your argument to do with orders of magnitude. Universe 4.5 billion years - OK. Planet 4 billion - fine. Life 3.5 billion. OK. Humans, 5 million years. Ouch! Suddenly we got WAY accurate, by three orders of magnitude. What we should have said, to be consistent on timescales, was "less than a billion". Broadcast civilisation, 100 years. Ouch! Another FOUR orders of magnitude again. Still we should be saying "less than a billion" to be consistent. Life here took 3.5 billion years to go from just being here to broadcasting our presence. If the "rate" of evolution (a fallacy in itself because evolution proceeds in fits and starts rather than continuously, but that's another debate) on another planet differs from ours by only ONE per cent, that would mean they could be ahead of us by 35 MILLION YEARS! It is worth asking whether a civilisation 35 million years advanced on ours would even be recognisable as life. The Copernican principle demands that we do not consider ourselves in any sense a special case. Therefore, we can't assume planets exactly as old as ours. You have give reasonable leeway. Given that leeway, if there was anyone else, the galaxy should be crawling with them , their artifacts or at the very least their signals or other evidence of their existence. So far, nothing. Absolutely nothing indicative of any intelligence other than our own. I find this incredibly depressing, speaking as an avid SETI@home processor. I want to be incredibly famous because I found the signal from another world - but I don't believe I or anyone else will find it. I've yet to hear a convincing argument against the above that doesn't expect you to conveniently imagine other worlds evolving just like ours at very close to the same time.
Negative as all this is, I think any discussion of SETI should at least mention the possibility that we are truly alone, and the reasons to think so. Personally I prefer the Babylon 5 interpretation. We are not alone. We are the First Ones.

Those different timescales are not a flaw in the argument at all - those really are the numbers. That's why this appreciation of relative scale and orders of magnitude is so important to grasp - everything notable on this planet - but particularly to do with communications - has 'only just happened'. Why do you think these times should have to be consistent with each other? They just aren't - that's the whole point. If we've undergone this astonishing speed-up recently, there's every possibility that other civilistions might have done as well.

The Copernican theory only spoke about astronomical organisation as a case against the prevailing and all-too-powerful religious views at the time. Sure, he was right, but you seem to be implying that we are uniue because of that. I don't understand how you think that because Earth is 'nothing special' that there should therefore not be any other planets like ours - surely that proviso should mean that there *are* lots of planets like ours... It's prefectly acceptable to assume that there are other planets like ours out there - why shouldn't there be? There's plenty of other identical suns that we can see, and there's nothing exotic about the elements found nearby.

So, the Galaxy may well be crawling with them, but the light speed barrier prevents us from hearing them because they're so far off. There's a certain amount of 'belief' that's required for SETI, but I'm convinced that something will turn up before I peg out.

Judging from the way that space looks around us (i.e. really very uniformly expanding in all directions) there is a very real possibility that we *are* at the the universe's centre, and we *are* the oldest and thus the first, in which case it's going to be pretty dull around here for a while... Some other civilisation, therefore, will have the pleasure of being the first to pick up radio signals from space - our signals!

Quote -"I don't understand how you think that because Earth is 'nothing special' that there should therefore not be any other planets like ours". This is exactly the opposite of what I said. Because we are "nothing special", there *should* be, amongst the hundred billion stars in the galaxy, millions of planets with transmitting civilisations. Equally, these civilisations should be spread reasonably evenly in time as well as space, across a reasonable span of time. Which is where the order of magnitude thing comes in. In this context, "reasonable" is a billion years. So your "lightspeed barrier" argument falls down. In case you think I'm being over generous, let's refine that span by a factor of a thousand. So, a span of a million years. We should expect, reasonably, at least one broadcast civilisation to be one million years ahead of us. In which case, no matter where in the galaxy they are, their signals should have been streaming through or past us for AT LEAST the last NINE HUNDRED THOUSAND YEARS (assuming constant broadcasting, or at least constant observable evidence of their presence, e.g. interstellar drive signatures from things like ramscoops or laser-driven lightsails). As we know, we've seen absolutely NOTHING. In any direction. Of any kind. At all. Admittedly, there are directions (e.g. towards the core) where the view is restricted, but every direction *should* be equally promising.
I'm hoping I live to see a man on Mars. I think I could. I dream of living to see mankind's first contact. I don't believe I will.