Yeah, I’m still at it – there are links where you can find Part One and Part Two of this extended essay to catch up or keep continuity. Meanwhile, I’ll keep going with the idea, which basically is, what are the chances of us contacting intelligent life elsewhere in the Galaxy? This time, I talk about long-distance life affairs.
Drake’s Equation has, as part of its formula, the rate of new stars being formed in the Milky Way Galaxy per year, which to my mind is kind of a funny thing to calculate. I believe it was included to show the chances, at any time, of a new life form popping up somewhere in a “close proximity” (more on that in a sec,) but it’s a little misleading. Life took a billion years to start after our planet formed, and another 3.5 billion to get to intelligence (as defined in Part Two) – so new stars may not result in life forms to contact for a good long time, and I doubt it’s safe to assume star formation has been going along at the same rate all this time. Even so, we’ll argue that there’s a certain number of chances for new life every year.
The primary thing is, we figure the Milky Way Galaxy is roughly 100,000 light years across and holds roughly 200 to 400 billion stars, any one of which might have planets capable of supporting life. That’s a lot of chances, right? Which means life is pretty likely to be out there, though intelligent life is a bit less likely than simply bacterial or basic, algae-like life forms. But with those numbers comes some other big numbers. A light year is the distance light travels in a year at its damn fast speed, and is roughly 10 trillion kilometers (6 trillion miles). Bear in mind I use the American version of trillion here, which is a million million (unlike Great Britain, which considers a billion a million million.) I just never liked expressing numbers exponentially, even though it’s more accurate.
The point is, those are much bigger numbers, which means that most of the Galaxy, despite being pictured as simply brimming with stars, is empty space. Our nearest neighbor star is 4.2 light years away, which is close in galactic terms but extremely far in terms of the distance we’ve traveled so far (which isn’t even to Pluto yet.) Now, a quick illustration. If we were on Pluto, our Sun, as big as it is, would look like a quarter held up 100 meters (yards, close enough) away. The closest star, Proxima Centauri, is more than 5,700 times that distance. Most stars are a whole lot further away – in fact, they average about twice that distance from each other. There are about 200 stars within 25 light years of Earth. Radio waves travel at the speed of light (since radio and light are simply two different frequencies of electromagnetism anyway,) so if we sent out a signal fifty years ago, we might stand a chance of hearing from 200 stars by now – you know, time for it to travel there, and the time for the reply. But don’t run with that figure yet.
Light from a star on one side of our Galaxy takes 100,000 years to get to the other side – that’s roughly how long we’ve been Homo sapiens, and about twenty times longer than we have any records of civilization. If we simply sent out a “Hello there” signal of some sort to contact any intelligent life in our Galaxy, we could actually be a different species by the time the “‘Sup?” signal came back to us. If we still existed at all.
But, wait, no, that’s not likely either. Even though we’re not at the very edge but roughly two-thirds of the way from the center, we can’t even see stars at the center – there’s too much junk in the way, dust and gases and general debris. That’s what that strange mottled pattern is when get a good look at the night sky from a really dark location (or, we can cheat and use photos like this – click on it to see the high res version.) Sending a signal through that muck would be next to impossible, as would receiving one from another life form. So we can scratch off a significant portion of our Galaxy from the list simply because it’s unlikely any species could get a signal through.
And, there’s the issue of energy. Just like a cell phone becomes worthless if a tower isn’t close enough, there’s only so far a radio signal can travel and not become blocked by dust or overloaded by the Cosmic Microwave Background (CMB), which is residual heat/radio signals/radiation (really all the same thing at this level) from the beginning of the universe. For now, just call it static – which is more accurate than you might think, and here I’m going to show my age. Old, pre-digital televisions had VHF and UHF channels, and if you tune one to a UHF channel right now, you’ll get nothing but static. Some of that is actually produced by the CMB. Anyway, there’s this little problem of energy in an expanding sphere, which is what a radio signal would be. At twice a given distance from the source, the power of the signal is 1/4 as strong, and this loss continues – I was going to link you to Wikipedia’s Square-Cube Law page, but it’s written by math geeks and is needlessly obtuse. I’d illustrate it, but just take my word for it right now.
What it comes down to is, in order to send a decent coherent signal through a reasonable portion of space, we (and everyone else) would need a lot of power to cross the distance. It’s easy to see stars – at night. But remember that they are vast uncontained nuclear fusion generators. Any intelligent life’s radio transmitter is going to be a lot smaller and use a lot less power. According to this page, assuming 100 Megawatt transmitting power from the originator of the signal (that’s a significant chunk of one of our power stations’ full output) and a receiving dish the size of Arecibo’s, we can expect to monitor a 60 light year range. Except that we can’t, because that’s in ideal conditions and a dish the size of Arecibo’s isn’t pointing in any direction but one. Basically, it means 13 stars – that’s a ridiculously tiny fraction of 200-400 billion. A smaller dish, less transmitting power, or a greater distance means we hear nothing. Yes, we can speculate that intelligent life more advanced than us might have found a way to generate a lot of power that they’re happy to throw into a hailing signal, but it’s only speculation. We have to be careful of the idea that intelligence will defeat any law of physics we care to name – there’s absolutely no reason to believe this (we certainly haven’t even come close.) And there’s that signal-loss-with-distance thing to calculate – they’d need thousands of times the power to increase the chances of contact all the way up to one percent of the stars in the Galaxy.
It would seem like relying on radio waves might be a bit archaic. The reason we entertain the idea (and indeed, even monitor them through SETI, the Search for Extra-Terrestrial Intelligence) is because radio waves are simple, basic, and omnipresent. Stars emit them, and a magnetic field is all you need to generate them. And, they expand in a sphere, so you reach in all directions. But what about other, more efficient methods? For instance, a laser is an efficient use of signal. And this is certainly considered, but there are two major issues with it. The first is that, it has to be aimed, and how do you choose which star system is most likely to interpret your signal? How likely is our little sun to be the one chosen by other life forms? Not very likely, since it’s fairly common and unremarkable, in only a small cluster of stars, and far from the center of the galaxy (where the spread of even a tight beam laser signal might reach many more candidates for life.) The second really big problem is the proximity of the system’s star. From the viewpoint of even a close neighbor, a planet in the habitable zone is too close to its parent star to distinguish a light signal. Right now, we’re slowly finding major planets around other stars because the planet passing in front of its star reduces the light from that star by a smidgen, and we finally have cameras sensitive enough to measure that. Get that? Something the size of a large planet blocking a portion of the star’s light is something we’re just starting to be able to notice – as of this writing, a planet the size of Earth can’t be registered [Edit: I clarify this a little in a new post here.] It would be a long time, if at all, before we’d pick up a laser signal. We’d far more likely determine the presence of life artifacts in the atmosphere of the planet because of the tiny color shift it imparts to the star’s light, just like our sunsets get a red hue because of the thickness and humidity of the air.
Are there other methods? We know of a few, but most have the same kinds of problems. And while advanced intelligence might find better ways of communicating, we’re extremely unlikely to interpret those correctly until we discover them ourselves.
The point of this whole three-part essay (wordpile) is, when we talk about contacting other intelligent life we can say, “It’s possible,” but when we sit down and try and calculate the actual chances, we find that we have too little information to work with, and what we do have points to very, very slim chances of ever making contact. The Galaxy might be large, but the area we can interface with is tiny in comparison. This might change, as we learn more about our Galaxy and physics, but for right now it’s looking pretty bleak.
This isn’t to say we shouldn’t bother looking – there’s always a chance. But it seems more like a lottery than anything else. Despite common misconceptions, playing against overwhelming odds is overwhelmingly likely to be a waste of time. And making any kind of assumption that we’d have to have found alien intelligence by now is ignoring lots of evidence that says otherwise. Don’t get me wrong at all – I myself would dearly love to know that any kind of life is present someplace else. But I think what we’re most likely to find is some basic bacterial-level stuff in niche conditions, like thermal vents under ice caps someplace within our own solar system. A signal from intelligent life around another star has a lot of factors against it.
The most interesting part about it all is, if and when contact occurs, we may just find out how useless most of our speculation really was.
[Illustrating image: Okay, are you ready for this? It’s a shot I created for a casual competition a few years back. The big white thing to the left is a white balloon, sprinkled with powder and illuminated from behind with one strobe. The blue planet is actually a racquetball. And the starburst is another strobe just peeking out from behind the racquetball, creating some flare effects in the camera lens. I’m aiming straight down to hide the stand that holds the racquetball.]
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