Podcaster: Richard Drumm
Title: Are We Alone?
Organization: Cosmoquest
Link : https://cosmoquest.org/x/365daysofastronomy
Description:
From July 24, 2014. This episode won a Silver Communicator award for 365 Days of Astronomy.
Today in Q&A I’m going to tackle (or at least try to tackle) the biggest question there is:
Are We Alone?
Well, that’s the biggest question in science that I can think of anyway. So what’s the answer? Well, the short answer is “We don’t know.” We have only one place that we know has life and we’re standing on it. Earth. We have a dataset of one point. Easy to graph, huh?
But let’s take a few minutes to think about that one point and examine it closely. It’s all we’ve got, so what else are we gonna do? We don’t have dozens of data points, but we do have this one and all the scientists in the world are studying it!
Bio: Richard Drumm is President of the Charlottesville Astronomical Society and President of 3D – Drumm Digital Design, a video production company with clients such as Kodak, Xerox and GlaxoSmithKline Pharmaceuticals. He was an observer with the UVa Parallax Program at McCormick Observatory in 1981 & 1982. He has found that his greatest passion in life is public outreach astronomy and he pursues it at every opportunity.
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Welcome to the 365 Days of Astronomy.
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Today in Q&A I’m going to tackle (or at least try to tackle) the biggest question there is:
Are We Alone?
Well, that’s the biggest question in science that I can think of anyway. So what’s the answer? Well, the short answer is “We don’t know.” We have only one place that we know has life and we’re standing on it. Earth. We have a dataset of one point. Easy to graph, huh?
But let’s take a few minutes to think about that one point and examine it closely. It’s all we’ve got, so what else are we gonna do? We don’t have dozens of data points, but we do have this one and all the scientists in the world are studying it!
Life likely arose fairly quickly, 500 million years after the Earth’s formation, and has been here for 4 billion years. It likely took a billion years for life to “invent” photosynthesis, it lived on minerals and chemical energy before that, kind of like the bacterial colonies at today’s undersea vents. Life consisted of single celled organisms for an additional 1.75 billion years till multicellular organisms happened. Life got off to kind of a slow start.
Then life re-invented itself with the appearance of the Eidacaran biota, which in their turn were replaced in the Cambrian explosion, which in IT’S turn was replaced during the Great Ordovician Biodiversification Event a mere 40 million years later. Yeah, mere.
Only after all that did plants invade the land! Before that the surface of the Earth was gravel & rock. The dinosaurs? They were still a long ways away!
So you can take the timeline of life on our one data point and split into approximately 3 big chunks:
– The first third was unicellular life with no photosynthesis. Simple bacteria basically.
– The second third (a little bigger than the first third, truth be told) had photosynthetic single celled organisms, like free-floating algae cells. Time passed slowly. (OK, it passed at the same rate as today… I’ve got my poetic license right here!)
– Then the last third can be split in 2 approximately equal pieces, before the Cambrian explosion, dominated by things not unlike today’s algae colonies and after the Cambrian explosion, where the oddball Ediacarans morphed into trilobites which morphed into fishes, and finally dinosaurs, then evolved into mammals, then flowering plants, then no dinosaurs & the mammalian explosion and only then do you get to us.
That second half of the final third was a busy time for life, wasn’t it?
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OK, that’s a bit over simplified, but at the time scale of hundreds of millions of years things might appear to happen pretty quickly.
So that’s life’s timeline. Half a billion years of no life. 3 1/4 billion years of bacteria & algae, capped by 3/4 of a billion years of worms, fish & dinosaurs. We humans hardly make a dent in there. At this scale we’re for all intents and purposes invisible!
And now for something completely different! Lets turn our eyes to the night sky.
The Milky Way Galaxy has something like 300 billion stars and it’s estimated that basically each star has at least 1 planet and quite probably has half a dozen or more.
The question at hand is “Are we alone?” But let’s take this as really 2 questions. “Is there life out there?” and “Is there intelligent life out there?” — More specifically “Is there detectable intelligent life out there?”
So we find ourselves surrounded by hundreds of billions of stars, with many hundreds of billions of planets but probably only 10-20 billion habitable planets & moons, in the so-called habitable zone where water can be liquid.
So there’s no shortage of worlds for life to spring up on. And spring up quickly, too!
Now, imagine, if you will, that we have the most powerful telescope in the universe and can see even microscopically into the soils & oceans of all the worlds in the galaxy. What do we likely see?
Lots of bacteria & algae. Lots. And lots. A few jellyfish and simple plants. More bacteria & algae. And more. A very, very few dinosaur-like creatures.
OK, let’s look at our timeline of life on Earth another way. Let’s break it down into centuries. We humans have been detectible from off-world for less than a century, but let’s say for the sake of simplicity it’s been a full century. Our radio transmissions & old TV shows have been announcing our presence for that century, expanding outward at the speed of light.
There were no transmissions for 45 million centuries and then 1 century of transmissions.
So in a way, though life is probably very abundant, intelligent life has a 1 in 45 million chance of being detectable. You’d have to look at 45 million habitable planets to find one with detectable intelligent life. Admittedly we’ve been intelligent but undetectable for a number of centuries, maybe as many as a hundred.
Sounds pretty dismal, doesn’t it? But even so, if we conservatively say that there’s only 10 billion planets with life, well that means that there could well be over 220 planets with intelligent life out there in our galaxy. Let’s ignore all the other galaxies. Inter-galactic communication may forever be unattainable.
With the galactic diameter being approximately 110,000 light years and the disk of the galaxy being 1,000 light years thick, this gives us a galactic volume of 9,500,000,000,000 (9.5 trillion) cubic light years. Give or take. Hey, what’s a few million cubic light years between friends, eh?
I have seen the figure 39 trillion ly³ for the Milky Way’s volume, so it could be bigger than my numbers indicate, especially if you take the galaxy’s halo into consideration. But let’s stick with 9.5 trillion and just concern ourselves with the disk.
Divide that volume by 220 planets with detectable intelligent life and you have 43.18 billion ly³ per planet. Solve that volume for a sphere of unknown radius by the standard V=4/3 Pi r^3 equation and you get a 2,176 light year radius sphere with intelligent life in the center of a sphere filled with much life but no other intelligence.
But, you might hasten to say, the galaxy is only 1,000 LY thick! True that. So we solve for a cylinder with a height of 1,000 LY and the 43.18 billion ly³ volume and we get a radius for the cylinder of 3,707 LY. Basically 37 hundred LY.
This assumes, or course, that intelligent life and life in general is evenly distributed throughout the galaxy, which is probably a wrong assumption but is a good enough starting point.
With a truly randomly scattered distribution of intelligent life in the galaxy, the closest intelligence might be closer, and concomitantly may be much farther away. For all we know we’re the only intelligence in this quadrant of the galaxy. Or this could be the crowded one. We just don’t know.
So if we have a 3,700 light year radius cylinder of no intelligence around us, and a neighboring star with intelligence has the same cylinder about it, then another intelligent civilization might be, on average, 7,400 light years away. Actually the number might be a few percent smaller than that as the circular cross sections of cylinders don’t pack perfectly together. They leave little gaps.
Now don’t get me wrong! I’m a firm believer in SETI, the Search for ExtraTerrestrial Intelligence. I think this is something very worthwhile for us to do. For all we know there’s a planet full of nice aliens 25 light years away! We could strike up a very interesting conversation. We have to try.
If these back-of-the-envelope calculations of mine are even close to accurate, this spells doom for the “UFOs are alien spaceships” crowd. Sorry guys. I REALLY, REALLY want the UFOs to be flying saucers, but I don’t think they are. If wishes were horses (or flying saucers) beggars would ride.
Meanwhile our expanding-at-light-speed 80 year old radio transmission shell probably hasn’t reached anybody intelligent yet. Another 7 thousand years ought to do it.
Man, I hope they’re listening!
I’m glad you were! This is Richard Drumm, AKA Richard Drumm The Astronomy Bum. Thank you for listening to this episode of 365 Days of Astronomy!
365 Days of Astronomy is a community podcast made possible thanks to the contributions of people like you. Please consider donating at 365DaysofAstronomy.org/Donate
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