Roswell, Dyson Spheres, and the Price of Photons
"I wouldn't even listen to this part of the tape."
Seth Shostak: "...something I probably shouldn't talk about, because the boss will get
very upset about it. [mumble mumble] invasion of privacy. But, I mean, you can
talk in general about the fact that the public, of course, is often unable to
distinguish among things like alien visitation, abduction, the idea that there
might be, you know, monuments on Mars that have been left for our edification
and things like that, and what we do. There is that continuing problem,
because it seems that the level of science education in the country is not
very high, so they don't understand the difference between science and other
approaches to trying to understand things.
And I guess from our point of view, scientists are often fairly impatient with
people who don't understand science, their line of argument. That becomes
obvious to me whenever I'm on a radio show where there are call-ins, because
people will often call in and say, "well what do you really think about
Roswell," for example. That question's almost guaranteed on a radio show. And
what do I think about Roswell? I think Roswell's probably a very nice town.
And I think the fact that it's claimed that aliens made a navigation error
there and, y'know, somehow crashed, even though they haven't any other time,
has been pretty good for the Roswell chamber of commerce. But I don't think
the story has anything to do with aliens.
Siduri: Well, so, how does SETI—just as, you know, a first groundstarting
question—how did SETI decide on radio signals rather than any other form of
trying to see whether there was extraterrestrial life?
Seth: Well, that's a good question, because in fact...
[At this point The Compulsive Splicer starts menacing Seth with a camera.]
Seth: You got her, I hope, because my eyes were closed in that shot.
The Compulsive Splicer: That's fine. Yeah, I need to get all of us.
Seth: Okay. Yeah, how did SETI get started with radio. That's a good question
because in fact if you think about, sort of step back from the whole question
of what particular SETI experiment you're doing, you might say, "Well, how do
you know whether there are aliens out there?" There are lots of ways you could
conceivably know. You could look around and see if they're walking the planet.
That's legitimate, although I don't think they are, but you know, you could
ask that question. The second thing is you could look for astroengineering,
for example. You could look for giant artifacts in space. I mean, the galaxy's
been around for two or three times as long as the earth has been around, so if
there are civilizations out there a lot of them—most of them—will be way
ahead of us.
Unless civilizations routinely destruct very quickly, they self-destruct
because they invent technology and then they invent the H-Bomb and they blow
themselves up. If that's what normally happens then maybe there aren't very
old civilizations. But I'm more optimistic than that.
So a lot of civilizations could be way beyond us, so maybe they're doing stuff
that you can see, that's obvious—you know, they're building something
that's big. Let's see here, maybe they have giant rockets and you can see the
exhaust from these rockets. Maybe the rockets have magnetic brakes and you can
see the radiation from the magnetic brakes. People have thought of a lot
of things. Maybe they've left, you know, giant monoliths on the moon for us to
dig up, a la 2001. You know, it's not impossible. We wouldn't know, because
nobody's really looked at the moon for those sorts of things.
So those are all possibilities. The trouble is most of them don't sound
terribly fruitful because even though the aliens might be building big stuff,
you don't quite know what to look for. I mean, how do you see it. There have
been some experiments in that regime, I mean some people have done some
things, they look for what are called Dyson spheres. Do you know what a Dyson
Siduri: Um, I know of it only...
Seth: Take Freeman Dyson, you just roll him up like a marble and you have a
Dyson sphere. No, Dyson spheres...
TCS: It's the Ringworld except a sphere world, right?
Seth: Yeah, exactly, exactly, which...turns out the Ringworld's a little
Siduri: I was about to say, I know of it from an old Star Trek text adventure
game ["The Kobayashi Alternative"], where you went to visit a Dyson sphere
Seth: Yeah, exactly. You take apart some outer planet. Like Neptune—Neptune's
not big in your life; you don't mind taking apart Neptune. They take
it apart and rebuild it as a giant sphere, cover the inside with solar cells,
for example, and that might be something that an advanced civilization might
do. That kind of thing. People look for that, they look for Dyson spheres by
looking for stars that have a lot of infrared. But you know, they've only
looked a couple hundred stars. Not much is it?
So, there are all those approaches, but then people thought "well, maybe the
best thing to do is look for signals." And the reason that got started is that
a couple of guys, they were at Cornell University, a couple of physicists,
just worked out really simple calculations. They said "If you take the most
powerful radio transmitter on Earth, and our best receivers, how far apart can
you separate these two things and still be able to pick up the radar
transmissions?" And they figured, oh, well, it'd be, you know, thirty thousand
miles or a thousand miles or something like that. And it turned out it was
So they realized, hey, it's pretty easy to send a message that can go from
here to another star. So maybe aliens are doing this. So that was 1959 and by
1960 people were already looking for the signals. Now, immediately other
people said, well, maybe that isn't the only way to do it—maybe they'd be
flashing lights at you or something like that. And it turns out that the
physics tends to favor the radio. Mostly because, I don't know if you remember
high school physics, but the amount of energy in a photon is proportional to
the frequency of [Seth starts muttering equations]. Energy equals hf or
[mumble mumble]. Anyhow, all that means is that light photons, a single light
photon has got a lot more energy than a single radio photon. So if you want to
send a bit of information from here to Alpha Centauri it's cheaper, in terms
of the energy, to do that with radio than to do it with light.
So, you know, that's been the argument for many years. Now that argument isn't
very solid anymore. I wouldn't even listen to this part of the tape.