DAVID: So welcome to Google,
Google in Cambridge here.
Today it's my
pleasure to introduce
Paul Horowitz, professor at
Harvard down the road from us.
I knew Paul Horowitz when
I was in college back then.
Many of you know him as
the author or the co-author
of a book called "Horowitz and
Hill-- the Art of Electronics,"
which is a fantastic textbook
in reference for people who
are both electronics
hacker professionals
and electronic hacker amateurs.
Paul has a third edition
of the book just out,
and I contacted him, and
I said, come talk to us,
and come give us a book talk.
You can come read from the
chapter on field effect
transistors, entertain us, and
I thought that would be great.
But he said, you know,
he's got his day job.
His day job is looking
for extraterrestrials,
and that turns out to
be interesting as well.
So I said, sure, come
talk to us about that.
So he'll do that.
I think he'll be taking
some questions at the end.
We can talk about the book
a little bit then as well,
but I imagine this
will all be great fun.
So without further
ado, Paul Horowitz.
[APPLAUSE]
PAUL HOROWITZ: So I'm
going to talk generally
about the subject of
SETI, and specifically
about some of the stuff
we've been doing at Harvard,
and I'll tell you also about
some of the new stuff going on.
You may have heard
that $100 million
got given in a thing called
the Breakthrough Listen
Initiative by the Breakthrough
Foundation, Yuri Milner,
and that thing is
just starting up now.
OK, so it's really nice to
see David after 25 years.
I should just tell
you about David.
When he took our
electronics course, he did,
as he's described
here, he's a zealot
to show what he could do
with our little computer
that you build.
This is a circuit of it,
in case you'd like to see.
From the bare metal, we had
the students build this thing
really wire by wire.
And it's really bare metal.
You may notice some
things that are missing.
For instance,
there's no keyboard.
There's no monitor.
There's no disk.
There's no operating system.
There's not even a
serial port, and David
managed to outfit this
thing with a set of DACs
and extra memory, and he did bit
banging to make a serial port,
and he programmed this
thing to play Asteroids.
So we thought that was
pretty spectacular,
and he earned this little
notice in our student manual.
So that was pretty cool.
I'm not surprised to see
him at the Googleplex.
He's that kind of guy.
I remember he needed a
quad DAC for this thing,
and he got on his bike and
bicycled out to Analog Devices
to get the part to
make this thing.
So pretty cool.
I'm going to try here to put
an awful lot of stuff in here,
and since I'm not really
quite sure what backgrounds
are out here today, I'm going to
try not to be boring and throw
a little bit in for everything.
I'm going to start with
a slide after this one.
There was a series of
talks at the MIT Museum
a few years back called
Life in the Universe,
and the last talk was on finding
them, and the one before that,
I went to just to see what kind
of people go to these things.
And one of the questions
during that session
was something like
this-- I've heard
that spy satellites can read
license plates down on Earth
here.
Can't we just do that on
planets around other stars?
And the guy who was
talking said, well,
I think that's a
question for next time.
Well, next time
was my time, so I
decided I'd start with a slide.
So here's the slide,
which is well,
what about the
license plate myth,
and what about other planets?
So here's the deal.
You can just do a basic
optical calculation, which
is look at diffraction limited
resolution looking down,
but turn the Hubble in the wrong
direction, programming error.
You're probably running
Windows or something,
and if you take the actual
parameters of the Hubble,
fly it a little low,
about 100 miles,
and just look at what the
diffraction limited resolution
is.
It's about 1.6
inches, so you could
reach large license plates.
Of course, license plates
are on the back side of cars,
so if you're looking straight
down, you wouldn't see it.
You'd have to put the
license plate on the top,
but anyway, the
number is about right.
But then what about doing
this on other planets?
Well, let's go for some
serious distance here.
Let's try a planet around a
star about 25 light years away.
That's far enough out to
have some reasonable number
of candidates for
habitable planets.
And the good news
is that there's
no problem with the brightness.
You might think,
well, far away, you
don't have very many photons.
But that's not the
problem, because you
have to use a bigger
telescope to get
the same diffraction
limited resolution,
and that's going to scale
up like the distance.
So when you scale up the
telescope proportional
to the distance, then to
keep the same resolution
in the collecting area goes up.
It can square the
distance, and that exactly
compensates for the
falloff of light, which
is the square of distance.
So you've got plenty of photons.
No prob.
The prob is you need
kind of a big telescope,
and here's how big it is.
It works out to be about 18 AU.
18 AU is the mean distance
of Earth from sun.
And so I made a little
scale model here.
There's an antenna that's about
the size of Saturn's orbit.
Kind of big, and I people
don't make optical telescopes
that big, so I just stole a
radio telescope picture here.
But the other thing is it
has to be kind of accurate,
because this is light, and it
has to be diffraction limited,
so it has to be accurate
to better than 1/20
of a wavelength of light
works out to be about 1/1000
the diameter of a human hair.
This is an interesting antenna.
But then you think, OK, if
they have license plates,
then they have cars,
and they have laws,
and that means they have police.
And that means they
have police radios,
so they know about radios.
So they know what
radio communication.
Why don't we just ask
them what the license
plates look like instead of
doing this kind of crazy thing?
So that gets into the whole
business of communication
over these distances.
So here's a nerdy slide.
Some of these slides are
sort of warning away nerds,
but you guys are nerds, so
there's no problem here.
So here's the question.
Can you communicate
over these distances?
And you might start
with-- by the way,
I'm not a PowerPoint guy.
Maybe you can tell.
But I did learn
about the animation,
but all I could figure was you
could fly in from the left.
So a lot of stuff
flies in from the left.
Sorry about that.
So take a couple of modest
sized digits, 300 meters.
That's the size of the Arecibo
great dish down in Puerto Rico.
Put these things
a modest distance
apart like 1,000 light years.
Within 1,000 light
years, there are
about a million sun-like stars,
so this is a reasonable piece
of the galaxy.
It's about the thickness of
the galaxy out where we live.
And transmit $1 worth of
electrical energy converted
into radio waves.
So here's the thing
called a nerd box,
and the nerd box
simply calculates
how much energy will
be received if you
transmit $1 worth with the
fraction limited antennas
of this size.
And it works out to be about
2 times n minus 11 ergs when
you scratch through the thing.
By the way, the antenna has
quite a lot of gain there.
I just marked in there
it's about 90 db of gain,
factor of 10 to the ninth.
So that helps a lot.
Big antennas, short
wavelength-- that's good.
But what's 10 the minus 11 ergs?
What does it compete with?
Well, it competes with
background-- oh, yeah, you've
got to have the little
thing here, again,
for the regular
audience, which is
when you get to the punchline,
that's the good part.
This is one of those
Sid Harris cartoons
used without permission here.
This works out to be
about a trillionth
the energy of a
falling snowflake,
so it's not a lot
of energy there.
But it competes with even
smaller background numbers,
which is thermal noise.
And at these kinds
of wavelengths,
you can achieve
system temperatures
of 25 Kelvins or even
less, or about 10
to the minus 15 ergs, a few
times 10 to the minus 15.
So in other words,
the receive signals
about 10,000 times noise.
No problem.
In fact, you could chop
it up into little bits
and send a whole bunch of bytes.
So interstellar
telegrams are cheap.
Here's, again, the same
diagram, and they cost something
like half a cent per word.
This is a calculation
originally that I
saw from a wonderful
professor at Harvard
by the name of Ed Purcell.
Perhaps, some of you
know his E&M book.
Anyway, that sounds good.
What's coming next?
I guess what's
coming next is OK,
but what's out there
within 1,000 light years?
And here's a little
picture of the galaxy.
It's kind of a flat
thing with lots of stars.
Some are red.
Some are blue.
There we are out in the--
does this pointer work?
Oh, this pointer works.
Can you see that?
Here we are, sort of in
the galactic suburbs.
And in the immediate
region where we are,
the galaxy is about
1,000 light years
in thickness from where most
of the stars are in the disk,
and there's about a million like
the sun number I made before.
So there's plenty of
candidates, and as we
know from recent exoplanet
searches, experiments,
things like Kepler, and so
on, most stars have planets,
and probably 20% of them
have Earth-like planets--
inhabitable.
Maybe 10% or 20% habitable
Earth-like planets.
It's an amazing number.
20 years ago, nobody knew that.
In fact, nobody had any examples
of planetary systems anywhere
except here and one
weirdo with pulsars.
What's this say?
Oh, yeah, and if you're worried
that that's not the stars--
I don't know why
you'd worry-- there's
10 to the 11th galaxies.
The only problem is there's
that pesky speed of light thing,
so they may be out
there, but it's
kind of annoyingly long
round-trip latency.
If you want one of
these gee whiz numbers,
here's the gee whiz number.
There are more stars in
the universe than grains
of sand on all beaches of
Earth, and I can say this
with some authority having
done the back of the envelope
calculation, which was
just flew in from the left.
And what I did was I was
generous with my beaches.
I let there be 100,000
kilometers of beaches.
Shorelines are fractal kind
of, and they zigzag in and out.
I gave these things
100 meters of depth.
That's a pretty good beach,
and toward the water--
30 feet deep.
Not bad, huh?
So there's 10 to the 11th
cubic meters of beach,
and I gave sand a half
a millimeter cubed.
That's about 10 minus
10 cubic meters,
so you get 10 to the
21 grains of sand,
but there's 10 to the 22 stars
at least in the universe.
So there you go.
This is done on the back of
a crane's beautiful envelope,
and I showed this
thing at a conference
called EG in California.
A whole bunch of very
interesting people go to that,
and one of them is
the MythBuster guy,
the guy with the red hair.
What's his name?
Adam Savage.
And he said afterward,
he looked at this thing.
He said, I've got to
have that envelope.
He said, send it to me.
I'll send you
something really cool.
So I mailed the actual envelope.
This is all I have left, and
he never sent me anything.
So Adam Savage.
OK.
So planets-- how do
you find planets?
Well, people have been
finding planets like crazy
in the last decade.
One way to do it, the first
way that really worked
was spectroscopic.
You look at the spectral
lines of a star,
and the recoil kind
of going around
gives you a Doppler shift,
periodic Doppler shift.
It's not so easy to do.
There's turbulence on the star.
You have to do this
very precisely.
They threw an [INAUDIBLE]
absorption cell in there
to give calibrated lines
to sort of compensate
for everything that goes wrong.
And then you look at the
Doppler shift over time,
and here's an example
of a pretty heavy planet
and a pretty slow orbit
around another star.
You see this one has been going
on for about 10 or 12 years.
You see about one full cycle.
So this is the radial
velocity method.
It has a strong bias
toward heavy close
in planets, close in
because it goes rapidly,
and you get to see
several cycles.
Heavy, because you get
a big recoil velocity.
Actually, the close in also
gives you more velocity.
So what it tends to
favor, heavy close in.
That is hot Jupiters, and
the very first planet found
was that the Jupiter
in a several-day orbit.
Completely unexpected.
We don't have those things here.
And so people start
to wonder, do we
live in the weird
planetary system?
In fact, the whole universe
out there is hot Jupiters.
But no, it's really
a selection effect,
and when you do more
careful measurements
and try to dig down into the
harder to detect planets,
you actually find that
Earth-like planets
are rather common.
Now I have a little
bit of stuff on this.
Let's see.
Here's a graph that was
put together, actually
by a former student
of mine in SETI,
and he's become a big stick
in the business of Exo-Earth.
And looking at a
bunch of stuff, this
was the radial
velocity measurements
and the spectroscopic
thing that I just showed.
The fact is that-- and
what he's plotting here
is mass here or minimum mass,
because it depends on-- all
you can see is what-- if
the thing is inclined,
then you only get the
trigonometric projection
of the thing.
But here would be an
Earth mass down here.
And what you see, this
part here that's all blue
is basically the search
is incomplete down there.
In fact, it's 0% complete,
because it's really hard
to see slow light planets.
But you could take
what you have here
and extrapolate based
on the incompleteness,
and from that, you can get a
measure of what's down there.
And from extrapolation, which
is admittedly a bit hazardous,
you get something like a
quarter of sun-like stars
harbor a close in planet
of Earth-like mass.
So more recently,
this other technique,
which is of transits, so a
planet goes in front of a star,
and if we happen to be in
the plane of the orbit,
then we're going to see a
little dimming of the star.
Not much.
Look at the scale
on the left there.
So we're seeing five
parts in 10,000,
and that's a pretty big one.
And you get this
periodic, and this
is a star with a period
of, I don't know, looks
like 40 days there, Kepler 10.
So what have I got here?
And based on this kind
of stuff, Kepler data,
we can try to back
out of this bias.
So here is the orbital period,
and again, we favor short ones.
And here's radius or
mass-- two graphs here.
And again, we favor
a lot of mass.
So it's complete out
here in these regions.
But down in this corner here,
that's the hard place to be.
And this is where we live.
We live right here, one radius
and 365 and a quarter days,
except we make a correction
every four years.
That's the four days.
We make a correction every
100 years, or 300s out of 400.
You know about that stuff?
Most people don't live long
enough to care about it.
Astronomers worry
about it, because we've
got to keep track
going all the way back.
Anyway, this is the
impossible place to go,
but we can try to
extrapolate and see
what you can do with this,
and people have done that.
The ones that are hardest
to see, we've tried hard.
And here's four examples from
Astrophysical Journal, 2012.
Again, this is my student here.
SETI is not a dead end.
You learn lots of
cool stuff, and you
can do other things with it.
Here's four Earth-like--
closest to Earth-like planet.
These things have a radius
of between two and three
times Earth's radius, and this
is the kind of dimming you get.
And you see again, we're
pretty small numbers here.
These are fractional
percent that
have been [INAUDIBLE] here.
So that's another
way to do this thing.
Now wait.
It says here I've got
another slide in here.
Must be here somewhere.
Let's see.
Got it down.
Anyway, here's a picture
based on the Kepler
stuff, the transits of what we
found, as of a few years ago.
And here's where we want to be.
And again, it's a
hard extrapolation,
but the best people have
been able to do-- backing out
the selection effects is
that there's plenty of Earths
out there.
Here's one more graph, again,
of that same incompleteness.
Here, it's orbital period
versus radius again.
And again, Earth
would be out here
about where my arrow
is right there, 365.
So Earth-like
planets are common.
Again, doing the
extrapolation, 10%, maybe 20%,
depending upon how you do
this, and we will know more
when we have more data, and when
we have new missions like tests
and some other things going up.
So there's all reason
to believe that there's
plenty of planets out there,
and let me switch gears
now and just talk about
a different parameter
than space, which is time.
You might ask, has there
been time for them to evolve?
Are they as smart as we are?
Are they as smart
people at Google?
So let me just show you
my little timeline thing.
Astronomers love to do
this kind of stuff--
give you the astronomical
perspective, which
is everything you know, everyone
you know is the thinnest
slice of time possible.
I think for you guys,
this is kind of obvious,
but anyway, here we are.
Big Bang-- Earth's sun
and the whole solar system
formed about four and
1/2 billion years ago.
And what we do is
expand that to one day.
So if we call that
one day, we can
talk about when events
happened in this day.
The day started when the Sun and
Earth were born, approximately.
So life arises early on Earth.
Look at that-- 5:00
in the morning.
The Sun wasn't even up yet.
Well, that's a bit
of a mixed metaphor.
But life didn't get
interesting until a few hours
before midnight, so now
we'll expand that last hour.
Here we are at the last hour.
Dinosaurs went extinct about
20 minutes before midnight.
That's 65 million years ago.
So where's the action?
Well, the action's really in the
last minute, the last minute.
Let's see.
A minute is-- well, it's
50,000 years per second,
so you can figure this out.
It's a few million years.
Here's the Neanderthals.
That was about
100,000 years ago.
Maybe things were happening
here, but not very interesting.
Certainly not for
Google kind of interest.
So let's take the last second,
so a second is 50,000 years.
Now things are
starting to happen.
10,000 years ago-- agriculture.
And recorded history
basically 5,000 years ago,
but look at it.
It's a tenth of a
second before midnight.
Does that give you
an interesting idea
of the compression of time or
expansion of time or whatever?
Anyway, let's take the
last tenth of a second.
Now things are happening.
Here's Jesus, and
here's Columbus.
And here's the
American Revolution,
but it's sort of getting
squeezed in here.
Marconi was two milliseconds
before midnight.
And lasers and radio
telescopes and all the stuff
that we think you
need to communicate
is one millisecond
before midnight.
I don't have any
more milliseconds,
but 20 microseconds
is a Moore law factor
of two doubly on this scale.
And our timeline
for technical people
is one or two years,
everything changes.
How's your 10-year-old
laptop doing?
So what's the takeaway
besides this is totally cool?
I think the takeaway is if
we find anybody out there,
and if they can
communicate at all,
they're going to be in this
little millisecond just barely.
But they can be anywhere
to the right where
the question mark here is.
In other words, anybody
we communicate with
is-- anyone out there is
either incredibly dumb,
or they're so advanced that
they're going to blow us away.
And so in fact, if you ask
what should we be looking for,
we're looking for
civilizations that can really
do pretty amazing stuff.
They can do magic
with communications
and know all about it.
And if they're interested
in communicating with us,
it's not going to be to learn
about Maxwell's equations
or how you make cool
gallium arsenide stuff
or how you take over the whole
world with Google and Amazon.
It's going to be about
what's your culture like?
What wars are you
fighting this year?
Tell me about Bach and Picasso
and that kind of stuff,
Beatles.
So that's sort of an
interesting perspective.
Let's see.
What have I got here?
Radio works.
Anything else?
So I showed you before that
radio is pretty efficient,
and just to set the stage
for some of the searches
we've done, so is optical.
And this was something it
recognized by Charlie Townes
just a year after the
invention of the laser when
he wrote a little paper
about communication.
So state of the art laser
is really a bright thing,
and it's coherent, so if you
use a large mirror to make
a collimated beam and
shine that out somewhere,
then someone in
that line of sight--
and let's assume they cannot
distinguish our planet where
we're transmitting this
from, from our star--
will see the starlight, but
during the time of the laser
flash, the star will appear
to get much brighter.
In fact, about a
factor of 10,000.
Here's the nerd box.
Well, let's see.
Here's some laser thing.
Here's a little wimpy helium
neon laser of ancient times,
but here's sort of
something a little fancier.
This is a NIF-type laser that's
meant to put out a petawatt.
People know how to
design these things.
They don't know
how to build them.
And here's a graph
of laser power
through the ages, where the
ages begin in the '70s here.
Again, that's only
milliseconds on the time--
not even a millisecond
on the time scales
that anyone cares about.
Here's the most powerful
lasers over time.
And then it started
shooting up here after 1990.
Here's this petawatt
laser that was actually
realized in 1996 at Livermore.
This little dashed line here,
just for interest-- by the way,
this is a super Moore's law.
We go two orders of magnitude
in just a few years.
What's this dashed line?
This is the world's total
electric power production,
and I know this-- see, this is
the California energy crisis.
Do you remember that thing?
When Enron sort
of took them down.
And I drew this graph based
on the data point from here
and a data point from
here, straight line.
It's the easiest approximate--
[LAUGHTER]
Anyway, these are
powerful pulses.
It's only a few nanoseconds,
but what the heck?
So here's the nerd box.
We take one of these
diode-pumped solid-state
lasers.
It's in a terbium doped
strontium flora appetite,
if you're into that stuff.
I'm not.
And imagine, they're
doing the transmitting.
Remember, they're
smarter than us.
We're not going to
do the hard work.
We're just going
to look for this.
So here they are,
and they shine it out
with a Keck-type
telescope, and they send
this diffraction limited beam.
And here we look with our
Keck, and assuming they only
have 10-meter
telescopes is really
a very conservative assumption.
These guys are good.
Anyway, here's what you get.
You get lots of equations.
You count photons.
You fiddle around, even
throw in some reality
here like extinction, and get
the pi squared over 16 right.
There might be someone out there
who actually cares about that.
And it turns out what you
get at 1,000 light years,
you get about 1,000
photons per pulse,
per three-nanosecond pulse.
And the stellar background,
you say, what about the star?
Isn't that putting out light?
Sure, but in a nanosecond,
it doesn't do much.
It puts out 3 times 10 to the
minus 2 photons per nanosecond.
So you get about 1/10 of
a photon from the star,
and you get 1,000
photons from the laser.
So 10,000 to one.
Not bad.
And by the way, this is
independent of distance.
Inverse square, inverse square.
You can't beat that.
So lasers are OK.
Lasers are OK.
So let me tell you
about some searches.
Oh, a little silly slide here.
You know, what
other wavelengths?
Well, if you want to
do it from the ground,
you've got to get
through the atmosphere.
And that pretty much limits
you to the atmospheric windows.
How am I doing for time here?
Well, we'll just speed
up here a little bit.
This is going too slow, right?
There's the radio window
and the optical window.
This is actually a nice
drawing done by Ed Purcell.
Again, this is a wonderful
guy from Harvard.
And astronomers exploit
these things with telescopes.
This is the optical window.
So do humans.
That's why we have eyes.
If the atmosphere were
opaque in the visible,
it would be kind of
silly to have eyes.
Nature understood that.
In the radio, we build
radio telescopes.
And here's our little
one at Harvard.
Actually looks
bigger than Arecibo.
This is Arecibo.
This is 1,000 feet.
This is 84-foot.
This is my son.
Can you see him down there?
He's about six pixels high.
He was six years old.
He's a year per pixel.
And you might ask
the question, what
about the analog of the eye?
Why don't humans have antennas?
I don't know.
I wonder if there's
other creatures that can.
That could be really helpful in
a dense fog or, I don't know,
in the woods where you don't
have direct line of sight.
Anyway, and remember, these are
very efficient communications.
A trillionth of the
energy of a snowflake
gets good communication
over these distances.
Here's the first detection
of radio waves in space.
This is Jansky in 1931.
He was working for
the Bell system.
Bell system in those days
owned the telephone networks.
You may not remember
back that far.
When I was a kid, you
had your dial phone.
It was owned by the
Bell system, and you
couldn't plug your own phone
in if you could even find one.
They owned it.
I took one apart, but I had
to put it back together,
because it was the
only phone we had.
Anyway, Bell system was
also doing transatlantic
communications, and there
they were getting static,
and they wanted
to find out what's
the origin of the static.
Of course, a lot of
it was thunderstorms.
But there was this irreducible
hiss in the background
that Jansky noticed, and being
a smart guy, he didn't neglect.
That's how penicillin was found.
It was a rotten cantaloupe
in a marketplace.
Turned out to be
pretty cool stuff.
Not the cantaloupe, but the
fact that some of the mold
wasn't growing in certain
places around the cantaloupe,
and there was a little
penicillin there instead.
Anyway, he noticed that this
stuff was coming every day
from-- when he
pointed to this thing,
it was diurnal, 24 hours.
But then when he
looked more carefully,
he thought maybe it was the sun.
It wasn't 24 hours.
It was 23 hours and 56 minutes,
so you think a day is 24 hours,
don't you?
Except wait.
I'm at Google.
You know a day is not
24 hours, don't you?
You know how long
it takes the Earth
to rotate once on its axis?
23 hours and 56 minutes.
You're fooled by the fact that
we're going around the sun,
and you think the sun is in
the same place every day.
But of course, it's not.
We're going around it.
So anyway, sidereal time.
He figured that one out.
He's a smart guy.
This was continuum
radio waves from space.
This is basically the
birth of radio astronomy.
Here's a little later, a
birth of spectral line radio
astronomy.
This is the fourth floor
of Lyman Lab at Harvard,
and this is Doc Ewan--
Harold Ewan-- with his horn
antenna looking for a mission
from neutral hydrogen.
This is 1951.
This is what antennas
looked like then,
sort of a hacked
together piece of stuff.
Look at little patches
stuck in there.
So this is basically
plywood with copper sheeting
stuck on there.
This thing here is actually
a thing that you flip over
to cover the aperture,
and the reason
that Doc Ewan put
that there is that he
didn't used to have that.
And then in a rainstorm,
it filled up the lab
with water, which he referred to
as his first signal from space.
So he put that thing in.
Here's what it looked
like on the other side
of the wall coming in here.
So here's the
waveguide coming in,
and it goes the whole rack of
really fancy-looking equipment.
This is radio astronomy 1951
style-- leftover war surplus
local oscillators,
and look, it's
even got earphones
so that Jodie Foster
can listen for the signal.
Anyway these guys
with a $500 grant,
they did this
experiment, and they
found the 21-centimeter
line from hydrogen
and found the whole
spectral line thing.
Nine years later, the Harvard
put up the 60-foot radio
telescope.
This is Purcell and
Ewan, and here's
the horn that had made
the 1951 discovery.
And here's that same
radio telescope pedestal
with a larger dish
on it, now 84-foot.
Again, with my
son there is 1983.
So we press this
thing into service,
and I guess I should say about
1960, this is about the time
that people first started
looking seriously for microwave
signals from space.
And here's a shot of
Frank Drake's 84-foot.
Coincidentally, the
same size as our dish.
And here's Frank back
then, graduate student,
and looked at two stars
for a month or two
with a one channel radio.
It says down here at the
bottom, we turned the telescope
to epsilon eridani,
and then it happened.
Wham, and as Frank likes
to say, all of a sudden out
of the loudspeaker came
choo-choo-choo-choo,
and they said, can
it be this easy?
Turns out not to be this easy.
It was a satellite.
Could it be a satellite in 1960?
It was something that
went choo-choo-choo.
It was probably radar.
Anyway, here's Frank a little
later at our telescope,
a little older than when we
were looking for radio signals.
Let me tell you-- oh, I've got
one more thing about Frank.
He's a cool guy.
He visited Harvard, and
we named our servers--
that thing's a server--
after SETI people.
So this one's called
Frank, so we said, Frank,
will you autograph Frank?
He said sure, so this
is the Drake equation.
How many people have heard
of the Drake equation?
Yeah, good.
There it is.
And Frank's trying to
think, what comes next?
[GIBBERISH]
Frank Drake-- he's quite amused.
He's never been asked
to sign a server before.
So we started looking for these
spectral lines from aliens,
and we wanted more than
a one-channel receiver,
which is what he used
for his search in 1960.
And what we needed was a Fourier
transform type technique.
So here's just a little bit
of nerd history on the Fourier
transform, the fast
Fourier transform, which
you guys all take for granted.
It wasn't always forever.
In fact, it was
rediscovered in the '60s,
and here's a little
piece of the story.
Dick Garwin, who was
at IBM, was the midwife
between Cooley and Tukey,
and he describes this thing.
And Garwin mentioned
to Tukey that he
was competing Fourier
transforms and asked Tukey if he
had a faster way of doing it.
Tukey did.
He described the
essence of the FFT.
Garwin came to the computing
center to get it programmed,
and as Cooley puts it--
I'll read it for you,
because I probably read
faster than you read.
"I was new at the
computing center.
I was doing some
of my own research.
Since I was the only one
with nothing important to do,
they gave me this
problem to work out.
It looked interesting, but I
thought that what I was doing
was more important.
However, with a little
prodding from Garwin,
I got a program out in my
spare time and gave it to him.
It was his problem,
and I thought
I'll hear no more
about it and went back
to doing some real work.
The significance
of the factor n log
n versus n squared was lost
on me, since I had never had
any use for Fourier transforms.
The experience since then has
given me quite an education,
and when I realized
what happened,
I told Garwin that if he had
any more ideas like that,
I would be glad to
help him out again."
So it's a wonderful
little thing,
and Garwin describes-- I'll
send this thing off to David,
and he can forward it around.
But basically what happened
was that Garwin was sitting
in a boring meeting,
and he noticed
Tukey doing, as he
says, doing Fourier
transforms with his left hand.
He doesn't say whether
Tukey was right-handed,
but I think that must be the
implication that this guy was
so cool, he could do Fourier
transforms with one hand.
Anyway, he asked, was there
anything that he knew about it?
He said, yes, indeed.
And there it was.
And that's how it happened.
So this is the '60s.
We're back with
Frank Drake here,
and where do you look
for these radial lines?
And Cocconi and
Morrison-- Phil Morrison
from just down the street there
at MIT-- looked into this.
He was at Cornell at the time.
Where should you look?
Well, you look at the whole
radio frequency spectrum,
and electromagnetic
radiation really
is the way to go, sort of
by elimination of everything
else we know about.
And there's this one line,
this 21-centimeter line,
the thing that was discovered
by Purcell and Ewan.
And it's the marker out there.
It's really the place you look.
So these guys suggested
that's where you should look.
It also happens to be
in a pretty quiet region
of the radio and noise spectrum.
Here's roughly what
sky noise looks
like viewed from
down on Earth, so you
get these atmospheric lines.
The galaxy itself
makes a lot of noise,
and here's this quiet region in
the gigahertz in the microwave,
centimetric microwave.
So that's where people look.
And now let me show you a few
experiments in the 29 minutes
and 40 seconds, 39 seconds,
38 seconds remaining.
So I had a sabbatical in '78
and went down to Arecibo.
Actually, I wrote a letter--
remember those days--
to Frank Drake saying
that was interesting.
Looking for life in Puerto Rico.
He got the joke.
And he sent me down there, and
I built this little system here
that involved-- well,
actually, Arecibo
has all kinds of receiver
things, and all you have to do
is plug them together.
So I did real time
digitizing of what's
coming in off the
antenna and recorded this
all on a tape, which
then got FFTs offline.
Computer wasn't fast enough
to do 64k FFTs in real time
at a kilo sample per second.
Can you remember those days?
I mean nowadays, your smartphone
will do mega channel FFTs
in real time of
anything you like.
And here's this Harris computer.
I remember this is a curious
computer, a 24-bit word.
Isn't that weird?
And it had a disk drive,
which was the size of kind
of a small refrigerator.
And you stuck these things in.
Do you remember
those top loading--
and it held 20 megabytes.
Megabytes.
Not gigabytes, and
definitely not terabytes.
And I remember one day
going back and forth
on the Pulsar, which
was the name of our bus
that drove us to this place.
Calculating what you could
do with 20 megabytes,
you could fit most of the text
of all the books in the Library
of Congress onto one of those
giant 20-megabyte multi-disk
things.
That was exciting days.
Here's how you built a
receiver in those days.
That's me, actually.
You put your hard hat on.
That's mostly for the picture.
But you basically
built a receiver.
It had racks full of things
like mixers and attenuators
and power level meters.
You can see those two meters
and A to D converters.
And you just plug them
together with BNC cables.
You sling a bunch of
them over your neck,
and you just plug them in.
And you do it real quick,
because your telescope time
is coming up.
So I did a search down there,
actually looked at 250 stars.
It was actually the
most sensitive search
ever done, and kept that
record for about 20 years.
It was also a very
narrow search.
It only looked at
about one kilohertz
centered on the hydrogen line
and corrected for the Earth's
motion around the sun, assuming
that the folks out there
sending to us don't know
what the Earth's doing,
but they know what
the sun's doing.
And it exploited a
very cute little way
to get rid of
interference, which
is that because the Earth's
turning-- the Earth does turn--
the Doppler shift along any line
of sight is changing with time.
And that means that
a frequency received
from an external fixed
frequency oscillator
appears to be changing
with time instead
of changing Doppler shift.
And it changes to the tune of
about-- at the hydrogen line
frequency, it's about point
0.15 hertz per second.
It's actually always going down.
From the time a source
rises until it sets,
the frequency is
always dropping,
and when it's overhead,
that's the rate
at which it's dropping.
So what I was doing is 60-second
integrations, which gave me
a resolution of 0.015 hertz.
You know how Fourier works.
But a fixed frequency
signal during that time
would chirp about 10 hertz.
So it actually would chirp
over about 600 channels,
so unless you adjust
your receiving frequency
to compensate for the
acceleration on the Earth's
surface, a signal from space
will seem to be chirping,
and everything on Earth,
all the interference
will be fixed and make a
big forest of interference.
But what do you is you
chirp your receiver.
It's in here somewhere.
Something's chirping.
Does it show some chirping?
Yeah, here.
See, we're programming
this first LO.
Also this guy.
You compensate for
that, and the only thing
that'll look like
a fixed frequency
is stuff coming from space.
So that was a cute technique.
It really worked.
We didn't see anything.
That's the example of
a great search here.
You don't see anything.
Well, anyway.
What happened after this search?
I took the stuff
I built from there
and converted it into what
I called Suitcase SETI.
This was a little
portable apparatus.
I'll show you what
it looks like.
It basically looked like this.
This is, again,
1980s technology.
Here's a dual Fourier processor.
Look at that.
It's a whole rack.
And it's got a couple of 68,000s
cranking away doing 128k FFts,
and here's a machine
actually running Unix.
In 1980, that was pretty hot
stuff, portable computer.
It was made by a
company called WICAT
that you've never heard of.
That's the World Institute
for Computer Aided Teaching.
Hm?
How do you know about WICAT?
Did you work--
AUDIENCE: The early [INAUDIBLE].
PAUL HOROWITZ: Yeah, yeah, yeah.
So they had this machine.
It only cost a few
thousand dollars,
and it had a-- it was great.
And here's a little
video cassette recorder.
We put all our data on that.
Anyway, here's the box of
the Fourier transformers.
It's a bunch of 16k
memory chips here.
There's a whole wire
wrapped on the back.
Here's your 68,000 here.
Here's a 16 by 16 multiplier.
These things cost a few
hundred dollars back then.
This is expensive stuff.
Anyway, so Suitcase SETI
went down to Arecibo,
and we looked at some
other frequencies of that.
But then done with Arecibo,
came back to Harvard,
and we discovered there's
this dish out there.
This is in Harvard,
Massachusetts on the hillside.
Or was.
You can see it's kind
of pretty out there.
And so what we did was we got
some money from the Planetary
Society, and built the
thing called Sentinel.
And we just took
this 84-foot dish
and built a bunch
of RF electronics
and made it look
like Arecibo to us.
We had to build our own local
oscillators and all that,
and here it is.
And we built a system called
Sentinel and looked again
at pretty narrow frequencies.
Again, we didn't find anything.
It has this wonderful
interference rejection.
It rejects everything.
You never find anything.
So then what do you do?
You build a bigger system.
So we decided that we
needed more bandwidth.
We really want to be
able to see not just
signals that are corrected for
our helio center for the sun,
but also for other
frames of reference
like the galactic center
or the local standard rest
or the cosmic background
standard of rest.
So we built a
system called META.
META stands for Mega Channel
Extraterrestrial Assay,
and it had 8.4 million channels.
And this was amazing for 19--
when was this-- about 1985.
It was really impressive.
There's our META processor.
It had 128 68,000ths with a pile
of memory on each one and lots
of block diagram-y
looking things.
Here's a picture of
the control room.
It's got two racks
here full of stuff,
and you can't read
that, which is good,
because it would be
embarrassing if you knew
that it said META Supercomputer:
75 million instructions
per second.
You know, the Cray-1 wasn't
much faster than that.
This was a supercomputer.
This had 7,064k DRAM chips.
I soldered them all in.
I know.
And they cost $3 apiece.
We spent $21,000 to get
60 megabytes of memory.
You can't imagine yourself in
this-- it was really like that.
Anyway, so some more pictures.
Here's a rack full of these
that had nine of these racks.
Each one of those
has the memory on it.
You can see that.
And then it produced this stuff.
This is, again, on
the WICAT screen,
and it gave you
the whole spectrum.
And then it sort of zoomed
in on the largest thing,
and then it zoomed
in some more so you
could see that at single
channel resolution here.
And if it found
something big like this,
then it put something
up on the screen,
and a colleague of
mine, Bill Press,
said, what's it going to say?
And I said, oh, it'll say
big peak, eight sigma.
And he said, no, no, no.
He said, there's going
to be journalists there.
Have it say
something impressive.
I said, like what?
Have it say, notify
operator immediately.
Possible signal of
extraterrestrial origin.
So there's Bill Press of
the Numerical Recipes fame.
So this is what you
could do back then.
It was hard work, but we did it.
We didn't find
anything there either.
Again, we had that same
interference rejection.
I want to show you just
something about the times.
So you think, oh, this
stuff seems so primitive.
You can't believe that
it was hard to do.
But let me just show you
how hard things were to do.
Anybody recognize what this is?
This is an 8k memory board.
This probably cost about $8k.
And it has 16
bitwords, so I guess
you'd call it 16 kilobytes.
And so it's got, I don't
know, about 100,000 cores.
Individual cores--
these black squares
are actually just a
mat of little itty
bitty sticky magnetic cores
with three wires going
through each one and an xy
wire and the readout thing,
and this is for a
deck computer if you
recognize that kind of thing.
And these things cost lots
of money, and this is 8k.
So the idea of a
megabyte, you know
the reason those machines
had 16-bit addresses,
nobody could afford more
than 16 bits worth of memory.
64k-- my god, you'd
have to be rich.
Do you remember these things?
No.
This is seven track.
I bet you don't remember those.
This is-- yeah.
You can see the bits on this.
You put it in
[INAUDIBLE] and you just
look at it with a magnifying
glass and see the bits.
How about this?
[LAUGHTER]
Yeah, yeah, yeah.
Does anybody know the
capacity where it's like 100k?
AUDIENCE: Yeah, it was
between 100 and 150k.
PAUL HOROWITZ:
Yeah, this one says
single-sided double density.
This might be 200k.
Eight inch floppy.
You can see where the
word floppy came from.
Floppy.
OK, wait.
I got a couple of
other toys in here.
Wait, this one I
want to-- just a sec.
Don't look.
Don't look.
I've got to give
you the quiz here.
OK, there we go.
Anybody recognize this?
AUDIENCE: Oh yeah.
It's for printing
out a punch card.
PAUL HOROWITZ: Someone
told me the other day
that there was
the analog of this
that was for print punching.
But this was for?
AUDIENCE: Printing the pattern.
PAUL HOROWITZ: OK, well, yeah.
I guess you could-- that
was a thing you could do.
This was a programming drum for
an IBM keypunch, the 026, 029.
And what you did was you
showed this to somebody,
and they'd say, oh, look.
It's got a little
set of contacts,
and it's got a cam here.
So it's some sort of mechan--
electro blah, blah, blah.
Nah.
It's got these little
prongs so that you
can stick this thing in and get
the ends in without sticking
them, and you turn this
thing a half quadriturn,
and then you go
around like that.
Oops, I did it backwards.
See?
And this thing told it to
skip the first eight columns
if you hit the Tab, because
that's where the-- you go
to column eight, right?
Unless you do a continuation.
You remember this stuff?
Remember Fortran?
6?
7?
Yeah, OK.
And then after '72 was
[INAUDIBLE], right?
Yeah, this one says dupe
one to 50, 78 to 80,
so this was for--
OK, what you say.
Why isn't this staying in?
I obviously don't know
how to use this anymore.
I grew up in an 026.
I should know.
Anyway, I got one last thing.
It's older.
You won't know this one.
Wait, I got two things.
How about this?
Yeah.
What's this whole thing?
It's an op amp.
This is the first
kind of commercial op
amp from Philbrick.
I had a couple of 12AU7s.
Cool thing.
Four transistors, if you
want to think of it that way.
Can you build an op amp
with four transistors?
Those guys are smart.
Here, how about this?
See, it turns.
It's got double cotton covered
copper wire on the inside,
and if you look
carefully, there's
a winding inside the outer one.
Somebody with very steady
hands, and it's got a shaft,
and it's got two terminals only.
There they are.
AUDIENCE: Oscillate [INAUDIBLE].
PAUL HOROWITZ: Yes.
You've got some old timers here.
This thing appeared in
the Sears Roebuck catalog
in the '20s and '30s.
If you wanted to build a
radio, you wanted to tune it,
you had to tune each RF stage.
And they didn't like
variable capacitors.
You had to get all those plates
to fit in between each other,
and it didn't make coils,
Bakelite, great stuff.
You guys pass as a group.
Individual report cards
will come out later.
Let's see.
We've been on-- oh, let's see.
What did we do?
Let me just show you some
results from this META thing.
We get a lot of
events like this.
These are chirped in
the chirped frame.
Therefore, they're not real.
And here's three
examples of things
that didn't do the right thing.
But we came up with a few events
that we couldn't get rid of.
The rejection wasn't
complete in this little paper
I wrote with Carl Sagan.
And you see here that we
found 37 candidate events that
exceeded the threshold.
Here's what they
look like on the sky.
They're sort of
all over the place.
Maybe a little bit of preference
for the galactic plane, but not
much.
I think the best thing
that came out of this
is the food chain of SETI stuff.
There's a company that decided
to name itself 37signals.
Here's their logo, and they
got it from our search.
I don't know what they do.
It has nothing to do with SETI.
Then we decided, eight
million channels.
That's not nearly enough.
We're not finding
anything interesting.
We need more channels.
So we built a thing
called beta, which
is supposed to be billion
channel extraterrestrial assay.
We got only 250 million.
That was a lot of work
in those days, again.
And the idea here was, let's
get rid of these single events
that we can't pin down.
We're going to have
a two-beam telescope,
and because the telescope is
fixed, an east and a west beam,
a source will
transit through them.
So we should see it appear
first in the east and then
in the west, and
just to make sure,
to make it more robust
against local interference,
we'll have a horizon sensitive
antenna at the top of a tower,
and that'll be the veto
that's terrestrial.
So we built this thing, and
here's our block diagram.
You don't really care
about that, do you?
Here's the control room.
You can tell something's a
little fake, because I'm just
looking at the green screen of
whatever we're running then.
It must have been Unix.
Linux?
I don't know.
Something.
So here's our rackets.
We're down to one rack now, and
we actually have lots of bytes.
And here's a whole bunch of
90 megahertz Pentium PCs.
That was state of
the art back then,
and we cobbled these
things all together.
And here's what one
rack looked like.
So it's now the billion-channel
extraterrestrial assay.
It no longer brags about
being a supercomputer.
We learned our
lesson from that one.
So that's what we
did, and this thing
was able to search
the full water hole.
That is that whole region from
hydrogen to hydroxyl radiation.
And the best we got out of this
was a few occasional things
that never repeated, and we
got sort of tired of this,
so we said, let's do optical.
Whoops.
Oh, yeah.
We were sort of proud of how
fast this thing produces data.
Two seconds of
data would fill up
a CD, which was state of the art
optical storage in those days.
And it's also the world's
biggest garbage can,
because we threw this all out,
except for the occasional stuff
that we didn't.
So that was cool.
That was cool.
I'll show you something
that's an even bigger garbage
can coming up.
So we decided to get into
the optical business,
and you'll remember that
calculation, optical works.
And we had this
ancient telescope.
Look at this thing.
Is that cool?
Isn't that-- look at this.
They don't build them
like that anymore.
And what we did was we
tacked this little box
that you see here onto
the bottom of this thing
and took half of the light
out that other people were
using for their experiments.
And they were looking at solar
type stars for various reasons,
and so we just decided we'd
take some of the signal
and look for bright flashes.
Here's a picture of the
little box we built.
It's made out of half-inch
thick aluminum walls,
because we decided
that's the easiest
way to tap directly into it.
And it weighed about 100 pounds.
There's probably a better
way to screw things together
that you don't have to make
them a half inch thick,
but we were kind of-- all right.
Here's a schematic.
You know we do do
electronics in this business.
This is sort of the
front end of this thing.
We used what are called
hybrid avalanche photo
detectors and a whole bunch
of other crazy stuff here.
And we decided in order
to make this more robust
and set up a collaboration
with Princeton,
so here's our telescope,
and at Princeton, they
had a 36-inch
telescope on campus.
And Dave Wilkinson
basically arranged
for them to build an
identical copy of our system
on a somewhat smaller
telescope and to do
simultaneous observations.
And the nice thing
about that is that when
you do simultaneous
observations,
you're rather insensitive to any
local events that could produce
a flashing light
at 250 miles apart,
300 miles apart it says here.
And better than that,
because that's about
1.6 light milliseconds apart.
If you're pointing some
direction in the sky,
you should get your flash of
light at a different time.
You know exactly when
you should get it,
and we did timing with
GPS, so we could actually
check to see not
only if anything ever
happened at the same
time, but whether it even
had the correct delay.
And the result of
this was that we got
basically no further events.
Here's some pictures
of their telescope
getting this stuff on it.
We had something like a
few hundred single events
before we started teaming
up with Princeton,
but once we did, it drove
the event rate to zero.
So here's some results.
What about all this?
If you don't find anything,
does it mean anything?
Well, it means that the sky is
not completely full of people,
of flashy things, men
in black, flashy things.
But the limits are kind of weak.
You can set limits of
the fraction of stars
that have transmitting
civilizations that happen
to be transmitting at us with
a nice bright thing at the time
we're looking.
So that's the kind
of numbers you get.
I'll show you a
better slide on this
when we got to a bigger
experiment, which
is the next one, which is
we decided we need not just
look at star by star,
but the whole sky.
And this came out
of a challenge.
I was on a committee
thinking about how
to do SETI for
the next 20 years,
and there was an optical
astronomer there,
a rather famous one, who
said, of course, optical--
you can't do all sky, because
you're using telescopes,
and they only look at one thing.
I thought that was a
really cool challenge,
so I came back and said, let's
build an all sky optical SETI.
So here's how you do it.
You get one of these things,
and you start knocking down
trees and building
and dig ditches,
and you find that there's wires
in there, and then it snows.
And you pour a foundation,
and then the foundation,
you get this kind of thing.
This is where the
telescope's going to go.
And then you start
putting a roof.
You make this
thing out of steel,
and you put a roof on
it, and there it is.
Look at that.
It's got a roof, and
it goes on the rails.
It's a rolloff observatory.
Here comes the telescope.
It was made in
Arkansas by some guys
who didn't need much money.
They gave us a 72-inch,
six foot optical primary,
a three-foot secondary, the
mount, and the drive system
and everything for $50,000.
A real bargain, so
we got this thing.
And here it is
with our telescope.
The roof rolled off.
Here's a couple of
graduate students
who were working on
this, and there you
can see this telescope
pointing up into the sky.
This is at Harvard.
And this thing is still working.
Working now.
I ran it just the other night.
Here's some pictures.
This is what it looks
like from the inside.
Here's the control room.
This time, we're
actually running Linux.
This is for real.
And Andrew, the student
in that picture,
designed a chip to do optical
coincidence and amplification
and all that, and here's
a bunch of these boards
with these chips and a whole
pile of fans inside this box
that hangs on the telescope.
Here's some fat
wire, because we're
running about 80 amps and
3 volts to this thing.
Here's the motherboard
and the daughterboard
and a detector and a pencil.
People don't use these anymore,
except hey, isn't there a thing
called Apple Pencil?
What's that thing?
Remember, if a stylus
shows that you failed,
but then there is one, but
it's not called a stylus?
You know about that?
No?
Yeah.
OK.
Whatever.
Anyway, here.
This is a real pencil.
This is-- OK.
Oh, yeah.
So I stole this slide from
my student, and you see.
Look at that.
I don't know how to do that.
Anyway, here's his chip.
Chip took him four years
to get it to work right,
and it was a lot of work.
And this thing
basically lets you
look at about a giga sample
per second of data coming
in on a big panel of stuff.
Here's us building these things
and bringing out the door
and over to the
telescope, and here we
are inaugurating
the observatory.
And here's first night.
First light, first night.
So this guy went from
senior at Harvard to Google.
You guys swallowed him whole.
This guy went to Apple.
And this guy went to Harvard.
This guy by way of the
South Pole for a year
went to Harvey Mudd College.
So there's life after SETI,
although it may not be SETI.
And here we are basically
getting all this stuff working.
It's a really nice interface.
You have these little
things you click on
and a whole panel opens.
It shows you what the
observatory is doing,
it shows you what the power
is doing, has a few web cams,
and it shows you pulsed-like
optical events down here.
Let's see, what's
coming up here?
Oh, it says "Show
time-lapse skycam movie."
All right.
So this is what
the sky looks like,
just out in the countryside
here at Harvard.
You don't see this
from Cambridge.
People who live in cities don't
know that there are stars.
And those little flashes, those
are airplanes going through.
These are 10-second exposures,
taken every few minutes.
So you just get little
flashes of that.
Probably an occasional
satellite in there.
You may recognize
a constellation,
and then you'll recognize
moonrise, because it completely
clobbers the sky here.
I think that's what's happening
there-- something very bright.
That's not the moon,
that's light reflecting off
the tree that's over here.
Anyway, here comes
the moment-- OK, wham.
Wow, OK, and now I
think in one here,
you see the roof open
in one of these things.
Let's see, look at
that-- that was a roof.
Whoa, look at that, OK, anyway,
that's kind of cool, huh?
All right, whoa, there
are some clouds--
we get that, too, here.
Look at that-- is that great?
Show you the kind of events
we see with this thing.
So we're looking for
short pulses of the kind
that the calculations
show that you
can project across
these distances,
and outshine your star.
And here's the kind of
thing we occasionally get,
this is an interesting event.
And here's what it looks
like on these detectors.
I didn't describe this,
and I won't really,
except to say that we have
these detectors that are eight
by eight arrays of
photomultiplier tube, photo
cathodes.
And they're arrayed
with a beam splitter,
so they form a coincident pair.
And we insist on
the coincidence--
that as something
hits the right panel,
has to hit in the corresponding
place on the left panel.
And here's such an event
that occurred back in 2007,
and tickled these two detectors.
And the red and blue
tracers here show the right
and left signals coming
out of these detectors.
So this is the kind of thing
that we've been looking for.
And here's the
kind of sensitivity
it sets for fraction of
stars with transmitting
civilizations.
And you can see, it's
really quite a bit better
than-- oh, here's one we
covered more of the skky--
than when we had the targeted
search that I showed you
earlier, with that
ancient-looking telescope.
And the reason is we're just
covering a lot more sky.
We're covering it for less time.
So it's less sensitive
to transmitters
that don't repeat very
often, because we only
spend about one minute on
any given place in the sky.
And here's some
sort of a little bit
of interpretation about
the context in which that
makes sense.
Now I'm going to accelerate
a little bit here,
because there's some
cool stuff coming up.
The last thing we did
with this experiment
is this student, Curtis,
who wound up now at Amazon--
I'm sorry, he wound up at Apple.
Those "A" companies.
And this is the thing
he built-- he came up
with a really clever
idea, which is this--
if you take a fancy FPGA,
one of these Xilinx parts,
they have a whole
bunch of inputs which
are meant for digital
signals, they're
LVDS differential pairs.
But they're very
good comparitors,
so you can trick it
into being a flash
analog to digital converter,
even though it doesn't
know that's what you're doing.
So you tie eight of these
with a common signal,
and put in a
progression of biases,
and you've got yourself an ADC.
And you can run these things
at 1 and 1/2 giga samples
per second.
And you can put 32 of
these into one chip--
so he's got two pairs for the
left and right matching pixels,
and then he's got 16 of those
things in one of these chips.
And it's got all
kinds of other junk
in here-- you know, these
chips are full of stuff.
And in fact, here's
this whole little thing
with this front end.
It's also got-- heck you can
drop a MicroBlaze into there,
and you've got an ethernet
MAC in this thing.
And you name it, it's got it.
So each one of these things
is a node on our network.
And he put these
things together.
And the damn thing
works-- here's
an example of a double pulse
feeding into this thing.
Notice we use nonlinear
levels, because you
can do that if you set
your own drip points.
And the jiggly red
line is ground truth,
with a gigahertz scope.
And the black line is what this
crazy kluged up ADC measures
for a double pulse.
So it works great.
Thing really works.
So we've had this thing looking
at the sky, and we see events
like this.
This is a cool
event, because look
at this-- it's matching
left and right,
and it's a short pulse,
even when expanded here.
Here's something
that-- something
a little fishy about it, hid
an awful lot of pixels here.
And look how long the
thing took to spread
like that-- it's really
greatly expanded in time.
It's actually taking
a significant fraction
of a microsecond.
Guess what that is?
It's an airplane.
Because our skycam
caught it in the act.
Here it is, flying
toward our thing,
and then it went through, and
we saw this gigantic thing.
So we see some of
those things from time.
Now it says, "show--" OK.
Here's another kind of event.
This is a cosmic ray, which
hits a whole bunch of pixels
like that, but also
is short-pulse,
and we're sensitive
to these things.
I'm going to skip the
movie and just show you
this is the amount of the
sky that we've covered now.
If it's brighter
red, like that, it
means we've covered
it multiple times.
So we've covered basically
the whole sky multiple times
with this search.
Here's an example
of another event.
Here is, again, the sky, and
here's these little pulses.
And we see these things
from time to time.
They've never repeated.
The telescope automatically
goes back to that declination,
and tries to do it
again the next night.
So this is some
of our non-events.
Now, here's an example
of a real event.
We have another camera at
the observatory that looks
from the Central building.
And we get these
kind of creatures--
not exactly extraterrestrial,
some degree of intelligence,
though.
What we did is we decided in
order to eliminate isolated
events, we need two sites.
So here's Curtis at the Mount
Hopkins Observatory in Arizona,
with this big telescope
used for cosmic rays.
Cosmic rays generate
light flashes
when they come through
the atmosphere.
And what he did-- there is what
its detector looks like-- he
rigged it up so we were
running both experiments,
since ours runs remotely.
Here's the Massachusetts, our
observatory, here's Arizona,
and here's Curtis looking
for simultaneous events.
And that drives the data rate
all the way down to zero.
Well, here's where we are
now with this experiment.
This is actually just
a few nights ago,
this is January
6th, and we're still
running this thing
on every clear night.
People always want to know what
you found, it's sort of sad.
We find occasional events.
This is Wow Signal from
Ohio State in the '60s.
Here's this kind of thing,
with a notifier operator
immediately, occasional events.
Here's the optical SETI, and
we get these occasional events.
What we need, really,
is more observatories,
greater sensitivity,
immediate follow-up.
So let me just tell you in the
last one minute and 50 seconds
what's happening.
There is this new
initiative called
the Breakthrough
Listen-- it's funded
by a Russian billionaire.
He pledged $100 million.
And what they've done
is bought telescope time
for at least the first few
years, on three of the best
telescopes.
This is the Green
Bank steerable,
100-meter dish, biggest dish
in the world, steerable dish.
Very good system
temperature, it's
got an offset Gregorian feed.
It's a really classy
piece of stuff.
This is the Parkes telescope
in Australia, which
gets you the southern sky.
And this is the
Automated Planet Finder
at Lick, which has a very high
resolution spectrometer used
for planet finding, but it's
also a terrific telescope
if you want to look
for little laser lines
in the middle of the thicket
of lines that come from a star.
So these have all been
pressed into service.
Here's some of the
technology-- let's see,
I want to get to the target--
here's the technology.
The guys at Berkeley who have
designed some really fast
stuff, have these
FPGA-based boards
that can do a
26-gigasample sampling,
they generate 320 gigabits
per second of data.
They're doing 10
giga-channel spectroscopy
on a 10-gigahertz bandwidth.
Really, incredibly nice stuff.
And here's the stuff they're
going to look at, some targets.
Produce a lot of data.
Look where it winds
up-- in your cloud.
You are here.
Here's one of
their boards that's
a 26-gigasample
per second thing.
And here's one of
their block diagrams.
These guys are
very good at this,
and this Casper
project has built
beautiful, FPGA-based
hardware that's
used for all kinds of things,
not just astronomy-- radio
astronomy-- it's used for
protein folding stuff,
and MRI, and all
that kind of stuff.
Future-- couple things going up.
There's some arrays going up--
four seconds, three seconds.
This is in China, this is
going to be the world's biggest
telescope-- 500 meters.
I think it's now finished.
Here's an array
that's coming up.
And here's a piece of the SKA--
the square-kilometer array
in South Africa.
It's called MeerKAT-- which
is an acronym for something,
but that's also that
funny looking animal.
Kind of looks like this, if
you've seen those things.
Interesting question--
what do you do with arrays?
Arrays are very
good because they
discriminate against things
in different directions.
They also can produce multiple
beams at the same time,
with full sensitivity.
So they're nice things.
This is actually my last
slide-- zero seconds.
Let me just show you-- this as
an interesting thing in which
you can put a bunch
of antennas up,
do you make them big or small?
If you make them small, and
you want a lot of aperture,
you need more of them.
So you spend more.
The smaller dish is cheaper,
but you need more of them,
and you have to
connect them together.
This is sort of showing you
the partitioning of costs
in euros of telescopes as a
function of dish diameter.
So a few big ones, a
lot of little ones.
Building a lot of little ones
is cheaper on the dishes,
but you got to need
more wiring, and you
need a lot more
electronics in the car
later, and in computing.
This figure of merit
here is a figure of merit
that has to do with
degrees of sky covered,
times collecting area,
divided by system temperature.
It's sort of the right figure
of merit for this kind of thing.
And what you see is you actually
get a much better figure
of merit with small dishes.
And the reason is that each
dish, because it's small,
covers a lot of the sky.
And anywhere within
that sky, you
can form beams using
all of the dishes.
So you cover a large
piece of the sky,
with as many as N or N
squared beams, simultaneously
with a lot of small dishes.
Whereas with the big
dishes, you can only
look at a small
piece of the sky.
So it actually pays to do that.
Right now it costs
kind of a lot.
On the other hand,
this is the stuff
that gets cheaper-- the
computing and the correlating.
And so really what
you should do is
you should bias towards the
left side of this bar graph,
and build a lot of small dishes.
And that's where people
are going with this.
Anyway, I would say,
in spite of all these
rather stupendous
efforts, we're still
in that last tenth of a
millisecond of Earth's attempt
to do this right.
We're still the small
fisherman in this business.
And for it to succeed
at this point,
we have to be
extraordinarily lucky.
That's my story, thank you.
[APPLAUSE]
Did I leave you questionless?
Impossible.
AUDIENCE: So I'm
wondering-- I mean,
this sort of assumes
that somebody out
there has identified us as
a potentially interesting
candidate, and they're
sending a pulse directed at us
to see if we're listening.
But what would we look
like to a civilization
1,000 light years away?
Like we're sending out
a bunch of RF stuff.
Is it theoretically
possible for somebody
to look at what a civilization
that just started emitting
RF signals would look like?
PAUL HOROWITZ:
Yeah, good question.
So the question is,
could we detect ourselves
with these kind of experiments?
The answer is no, maybe from
the nearest star, but unlikely.
Because the radio
signals we're creating
our not intended to
establish communication.
They're either piped through
pipes, or they're radars,
and they're just briefly
pointed in any given direction.
If they're radars,
they're broadband.
If they're FM broadcasts,
they're aimed horizontally.
We're doing it all wrong.
But we're not looking--
maybe a sufficiently advanced
civilization could
do huge antennas,
and find us in our
primitive stage.
We're looking for
intentional beacons.
And the idea of those
first couple slides
is, if we wanted to make
an intentional beacon,
even with our technology,
we could do it now.
But we're certainly
looking for something
optimized in that way.
And once it's
optimized in that way,
it becomes detectable
even with our technology.
But we could not detect
twin if they don't
go to the effort of doing that.
Some of these targets
in that breakthrough
are interested in when
two planets are aligned
around some other
star, might you
pick up, by chance, a
communication that's
between their two planets?
You know, if you look at
the piece of phase space
that occupies, the answer
is, what are you smoking?
It's just too improbable.
AUDIENCE: So are there any
efforts, or discussion,
about doing things like picking
star systems with exoplanets,
and--
PAUL HOROWITZ: Yeah,
so somewhere in here,
I had the targets-- I zipped
through at warp speed-- here's
one thing to look at.
Nearby stars, why not?
Nice, strong signal.
Some night stars--
yeah, because we
know you can live
around a sun-like star,
at least for awhile.
Known exoplanet-- sure, but
that's a pretty small fraction.
Kepler only picks up planets
that are in our plane,
so it misses a lot of them.
Here's this alignment thing.
I think this is nut case SETI,
but there it is on the list.
And a few other ideas.
And the galactic plane, because
there's more demography there.
And I think, also, not on this
list are other nearby galaxies.
You point your
beam at Andromeda,
and you pick up 10 of the
11th stars in one shot.
And you might say,
oh, but that's
2 million light years away.
That's a weak signal.
Well, think again.
If Andromeda is trying
to illuminate our galaxy,
they'll make a beam that
just covers our galaxy.
Arrives with the same
strength as a signal
of someone within our
galaxy, also trying
to illuminate the whole galaxy.
So it really doesn't
matter how far away
you are, if you tailor your
beam to match the target size.
So I think that's a perfectly
reasonable thing to do.
Did that answer the question?
AUDIENCE: Sure, thanks.
PAUL HOROWITZ: Over there.
AUDIENCE: Possibly,
sort of related-- I
totally buy the concept
that we are really
early on the technology side,
in a cosmic scale of time.
But that's still going to be
true in 50 years, that's still
going to be true in 500 years.
What if everybody
feels that way?
What if they're
all just listening,
waiting for the other guy to
do the hard part of sending
signals?
PAUL HOROWITZ: Yeah, well,
I hate that question.
[LAUGHTER]
So I guess I'd say, ask
me again in 500 years.
You know, there comes
a time in which you
think you've done a thorough
scouring of receiving,
given the distances and
what you know about planets.
You know, we're learning an
awful lot about these planets,
and I think we're going to
have much smarter searches in
awhile.
You'll always be able to make
an argument like that-- maybe,
ultimately, we'll just decide
we're the only ones there.
I find that a
completely implausible--
AUDIENCE: Well, I'm
wondering if there's
any sense of a technology
that you might expect
to hit at some
point, where you go,
oh, wow, we can
send signals now.
PAUL HOROWITZ: Some people
argue we should be symmetric
right now.
I mean, that we only earn the
right to listen if we transmit.
And I'd say, we'd be so
embarrassed with what we sent,
if we do it now, because
we're so primitive.
And the other thing-- so let
me just toss this idea out--
when we first make
contact, it's not
going to be the first
time it's ever happened.
That would be astonishing--
it's happened lots of times.
And in fact, if there's
sufficiently high density
of such civilizations, then
they sort of a network,
they have a galactic internet.
They've fashioned the
ideal acquisition signal.
They've done this
a million times--
it's like the movie, "Contact,"
they know what they're doing.
And we just go shouting in
there with a bunch of garbage
and noise like
mumblings, and tell them
about the wars we're
fighting, and you know,
is Donald Trump going
to be the president.
And they're just going
to say, oh, there's
no intelligent life on Earth.
[LAUGHTER]
So no, I think at this point,
we definitely don't transmit.
Although there are people
who say, that's wrong.
There's other people who
say we shouldn't transmit,
because they're going
to come and eat us.
I think that's kind
of extreme, because I
think if they can
actually come here,
then they've grown
up enough to know
not to go killing stuff off.
And you can find
argument against this.
But I guess I can say, in
the next few decades, I'm OK.
And after that, I don't
have to worry about it,
because I'm already
73 years old,
and the average lifespan--
I'm pushing up against that.
It's your problem.
[LAUGHTER]
Are there any other--
there's a question.
AUDIENCE: So if there are
really advanced civilizations,
like galactic scale
civilizations,
do you think that looking
for pulses of light
from these things
is the only way
to detect such civilization?
Or might there be other
things we would look for?
PAUL HOROWITZ: Yeah, you have
to think about what we know now.
I mean, we know that
electromagnetic communication
is cool, and can do the job.
If the galaxy is
really colonized,
you might imagine that they
might have robotic probes that
go in orbit around
likely stars, and where
they'll have planets, and maybe
do some local back and forth.
Wouldn't that be a
smart thing to do?
People who have looked for stuff
like that haven't found it.
I think if we discover new
modalities of communication,
they're fair game.
But from what we
know now, we don't
like particles that have
mass, they go too slow,
and take too much energy.
We don't like charged
particles, because they
bend in magnetic fields,
and they scatter.
We don't like neutrinos, and
gravity waves, gravitons,
because they're too hard
to make and detect--
and this is certainly
decent physics.
Whereas, spin one mass
zero, electromagnetic waves,
just seem to have all the
right characteristics there.
It works at extremely
sensitive level,
and they go at the
speed of light-- that's
as fast as you get to go.
But we're certainly
open to other things.
And if there is a
galactic network,
they'll eventually notice us.
Maybe to join the club, we
need to detect their signal.
Maybe they don't
like getting in touch
with too primitive
civilizations,
and we haven't earned
our entrance ticket yet.
But this is all
crazy speculation.
You can speculate about
it, but if you actually
want to make something happen,
you go look for the signals,
and do it the best way you can.
AUDIENCE: Hi, so how well can
you plausibly aim a laser?
Right now, if we wanted to,
and NASA would shoot it up
into space, or whatever we
were going to do with it,
could we pick a star
at 70 light years,
and say there is an
earth orbit around that,
and we want to bathe that
orbit in light-- we could
we hit that point in space?
PAUL HOROWITZ: Yeah, actually it
was part of that nerd box that
had a lot of stuff in there.
Talked about the size--
you would actually
would have to broaden it.
The calculation I did was
for a 1-au target diameter
at-- I forget what
the distance was, I
think it was 1,000 light years.
And that's diffraction limited
for the 10-meter telescope.
If you want to spread
it out, because you
think the planets might be
further out, you can do that,
and it reduces the flux
by the square of the--
AUDIENCE: [INAUDIBLE].
PAUL HOROWITZ: Yeah, well, not
going through the atmosphere,
you can't.
And so this would have
to be an orbital thing.
And the question is, can
you do fractional arcsecond?
You can do diffraction limited
with a 10-meter telescope.
And we're going to
get better at that.
I mean, it's really easy
in space-- everything
is very quiet.
There's no weather,
there's no wind,
you don't get snow advisories.
Or the backside of the
moon might be a good place
to put a telescopes, you
know it's quiet there, too,
and it shields you from
all the interference
from Earth, if you want
to do that kind of thing.
Another one?
Yes.
AUDIENCE: I've got a really
down to earth question.
In the edition of your
book I have-- it's probably
the second, if the third
one is the new one-- there's
this wonderful
looking technology
where you put these
sticky wires on a board,
and you can prototype your
thing without a circuit mill,
or without any chemicals.
And that disappeared.
Do you know why?
PAUL HOROWITZ: Gee, I remember--
I had forgotten completely
about that.
AUDIENCE: A
Kollmorgen multi-wire.
PAUL HOROWITZ: Yeah,
so what it did was,
it was basically an alternative
to the PCBs, or wire wrap.
And what it did was it just spit
out a sticky, inflated wire,
they could cross
over each other.
I remember, I got a board for
a nova that was a video board,
and it was made by
a local company,
and they did it with the system.
And they went around, and
when it got to the pad
that it was supposed
to go to-- everything
was through hole in those
days, it actually just made
a welded spot-- and
so the wires could
cross with reckless abandon.
You didn't need multiple
layers or anything else.
Why did it disappear?
It's probably a crappy way
to make more than one board
of anything, and etch boards
are much more effective--
particularly a multi-layer.
I don't know-- wire-wrap
kind of disappeared.
AUDIENCE: The problem was the
pulling from the [INAUDIBLE]
if you flexed them.
PAUL HOROWITZ: Is that right?
AUDIENCE: I heard
that somewhere.
PAUL HOROWITZ: So
don't flex them.
AUDIENCE: You had to have
board stiffeners on it.
PAUL HOROWITZ: I mean,
who would ever think
that surface mount could work?
You have these
little ceramic chips,
and you're soldering
both ends down.
And now it's on a board, and
you go like that, why don't they
just all pop off?
You know when you shove
the heat sink down,
when you stick the CPU
on your motherboard,
and then you push
that thing down,
and it's supposed to snap in,
and the board goes like that?
And you know it's all
full of these little--
why don't they all just
[MAKING EXPLOSION SOUND]
like that, and fly into the air?
They don't, but
it shouldn't work.
[LAUGHTER]
Jim Williams, at
Linear Technology,
used to say all the things
that shouldn't work.
He says, disc brakes can't work.
He said, ball point pen,
I would've fired that guy.
So you can make
things work, you just
have to work hard
to make them work.
AUDIENCE: A theme that
recurred throughout the course
or your talk was the advances
in technology over time.
And corresponding
with that, there's
also a decrease in the cost
for any given unit of, say,
computing power over time.
And something I thought
was really cool that
happened a year or so ago,
was the IS EE3 reboot project,
where a bunch of
guys in Mountain View
took over McDonald's, and
took over a NASA probe,
and tried to adjust
its orbit, and so on.
And they failed, because there
was no pressure [INAUDIBLE]
in the fuel tank for the thing--
but this ideas of reclaiming
old technology at
the individual level.
And now I'm kind of wondering
what your thoughts are on,
at the individual
level, somebody who's
interested in the stuff,
going into their basement
and building a device with
the same computational power--
the meta array that you guys
built in the '70s and '80s--
and trying to do the same
experiments you guys were
doing.
Is there any merit to that?
Does that add scientific value?
PAUL HOROWITZ:
Yeah, interesting.
So this big supernova
that was just
discovered this
week, or last week,
was found with a bunch of
automated small telescopes,
that's run with a
small consortium.
And there's nothing there
that's beyond amateur status,
in particular-- by amateur,
I don't mean not smart,
I mean doing it for the love.
That's where the
word comes from.
You can do an awful
lot of computation,
and as that graph
showed about how
you build your big
telescopes, the computations
is where it's at if you have
a bunch of small telescopes.
And you can do amazing things.
So I think that amateur
astronomers are definitely
in play, particularly when
the phase space that you have
to explore is the whole sky,
and most of these projects
are looking through soda
straws at particular places.
I think there's
definite chances.
In fact, you might say, why
aren't these signals strong?
Given that even now,
we could make signals
that are quite detectable.
We can make a CW laser
at 100 megawatts,
diffraction limited, is
much brighter than a star.
It would be a
spectral [INAUDIBLE]--
a star would turn
suddenly green or blue.
Why don't we see those things?
Well, probably
because they don't
need to go that much overboard
to bring a new civilization in.
But if they're interested in
bringing a new civilization
in before we blow ourselves
up, or elect a really
untenable president,
then it may pay for them
to send pretty strong signals.
In which case, I think
one-meter class telescopes,
or robotic telescopes
on which you
can drive some stream of data
from it, or these data streams
can be split and provided
to multiple users,
I think it's definitely
a thing to do.
And with the availability
of cheap GPUs, and FPGAs,
and boards that do all
this stuff-- you know,
the Adafruit and SparkFunds
of the world, really
make this easy stuff.
So I say go for it,
and report back.
AUDIENCE: I remember there was
a SETI at Home program, that
would take spare compute cycles
and go off and look at signals.
Is that still ongoing?
PAUL HOROWITZ: Yeah, in fact
SETI at Home, so SETI at HOME
is run out of Berkeley
by the same folks
who bring you this Casper
project and the FPGAs
that I showed you.
And SETI at home takes data
from the Arecibo telescope.
The Arecibo telescope
is this dish
with the thing sticking down.
And because they want to keep
pointing at the same thing,
the feed has to move, so
the thing swivels around
and goes in and out.
And other feed isn't
doing anything--
it's doing curlicues.
So SETI at Home took data
from the curlicue feed
that nobody wanted, and
basically parsed it up
and sent it all the
way out to everybody
to run on their things.
And there's wonderful maps of
the sky, as curlicued with SETI
at Home.
That's alive and well.
And in fact, this new
project Breakthrough
is going to make
public all of its data
in some form that's actually
usable-- not the full 320
gigabits per second, but some
cleaned up version of that.
Part of their mandate is
not to sit on this data.
The same way Kepler
data is made public,
and the public Genome Project
published their stuff, too.
So if what you want
to do is software
on someone else's data, you'll
have more than you can handle.
And I don't know if
that's going to be turned
into-- I see flashing lights.
That could be a laser pulse
from alien intelligence,
or it could be a sign that
I'm supposed to stop talking.
I think the latter.
Thank you.
[APPLAUSE]
