Transcript Slide 1

E.T.
The Search for
ExtraTerrestrial Life
LOJ Feb 2004
Syllabus Extract: How can
we search for ET?
• We may be able to observe living
organisms (e.g. microorganisms), or their
fosilised remains, directly, for example, by
actually going to Mars or Europa (a
satellite of Jupiter), by using robots to
send back pictures or by using robots to
collect samples to bring back to Earth;
LOJ Feb 2004
Syllabus Extract: How can
we search for ET?
• We may be able to detect living organisms by
the chemical changes they produce in a closed
system (e.g. inside a closed container or in the
atmosphere of their planet).
• Because of living organisms, the atmosphere of
the Earth is very different from what it would be
purely from chemical and geological processes;
for example, there is much more oxygen;
LOJ Feb 2004
Syllabus Extract: How can
we search for ET?
• We may be able to receive signals from
other species with technologies that are at
least as advanced as our own.
• The search for extra-terrestrial intelligence
(SETI), using radio telescopes to try to find
meaningful signals in a narrow band of
wavelengths has gone on for more than
forty years, so far without success.
LOJ Feb 2004
Syllabus Extract: How can
we search for ET?
• Candidates should be able, when provided
with appropriate information, to evaluate:
– the methods scientists use to discover
whether there is life elsewhere in the
Universe;
– evidence that such life exists.
LOJ Feb 2004
SETI
• SETI is an acronym for
Search for ExtraTerrestrial Intelligence.
LOJ Feb 2004
What is SETI?
• It is an effort to detect evidence of
technological civilizations that may exist
elsewhere in the universe, particularly in our
galaxy.
• There are potentially billions of locations
outside our solar system that may host life.
• With our current technology, we have the
ability to discover evidence of cosmic
habitation where life has evolved and
developed to a technological level at least as
advanced as our own.
LOJ Feb 2004
What is Project Phoenix?
• Project Phoenix, run by the SETI Institute, is the
most ambitious search for extraterrestrial
intelligence ever undertaken.
• Since 1995, it has been scrutinizing the vicinities
of nearby, Sun-like stars, hoping to pick up a
signal that would tell us that we're not alone.
• Project Phoenix is a direct descendent of the
NASA Targeted Search that was ended by
congressional action in 1993.
LOJ Feb 2004
How is Phoenix different
from other experiments?
• It is the only targeted search.
• In other words, rather than sweeping large
swaths across the sky, Phoenix zeroes in
on nearby stars. By restricting its attention
to carefully selected targets, the 28 million
channel Phoenix receiver can accumulate
radio energy for minutes (rather than
seconds), providing unequaled sensitivity
to weak signals.
LOJ Feb 2004
How is Phoenix different
from other experiments?
• Project Phoenix also checks out all signal
candidates within 20 minutes of their
discovery, using a second radio telescope
in Jodrell Bank, England. This is important,
because the hot gas between the stars
can cause signals from distant star
systems to fade up and down over a few
hours' time.
LOJ Feb 2004
How do we know if the
signal is from ET?
• Virtually all radio SETI
experiments have looked for
what are called "narrowband signals."
• These are radio emissions that
are at one spot on the radio
dial. Imagine tuning your car
radio late at night… There's
static everywhere on the band,
but suddenly you hear a
squeal - a signal at a particular
frequency - and you know
you've found a station.
LOJ Feb 2004
How do we know if the
signal is from ET?
• Narrow-band signals, say those
that are only a few Hertz or less
wide, are the mark of a purposely
built transmitter. Natural cosmic
noisemakers, such as pulsars,
quasars, and the turbulent, thin
interstellar gas of our own Milky
Way, do not make radio signals
that are this narrow. The static
from these objects is spread all
across the dial.
LOJ Feb 2004
How do we know if the
signal is from ET?
• In terrestrial radio practice, narrow-band
signals are often called "carriers." They
pack a lot of energy into a small amount of
spectral space, and consequently are the
easiest type of signal to find for any given
power level. If E.T. is a decent (or at least
competent) engineer, he'll use narrow-band
signals as beacons to get our attention.
LOJ Feb 2004
What happens if we find
something?
• The receivers used for SETI are designed to find
constant or slowly pulsed carrier signals… something
like a flute tone against the noise of a waterfall.
• But any rapid variation in the signal - known as
modulation, or more colloquially as the "message" would be smeared out and lost.
• In order to understand anything that E.T. might be
saying to us, we'll have to build far larger instruments to
look for the modulation of his signal. It's more than likely
that, once a detection is made, the money will become
available to build this far larger instrument.
LOJ Feb 2004
What happens if we find
something?
• Until we can measure the modulation, all we'll know is
that there is intelligence out there.
• We can pinpoint the spot on the sky where the signal is
coming from, and slow changes in its frequency will tell
us something about the rotation and orbital motion of
E.T.'s home planet.
• Even with this limited information, the detection of alien
intelligence will be an enormously big story.
• We'll know we're not alone, and we're not the smartest
things in the universe. And of course there will be a loud
clamor to build the big dishes that would allow
eavesdropping on E.T.'s message.
LOJ Feb 2004
Then what?
•
•
•
•
Suppose we get the message?
Will we understand it?
No one knows, of course.
It's conceivable that an advanced and
altruistic civilization will send us simple
pictures and other information.
LOJ Feb 2004
Why do we think that life
is "out there"?
• Over the last half-century, scientists have developed a theory of
cosmic evolution that predicts that life is a natural phenomenon
likely to develop on planets with suitable environmental conditions.
• Scientific evidence shows that life arose on Earth relatively quickly,
suggesting that life will occur on similar planets orbiting sun-like
stars.
• With the recent discoveries of extrasolar planetary systems, and the
suggestive evidence that life may once have existed on Mars, this
scenario appears even more likely.
• Additionally, one should keep in mind that we are only one planet
around a very ordinary star. There are roughly 400 billion other stars
in our Galaxy, and nearly 100 billion other galaxies. It would be
extraordinary if we were the only thinking beings in all these
enormous realms.
LOJ Feb 2004
What is the Drake
Equation?
• The Drake Equation was originally developed as an agenda for a
1961 scientific meeting.
• It provides a way of estimating the number of intelligent civilizations
existing in our galaxy that might be broadcasting signals.
• Among the factors considered are the number of sun-like stars in
our galaxy, the fraction of habitable planets supporting
communicating civilizations, etc.
• When these various factors are multiplied together one can compute
N, the number of transmitting civilizations. Unfortunately, many of
the factors are poorly known, so estimates of N range from one (we
are alone in the Galaxy) to thousands or even millions.
• Try it out yourself
http://www.classbrain.com/artmovies/publish/article_50.shtml
LOJ Feb 2004
Why do SETI at all?
• There are many reasons, including such practical
considerations as the technological spinoff. The signal
processing techniques used for Project Phoenix have
already been applied to the detection of breast cancer.
• But SETI research is first and foremost pursued because
it is designed to answer questions that previous
generations could only ask.
• How do we fit into the biological scheme of the cosmos?
• Is intelligent life a rare event or a common one in the
universe?
• Can technological civilizations last for long periods of
time, or do they inevitably self-destruct or die out for
some other reason?
LOJ Feb 2004
Why do SETI at all?
• If we could understand any signal that we detect,
there’s always the possibility that we could be
presented with enormously valuable knowledge.
• It is likely that any civilization we discover will be
far more advanced than ours, and might help us
to join a galactic network of intelligent beings.
• But even if we detect a signal without being able
to understand it, that would still tell us that we
are not unique in the universe.
• The effect on society might be as profound and
long lasting as when Copernicus displaced the
Earth from the center of our universe.
LOJ Feb 2004
What can you be asked?
• To recall that life as we know it requires
sunlight, carbon and water (at
temperatures that allow it to be liquid).
• To recall what SETI stands for and how
and why it uses radio signals.
• To be able to make sensible comments on
data provided on the methods used to
detect and evidence for life outside our
Earth.
LOJ Feb 2004