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Search for Extraterrestrial Life
PHY 100
How life emerged on earth
 Amino acids, “building blocks of life” form via
chemical reactions
 With help of nucleic acids, they combine to form
proteins in living things
 Sequence of chemical events that leads to
creation of nucleic acids is unknown but two
notable theories have emerged from research:
Iron-Sulfur World Theory and RNA World Theory
Theories of Early Life
 Iron-Sulfur World Theory
 Early life may have formed
on the surface of iron
sulfide minerals in volcanic
hydrothermal flow at high
pressure and high
 Developed by retrodiction
from extant biochemistry
combined with various
chemical experiments
 RNA World Hypothesis
 Theory that proposed that
a world filled with life
based on ribonucleic acid
predates the current world
we live in based on
deoxyribonucleic acid
(DNA) and protein.
 The RNA world is proposed
to have evolved into the
DNA and protein world of
Miller Urey Experiment
• Amino acids can form via natural
chemical reactions
Alternative Biochemistries For
Extraterrestrial Life
 Perhaps we are Carbon Chauvinists
 Nitrogen and Phosphorous
Make stable covalent bonds and could
be a basis for biochemistry. Has a strong argument,
however, is not plausible.
 Silicon Based Organisms
Has very similar chemical properties to Carbon
but has a lot of drawbacks. Silicon is far more abundant
than Carbon (925:1). May be plausible in different
temperatures and pressures than earth.
 Search for Extra-Terrestrial Intelligence (SETI) is the collective name
for a number of activities involving the search for extra terrestrial
 Projects use various methods to search for electromagnetic
transmissions from civilizations on distant planets
 Formerly funded by U.S. Government, mostly privately funded
Radio Experiments
 Since radio frequencies are able to penetrate
our atmosphere, radio telescopes are often used
to investigate the cosmos.
 Earth emits considerable radio radiation as a
result of TV and radio. These radiations are easy
to recognize due to their short wavelengths and
repetitive nature.
 Therefore, one way of discovering extraterrestrial
civilizations is to detect non-natural radio
emissions from outside our solar system
SETI Radio Experiments
 1960 Frank Drake
performs first modern SETI
experiment, Project Ozma
 Ohio State University SETI
Program and the Wow!
Signal- 1977
at U.C. Berkeley
Further SETI Projects
 Suitcase SETI and Sentinel
 Project META
(Megachannel Extraterrestrial Assay)
 Project BETA
 Project Phoenix
 Allen Telescope Array (ATA)
The 21 cm Line
 The 21 cm Hydrogen line is considered a
favorable frequency to search for signals from
another civilization, as part of the SETI program.
 Pyotr Makovetsky proposed to use for SETI a
frequency which is equal to pi times 1420.4 MHz.
 Since pi is a Transcendental number, such
frequency couldn't possibly be produced in a
natural way as a harmonic, and would clearly
signify its artificial origin. Such signal would not be
jammed by HI line itself, or any of its harmonics.
 Volunteer distributed computing project
launched by U.C. Berkeley in 1999
 Allows any individual to become involved in SETI
 Has over 180,000 active participants which gives
this program a computational power greater
than that of the fifth most powerful computer in
the world
Criticism of SETI
 The search for extra terrestrial intelligence is not
an assertion that extra terrestrial intelligence
exists in the first place
 Other objections to SETI’s projects include
questioning the amount of energy necessary to
execute the projects and why advanced
civilizations would use radio in the first place
 Regardless of criticism, SETI does collect useful
scientific information
The Drake Equation
 An equation used to guess the potential number
of extraterrestrial civilizations in our galaxy
Fermi Paradox
 Contradiction between the high probability that
extraterrestrial civilizations exist and the lack of
contact with these civilizations
 Extraterrestrial civilizations’ reasons for spreading
beyond planet of origin
 Exploration
 Colonization
 Survival
Solutions to Fermi’s Paradox
 It is difficult for life to start and evolve to a point
that is intellectually and technologically
advanced and we are the only one in the
 Advanced civilizations destroy themselves on
short timescales so they may not have had time
to reach us
 Research on the existence of extraterrestrial life
still remains inconclusive
 SETI efforts continue to search spectrum for
signals from outside sources but the increasing
belief is that civilizations, if they did exist, did not
have enough time to reach us
For your entertainment…