Lecture 16 Flashcards
In 1950 Enrico Fermi shouted “Where are they?”. Why did he do that?
because he estimated the time it would take to colonize the entire milky way, and it is much shorter than the lifetime of the sun
Problem with interstellar travel?
Enormous distances to even the nearest stars are the biggest challenge for interstellar travel!
What did the Voyager Gold Disk contain?
Images and sounds (speech and music) from Earth.
Fermi Paradox
The apparent size and age of the universe suggest that many technologically advanced extraterrestrial civilizations ought to exist. However, this hypothesis seems inconsistent with the lack of observational evidence to support it.
An advanced civilization should be able to launch much faster, possibly self-replicating probes => they should reach EVERY interesting star system in our galaxy in a few billion years. As there are stars that are billion years older than the Sun, they should already be here!
The many possible solutions for the Fermi Paradox
*They are here (UFOs, Ancient Astronauts, etc) but compelling evidence is non-existent.
*Humans are the descendents of ancient alien civilizations. Problem: where are the original aliens and all the other alien civilizations? Evidence for normal evolution
*Zoo Hypothesis (Prime directive from Star Trek)
*They exist but have not yet communicated, they have not had time to reach us, building self-replicating Bracewell-von Neumann probes is harder (slower) than we think
*The Galaxy is filled with aggressive civilizations looking for signals. ET is keeping low. Problem: where are the berserkers coming after us? Energy requirements for interstellar invasion are enormous
*They have no desire to communicate (but with millions of possible civilizations, someone would have some curiosity.)
*They develop different mathematics (but then where are their incomprehensible signals?)
*The Great Filter (civilizations only have a limited, short lifetime, they are all dead.)
*We are the first civilization in the Galaxy (but there are many stars older than the Sun)
*Habitable planets are rare (unlikely after Kepler)
*Life is rare (origin of life unclear)
*Emergence of complex life is very rare (Rare Earth Hypothesis)
*Intelligent life is rare (remember the dinosaurs)
*Science & Technology is not common for intelligent life (dolphins…)
Oumuamua is the
first interstellar object
Some Oumuamua descriptions
*Non-gravitational acceleration detected
*Comet outgassing? But no tail visible?
*Piece of a dwarf planet? nitrogen ice
*Solar sail? HIGHLY CONTROVERSIAL!
Why do scientists generally regard UFO sightings not as compelling evidence that we are visited by advanced extraterrestrial and intelligent beings?
because of multiple reasons (e.g. eye witness reports are bad, they are not reproducible, etc)
What is the main argument in the Fermi paradox?
it is primarily a time scale argument: the milky way is old enough for even just one technological civilization having ample enough time to colonize the entire galaxy
In the 2nd video you saw an example of how large the difference in the level of comprehension could potentially be between different intelligent species. What example was this?
how much a squirrel would understand human deforestation activities
Which type of life is subject to the Fermi paradox?
only technological life
Approximately how soon might we expect an immediate response from a civilization
that received the signal we sent to the globular cluster M13 (21,000 light-years away) in
1974?
in 42,000 years
Traveling at their current speeds, how long would it take the Pioneer and Voyager
probes to travel the distance to the nearest stars?
at least 100,000 years
Which is the most common type of spacecraft propulsion used today?
chemical rockets
The Luyten 726-8 binary system is approximately 9 light-years away. If we send a spacecraft to visit this system traveling at 90% of the speed of light, how long will a one-way trip take as measured from the Earth?
10 years
