E
--> ' as v --> c so that nothing
with mass moves faster than the speed of lightTopics covered so far
The Drake Equation:
N = Ngal* fps* n * flife* fintel* ftech* (L/LMW)
where N = the number of independently arising technical civilizations in the Milky Way Galaxy
-basically, it is a way to quantify how many ETs are out there that we can communicate/detect a signal from
|
Variable |
Meaning |
Estimate |
Uncertainty |
||
|---|---|---|---|---|---|
|
! |
|
||||
|
Ngal |
# stars in MW Galaxy |
2 x 1011 |
2 x 1011 |
Well known |
|
|
fps |
Frac. Of stars with planetary systems |
1 |
0.1 |
Limited by planet detection methods |
|
|
n |
# of planets with life favorable conditions per star |
3 |
1 |
Need continuously habitable zone; may be affected by factors such as presence of moon, Jupiter |
|
|
flife |
Faction of these planets where life arose |
1 |
10-12 |
We only have 1 data point, huge uncertainties; depends on if we can find life elsewhere in the solar system |
|
|
fintel |
Frac. of planets with life where intelligence arose |
½-1/3 |
1/1000 |
Again, only one data point; is intelligence an evolutionary advantage? |
|
|
ftech |
Frac. of planets with intel. that develops technology |
1 |
1/1000 |
One data point, and, what does intelligence depend on? Big brain, complex speech, agile hands? |
|
|
L |
Lifetime of technical civilization |
1 x 106 |
200 |
Do we destroy ourselves? Do we run out of spaces to live? Ability to survive disasters? |
|
|
LMW |
lifetime of MW |
1 x 1011 |
1 x 1011 |
Since the creation of the MW, well determined |
|
(see G&O, p. 413)
The optimistic view: N = 1 * L, so, N ~ 1 million. There are lots of technical civilizations in the universe
The pessimistic view: N ~ 1, that means we're it, the only technical civilization in the universe.
Ancient Astronauts
Communication With ET
-reasons for searching in the Radio frequency (advantages, disadvantages)
-specific campaigns to look for ET signals
-e.g. Drake; Zuckerman & Palmer; Drake & Sagan (know what they looked for and why)
-The NASA's SETI program
-what it looks for (e.g. The Parkes Project)
-problems with SETI
-current status (privately funded)
-Future Projects
-Project Cyclops
-space telescope arrays
Special Relativity
-2 postulates:
1. the laws of physics are the same for all observers who are moving at constant velocity relative to each other.
2. the speed of light, c, in free space, is a constant independent of the motion of the observer or the source
-consequences of special relativity
-time: time is personal, clocks run slower on moving objects; evidence: cosmic rays
-energy:E
--> ' as v --> c so that nothing
with mass moves faster than the speed of light
-length: bodies shorten in the direction of motion
Interstellar Rocket Travel
-rocket propulsion: know the physics behind rocket propulsion, know the kinds of reactions and fuel needed
-current rocket propulsion: chemical energy, only can go up to about 10 km/s (limitations)
-future rockets: new energy source: know types, advantages and disadvantages
-e.g. H bomb rockets, pellet stream rockets, laser propulsion, antimatter-matter fuel
-special relativistic effects in rocket travel
-rocket time vs. earth time, know the graph of elapsed time vs. time in rocket ship
-twin paradox
Population Growth
-exponential growth:
,
t = time, the solution is:
,
where alpha is the percentage growth per year
-doubling time: 70/alpha years
-currently, Ñ is 1.3%, this means that the doubling time is 54 years
-even faster growth:
,
so,
doomsday
prediction, t_inf = 2026
-population growth factors: growth-death rate, immigration-emigration rate
Terraforming and Super Civilizations
-one solution to the population problem: move into space
-difficulties involved in moving to other planets: terraforming, transporting colonists, etc.
-alternative: space colonies (advantages, disadvantage)
-current limiting factors to space colonization
-kardeshev civilization types
Evidence for a pessimistic point of view towards other intelligent life in the Universe
-curiosity drives exploration. IF there are civilizations out there, surely they would have arrived by now
Key Terms
All terms in the Drake Equation
Eccentricity
Continuously Habitable Zone
Terrestrial Planet Finder
Gaia hypothesis
Obliquity
Geometric Mean
Terraforming
Dyson sphere
Pusher Plate
Kardeshev Civilization
Review Questions
What are the uncertainties in each of the factors in the Drake equation?
See above table
What is direct planet detection? Why is it so difficult?
Observing the light from the planet itself. The star next to the planet greatly outshines the planet.
What kind of star was the first extra-solar (outside of the solar system) planet found around? By what method?
Pulsar. Detecting planet wiggle (Doppler shift of central star)
What is the most successful planet detection method? What types of planets do this method find?
Doppler shift of host star. Giant planets (Jupiter like) close to the star.
What role does the moon play in aiding life to develop/continue on Earth?
Stabilizing the wobbling of the earth
What factors are involved in determining the range of the Continuously Habitable Zone around a star? What are the uncertainties?
Planet's primordial atmosphere, distance from star, luminosity change of star, albedo change of planet. Atmospheric feedback from CO2.
What may have helped the domination of Homo Sapiens over the Neanderthals?
Complex speech
Why is the Drake equation not a good way to measure the number of ETs out there?
Too much uncertainties
What wavelengths has traditionally been used to search for ET signals? What is the main reason for that?
Radio wavelengths. Can penetrate atmosphere
What kind of signals are we looking for when we search for ETs (i.e. width of signal, type of signal)?
Narrow band signals, either continuous or pulsed
Name some NASA projects (past, current, or future) that involve searches for ETs.
e.g. SETI (see notes on details)
What is project Phoenix? Why is it privately funded?
Continuation of SETI after gov't funding stopped.
Name 2 methods people have come up with to detect earth-like planets around other star.
Large telescope arrays in orbit, project Cyclopes
What are the two postulates of special relativity?
Laws of physics are same for all observers. Speed of light, c, is constant for all observers.
If you have something going at v = c/2, how much more energy does it have compared to when it is at rest?
See above equation. Sub in v=c/2, you get that E = mc2/root(1-0.25) = mc2/0.87, or, 1.15 x the rest mass
Why can nothing with mass go at the speed of light?
It takes infinite amounts of energy to accelerate it to the speed of light
Describe rocket propulsion. Why are we currently limited to traveling around 10 km/s?
Chemical combustion, expelling fuel out back, which determines rocket speed. The fuel goes at ~ 3km/s, multi stage rocket can go up to 10 km/s
Describe one alternate rocket fueling system. What are its advantages and disadvantages?
Hydrogen bomb. expensive
What is the twin paradox? What is its resolution?
Twins each can claim the other is moving relative to herself. The younger twin experiences acceleration.
Given that the world population grows at a rate of 1%, what is the population doubling time? How long before we reach 10 billion people given today's population of 6 billion?
70 years. 10 billion = 6 billion x e^(0.01*t), t = 51.08 years
Why is living in a space stations more attractive than living on planetary surfaces? Name two advantages of space colonies over planet surfaces.
More surface area per amount of mass needed. Easy to send off space ships, can move to new places
Why is it unlikely that, if there were super civilizations in our Galaxy, we have not been visited by them yet?
They could easily have reached us, or monitored us, and surely some would have the drive to visit us already.
Reading new: G & O: pp. 421-43, ch. 18, 20, 21
Z & H: ch. 1, 3-11
for Finals: G & O : ALL
Z & H : ALL except: ch. 12, 14, 19, 21