Life in the Universe

1. Life in the Universe What We Want to Know • There is intelligent life on Earth • Could it have happened elsewhere? • Alien Spacecraft/UFO’s? • Evidence is unconvincing • Can we calculate probabilities? • No • Drake’s Equation is a way to estimate how many intelligent civilizations (besides ours) are in the galaxy

2. Drake’s Equation N = R* fPnPMflfiL N = number of civilizations in our galaxy R* = rate at which solar-type stars form fP = fraction of those stars with planets nPM= number of suitable planets and moons fl = probability of getting life fi = probability of life evolving intelligence L = lifetime of intelligent species

3. Stars, Planets, and Moons N = R* fPnPMflfiL R* = rate at which solar-type stars form = 1/year fP = fraction of those stars with planets = 0.1 – 0.5

4. The right temperature N = R* fPnPMflfiL Too cold nPM = number of suitable planets and moons = 0.1 - 1 Just right Too hot

5. Getting Life Started N = R* fPnPMflfiL fl = probability of getting life started = ?? – 1 • The basic building blocks of life (elements, amino acids) are common • Life started fairly quickly on Earth • But even very simple life is extremely complicated/unlikely

6. Getting Advanced Civilization N = R* fPnPMflfiL fi = probability of life evolving intelligence = ?? – 0.5 • Evolution follows naturally from physical laws • Evolution naturally leads to some complexity • Intelligence is a very useful kind of complexity • Catastrophes could wipe out advanced life • Evolution may sometimes lead to dead ends

7. Keeping Civilization Alive N = R* fPnPMflfiL L = Mean lifetime of intelligent life = 100 – 109 years • We have the ability to destroy civilization • We are also damaging our environment • We are using up non-renewable resources • Civilizations may “mature” – some evidence • Sustainable civilizations is technically possible

8. Are We Alone? R*= 1/yr fP = 0.1 – 0.5 nPM = 0.1 - 1 fl = ?? – 1 fi = ?? – 0.5 L = 100 – 109 yr N = R* fPnPMflfiL = 0 - billions • Intelligent life could be rare • Intelligent life could be common • My opinion: • We are first in the galaxy, and possibly the visible universe • Ultimately, this is an experimental question

9. Searching Stars for Life • How can we know if intelligent life exists around other stars? • Visitors from outer space? • Fermi paradox – If they exist, why aren’t they here? • Travel to distant stars? • Search for signals from space?

10. Traveling Between the Stars • How Best to do it? • Best chemical rockets: 10-4c – 10-3c • Millenia to nearest star • Nuclear rockets, solar sails, ion engines • 10-2c – 10-1c • Decades – centuries to nearest star • Solutions: • Unmanned missions • Generation ships – parents have children • Long life span/hibernation

11. Signals From Space • We can send/receive electromagnetic signals throughout the universe at c • The universe is a noisy place • Dust/gas/etc. blocks many wavelengths • Some radiation can penetrate gas and dust • In radio waves, the Earth outshines the Sun

12. Signals From Space • We send accidental and intentional signals into space • We also look for signals from alien civilizations • Nothing found so far

13. Final Exam Equations P2 = a3 (M + m)P2 = a3 c = lf c =3  108 m/s F = ma E = hf P = knT lmaxT = 2900 Km 4 H + 2e - He + 2 neutrino + energy L = 4d2B v = H0d H0 = 22 km/s/Mly

14. End of Material for Test 4 Questions?