In Class:
Question to Ponder
You get a ticket for running a red light on Market St. At your
hearing, you tell the judge that since you were moving toward the
light, the 600nm red light looked to you like 500nm green light
because of the Doppler Effect. Therefore, you shouldn't have to pay
the fine for running the light.
Is this a valid argument based on your understanding of the Doppler Effect?
- a) yes, because the red light should appear shifted to shorter
wavelength light.
- b) no, because the red light should appear shifted to longer
wavelength light.
- c) well... the Doppler argument is fine, but you're gonna pay
a heck of a fine for speeding...
Needs for an Environment that Supports Life
- energy source -- starlight?
- consistent exposure --> low eccentricity orbits
- protection from uv and x-ray light --> atmosphere
- construction materials: life here is based on carbon, oxygen, and
hydrogen (mainly). These are abundant in the universe, but probably not
the only way to construct complex molecular material.
- time: life took 3.5 BYr to develop here. Do we need stability for
that length of time elsewhere? If so, don't look for life to form
on planets around massive stars -- these blow up on shorter timescales.
The Drake Equation for Framing the Discussions About the Liklihood
of Intelligent Life Elsewhere
- N = Nstars * frac_planets * frac_goodplanets * frac_life
* frac_intell_life * frac_tech * L
- N = number of intelligent civilizations
- Nstars = number of stars in galaxy (100 billion)
- frac_planets = fraction with planets (~50%?)
- frac_goodplanets = fraction of those planets whose environments
are conducive to the development of life (~10%?)
- frac_life = fraction of those planets on which life actually
forms (0% or 100%)
- frac_intell_life = fraction of those life-filled planets that
allow for evolution to intelligent status (??)
- frac_tech = fraction of intelligent life planets that develop the
technology to communicate over interstellar distances (??)
- L = lifetime of a communicating civilization as a fraction of the
planet's total history
Limits on L
- How long before we are destroyed?
- Does civilization inherently produce the seeds of its own demise
(e.g., nuclear capability, pollution, global warming)?
- Civilization-destroying asteroid impacts occur once every 10-100
MYr around here these days
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