Transcript Physics 1910W, Spring 2016 In PAN 210, 10:15am

How likely is extraterrestrial life?
Physics 1910W, Spring 2016
In PAN 210, 10:15am-11:00am TTh
JW Halley
181 Shepherd Labs
612 624 0395
[email protected]
Office hours: TTh 3:30pm-4:30pm and by appt
Course:
https://www.physics.umn.edu/classes/phys/2016/spring/Phys%201910W.001/index.html
Format: Lecture/discussion in class periods.
Student presentations in the last two weeks.
Prerequisites: High school general science
course and elementary algebra.
Work load and grades. A few hours of reading
from book and notes/week. One written
exercise per week. 10-15 page term paper and
oral presentation. Two short, unannounced
quizzes on reading material.
Grades: Exercises 65 %, quizzes 10%, paper
and presentation 25 %.
Weekly reading assignments and
a schedule of deadlines for the final
paper appear in the syllabus. Make
an appointment with the instructor to
select a topic within the first two weeks.
Exercises will usually be distributed on
Tuesdays and collected on the following
Tuesday.
Overview
The emphasis is on what science can tell
us about this ancient question.
I will review evidence from two points of
view during the next weeks:
1. ‘Bottom up’. We start with well established
physical and chemical laws and ask what
they imply about the answer to the question.
We organise the discussion with the Drake
Equation.
2. ‘Top down’. We start with the results of experiments
to try to directly observe life and civilization
elsewhere (which have shown nothing so far:
Fermi paradox) and ask what they tell us.
Drake equation. (due to radio astronomer
Frank Drake in the 1950’s. This is a simplified form)
Nciv =Ngal fstar fplanet flife
Ngal = number of stars in a typical galaxy
fstar= probability that a star has the right
chemistry for life
fplanet = probability that a star with the right
chemistry has a solar system including
earthlike planets with the right climate
for life.
flife= probability that life evolves on a ‘habitable’
earthlike planet.
Quick summary:
Ngal is quite well known. We will use 1011
We will discuss fstar at some length. A lot is
known about it, and we will use the number
10-2
Information on fplanet is rapidly accumulating.
We estimate 10-3. More discussion later.
Very little is known about flife. Estimates range from
1 to less than 10-11!
Putting these numbers back in the equation
10-5 < Nciv < 106
Practically all the huge uncertainty comes from
the fact that we don’t know how likely it
is for life to evolve on an earthlike habitable
planet.
Question:
What does it mean to say that
Nciv < 1 ?