Download The Drake Equation - d

The Drake Equation
Assumptions & Science
A demonstration
internal assessment
oral for IB Theory of
Knowledge
[ S.Kern, 2015 ]
NOTE: This is a demo!!!
• With few exceptions, these slides are WAY TOO BUSY!
• You’ve got all this text so that you have a record of the
type and depth of content covered.
• Generally: This (first) “bullet level” would remain for a real
(not a demo) oral.
– This level would be omitted.
• The timings listed on slides are approximations to give an
idea of relative weighting.
• A PowerPoint (Prezi, etc.) is not required,
– and only what you say is assessed.
SETI and the Drake Equation
• The first SETI (Search for ExtraTerrestrial Intelligence)
conference in 1961 at the National Radio Astronomy
Observatory in West Virginia with Dr. Frank Drake, presiding:
• “As I planned the meeting, I realized we needed an agenda.
So I wrote down all the things you needed to know to
predict how hard it’s going to be to detect extraterrestrial
life. And looking at them, it became pretty evident that if you
multiplied them all together you got a number, N, which is
the number of detectable civilizations in our galaxy.”
• Here is the “Drake Equation:”
N = R* fp ne fl fi fc L
N = R* fp ne fl fi fc L
Where N = The number of intelligent, communicative
civilizations in the galaxy
R* = The rate of formation of suitable stars [5 per year]
fp = The fraction of those with planets [50%]
ne = The number of Earth-like worlds per system [2]
fl = The fraction of those where life develops [100%]
fi = The fraction of those where intelligence develops [20%]
fc = The fraction of the those that develop communicative
technology [100%]
L = The "lifetime" in years of those civilizations [10,000]
Drake’s original estimate:
N = 10,000 intelligent, communicative civilizations in the galaxy
Knowledge Question
How do scientists justify the
assumptions they use to make
estimates?
In this context, an assumption is an unproven
but plausible speculation.
Assumptions
• Purpose: Critical to research and unavoidable
– Start somewhere: like “givens” in math
– Determine what/how we investigate
– Fine-tuning & improvement
• Main ways of justification
– Extrapolating
– Constructing models
– Making arbitrary guesses
• Limitations
– Reliability: Data
– Validity: Models
– “The problem of induction”
How were Drake’s
assumptions justified?
•
•
•
Extrapolating from known facts (data)
– R* = rate of suitable star formation [5 per year]: well-justified based on extensive data through direct observation
– fp = fraction with planets [50%]: less well-justified - based on
some empirical data and indirect observation
Use of models (our earth and solar system)
– ne = Earth-like worlds per system [2]:
– fl = The fraction of those where life develops [100%]
– Validity: Are these models representative of other systems?
Arbitrary guesses
– fi = The fraction of those where intelligence develops [20%]
– fc = The fraction of those that become communicative [100%]
– L = The "lifetime" of these civilizations [10,000]
– Little justification: little or no data (deductive not inductive)
If N is 10,000, where are all the ET’s?
Could some of Drake’s assumptions been faulty?
Over the years, other perspectives have offered very different
assumptions (and N’s)!
Other real life situations
• Other RLS’s in which assumptions play major roles
– Global warming / climate change
– Battling epidemics/pandemics of “spillover” diseases
• Common denominators
– Extrapolation
– Projecting trends
– Building representative models
– Using computers to simulate complex situations
Significance: So what?
• No exaggeration: Improving our assumptions can be a
matter of life and death.
• Well-justified assumptions…
– Clarify expectations & potential outcomes
– Inform action
• Next steps for research
• Policy decisions
– i.e., If our assumptions make a dangerous
outcome seem unlikely, we are less likely to act.
• The problem of arbitrary guesses:
– “Garbage in, garbage out” vs. “but we have to start
somewhere.”
• Therefore, even the most well-justified assumptions need
to be explicit, debated, and revised with further research.
Want to add your own perspective?
Check out an interactive version of the Drake Equation
with you can adjust the assumptions:
• http://www.pbs.org/wgbh/nova/space/drake-equation.html
• http://www.scribd.com/doc/28455374/The-Mathematics-of-Drake-sEquation-Planets-stars-and-life-elsewhere-ppt-presentation
• http://www.pbs.org/lifebeyondearth/listening/drake.html