Does life exist elsewhere?
Microbes count.
A biosphere beneath an icy ocean counts. Something photosynthesising under another sun counts.
Plausible.
NOTES ON LIFE ELSEWHERE
Is anyone
else out there?
Maybe.
That's not a disappointing answer.
01
We know that life emerged at least once.
That's both an extraordinary fact and a frustratingly small sample size.
One inhabited planet cannot tell us whether life is common, rare, inevitable under the right conditions, or an accident so improbable that it happened only here.
THREE DIFFERENT QUESTIONS
We keep collapsing them into one.
Does intelligent life exist elsewhere?
Intelligence is not necessarily an inevitable destination of evolution.
Even on Earth, technological civilisation appeared extremely late in the story.
Unknown.
Has any of it visited Earth?
That's a separate claim with a much higher evidentiary burden.
A very large universe does not automatically make interstellar visitors nearby.
Show me the evidence.
FRIENDLY INTERRUPTION
“Cindy thinks everything is interesting right up until I say it is definitely aliens.”
— Zack
visit Zack's considerably louder website →
02
The numbers are enormous.
Stars are not exceptional objects surrounded by empty space. Planets are common enough that the question has changed.
We are no longer asking whether other planetary systems exist. We are asking what happens on them.
A useful thought experiment
The Drake equation
N = R* × fp × ne ×
fl × fi × fc × L
It isn't a machine that tells us how many civilisations exist.
It is a way of exposing the assumptions hidden inside the question.
Some terms are increasingly constrained by astronomy. Others remain enormous unknowns.
03
Somewhere between chemistry and conversation, a lot has to happen.
-
01
suitable environment
Conditions allow complex chemistry to persist.
-
02
life begins
Non-living chemistry becomes something capable of replication and evolution.
-
03
complexity
Life persists long enough for more elaborate forms to develop.
-
04
intelligence
At least one lineage develops sufficiently flexible cognition.
-
05
technology
Intelligence produces detectable technology.
-
06
overlap
Their detectable period and ours occur at the same time.
THE FERMI PROBLEM
If life is common,
where is everybody?
Maybe life is rare.
Perhaps one of the early biological transitions is extraordinarily difficult.
Maybe intelligence is rare.
Billions of years of life need not produce radio telescopes.
Maybe technology is brief.
Civilisations could appear and disappear without overlapping.
Maybe we're looking badly.
Our searches cover only a small part of an enormous possibility space.
Maybe distance wins.
A populated universe can still be a very lonely place.
Maybe we're early.
Cosmic history is not finished.
Silence is data.
It is not yet an explanation.
04
What would actually change my mind?
weak
a strange light
Interesting observation. Many possible causes.
better
repeatable measurement
Multiple instruments, known conditions, independent observers.
strong
anomalous signal
Persistent, independently confirmed, difficult to explain naturally.
extraordinary
unambiguous artefact or biology
Evidence whose origin survives serious attempts to explain it otherwise.
CINDY'S HIGHLY SCIENTIFIC DEVICE
How crowded do you think the universe is?
50%
A respectable amount of uncertainty.
This slider has gathered no new evidence.
1 Zack has requested that I include the pigeon incident among the unresolved phenomena.
Request denied.
His version of events →KEEP LOOKING
Good places to go next.
I don't need the universe to contain anyone else for it to be extraordinary.
I'd still like to know.