Despite being extremely unlikely, is
there a possibility that Earth is the
only planet in the universe with life?
originally appeared on Quora : the
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Answer by Viktor Toth , IT pro, part-
time physicist, on Quora :
Expressing my personal opinion here on
whether or not Earth is the only planet
in the universe with life, yes, it is a huge
universe, but it is also a young
universe. This means that life on Earth
appeared pretty much the instant
conditions became favorable to life. Yes,
this is a sample of one, but it
nonetheless leads me to suspect that
primitive life may be common in the
universe. In fact, I would not be
surprised if within the next decade, we
found direct evidence of life on Mars or
life on an exoplanet.
But complex life? On Earth, it took
nearly two billion years for eukaryotic
cells to emerge, and (as far as I know)
there may be a common ancestor to all
eukaryotes; which means that this
incredible accident only happened once
in all those billions of years.
As I mentioned, the universe is young.
Only 13.8 billion years old. For much of
that time, it was too “metal poor”, as
astronomers call it, namely it had too
little of the elements heavier than
hydrogen and helium. So it’s really
unlikely that there were solar systems
much older than our own with the right
ingredients for life. How many of them
had that lucky accident already? How
many had it sufficiently long ago for
those eukaryotes to grow up and start
building airplanes and computers and
discuss the possibility of life elsewhere?
How many are planets on which the
right conditions persisted for billions of
years, not interrupted by some
calamity?
Another point to consider: if our
civilization survives, very soon it will
become a civilization, at least in part, of
machines. Machines that are not limited
by human biology. Machines that can
survive centuries in space or accelerate
to near the speed of light. This suggests
to me that in a few million years (an eye
blink compared to geological/
astronomical time scales), the products
of our civilization will have spread
throughout the Milky Way. Conversely,
had there been another advanced
technological civilization around already
a few hundred thousand years ago, its
artifacts likely would have reached us
by now. In fact, we might never have
had a chance to evolve. But, evolve we
did, and for all I know, we are the first.
So yes, unlikely, but I don’t consider it
impossible that if not in the whole
(possibly infinite) universe, but at least
in a large slice of it, we are the only kids
in town.
Of course if tomorrow a UFO lands on
the White House lawn, all my nice
reasoning based on a sample of one
goes out the window, and then there
might be “life” completely unrelated to
the carbon-based chemistry that is the
basis of our own, and who knows what
that means.

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