What a fantastic question! To which there is
still no definitive answer, but maybe I can point
you to some research and thought experiments.
This is certainly a question that astrophysicists
have been pondering for many years. The universe
is huge and old, composed of many galaxies; Earth
is just a blip in our own galaxy, known as the
blip on our galaxy
It is estimated that 100 billion (that's 9 more
zeros!) galaxies exist with even more stars. Our
sun is just one of those stars.That's a lot of
galaxies and a lot of stars. It seems plausible
that somewhere in those galaxies there could be a
solar system like ours with planets that orbit
different stars (known as exoplanets). So life
from outer space seems probabilistically possible,
even in our own galaxy. This argument is known as
the Drake equation, which just makes explicit a
probability calculation of the number of active
(i.e., not extinct), intelligent (i.e., have some
form of "language"), and communicative (i.e..
looking for other active, intelligent
civilizations). It looks like
this The Drake equation is nice and all, but
it doesn't tell us how to find the values of each
variable, so we can't get a number out of this.
Still, it makes you think of the vast possibility
that other life forms could exist out there...
Scientists have found that the universe is pretty
much made of the same elements you find on the
periodic table (through very
clever means of measurement, if I do say so
myself). There is a particular combination of
elements that is conducive to life. But is that
something unique to Earth? This is a question
that many scientists have asked themselves. There
are quite a few things you need to be able to
sustain life, of which I list a few to give you a
That is, you need to be at just the right distance
from a "sun" (i.e., star). If you are too close,
it's too hot; likewise, too far, and it's too
cold. Additionally, you want your planet to be
able to rotate on its own axis (i.e., have day and
night cycles), so that one side is not left hot
and other col. This is especially important with
respect to water. Keeping water in its liquid
state is essential for all kinds of biological
functions, and by extension life itself. Too hot,
and it vaporizes; too cold, and it freezes.
This is also true about the distance with
respect to the center of the galaxy you are in.
For instance, in our Milky Way, the center is rife
with supernovas (exploding stars) and a
supermassive black hole that would kill all life
with intense radiation.
You also don't want a star that is too big.
These tend to be stars that have shorter life
2) A bigger planet nearby
It turns out that because Jupiter is so big, it
helps "absorb" many of the comets and asteroids
that could otherwise hit Earth, which, as you may
know from the dinosaurs, could wipe out quite of
bit of life.
3) A large enough planet
Primarily, you have enough gravitational pull to
sustain an atmosphere, though there may be other
4) A planet with plate tectonics
The Earth's crust (i.e., surface layer) is
composed of many plates. The motion of these
plates recycles carbon, which is the backbone of
nearly all organic matter. This helps maintain the
levels of carbon dioxide levels (CO2)
at a level habitable life.
There is even discussion of colonizing Mars so
that does become habitable. This would entail
getting and maintaining levels of CO2
needed to warm up the planet, putting in some
organisms that produce oxygen that will eventually
lead to more complex forms of life. This is
actually how life on earth developed (in a very
simplified and curt manner). (And another
interesting tidbit, it is the release of too much
CO2 in our own atmosphere that has been
center of the climate change debate, but that is
another story for another time.)
This actually leads me to an interesting point.
Perhaps the image of Aliens you have is that from
science fiction- ones that look humanoid with big
eyes and are green. Although finding another
civilization in outer space would revolutionize
what we know of the universe, finding even simple
organisms like bacteria would be monumental. There
are several planets that have been identified as
potential places that could have sustained life at
some point- some in our own solar system (e.g.,
Europa, one of Jupiter's moons, and Mars) and many
outside, such as
Kepler-186f That is the conditions have
been found that could have at one point sustained
life. So there are lots of places that meet
conditions to sustain life, but so far no dice.
But with so many requirements, it really makes you
wonder at how amazing it is that life exists
So perhaps there is life out there, we just
haven't found it and perhaps they have not found
us either. Or perhaps, we communicate
differently and missed each other. Or maybe they
are so advanced, they think us too primitive.
Conversely, we may be too advanced for their form
of communication. I think my favorite analogy is
communicating to aliens may be like us
communicating with ants (or vice versa). While we
have spoken/written language, ants communicate
primarily through pheromones (chemicals secreted
into the air), which we have very poor receptors
for! What do you think?
If you are especially interested in
astrophysics, I recommend watching Cosmos with
both Carl Sagan and then more recently with Neil
deGrasse Tyson. They are really quite rewarding.
Hope this helps!
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