
Probing Planets in Extragalactic Galaxies Using Quasar Microlensing - IntronExon
https://arxiv.org/abs/1802.00049
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zaroth
My first thought is of the sheer quantity of extraterrestrial organisms which
must exist in the incomprehensible vastness our universe.

Maybe the laws of physics and mortality will prevent us from meeting them, let
proving their existence, but in such an ultimate vastness where we know that
life does exist, _life must exist_.

I don’t get Fermi though. If you take the inconceivably large problem space
that is “life finding other life in the universe” and cross it with the
infinitesimally small amount of space-time we’ve occupied actively looking for
other life, how is not having found other life yet a paradox?

~~~
cdelsolar
Then, to quote Fermi, where are they? If even one of those species had become
intelligent enough to build self-replicating Von Neumann probes, then we would
see evidence of it somewhere in our solar system. Unless... we are the Von
Neumann probes.

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philipov
The farther we look, the earlier back in time we see whatever we look at.
There is good reason to think that the rise in complexity of organisms is a
global feature of the universe, so other intelligent life may simply not have
developed early enough that we've had time for the light from them to reach us
yet.

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jerf
Life on Earth is about 3.5 billion years old. If some other species in the
Milky Way had beaten us to intelligence by 1%, even assuming they didn't start
out another billion or two earlier, that would give them 35 million years to
spread exponentially through our 100,000 light-year-wide galaxy.

It is possible we are first. The Copernican principle, to my eyes, is taking a
bit of a beating lately anyhow. It was a fine heuristic for a while, but many
people seem to have forgotten it is only a heuristic that seemed to work for a
while and not an actual law of the universe. So maybe we are that unique. But
it is worth pointing out that would itself be a significant sea change in the
current philosophy dominant in science.

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ptrincr
It's possible that whilst the universe is full of life, intelligent life is
quite scarce. It could be we are the first in this Galaxy.

It could be that others have come and gone but never quite made it to space.
Cave paintings go back 40,000 years. I'd say that displays a level of
intelligence. Yet there was a significant period of time until we managed to
develop agriculture (30,000 years), or writing (37,000 years).

At lot can happen during that time. In fact during these years humans could
have died out many times, succumbed to the changing climate or disease.

But considering all this, you have to take into account that the universe
consists of upwards of 2 trillion galaxies, at least as far as we can see.
That's a lot of potential. But if we can never make contact, does it even
matter if its there or not?

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dmitrybrant
Just a nitpick, but wouldn't it be simpler to say "extragalactic planets"
instead of "planets in extragalactic galaxies"?

That's like saying "life on extraterrestrial earths."

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Keysh
To be honest, I think "planets in other galaxies" would be better (since
"extragalactic galaxies" sounds a bit like "galaxies outside of galaxies").

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mabbo
> We constrain the planet mass fraction to be larger than 0.0001 of the halo
> mass, which is equivalent to 2,000 objects ranging from Moon to Jupiter mass
> per main sequence star.

So the paper is saying there there probably aren't more than 2000 planets per
star? That seems like a pretty large upper-bound.

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whorleater
No it's saying the planet mass fraction (the ratio of planet mass to halo
mass) is bounded by 2000, not the actual number of planets.

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jxub
This title sounds amazingly cool for a science paper.

