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Astronomers Detect a Possible Signature of Life on a Distant Planet

(www.nytimes.com)
168 points julienchastang | 2 comments | 16 Apr 25 23:20 UTC | HN request time: 0.425s | source
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jmyeet ◴[17 Apr 25 01:25 UTC] No.43712152[source]▶
This is your daily reminder that if we do indeed discover life so close (~120 LY) to Earth, it's an incredibly bad sign for us. This is an exercise in Bayesian reasoning.

Imagine there are 2 planets in the Milky Way where life has developed. The odds are incredibly low they're next to each other, assuming a random distribution. So it's way more likely that there are more than 2. Imagine a sphere of radius 60 LY (120/2). Our Earth is the center of one. This planet is another. That's a volume of 10^6 LY^3. The Milky Way volume (from Google) is ~17T LY^3 so there'd be roughly 170M such spheres in our galaxy.

Now imagine if the odds of simple life becoming intelligent life that we could detect and could become spacefaring is 1 in 1 million. There'd be ~170 such civilization in the Milk Way.

We have absolutely no evidence of this So simple life is a lot less common, intelligent life is a lot less likely or, and this is the scary part, something tends to wipe out sentient civilizations and that's likely in our future.

In Fermi Paradox terms, we call this a Great Filter.

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1. awb ◴[17 Apr 25 02:41 UTC] No.43712584[source]▶
There’s no evidence yet, but we also haven’t looked very carefully or in very many places. And we only know to look for planetary life as we know it.

The middle of the galaxy could have a wildly different composition and habitat for life than the outer reaches where we are.

Time is also another factor. Maybe the galaxy is perfect for complex life, we just happen to be early on the timescale and in another billion years or two life will be clearly abundant everywhere.

For some perspective, if you take the size of the Milky Way (100k light years) and relate it to the size of NYC (~30 miles), then 120 light years ends up being ~190 feet in NYC, or less than a city block.

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2. jmyeet ◴[17 Apr 25 03:33 UTC] No.43712862[source]▶
The middle of the galaxy is unlikely to be conducive to forming intelligent life simply because it's not stable enough for long enough.

In our part of the galaxy, the mean distance between stars is around 4-5 LY (at a guess) in terms of nearest neighbours and ignoring binary (and up) systems. At the galactic center it's a few light days.

We've had many events that have caused mass extinction. There are many more that could end all life as ew know it (eg gamma ray bursts, a sufficiently close supernova. We have ~10 stars within 10 LY of us. Imagine if that were millions instead. I find it hard to believe conditions would be stable enough for the millions or billions of years necessary to create and sustain complex life.

As for our galaxy being "perfect" this touches on a coupole of concepts, notably the Anthropic Principle. But again we return to Bayesian reasoning. If there was going to be 1000 spacefaring civilizations in our galaxy, what are the odds that we are first? And while the Sun is <5B years old, there are stars up to 14B years old. There's been a ton of extra time for civilizations to develop elsewhere.