[rewgs]

Yeah, I think that the Fermi Paradox can be pretty easily explained: the universe is fucking huge.

Those who talk about the feasibility of alien life visiting us very simply haven't thought it through, or are ignorant of the reality of space.

It's just too staggeringly big.

[omnicognate]

Yep, the Fermi "paradox" is no paradox at all. We have basically no evidence that life (including intelligent life) isn't common yet.

There are so many ways to think of how big our galaxy is but two are particularly relevant to how difficult it would be to detect other life, or be detected:

1. The first radio signals the human race produced have so far travelled something like a thousandth of the distance to the other side of our galaxy. Light travels really slowly on astronomical scales.

2. A supernova goes off roughly once every 50 years in the milky way. That's an energy release that is utterly incomprehensible to a human being. A system-incinerating catastrophe briefly producing an energy output comparable to that of all the stars in the galaxy combined. But to us they appear as just brighter-than-usual dots in the sky. We (humans) have only noticed a handful of them. It's not that we're shielded from them. These events happen in direct line of sight. They're just insanely far way and light intensity falls off with the square of distance. The kinds of energy outputs produced by a species of comparable technology to our own are simply not visible to us over these kinds of distances, even with the very latest technology.

And that's just our galaxy. If you consider the entire universe the things happening in direct line of sight include billion-solar-mass supermassive black hole mergers, and you need a gravitational wave detector to even tell they're happening.

We've only just recently started to be able to detect the presence of planets around other stars. The Fermi Paradox, Great Filter, "Where's the intelligent life?" stuff is absurdly premature.

[ncmncm]

I wonder whether any organic life in a galaxy could survive merger of a pair of 1e9-solar-mass black holes. Would 25,000 light years be far enough out? 5,000? 500 light years is supposed to be the sterilization range of a minor magnetar hiccup, 5 light years for a workaday supernova, IIRC. We will soon find out how much energy is released in such a merger; one is about to happen in a year or three, about a billion light years out. Sadly, we will not have deployed a gravity-wave detector big enough to measure it with, by then, and will have to wait for the next one.

If life sorts more or less neatly into expansionist and sedentary cultures, the sedentary species will generally be much older and, typically, much more technologically advanced than the expansionists that try to encompass them. Aggressive expansionists will tend to be destroyed by the first, second, or anyway tenth sedentary culture they try to strong-arm. So, the galaxy is full of very old, sedentary cultures not interested in visiting us, and young expansionists popping up all the time and being obliterated before they reach us.

[WillPostForFood]

is absurdly premature.

Only relative to our own existence. If the universe is ~14 billion years old, and life was plentiful, you might expect life to have emerged elsewhere hundreds of millions or a few billion years before us. That allows for enough time for signals to have reached earth, even at slow light speeds.

[omnicognate]

That part was more about us being detected by others, really. The portion of the galaxy within which aliens could theoretically have noticed us since we developed radio technology and responded in a way we could have noticed by now is tiny.

As far as us noticing other civilisations is concerned the second point is the major one: the signals involved would just be really, really tiny. The "prematureness" is relative to our development of technology that could detect them.

You can of course posit that really advanced civilisations would produce massive energy signatures but I'm not sure that makes sense. The visible night time glow our planet produces due to our presence is a signature of inefficiency and light pollution. I'd hope that with better technology and politics we could make our planet look dark again from space. Efficiency, lack of wasted energy seems at least as likely to be a hallmark of a very advanced civilisation as huge, catastrophic energy releases. And even if those energy releases exist and really are spectacularly huge they'd still be massively hard to spot.

[WillPostForFood]

It is plausible that our visible light signature might be reduced (though I don't agree it is necessarily wasteful - like lighting up evening outdoor events). But we should consider the entire RF spectrum. You'd have to go to an extreme to not have a modern civilization without notable RF emissions at some level. (e.g. Dyson sphere).

Section 2 of this paper has some fun info on the ability to detect our radio signature at great distances.

https://arxiv.org/pdf/1207.5540.pdf

For example, the Arecibo Planetary Radar typically transmits at a power of 0.8 MW and a frequency of 2380 MHz, with a gain of ~108. This means that low bandwidth transmissions from Arecibo, with B ~ 0.1 Hz, would be detectable by a watcher with a 1 km2 receiving antenna at distances up to 200,000 light years, while high bandwidth signals, with B ~107 Hz, would be detectable out to about 5 light years by the same watcher.

By comparison, television carrier waves have similar power but gain ~10, B ~ 1 Hz, and frequencies in the range of 100 to 2700 MHz; such signals could be detected with a square kilometer array out to a distance of about 50 light years.

RIP Arecibo

[softjobs]

To drive home the enormous scale of the local solar system, and by extension the universe, I'm fond of this: https://joshworth.com/dev/pixelspace/pixelspace_solarsystem....