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Comment by gfodor | Hacker News Reader

A universe peppered with black holes may also explain the Fermi paradox. A terrifying but logical thought.

Black holes do not vacuum everything around them - the law of gravity is a function of distance. That does not explain the Fermi paradox at all.

Yeah, I was thinking the same thing, but on average they'll be lightyears apart. I think the chance of them hitting each other is astronomically small.

Even when Andromeda and the Milky way collide, almost nothing will hit each other, because there is no much empty space.

This being said there was a paper recently studying the frequency of meteor impacts with the frequency of the solar system passing by arms of the Milky Way, and it did suggest there were more meteor impacts when the solar system passed in slightly more dense zones.

Do they? These black holes would have masses of some multiple of ten times the mass of the sun, which doesn't seem terribly heavy (relatively). How does this explain the Fermi paradox?

Could black holes also be masking an infinite number of stars?

Stephen Hawking notes in his book "A Brief History of Time" that we know that there aren't infinite stars because otherwise the night sky would have no patches of darkness since an infinite number of stars would imply that you could shoot out an arbitrary ray from earth and it would always reach a star.

However, black holes (lots of them!) could trap light and obscure line-of-sight stars.

This line of reasoning works only in a static universe. In a expanding universe, stars can move apart faster than the speed of light. Thus there might be a lot beyond the observable universe that can never be detected.

I mean... isn't it still technically correct though? We have an opaque horizon of light, it's just all in the microwave spectrum.

This is Olbers' paradox, and I don't think you need black holes to explain it: https://en.wikipedia.org/wiki/Olbers%27_paradox

I've always wondered about the CBM in this instance. Isn't that technically an opaque horizon of light? I understand that it's not stars per se, and that there is technically stuff "beyond" that, but doesn't that count as a "bright" night sky? Just not in the visible spectrum.

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