As I understand it black holes are infinitely dense. Yet some are larger because they’ve consumed more material than others.
So I’m confused because if they are infinitely dense shouldn’t they all be the same size? Or is infinity + a few hundred solar systems larger than just infinity? Maybe I just don’t understand infinity that well…
In: Planetary Science
So, a couple of things.
1. when we talk about the size of a black hole, we’re measuring its event horizon, which is larger or smaller (farther or closer from the center) depending in the black hole’s mass. There’s no real-life hard boundary there, like a wall of black you’d see approaching you or whatever. It’s just that closer than that, the speed required to fully escape its gravity is faster than the speed of light.
2. *According to our math*, the entire mass of the black hole, of any size, is entirely in a single point of 0 volume and infinite density. But another way of saying that is that… when we use our math to try to calculate anything within the event horizon, our equations return 0s and ∞s. I’ve only done college-level physics and engineering, but in my experience, whenever something spits out infinity, that means you’re doing something wrong and you’ve broken something. I’m not qualified to say much about black hole physics, but it really seems like “a singularity with infinite density” is a way of saying “our models of how the universe works break down and no longer produce real results here”. That is to say, I wouldn’t be shocked if the whole idea of a singularity is just a big clue that we need something other than Einstein’s relativity to model what a black hole even is. Which isn’t crazy, I mean relativity replacing Newton’s equations must have felt insane and impossible at the time too.
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