I’ll agree on Dark Matter, things like the Bullet Cluster need something more than modifyed gravity, but I’m not so sure about Dark Energy. As far as I know, Dark Energy is the difference in the energy we measure in space and the energy necessary to fuel the acceleration of expansion. This whole idea could change radically with a new understanding of space or the nature of the universe.
Dark Matter is a relatively known unknown; we know there must be some thing here, and are nearly certain it’s more than just a force. Dark Energy is an unknown unknown; something doesn’t match up, but we don’t know what.
I saw a paper on here recently that basically said they’ve explained dark energy through what they called “cosmological coupling” of black holes. Basically, black holes absorb space over time, and since space has a base level of energy and energy is kind of a form of mass then the black holes are gaining mass over time and so they are less massive in the past than they are today. I don’t 100% understand why that explains dark energy, but it is a very new paper and as far as I know hasn’t been peer reviewed yet, so who knows!
Interesting. I’ve heard about cosmological coupling before, I wonder if PBS Spacetime or Dr. Becky have mentioned this theory yet.
Showing that BH energy density stays constant, like the proposed cosmological constant, is quite interesting, but I also don’t understand the leap to how that drives expansion. If vacuum energy was everywhere, I can see how that would push things apart and push harder as space grew, but if vacuum energy exists in BHs I can’t make the connection to a repulsive force. Perhaps this is a event horizon resonance mode or something? Where event horizons exists for everything, and they’re size and relativistic motion press upon the universe? I don’t know.
Wikipedia seems to have this paper’s theory listed already (here), though reception seems mixed.
EDIT: Yes, I knew I’d heard of this before. Both PBS Spacetime and Dr. Becky have fairly technical videos on this. Dr. Becky in particular does a great analysis of the paper, as the growth of supermassive BHs is her specialty.
Also, both the proposed Dark Energy and these cosmologically coupled BHs end up exibiting negative pressure in their energy. This is how more energy = more expansion. Exactly how that happens is a complicated relativistic relationship, but it’s not unique to this paper.
Yeah I figured it maybe also had something to do with the distribution of matter throughout the universe. We assumed when we made predictions of the distant past that the supermassive black holes at the center of galaxies were the same mass as they are today, but if they were less massive then it might help explain why black holes didn’t gather as much material into it’s orbit as we would have thought.
I think you’re right though that it has more to do with the negative pressure that space and the black holes seem to exert although I must admit I don’t really understand what that means or how you would get a negative pressure from a black hole or from space.
I’ll agree on Dark Matter, things like the Bullet Cluster need something more than modifyed gravity, but I’m not so sure about Dark Energy. As far as I know, Dark Energy is the difference in the energy we measure in space and the energy necessary to fuel the acceleration of expansion. This whole idea could change radically with a new understanding of space or the nature of the universe.
Dark Matter is a relatively known unknown; we know there must be some thing here, and are nearly certain it’s more than just a force. Dark Energy is an unknown unknown; something doesn’t match up, but we don’t know what.
I saw a paper on here recently that basically said they’ve explained dark energy through what they called “cosmological coupling” of black holes. Basically, black holes absorb space over time, and since space has a base level of energy and energy is kind of a form of mass then the black holes are gaining mass over time and so they are less massive in the past than they are today. I don’t 100% understand why that explains dark energy, but it is a very new paper and as far as I know hasn’t been peer reviewed yet, so who knows!
Here’s the paper: https://www.ifa.hawaii.edu/2023/02/first-observational-evidence-linking-black-holes-to-dark-energy/
Interesting. I’ve heard about cosmological coupling before, I wonder if PBS Spacetime or Dr. Becky have mentioned this theory yet.
Showing that BH energy density stays constant, like the proposed cosmological constant, is quite interesting, but I also don’t understand the leap to how that drives expansion. If vacuum energy was everywhere, I can see how that would push things apart and push harder as space grew, but if vacuum energy exists in BHs I can’t make the connection to a repulsive force. Perhaps this is a event horizon resonance mode or something? Where event horizons exists for everything, and they’re size and relativistic motion press upon the universe? I don’t know.
Wikipedia seems to have this paper’s theory listed already (here), though reception seems mixed.
EDIT: Yes, I knew I’d heard of this before. Both PBS Spacetime and Dr. Becky have fairly technical videos on this. Dr. Becky in particular does a great analysis of the paper, as the growth of supermassive BHs is her specialty.
Also, both the proposed Dark Energy and these cosmologically coupled BHs end up exibiting negative pressure in their energy. This is how more energy = more expansion. Exactly how that happens is a complicated relativistic relationship, but it’s not unique to this paper.
Yeah I figured it maybe also had something to do with the distribution of matter throughout the universe. We assumed when we made predictions of the distant past that the supermassive black holes at the center of galaxies were the same mass as they are today, but if they were less massive then it might help explain why black holes didn’t gather as much material into it’s orbit as we would have thought.
I think you’re right though that it has more to do with the negative pressure that space and the black holes seem to exert although I must admit I don’t really understand what that means or how you would get a negative pressure from a black hole or from space.