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'Dark fluid' with negative mass could dominate the universe

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Re: 'Dark fluid' with negative mass could dominate the universe

#21

Post by shepardrtc »

mrfusion wrote: post #11
galadran wrote: post #8

Paper: https://arxiv.org/pdf/1712.07962.pdf Not a physicist, but my summary of the author's point would be: If you allow for matter with a negative mass and plug it into a n-body simulation. You seem to get what looks like dark matter from first principles. Namely, a halo of non interacting matter around galaxies in just the right "non-cuspy" shape. Their conclusion is that this is worth considering, as almost all ma…

Are they pretty sure it’s different than antimatter? Last I heard we weren’t sure if it has negative gravity or not.

Matter-antimatter annihilation would produce gamma rays that are detectable. I believe there was a study that went looking for that but didn't find anything.

Re: 'Dark fluid' with negative mass could dominate the universe

#23

Post by AnimalMuppet »

duality wrote: post #13
galadran wrote: post #8

Paper: https://arxiv.org/pdf/1712.07962.pdf Not a physicist, but my summary of the author's point would be: If you allow for matter with a negative mass and plug it into a n-body simulation. You seem to get what looks like dark matter from first principles. Namely, a halo of non interacting matter around galaxies in just the right "non-cuspy" shape. Their conclusion is that this is worth considering, as almost all ma…

"Every other force besides gravity is polarised, so why not also gravity?" Gravity is mediated by a spin-2 gauge boson, the graviton, whereas the other known fundamental forces are mediated by vector (spin-1) bosons. There is an exercise in Peskin & Schroeder (I believe) working out the lack of a gravitation "repulsion" resulting from this difference. That being said, I think this kind of phenomenology is excellent a…

Um, correct my amateur understanding if it's wrong, but... we don't actually have a working quantum theory of gravity, do we? So how certain are we that gravity is mediated by a spin-2 gauge boson?

Re: 'Dark fluid' with negative mass could dominate the universe

#24

Post by XorNot »

DiabloD3 wrote: post #7

A "dark fluid" with negative mass COULD dominate the Universe, sure. But so could galactic-scale electric currents and magnetic fields, and is more likely. No one ever talks about that.

Both these are real things we measure with radiotelescopes.

They are not strong enough to produce the necessary effects, they are however interesting phenomena - https://arxiv.org/pdf/1302.5663.pdf.

Re: 'Dark fluid' with negative mass could dominate the universe

#25

Post by jazzyjackson »

DiabloD3 wrote: post #7

A "dark fluid" with negative mass COULD dominate the Universe, sure. But so could galactic-scale electric currents and magnetic fields, and is more likely. No one ever talks about that.

don't EM fields require a persistent source?

Re: 'Dark fluid' with negative mass could dominate the universe

#26

Post by AnimalMuppet »

shepardrtc wrote: post #21
mrfusion wrote: post #11

Earlier quoted context omitted.

Are they pretty sure it’s different than antimatter? Last I heard we weren’t sure if it has negative gravity or not.

Matter-antimatter annihilation would produce gamma rays that are detectable. I believe there was a study that went looking for that but didn't find anything.

To clarify (presuming I understand correctly): Antimatter might have negative gravity, but dark matter can't be antimatter, because we'd see the gamma rays from the collisions.

Re: 'Dark fluid' with negative mass could dominate the universe

#27

Post by jetrink »

darkWWWeb wrote: post #5

Every " dark " physics piece is essentially a science opinion piece, with " darkness " included in the title as the general prevailing clickbait advertising strategy, because the layperson interpretation is that it implies sinister mysteriousness. It's never news, it's just a refresher listing of unknowns.

The word 'dark' is used in titles because the articles are about the nature of dark matter and dark energy, which are widely accepted terms. You would have to go out of your way not to use the word dark when talking about these subjects and it would make titles less descriptive.

Re: 'Dark fluid' with negative mass could dominate the universe

#28

Post by blincoln »

duality wrote: post #13
galadran wrote: post #8

Paper: https://arxiv.org/pdf/1712.07962.pdf Not a physicist, but my summary of the author's point would be: If you allow for matter with a negative mass and plug it into a n-body simulation. You seem to get what looks like dark matter from first principles. Namely, a halo of non interacting matter around galaxies in just the right "non-cuspy" shape. Their conclusion is that this is worth considering, as almost all ma…

"Every other force besides gravity is polarised, so why not also gravity?" Gravity is mediated by a spin-2 gauge boson, the graviton, whereas the other known fundamental forces are mediated by vector (spin-1) bosons. There is an exercise in Peskin & Schroeder (I believe) working out the lack of a gravitation "repulsion" resulting from this difference. That being said, I think this kind of phenomenology is excellent a…

My understanding is that the entire existence of the graviton is still theoretical. Has that changed recently?

Re: 'Dark fluid' with negative mass could dominate the universe

#29

Post by jerf »

XorNot wrote: post #24
DiabloD3 wrote: post #7

A "dark fluid" with negative mass COULD dominate the Universe, sure. But so could galactic-scale electric currents and magnetic fields, and is more likely. No one ever talks about that.

Both these are real things we measure with radiotelescopes. They are not strong enough to produce the necessary effects, they are however interesting phenomena - https://arxiv.org/pdf/1302.5663.pdf .

The biggest tell that the Electric Universe theory is bunk is that anybody who ever talks about it can't hardly get two sentences in before dropping in the "but nobody ever talks about magnetic fields or electric currents at this scale"... which is easily observed to be utterly false. Astrophysicists talk about it a lot, and you can find even more discussion if you add "plasma" to the search terms.

If Electric Universe advocates are so wrong about something so easy to check, it doesn't give me much reason to check out anything else they say. (The fact that I have done so nevertheless and I've never managed to find them making an actual prediction is another. It seems to be one of those recursive handwave theories that never quite lands on anything concrete no matter where you search, but it sure does know that the standard theory is wrong.)

Re: 'Dark fluid' with negative mass could dominate the universe

#30

Post by mrfusion »

AnimalMuppet wrote: post #26
shepardrtc wrote: post #21

Earlier quoted context omitted.

Matter-antimatter annihilation would produce gamma rays that are detectable. I believe there was a study that went looking for that but didn't find anything.

To clarify (presuming I understand correctly): Antimatter might have negative gravity, but dark matter can't be antimatter, because we'd see the gamma rays from the collisions.

But if they’re repelling each other and for billions Of years. Why should there be any collisions?
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