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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

#31

Post by nerdponx »

autopoiesis wrote: post #18
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…

Please post links to the arXiv abstract pages, everyone: we don't always want to download a PDF just to read the abstract! https://arxiv.org/abs/1712.07962 Edit to add: the abstract pages also often contain useful extra information, such as (in this case) a link to YouTube videos of the simulations -- https://www.youtube.com/channel/UC8ltFtaETXDphec0l-VxMsg -- or the publication history (in this case, a DOI is given)…

I actually started a Firefox extension that made a popup to redirect Arxiv PDF links to the abstract page, but never finished it for some reason.

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

#32

Post by [deleted] »

AnimalMuppet wrote: post #23
duality wrote: post #13

Earlier quoted context omitted.

"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?

[deleted]

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

#33

Post by wwarner »

ams6110 wrote: post #6
lawlessone wrote: post #4

>The gravity from the positive mass galaxy attracts negative masses from all directions, and as the negative mass fluid comes nearer to the galaxy it in turn exerts a stronger repulsive force onto the galaxy that allows it to spin at higher speeds without flying apart. I don't get this, seems contradictory.

I was just about to quote that same sentence. How can positive matter attract negative matter which at the same time is repelling positive matter? The author is described as an Astrophysicist at Oxford (a reputable place) so I assume I'm either just not getting it or this is poorly worded.

I didn't read that positive matter is attracting negative matter. What I gathered is that the presence of a cloud of negative matter in the right place would be held in place by mutual repulsion of the outer arms of the galaxy and the inner galaxy. And that the neg matter supplies enough repulsion to the diffuse outer galaxy that it can spin a bit slower than it would have to otherwise.

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

#35

Post by acqq »

zamalek wrote: post #16
duality wrote: post #13

Earlier quoted context omitted.

"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…

> raises lots of interesting questions Exactly. What I liked about MOND was that it basically amounted to "we don't know." The populist notion that dark matter is conclusively matter, and dark energy is energy seems a bold claim for such a young species. Crazy theories like non-universal constants are probably crazy, but they do explore unconventional lines of thought. One of those, most likely an unknown unknown, ma…

“What’s most impressive is that the predictions of dark matter were first made in the 1970s and 1980s, and were observationally confirmed later. This is not a case of tweaking the model to fit the data; this is a case of the best kind of science you hope for: where you make predictions, make the observations, and what you see validates and confirms the predictions you had made. And yet, even 35 years later, there are no modifications of gravity that achieve the galaxy-scale successes of MOND that also explain these other observations. The best tests of dark matter vs. MOND, which are on large, cosmic scales, have a clear winner and a clear loser.”

https://medium.com/starts-with-a-bang/theres-a-debate-raging...

In short: looking at everything we can observe and can model, we do know that the “dark matter” is matter. Because we first made predictions (“it should behave as matter”), then confirmed them, many times. And MOND can’t even explain that what’s already observed.

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

#38

Post by therein »

sulam wrote: post #20

Sounds a lot like phlogiston, especially since it apparently must be continuously created to matched observable behavior.

  Beware the Physical Chem, my son!
  The laws that arn’t, the constants that vary.
  Beware the phlogiston, my little one
  And of the molality be wary.

  He took his entropy in hand
  Long time the adiabatic foe he sought
  So rested he by the delta T
  And stood awhile in thought.

  And as in Newtonian Thought he stood
  The Physical Chem with Beer’s Law Plot,
  Came Bohring through the orbital wood
  And took quantum leaps when hot!
  PV! RT! And with fugacity,
  The entropy discharged his wrath.
  It reached a degenerate state, and being late,
  He returned by the mean free path
I wonder if anyone will recognize this. :)

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

#39

Post by lmilcin »

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…

The definitions you brought are tailored to what is our best understanding of the universe. Nobody ever said that these are immutable. Newtonian physics also must have felt rock solid, time and time again explaining new phenomena until it did not and there came about a better explanation.

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

#40

Post by Pxtl »

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.

If it's antimatter why isn't it coalesced into antigalaxies that we would be able to see visibly, and is instead diffused as a dark fluid?
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