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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

#11

Post by mrfusion »

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.

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

#12

Post by jbay808 »

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.

To approximate with Newtonian laws:

F=ma

Meaning that positive and negative masses will accelerate in opposite directions in response to the same applied force. The effect is different, but it's a bit like how when you are in a car and hit the gas pedal, and your kid is in the back seat holding a helium balloon, the kid feels pushed backward into the seat but the balloon flies forward toward the windshield.

F = GMm/r^2

Meaning that gravitational forces between opposite signed masses is the opposite direction from the force between masses of the same sign.

Thus, the gravity force repels the normal mass away, but this repulsive force actually drags the negative mass along with it, because the negative mass accelerates the wrong way when "repelled".

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

#13

Post by duality »

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 and raises lots of interesting questions. There may be reason to rule out this author's new idea, or maybe rethink an established tenet. That's why science is such an exciting field.

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

#14

Post by mklauber1 »

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 think what they're saying is that positive mass galaxies attract the negative mass, even as the negative mass repels the positive mass (and all other negative mass). In a stationary system, eventually the two will reach an equilibrium.

However, the effects of this in a system in which the positive mass galaxy is spinning is that the negative mass counteracts the forces of inertia, allowing the galaxy to spin at higher speeds without shattering like a cd spun too quickly. Now, whether the math of all that makes sense, I'm am not in a position to comment on.

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

#16

Post by zamalek »

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…

> 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, may be answer. Focusing all our energy on one explanation (that has been falsified more than once) seems like a waste.

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

#17

Post by zamalek »

jbay808 wrote: post #12
ams6110 wrote: post #6

Earlier quoted context omitted.

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.

To approximate with Newtonian laws: F=ma Meaning that positive and negative masses will accelerate in opposite directions in response to the same applied force. The effect is different, but it's a bit like how when you are in a car and hit the gas pedal, and your kid is in the back seat holding a helium balloon, the kid feels pushed backward into the seat but the balloon flies forward toward the windshield. F = GMm/r…

We have an intuitive ~~example~~ approximation of this in real-life: balloons in a car[1].

[1]: https://www.youtube.com/watch?v=uAJlg8MDAlU

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

#18

Post by autopoiesis »

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).

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

#19

Post by raverbashing »

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…

Given there have been no detections of individual gravitons, saying it's a spin-2 gauge boson is speculation at best (though it might be what the model predicts)
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