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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

#161

Post by FabHK »

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…

That's what the article (https://arxiv.org/pdf/1712.07962.pdf) says:

> In theories of quantum gravity, gravitation is mediated by the graviton – a massless, spin-2, boson. This means that any pair of negative masses would attract, and not repel as suggested in this theory. However, there are also theoretical arguments that gravitons cannot, and will not ever, be detected experimentally (Rothman & Boughn 2006). There appear to be two options: either it is possible that the graviton could be modelled as a bound state of a positive and a negative mass, in a theory of composite gravity or some other mechanism which provides a modification of graviton properties. Alternatively, this could also indicate that the proposed theory cannot be modelled by real, physical, particles, but rather by the presence of effective negative masses within a superseding theory.

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

#162

Post by nonbel »

acqq wrote: post #156
nonbel wrote: post #151

Earlier quoted context omitted.

> "only dark matter matches all." Dark matter can be placed arbitrarily so it can match pretty much anything. I remember recently there was a galaxy with negligible deviation of the GR-predicted rotation curve and that was taken as evidence for dark matter too (even though MOND was still the better fit for that case). "Dark Matter" started out ok but has become a "god of the gaps" argument, I expect eventually MOND o…

> Dark matter can be placed arbitrarily so it can match pretty much anything. Quite the opposite, and that statement is obviously uninformed. The science behind dark matter is very precise and exact. That's why the alternative theories can't come even near: once the same rigor which was applied to test dark matter is applied to the alternatives, the alternative theories simply break. > I'm afraid I have never seen th…

>"Quite the opposite, and that statement is obviously uninformed. The science behind dark matter is very precise and exact."

From what I have seen they can get precise post-dictions but not precise pre-dictions because there are so many free parameters (basically you can put dark matter wherever you need it).

>"I've given you the link to the complete articles and also highlighted the major points. Try to read and understand them fully, then search for more."

The claimed predictions from the 1970s and 1980s are not mentioned on that page.

Also, that "startswithabang" guy is more like a catholic inquisitor than a scientist. I wouldn't consider him a reliable source because this behavior indicates he lacks the required capacity for curiosity, he can only repeat what authority figures say:

"The blogger (@StartsWithABang) contacted @scilogscom on January 24 by replying to a 15-day old tweet that announced our blog’s move to the new domain. He tweeted “Bummed that @scilogscom is in the business of promoting contrarian scientist viewpoints.”, and asks the SciLogs.com community manager (@notscientific) “[Why] are you allowing @scilogscom to promote contrarian voices that undermine public understanding of [science]?”, adding “You have taken on “Dark Matter Crisis” blog, whose mission is to undermine all of physical cosmology & promote MOND.”

The two agreed to discuss the issue via email, with the blogger adding that he was “personally worried that you are promoting clicks & false controversy over quality science content”, and states that he is “very, VERY disappointed about this move that @scilogscom has made”.

By now the SciLogs.com community manager has explained to us what happened after these tweets. He and the publishing director responsible for SciLogs.com unfortunately assumed that the blogger’s criticism was justified. They decided to close our blog without conferring with others or asking us for a statement. After we complained about the discontinuation, they performed an internal investigation, which involved reaching out to astrophysicists and other people, and have realized that discontinuing our blog was a big mistake. We attribute SciLogs.com’s poor judgement to two factors: neither the community manager nor the publishing director has an (astro)physical background, it was the first time that SciLogs.com had experienced an attack against one of its blogs." https://darkmattercrisis.wordpress.com/2013/03/08/the-dark-m...

Anyway, I can tell you know even less about this topic than me so let's leave it at that.

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

#163

Post by deytempo »

thaumasiotes wrote: post #102
andrepd wrote: post #50

Earlier quoted context omitted.

Here's an argument: If you think about it, "mass" actually means two different things. One one hand, there is mass as the "charge" of gravitational interaction, that is, the gravitational field generated by a body is proportional to its mass. Let's call this concept "gravitational mass". On the other hand, you have mass in the sense of "intertial mass", a body's resistance to change of velocity. Although we kinda tak…

> On the other hand, you can show that the inertial mass cannot be negative (else the Lagrangian would not be bounded from below and therefore you could not minimise it; the whole of physics then comes crumbling down). Here's a purely thought-experiment argument for inertial mass not being negative: If you had an object with negative inertial mass, then pushing on that object would cause it to accelerate into your ha…

How do you think Thor’s hammer works when it’s sitting on the toilet seat?

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

#165

Post by dmurray »

dnautics wrote: post #135
acqq wrote: post #110

Earlier quoted context omitted.

That doesn’t disprove the “matter-like” observed behavior, it just shows that the particular assumptions under which exactly these non-found WIMPs were imagined were false.

If you have an infinite space of particle parameters and a series of tests keeps eliminating large swaths of this space, at some point it feels like you're playing a god of inbetweens game a la creationists arguing using gaps in the fossil record. There is a categorical difference, of course, but as a practical matter the parallels are useful, at what point do we table (for now) the search for the populist position a…

> If you have an infinite space of particle parameters and a series of tests keeps eliminating large swaths of this space, at some point it feels like you're playing a god of inbetweens game a la creationists arguing using gaps in the fossil record.

Or you're getting closer to finding out what the real parameters are?

If you eliminate all possibilities and have to make up some new parameters, sure, that feels like you're not doing science and might as well be a creationist. But what you describe, narrowing down the space of possible explanations from infinitely many to only a few, is the dream of every theoretical physicist.

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

#166

Post by deytempo »

FabHK wrote: post #137
thaumasiotes wrote: post #102

Earlier quoted context omitted.

> On the other hand, you can show that the inertial mass cannot be negative (else the Lagrangian would not be bounded from below and therefore you could not minimise it; the whole of physics then comes crumbling down). Here's a purely thought-experiment argument for inertial mass not being negative: If you had an object with negative inertial mass, then pushing on that object would cause it to accelerate into your ha…

Here's a thought experiment that shows that there can't be electrons: "If you had an object with negative charge, then putting that object near a positive charge would cause it to accelerate towards the positive charge." Getting closer increases the force. "This is a positive feedback loop that immediately results in the object and the positive charge exerting infinite amounts of force on each other, because" getting…

The problem with these papers is there is no compilers to perfectly test the logic except peer review so no one knows if its horse shit or not until someone comes along and comes up with some way to prove it wrong, so I would not be so quick to say “if that’s an obvious contradiction, the author would have caught it”

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

#167

Post by deytempo »

dragonwriter wrote: post #148
thaumasiotes wrote: post #102

Earlier quoted context omitted.

> On the other hand, you can show that the inertial mass cannot be negative (else the Lagrangian would not be bounded from below and therefore you could not minimise it; the whole of physics then comes crumbling down). Here's a purely thought-experiment argument for inertial mass not being negative: If you had an object with negative inertial mass, then pushing on that object would cause it to accelerate into your ha…

> If you had an object with negative inertial mass, then pushing on that object would cause it to accelerate into your hand. This is a positive feedback loop that immediately results in the object and your hand exerting infinite amounts of force on each other No, it doesn't; since this turns the repulsion of normal objects (which is what makes them resist interpenetration) into attraction by switching the orientation…

What makes us think the objects would actually interact at all?

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

#168

Post by ars »

privong wrote: post #103
ars wrote: post #45

> Negative masses are a hypothetical form of matter that would have a type of negative gravity – repelling all other material around them. Unlike familiar positive mass matter, if a negative mass was pushed, it would accelerate towards you rather than away from you. That assumes that inertial mass = gravitational mass, which is assumed to be true, not not proven.

> That assumes that inertial mass = gravitational mass, which is assumed to be true, not not proven. The assertion has been tested experimentally. Inertial and gravitational mass are seen to be equivalent within the bounds of experimental accuracy. The wikipedia article on the "Equivalence Principle" has lists of tests for various versions of the principle: https://en.wikipedia.org/wiki/Equivalence_principle#Modern_u…

And the negative mass postulated here? We don't know if it's still equivalent there because we have never tested it.

It would be a lot simpler if inertial mass was negative gravitational mass in this theory.

Then you have repulsive gravity with normal behavior under force.

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

#169

Post by deytempo »

nonbel wrote: post #147
duality wrote: post #56

Earlier quoted context omitted.

If it weren't, general relativity would be wrong as well and we know that (in its domain of applicability) it's a highly accurate model. GR models gravity as fluctuations in the metric tensor of spacetime, which is a symmetric rank-2 tensor. This is all you need to know to conclude that a graviton (a quantize fluctation of that tensor) must be spin-2. https://en.wikipedia.org/wiki/Graviton mentions "[I]t can be shown…

> "If it weren't, general relativity would be wrong as well and we know that (in its domain of applicability) it's a highly accurate model." Somehow I doubt it. I bet as a save someone would propose "dark spin" or some elaborate calculations that shows a few factors happen to cancel out exactly but no one noticed before now.

Dark spin? It spins in a direction that nothin else can?

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

#170

Post by dragonwriter »

deytempo wrote: post #167
dragonwriter wrote: post #148

Earlier quoted context omitted.

> If you had an object with negative inertial mass, then pushing on that object would cause it to accelerate into your hand. This is a positive feedback loop that immediately results in the object and your hand exerting infinite amounts of force on each other No, it doesn't; since this turns the repulsion of normal objects (which is what makes them resist interpenetration) into attraction by switching the orientation…

What makes us think the objects would actually interact at all?

I'm assuming that you can push in the classical sense but for what negative mass does to the equations, but sure, if you can't then the whole question is moot.
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