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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

#231

Post by d--b »

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.

This is being tested at CERN:

https://cerncourier.com/does-antimatter-fall-up/

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

#232

Post by RootKitBeerCat »

hirundo wrote: post #34

What's the relationship between negative mass and negative gravity and anti-gravity? Dark fluid is repulsive, so is it theoretically possible to collect a ball of it, put it between you and another positive mass, and fly apart?

Yes, that is essentially my understanding

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

#233

Post by starbeast »

feanaro wrote: post #224
marcosdumay wrote: post #108

Earlier quoted context omitted.

> Or do I have that wrong and photons merely follow the distortions and not cause any of their own? You have that wrong in the momentum of massless particle has mass, independently of its carrier. Massless particles do not actually exist, what exist are particles with zero "mass at rest" and that are never at rest.

You're talking about relativistic mass, but that isn't a commonly used concept anymore. Today it is indeed the norm to think of "mass" as being the mass at rest. Massless particles are really massless and have momentum without having mass.

In which case, we seem back to having two things distorting spacetime. Could mass just be the momentum of massless particles going in really small circles such that you can pack them together and call them matter?

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

#234

Post by wallace_f »

thaumasiotes wrote: post #218
wallace_f wrote: post #212

Earlier quoted context omitted.

Thanks, that's obviously a much better way to think about it. However, you're wrong in at least the typical physics definition of inertia found in dictionaries is in fact, "resistance of change (velocity, acceleration, momentum)." In that same framework, the maths definition of inertia is also momentum = mv and a google search confirms this. What would negative momentum even look like? Because that's not just movemen…

Velocity, the v in the definition of momentum, is also a vector, so yes negative momentum is just momentum in the opposite direction from positive momentum, whatever direction that may be. Inertia is generally not defined as being momentum, because an object's momentum in any direction increases along with its velocity in that direction, while we like to think of inertia as being determined solely by mass. https://en…

But that's what I just said: resistance to change in v, a, p are the dictionary definitions I found on Google.

You're right about v. I thought a negative velocity was equally absurd, but it looks like it's defined as a vector which makes sense of course. The last time I took a proper physics course was in high school. How embarassing though, as I've read and watched more popular science/physics material than most people, probably. Hah.

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

#235

Post by throwaway487550 »

How abstract concepts, introduced to establish artificial symmetry, could be used to describe aspects of reality which does not rely on any abstract notions whatsoever?

Some processes are symmetrical to an outside observer, which does not imply that anything must be or should be symmetrical. It is an observer's preference to see symmetry everywhere.

There is no such fucking things as "dark" liquids or negative "masses" merely because a model superimposed on reality have nothing to do with reality itself.

The impossibility is the same as the principal impossibility of revealing the CPU's actual wiring from the level of code it runs. There is not a single fucking way to do it in principle, no mater what fancy guesswork one would use or what kind of a wrongly simulated model one will superimpose on what one is able to "see" and examine.

This is not even science, but some sort of contest of abstract theology, crafted to please fellow reviewers and sectarians.

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

#236

Post by drjesusphd »

btilly wrote: post #182
millstone wrote: post #171

Earlier quoted context omitted.

> they don't make it all the way there because they are repelled by some other force A repulsive force is not the best way to think about it. The potential of the nucleus is the usual -1/r, and goes to (negative) infinity at zero. A repulsive force would be incorporated into the potential and appear as a bump around the nucleus, and would mess up the electron orbital. A hand-wavy explanation of why the electron doesn…

A different hand-wavy explanation. The places that an electron can be found are described by a wave pattern. If the electron is staying in place around a nucleus, that wave pattern has to be a standing wave that reinforces itself. To reinforce itself it has to wrap around the nucleus an integer number of times. This explanation doesn't just explain why it doesn't fall in, it also explains why there are discrete shell…

This is the Bohr model of the atom, but was replaced by a proper quantum theory.

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

#237

Post by drjesusphd »

feanaro wrote: post #225
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…

Well GR is potentially very wrong both at very large scales (seemingly requiring dark matter and dark energy) and very small scales (due to known present incompatibilities with quantum mechanics). It's only been shown to be a highly accurate model everywhere in between.

I think both dark matter and dark energy are perfectly consistent with GR. Hitherto unobserved matter would contribute to the stress energy tensor and dark energy is (I believe - has this changed?) the cosmological constant.

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

#238

Post by gus_massa »

mklauber1 wrote: post #15

I'm curious about the idea of "allow[ing] negative masses to not only exist, but to be created continuously." Given the law (in the scientific sense) that matter/energy cannot be created or destroyed, on a scale of 1 to FTL travel, how crazy is this idea?

Probably more close to 1 to than FTL travel.

This is very new research without a deep check by other groups and without experimental support, so wait 5-10 years before getting too attached to this result. Anyway, there are weird somewhat similar things that are cannon https://en.wikipedia.org/wiki/Vacuum_expectation_value

The technical details and the experimental support are very very very important to distinguish between weird things that are true and weird things that are false.

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

#239

Post by drjesusphd »

krastanov wrote: post #194
AnimalMuppet wrote: post #98

Earlier quoted context omitted.

That does not appear to have any details that relate to your comment whatsoever. All it says is that renormalization doesn't work on gravitons. However, if I understand your comment correctly, you're saying that the underlying non-quantum theory (GR) uses a symmetric rank-2 tensor, therefore you have to have a spin 2 particle - as opposed to photons, whose underlying non-quantum theory has an antisymmetric rank-2 ten…

I recollect that Feynman's Lectures on Gravitation (Frontiers in Physics) has an amazing and detailed explanation.

"Quantum field theory in a nutshell" also covers this well.

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

#240

Post by v_lisivka »

phs318u wrote: post #177
deytempo wrote: post #166

Earlier quoted context omitted.

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”

Physics is highly mathematical and as such, can indeed be "tested" (i.e. proven) to be consistent with mathematical laws. This is fairly straightforward (for suitably mathematically literate people). The real issues are: 1. can the theory make testable predictions that can be verified by observation? e.g. string theory has had issues with this. 2. what does "mean"? e.g. negative mass, spooky action at a distance, spa…

1. OpenGL makes good predictions. Why not to switch to OpenGL terms when talking about physics?
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