Presumably you could describe this as a theory of levity. For happy spacetimes.
'Dark fluid' with negative mass could dominate the universe
101–110 of 302 posts
Re: 'Dark fluid' with negative mass could dominate the universe
#102Paper: 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…
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 hand. This is a positive feedback loop that immediately results in the object and your hand exerting infinite amounts of force on each other, because applying force just leads to applying more force.
Re: 'Dark fluid' with negative mass could dominate the universe
#103> 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...
Re: 'Dark fluid' with negative mass could dominate the universe
#104>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.
Positive matter creates a gravity well. This much most people are familiar with.
Seems to me what they're saying is that this well will pull in negative matter until a balance is reached, this will, in turn exert force on the internal structure of the galaxy.
Re: 'Dark fluid' with negative mass could dominate the universe
#105Paper: 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…
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…
Don't you have two things that can generate gravitational fields though? As distortions in spacetime can be caused by either mass or the momentum of massless particles, such as photons. Or do I have that wrong and photons merely follow the distortions and not cause any of their own? As presumably, you could have a negative gravitational field from a photon traveling backward in time, without having any issues with changes in inertial mass.
Re: 'Dark fluid' with negative mass could dominate the universe
#106>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.
Think of it as one pushes while the other one pulls.
Re: 'Dark fluid' with negative mass could dominate the universe
#107Earlier 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…
This assumes that the objects of opposite inertial mass are able to interact in the way you describe.
Re: 'Dark fluid' with negative mass could dominate the universe
#108Earlier 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…
Don't you have two things that can generate gravitational fields though? As distortions in spacetime can be caused by either mass or the momentum of massless particles, such as photons. Or do I have that wrong and photons merely follow the distortions and not cause any of their own? As presumably, you could have a negative gravitational field from a photon traveling backward in time, without having any issues with ch…
> 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.
Re: 'Dark fluid' with negative mass could dominate the universe
#109Sounds a lot like the concept of the Dirac sea to me. https://en.wikipedia.org/wiki/Dirac_sea Rather than have dark matter particles, have negative mass dark matter particles in every other location instead.
This is explicitly very different from that. There's no claim of "negative mass dark matter particles" in _ever_ location, rather, they have a specific distribution.
That distribution being all the places that aren't normal matter particles. So primarily outside of galaxies.
Re: 'Dark fluid' with negative mass could dominate the universe
#110Earlier quoted context omitted.
> that has been falsified more than once What has been falsified more than once?
We haven't observed any of the predicted WIMPs at the LHC, as one example. They were subsequently relegated to a higher energy level.
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.