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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

#171

Post by millstone »

thaumasiotes wrote: post #155
FabHK wrote: post #137

Earlier quoted context omitted.

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…

So, electrons are attracted to protons by the electromagnetic force, but they don't make it all the way there because they are repelled by some other force. You don't have a paradox because our model of the electromagnetic force doesn't specify that it's the only force there is. But if a negative mass is moving towards you and encounters a repulsive force, that repulsive force will, by definition, move the negative m…

> 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't fall in: if you try to push the electrons into the nucleus, you necessarily localize the electron into a smaller volume; this means its wavefunction must get "spikier" and therefore it has more kinetic energy. This kinetic energy rises faster than the potential energy drops, so the state of lowest energy is actually found at an average radius > 0.

Note that it took quantum mechanics to rescue the atom. A classical electron could fall into the nucleus.

I do not see any problem with a negative-mass particle accelerating towards the force. The analogy with opposite charges seems right to me.

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

#172

Post by astrocat »

sp332 wrote: post #9
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.

Maybe it was modeled as a curvature of space? So positive masses curve space so that everything moves toward them - including light, massless particles, and negative mass. And negative mass repels everything, including other negative mass, by shaping space differently. [Edit: jbay808 has a better explanation below, and negative mass attracts negative mass.] That behavior is described here https://en.wikipedia.org/wik…

Yeah this helped me create a mental picture that kind of makes sense. It would clarify why negative mass is also concentrated in areas of high mass, and could also provide the mechanism for constant universe expansion, as the space between masses is constantly being pushed away by the diffuse negative mass. Heh, armchair physics is fun :)

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

#173

Post by vesinisa »

thaumasiotes wrote: post #155
FabHK wrote: post #137

Earlier quoted context omitted.

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…

So, electrons are attracted to protons by the electromagnetic force, but they don't make it all the way there because they are repelled by some other force. You don't have a paradox because our model of the electromagnetic force doesn't specify that it's the only force there is. But if a negative mass is moving towards you and encounters a repulsive force, that repulsive force will, by definition, move the negative m…

> But if a negative mass is moving towards you and encounters a repulsive force, that repulsive force will, by definition, move the negative mass further toward you

I am not sure you understand what "repulse" means..

Joking aside, it's easy enough to imagine negative gravity. Do you mean that such counter intuitive behavior would be the natural consequence of negative inertial mass?

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

#174

Post by Novashi »

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…

Positive mass has a speed limit though, so I think there would be an upper limit on the amount of force returned?

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

#175

Post by RootKitBeerCat »

Completely a layperson who’s only read science for the masses type physics and astrophysics, but now imagine that there are all sorts of undiscovered phenomena that are actually just the inverse of existing properties of nature we know. Does that make sense, or resonate with more rigorous scientists, Reade archers, students?

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

#176

Post by archibaldJ »

radarsat1 wrote: post #132

> Air bubbles in water can be modelled as having a negative mass. Forgive the naive take on this, but it's a weird point to me... if air bubbles in water can be modelled as having negative mass, but clearly do not (they are made of particles with positive mass), then they are only "negative" in relation to the material surrounding them. So even if they can be modelled this way successfully, clearly the model doesn't…

The concept of whether something is "real" is a metaphysical amusement. And it is never meant to be answered in modern physics. Physics has come a long way into what it is today from natural philosophy. I believe all physicists in this day and age subscribe to the notion of model-dependent realism in one way or another. https://en.m.wikipedia.org/wiki/Model-dependent_realism

Perhaps someday in the distant future we will discover that many assumptions in physics are simply wrong since we really do indeed live in a computer simulation and it is one where the Von Neumann architecture holds so it is always possible to alter "physics laws" like the Pauli exclusion principle and "physics constants" like the speed of light. And these "physics laws and constants" do get altered under certain if-statements or else there will be bugs and the simulation will crash, rebooting itself as a result.

Or perhaps this simulation does crash and reboot itself very often. It's like elixir. We simply are not aware of it. Maybe that could be why we have things like the Heisenberg uncertainty principle and quantum tunnelling.

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

#177

Post by phs318u »

deytempo wrote: post #166
FabHK wrote: post #137

Earlier quoted context omitted.

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”

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, spacetime singularity.

In practice, only 1 really matters. However, 2 tends to bug a lot of people (consider the arguments around what the quantum world really represents). I'm one for whom 2 is important. "But what does it really mean?"

Back to your original point, looking at the paper [0], it doesn't seem too ridiculously hard to validate the math for someone familiar with this space (see what I did there?), unlike me who has forgotten everything I was taught [1].

[0] https://arxiv.org/pdf/1712.07962.pdf

[1] I have a physics degree but that was 33 years ago and I've been doing nothing but IT since.

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

#178

Post by InclinedPlane »

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.

Negative mass is like playing opposite day. Negative mass is attracted to other negative mass, but because of the inverse acceleration to force relationship of negative mass the end result is that it is pushed away from other negative mass. Negative mass would also repel positive mass, which is straightforward for the positive mass but for the negative mass (again, inverse acceleration) it would end up with an "attractive" motion toward the positive mass.

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

#179

Post by Filligree »

delecti wrote: post #93
excalibur wrote: post #66

Earlier quoted context omitted.

It is, we can't see them because they emit dark energy "light". /s

I know you put the "/s", but in case anyone isn't aware, as far as we know the photon is its own anti-particle. So light from anti-matter stars would still just be light.

Given the spacetime interval between photon creation and destruction is always zero, I'd find it moderately bizarre if there was an antimatter version of them.

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

#180

Post by Filligree »

archibaldJ wrote: post #176
radarsat1 wrote: post #132

> Air bubbles in water can be modelled as having a negative mass. Forgive the naive take on this, but it's a weird point to me... if air bubbles in water can be modelled as having negative mass, but clearly do not (they are made of particles with positive mass), then they are only "negative" in relation to the material surrounding them. So even if they can be modelled this way successfully, clearly the model doesn't…

The concept of whether something is "real" is a metaphysical amusement. And it is never meant to be answered in modern physics. Physics has come a long way into what it is today from natural philosophy. I believe all physicists in this day and age subscribe to the notion of model-dependent realism in one way or another. https://en.m.wikipedia.org/wiki/Model-dependent_realism Perhaps someday in the distant future we w…

Okay, but does this stuff break the weak energy condition? Could we build Krasnikov tubes with it?
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