Earlier quoted context omitted.
How?
By offsetting the mass of a system, to produce a zero mass vehicle.
Take a net negative mass vehicle, and accelerate it by having it collide with its propellant. Would this be an anti-rocket?
'Dark fluid' with negative mass could dominate the universe
191–200 of 302 posts
Re: 'Dark fluid' with negative mass could dominate the universe
#192Paper: 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…
Actually the lagrangian is not minimized, it is merely stationary. An example of this is the harmonic oscillator, the lagrangian is clearly not bounded from below.
Re: 'Dark fluid' with negative mass could dominate the universe
#193Negative mass is required to produce warp drive... We might not be stuck here forever
Re: 'Dark fluid' with negative mass could dominate the universe
#194Earlier quoted context omitted.
Yes, because they are fluctuations of the metric tensor field, a symmetric rank-2 tensor. Take a look at https://en.wikipedia.org/wiki/Graviton#Gravitons_and_renorma... for details.
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.
Re: 'Dark fluid' with negative mass could dominate the universe
#195Paper: 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…
I think this might be dumb, but, what if negative mass was just positive mass in some alternative dimension? If mass could be negative with respect to our observable space time, does that actually mean it is a binary kind of thing, or could there be lots of mass in lots of others semi-or-non-interacting dimensions? Maybe even the mass we can observe is only part of anything’s actual substance...
Re: 'Dark fluid' with negative mass could dominate the universe
#196One of the most interesting properties of matter with negative mass is that if something collides with it it accelerates in the opposite direction of the incoming object.
Re: 'Dark fluid' with negative mass could dominate the universe
#197Would this be only gravitational mass that's negative or would it be both gravitational mass and inertial mass? Because negative inertial mass is zany and wierds me out. Negative gravitational mass behaves in a way that makes sense to me.
The paper uses the version where both gravitational and inertial mass is negative. This means that everything wants to accelerate towards positive mass and away from negative mass. So positive mass naturally forms clusters (galaxies) and negative mass naturally spreads out evenly but concentrates around the galaxies (forming the dark-matter halos).
Re: 'Dark fluid' with negative mass could dominate the universe
#198Earlier 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…
> that repulsive force will, by definition, move the negative mass further toward you.
only if the repulsive force is negative gravity.
If a positive-mass electron attracts a negative-mass electron, the repulsive electromagnetic force will still keep them from making it all the way there.
Re: 'Dark fluid' with negative mass could dominate the universe
#199Earlier quoted context omitted.
> If you stand on the balloon it doesn't make sense to ask "where is the balloon expanding from?". Sure it does, and there is a well-defined answer, it's just the answer does not lie on the surface of the balloon. (And for a perfectly spherical balloon, is equidistant from every point on the surface.)
That of course only works because the surfaces of balloons we are used to are always embedded in spacetime. There is however no [good][known] reason to assume that spacetime itself is embedded in any space.
I've always thought this would be an interesting experiment. Assume that spacetime does live in a higher dimensional space, and try to arrange masses so that spacetime is forced to intersect itself. See if anything interesting happens.
Of course this probably requires some stellar engineering.
Re: 'Dark fluid' with negative mass could dominate the universe
#200Earlier quoted context omitted.
"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…
My understanding is that the entire existence of the graviton is still theoretical. Has that changed recently?
It's hypothetical, but less so than a lot of the things theoretical physicists consider.
Any quantum theory which reduces to general relativity in the classical limit will look like a theory of gravitons when quantum effects are small. This is just how the math works out in effective quantum field theories involving massless spin-2 particles.