Total crap made up to suit a failing theory of relativity and Big Bang.
'Dark fluid' with negative mass could dominate the universe
121–130 of 302 posts
Re: 'Dark fluid' with negative mass could dominate the universe
#122>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.
The galaxy is in the center, and with a large positive mass it attracts negatively-massed matter towards it. But the negatively-massed matter repulses rather than attracting, so it has the effect of "squeezing" the galaxy in on its self.
Re: 'Dark fluid' with negative mass could dominate the universe
#123Stupid non-physicist question here: we know the universe is expanding, but where does it expand at? Are there physical areas which we can observe growing? And if so, shouldn't that mean that we observe distant objects as lighter than their interactions with closer objects would imply?
Think of if space were just two dimensions and it was on the surface of a balloon. Space is expanding in the sense of inflating the balloon. Every point on the balloon is getting farther away from every other point.
If you stand on the balloon it doesn't make sense to ask "where is the balloon expanding from?". Its expanding in every direction. Every observer on the balloon sees all points around them getting farther away.
Now try to picture that but in 3d. It might help to think of it as like a cake with raisins in it expanding in the oven.
Re: 'Dark fluid' with negative mass could dominate the universe
#124Stupid non-physicist question here: we know the universe is expanding, but where does it expand at? Are there physical areas which we can observe growing? And if so, shouldn't that mean that we observe distant objects as lighter than their interactions with closer objects would imply?
Think of if space were just two dimensions and it was on the surface of a balloon. Space is expanding in the sense of inflating the balloon. Every point on the balloon is getting farther away from every other point. If you stand on the balloon it doesn't make sense to ask "where is the balloon expanding from?". Its expanding in every direction. Every observer on the balloon sees all points around them getting farther…
> 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.)
Re: 'Dark fluid' with negative mass could dominate the universe
#125Paper: 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…
Please post links to the arXiv abstract pages, everyone: we don't always want to download a PDF just to read the abstract! https://arxiv.org/abs/1712.07962 Edit to add: the abstract pages also often contain useful extra information, such as (in this case) a link to YouTube videos of the simulations -- https://www.youtube.com/channel/UC8ltFtaETXDphec0l-VxMsg -- or the publication history (in this case, a DOI is given)…
I am of the opposite opinion. Don't post links to the abstracts as the pdf's contain them too. But the pdf's also contain figures and other things which make it easier to browse, whereas the arXiv abstract page contains a lot of unnecessary fluff.
Re: 'Dark fluid' with negative mass could dominate the universe
#126If you put a negative mass and positive mass side by side and release from rest, they will accelerate indefinitely and break conservation of energy. Of course science should be open to any possibility, no matter how strange. But I feel the author understates its strangeness. And requiring negative mass to be continually created makes this theory not all that much "simpler" than the standard dark matter+dark energy.
They would accelerate indefinitely, but it wouldn't break conservation of energy. Gravitational force is inversely proportional to distance^2, so potential energy (integral from 0 to infinity of Force dx) still converges to a finite number. Same with normal gravity, but backwards.
I think the weirdness is, the distance between masses wouldn't change, they'd just accelerate together, in the same direction, indefinitely.
Both mass would experience negative repulsive force:
F=Gm(-m)/r^2
=-Gm^2/r^2
The positive mass accelerates away from the negative mass, because F=ma
=> ma=-Gm^2/r^2
=> a=-Gm/r^2
Now here's the kicker. If inertial mass (the m in F=ma), is the same thing as gravitational mass. Then, the negative mass accelerates towards the positive mass. Because
F=(-m)a
=> F=-ma
=> -ma=-Gm^2/r^2
=> a=Gm/r^2
So accelerates in same direction as positive mass.
Technically, conservation of energy & momentum is maintained, because the negative kinetic energy of negative mass would cancel out positive energy of positive mass.
But I think the above can't be natural, because the magnitude of kinetic energy would grow to infinity, leading to even more impossibilities.
So you'd need to 'hack' the theory of gravity and make inertial mass different to gravitational mass. So the particle has negative gravitational mass, but positive inertial mass, to make laws of physics stay sane :)
Re: 'Dark fluid' with negative mass could dominate the universe
#127Earlier 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…
That's assuming your hand has negative inertial mass.. which I'm assuming it doesn't.
Your scenario could create a black hole if I'm understanding correctly. Enough 'negative inertial mass' trapped in a feedback loop..
Re: 'Dark fluid' with negative mass could dominate the universe
#128Reminds me of this (very old) theory of gravity: https://en.m.wikipedia.org/wiki/Le_Sage's_theory_of_gravitat...
Re: 'Dark fluid' with negative mass could dominate the universe
#129Would 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.
Has to be gravitational only. Otherwise positive mass is repelled from negative mass, but the negative mass accelerates towards it. So both masses accelerate in the same direction, until they have infinite kinetic energy!
Conservation of energy & momentum would still hold, because negative mass would have negative energy & momentum, cancelling out that of the positive mass.
But the above surely would be an 'unphysical' situation.
Re: 'Dark fluid' with negative mass could dominate the universe
#130Earlier quoted context omitted.
Strong nuclear force is always attractive.
It most definitely isn't. https://en.wikipedia.org/wiki/Nuclear_force
Apologies, you are correct, jumped the gun a bit there.
It's repulsive at short distances, attractive at longer distances. And oddly, the longer the distance, the stronger the force, it doesn't follow the inverse square law!