Gravity Without Mass Could Explain Dark Matter

I recently read that you can have gravity without mass. Ha, no way, I thought and had a look at the paper. It's wild, people. The author says that there are hollow spheres scattered across the universe that have no gravitational attraction and that these spheres explain dark matter. I will try to sort it out for you.

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#science #sciencenews #darkmatter #astrophysics #physics

[slaphead]

Honestly it's got to the stage where if somebody wrote a paper saying "it's not dark matter, it's magic moonbeams", then, quite frankly, I'd consider that just as valid as any other explanation so far.

[hermaeus_jackson]

Wow, what a clever solution. Instead of the effects of dark matter being caused by undetectable positive-mass particles, they're caused by undetectable NEGATIVE-mass particles. Truly... stunning thought process there.

[alieninmybeverage]

"...suppose you have a laser-eyed unicorn, but let's leave this aside for now. I'll come back to this later."

Promises were made!!

[leeoldershaw]

Time to apply Occams razor and look for flaws in the theories that predict dark stuff.

[adbraunstein]

"It's like when people complain about me on Twitter. It averages out to zero." Literally LOLed at that one. Well done!

[mecha-sheep]

This is basically like "we can't find dark matter, MOND does not work... let's try invisible pink unicorn pulling stars with giant harness".

[yeroca]

If the mass is effectively zero, how does it somehow still curve spacetime?

[krensak]

If the equivalence principle continues to hold for negative mass (i.e. if gravitational and inertial mass are the same), then a negative mass, while being repelled by a positive one, would still accelerate towards the positive mass, because the direction of force and acceleration would be opposite. You could immediately construct a self-accelerating structure by fixing two opposite masses to the ends of a stick. The positive mass would always try to accelerate away from the negative one (because it is repelled and the force on it and its acceleration have the same direction), the negative mass would always try to accelerate towards the positive one (the force on it points away from the positive mass but it accelerates in the direction opposite to the force), so our stick would accelerate in the direction pointing from the negative to the positive mass... Of course, this would immediately lead to problems with momentum and energy conservation (if the stick itself was not massless).

[jimsackmanbusinesscoaching]

I have been curious for a long time about the potential of space-time curvature from powerful enough photons. That would not explain dark matter or anything, but I am curious about this from a mass-energy equivalence and some descriptions of gravity that I have read.

[jounik]

01:22 That explains why I suddenly can't find my laser-eyed unicorn anywhere.

[whatitmeans]

I have few questions:
i) Why it is llamative to have gravity without mass? So far I know it is exactly what happens in stable Lagrange points like L4 and L5
ii) Could be considered what happens in unstable Lagrange points L1, L2, L3 as a negative mass point?

[bartroberts]

There appears to be a divide by zero issue somewhere in the logic of this example. Hardly the most significant issue with the idea, but still: acceleration is produced in the space between the two shells? But there's no space between the two shells.

[MrMSBranham]

I'm thinking your analogy of a mass offset from the center of a hollow sphere is being wrongly integrated. If I approximate all opposite directions using a simple episol delta approximation there is a net attraction to the nearer wall. You have to integrate in two halves based on calling one side positive for the nearer wall and one side negative because that force is in the opposite direction. It only balances perfectly if the nass sits at the center of the sphere.

[Dinofaustivoro]

We should not be looking for an "unknown kind of mass" but for an "unknown source of gravity".

[Thomas-gk]

As a passionated biker, I support the physics of snacks: You indeed have to pedal faster if you want to fix the mass while consuming snacks. Either the mass or the acceleration increases, law of energy conservation confirmed and (E=mc²).
Seriously, even if there are negative mass particles out there, which astrophysical process would be conceivable to create such a shell?

[petertard]

Gravity travels at the speed of light, which means a particle could exist for long enough to exert a gravitational effect but disappear before it can be detected. That means that particles which could not exist on their own, like quarks, might exist on their own for long enough to cause gravity, but disappear before they could be detected. But quarks are not supposed to exist on their own. They might do.

[nadiakent]

I know that Sabine has said in the past we got to get away from theories that were developed in closed room and a calculator, and instead do some experiments to find truth. I agree. Such speculations and it is here is really useless.

[t.h.]

1:59 this isn't quite correct: since the acceleration is determined by the force as well as the mass (a = F/m), the negative mass would still be attracted to the positive one, while the positive is repelled by the negative. But I guess this doesn't affect the rest of the video in any way.

[earlygenesistherevealedcos]

I have thought for years that virtual particles, which are always popping in and out of existence in an instant, made a bit of contribution to gravity before they vanished. I think this is where much of the supposed missing dark matter is coming from. Apparently certain conditions make them last a bit longer in some places which we see as extra gravity.

[jimalbi]

Your negative mass could be made of WIMPs so it would have hard time clumping together, just like neutrinos. You'd have a galaxy-cluster size fuzzy transparent cloud of WIMPs.
Those would be likely to «cluster» in the great intergalactic voids and might leave an observable trace in the CMB or by «concave» gravity lensing.