A new study by astrophysicist Richard Lieu suggests that gravity can exist without mass, proposing thin, shell-like layers of ‘topological defects’ as an alternative to dark matter for explaining the gravitational binding of galaxies. This theory posits that these defects create a gravitational force without detectable mass, potentially eliminating the need for dark matter in current cosmological models
Lieu started out trying to find another solution to the Einstein field equations, which relate the curvature of space-time to the presence of matter within it. As Einstein described in his 1915 theory of general relativity, space-time warps around bundles of matter and streams of radiation in the Universe, depending on their energy and momentum. That energy is, of course, related to mass in Einstein’s famous equation: E=mc2. So an object’s mass is linked to its energy, which bends space-time – and this curvature of space-time is what Einstein described as gravity, a notch more sophisticated than Newton’s 17th-century approximation of gravity as a force between two objects with mass. In other words, gravity seems inextricably linked to mass. Not so, posits Lieu.
In his workings, Lieu set about solving a simplified version of the Einstein field equations that allows for a finite gravitation force in the absence of any detectable mass. He says his efforts were “driven by my frustration with the status quo, namely the notion of dark matter’s existence despite the lack of any direct evidence for a whole century.” Lieu’s solution consists of shell-shaped topological defects that might occur in very compact regions of space with a very high density of matter. These sets of concentric shells contain a thin layer of positive mass tucked inside an outer layer of negative mass. The two masses cancel each other out, so the total mass of the two layers is exactly zero. But when a star lies on this shell, it experiences a large gravitational force dragging it towards the center of the shell. “The contention of my paper is that at least the shells it posits are massless,” Lieu says. If those contentious suggestions bear any weight, “there is then no need to perpetuate this seemingly endless search for dark matter,” Lieu adds.
The next question, then, is how to possibly confirm or refute the shells Lieu has proposed through observations. “The increasing frequency of sightings of ring and shell-like formation of galaxies in the Universe lends evidence to the type of source being proposed here,” Lieu writes in his paper. Although he admits that his proposed solution is “highly suggestive” and cannot alone discredit the dark matter hypothesis. “It could be an interesting mathematical exercise at best,” Lieu concludes. “But it is the first [mathematical] proof that gravity can exist without mass.”
The study has been published in Monthly Notices of the Royal Astronomical Society.
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I’m not saying it’s dark matter
But it’s dark matter
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I don’t understand either, but dark matter always seemed unlikely to me. It doesn’t make sense that we couldn’t see it and the particles that could explain it seemed like they were invented just to justify dark matter. When I heard of modified gravity it just feels more plausible. Plus it was fun in the last years because there has been a lot of back and forth between supporters and those who want to disprove it.
Now this! Cant wait to watch this on Sabine hossenfelders channel!
dark matter always seemed unlikely to me
Yeah, same. I’ve always assumed (and probably read somewhere, too) that “dark matter” is basically a placeholder for some yet unknown phenomenon/energy/etc.
Yes. Anything “dark” (dark ages, dark matter) just means we don’t know what it is, basically. There’s a lack of information, we can’t see more.
It doesn’t make sense that we couldn’t see it and the particles that could explain it seemed like they were invented just to justify dark matter
It always seemed like a natural assumption to me: the particles we know about were discovered because they interact with each other via at least one other force in addition to gravity. But there’s no other force common to all particles, so why not expect particles that only interact via gravity? They’d naturally be hard to detect, since gravity is so much weaker than the other forces.
Assuming that the only particles that exist are the ones that happen to be easy for us to detect feels like observer bias.
It’s not intuitive. Especially having so much of it. I don’t know, I’m not a physicist, the modified gravity made more sense to me, even though it seemed unlikely for a time. It’s again more popular today.
I’ll go along with anything less bullshit than dark matter.
Well this one depends on negative mass, which is, as far as I know, no less weird and speculative than dark matter.
How much dirt is in a hole 3ftx3ft?
But wouldn’t that be more like the absence of matter? A hole is a negative space. But it’s not a negative mass.
It’s like gravity is a thing that is influenced by matter, but not the matter itself. The hole isn’t matter, but a shape caused by the arrangement, and that shape itself may have influential properties.
I’m guessing they mean like in the absence of energy, right? Because can’t massless photons warp spacetime as the get to higher and higher energies?
Well E=mc² so makes sense both can have affect spacetime.
But this researcher seems to suggest gravity can exist in a void.
If I’m reading his idea right it’s putting forth that the geography of space can (very simply) have an effect like natural hills and valleys, without mass nearby. He calls it shells, but I haven’t had enough coffee to wrap my mind around that image.
Space is 3D, so we would observe it as shells.
My layman’s interpretation anyway.
So, we are repurposing parts of string theory? These “shells” are postulated in string theory if I remember my Brian Greene… I agree with his view on dark matter, it’s starting to become more than just a placeholder.
I think he means the very large cosmic strings that appear when you look at the universe on the scale of galactic clusters.
I could be misreading it though.This was my takeaway from this as well. I’ll have to see if I can locate an Arxiv copy of the full paper, but this just seems more like a thought exercise to explain dark matter using String Theory principles.
I’m going to have to hold my thoughts until I hear what Terrance Howard has to say about this
I don’t get the reference? lol
He can kill gravity apparently
Ah, okay. lol. Still lost, but less so.
My best guess was that he was the center of the universe (re: getting fired from Iron Man). lol
He has some wild ideas. Inventing new math ideas
I suggested something like this in high school.
“If gravity is the deformation of space, and dark matter is matter that we expect to exist because of gravity, is it possible that dark matter isn’t real and instead we’re just seeing space deformed [on a local scope] without any mass?”
I’ve since been disuaded from this position by observations of dark matter between the remnants of collided nebulae, suggesting that whatever makes up dark matter doesn’t flow past itself as easily as diffuse gas. Unfortunately, I don’t understand the implications of my own conjecture enough to say if this was an expected result, but it seems unlikely.
Huh… I’m not smart enough to comment on the validity of this but it seems interesting.
Basically my take on it. It’s a new
theoryhypothesis on gravity, but I’m not equipped to properly peer review it. For me, it’s an interesting read and is from a reliable source.It’s a hypothesis - we need to be able to test it before it can become a theory. Think of this along the same lines as the solutions of the field equations that allow for black holes to be wormholes, or the correct configuration of spacetime can allow you to travel through time.
It’s certainly interesting though
Thanks for pointing that out. Updated my comment. “Theory” has a specific meaning in science, so definitely don’t want to use that when it’s not.
Tangent: Whenever the news reports a major earthquake somewhere, I like to remind people that Plate Tectonic Theory is “just a theory” and that some religious leaders confidently assure us that earthquakes are caused by promiscuous women.
Almost missed this precious comment. TY for the smile.
My favorite of late was the congressman who said the eclipse was a result of our hedonistic ways. Surely the moon would move to a different orbit if we made trans illegal.
So what you’re telling me is we should be more hedonistic to get cool astral phenomena?
I think it’s just a shit stirring paper to say “look, here’s something that has zero observational evidence to its existence and look how ridiculous it sounds. Dark matter also has zero observational evidence, so why is that not ridiculous?” Which I’m not sure I agree with, but based on the faaar stretches he makes in the paper and the comments by the author later, that’s what I gather.
Source: I am a PhD student in physics
What exactly is negative mass?
The weight of your brain. Gottem
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These sets of concentric shells contain a thin layer of positive mass tucked inside an outer layer of negative mass.
The next question, then, is how to possibly confirm or refute the shells Lieu has proposed through observations.
First, we take some negative mass… Oh, wait.
Still, fresh blood!
Would negative mass be the same as antimatter?
No antimatter has normal mass. It behaves just like normal matter it just has the opposite charge for it’s fundamental particles.
It’s a good question though. Although it was expected that antimatter would fall down not up it wasn’t proven experimentally until 2023.
So in terms a biologist can understand: If it’s not charge what is the difference between normal and negative matter?
Mass makes a dent in space time changing the path of objects. That effect we call gravity. Think a person on a trampoline with balls rolling bye. Negative mass would flatten space time or make a hump in it.
The idea here is sort of like an atom looks neutral from far away if you get close there is a big positive charge in the center and a big negative charge in the electron cloud.
So you have normal mass from far away but some wierd effects at very small distances that have effects.
The charge is the difference.
I’m saddened that you’re being downvoted for this correct reply.
These sets of concentric shells contain a thin layer of positive mass tucked inside an outer layer of negative mass.
So how much evidence is there for negative mass, then? Sounds like just replacing one unknown with another.
Moreover, as the width of the two Gaussians tends to zero, there is no finite spherically symmetric region (be it cavity or shell) over which the integral of ρ(r) yields a resolvably negative mass m(r) and its potentially undesirable consequences.
damn I am a cave person
Yeah apparently gravity can be caused by gravity, which is how gravitational waves work.
Gravity begets gravity.
Slightly related question: if mass/energy distorts space, creating gravity, why is radiation massless?
Because radiation = photons.
To elaborate, photons do not have mass. Radiation has no mass. Because they have no mass, they can travel at the speed of light without distorting space and time.
And just to further clarify, even though they are massless, photons are effected by gravity. So they will whiz through space at C and then follow the curvature of space that’s around an object (which creates the warped lensing effect around stars) and continue on their way afterwards.
But they have energy, which distorts space too, no?
I don’t think it is. If there are photons bouncing around in a material it contributes to its mass. Thought it’s an interesting question, does a singular photon traveling through space warp spacetime?
Also photons being defined as massless is the reason they can travel at the speed of light.
Photons have zero rest mass, right? They have mass while moving, don’t they?
It helps to realize that mass is just a bookkeeping label that we assign to the “internal” energy of a system, where the choice of what counts as being “internal” is somewhat arbitrary and depends on the level we are studying.
For example, if you measure the mass of the nucleus of some atom, and then compare your measurement to the sums of the masses of the protons and neutrons inside of it, then you will see that the numbers do not agree. The reason for this is that much of the mass of a nucleus is actually the energy of the strong force bonds holding the nucleons together.
But you can actually drop down another level. It turns out that the vast (~ 99%) majority of the mass in the proton in turn does not come from the quarks but from the energy of the gluon field holding them together.
And if you drop down yet another level, the quarks get their mass through their interactions with the Highs field.
So in short, it is energy all the way down.
So gravity is
the weak forceall forces scaled up?Uuh, reading up on the 4 forces again, there’s bosons and stuff. Looks like i simplified a few things in my memory.
