Gravity can exist without mass, dark matter could be myth: Study
Gravity can exist without mass, dark matter could be myth: Study
A new study challenges the existence of dark matter, proposing that gravity can arise from 'topological defects' in spacetime.
This headline is pretty dumb. Dark matter is not a myth, it's clearly there in the data, so it exists for sure. Now the name might be completely wrong as it's neither dark and may not be matter, but it still exists. We should have just called it Pete or something, so the name wouldn't imply anything about it's properties. But the press always seem to think dark matter is something thought up to fix something, but that's not the case at all.
The numbers in the data don't match up and the difference is what's labeled as "Dark matter", simply putting another label on it or dismissing it doesn't fix the underlying data not matching up. And it isn't like a fault in the data, we've seen it in ALL the data, no matter what you look at or how you look at it, the signs of dark matter can be seen.
Listened to a dark matter researcher a while back and he said "Dark matter is a name for an observation, not a theory" and I think that's a pretty good description.
They saw something weird with large scale observations and gave it a bad name. It's something that's done on a pretty regular basis in Astronomy. They really need to stop naming things before they're fully described. Of course how do you talk about something before it's named? No idea.
Maybe they just need to be better about letting go of poorly named phenomena.
I don’t know, so just asking but you say dark matter is not a myth, but the paper’s author says,
This unique theory “is in turn 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,” Richard Lieu, study author and a distinguished professor of physics and astronomy at the University of Alabama in Huntsville (UAH), said.
(emphasis added) Is this one of those situations where you agree but it sounds like you don’t?
Well that's a perfectly valid question, thank you for asking. I think the key word here is "direct". He is totally right, there is no direct evidence of dark matter, regardless of what it exactly is. We have a bunch of observations that don't match up with our expectations and models. Where the difference could be explained by adding non EM interacting matter, it's categorized as being caused by dark matter.
Great examples for this are the rotation curves of galaxies and the Bullet cluster, but there are others. The interesting thing about the rotation curves is they are all different. Not only different from our expectations, but also different from each other. We can clearly see the rotations don't match up, but we can't see why this would be the case. Since they differ from each other, it seems like a physical thing which is different in each galaxy, rather the some fundamental systematic difference in reality from our models. With the Bullet cluster the same thing, looking at that thing it's clear something really weird is going on. It's hard to figure out what is happening, but it would be explained by some non EM interacting material, so it gets put down to dark matter.
But neither of these examples are direct observations of dark matter. Dark matter doesn't interact with em, but does seem to interact gravitationally. Since almost all of our observations of the universe are using EM radiation. Be it optical, ir, radio, xray etc. Since dark matter doesn't interact with EM seemingly in any way, we can't observe it. We can only model it based on things we can see.
So in that way the author is kinda reasoning in circles, there is no direct evidence because by definition we can't directly observe it. And I feel like inferring the existence of something based on other observations is perfectly valid. For example elements on the periodic table and the planet Neptune are well known examples (among many others) of something that fell out of models and were later confirmed. And since the observations don't match up, we know for sure there is something there regardless of what label gets put on it. It even might turn out there are several things combined that have the end result we see, although Occam's razor would have something to say about that.
There are several things we are trying to learn more about dark matter. For example giant gravitational wave detectors can help to figure some stuff out. But great progress is also made in WIMP detection systems. I feel both of these paths would qualify as "direct" detection, if any of these pan out.
But the press always seem to think dark matter is something thought up to fix something, but that’s not the case at all.
The numbers in the data don’t match up and the difference is what’s labeled as “Dark matter”,
Is defining something as the difference between a prediction and measurement not exactly the same as thinking something up to fix the discrepancy?
They keep saying "study" but this isn't a study, it's a math paper. This is a "model." The "model" shows this and that and those things, not "the study" of which there wasn't.
And what the "model" shows is that instead of invisible mass we can't see causing gravity, it could be alternating layers of invisible positive and negative mass.
There's even less evidence for negative mass being possible than for many dark matter candidates that "only" have to be massive and non-interacting (or weakly) with photons. It's always cool to kick around some new possibilities but this seems pretty weak. Negative mass opens up a big old can of worm(holes) too.
Does a study have to be empirical? I'm not aware of any rule.
When you see study, it's more statistical analysis of things.
So things like clinical studies doing studies on population of people.
Where this is more publication of a mathematical idea.
Source: have a degree in physics and it's one of those unwritten rules. Kinda like how English sentences have an order. The soft brown big bunny sounds wired.
According to Lieu, the gravity needed to hold some galaxies or clusters together might come from “shell-like topological defects.”
Topological defects are unique compact structures in space that have a high density of matter.
Such defects likely first occurred in the early universe during phase transition — an event during which matter throughout the universe goes through a major physical change.
These defects might appear as long, linear formations called cosmic strings, or as flat, shell-like shapes.
“The shells in my paper consist of a thin inner layer of positive mass and a thin outer layer of negative mass; the total mass of both layers — which is all one could measure, mass-wise — is exactly zero, but when a star lies on this shell it experiences a large gravitational force pulling it towards the center of the shell,” Lieu explained.
It is somewhat similar to how photons, which themselves do not have mass, still experience gravity due to the presence of big astronomical entities. This is because when gravity warps space and time, it interacts with everything within the curvature whether it has mass or not.
Is this the sort of negative mass that would possibly allow for stable wormholes and therefore time travel?
Does this explain the bullet cluster? If it doesn't, it's kinda useless.
the current theory is “not by itself sufficient to discredit the dark matter hypothesis — it could be an interesting mathematical exercise at best, but it is the first proof that gravity can exist without mass,” he added.
(Quote by the author of the study himself)
It's a purely mathematical construct that could explain bending of light without mass.
Typical, scientist: "My paper does NOT say THIS". Press: "Scientist claims THIS!"
Sure, I'm blaming the concerned journalist(s) here. It's rlly scummy to hype up an evidenceless hypothesis like this. Does injustice to both, the scientists and the public.
To be fair dark matter is a purely mathematical construct to explain the presence of gravity without (visible) mass. Certainly dark matter has more credibility than this new idea but hypothetical mathematical constructs make up a good chunk of physics.
But per the definition given involving negative mass, it should be "meassurable mass in the presence of exotic matter". Anywho...
I mean, cool to prove a theory of massless gravity though, whatever their motivation.
This is so hot ! Thanks 😋
https://en.m.wikipedia.org/wiki/Bullet_ClusterNp <3
You say that about everything
This will be a great comfort next time I step onto the scale
My pet hypothesis is that it's all virtual particles. Sometimes stuff just happens. Literally, stuff happens. Matter spontaneously emerges from a vacuum, as a consequence of quantum fluctuations. A divot and a hole form at the same time. When they rejoin, they zero out. And they will tend to rejoin immediately because they both have mass and there's nothing else for a zillion miles.
We observe this as the Casimir effect. Stick two flat surfaces really close together, in total vacuum, and they can act like there's gas pushing them apart. The divot and hole bounce off separate things. Clever tricks to abuse this have not worked: see every EM engine blasting energy into a vacuum chamber. As an engineer, not a scientist, I suspect some of the particles being blasted get negative momentum, somehow, and that's why the net force is immeasurable. Virtual particles play by their own rules.
But virtual particles still have mass. They bend spacetime as gravity. Cancelling that out would require negative mass, and antigravity, which sadly seems too cool to exist. This means all those pseudo-atoms in deep space drag things toward them. It looks like there's stuff out there, because... there was. Briefly.
This could also explain universal expansion. This transient noise in the fabric of reality means empty space has mass. So whatever we consider our universe, it's surrounded on all sides by unfathomable quantities of nothing, and the nothing is tugging it in all directions. It's not just escape velocity from the initial explosion; things are accelerating.
The MOND crowd pops up every now and then and makes some noise in the dark matter community. Evidence we do have points us toward matter, which is why we have billions being spent on detectors through various governments and collaborations around the world.
I’m not sure what direct detection experiments are going to do once we hit the neutrino floor.