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.
TIL.
I’ve also got a degree in physics and I think it’s a valid if kinda wonky use of the word study. They studied whether or not GR allowed this specific thing and that’s enough to say it’s physically possible. It’s not just publishing an idea so much as proving the validity of it within current models, to me a study implies investigation of some kind and that’s definitely what went on here.
I’ve definitely heard it used this way before, even if it is less common. I wouldn’t say it’s an unwritten rule so much just that people have learnt to infer that there’s some direct observation going on.
Agreed that it’s valid if wonky.
It’s why I compared it to the sentence structure. It just rings a little weird in my ear and that’s why.
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?
I’d recommend Stephen Baxter’s “Ring” novel as a primer on cosmic strings, domain walls (the shell-like mass described here) and using wormholes for time travel.
Basically covers all of the funky science described in this article
It’s also really well written. You’ll have to read the rest of the Xeelee sequence afterwards though
Agreed. My favorite is still Raft
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.
Does this explain the bullet cluster? If it doesn’t, it’s kinda useless.
This is so hot ! Thanks 😋
https://en.m.wikipedia.org/wiki/Bullet_ClusterNp <3
I mean, cool to prove a theory of massless gravity though, whatever their motivation.
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.
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.
Typical, scientist: “My paper does NOT say THIS”. Press: “Scientist claims THIS!”
But per the definition given involving negative mass, it should be “meassurable mass in the presence of exotic matter”. Anywho…
You say that about everything
This will be a great comfort next time I step onto the scale
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.
It’s not there in the data. There’s a hole in the data and we’re making up dark matter to plug it.
You are wrong, just look at rotation curves of galaxies for a very easy to understand example. It’s right there.
If it was right there and easy to understand we wouldn’t still be trying to justify it or figure what it might be. But I’m sure you’re working on a counter publication to refute all of this since it’s so easy right.
The question is what exactly dark matter is, nobody knows at this point. We have a bunch of data and a lot of different ideas, but nothing that neatly explains everything.
The point was that the publication was questioning whether dark matter exists. It exists for sure, there is nobody who has seriously looked into it and thinks it doesn’t exist. We don’t know what exactly it is, but it exists. And we also know for sure the name sucks, but hey that’s the name we’re stuck with.
Like what the other comment said, dark matter is an observation, not a theory.
No ‘Dark matter’ is a theory trying to explain an observation based on our incomplete understanding of gravity. Same as ‘dark energy’. They saw something, couldn’t explain it and came up with a theory of ‘something’ rather than simply saying ‘We have no clue. That shit don’t fit’
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?
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.
I agree with the other commenter, this is a great answer.
As far as I know, all so far proposed models that eliminate dark matter have other problems that are greater than"just" adding invisible mass. Would be cool though to just activate gravity without the need for mass.
Great answer, thanks!
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.
It’s the same idea as “the dark ages”. All it means is we don’t have information about it.
I take “the dark ages” to mean a lot more than that. And I don’t think that’s particularly unique.
How do you mean?
It’s just a term to describe not having enough information to know what happened.It’s “dark” because we can’t see/have no knowledge of what the events were. For history we don’t have written records that describes events during those years. For dark matter we don’t have any information on what it might be.
That’s simply the historical and scientific method of labeling things like that. There is no other deeper meaning to it.
The concept of a “Dark Age” as a historiographical periodization originated in the 1330s with the Italian scholar Petrarch, who regarded the post-Roman centuries as “dark” compared to the “light” of classical antiquity.[1][2] The term employs traditional light-versus-darkness imagery to contrast the era’s supposed darkness (ignorance and error) with earlier and later periods of light (knowledge and understanding).[1] The phrase Dark Age(s) itself derives from the Latin saeculum obscurum, originally applied by Caesar Baronius in 1602 when he referred to a tumultuous period in the 10th and 11th centuries.[3][4] The concept thus came to characterize the entire Middle Ages as a time of intellectual darkness in Europe between the fall of Rome and the Renaissance, and became especially popular during the 18th-century Age of Enlightenment.[1] Others, however, have used the term to denote the relative scarcity of records regarding at least the early part of the Middle Ages.
Source. I use it in the former sense, which I think is more common.
Laymen may use the former. But historians use the latter:
Others, however, have used the term to denote the relative scarcity of records regarding at least the early part of the Middle Ages.
That’s literally the meaning of the the term, and why it’s also used for ‘dark’ matter.
It doesn’t matter how you decide to use it, what matters is how the scientific community uses it.
Or start calling it Ninja Phenomena. Why is the observation not matching with the models and vice versa? It’s those Ninja Phenomena at it again, wrecking stuff and hiding away!
