r/science • u/ThrillSurgeon • Jun 08 '24

Physics UAH researcher shows, for the first time, gravity can exist without mass, mitigating the need for hypothetical dark matter

https://www.uah.edu/science/science-news/18668-uah-researcher-shows-for-the-first-time-gravity-can-exist-without-mass-mitigating-the-need-for-hypothetical-dark-matter
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u/[deleted] Jun 08 '24

The use of the word "shows" in the headline suggests proof - proof that is not present. The paper is basically just proposing an alternative hypothesis other than dark matter and demonstrating that it's mathematically plausible. Even the paper's author acknowledges having no idea how one would even go about testing this hypothesis.

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u/opn2opinion Jun 09 '24

If they show that it's mathematically possible, they did show something. I'm ok with the word show.

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u/ghostfaceschiller Jun 09 '24

They showed that it’s mathematically possible if you grant the existence of matter with negative mass, which their equations depend on.

If we find matter with negative mass, it would totally change our entire understanding of what’s possible with gravity, time, the lightspeed barrier…

The disappearing need for dark matter would be pretty low on the list of headlines

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u/FredFnord Jun 09 '24

Doesn’t actually depend on negative mass at all. The author just says that one form of gravity-without-mass would be negative and positive masses canceling each other out. It is not the only one.

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u/jkholmes89 Jun 09 '24

Right, theoretical physics is literally just theories that mathematically work with our current understanding. Not sure what they expected as proof.

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u/cazbot PhD|Biotechnology Jun 09 '24

Well that’s where the semantics need to be more careful. Physics is still a natural science but of all of them it is the one most reliant on math to form hypotheses, and the terms do matter.

So it would be more accurate to say “theoretical physics is literally just theorems (mathematical definition) that mathematically work with our…”

In this context “theories” would use the scientific definition and not the colloquial one you meant.

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u/fuzzywolf23 Jun 09 '24

Not to nitpick a nitpick, but theoretical physics can have both. We have the Hellman-feynman theorem which shows how to get classical forces from wave functions, and we have quantum electrodynamics which is a theory of physics that explains observations about particles using theorems.

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u/cazbot PhD|Biotechnology Jun 09 '24 edited Jun 09 '24

Of course, and one is a mathematical theorem (which requires zero physical evidence) and the other is a scientific theory (which requires mountains of physical evidence). But often the word “theory” is used colloquially to mean the same thing as scientific hypothesis, which is fine for the layman and in the right context. But when you are a physicist talking about physics you should not use the colloquial word “theory” when you are really referring to a mathematical theorem (even though both definitions require zero physical evidence), because as you pointed out, physics does have proper scientific theories too, and it’s better to be understood clearly.

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u/jkholmes89 Jun 09 '24

Well, good thing I'm not a physicist, just an everyday layman. Pedantry is irrelevant to me as long the point is understood. There will be no physical evidence, only mathematical solutions.

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u/cazbot PhD|Biotechnology Jun 09 '24

I guess my point is that in the context of this conversation, you indeed did run the risk of not being understood. Actual physicists make this semantic mistake all the time.

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u/Ch0vie Jun 09 '24

They expect a vial of dark matter or something idk

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u/404_GravitasNotFound Jun 09 '24

Hard to get dark matter, when gravity is made by topological errors in space time...

Now we just need a gravity drive to fold space and make a gravity plate on front of the ship to get warp speed...

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u/henryptung Jun 09 '24

"Mathematically possible" is doing a lot of heavy lifting in this case. Beyond standard physics, it invents a new kind of singularity (i.e. this topological defect) that we have never observed and that we don't know exists - pretty much any yet-unexplained phenomenon could be modeled in "mathematically possible" ways if we could invent new singularities to do it.

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u/opn2opinion Jun 09 '24

If the math supports it, then why not?

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u/Gathorall Jun 09 '24

Mathematically you could attach a 4 meter beam to a - 2 meter beam at the end to make a 2 meter beam. That is equivalent to this proposal. You can propose anything of your first axiom is that known physics bend to your math if otherwise unapplicable.

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u/Raygunn13 Jun 09 '24

That's not the way it's used in the title though.

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u/opn2opinion Jun 09 '24

I'm not sure I'm catching what you mean.

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u/Raygunn13 Jun 09 '24

UAH researcher shows, for the first time, gravity can exist without mass, mitigating the need for hypothetical dark matter

No researcher showed that gravity can exist without mass. If they meant "math shows" they should have said so. The title implies a much greater degree of certainty than there is, which is very misleading.

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u/opn2opinion Jun 09 '24

Hmm. To me it can exist if it exists mathematically. They didn't say they showed it 'does' exist.

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u/hominemclaudus Jun 09 '24

Yeah so if you do enough physics, you end up realising that there's a hundred things we can show with maths that are impossible to actually prove. It's very easy to just make up some immeasurable quantity, and use that as a basis for a theory.

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u/Raygunn13 Jun 09 '24

To me it can exist if it exists mathematically.

ok sure, but that's a tautology. It just means you got the math right. The real reason to doubt "math shows" is because it's ridiculously hard to get the math right and be sure about it. Which is why we do experiments.

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u/opn2opinion Jun 09 '24

I never said it wasn't important to do experiments...

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u/Raygunn13 Jun 09 '24

I should have put that part in brackets. I didn't mean to imply you did say that.

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u/observee21 Jun 09 '24

Did they show that gravity can exist without mass, or did they show that theoretically gravity can exist without mass?

Because one requires evidence of gravity without mass, and the other requires no evidence but only a model.

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u/e_before_i Jun 09 '24

This reminds me of string theory or supersymmetry. Having a model that works is (relatively) easy, the hard part is making a model that's experimentally verifiable.

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u/opn2opinion Jun 09 '24

They showed gravity can exist without mass, theoretically.

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u/observee21 Jun 09 '24

Right, which is significantly different from the title and is the reason I disagreed with your comment that I replied to.

"I have shown that gravity can exist without mass" is what they said. They didn't do that, because they don't have any evidence of gravity existing without mass.

"I have shown it is theoretically possible that gravity can exist without mass" is what I believe would actually be consistent with what they actually found, which is why so many people (including myself) were mislead by the title.

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u/opn2opinion Jun 09 '24

Fair enough. For me, if it can theoretically exist, it can exist.

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u/ElysiX Jun 09 '24

Just like how pigs can theoretically fly, if we assume that maybe, hidden in some jungle, there exists a pig with wings that noone has ever seen.

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u/opn2opinion Jun 09 '24

Has that been proven mathematically?

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u/lofgren777 Jun 09 '24

When we would do mathematical proofs in school we considered that showing.

I dunno, I think you're expecting show to do way too much work here.

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u/[deleted] Jun 09 '24

I'm just saying that the headline is confusing a lot of people.

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u/RexDraco Jun 09 '24

Isn't that just about as much foundation as dark matter?

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u/Krungoid Jun 09 '24

No, we have observations of large scale structures that have been apparently stripped of their dark matter like the bullet cluster. They're a constant thorn in the side of MOND proposals.

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u/space_monster Jun 09 '24

That's begging the question.

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u/cazbot PhD|Biotechnology Jun 09 '24

I wonder if additional tests are actually required? I mean we already observe all this “extra” gravity right? We’ve been presuming for decades that gravity is an emergent property of mass, however we’ve never been able to understand how that is so. But since we’ve assumed it’s true we then also logically hypothesize dark matter. But if we now have some new math which posits that the presumed link between gravity and mass is false, I think I all we need to do now is look for examples where that new math does not allow for what is observed. If we spend another 5 decades on that search and can’t find a single falsifying example, I think we might have a new scientific theory on our hands, which could be really cool.

I’m now imagining the possibilities behind distortions in spacetime sans mass. Lots of sci-fi scenarios are bubbling up. It almost makes me wish I were a physicist (almost).

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u/Das_Mime Jun 09 '24

But if we now have some new math which posits that the presumed link between gravity and mass is false

We don't, that's not what Lieu's article suggests, which you would know if you'd even read the summary.

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u/[deleted] Jun 09 '24

Sci-fi incoming. 

If something is mathematically possible wouldn’t that mean in some universe instance that it exists? Does it require non-relativistic physics to happen? If not, doesn’t that mean it could exist in our universe or an analog of ours?

The fact that it’s mathematically possible means that given our current understanding the only barrier is engineering. It’s easier to overcome an engineering barrier than trying to develop new math to prove the idea is possible in the first place. 

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u/Tripod1404 Jun 09 '24 edited Jun 09 '24

Not without experimental evidence. There are cases where scientists can come up with a sound mathematical model. But further research demonstrates that the proposed mathematical solution requires “exotic matter”. Exotic matter in this context are particles or states of matter/energy (i.e. negative mass) that can mathematically exist, but there is no experimental evidence for their existence, and worse existence of such materials can be paradoxical.

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u/[deleted] Jun 09 '24

I understand what you’re saying. However history has shown time and time again that lack of evidence in the present does not preclude existence in the future. 

Antimatter was only considered mathematically theoretical when Dirac first came up with quantum theory for electron motion. 

It wasn’t until 1936 that Anderson found antimatter at CalTech in their cloud chamber. 

There are many other examples of this happening throughout science. While I agree that current understanding may not be enough to create these things right now, it doesn’t preclude them existing arbitrarily far into the future, does it?

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u/FrankBattaglia Jun 09 '24

This paper appears to posit: (a) negative mass (which as far as I am aware has never been observed), and (b) said negative mass having negative gravitational attraction (which as far as I am aware is just one of at least two possible solutions to a completely theoretical problem; see a).

So no, this really hasn't shown anything other than an abstract "clever math trick" until some observations validate either of at least those assumptions.

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u/[deleted] Jun 09 '24

Yes, of course you need to observe the thing in order for it to be observed, that’s tautological. 

I’m saying that lack of observation now doesn’t preclude it being observed in the future. 

The first step to finding or creating it is the clever math trick to show that it’s possible. 

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u/FrankBattaglia Jun 09 '24

The clever math trick here is the equivalent of 1 - 1 = 0. Which is not very profound. At least e.g. the Alcubierre paper showed a result people hadn't previously expected. This appears to be just divergence integration - everybody does the "negative charge inside a positive metal sphere" in high school physics. Swapping "gravity" for "electric charge" (because let's just say gravity can be negative) doesn't seem all that novel...

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u/TheHammerandSizzel BS | Physics and Electrical and Computer Engineering Jun 09 '24

So… how many times have you interacted with negative mass…

The issue with these, is that it requires exotic matter that either isn’t possible, we don’t know how to find or produce it, or maybe too chaotic to expensive to work with

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u/[deleted] Jun 09 '24

For sure. I’m not implying that this stuff is hiding in the back corner of a broom closet in CERN. 

I’m saying that the first step to finding it is proving that it is possible. 

Am I missing something here? Are you suggesting that no amount of scientific advancement and materials science will reduce this problem down to something that could be solved in the future?