'Unbelievable': Astronomer Claims 'Direct Evidence' of Gravity Breaking Down | Hacker News Reader

'Unbelievable': Astronomer Claims 'Direct Evidence' of Gravity Breaking Down

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155 pointssigna1197 comments

This would be an incredible result and probably the biggest experimental physics discovery in decades (bigger than gravitational waves and the Higgs). But MOND has so many problems on so many levels and some of the people who promote it in the scientific community are borderline crackpots. So I'd treat this veeeeery carefully until confirmed by independent groups and measurements. For the moment, this is like the room-temp superconductor: Revolutionary if true, but I'd still bet on poorly executed measurements in combination with unknown errors as the real explanation.

> But MOND has so many problems

The fact that the results happen to fit some MOND model(s), while interesting, doesn't really mean much: these results could be 100% correct and all of MOND a pipe dream at the same time. The crucial question is, is the analysis correct?

If the results are correct, it means that extreme weak field gravity laws are actually in need of modification. I'd be very surprised if any existing variant of MOND got it right, but it would still mean that the premise of MOND is correct, which would be a huge deal.

> premise of MOND is correct

Well, typically the term MOND refers to very specific modifications of Newtonian gravity and doesn't even take into account GR. So I'm not sure I would agree with the statement in general terms (note, I haven't read the paper so far, so I don't know what they claim). There's _plenty_ of extensions of GR though that modify gravity. That in itself isn't really that surprising. Scalar-Tensor theory and the like. And there's a reason these are usually not called MOND. Some go by "MOG" for modified gravity.

The paper actually mentions a specific form of MOND called AQUAL [1]. The original version of MOND was a very specific, simple modification of Newton's laws, but over the decades it has become more of a synonym for all attempts at modifying gravity at long distances. Especially since all of these attempts modify the weak field regime, which is equivalent to modifying Newton's law of gravity.

[1] https://en.m.wikipedia.org/wiki/AQUAL

This particular proposed modification is for very weak accelerations. That's where Newtonian gravity is least corrected by GR.

> I'd be very surprised if any existing variant of MOND got it right

I'm not sure why this would be surprising, MOND has made many more successful predictions than DM.

That is simply not true. Like, it's literally the opposite of the truth.

Don't confuse post-hoc curve fitting with predictions:

From galactic bars to the Hubble tension: weighing up the astrophysical evidence for Milgromian gravity, https://arxiv.org/abs/2110.06936

You should read up on how DM is fitted vs how MOND is fitted. But neither preceded the data in the way you imply and DM is vastly more successful at predicting all observations with a single fit.

What I know is that MOND predicted the high redshift galaxies we're now seeing 20 years ago, and DM did not:

https://tritonstation.com/2022/01/03/what-jwst-will-see/

There are many instances like this as outlined in the paper I linked.

If these observations are confirmed, then Newton is wrong (which we already knew), GR is wrong, and MOND is wrong. I don't think the solution is going to be tweaking GR - it's going to be something radically different. This could be so big we might even uncover something causing us to re-think QFT and then put all the forces on equal footing. That would be huge, because where we are now we're stuck. We've been looking for hints for how to move forward, this could be it.

But if the analysis is correct, it does mean that general relativity will need to be different to the current formulation and that dark matter is unlikely to be the (entire) explanation for observed galactic rotations.

No, some form of dark matter could have interactions that produce MOND dynamics in the correct regime. This is compatible with GR. For instance, various superfluid dark matter proposals that are being researched.

My understanding is that dark matter cannot explain this motion in wide binaries, which is why these are interesting observations.

Dark matter is not one theory, but a class of theories. The point of superfluid dark matter proposals is that it reproduces MOND dynamics, therefore it would explain these observations.

The paper states:

"First of all, the gravitational anomaly in the dynamics of binary stars cannot be attributed to dark matter because the required amount is absurd, and thus there is no way to save the standard theory of gravity."

Which applies to classical dark matter theories, not ones that naturally reproduce MOND dynamics.

I could easily be mistaken here, but wouldn't applying any dark matter theory to a binary system require it to have its own dark matter halo and core?

I can understand how things like superfluid DM might help explain galactic rotations, but I'm having a harder time applying it to things like wide binaries.

On further reading, I am fairly confident you are wrong. No dark matter theory can explain wide binary gravitational anomalies.

I guess we'll just have to wait and see. Many of the superfluid dark matter proposals have already been ruled out by other observations anyway.

We will indeed! I had heard superfluid DM had been ruled out for some things too.

Exciting times!

"So I'd treat this veeeeery carefully until confirmed by independent groups and measurements."

So would I, and most would especially with the LK-99 incident fresh in our minds.

I'm not an astrophysicist, so it would be stupid of me to discuss the specifics of MOND, so I'll just make a few observations from the perspective of a lay observer. First, I have no fixed position on the matter except to say that if MOND were determined as fact then it would only be so after possibly the most extensive verification process yet undertaken in science—and it would upend everything, and science would be in turmoil for years.

That said, being an outsider, I have the luxury of having an opinion that if wrong won't wreck my career—no one would care, not even I. That preface was necessary because I come at physics from a slightly different perspective to many. Decades ago I spent much of my professional life trying to make electronic circuits, amplifiers etc., as linear and distortion free as possible and it's not an easy task. When one gets distortion figures down to -120dB and below even capacitor dialectics conspire against one by exhibiting nonlinear responses that contribute distortion. That experience instilled a distrust in me that made me question even the intrinsic nature of the physical constants, their stability over time, variation with energy levels etc.

Sure, the transfer characteristics of the electronic circuits I was working with were way, way up the chain from any physics that could be responsible for variations in the physical constants—so far as to be irrelevant—and their properties were emergent anyway. What mattered was my perception of the physical world changed. Let me give you an example: take a large volume of space somewhere in the universe that's free of physical matter, over time dust and matter drifts in and a star forms and eventually dies and forms a black hole and after 10^xyz eons it evaporates and we are left with empty space again (all else being equal of course). Can we say for certain that that volume of space is absolutely identical to that before the dust drifted in? Specifically, is spacetime perfectly elastic and that the black hole left no distortion in its fabric—not even the most infinitesimal amount?

Same goes for physical constants, are we certain the electric constant (vacuum permittivity), ε0, is immutable and has never changed (since the end of inflation anyway), if it has then so has c changed. Same goes for the cosmological constant and we still have the problem of the 'vacuum catastrophe' to contend with. Then there's alpha, α, the fine structure constant, we have its precision to nine or more digits, but there are still questions whether it varies over time and or by location, and its liable to vary with energy levels. If α changes so does the electric charge, e, and also does c. (Simply, it's unlikely every constant is immutable and perfectly linear/predictable over almost 'infinite' time and scale.)

Now to the gravitational constant, we have its accuracy to only about five digits, some four orders of magnitude less than, say, c and α, which is a bit of a worry. Thus it seems to me there's potential wiggle room in those constants, and whilst it's unlikely MOND has substance, we shouldn't rule it out without further research.

> some of the people who promote it in the scientific community are borderline crackpots

Is the astronmer making this particular "claim" among the borderline crackpots?

Why don't you check the claims yourself before making such a comment?

You seem to be one of those people who are afraid that their cherished orthodox views may not hold, and so respond by bring up the crackpot angle.

It's always funny when people accuse physicists of cherishing old views and not wanting change, when in fact any real good physicist loves to see conflicting data, because this is the only way progress is made. In fact, we have been hoping for someone to show how gravity breaks for more than a century. I don't think anyone wants this to be false. But good physicists are also very careful and reserved about analyses like these, because they know how difficult they are and exactly how much can go wrong. It wouldn't be the first time that a trivial bug in some self written software causes a fantastic publication, only to get trashed when other people try to replicate it. And unfortunately there are also bad physicists who actually trim data, which made the good ones even more careful and reserved. And if the academic MOND literature is known for anything, it's trimming data. So yes, I would love for this to be true, but no, I will not believe it until there is independent confirmation.

The fulltext of the study, which is free, is here: https://iopscience.iop.org/article/10.3847/1538-4357/ace101/...

What's important to note is that while the work is suggestive, it's far from conclusive. The author notes, however, that "even stronger results than the present results are expected with later data releases of Gaia." So, presumably, we'll have more evidence very soon --- and, if not, the way to bet is that this finding will turn out to be due to the instrumentation's margins of uncertainty.

The author also notes that "a recent study by Mistele (2023) showed that predictions of the AeST theory agree broadly with the results of this work." Which suggests that the AeST theory might be worth a look!

have any link explaining aest ?

The Mistele paper referenced is pretty interesting: https://arxiv.org/pdf/2305.07742.pdf

It's a MOND-derivative theory, so the Milgrom and Bekenstein MOND papers are foundational.

https://arxiv.org/abs/2007.00082

I'm a follower of the "Quantized Gravity" flavor of modified gravity, as proposed by Mike McCulloch[1]. I fully realize it's a fringe theory, but there should be experimental evidence from an actual thruster flown in space, launching in less than 90 days..[2] I hope he's right... but the only way to know is to wait and see.

Reactionless thrust would be a handy way to get around the cosmos.

[1] https://physicsfromtheedge.blogspot.com/

[2] https://ivolimited.us/launch/

This is the first time I'm hearing about Quantized Inertia. Are there any good, independent overviews over McCulloch's papers and the current state of affairs? Looks like the Wikipedia page (and references to it) have been deleted, and the QI subreddit has largely become inactive.

Hope there's a stronger theory behind that than behind the https://en.wikipedia.org/wiki/EmDrive …

From the linked blog:

> and there should be a property office for space to encourage space mining and a new gold rush

Run by who? On the surface, that seems like a statement that all of space belongs to the author's favorite country.

Run by whomever can provide rescue services if something goes wrong, and/or enforce a monopoly on violence.

You mean “quantised inertia”.

Mad clickbait, as expected. Gravity is not breaking down.

The study author claims the results offer support for MOND which really ought to be interesting enough to reflect in the title.

It doesn't seem like clickbait to me. "Breaking down" is a common way of expressing that a scientific theory isn't explaining experimental data in a certain set of circumstances, which is exactly what the person they're reporting on is claiming.

The theory may be “breaking down” but is gravity? That was the title’s confusing implication.

After the superconductor flop I imagine we will see a lot more stories like this where journalists hype up anything they possibly can.

This is just every single news cycle. If it's not going to revolutionize everything then you're going to bore your audience to death. Hype is overhyped. Welcome to the 21st century.

Here's a relevant thread by someone in the field:

https://threadreaderapp.com/thread/1667141734055264256.html

It's interesting that different teams are making statistically significant contradictory claims from the same dataset.

...but different samples of the same dataset, surely?

"Banik et al. only consider binaries with separations >2000 AU. Those are already quite close to the MOND regime, i.e. a0. You expect to find a change in behavior for different separations, i.e. once you approach the MOND regime, which they do not see.

"Chae additionally considers tighter binaries than Banik, which must be in the Newtonian regime even in MOND (a>>a0). He uses these to calibrate his analysis, since he knows what Newton should do. He finds that MOND behaviors begins at 2000 AU!

"Right where Banik's sample starts."

He then goes on to mention a third sample which excludes triple systems.

Yeah, that's what I mean. All the groups have downloaded the same dataset from Gaia, and yet have come to completely opposite conclusions based on the analysis techniques, filtering, etc.

We're looking at a system of stars and talking about accelerations below one nanometer per second squared? Really...?

Really. The study is looking at wide binaries, where stars are in very far orbits around each other, moving very slowly, but still gravitationally bound.

For example, the closest (non-sun) star to Earth, Proxima Centauri, orbits Alpha Centauri A and B with a semi-major axis of ~8700AU, or ~0.14 light years. It's orbital period is more than half a million years, it's orbital speed is ~500m/s, and the gravitational acceleration that keeps it in orbit is just 0.17nm/s².

That 0.17nm/s² is tiny, but it really adds up over half a million years.

> That 0.17nm/s² is tiny, but it really adds up over half a million years.

True. But we don’t have half a million years to make an observation. 0.17nm/s² over a year only adds up to a displacement of 85 km, and now we’re looking for a relatively small discrepancy in this expected movement? The radius of the sun is about 696000 km, for comparison.

I know nothing about physics, but just finding that an orbit isn't that if a body has an elliptic orbit means it is accelerating and decelerating constantly depending where it is in the orbit?

I guess it's quite easy to measure periapsis and apoapsis even for stars or planets that have a nearly circular orbit.

You just end up with very small numbers (acceleration) when you divide trivial numbers (distance) by very large numbers (orbital period).

You even divide it by a large number squared.

That makes me think “could easily be a numerical issue with precision or accuracy of the software used”.

I couldn’t find the software, so I couldn’t check a bit deeper.

Both the data and the code (Python) is here: https://zenodo.org/record/8065875

That link came from the paper. Zenodo.org is a open science site curated by NASA.

The analysis is interesting. He is using Gaia space observatory data to identify "nearby" binary systems, filtering out those with a high likelihood of being compromised by additional bodies in the system, and those for which the bodies have poor mass estimates, then measuring the orbits of the remaining 26k systems that can be confidently projected to three dimensions and aren't too eccentric, etc. His results are that below some small level of gravitational acceleration (the stars are far apart with long orbital periods,) the orbits predictably deviate from Newtonian gravity, and that due to the small size of binary systems Dark Matter cannot be a factor.

It's a Nobel prize winner if correct. Good old fashioned falsifiable Science: future data sets and peer review of the work will tell us.

Too bad Gaia runs out of fuel in two years. The longer the data set the more confidence can be achieved in this sort of work. It's interesting that only the most recent of the so far three data sets from Gaia provides the data necessary (tangential and radial velocity,) to do this.

I looked at the code for a bit, and it's just like most academic code I've ever seen/written: incredibly dense and cryptic. What is the likelihood that he has a transcription error somewhere? The average number of characters in the main file accel_ortho_wb.py is 52 characters per line (5 of the lines have over 300 characters).

Aside from the question of whether the code is semantically/notionally correct, what about numerical precision issues? Python floats are 64-bit IEEE doubles. I've read through enough "floating point representations are fraught with peril" articles in the past to be default-skeptical of code written by people who haven't already run into--and addressed--computational issues specifically with them.

I've never used numpy or done any hard mathematical analysis either in python or anything else. Does numpy somehow change the float type in python to use some other representation than doubles? How much precision is in a double? Is there "enough" for these astronomically large(/small) calculations? I guess a 52-bit mantissa can represent 2^52 = 4,503,599,627,370,496 ~= 10^15.65356. Is that ~"15 and a half digits" of precision? How does error propagate through all the calculations?

edit: I don't want to just poke holes in this person's research. I'm crossing my fingers and hoping it's all correct both for their sake and for mankind's.

If it's anything like the academic code I've seen, the likelihood approaches 2.

> Zenodo.org is a open science site curated by NASA.

No offense, but Zenodo is a CERN project. [0]

[0]: https://about.zenodo.org/

Ok. I was mislead by this, which appears as the first element of a carousel every time you load the Zenodo landing page:

"Transform to OPen Science (TOPS) is a $40 million, 5-year mission, led by NASA's Science Mission Directorate's Open-Source Science initiative. Within the TOPS mission, NASA is designating 2023 as the Year Of Open Science, a community initiative to spark change and inspire open science... Curated by: nasatransformtoopen"

> curated by NASA.

Er, it's actually maintained by CERN and funded by the European Union. NASA does somehow participate in it as part of its "Transform to Open Science" initiative.

Do you know if Euclid will be able to collect this data after Gaia dies?

Good question. I think perhaps not. This work is based on the data Gaia delivered in its most recent data release; the third so far. Only that release has provided both tangential and radial velocity of stars, which are crucial figures to compute the orbits of the binaries. This was done by correlating data collected simultaneously from the three instruments onboard Gaia. Does Euclid have the same three instruments or their moral equivalent? Will they operate Euclid such that they'll be producing similar data?

I don't know. Even if there are equivalent capabilities, it's a different instrument, so the data will not simply slot in as the next tranche of observations.

It says "unbelievable", right in the title.

Over millions of years and distances of light years it all adds up.

That is irrelevant for discussing how amazing it is that we (think we) can measure such quantities. They didn’t observe over millions of years.

I got this feeling alot of physicists are trying to get grant money from massaging noise.

That’s a pretty cynical way to look at it. If you look at LIGO, that thing is detecting changes in length of 1/1000th the width of a proton. The actual data looks like noise. But it’s not noise. GPS data looks like noise in raw form and yet it gets millions of people to their destinations daily.

Surely you can use statistical methods to get proper answers. It is very hard though.

What is the famous physics dude's quote. "If you need statistics redesign you experiment"? Or was it "math"?

for some things you don't have a choice. Gravity is too weak.

> “When the results started to show up from my new and more reliable code, my initial reaction was that it was unbelievable,” Chae said in an email to Motherboard. “I was feeling like I was dreaming. It seemed so unreal. This is because my results did not match any previous results.”

as a dev I'd be deeply skeptical of my own feelings here

but, wow, amazing news if it turns out legit!

https://twitter.com/8minutesold/status/1667141734055264256

Thread with some more info.

https://threadreaderapp.com/thread/1667141734055264256.html

Whenever MOND comes up I feel obligated to refer interested readers to this expert astrophysicist's blog on the matter:

https://tritonstation.com/new-blog-page/

https://en.wikipedia.org/wiki/Stacy_McGaugh

Blast from the past, I hadn't realised he had a blog - thank you for that.

Clickbait title makes it sound like some doomsday scenario, when in reality it's just some evidence of gravity working slightly differently than believed.

"Slightly different" is a breakdown in precise sciences like physics.

A breakdown of the theory maybe, but not of gravity itself. There is a difference between "Gravity Breaking Down" and "The Theory of Gravity Breaking Down".

Breakdown of GR, maybe, not gravity. Which even though it would be groundbreaking is still a different thing.

This is splitting hairs. Our entire understanding of what gravity is and how it works rests on GR. If GR "broke down" in major ways, then the same would hold true for gravity, as we understand it.

Just call it dark gravity. Problem solved.

General relativity is more fundamental than gravity. If general relativity breaks down, it completely redefines what we think gravity is. And much, much more -- practically everything beyond our solar system has to be reconsidered.

Mildly clickbaity but gravity always does its own thing and always will. Our theory might be breaking down and could have to be adjusted to new measurements.

By the way, more precise measurements always settled fights between theories, with the caveat of having to wait for the funeral of the last heir of the losing theory (Plank's Principle.)

https://en.wikipedia.org/wiki/Planck%27s_principle

Knowing nothing about astrophysics, synthesizing:

> binaries located within about 650 light years of Earth

> developing a new code

> below one nanometer per second squared

we see a claim that an astronomer developed new code which produces a novel result relying on some very large numbers and a very small number. Red flags abound.

These extremely low-acceleration regimes are precisely where the issue is, and why dark matter and MOND were both developed as competing frameworks for understanding discrepancies vs our current understanding. It's the only regime where these questions can be probed and investigated.

I've always been uncomfortable with the fudge-factor physicists call Dark Matter/Energy and confidently act like is real. Would be nice to see it destroyed.

I went down the mond rabbit hole a while ago, The bullet cluster is one of the things that makes mond hard to support https://en.wikipedia.org/wiki/Bullet_Cluster

Your link seems to suggest that it being proof of dark matter and against MOND was based on bad data that has since been rectified.

Could be, this is interesting https://pursuit.unimelb.edu.au/articles/digging-deep-for-dar...

> the fudge-factor physicists call Dark Matter/Energy

Those are two very different fudge factors (as in, those hypotheses are distinct; the observations they attempt to explain may turn out to have a single cause instead, but we don't yet know)

> Would be nice to see it destroyed

If you don't like fudge-factors, then you probably won't like MOND (the sort of hypothesis TFA is about).

Edit: MOND theories put a fudge-factor "a₀" in their acceleration calculation; the value of a₀ is chosen such that (a) it is small enough to make no measurable difference from standard gravity in any existing observations; and (b) it can curve-fit observations of charged matter distribution to galactic rotation curves.

https://archive.is/Xdml7

Only geographically related, but Sejong Village Food Street is awesome.

Note about mentions of the Higgs discovery: The Higgs boson was not observed. Never has been. Rather, an effect predicted to be caused by the Higgs boson was observed.

This explains all those levitating rock videos I’ve been scrolling past recently

Please, this won't give us ufo technology. Quit sperging out and get into materials science stat!

Very nice but the article could do without using the term "standard model".

I get that she is talking about the standard cosmological model and she leaves it uncapitalized, but it really confuses readers familiar with "the" Standard Model as a QFT theory

In the literature, LCDM is commonly referred to as the "standard model" (in cosmology of course). So there is nothing wrong with that. Though I wouldn't trust Vice to get their terminology right, so they probably got it from the authors.

This seems suspect coming from Vice.

Vice is reporting on the paper, the source of the paper is here:

https://iopscience.iop.org/issue/0004-637X/952/2

which of the companion pieces are you also dismissing without reading?

Do you feel this way about every paper in The Astrophysical Journal or just these papers that appear in Volume 952 Number 2, 2023 August 1st ?

Yes, the problem is not the paper, but Vice's reporting. It is, as usual just clickbait.

The GP comment has been edited down .. originally it was along the lines of "appears in Vice == not worth reading further".

The Vice reporting may well be subpar .. the paper, MOND, and general subject area is well worth reading more about especially given the level of conjecture and almost noise level data (well, for some of us at least).

"Extraordinary claims require extraordinary evidence”

- Sagan

Koreans hitting it out of the park lately with new theories/materials, although unproven

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