One night of telescope time rules out black hole/dark matter idea

https://arstechnica.com/science/2019/04/one-night-of-telescope-time-rules-out-black-holedark-matter-idea/

by Tomte • 7 years ago

155 83 7 years ago

arstechnica.com

karmakaze• 7 years ago

Here's a different observation report[0] which alludes to smaller scales of primordial black holes but wasn't explicit.

[0] https://news.ycombinator.com/item?id=19591020

mirimir• 7 years ago

It's the same report. Suprime camera on Suburu telescope, observing Andromeda.

toufiqbarhamov• 7 years ago

To be fair, this is after years of lending surveys already closed the loophole for MACHO theory down to the pinhead closed by this last survey. Still a good read.

jniedrauer• 7 years ago

When I write a test, I intentionally make the condition fail to validate that the test works like I think it does.

The experiment described here uses new equipment that presumably has never been used for this purpose before. But I don't see any mention of efforts to verify that it can actually be used to detect black holes. Hopefully the remaining 10 days of their experiment can confirm that it works...

maxander• 7 years ago

The “Hyper Suprime-cam” instrument came online in 2012, so it’s not new, and was presumably calibrated against well-understood targets; so its light-detection capabilities have been well tested. The physics of gravitational lensing is also well understood and verified, so they know what light they’re looking for.

If you can test each part of a system independently, and the parts connect in a reasonably trivial fashion, it’s about as good as testing the whole.

Chilinot• 7 years ago

If you can test each part of a system independently, and the parts connect in a reasonably trivial fashion, it’s about as good as testing the whole.

Not really, which is why integration tests are so important.

skybrian• 7 years ago

Given that they're staring at an entire galaxy for such a long time in quite high resolution, I wonder that they didn't notice anything else that's unusual?

Etheryte• 7 years ago

Given the sheer amount of data (870 megapixels every 90 seconds for a night) you will only find or not find things you're very specifically looking for. The volume of data is simply too large for random discovery. As the article covers, looking for a very specific type of interaction, the researchers were still faced with 15,500 possible matches that they then needed to filter.

EnigmaticLion• 7 years ago

7 hours of observation, one image every 90 seconds: that's 280 images. My phone takes 8 megapixel photos and those are about 2 MB, based on that the 870 megapixel image would be about 200 MB. 200 MB * 280 = 56 GB. Doesn't sound that much.

Did they publish the images? I'm sure many astronomers would be happy to examine them.

PhantomGremlin• 7 years ago

One of the best pithy comments on general relativity and dark matter was made by someone on HN about a week ago. I think it summarizes the situation quite well. But, inexplicably, people don't seem too concerned about it:

"[dark matter] seems to make up about 95% of the galactic mass...crushingly narrow passages between observation and tests of GR"

GR only matches observation because you added in 20x more stuff that is undetectable other than as a deviation from the predictions of GR.

https://news.ycombinator.com/item?id=19537192

wyattpeak3• 7 years ago

People aren't worried about it because it doesn't seem like a problem. We know that weakly-interacting matter can exist (as demonstrated by neutrinos), and there's nothing odd about the behaviour of dark matter: it seems to behave exactly as we'd expect weakly-interacting matter to behave. That's certainly not case closed * , but it's plenty to make the explanation perfectly reasonable as a working theory.

On a more philosophical level, though, if experts aren't concerned about something, and you as an amateur are, you're almost certainly the one who is wrong. Assume you are, and look for why, rather than questioning their conclusions. It's like the old adage about compiler bugs: they exist, but if you think you've found one, you haven't.

* And indeed scientists don't treat it as though it is - there are several other theories, though it's the strongest contender.

thatoneuser3• 7 years ago

Id take what you say about amateurs worrying what professionals don't to be true for the most part, but it's also not always true. Even in physics.

Iirc about a hundred years ago when we were trying to measure electron diameter, several iterations of scientists bsed there results assuming the last guy was accurate. Dark matter has a lot of similar mysticism and I would not be at all surprised to see a metric shit ton of scientists just being sheep and going along with incorrect models. I'd also not be surprised if they were all spot on too.

For reference in grad school I worked in a neutrino lab right by a dark matter lab underground. So I'm not an expert but do have decent exposure.

Tor3• 7 years ago

It's like the old adage about compiler bugs: they exist, but if you think you've found one, you haven't.

I'm not sure if that's a good simile. I've found several compiler bugs in my time, and I proved that with assembly output from the compilers and I've received updated compilers from the vendor as a result of my reports.

I suspect that to find "bugs" in physical theories must be orders of magnitudes more unlikely.

mikorym10• 7 years ago

When I went to listen to a dark matter talk at the observatory in Cape Town, my first response was: Why on earth do they keep insisting that the r^2 rule should hold?

Maybe a physicist can explain why, but as a mathematician my first quest would be to try to form a mathematical system that follows what we are observing, without introducing physical objects that we aren't actually seeing.

chopin3• 7 years ago

You should look up MOND. However, it seems to have a hard time explaining all phenomena we see.

mikorym10• 7 years ago

For those wondering:

"Modified Newtonian dynamics (MOND) is a theory that proposes a modification of Newton's laws to account for observed properties of galaxies. It is an alternative to the theory of dark matter in terms of explaining why galaxies do not appear to obey the currently understood laws of physics." [1]

Seems like this is (one approach to) exactly the question I asked! Even if proven not to lead to any satisfactory cosmological model, these kind of studies will at least tell you why the alternatives (to r^2) don't hold.

[1] https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics

maxnoe• 7 years ago

It's not like physicists didn't try.

Nobody really likes the idea of particles or other stuff that is impossible to measure.

But until now, General Relativity has passed every experimental test and most alternative approaches to dark matter other than "Some heavy stuff not interacting electricly" is basically ruled out by one or another observation.

There are solutions that fit the large scales pretty well (Cosmic Microwave Background, Galaxy Formation) but fail at the smaller scales (Orbital speeds) and vice versa.

mikorym10• 7 years ago

Sorry for a perhaps simple question.

Which part of GR requires that GR => r^2?

I can try to think of why, but I'd be guessing. I understand that many things in GR follows from when we translate reference frames that there is a light speed constancy requirement. My exposure to physics is via category theory and specifically self-dual theories that apply to the quantum sized world.

acqq4• 7 years ago

It simply matches the measurements.

Modern science has available modern technology to measure so much and with such a precision that any theory that attempts to be scientifically accepted has to match with the existing measurements.

The only approach that is not "dark mater" which is not completely disqualifying itself on all scales (by not matching anything) is MOND, which is still more "let's try to find some formulas that can match at least some observations" than something that even now can be consistent with all observations and measurements. Still, where MOND doesn't match the observations, it fails not in the orders of the magnitudes, it even results in the wrong shape of the curve:

https://arxiv.org/abs/1112.1320

"The biggest challenge facing MOND today is the shape of the matter power spectrum. The shape depicted in Fig. 1 is related to the acoustic oscillations observed in the CMB. If the Universe is dominated by dark matter, these matter oscillations, dubbed Baryon Acoustic Oscillations (BAO), are highly suppressed as the baryons fall into the potential wells created by dark matter, leaving only percent level traces of the primordial oscillations. In a no-dark matter model, on the other hand, the oscillations should be just as apparent in matter as they are in the radiation. Indeed, Fig. 1 illustrates that – even if a generalization such as TeVeS fixes the amplitude problem – the shape of the predicted spectrum is in violent disagreement with the observed shape."

Or to summarize:

https://medium.com/starts-with-a-bang/theres-a-debate-raging...

"On the scales of groups of galaxies, individual galaxy clusters, colliding galaxy clusters, the cosmic web, and the leftover radiation from the Big Bang, MOND’s predictions fail to match reality, whereas dark matter succeeds spectacularly. It’s possible, and perhaps even likely, that someday we will understand enough about dark matter to understand why and how the MOND phenomenon on the scales of individual galaxies arises. But when you look at the full suite of evidence, dark matter is practically a scientific certainty. It’s only if you ignore all of modern cosmology that the modified gravity alternative looks viable. Selectively ignoring the robust evidence that contradicts you may win you a debate in the eyes of the general public. But in the scientific realm, the evidence has already decided the matter, and 5/6ths of it is dark."

dnautics3• 7 years ago

The r^2 rule should hold because there is a concept called "flux". Imagine a field of force emanating from the center of a sphere. Now twiddle the radius of the field. Presume the intensity of the field will be distributed evenly, but diluted by the net surface area of the sphere, that surface area will in proportion to the square of the radius.

That said there are some fascinating alternative theories of gravity such as mond or the unruh effect which don't invoke an inverse swuare rule.

mikorym10• 7 years ago

I have had rudimentary exposure to this and do find this perhaps one of the best intuitive approaches.

Why is the rule not r^3 though? And what would the rule be in a 2-dimensional world?

TomMckenny• 7 years ago

Not an analytic answer but I understand there are galaxies without dark matter.

I imagine a theory that approaches r^2 on some galactic scales but not others would not very elegant.

appleflaxen• 7 years ago

what is the r^2 law in the context of dark matter? i read the post, and didn't see this term anywhere in it.

mikorym10• 7 years ago

Dark matter is introduced to account for discrepancies with the r^2 rule when just accounting for "visible" matter.

noselasd• 7 years ago

But that's what the physicists have tried (and not been successful at so far).

The issue is that modifying how we think gravity and matter works is not just a change in a math equation.

Changing those equations would also mean a whole chunk of modern physics, including general relativity is wrong - yet all those theories can be observed and confirmed in many very different ways to be consistent and valid.

So if you change those equations to adjust for dark matter, they no longer give the result for many other phenomena that we observe.

Gravityloss• 7 years ago

There are theories. I don't claim to understand this but there are persistent physicists having driven alternate formulas for many many years. Example: http://riofriospacetime.blogspot.com/

nwallin• 7 years ago

They did try. Those alternative theories fall under an umbrella called MOND- MOdified Newtonian Dynamics. They were actually some of the first real proposals to solve the dark matter problem. Unfortunately, none of these theories panned out.

The easiest to understand evidence against MOND is shown in the bullet cluster. The bullet cluster is a pair of galaxies in the process of colliding. They also happen to be gravitationally lensing galaxies behind them. While the xray and visible light observations show that gas clouds that make up the bulk of the normal matter in the galaxies stopped when they hit each other, (like two cars in a head on collision) the gravitational lensing shows that the overwhelming majority of the mass in the galaxies simply passed straight through, the way dark matter as particles would.

So in order to accommodate the bullet cluster, MOND will need to show that empty space has some sort of momentum and memory, which is going to be much less elegant than a second hierarchy of particles which do not interact via the electromagnetic or strong nuclear forces.

There are a very large number of other observations which also disprove MOND or variations on them, the bullet cluster is just the easiest to describe in a paragraph.

It's actually very, very common for laypeople to come up with MOND as a solution for dark matter. I'm pretty sure I did when I first heard about dark matter. I don't think I've ever seen a dark matter post on HN or reddit that didn't include at least one post positing MOND, even if (especially if) they don't that the theory they came up with has a name, an acronym, and had already been thoroughly disproven by the scientific community.

https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics https://en.wikipedia.org/wiki/Bullet_Cluster

thaumasiotes• 7 years ago

even if (especially if) they don't [know] that the theory they came up with has a name, an acronym, and had already been thoroughly disproven by the scientific community.

Without commenting on the merits, I think the theory "traditional kinematics need to be adjusted somehow at large scales" is a little too vague to have been disproven.

zuminator• 7 years ago

Galaxies don't all have a proportionally equal amount of dark matter. So if you invented maths that would account for some dark matter, they would fail in other cases. You'd still have anomalous events that would require the type of ad hoc explanation that dark matter solves. Plus an extra superfluous theory on top of that.

tylerjwilk002• 7 years ago

The counter point is that with dark matter you can just keep adding more dark matter until it fits with observations.

Seems a bit lazy and not very innovative.

GuB-42• 7 years ago

1- 1/r^2 is the most natural in 3D space. Think of it as the surface of en expanding sphere. A lot of things follow the inverse square law: electric fields, light intensity, sound intensity,... It is not a strong argument: there are other things that don't follow 1/r^2 and we are not even sure our universe really is 3D (though there is strong evidence for it).

2- Theories that don't involve 1/r^2 (MOND) exist, but they are not sufficient to match observations without involving dark matter. And following Occam's razor, since MOND introduces another parameter (the behavior of gravity on long scales), but doesn't simplify anything (dark matter is still there), it is not preferred.

3- While we don't know the details about dark matter, we "see" it in a way. We see it affect the movement of galaxies, and the gravitational lensing effect it has. It is just that we can't observe it with our preferred methods, which involve electromagnetism. I mean, we don't need to see a glass panel to know that it's there. Sure, we'd like to know more, and evidence of dark matter is weaker than our glass pane, but we simply don't have anything better right now.

mikorym10• 7 years ago

A question on 1-: does introduction of intermediary objects stack well? What I mean, for instance: If the moon is between us and the sun, the light gets blocked out but gravity does not. Light intensity then does not stack well (for visible light frequencies) when there are intermediate objects. Or does the analogy here require a more formal transposition to GR and the distortion of spacetime?

nabla9• 7 years ago

As a mathematician, you might want to start from Gauss's law for gravity (flux theorem for gravity). You need only the Gauss law and zero curl assumption to derive Newton's law of gravity.

mikorym10• 7 years ago

It is interesting to see some of Gauss's side quests during his life and the scope of his interests.

I remember reading that Gauss's (and his contemporaries') foray into statistics was greatly motivated by the central limit theorem. Every now and then one sees a question about least squares, asking why we don't usually use least cubes. [1]

Abel said of Gauss: "He is like the fox who erases his tracks in the sand with his tail."

[1] In such a discussion, if we are lucky to have a healthy discusion, we see references such as https://en.wikipedia.org/wiki/Gauss%E2%80%93Markov_theorem.

pchiusano3• 7 years ago

You might be interested in quantized inertia http://physicsfromtheedge.blogspot.com/ which is a model that does away with the need for dark matter and that has been gaining some interest. For instance, author claims it replicates the success of MOND but also predicts where MOND and GR both fail (see wide binaries posts on the blog).

I 100% agree that when the model doesn’t fit the data, making up some hitherto undetected kind of matter, distributed in just the right way to explain the discrepancies, is kinda odd... the QI author is constantly complaining about this.

perl4ever4• 7 years ago

"making up some hitherto undetected kind of matter, distributed in just the right way to explain the discrepancies, is kinda odd"

That seems totally backwards to me. Matter, by definition, is what is distributed spatially in just the right way to explain our observations. Physical laws, by definition, are not; they are universal. So why keep trying to explain what appears to be matter with adjustments to physical laws?

It's like you kept seeing elephant footprints appear out of nowhere, but insisted that rather than believe in invisible elephants, the most parsimonious explanation is that they are a natural consequence of a corrected law of gravity. That is, to me, turning Occam's Razor inside out.

kryptiskt• 7 years ago

It's very natural in a three-dimensional space that the force tapers off by r^2 as the area it has to cover increases by that.

But Newton didn't take that for granted, he examined other laws and proved that there were no stable elliptical orbits under them.

virgakwolfw• 7 years ago

I've been reading Ars for many years now and I just wanted to say that the clarity this specific article displays in explaining astronomical concepts to a layperson is really impressive and appreciated. Sometimes I get lost in these types of write-ups, but you gave readers the state of the field and why this study - which simply provides evidence that helps likely nix one potential explanation - truly was important in that context. It was all just so digestible and satisfying.

cmroanirgo• 7 years ago

Totally agree. I loved the implication that one simple 7 hour viewing yielded 15500 events to be filtered and that they could observe a binary star system's change in that time frame. To me, that's awesome!

didibus3• 7 years ago

The article doesn't seem to say it rules out black holes or dark matter, at least as I understand it. It just rules out primordial black hole.

Am I reading it wrong? Or why is the title so misleadingly?

SargeZT2• 7 years ago

The thing is that there's no conceivable mechanism we know of for a non-primordial black hole to form and be as small and common as would be required to explain away dark matter.

didibus3• 7 years ago

Yes, I understand that. So primordial black holes don't explain dark matter, but dark matter as a hypothesis came before it no? To explain something else no? The article wasn't very clear about all the links.

Also, there's zero indication in the article that this invalidates the existence of black holes.

And about dark matter, the last sentence says: "But the study does slim down the already thin chances that they are the source of dark matter's effects."

Insinuating that primordial black hole were a hypothesis for the effects of dark matter. Not that dark matter theory is proven inconsistent by the lack of evidence for primordial black holes.

I'm looking for someone who knows better I guess, to clarify. I'm only interpreting this using my reading skills from the article itself.

chopin3• 7 years ago

Even more the article mentions that primordial dark matter is required to explain the signature of the CMB. Therefore, if black holes form the dark matter they must have been formed primordial.

joemag• 7 years ago

Sixty Symbols, which is a great channel for these kinds f topics, did a great video on primordial black holes a few years ago: https://youtu.be/gs3mtZPySeM

UweSchmidt• 7 years ago

It seems like the number of telescopes are a limiting factor in astronomy, and while expensive, new telescopes seem to be a straightforward way to get interesting new results. It is unfortunate that researchers have to wait for telescope time like computer scientists had to wait for computer time back in the day.

petschge• 7 years ago

The request for additional funding for extra telescopes is always met with the question "but what use is that knowledge?" Politicians don't want Moon missions, they want Teflon coated no-stick pans. They don't want Higgs bosons, they want the WorldWideWeb. Problem is you never know what commercially useful things you will accidentally find while you hunt pure knowledge.

ngcc_hk• 7 years ago

We have burnt before. We invent something to fit our idea eg all wave need a medium. Hence light run in ether and ... in fact we even call Ethernet in remembrance of this ether. But it does exist.

We have done it before. We believe there is one rule from smallest to the largest. God does not play dice with us and definitely not in the dark. We were wrong.

Do not know whether this dark material (and the total different case of dark energy). Just to say eliminate one more theory like dark hole may not be the end of non- or better the birth of Dark Matter. If it is just weak ... but dark. Still need convincing most positively.

* search for why Ethernet is called Ethernet you should find this :

“In 1973, Metcalfe changed the name to “Ethernet.” He did this to make it clear that the system he had created would support any computer, not just Alto’s.

He chose the name based on the word “ether” as a way of describing an essential feature of the system: the physical medium carrying bits to stations.

He thought this was much like the old luminiferous ether was once thought to propagate electromagnetic waves through space.”

One night of telescope time rules out black hole/dark matter idea

Related Stories