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Is dark matter’s “nightmare scenario” true?

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Re: Is dark matter’s “nightmare scenario” true?

#141

Post by igiveup »

api wrote: post #124

I’m sure physicists have already thought about this but… Has anyone considered modeling the effect currently explained via dark matter as a new kind of force or field? Like a distinct force generated by mass and its relationship to space time? This wouldn’t be modified gravity but a proposal for an entirely new force whose effect is what we currently explain with the “fudge factor” of dark matter. From the rough pict…

If the unmodified gravity and this new force always oocur together, why not just call them one force? What is it that makes them "distinct"?

Re: Is dark matter’s “nightmare scenario” true?

#142

Post by ephimetheus »

denton-scratch wrote: post #122
ephimetheus wrote: post #50

Earlier quoted context omitted.

It’s not good because it means there is something in nature that we cannot understand and study, because we cannot in fact observe it directly. The gravitational discrepancies we have already, but without an explanation or observation, they’re not very satisfactory.

> because we cannot in fact observe it directly. We can't observe anything "directly", other than the contents of our own minds. The "gravitational discrepancies" are an observation. It seems to me (non-physicist, non-cosmologist) that DM proponents can't tell us what DM is, despite being able to observe it. The article's "nightmare" is that it might turn out to be impossible to do that in principle. To my mind, that…

Directly here refers to explicit detection (“here is a signal that is DM and gives us immediate knowledge about its properties”) as opposed to implicit detection through inferring DMs existence from a lack of something.

A lot of people complain about DM being fuzzy, and that’s exactly why: we only have indirect evidence. So what everyone wants is a direct measurement of DM, for example a particle signal if DM is a WIMP.

And to your last point: that’s exactly it, the thought of an unknowable thing in the universe is terrifying, frankly. And this has nothing to do with wanting to be right, whatever DM is, I just want to know, even if it’s fancy MOND without defects somehow, or MACHOs.

Re: Is dark matter’s “nightmare scenario” true?

#143

Post by thriftwy »

treis wrote: post #119
panda-giddiness wrote: post #115

Earlier quoted context omitted.

On the contrary, if dark matter were to interact purely gravitationally, then there would be little friction to slow it down. This would prevent dark matter from clumping, which is in agreement with observations.

I don't think so. Say you had two stationary whatevers of dark matter 1 meter apart alone in the universe. At t=0 they accelerate towards each other. At some time they cross and occupy the exact same point. R becomes 0 and the force becomes infinite. They should be stuck together.

Nope - they would bounce.

Re: Is dark matter’s “nightmare scenario” true?

#144

Post by stouset »

CuriouslyC wrote: post #118
mr_mitm wrote: post #43

Earlier quoted context omitted.

Probably because it's the only piece of evidence you can understand with just high school physics. Most laypeople have trouble understanding that the universe is not expanding from a single point, so how would they be able to understand what the cosmic background radiation is, much less why its angular power spectrum has peaks at particular positions? It's a common pattern with crackpots as well, that they focus on "…

Crackpots emerge when a conceptual model is weak. They don't care how strong a mathematical model is, which is why they ignore SM and other areas where "theory" literally means a mathematical model, and nothing else. Having a lot of crackpots proposing bad theories is a sign that your conceptual model is garbage, just a bad attempt to hand wave a bunch of math that happens to predict reality, and you should stop pret…

> Having a lot of crackpots proposing bad theories is a sign that your conceptual model is garbage

We have crackpots proposing that the Earth is flat.

Re: Is dark matter’s “nightmare scenario” true?

#145

Post by lamontcg »

doliveira wrote: post #35

Why do people in the comments always ignore that dark matter has way more evidence for it than just galaxy rotation curves (something very well explained in the article)? It's quite tiresome to read the same objections as if physicists somehow hadn't thought of them.

> It's quite tiresome to read the same objections as if physicists somehow hadn't thought of them.

Okay now do climate change and climatologists.

And most people just don't bother to read the article at all it seems. No better than reddit.

Changing gears, though, and trying to be more useful, if you want more coverage on this topic there's a note in Peter Woit's blog:

https://www.math.columbia.edu/~woit/wordpress/?p=13232

Points to another blog which attacks the "nightmare scenario":

https://tritonstation.com/2022/11/29/the-angel-particle/

I don't particularly buy that a gravity-only interacting particle "is not physics". If that is what exists, that is what exists. And we've already detected it via dark matter observations. So it is physics. What we can't do is ever really prove it other than by exclusion, but if we racked up a thousand years of failure, we'd have to accept that it was real (hopefully by then not dogmatically and we'd let any kid who wanted to tilt at windmill to go for it).

And Woit links to a paper on dark matter being only a right handed majorana neutrino, requiring no real physics beyond the standard model (plus three right handed non-interacting neutrinos): https://arxiv.org/abs/1803.08930

And links to a comment on that in John Baez's blog:

https://golem.ph.utexas.edu/category/2022/12/neutrino_dark_m...

Re: Is dark matter’s “nightmare scenario” true?

#146

Post by treis »

thriftwy wrote: post #143
treis wrote: post #119

Earlier quoted context omitted.

I don't think so. Say you had two stationary whatevers of dark matter 1 meter apart alone in the universe. At t=0 they accelerate towards each other. At some time they cross and occupy the exact same point. R becomes 0 and the force becomes infinite. They should be stuck together.

Nope - they would bounce.

If they bounce then they interact with some force besides gravity

Re: Is dark matter’s “nightmare scenario” true?

#147

Post by miika »

miika wrote: post #7

Nightmare for who? How hard it is to admit that their equations are incorrect? Even amateur like myself can see that the dark matter is adhoc value that was calculated in order to patch the standard model. There are several better alternatives but do we need to wait until these stubborn believers have passed away until the world can move forward?

Maybe problem is they do consider Space to be empty. Maybe if they would take into account all those quantum fluctuations in there and add that energy maybe they would land at critical mass of the Universe.

To paint this idea with other example, if you were to figure out mass of a world, but the world was just an image reflecting off a surface of water, then they would focus only on the light particles coming off the surface and ignore the water. At some point they would come to realize that something big is missing. They could find out the value for how much it should be. That’s exactly the case with dark matter I’m quite sure. Space is like water they ignore.

But I don’t know anything, really (sorry to hear if that’s a problem for someone). Why there is possibility to comment on these articles anyways?

Re: Is dark matter’s “nightmare scenario” true?

#148

Post by oneoneonetwo »

antonvs wrote: post #47
choeger wrote: post #30

My intuitive objection against dark matter is that it's basically an infinite amount of additional parameters to be fitted to the observations. Galaxy behaves weirdly? Add dark matter! It behaves as expected? It obviously has lost its dark matter! It stands to reason that for every possible observation, a particular DM configuration can be calculated. I fail to see how dark matter could ever be falsified. The best po…

Dark matter is not a “recursive property of gravity” because it’s not consistent like that, as your own initial objection suggests. The concept of a particle that only interacts via gravity is straightforward. Consider neutrinos, which only interact via gravity and the weak force. Trillions of them pass through your body every second. Take away the weak force interaction and add some mass, and you have a dark matter…

>which admittedly, many people still seem to want to do.

This occurs because most science is not the "the frontiers of modern physics". But even then, falsification in the frontiers of modern physics is still a useful tool.

Re: Is dark matter’s “nightmare scenario” true?

#149

Post by rapjr9 »

Reading this I realized that dark matter is starting to sound somewhat like the idea of the "ether". It's everywhere, it affects everything, but we can't see it or interact with it easily. It's somewhat different than the idea of the ether in that it is not thought to be a homogenous, pervasive field; instead it clumps around gravity. But it has some very ether-like aspects, maybe some we have not discovered yet. I always thought we abandoned the idea of an ether too soon. Why does it have to be evenly spread? Why does it have to respond to things like direction or EM waves? Maybe there are some simple experiments that could explore the idea of an ether/dark matter further. Pure speculation but that is my intuition.

Re: Is dark matter’s “nightmare scenario” true?

#150

Post by credit_guy »

doliveira wrote: post #35

Why do people in the comments always ignore that dark matter has way more evidence for it than just galaxy rotation curves (something very well explained in the article)? It's quite tiresome to read the same objections as if physicists somehow hadn't thought of them.

Here. I'll come with a different objection.

Everything we see in the Universe outside our own galaxy is static. We don't have enough parallax to actually perceive objects (stars) moving outside our galaxy. Ok, there's an exception, people were able to perceive the movement of one star in one of our satellite galaxies in 2012. That's about it. So, when people talk about galaxy rotation curves, that's based on a sample of one, our own galaxy. Actually, we can plot galaxy rotation curves for other galaxies, but based on indirect evidence, such as the redshift. How accurate is that? Come to think of it, we can't estimate directly the distance to any galaxy beyond and including the Andromeda galaxy. But again, we can estimate indirectly. Only that estimation is based on a stack of estimations each with its own uncertainties.

Now, if you work in the area, stop me right here and tell me you went through that stack of estimates, and check all the uncertainties, and are confident there's no potential error anywhere.

Because, as an outsider, if I do a bit of Bayesian estimation, and I have to choose between the dark matter and the possibility that everything that can be explained with dark matter is actually a result of estimation errors, I'm somewhat on the fence. Every year that the hunt for dark matter brings nothing I'm more inclined to think there's a different explanation out there. Like the frame dragging explanation discussed in [1].

[1] https://physics.stackexchange.com/questions/618981/has-frame...

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