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Comment by miika | Hacker News Reader

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?

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At the moment there are no better alternatives that satisfy all the observations. If you try to replace General Relativity with something like Modified Newtonian Dynamics (MOND) [1], then you can get good fits to galaxy rotation curves. However, there are many sources of astronomical/cosmological data that will not bend to alternative gravity models, e.g the precise fluctuations of the cosmic microwave background put stringent bound on the matter components of the Universe.

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

I vaguely recall hearing that there are galaxies "without any dark-matter". Or, more accurately, galaxies whose rotational speed is consistent with general relativity without needing to presume dark matter exists in those galaxies.

If that is correct, does it not immediately invalidate MOND?

I think every physicist on the planet would love a nice elegant model of gravity that explains away “dark matter” observations. The next layer after Newton and Einstein. Clean and simple.

… but that’s just proven to be very very difficult. Evidence for dark matter comes from a wide range of observations, and while it’s pretty easy to come up with relativity replacements that could explain things like rotation curves nicely… other observations, from lensing and colliding galaxies like the bullet cluster are, just, well, messy.

An amateur seeing something that almost no respectable cosmologist can see is a red flag. It's not that simple.

Pretty much the only alternative is MoND, and judging by the how well it fits the observations, it's not better.

All modified gravity theories are falsified by astronomy as far as I know. There are galaxies out there without dark matter halos for example. Or where the dark matter halo is not centered around the core. This alone shuts down modified gravity.

I guess the nightmare is more that it might be undetectable. There’s a real possibility that DM is real, but we hit the neutrino floor at some point without finding anything (maybe couplings are too weak).

Until there’s an actual convincing alternative, that indeed is not as apparent as you make it out to be, that would be pretty terrible for a lot of physics.

Why isn’t it good for physics? It has found DM and can observe it via gravitational discrepancies, gets finally “solved” in this part. Does physics really need infinite modifications?

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.

"The eternal mystery of the world is its comprehensibility … The fact that it is comprehensible is a miracle."

If the nightmare scenario is true, there would finally be a counterexample to this.

> 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 would indeed be a nightmare; we would have to accept that there are limits to what we can learn about the Universe. I don't believe we have encountered any such limits before.

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.

> Even amateur like myself can see that

Appealing to your own ignorance doesn't actually strengthen your argument.

> dark matter is adhoc value that was calculated

Well the overall tone of your comment is pretty crummy but this is absolutely not true. You got this exactly backwards. Dark matter is just missing mass that is being observed. It doesn't patch any model, because physicists don't know what it is or what it is made of. But whatever that mass is, it is there, because all the standard ways that we observe mass, it exhibits. So it would instead be a leap to "patch the standard model"--whatever you mean by that--with these other "better alternatives" (I assume you mean MOND? No dice there, doesn't explain gravitational lensing).

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?

This is where I reference Mike McCulloch's theory Quantized Inertia, which predicts Galactic Rotation curves far more accurately than Relativity / Newton, without any fudge factors. (This is also where someone jumps in to inform me that he is "a crackpot", and should be ignored. FWIW QI seems like a promising theory to me, and I think it should be tested experimentally. )

How accurately does it predict the CMB fluctuations? Or weak lensing observations? Rotation curves might have been first, but they're actually not the strongest evidence for DM.

One funeral at a time, as the saying goes.

There are many good reasons to think that dark matter is a good solution to certain cosmological problems. There are also a few good reasons to think that dark matter is total BS. It is a genuine open question. No theory in this area is a good fit for all available evidence.

This is not a case of "progress by funeral" like, say, the Alzheimer's situation also on today's front page. The linked article is a good summary.

Anecdotally it seems like, inside the scientific community, the dark matter skeptics are all in the older generation.

science advances one death at a time. not the only domain in which the current experts and holding things hostage

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