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A Physicist Who Denies Dark Matter

nautil.us

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Re: A Physicist Who Denies Dark Matter

#161

Post by dnautics »

hwillis wrote: post #99
maratd wrote: post #51

Earlier quoted context omitted.

When we're confronted with something we can't explain using our existing equations and theories, the conclusion is that there must be some mysterious thing there that fixes our current equations and makes them work again? A thing we can't detect or see or have any other evidence of ... other than our equations and theories need that thing there for them to work? > In other words situations where we see twin images of…

Dark matter is predicted at every level of astrophysics. It's not just "hey, galaxies look weird". The amount of visible matter only accounts for 4% of the cosmic microwave background. The CMB is extremely smooth, but visible matter is highly clumped up. This can only be explained by a huge amount of matter that doesn't clump up ie non-baryonic. The ratio of deuterium to hydrogen rises based on the density, since the…

> solved exactly by using the measurements of dark matter that already existed...

Just be careful. Dark matter distributions are highly paramterized quasi-continuous functions, so getting measurements to match exactly is a function of their definition, not an emergent property. While we do feel confident that there could something reasonable there, a priori exactitude cannot be evidence because that's begging the question and also possibly over fitting parameters.

Re: A Physicist Who Denies Dark Matter

#162

Post by dnautics »

joeberon wrote: post #78
autokad wrote: post #72

Earlier quoted context omitted.

"there are no politics involved in this kind of research" While it might not be true in this case, you couldn't be further from the truth. there is an EXTREME amount of politics. people's careers are based on entire assumptions, thesis', papers, and work could be all for not if based on false assumptions.

Yeah there's a huge amount of politics in research IN GENERAL, but not so much in physics. Like there are no big questions covered up because they're inconvenient or anything.

I think the commenter meant politics in the "office politics"/"playing politics" sense, not the "political party" sense

Re: A Physicist Who Denies Dark Matter

#163

Post by tynpeddler »

badosu wrote: post #44
shakna wrote: post #7

Earlier quoted context omitted.

Maybe I can expand. I can deny the Earth is flat, because there is an abundance of evidence that it is round. I can't deny that there are 650 elements, because as far as I know, other elements may be discovered. But I can certainly doubt it, and supply alternative theories. I can deny allegations of wrong doing, because they either happened, or didn't. But Dark Matter isn't assured yet. Denying it means it either exi…

Dark Matter is not just 'something we don't understand yet'. It has predictable effects on observations and adheres to some properties, see: https://en.wikipedia.org/wiki/Bullet_Cluster .

That's evidence, not proof. We still don't have enough evidence to say conclusively that Dark matter is as we currently imagine it. And of course the same can be said about MOND.

Here's Milgrom's interpretation of the bullet cluster: http://www.astro.umd.edu/~ssm/mond/moti_bullet.html

Re: A Physicist Who Denies Dark Matter

#164

Post by kradem »

boomboomsubban wrote: post #150
kradem wrote: post #146

Earlier quoted context omitted.

Thank you very much for your effort here in explaining things. There's nothing here in the thread powered by "my logic". I'm just certain that dark matter, ether, the Holy Grail, or anything, could be abandoned in our minds once we find the prettier chick to cope with, no matter how well we understood the previous one.

Yes, we could abandon it. The point of science is that we never should. Before the scientific method was adopted, we would take that pretty woman, ignore any flaws, and make them essentially god. A new one had almost no chance to compete, even of they were much prettier. With the scientific method, we say that she's the best around, but there's probably a better one out there, and with a little work it might be the o…

Yep, the best around trying to stand the test of time.

Re: A Physicist Who Denies Dark Matter

#165

Post by effie »

hwillis wrote: post #126
effie wrote: post #120

Earlier quoted context omitted.

> The amount of visible matter only accounts for 4% of the cosmic microwave background. Could you explain what do you mean by 'accounts for 4% of the cosmic microwave background'? How is one supposed to account for CMB by matter density, when its spectrum is almost equilibrium one (thus consistent with almost any value of matter density)?

The CMB has a certain spectrum and temperature. The amount of energy in the universe correlates to the amount of mass in the universe. The more energy and mass was present in the big bang, the hotter the CMB will be. The amount of visible matter corresponds to a CMB temperature that is far lower than what we see.

> The amount of visible matter corresponds to a CMB temperature that is far lower than what we see.

Why would there be a relation between CMB temperature and amount of (visible+invisible) matter? I suppose the CMB temperature decreases in time. Would`s the relation you talk about imply that the mass or density of mass of the Universe then has to decrease as well?

Re: A Physicist Who Denies Dark Matter

#166

Post by jessriedel »

BoiledCabbage wrote: post #158
jessriedel wrote: post #145

Earlier quoted context omitted.

1. The proper question is "When a commenter is very wrong on a technical topic, is it net-positive for someone with expertise to point this out even if they don't contribute further?". I think the answer is obviously "yes". You seem to be more concerned with whether people are pulling their fair share, vs. being exempt/special, which I claim is the wrong question. 2. Effort scales with detail. The example comment you…

What you're writing shows you continue to miss the point.

I've engaged with the specifics of each of your points. We may disagree, but it's not because I misunderstood your claims.

Re: A Physicist Who Denies Dark Matter

#167

Post by michaelcampbell »

mark-r wrote: post #153
hwillis wrote: post #97

Earlier quoted context omitted.

Can't be black holes. For one thing they would start becoming visible through Hawking radiation if they were small enough to be homogenous like dark matter. Secondly baryon acoustic oscillations set a limit on how many black holes there can be. For your second part, the constant velocity is very well explained. The dark matter is just very broadly distributed. That's a natural consequence of not interacting with anyt…

How does this dark matter have enough gravitational effect to change the structure of the universe, yet not clump together? It doesn't make sense.

Unless it doesn't exhibit gravitational properties with itself?

Just a thought; I have no training or experience here.

Re: A Physicist Who Denies Dark Matter

#168

Post by droithomme »

jessriedel wrote: post #35

Almost ever sentence in this comment is wrong.

I reviewed the credentials of the person who made this parent post I am now responding to. I found him to be an exceptionally qualified expert and published scientist. He not only has high levels of credibility to make his statement, but is very likely to be the most qualified person in the entire thread to comment on the subject.

Thus it is very interesting and fascinating that his comments in his own field of expertise were downvoted by people who are almost certainly ignorant about the details of topics in his field. Also astonishing in its hubris was the ultimate detachment of the entire thread and the pronouncement by an unqualified individual that it is not on topic despite its clearly being on topic and exceptionally relevant.

Such are the dangers of fascist systems where unqualified individuals rule with an iron fist. The result no doubt will be similar to that of the Soviet farming system when ruled by small minded unqualified bureaucrats rather than experts in the field.

Re: A Physicist Who Denies Dark Matter

#169

Post by hwillis »

dnautics wrote: post #161
hwillis wrote: post #99

Earlier quoted context omitted.

Dark matter is predicted at every level of astrophysics. It's not just "hey, galaxies look weird". The amount of visible matter only accounts for 4% of the cosmic microwave background. The CMB is extremely smooth, but visible matter is highly clumped up. This can only be explained by a huge amount of matter that doesn't clump up ie non-baryonic. The ratio of deuterium to hydrogen rises based on the density, since the…

> solved exactly by using the measurements of dark matter that already existed... Just be careful. Dark matter distributions are highly paramterized quasi-continuous functions, so getting measurements to match exactly is a function of their definition, not an emergent property. While we do feel confident that there could something reasonable there, a priori exactitude cannot be evidence because that's begging the que…

I have become a little aggravated by people who don't believe in dark matter

Re: A Physicist Who Denies Dark Matter

#170

Post by dnautics »

hwillis wrote: post #169
dnautics wrote: post #161

Earlier quoted context omitted.

> solved exactly by using the measurements of dark matter that already existed... Just be careful. Dark matter distributions are highly paramterized quasi-continuous functions, so getting measurements to match exactly is a function of their definition, not an emergent property. While we do feel confident that there could something reasonable there, a priori exactitude cannot be evidence because that's begging the que…

I have become a little aggravated by people who don't believe in dark matter

why? Until direct evidence and predictions of properties emerge, from an epistemological point of view it's still a very shaky model. If it all turned out to be epicycles it wouldn't be surprising. Or maybe a better analogy is Vulcan. https://en.wikipedia.org/wiki/Vulcan_(hypothetical_planet)

The closest we have come to direct evidence are the independent calculations of the properties if it's a self-annhilating particle that agree with a certain set of observations. Even so that seriously breaks a conservation rule, because if there's no proposed way to create dark matter, the universe makes no sense.

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