Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

A Physicist Who Denies Dark Matter

nautil.us

Post reply on HN
Print view View original

41–50 of 182 posts

Re: A Physicist Who Denies Dark Matter

#41

Post by vivekd »

RockyMcNuts wrote: post #11

How do you explaining gravitational lensing with no visible mass, without dark matter? In other words situations where we see twin images of a very distant galaxy because light curves around intervening mass, without sufficient mass observable to explain the deflection? I was under the impression that we could map dark matter localized to a precision that tended to rule out measurement error or a general divergence f…

>How do you explaining gravitational lensing with no visible mass, without dark matter?

Black holes?

The physicist says:

>What struck me was some regularity in the anomaly. The rotational velocities were not just larger than expected, they became constant with radius. Why? Sure, if there was dark matter, the speed of stars would be greater, but the rotation curves, meaning the rotational speed drawn as a function of the radius, could still go up and down depending on its distribution. But they didn’t.

That seems pretty damning for any theory that relies on dark matter.

Re: A Physicist Who Denies Dark Matter

#42

Post by nightcracker »

RockyMcNuts wrote: post #11

How do you explaining gravitational lensing with no visible mass, without dark matter? In other words situations where we see twin images of a very distant galaxy because light curves around intervening mass, without sufficient mass observable to explain the deflection? I was under the impression that we could map dark matter localized to a precision that tended to rule out measurement error or a general divergence f…

In the scenario you're describing a black hole would qualify, however IIRC there are other aspects of dark matter that black holes can't explain.

Re: A Physicist Who Denies Dark Matter

#43

Post by hwillis »

douche wrote: post #36
hwillis wrote: post #34

Earlier quoted context omitted.

>One of the recent most convincing things was the bullet cluster as described here.[1] We saw two galaxies collide where the "observed" matter actually underwent a collision but the gravitational lensing kept moving un-impeded which matches the belief that the majority of mass in a galaxy is collisionless dark matter that felt no colliding interaction and passed right on through bringing the bulk of the gravitational…

We don't understand how matter acrually works on a large scale. Inventing imaginary terms that we can't observe to satisfy the equations in the models to match the observed reality seems a poor practice.

We understand that when two galaxies hit each other, the visible mass gets all tangled up and suns and nebula smash into each other. Meanwhile the invisible mass continues onwards, oblivious to everything else. We CAN observe it and we have.

Seriously this is basic object permanence. We can see hidden things moving around by themselves. Dark matter is still there even when there's normal matter on top of it.

Re: A Physicist Who Denies Dark Matter

#44

Post by badosu »

shakna wrote: post #7
Lordarminius wrote: post #5

Earlier quoted context omitted.

> ...But, dark matter isn't something to be denied. Because it isn't understood yet, to the point where we can doubt its existence.... There is something not quite right with your logic and I am struggling to identify what it is :/

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 .

Re: A Physicist Who Denies Dark Matter

#45

Post by jcroll »

agentgt wrote: post #25

This almost an exact duplicate: http://cosmos.nautil.us/short/144/the-physicist-who-denies-t... and original HN comments here: https://news.ycombinator.com/item?id=13743439 Do people not search Agolia before posting? Is it acceptable to repost things? (I'm not HN expert).

Actually what's disturbing (and I am a paid subscriber to nautil.us) is that nautil.us is duplicating content. They took that old interview and passed it off as new content in their latest edition.

Not really fair to us paying readers!

Re: A Physicist Who Denies Dark Matter

#46

Post by signa11 »

RockyMcNuts wrote: post #11

How do you explaining gravitational lensing with no visible mass, without dark matter? In other words situations where we see twin images of a very distant galaxy because light curves around intervening mass, without sufficient mass observable to explain the deflection? I was under the impression that we could map dark matter localized to a precision that tended to rule out measurement error or a general divergence f…

> How do you explaining gravitational lensing with no visible mass, without dark matter?

black hole would produce the same result right ?

Re: A Physicist Who Denies Dark Matter

#47

Post by Avshalom »

douche wrote: post #36
hwillis wrote: post #34

Earlier quoted context omitted.

>One of the recent most convincing things was the bullet cluster as described here.[1] We saw two galaxies collide where the "observed" matter actually underwent a collision but the gravitational lensing kept moving un-impeded which matches the belief that the majority of mass in a galaxy is collisionless dark matter that felt no colliding interaction and passed right on through bringing the bulk of the gravitational…

We don't understand how matter acrually works on a large scale. Inventing imaginary terms that we can't observe to satisfy the equations in the models to match the observed reality seems a poor practice.

No.

When the model is wrong, you build a new model. A bunch of weakly interacting particles is the new model.

Re: A Physicist Who Denies Dark Matter

#48

Post by yorwba »

Maken wrote: post #16
_0w8t wrote: post #4

What is puzzling about MOND and to lesser extent about Dark Matter is that both uses violation of Newton mechanics to justify themselves when we know that Newtonian mechanics is wrong. The problem is that we cannot yet model behavior of galaxies using just General Relativity. Typically models assumes Newtonian physics with minimal accounting for relativity. However there is no sound proof that it is a valid approxima…

There is something that always puzzles me and I would like if something could illuminate me. How are those kind of massive scale astrophysical calculations made? Do they take into account every visible mass aggregate in the galaxy and simulate them, or just apply cinematic at scale assuming the galaxy centre is a point of certain mass? I have played a little with N body simulations and I can't but be amazed about how…

You may be interested in this paper: http://dl.acm.org/citation.cfm?doid=3028256.3015569

Re: A Physicist Who Denies Dark Matter

#49

Post by _ph_ »

vivekd wrote: post #41
RockyMcNuts wrote: post #11

How do you explaining gravitational lensing with no visible mass, without dark matter? In other words situations where we see twin images of a very distant galaxy because light curves around intervening mass, without sufficient mass observable to explain the deflection? I was under the impression that we could map dark matter localized to a precision that tended to rule out measurement error or a general divergence f…

>How do you explaining gravitational lensing with no visible mass, without dark matter? Black holes? The physicist says: >What struck me was some regularity in the anomaly. The rotational velocities were not just larger than expected, they became constant with radius. Why? Sure, if there was dark matter, the speed of stars would be greater, but the rotation curves, meaning the rotational speed drawn as a function of…

>>How do you explaining gravitational lensing with no visible mass, without dark matter? >Black holes?

Well, black holes are not really black, you can see their accretion disk. Also, a centralized huge mass would create a different velocity profile from what we are seeing. So black holes are pretty much out.

Re: A Physicist Who Denies Dark Matter

#50

Post by boomboomsubban »

kradem wrote: post #24
kobeya wrote: post #8

Earlier quoted context omitted.

He expressed it badly. The point I think he is trying to say is that dark matter can be neither proven nor disproven at this time with the information available. An intellectually honest person should remain open to both possibilities. You can say "I am not convinced of the dark matter hypothesis." But unless you have information the rest of us do not, you can't really say "I deny the dark matter hypothesis could be…

I [too] don't think it's about bad wording, yet pure bad logic. The article is positioned on the principle that was imagined based on wrong assumtions of other theory and which acceptance will dissmiss the other theory. I'm not even being close to think of being positioned on a side there, but afaic one could easily take one in this subthread. TL; DR yep, dark matter could be denied no matter of the state of its unde…

Acceptance doesn't dismiss theories, evidence does. A physicist shouldn't truly deny anything, just look at the evidence and say it is not the best theory.

Even with a better explanation, we can't be sure more information won't see the return of dark matter. Milgrom should understand this well, he's suggesting the return of the cosmological constant.

Post reply on HN