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

A Physicist Who Denies That Dark Matter Exists

cosmos.nautil.us

Post reply on HN
Print view View original

41–50 of 193 posts

Re: A Physicist Who Denies That Dark Matter Exists

#41

Post by davrosthedalek »

simonh wrote: post #34
SagelyGuru wrote: post #15

There is another possible explanation instead of dark matter and that is electric charge and currents (plasma flows). Electric force is many orders of magnitude stronger than gravity. So, if the objects in the universe are charged, the repelling force between them could account for the expansion acceleration in a very simple way.

Except that electrical/magnetic forces are vastly more powerful than gravitational forces. Any such force that's noticeable at the cosmic scale would be powerful enough at the object scale (star, planet, even galaxy) to tear them apart or cause them to collapse. Lets suppose the Earth and the Sun were both positively charged sufficiently that their repulsive force was enough to noticeably affect the orbit of the Eart…

I don't think this is true. Let's assume every matter is our solar system is actually not neutral, but slightly positively charged. For Sun-Earth, let's say this reduces the effective force by 1%. Since both Coulomb and gravitational attraction has the same power law, this fixes the change everywhere, or in other words, you could absorb the change into the gravitational constant. Same goes for making everything 1% less dense.

Re: A Physicist Who Denies That Dark Matter Exists

#42

Post by chongli »

thechao wrote: post #31
corey_moncure wrote: post #25

Earlier quoted context omitted.

>particles invented before being directly observed as support of dark matter hypothesis Correct me if I'm wrong, which is quite likely, but isn't it one of the qualities ascribed to dark matter that it doesn't interact with 'ordinary' matter or photons in any way other than gravity, and therefore can't be directly observed? Or to turn the question around, is the dark matter hypothesis actually falsifiable?

You can observe it via gravitational lensing. For instance: http://scienceblogs.com/startswithabang/2011/04/20/how-gravi... .

We can observe the effect of gravitational lensing. The claim that dark matter causes it is part of the same claim that dark matter is responsible for galactic rotation curves looking the way they do. Thus it does not provide any further support for the dark matter hypothesis.

Re: A Physicist Who Denies That Dark Matter Exists

#43

Post by saalweachter »

mikeash wrote: post #24
michaelbuckbee wrote: post #16

Earlier quoted context omitted.

There used to be this theory of Phlogiston, which was a material substance of heat (if you put a lit match under a brick, phlogiston would move from the match to the brick.) Today of course, this sounds ridiculous. But my physics teacher was always keen to point out that the people involved weren't stupid and that it was an important theory because it was a good starting mental model of how things actually worked and…

Phlogiston is an absolutely reasonable theory given what was known at the time. It's a really interesting example. Phlogiston is basically negative oxygen. It's very similar to how our traditional notion of electrical current moves in the opposite direction from the actual electrons, because people had no idea whether positive or negative charge was the one that moved around, and they just arbitrarily assigned the po…

Oxygen is also really weird from a certain point of view.

Your fuel is exhausted by gaining something. Your fuel may even still be there, but you can't keep burning it because there is too much of an extra thing, which is also necessary for burning.

Re: A Physicist Who Denies That Dark Matter Exists

#45

Post by publicfig »

Cyph0n wrote: post #17
contravariant wrote: post #9

Earlier quoted context omitted.

It's also worth pointing out that several similar 'holes' in theories have turned out to be correct. Things like missing elements in the periodic table, and fundamental particles like the Ω− baryon or the Higgs boson, where all things that seemed like holes in a theory, but were later discovered to exist.

And how many "holes" proved to be incorrect? I think that using the history of past true positives is a weak argument for dark matter.

I'm not sure it's as much an argument for dark matter and more an argument against the idea that if you must create a force or type of matter (or matter itself) in order to make a model work, then the flaw is in the model. By showing examples of this being a useful method in the past, it helps discredit the idea that the model has to be wrong, as opposed to proving idea that the model has to be right which are two different arguments entirely.

Re: A Physicist Who Denies That Dark Matter Exists

#46

Post by fahadkhan »

contravariant wrote: post #9
snowwrestler wrote: post #5

Earlier quoted context omitted.

Ok, but physics has had a long and fruitful history of inventing invisible stuff when theory and results disagree. I mean, have you ever seen an atom? A proton? A neutrino? Scientific theories are generally not just amalgamations of tweaks. General relativity is internally consistent, explains so much , and just got a huge boost last year with the first detection of gravity waves... which BTW are invisible stuff that…

It's also worth pointing out that several similar 'holes' in theories have turned out to be correct. Things like missing elements in the periodic table, and fundamental particles like the Ω− baryon or the Higgs boson, where all things that seemed like holes in a theory, but were later discovered to exist.

Black holes were discovered in theory before any there was any evidence too.

Re: A Physicist Who Denies That Dark Matter Exists

#48

Post by [deleted] »

corey_moncure wrote: post #25
mikeash wrote: post #23

Earlier quoted context omitted.

Remember the discovery of Neptune? I mean, not directly, since everyone from that time is dead, but.... That's a nice example of a prediction being wrong, inventing an as-yet-unobserved chunk of matter to fix it, and that invention then being correct. Of course, there's a counter-example in the inner solar system in the form of Vulcan. It was invented to explain Mercury's orbit, but the solution ended up being Relati…

>particles invented before being directly observed as support of dark matter hypothesis Correct me if I'm wrong, which is quite likely, but isn't it one of the qualities ascribed to dark matter that it doesn't interact with 'ordinary' matter or photons in any way other than gravity, and therefore can't be directly observed? Or to turn the question around, is the dark matter hypothesis actually falsifiable?

[deleted]

Re: A Physicist Who Denies That Dark Matter Exists

#49

Post by cozzyd »

d3ckard wrote: post #8
roryisok wrote: post #3

> "If Newtonian physics can’t predict the fixed curves, perhaps we should fix Newton, instead of making up a whole new class of matter just to fit our measurements." I've always felt this way about dark matter, but as a lay person with no background in physics, it's an opinion I'm hesitant to express. if you have a model that predicts something, but the prediction is off by several orders of magnitude, the model is w…

Same feelings here. I genuinely do not understand how adding unobservable objects would be the right approach instead of just fixing the equations.

Adding a particle is "just" fixing another equation (the standard model Lagrangian).

Re: A Physicist Who Denies That Dark Matter Exists

#50

Post by chopin »

Afaik there is strong support for dark matter via gravitational lensing effects of galaxies. Unfortunately it is not mentioned in the article whether MOND can cope with these observations. At least I would expect that there might be some integration of MOND into ART which explains that.
Post reply on HN