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A Physicist Who Denies That Dark Matter Exists

cosmos.nautil.us

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Re: A Physicist Who Denies That Dark Matter Exists

#71

Post by dogma1138 »

mikeash wrote: post #23
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…

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…

Actually dark matter and dark energy are "fudge factors" that are being inserted in order to explain observations.

There are multiple "contenders" for dark matter, none of them actually explain observations and measurements.

Dark Energy is also in that same category especially in it's purest form as a "universal constant" that was added then removed then added back again to GR when we were sure if the universe is static, expanding at a constant pace or expanding under acceleration.

As far as MOND goes the biggest "curiosity" people have with it is that it works at all, because it shouldn't, you shouldn't be able to just fudge so many factors and have a theory that works, is stable, and predictive (even tho it has various issues especially with regards to cosmology like star and cluster formations).

Which might hint that there is actually something there. That gravity might not work in the same manner over distances, that maybe there is more than one gravity (there are hints that quantum gravity and what we call gravity might be different things already).

Re: A Physicist Who Denies That Dark Matter Exists

#72

Post by dogma1138 »

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?

That only is if dark matter is indeed "WIMPS" or weakly interactive massive particles.

But then again there are multiple contenders for dark matter.

Re: A Physicist Who Denies That Dark Matter Exists

#73

Post by danielweber »

dogma1138 wrote: post #71
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…

Actually dark matter and dark energy are "fudge factors" that are being inserted in order to explain observations. There are multiple "contenders" for dark matter, none of them actually explain observations and measurements. Dark Energy is also in that same category especially in it's purest form as a "universal constant" that was added then removed then added back again to GR when we were sure if the universe is sta…

Shouldn't there be a big lump of dark matter at the center of every planet, moon, and star?

If we were to hollow out an asteroid, would there still be a blob of intangible dark matter inside of it?

Re: A Physicist Who Denies That Dark Matter Exists

#74

Post by uf »

blueprint wrote: post #53
jerf wrote: post #13

Earlier quoted context omitted.

One of the mental problems that I think people get in this area is that you can't help but mentally imagine that there's just these few points of data that we need to hit, and so we have a lot of freedom in how to construct formulae that match the observation, so why are scientists being so obstinate about the possibility that MOND may be true? But that's not the case. We have petabytes of data from space (if not mor…

> but you start having to have some sort of really weird gravity memory effect in space or something, where space itself "remembers" that it used to have a lot of matter in it and still has a small amount of gravitation in it despite no longer containing the corresponding mass That's honestly not so "weird" at all. There are TONS of examples of objects and substances having that kind of behavior in nature. If I crash…

You can apply Occam's Razor here. Which is more likely?

That there's stuff that has a mass but doesn't interact well with light, or that space is able to curve itself without mass, thus also rendering Einstein false.

This immediately raises further questions: How long does space remember? How's the exact mechanism? Where and how does empty space store that information? What happens to E=mc2?

Re: A Physicist Who Denies That Dark Matter Exists

#75

Post by dogma1138 »

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've seen instances already where gravitational lensing was explained through other means (very dim clusters, dust, and even camera issues), we also don't know if the space time on those scales is "smooth", if it isn't then light will not travel in a straight line which would account for the lensing effects.

The spacetime curvature, mass/energy, and gravity have quite a few interesting interactions as in gravity as a force, vs gravity as a feature of spacetime, vs potential other forms of gravity. We aren't even sure at this point if a curved spacetime without mass/energy that would generate that curve, would actually produce gravity or not since we aren't able to observe this nor do we have a complete theory of gravity.

Re: A Physicist Who Denies That Dark Matter Exists

#76

Post by dogma1138 »

danielweber wrote: post #73
dogma1138 wrote: post #71

Earlier quoted context omitted.

Actually dark matter and dark energy are "fudge factors" that are being inserted in order to explain observations. There are multiple "contenders" for dark matter, none of them actually explain observations and measurements. Dark Energy is also in that same category especially in it's purest form as a "universal constant" that was added then removed then added back again to GR when we were sure if the universe is sta…

Shouldn't there be a big lump of dark matter at the center of every planet, moon, and star? If we were to hollow out an asteroid, would there still be a blob of intangible dark matter inside of it?

Which type of dark matter would that be?

Re: A Physicist Who Denies That Dark Matter Exists

#77

Post by cozzyd »

fuhrysteve wrote: post #4
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…

> 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. I have always had the same inclination. It seems like a classic candidate for using Occam's razor. Would love to hear someone who knows more about physics weigh in with a more nuanced viewpoint.

If it was just galactic rotation curves that would be explained by adding a (mostly) non-interacting dark matter particle, then MOND would probably have many more proponents. It's harder to understand how to replace non-interacting particles in explaining the cosmic-microwave-background power spectrum, galaxy clusters, and structure formation. Maybe it's possible to make a complicated theory do those things, but at that point, I'm not sure it wins on simplicity anymore.

Re: A Physicist Who Denies That Dark Matter Exists

#78

Post by [deleted] »

chongli wrote: post #42
thechao wrote: post #31

Earlier quoted context omitted.

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.

[deleted]

Re: A Physicist Who Denies That Dark Matter Exists

#79

Post by cwmma »

simonh wrote: post #29
cwmma wrote: post #18

So this doesn't actually get into the actual big issue with MOND which is that observational results [1] tend to imply some sort of dark matter so current MOND theories actually include some dark matter, just less of it. 1. https://en.wikipedia.org/wiki/Bullet_Cluster

> actually include some dark matter They include some non-luminous matter, but only require 1/5th to 1/10th as much as would be required by Dark Matter theories. So I think saying they require 'Dark Matter' is confusing. They don't really require a new class of matter and could easily be explained by the presence of some amount of non-luminous baryonic matter in some cases which hardly seems outrageous.

non-luminous baryonic matter has long been a contender for dark matter, I think the technical term is Massive compact halo object aka MACHO (as opposed to WIMPS or Weakly interacting massive particles) so saying it still requires dark matter is accurate we could rewrite it to 'actually include some possibly non-exotic dark matter'.

Because even though it reduces the amount of dark matter required it still has missing matter.

Re: A Physicist Who Denies That Dark Matter Exists

#80

Post by manigandham »

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…

> but the prediction is off by several orders of magnitude, the model is wrong. no other field would invent invisible stuff to explain that the model is still right

And yet physics has done this continuously with many discoveries happening in theory first before being verified by reality.

In fact, this is also part of making a model that works. There's no rule that models must be bound by what you only know right now.

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