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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

#81

Post by manigandham »

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?

We don't know what dark matter is (including whether or not it's even matter).

Re: A Physicist Who Denies That Dark Matter Exists

#82

Post by wyager »

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?

No, not if it's weakly interacting.

Matter forms big balls because it collides with other matter and turns kinetic energy into heat. If dark matter is weakly interacting, it won't collide, so after falling into a star it will just shoot right back out the other side. It might form a stable orbit, but it also might just fly away and fall through some other gravity well.

You can probably expect some bulk gravitational effects (e.g. Dark matter might tend to cluster along large matter distributions like galaxies), but in general it wouldn't be amenable to staying in one place.

Re: A Physicist Who Denies That Dark Matter Exists

#83

Post by blueprint »

uf wrote: post #74
blueprint wrote: post #53

Earlier quoted context omitted.

> 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?

If you know what Einstein discovered he clearly explained gravity can exist without mass. Look up the stress-energy tensor.

Clearly, Occam's Razor can only be applied correctly if you can distinguish what you really know from what are actually your assumptions. Not only do people hear what they want - but those who don't know don't know they don't know.

Re: A Physicist Who Denies That Dark Matter Exists

#84

Post by EGreg »

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…

It seems a bit like Pilot Wave Theory. It postulates a wave in order to let regular mechanics apply to the quantum mechanical phenomena.

Instead of postulating endless world-splitting or whatever.

Re: A Physicist Who Denies That Dark Matter Exists

#85

Post by wyager »

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?

There are several ways that dark matter might exhibit detectable interactions. For example, it could undergo weak interactions with itself or with ordinary matter. (See WIMPs.) It could also undergo some antimatter-annihilation interaction, emitting e.g. a Z boson, which could decay to a detectable particle-antiparticle pair. We might be able to observe Z bosons from matter interactions decaying to dark matter pairs, which would manifest as an unexplained shortage of matter after a collision. We're still looking for any such interactions.

Re: A Physicist Who Denies That Dark Matter Exists

#86

Post by bartj3 »

> Perhaps somewhere out there, in one of those galaxies I spent my life researching, there already is a known unified theory of physics, with a variation of MOND built into it. But then I think: So what? We still had fun doing the math.

His life's work: we had fun doing the math :)

Re: A Physicist Who Denies That Dark Matter Exists

#87

Post by pharrington »

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…

This isn't right. Dark matter is a shorthand of saying "our current theory is at least incomplete, there is probably an entirely new class of thing (as in, dark matter is known to be a misnomer), and maybe (with a ridiculously high degree of uncertainty) a separate theory is craftable that precisely explains both what we're currently calling "dark matter" and all other other observed gravitational phenomena.

The problem with MOND is that it straight-up isn't compatible with relativity. The core of relativity is that the laws of physics from all reference frames are the same. Sure, you can make a MOND that gels with alot of the math resulting from general relativity, but saying "MOND is correct at the large scale and Newtonian mechanics is correct at smaller scales" is gibberish if you actually want to keep relativity itself.

Re: A Physicist Who Denies That Dark Matter Exists

#88

Post by EGreg »

mikeash wrote: post #28
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?

It obviously doesn't interact with ordinary matter very much, or else it would have been observed non-gravitationally by now. It could interact a little bit, though. Consider neutrinos: they almost don't interact with ordinary matter at all, but they can be observed with enough patience and care, and they are definitely real. Neutrinos were actually an early candidate for dark matter. The numbers didn't work out, but…

How do we know dark matter isn't just really transparent matter? Like, we can't see it in space but it's there, not reflecting or deflecting enough light for us to detect it.

Re: A Physicist Who Denies That Dark Matter Exists

#89

Post by drjesusphd »

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.

Dark matter is not the same as dark energy.

Re: A Physicist Who Denies That Dark Matter Exists

#90

Post by [deleted] »

pharrington wrote: post #87
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…

This isn't right. Dark matter is a shorthand of saying "our current theory is at least incomplete, there is probably an entirely new class of thing (as in, dark matter is known to be a misnomer), and maybe (with a ridiculously high degree of uncertainty) a separate theory is craftable that precisely explains both what we're currently calling "dark matter" and all other other observed gravitational phenomena. The prob…

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