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The possibilities for dark matter have shrunk

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Re: The possibilities for dark matter have shrunk

#71

Post by Vecr »

bunderbunder wrote: post #52

If you've got the time, these YouTube videos are a nice counterpoint to a lot of popular communication and discussion on dark matter: Dark matter is not a theory: https://www.youtube.com/watch?v=PbmJkMhmrVI That dark matter video aged like milk: https://www.youtube.com/watch?v=qS34oV-jv_A the tl;dr is that "dark matter" is a bit of a misnomer. (But also a fun name so it's probably here to stay through sheer memetic m…

Tell the author of the videos that I want to debate her on AI. (ha ha only serious)

Re: The possibilities for dark matter have shrunk

#72

Post by SideQuark »

throwawaymaths wrote: post #70
SideQuark wrote: post #69

Earlier quoted context omitted.

> we can't claim that DM has been measured many ways Yes we can. It's shown up in 1) precise measurements of galaxy rotation curves (relevant to this paper, which only addresses this method), 2) velocity spread of bound stars, 3) x-ray emission from hot gas, 4) gravitational lensing, 5) cosmic background radiation measurements in CMBFAST and others, 6) provides solutions to issues in stellar strucutre formation, 7) s…

It's basically two major observations 0) Galaxy curves 1) cmb observations And a few minor ones. The 0th was the motivation for dark matter. The 1st is good, but also not predicted a priori by dark matter. In it's defense, it doesn't need fine tuning to work (it works out with ~the estimated amount of DM) For all the minor ones there's a lot of fine tuning necessary to obtain the results. So it's not surprising that…

> by e.g. MOND.

Which has an even longer list of fundamental results and empirical observations it fails to support ....

Re: The possibilities for dark matter have shrunk

#73

Post by throwawaymaths »

SideQuark wrote: post #72
throwawaymaths wrote: post #70

Earlier quoted context omitted.

It's basically two major observations 0) Galaxy curves 1) cmb observations And a few minor ones. The 0th was the motivation for dark matter. The 1st is good, but also not predicted a priori by dark matter. In it's defense, it doesn't need fine tuning to work (it works out with ~the estimated amount of DM) For all the minor ones there's a lot of fine tuning necessary to obtain the results. So it's not surprising that…

> by e.g. MOND. Which has an even longer list of fundamental results and empirical observations it fails to support ....

LCDM doesn't explain how the mitochondria function, or why my dog prefers to shit in the yard instead of in the house, so it is clearly a failed model for not having explanatory power on those observations

Re: The possibilities for dark matter have shrunk

#74

Post by nwallin »

mppm wrote: post #44
empyrrhicist wrote: post #34

Earlier quoted context omitted.

> apart from the fact that dark matter predictions have been contradicted by increasingly sensitive experiments over and over and over My impression is that many physicists would disagree with this characterization entirely, and that they're eagerly working to constrain what it is or isn't. Ruling out big classes of phenomena that could be responsible for the things we observe isn't "contradicting" the predictions in…

I'd normally agree with you, but in the particular case of dark matter particles something still smells fishy. The theories that the predicted cross-sections are based on are just too flexible and numerous. I'm not sure how much we gain from ruling out yet more. What if there are in fact no weakly interacting particles? At what point do we decide that enough has been ruled out to start looking elsewhere? Like plasma…

That's just how particle physics research works. You build a detector that is designed to detect things with specific properties. You run the detector. Did you find the thing? If so, great, if not, well, that's the way the cookie crumbles. Either way you write a paper and you build the next detector.

The Higgs boson has numerous experiments exclude numerous mass ranges excluded before it was finally found.

> At what point do we decide that enough has been ruled out to start looking elsewhere?

"We" don't make that decision. The various institutions who pay for these things decide, one by one, that they're going to fund some thing that sounds more promising instead.

It does kinda suck that there's something there in the universe that is perniciously difficult to see--in fact, that's how it's defined--but that is so important in the way the universe works that we can't simply ignore it. But this is the universe we're given, so this is the universe we'll run experiments on.

Re: The possibilities for dark matter have shrunk

#75

Post by rbanffy »

pfdietz wrote: post #68
rbanffy wrote: post #54

Earlier quoted context omitted.

Considering time dilation, a detector inside a relativistic spacecraft will be hit by a lot of neutrinos in the apparent short duration of the mission. I wonder what is the speed at which interstellar neutrino bombardment becomes lethal to a crew considering it’s essentially impossible to shield against them. You can put a mountain in front of the ship, but neutrinos will just pass through it like is a cloud. OTOH if…

Neutrinos already move at relativistic speeds, so they aren't much of a problem. The real possible problem would be massive dark matter particles. These would be traveling now at around 300 km/s, so a relativistic spacecraft would boost their speeds by three orders of magnitude and their energies by six orders of magnitude or higher. And, of course, the number passing through a given area in the vehicle per unit of t…

I wasn’t thinking of the speed of the neutrinos, but the increase in encounter frequency. From a passenger’s perspective, the number of interactions per second will be much higher, not just because the ship is covering large distances and hitting more particles (although I’m not sure about that - it might cancel out) but hitting them more frequently from the crew’s perspective because of time dilation.

Re: The possibilities for dark matter have shrunk

#76

Post by dave333 »

It's worth repeating for the Nth time that dark matter may be a previously unknown form of hydrogen that doesn't interact with light because the electron is bound in a lower energy state than the traditional ground state. This is based on a novel classical atomic model where electrons are bound in "orbitspheres" see

https://brilliantlightpower.com/theory/

Re: The possibilities for dark matter have shrunk

#77

Post by katdork »

dave333 wrote: post #76

It's worth repeating for the Nth time that dark matter may be a previously unknown form of hydrogen that doesn't interact with light because the electron is bound in a lower energy state than the traditional ground state. This is based on a novel classical atomic model where electrons are bound in "orbitspheres" see https://brilliantlightpower.com/theory/

Looking into this, I see it is some kind of crackpot / con-man "free energy" scam?

Looking at:

- https://rationalwiki.org/wiki/Randell_Mills

- https://en.wikipedia.org/wiki/Brilliant_Light_Power#Criticis...

- https://en.wikipedia.org/wiki/Brilliant_Light_Power#Peer-rev...

I assume you are related to, an investor in or some kind of shill for this organization, because many of your submissions are related to the organization you are speaking about. This could be untrue, but I would not trust any "theory" that you posit at ground value without peer review and all of this is never going to make it into the scientific mainstream.

If your theory depends upon denial of quantum physics and things which have experimental proof, it has no rigor. Especially if the organization in question feels the need to take wikipedia editors to court in order to silence them. Shame on this organization.

Re: The possibilities for dark matter have shrunk

#78

Post by westurner »

westurner wrote: post #9

There is no dark matter in theories of superfluid quantum gravity. Dirac later went to Dirac sea. Gödel had already proposed dust solutions, which are fluidic. PBS Spacetime has a video out now on whether gravity is actually random. I don't know whether it addresses theories of superfluid quantum gravity. >>> "Gravity as a fluid dynamic phenomenon in a superfluid quantum space. Fluid quantum gravity and relativity."…

What was this issue with this post which supports the premise of the OT?

Re: The possibilities for dark matter have shrunk

#79

Post by dave333 »

katdork wrote: post #77
dave333 wrote: post #76

It's worth repeating for the Nth time that dark matter may be a previously unknown form of hydrogen that doesn't interact with light because the electron is bound in a lower energy state than the traditional ground state. This is based on a novel classical atomic model where electrons are bound in "orbitspheres" see https://brilliantlightpower.com/theory/

Looking into this, I see it is some kind of crackpot / con-man "free energy" scam? Looking at: - https://rationalwiki.org/wiki/Randell_Mills - https://en.wikipedia.org/wiki/Brilliant_Light_Power#Criticis... - https://en.wikipedia.org/wiki/Brilliant_Light_Power#Peer-rev... I assume you are related to, an investor in or some kind of shill for this organization, because many of your submissions are related to the organi…

I have no interest in or relation to Brilliant Light Power other than as a long time follower. Mills went to court to defend himself against an accusation of fraud I believe. Wikipedia is about 10 years out of date. As for 'crackpot /con-man "free energy" scam' the theory is fully available for review. The energy is not free since it involves binding the electron in hydrogen more tightly to the nucleus thus releasing energy. Normal hydrogen is converted into its dark matter form.

Re: The possibilities for dark matter have shrunk

#80

Post by pfdietz »

rbanffy wrote: post #75
pfdietz wrote: post #68

Earlier quoted context omitted.

Neutrinos already move at relativistic speeds, so they aren't much of a problem. The real possible problem would be massive dark matter particles. These would be traveling now at around 300 km/s, so a relativistic spacecraft would boost their speeds by three orders of magnitude and their energies by six orders of magnitude or higher. And, of course, the number passing through a given area in the vehicle per unit of t…

I wasn’t thinking of the speed of the neutrinos, but the increase in encounter frequency. From a passenger’s perspective, the number of interactions per second will be much higher, not just because the ship is covering large distances and hitting more particles (although I’m not sure about that - it might cancel out) but hitting them more frequently from the crew’s perspective because of time dilation.

No large amount of time dilation is likely to be practical, even with laser propelled light sails or antimatter. And the heat load on the vehicle from running into interstellar matter would be very high.

The more massive DM particle issue I discussed might be problematic even with very little time dilation.

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