The Reason We Haven’t Directly Detected Dark Matter • Hacker News Board

Re: The Reason We Haven’t Directly Detected Dark Matter

#201

Post by TangoTrotFox » Sat, Oct 13, 2018, 8:10 PM UTC

cygx wrote: post #166

TangoTrotFox wrote: post #159

Earlier quoted context omitted.

That's really the problem here though. You cannot falsify dark matter, and you cannot prove a negative. Imagine I say there is a 5 headed green deer that weighs 2000 pounds and can speak Gaelic, but it's really good at avoiding being spotted - so good in fact that you can even look at right at it and might not see it. And you can even touch it and not even know you're touching it! What would you could consider an exh…

The idea of non-visible matter as a fix for stellar motion dates back to the 19th century, when our knowledge about the cosmos was far more limited (remember, we only learned about other galaxies in the 1920s - it post-dates general relativity!). That the hypothesis is still viable today with our more elaborate understanding of the universe does validate the idea to some degree: Our cosmological models cut have kille…

I'd generally agree with you, except for one thing. I'm not sure our models could have killed it off, excepting finding precisely whatever is causing the apparent mass abnormalities throughout the universe. Have you seen those ancient astronomic models used to illustrate a geocentric Earth? The one with the numerous spinning 'petals' surrounding the Earth? It's interesting imagining the amount of work that went into creating such models, constantly adjusting them over and over each time yet another little problem came up. Happily accepting planets just randomly changing direction, with no analog whatsoever anywhere else in nature, and so on.

When hypotheses are not falsifiable, they just tend to grow ever more elaborate rather than die. Dark matter started off as literally that - a place holder for bodies that did not significantly radiate. It's slowly changed into becoming the vast majority of all matter in the universe, existing practically everywhere, it can't be baryonic, it interacts with nothing except itself and gravity, there must exist near entirely dark matter galaxies, and so forth. So we're left with this ever evolving hypothesis that can't ever really be falsified and which every test, increasingly clever and precise, we create to detect it -- says it's not there.

And it seems that the zeitgeist is starting to increasingly treat dark matter as a fact whose proof is little more than an unscheduled formality. This seems illogical given that we've done more than ever to try to show it exists, and every result is saying - nope. And again this does not mean it does not exist, but each failure makes it more likely that this is the case, and there is an alternative explanation.

Re: The Reason We Haven’t Directly Detected Dark Matter

#202

Post by rpedela » Sat, Oct 13, 2018, 8:10 PM UTC

gmjoe wrote: post #63

krapp wrote: post #56

I like how we have an article explaining the rationale behind dark matter and the scientific principles that lead to the conclusion that it exists, but most of the threads here are simple declarations that no, they must all simply be wrong or not considering some simple alternative. Can people maybe, just maybe not assume that scientists are idiots or, as once dead commenter puts it, charlatans? If you disagree with…

Agreed 100%. Indeed, this is one of the best articles I've come across which covers several of the reasons we believe dark matter exists, as opposed to us just needing to modify the theory of gravity. For whatever reason, dark matter seems to repeatedly rub people the wrong way today, more so than any other scientific concept I can think of. I actually wonder if it's something psychological -- if the universe is only…

For me, I have always had a problem with how dark matter was portrayed in the media, even more scientific media. It is only fairly recently that scientists have been communicating dark matter as a problem with several possible solutions to laypeople. Before it went kinda like this: "we are unable to detect 80% (or whatever number) of the mass in the universe and we think it is non-baryonic matter". As someone trained in science, but not physics, that sounds like a huge discrepancy suggesting an incorrect theory. But I all hear until recently is that "our theories are right, our observations are wrong". But usually it is the opposite. I'm oversimplifying but that was the general impression. More recently the media and scientists have been doing a better job admitting that something may be wrong with general relativity but the leading hypothesis is non-baryonic matter.

Re: The Reason We Haven’t Directly Detected Dark Matter

#203

Post by hcs » Sat, Oct 13, 2018, 8:10 PM UTC

richardjennings wrote: post #179

As an uneducated layman I have 2 questions I have failed to understand that continue to confuse me. 1. How can relatavistic time resolve to a instant for which the mass in the universe applies? 2. Why does spacetime not have wave like tensional disortions?

Not following your first question, but isn't 2 the recently-observed gravitational waves?

Re: The Reason We Haven’t Directly Detected Dark Matter

#204

Post by GeekyBear » Sat, Oct 13, 2018, 8:24 PM UTC

nabla9 wrote: post #123

everdev wrote: post #71

Earlier quoted context omitted.

Almost all of our current scientific knowledge has come from challenging the consensus of the times. Scientific skepticism is always healthy and should be welcomed. Even if the original theory is correct, that doubt will simply help science better explain and prove the current understanding. I'd actually be more worried if everyone agreed about something. Even gravity we thought was fully solved until Einstein doubte…

>Scientific skepticism is always healthy and should be welcomed. I strongly disagree. Principled scientific skepticism from practicing scientist and expert is welcome and can contribute. Layman scientific skepticism in hard sciences like physics is worthless and even harmful. No matter how skeptical a layman who reads popular science magazines is, they don't contribute. Only thing we can do is to learn. Our judgment…

Science is about repeatable experimental outcomes that are predicted In advance by theory.

Demanding that people believe in a theory that so far has not been supported by the experimental data is more like religion than science.

Re: The Reason We Haven’t Directly Detected Dark Matter

#205

Post by pokemongoaway » Sat, Oct 13, 2018, 8:31 PM UTC

chriswarbo wrote: post #58

tychomaz wrote: post #5

Because it doesn’t exist. Dark matter is a fudge factor to prop-up a theory that astrophysics is too afraid to put to rest.

What do you mean by "put to rest"? Do you mean we should switch to using another theory, which reproduces all existing results, also correctly predicts some currently-unexplained observation or experiment, and has also correctly predicted previously-unobserved results (i.e. isn't just a "fudge factor")? If so, I would love to know what that theory is, since I certainly didn't encounter any such thing in the dark matt…

Many. Plasma physics more closely predicted many variables, including the beloved CMB. Observations of galaxies moving by each other are mirrored experimentally in the lab. Plasma effects scale so they can be studied this way... But no, this is censored because the mainstream insists that the weakest force is the God of their universe.

Re: The Reason We Haven’t Directly Detected Dark Matter

#206

Post by everdev » Sat, Oct 13, 2018, 8:35 PM UTC

Avshalom wrote: post #165

everdev wrote: post #71

Earlier quoted context omitted.

Almost all of our current scientific knowledge has come from challenging the consensus of the times. Scientific skepticism is always healthy and should be welcomed. Even if the original theory is correct, that doubt will simply help science better explain and prove the current understanding. I'd actually be more worried if everyone agreed about something. Even gravity we thought was fully solved until Einstein doubte…

Dark Matter IS the scientific knowledge that came from challenging the consensus.

Scientific progress has no end as far as we can tell. Just because we've found a theory that explains more than the previous one doesn't mean that we're done.

Re: The Reason We Haven’t Directly Detected Dark Matter

#207

Post by gus_massa » Sat, Oct 13, 2018, 8:43 PM UTC

philwelch wrote: post #176

krapp wrote: post #56

I like how we have an article explaining the rationale behind dark matter and the scientific principles that lead to the conclusion that it exists, but most of the threads here are simple declarations that no, they must all simply be wrong or not considering some simple alternative. Can people maybe, just maybe not assume that scientists are idiots or, as once dead commenter puts it, charlatans? If you disagree with…

I’ve written about this here before: https://news.ycombinator.com/item?id=16703193 It feels unintuitive to think about “dark matter” that can’t be directly observed outside of its indirect gravitational effects, but that carries with it an implicit assumption that we should be able to directly observe all the matter in the universe, with the further implication that all the matter in the universe obeys the four funda…

> with the further implication that all the matter in the universe obeys the four fundamental forces that our matter does. Except we already know of other particles that don’t quite do that, like neutrinos, which we can just barely detect directly.

Left-handed neutrinos interact mainly by the weak force and also by gravity. We have a lot of knowledge about them. You can create a neutrino ray and a neutrino detector, and (if wired properly) measure their speed. We know that there are three types of neutrinos (or perhaps there is a fourth neutrino). We know that they can change midflight from a kind of neutrino to another kind of neutrino. The change takes some time, so you can create a neutrino ray of one kind and a neutrino detector of the other kind and measure how many of the neutrinos changed midflight. So the neutrinos are well understood and there are many labs that can measure them.

(Right-handed neutrinos are more difficult to measure because they interact only by gravity. Some people think that they don't even exist. Some people think that they may be part of the dark mater. I think this is still not settled. Anyway, all the neutrinos we know are left-handed neutrinos.)

Re: The Reason We Haven’t Directly Detected Dark Matter

#208

Post by posterboy » Sat, Oct 13, 2018, 8:54 PM UTC

gmjoe wrote: post #63

krapp wrote: post #56

I like how we have an article explaining the rationale behind dark matter and the scientific principles that lead to the conclusion that it exists, but most of the threads here are simple declarations that no, they must all simply be wrong or not considering some simple alternative. Can people maybe, just maybe not assume that scientists are idiots or, as once dead commenter puts it, charlatans? If you disagree with…

Agreed 100%. Indeed, this is one of the best articles I've come across which covers several of the reasons we believe dark matter exists, as opposed to us just needing to modify the theory of gravity. For whatever reason, dark matter seems to repeatedly rub people the wrong way today, more so than any other scientific concept I can think of. I actually wonder if it's something psychological -- if the universe is only…

Yes, that must be it. Everything else about astronomy I'm perfectly fine with, but dark matter makes me feel insignificant. It's no problem however that many ... equate dark matter with some tangible notion of one theory or another and that their (and my) ignorance is staggering; Or that a negative result, like we can't bring two calculations into agreement, is treated like a result that found a real thing, while it's quite the opposite.

The simple problem is that DM is often defined as "a form of matter", when it could be multiple different forms. It's just the semantics that irks me. And then, if they will find maybe a new particle to account for at least some of the motion we couldn't explain, I will still be on the fence, because its not clear at all how to distinguish such from a virtual particle. That's nevertheless just a matter of semantics. The actual theory is probably way over my head. Therefore, doubt about the prediction for dark matter is just as much provoked by curiosity as for the proposed explanations. Ultimately, most explanations would be, in a mundane sense, turn out rather boring. So the question is, what's the deeper insight, as it goes for cosmology, what's the significance for life in general? There's a lot we don't know? I didn't even know that!

Re: The Reason We Haven’t Directly Detected Dark Matter

#209

Post by roywiggins » Sat, Oct 13, 2018, 8:55 PM UTC

reitanqild wrote: post #175

gbrown wrote: post #79

Earlier quoted context omitted.

I'm not a physicist, but my basic understanding of the state of the science tells me you're simply incorrect. We can observe the effect of dark matter via gravitational lensing, and folks much smarter than me have devised studies to exclude differential behavior of gravity at classical and galactic scales. Give me a recent and well supported study indicating that dark matter may be something other than matter, and I'…

As a non-physicist I assume the physicists have thought really hard about this. But it feels very strange to accept something that: - is a particle - doesn't interact with other normal particles (except through gravitation) - doesn't interact with particles of its own kind

Neutrinos are almost as strange. They interact a tiny bit via the weak force, and they interact via gravity like everything else, but that's it. We know they exist because of the weak interaction.

Maybe dark matter interacts with things via the weak force, but even less than neutrinos- not quite zero, but just small enough that we can't measure it, or can't measure it yet. Hopefully, they do interact a little bit by some other mechanism otherwise they'll be very hard to detect- I believe this is what current attempts to find dark matter are relying on.

Re: The Reason We Haven’t Directly Detected Dark Matter

#210

Post by posterboy » Sat, Oct 13, 2018, 8:58 PM UTC

rpedela wrote: post #202

gmjoe wrote: post #63

Earlier quoted context omitted.

Agreed 100%. Indeed, this is one of the best articles I've come across which covers several of the reasons we believe dark matter exists, as opposed to us just needing to modify the theory of gravity. For whatever reason, dark matter seems to repeatedly rub people the wrong way today, more so than any other scientific concept I can think of. I actually wonder if it's something psychological -- if the universe is only…

For me, I have always had a problem with how dark matter was portrayed in the media, even more scientific media. It is only fairly recently that scientists have been communicating dark matter as a problem with several possible solutions to laypeople. Before it went kinda like this: "we are unable to detect 80% (or whatever number) of the mass in the universe and we think it is non-baryonic matter". As someone trained…

The discrepancy though is that a lot of the "observation" as I'd put it, too, is rather theoretic. It's a false dilemma and that's the problem. It's not just better measurements that are needed, but knowing where to look. If one is so far removed from the topic that there is no difference, it doesn't really make sense to speculate, except to show how much one doesn't understand.