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imsmooth
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Does the astrophysics community really think dark energy/matter is real, or that we just haven't figured out the actual physics of what is happening and this just makes it work out (to our current understanding).
To expand on @Orodruin's answer:imsmooth said:Does the astrophysics community really think dark energy/matter is real, or that we just haven't figured out the actual physics of what is happening and this just makes it work out (to our current understanding).
Dark matter and dark energy are different things.imsmooth said:Does the astrophysics community really think dark energy/matter is real, or that we just haven't figured out the actual physics of what is happening and this just makes it work out (to our current understanding).
This is the subject of active academic debate upon which a consensus has not been reached.imsmooth said:Does the astrophysics community really think dark energy/matter is real, or that we just haven't figured out the actual physics of what is happening and this just makes it work out (to our current understanding).
Pretty much. "A" modified form of gravity is probably a stretch - there are quite a few versions, I believe.srb7677 said:And I understand that some scientists are proposing a modified form of gravity to explain the observations rather than invoking dark matter. Though insofar as I can tell majority scientific opinion seems to be behind the existence if dark matter, though there is no consensus on what it might actually be yet. Is this correct?
As I understand it there is some evidence in the cosmic microwave background for dark matter. The spectrum of the temperature variation has a peak that makes sense if there's some form of matter that only interacts gravitationally. However, various lines of enquiry looking to directly detect dark matter, whether it is a new particle, or a lot of small black holes, and probably other things I'm unaware of, have come up empty. Hence a resurgence of interest in modified gravity.srb7677 said:What evidence aside from the observed gravitational effects on galaxies, is there for the existence of dark matter? And what suggestions have scientists thus far come up with as to what it might be?
Loads. One that seems to be in the news lately is analysis of wide binary star systems. As far as I can tell, some analyses decisively rule out alternative gravity and some decisively rule out dark matter. So there's at least one thing we don't understand and it's very much not clear what the answer is. And nobody, so far as I am aware, has managed to make a modified gravity theory that leads to a cosmology that looks like what we see at really large scales.srb7677 said:And is there any evidence to support or refute a modified theory of gravity?
Yes and no. Bear in mind that we've got far fewer assumptions in our theories than we used to have, and the failures we're discussing are in fairly extreme circumstances. Our current theories are extremely accurate for almost everything (that's one of the reasons it's so hard to find flaws).srb7677 said:As an amateur in these matters, it does seem to me that the more humanity learns about the deep workings of the universe, the more we come to see how much we still don't know.
I like how there's a bit in the video where she wonders about people commenting on her video without watching it.Vanadium 50 said:Did not really like that video, but I only watched 10-15 minutes of it. 120 minutes is a heavy lift.
Guilty.Bandersnatch said:I like how there's a bit in the video where she wonders about people commenting on her video without watching it.
Vanadium 50 said:let me try again" it's not a very good sales pitch.
Besides, I know the data, and she's overselling.
Vanadium 50 said:In the part I watched, she was lamenting "How can so many people still believe in MOND? Where did I go wrong?" She even had a pie chart. To me, that sounds like she's unhappy that so many people "got the wrong answer".
I did watch the whole video. I think Vanadium's assessment is fair, perhaps even too mild.Bandersnatch said:I like how there's a bit in the video where she wonders about people commenting on her video without watching it.
The solution is always yet another hour+ video ...Bandersnatch said:Oh my. I guess she really is a failure at communicating. Maybe yet another video will do the trick.
Vanadium 50 said:I also like less the unscientific (IMO) dismissal of MOND, even by people I otherwise respect. "Look at the Bullet Cluster! A smoking gun!" "But what about Abell 520, which is just like the Bullet Cluster but the other way." "Well, everybody knows you can't draw conclusions from a single cluster!" What? What the...?
That's really a sociology question.Ken G said:I think what is emerging clearly here is we have to wonder why the great majority of people in the wider public prefer MOND type solutions, and the great majority in the astrophysics community favor the dark matter approach
Indeed. Neveretheless, it is the fundamental topic of those two videos, and I believe is a valid question to ask. After all, astronomy is a societal issue itself.Vanadium 50 said:That's really a sociology question.
That's not by itself a valid reason. If all of physics was organized in terms of the number of papers being proportional to the number of possible ways to address the problem, it would be the general equivalent of an army of blind squirrels looking for acorns. For example, much of what you just listed is based on the various types of possible particles in dark matter, but imagine the measure space of possibilities that don't involve dark matter at all. Indeed, MONDlike approaches have a vastly large measure space of possibilities, but only simple versions are considered, based on Occam's Razor. But there's a difference between considering one specific theory based on a single parameter, versus considering all the possible ways to build a theory based on a single parameter. If one considers the latter, the MOND space is equally vast as the dark matter space, but we're back to blind squirrels.Vanadium 50 said:The theory community writes more papers on DM because there is more to say. Maybe its the LSP - but which particle? Maybe its two particles. Maybe its axions. Maybe its PBH's. MOND is sterile. "Here's a new law of gravity, Deal with it." The experimental/observational community hears these talks and responds as you might expect.
Yes, and this is where the problem of the "bandwagon effect" comes in, and it applies equally in both groups. Astronomers want to specialize, so when they go outside their area, they don't want a long list of possible solutions, that's only what they want in their own area. But of course, all areas are like that, a long list of possible solutions, so the problem is in wanting all the other areas to be different. This may lead to the "amplification" you mention, the community as a whole gloms onto one approach because that's all the other astronomers want to hear about. But a bandwagon effect is exactly what I am cautioning against, it is the logical fallacy of her point that there are "only 3 people" doing MOND at any given conference on the problem of gravitational dynamics. Internet afficionados have the same problem. So when she says that MOND has better marketing in the internet world, she kind of overlooks how dark matter has better marketing in astronomy conferences.Vanadium 50 said:Remember too, that most asstronomers do not work on either family of models. If I study, say mass transfer and blue stragglers, my primary information comes from what other people tell me, in seminars and papers. So there is an amplification effect.
So these are focusing strategies (given how nonrelativistic the gravitational dynamics problem is, it doesn't seem like a terrible weakness of MOND, it's only that issue of "unifying what is behind the frontier" that comes up there). They are perfectly valid ones, we need focusing strategies, but still it's not just a question of measure space. Dark matter seems easier to test in the lab, but there's little success there yet. So it's hard to know how to apportion one's resources. Lots of money will be spent culling down the possible space for finding dark matter, which is a lot like looking for one's keys in a dark parking lot, not just under the streetlights, but also when one is not even sure one lost one's keys in the parking lot at all. Still, one wants to search the parking lot, that's clear, it's just a question of where else one might wish to also look.Vanadium 50 said:At the same time, MOND is incomplete. It's non-relativistic. People don't like that. It's also quite difficult to test in the lab. People really don't like that. \\
My point is that there is no problem with individual bias. We need people looking under all the rocks, and it never matters what an individual believes is the right rock to look under, it only matters that the rock is getting looked under. In other words, it is completely fine for an individual scientist to be utterly biased in what they choose to consider (Einstein was biased that the universal laws should be the same for all observers, for example), their success or failure will eventually dictate the truth regardless of their individual bias. But group bias is another matter altogether, because that dictates what rocks get attention, and what rocks get overlooked. Still, one needs focusing strategies, one does not want blind squirrels everywhere. So the question keeps coming back to, why does the astrophysical community use a focusing strategy firmly dominated by dark matter, and the internet afficionados use a focusing strategy dominated by MOND, and are both just examples of group bias?Vanadium 50 said:Also, Scientists are people too. At least 85% of us anyway. People get emotionally invested in their ideas. I an sure I have written more papers om DM than Stacy has written on MOND - including two moderately influential theory papers. Does that bias me? Maybe. How could I tell?
That's quite an ironic point, because that video makes the point that too much focus on solving rotation curves, rather than the larger puzzle, is what leads to MONDlike thinking. So you're agreeing with her that focusing on Vera Rubin's piece is also focusing too much on solving rotation curves, which is where MOND does better (at least according to that "score sheet" presented above, I don't know how controversial that is). But if the astrophysics community is too focused on rotation curves, they should be led to MOND, instead of dark matter. Why don't we say, therefore, that Vera Rubin discovered the need for MOND, rather than the need for dark matter?Vanadium 50 said:There is also some wokeness involved. The story is that Dark Matter was discovered by Vera Rubin, not Fritz Zwicky, and as such it is all about rotation curves. That's not true, and it overfocuses (IMHO) attention on that piece of the puzzle. It's a good story, and I understand why the public eats it up, but as usual reality is not so black and white.
Or of course, some combination thereof. Normally, we think of combinations as ugly, but that's why I brought up the Newton vs. Huygens debate. That was also resolved by a combination, but not an ugly one at all, it was quantum mechanics. Sublime and shocking yes, ugly no. I wonder if the resolution of the gravitational dynamics problem will be sublime and shocking, and will make a simple "search for dark matter" look like a red herring in hindsight, perhaps akin to the search for the aether. On the other hand, I agree there is no reason why most of the matter in the universe should come replete with low mass charged particles, that would be a classic bias toward things we can see. But the answer might involve generalizing our concept of what mass is and where it comes from, as well as how gravity and inertia work. Hopefully, in a way that is more beautiful and sublime than either new particles or parametric modifications to our laws!Vanadium 50 said:What we see is more acceleration than we expect. There are three possibilities:
- There is more mass than we think
- Gravity is stronger than we think
- At small acclerations there is less inertia per given mass.