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"Macro Dark Matter"

25 Comments -

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Blogger Phillip Helbig said...

"In other words, I wasn’t very convinced that partially interacting dark matter is anything more than something you can publish papers about."

I'm not so sure. That dark matter is simple (a WIMP, say) is just that, a simple assumption. Other matter self-interacts. Why should dark matter be any different?

8:50 AM, September 07, 2015

Blogger Sabine Hossenfelder said...

Phillip,

That's right. I have no problem with dark matter self-interacting in general. My issue is that this specific model is obviously construed to be "just about" detectable. There isn't any particular reason why dark matter should have this interaction with these interaction strenghts. It's just the simplest thing you can do that puts you in the ballpark for dinosaur extinction. It's too bad that the talk wasn't recorded (or at least I can't find the recording) because Lisa said this pretty much literally, that the motivation to look at this particular model is that it can be ruled out soon (to be fair, I think she didn't say anything about dinosaurs).

See, I've been working on phenomenological models myself for 10 years or so. There's no shortage of what you can do. You can always add something to the known physics and then hide it just beyond current experimental bounds. And if you run out of ideas, then take two unmotivated models and combine them to a new unmotivated model. I assure you chances are good it'll get published.

The important thing for pheno models is that you have a good theoretical motivation for why this is a good model. In quantum gravity pheno you take models that are motivated by findings in theoretical approaches to qg (extra dimensions, dimensional reduction, minimal length, discreteness, LIV, space-time fluctuations etc). Without that motivation, what's the point? I am missing that motivation in the partically interacting model. WIMPs (or some of them) and axions each have their motivation, which you might or might not buy, but at least they have one.

Sure, that model might be right. But think of it from a probabilistic perspective. In the space of all possible interacting models you pick one that you like because it's just around the corner. What are the chances of that being correct? I'd say, they're tiny, and that's why I'm totally not excited about this development. Best,

B.

9:03 AM, September 07, 2015

Blogger Shantanu said...

Bee, are the videos of this meeting on the web?
shantanu

9:05 AM, September 07, 2015

Blogger Sabine Hossenfelder said...

Shantanu,

There don't seem to be videos online. I'm a little puzzled about this because I thought I recalled it being recorded. I'll be back in Stockholm Friday and will inquire about this.

9:33 AM, September 07, 2015

Blogger Phillip Helbig said...

"The important thing for pheno models is that you have a good theoretical motivation for why this is a good model."

OK, we agree here. I have the same beef about f(R) theories. (See arXiv:0805.1726 for a nice review of this field (pun, as always, intended).)

10:17 AM, September 07, 2015

Blogger Uncle Al said...

Dark matter: Tully-Fisher relation (spiral galaxies at all redshifts), gravitational lensing. Dark matter distribution is not perturbed (cooling, collisional ejection) or purged (scavenging by stars, black holes, galactic central back hole). Lensing includes filaments unstable over redshift given only isotropic attractive interaction.

Tully-Fisher can be MoND's Milgrom acceleration. 10^(-10) m/s^2 non-conservation of angular momentum suggests Noether's theorems plus observed trace vacuum chiral anisotropy toward hadrons. Existing bench top apparatus decides, healing physics quantum gravitation to SUSY. Theory cannot judge itself to be empirically true. Look.

http://cast.web.cern.ch/CAST/CAST.php
Where are solar axions? doi:10.1103/PhysRevLett.112.091302

10:28 AM, September 07, 2015

Blogger Arun said...

If the dark matter is exotic quark & gluon stuff, as far as I can guess, it would affect cosmological nucleosynthesis, but maybe the constraints are weaker than the other ones?

3:05 PM, September 07, 2015

Blogger kashyap vasavada said...

Bee,
All known non-dark matter we know comes from atoms and eventually from fundamental particles like quarks, gluons and leptons. Why would dark matter be only clumps of material without any constituents? So I think, looking for just clumps will not solve the problem.

3:16 PM, September 07, 2015

Blogger N said...

Dark matter consists of epicycles :)

1:03 PM, September 08, 2015

Blogger JimV said...

Unsolicited typo patrol says:

"She shied no expenses" - this could be a usage which I am not familiar; I am familiar with "She shied away from no expenses" or "She spared no expenses" or "She shied at no expenses" (as when a horse shies at an obstacle which it is asked to jump).

"causing it to clump to efficiently" - the second "to" should be "too".

"it’s a story catchy enough to spread like measles, and equally spotty" - perfect.

5:23 PM, September 08, 2015

Blogger Kevin Van Horn said...

"The phases and properties of nuclear matter are still badly understood and certainly can’t be calculated from first principles even today."

Does this mean that the computations are intractable, or that we wouldn't know how to calculate them even if we had unlimited computing power?

7:31 PM, September 08, 2015

Blogger Sabine Hossenfelder said...

Hi JimV,

Thanks, I've fixed that. I'm afraid you're right, "shying no expenses" (keine Ausgaben scheuen) is a German expression, not an English one... Best,

B.

7:25 AM, September 09, 2015

Blogger Sabine Hossenfelder said...

Kevin,

Hmm, an interesting question. I'd say they are intractable since the underlying theory is known, but I'm not entirely sure you can prove that with the methods currently known on computers that presently exist they could be done in finite time. So is that intractable or not? Best,

B.

7:29 AM, September 09, 2015

Blogger Sabine Hossenfelder said...

kashyap,

I don't know what you mean with "clumps of material without any constituents". Of course the macros have constituents. The constituents are standard model particles, quarks and gluons, but really the exact composition isn't known. Best,

B.

7:31 AM, September 09, 2015

OpenID coraifeartaigh said...

I'm inclined to agree on theoretical motivation (or lack of) but the thing about lamposts is that one looks pretty silly if one didn't check and the keys were later found there (however unlikely the event). If science is about ruling things out, as Popper claimed, then there is a sense in which perhaps lampost investigations have their place!
Regards, Cormac

2:11 PM, September 09, 2015

Blogger Mike P said...

"(Want me to keep interesting stories on this blog? Please use the donate button in the top right corner, thank you.)"

Of course I do; and I imagine your donation income is not huge. But, I expect to know something about the finances of charities I give to. Mainly, I like to know approx. how much they receive and how they spend it. In your case, it's not about whether you deserve compensation. It's more like, will my small amount make a difference? Do you already receive enough that I can make a bigger difference to my neighborhood's homeless? There's no doubt I want people to keep seeing articles like your "I wasn't born a scientist". Would it be OK to inquire through your public staff address (full name@org)?

8:10 PM, September 09, 2015

Blogger Sabine Hossenfelder said...

Mike,

You can email me if you want, but I'm happy to answer your question publicly. I've only put up this donate button a month ago, so I can't give you any statistics, sorry. As to how I use the money. My employment contract is running out in November. I don't yet have a new contract. I have some grant money coming in after a gap, some time in December, and that is supposed to be worked into a contract which hasn't yet appeared. But roughly speaking the way it looks right now it won't be enough to cover employment benefits. Which means basically that all money I manage to make on the side will go into pension plan and health insurance.

Having said that though, I would prefer you think of this differently. Writing this blog is working over time. I work on my research 40 hours per week (on paper), I have two kids to raise. Writing a piece like this takes me roughly 2-3 hours. What do you think my time is worth?

Best,

B.

1:35 AM, September 10, 2015

Blogger Sabine Hossenfelder said...

coraifeartaigh,

By all means one should look under the lamp post. The question is though, how much should one expect to find something? And if you don't expect to find something, does it make sense to construe elaborated theories about how that something might look like? It just strikes me as a huge waste of time (and, in the end, of money). Best,

B.

2:01 AM, September 10, 2015

Blogger Mike P said...

Thanks, B, the cause is just & that's more than enough info. If 500 of us make the same donation, that will be ample. If 5000, that would be a windfall. It's more than I was thinking of. Not that I wouldn't be happy for you. :)

5:04 AM, September 10, 2015

Blogger Sabine Hossenfelder said...

Thanks for your support :o)

5:24 AM, September 10, 2015

Blogger Uncle Al said...

Lamp posts: A streetlight not radiating in the visible brightly baths lamp posts in darkness. Look to falsify, not to confirm. Euclid: maps; Newton: Mercury, Maxwell; Dirac equation: Otto Stern; particle theory: Yang and Lee. Macroeconomics models scientific socialism to Darwinian capitalism, all mocked by "guided" central interventions.

Theory elegantly demands vacuum mirror symmetric toward boson photons "must" be mirror symmetric toward fermion quarks (hadrons). Attempting falsification of established theory is silly (exceptions noted). Look to falsify, not to confirm.

11:30 AM, September 10, 2015

Blogger George Musser said...

By the way, don't blame Nature News for the dinosaur idea! That's straight from Randall.…

12:11 PM, September 10, 2015

Blogger Sabine Hossenfelder said...

George,

Is it? I looked at the paper, but it seems to be merely about comets. Besides this, I know I've said it before, but do they really have to jump on every piece of nonsense just because the author once wrote a well-cited paper? It is exceedingly annoying for people in the field, and I think it sets wrong incentives all over the place. Best,

B.

1:28 AM, September 11, 2015

Blogger Phillip Helbig said...

"In reality the meeting was dedicated to celebrate Katie Freese’s arrival in Stockholm."

Maybe the relaxed Scandinavian atmosphere will allow her to find time to write her own papers rather than copying them from another review by someone else from several years ago.

7:07 AM, January 13, 2017

Blogger Phillip Helbig said...

Let me take this opportunity to publicly apologize for a false accusation. I hope that it will be accepted.

I relied too much on automatic data from arXiv (something we should all be careful about). More extensive comments on this, by myself, Freese, and others (showing that I was not the only one to jump to conclusions) include this comment from me: "A variant of the common-source scenario is that Riotto got his text from an even earlier text from Freese (bad) while Freese merely re-used her own text (OK).". It turns out that this is what happened. Riotto has admitted to plagiarism, though in the view of most or all, not going far enough to make amends.

On the positive side, this should be a warning to arXiv and to those who use automatically generated data to be very careful with such accusations. It would have been possible to make the correct accusation in the first place, as Freese's paper which Riotto plagiarized is on arXiv, but arXiv goofed here. Freese comes out looking at least as good as if there had been no accusation at all, and perhaps this will serve as a warning to people not to commit plagiarism. Of course, just reformulating something is not enough; if one uses a source at all, it should be cited.

Of course, considering that Freese had been plagiarized and not vice versa, my original comment here is in the completely wrong tone. For this as well, I apologize.

(It's not a defense, but I once had an entire paper plagiarized. Not just text, but also new conclusions, etc. Fortunately, I was able to stop it from being published and get the offending paper withdrawn from arXiv. Again, not a defense, but it explains why I am rather sensitive on this issue. At least I hope that, as mentioned above, something positive comes out of the resolution. I do have a defense for not adding this comment and the last one at the URL above until today, as I was in hospital yesterday. No internet access during full anesthesia.)

4:17 AM, January 18, 2017

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