Undergraduate students in Cardiff now get to build Rube Goldbergmachines at the final lab session of the year.

Just a couple of pictures from my traditional, "spend-Christmas-in-the-Cardiff-Physics-Department-because-that's-how-I-roll" trip...

First, undergraduate students in Cardiff now get to build Rube Goldberg machines at the final lab session of the year. We never got to do anything fun like that back in my day...

And second, this notice board attests to the very important research being done in this student office.

New review process for the HST

Last year, despite efforts made to reduce bias, proposals for medium and large programs on the Hubble Space Telescope had an acceptance rate of 24% for programs led by men and 13% for programs led by women, an imbalance largely in keeping with the telescope's history. This year, in one of the most competitive cycles ever, that suddenly changed to a near-equivalent 8.7% acceptance rate for women and an 8.0% acceptance rate for men, reversing the trend seen over the past 15 cycles. What happened? Anonymized proposals.

Interesting but unsurprising. I'd be more interested to see what happens with regards to prominent researchers versus novices. Are people being awarded time essentially because they've already been awarded time, or are they more successful simply because they write better proposals ? My guess would be more variability in the proposal quality of famous researchers. That is, if you're well-known, you probably do have a better chance of getting a lower-quality proposal accepted, but on average your proposals tend to be better.

https://www.metafilter.com/178225/Focus-on-the-Science-Not-the-Scientist

We're hiring !

Just when I thought I was finally done for the year, I end up giving a seminar to some visiting PhD students yesterday morning. With a flight in the afternoon I wasn't planning to come it at all that day, but oh well... they enjoyed it anyway. One of them said it was one of the best talks they'd ever had !

[Readers will have to imagine me in a suitably heroic pose of the non-Blackadder variety at this point]

Seminars are now extremely useful though, as due to a surfeit of riches at the Czech Academy of Sciences they decided to fund all three of our group's grant applications. So I get a higher salary and the group is now searching for three (!) new postdocs : one in star formation in the galactic centre, one in star formation in clusters, and one in optically dark hydrogen clouds that don't do anything (you can guess which one is mine). Anyone want to become my assistant and fetch me tea on demand carry out important research in galaxy evolution ? Starts mid 2019, guaranteed funding until the end of 2021 with a healthy travel budget. We're also looking for an additional postdoc for ALMA-related things. More details to follow should we have trouble finding people (obviously I am not relying on blog posts to find postdocs because that would be completely mad).

In other news I won this year's institutional Jan Fric (the founder of the institute) award, so I get another shiny award ceremony in January (and another seminar...). And my position is now, if not exactly tenure track, on a rather more permanent basis that a postdoc position. Must be doing something right... of course, I expect Brexit will completely bugger the whole thing up, and then I will be sad. Until then I shall be enjoying Christmas.

Who needs dark matter when you can have... negative matter !

"This implies that our Universe is just one of those things that happen on occasion..."

That's one of the memorable lines in this very interesting paper that tries to replace conventional dark matter with something more exotic : negative matter. The other wonderful line is the extremely astute remark, "Observations clearly indicate that the Universe is not empty." That's one thing we can surely all agree on. But is regular dark matter too mainstream for you ? Is doing away with dark matter too contrarian ? Then this is the paper for you !

The press release was quite interesting but left me very puzzled so I decided to read the paper, even though this kind of thing is well outside my area. Here's my take on it for whatever that's worth.

I get the distinct impression that the author was having great fun writing this. The overall tone is - by the standards of academic research at any rate - frivolous and playful. I doubt it's supposed to be taken entirely seriously; he's clearly not saying that he's definitely overturned all of physics. Taken as a curious piece of speculation I wholeheartedly approve - taken as anything more than that and the guy's a nutter. Which is a nice summary of the some of the very best papers, really.

Anyway, the key point is figure 1, which illustrates how matter with negative mass accelerates due to gravity. As everyone's familiar with, normal (positive) matter accelerates towards other normal matter under gravity. Negative matter would accelerate away from itself. Weird, but okay. That might leave you wondering how in the world negative matter could possibly be a substitute for dark matter : observations indicate the presence of large amounts of unseen positive mass. How could stuff which tends to push itself apart possibly be a substitute for stuff that's supposed to be pulling everything together ?

Well, where it gets really strange is the interaction between positive and negative matter. Positive matter would accelerate away from negative matter, but negative matter would accelerate towards positive matter. Stick a mass of negative matter at the end of an equal mass of positive matter in free space and in principle they both accelerate forever, eventually reaching - says Farnes - lightspeed. He's quite explicit about equalling lightspeed, not just merely coming close to it. Conservation of energy is not violated; I'm guessing (but only guessing !) because a moving negative mass has negative kinetic energy. He notes that such claims have been labelled as "preposterous", however.

My guess is that if you have negative matter instead of positive matter, you don't need an equal amount of it to reproduce the effects of "ordinary" dark matter. It only has to provide that extra push to reproduce the apparent effects of unseen positive mass (e.g. galaxy rotation and motions in clusters). In very hand-waving terms I can sort-of see how negative matter could then act as a replacement for conventional, positive-mass dark matter : it wouldn't be a direct substitution.

A lot of the paper describes how this model can unify dark matter and dark energy. The latter is much easier to see (though I won't for a second claim to understand the maths) : if you've got some substance pushing everything apart, then sure, that could drive the acceleration of the expansion of the Universe. It's more difficult to understand how negative matter could be responsible for the evidence typically interpreted as large amounts of missing positive matter, at least in an intuitive way.

Farnes presents code, simulations and analytic formulae to address all of the major underlying objections one might raise. He notes that negative mass may or may not equate with antimatter; at least in principle the two need not annihilate each other. He shows that structures can form in a negative matter-dominated universe, even more rapidly, in face, than in one dominated by positive matter. Runaway accelerating particles do not occur, presumably because random motions dominate (also gravity is a very weak force). And he demonstrates how negative mass may lead to flat rotation curves, although to be honest I didn't really understand how that works.

He doesn't address gravitational lensing though (God knows how that would work with negative mass) or say much about the CMB power spectrum, which IIRC has been interpreted as very strong evidence for dark matter independent of galaxy rotation curves. Also, this theory requires a continuous creation of negative matter.

So as I said, don't get too excited. It's an interesting bit of speculation but it's also bloody weird. To mind mind a constant amount of missing positive mass, plus some other, unrelated component for dark energy, still feels like a simpler explanation. I hope there will be more serious and detailed responses from more knowledgeable people. It is Christmas, after all...

I haven't tried the code provided but I hope someone will.
https://arxiv.org/abs/1712.07962

Science is not fake news

The key word here is "best". The consensus isn't, and shouldn't, claim to be the Absolute Truth. Such a thing may well not even exist. All it can claim is to be the best possible approximation to such a truth given the current state of the understanding of the evidence at any time. That can and frequently does change, such that you get some people lambasting scientists for not being able to make up their minds, while others insist that they're all dogmatic and never change their minds at all. Or worse, they say that when they do shift, they rewrite history so it looks like everything was fine and that they were ignoring legitimate criticism.

In reality, what usually happens is that contrarians remain contrarian because their arguments simply lack sufficient power. If and when they accumulate more evidence, the consensus position shifts. What you have to remember is that there's usually a plethora of available contrarian positions to choose from, a sort of "dial a theory" if you like. This results in a survivorship bias when the consensus changes, when in fact the new position was previously rejected for what were, at the time, very good reasons.

https://astrorhysy.blogspot.com/2016/07/they-said-i-was-maaaaad.html
http://astrorhysy.blogspot.com/2015/06/consensus-and-conspiracy.html


You may be extremely intelligent and capable in a whole slew of ways, but you can immediately recognize the limits to your own knowledge and expertise. There are some things you know extremely well; possibly as well as the top few dozen people on Earth know it. But when it comes to most issues, there are people who have far greater levels of knowledge and expertise than you do.

This isn't a failing on your part, mind you. This is a result of the fact that, as human beings, we only get one life to live. However we've spent our time in this world — whatever we've studied, practiced, worked on, researched, etc. — that's where our greatest expertise lies. And this extends beyond ourselves as well: the expertise of others, particularly when we're lacking in that expertise, is something we need to rely on when we're out of our depths.

Which is why it's so dangerous and delusional to proclaim that you, when you're a non-expert, are better equipped to assess an expertise-requiring problem than the experts themselves.

You are not.

That doesn't mean the experts are always right. That doesn't mean there aren't frauds, charlatans, fools, cronies, and unimaginitive followers among the experts. That doesn't mean that people aren't corrupt, and it doesn't mean that the expert consensus won't change as more and better data comes in.

But that's why we not only have experts, it's why we have the enterprise of science.


Of course, that's not to say that you aren't allowed to question the experts or that they're entitled to pronounce judgement upon you. It's more a case of "you can ignore them if you like, but it's your own bloody fault if you get it wrong". Which you are far, far more likely to do than if you'd just accepted the consensus view. Doesn't mean you can't have hobbies or that amateurs can't be valuable, but if you actually want to make progress, it's worth considering the mainstream ideas first. Lots of people seem to think it's fine to debunk things they've never actually looked into in the slightest.

One of my favourite pieces on assessing credibility [REPLACE LINK !]:
https://plus.google.com/u/0/+RhysTaylorRhysy/posts/ExUtrBorfWs


https://www.forbes.com/sites/startswithabang/2018/11/29/science-is-not-fake-news/