## Friday, November 17, 2017

### Max the Demon and the Entropy of Doom

My readers know I've complained/bemoaned repeatedly how challenging it can be to explain condensed matter physics on a popular level in an engaging way, even though that's the branch of physics that arguably has the greatest impact on our everyday lives.  Trying to take such concepts and reach an audience of children is an even greater, more ambitious task, and teenagers might be the toughest crowd of all.  A graphic novel or comic format is one visually appealing approach that is a lot less dry and perhaps more nonthreatening than straight prose.   Look at the success of xkcd and Randall Munroe!   The APS has had some reasonable success with their comics about their superhero Spectra.  Prior to that, Larry Gonick had done a very nice job on the survey side with the Cartoon Guide to Physics.  (On the parody side, I highly recommend Science Made Stupid (pdf) by Tom Weller, a key text from my teen years.  I especially liked Weller's description of the scientific method, and his fictional periodic table.)

Max the Demon and the Entropy of Doom is a new entry in the field, by Assa Auerbach and Richard Codor.  Prof. Auerbach is a well-known condensed matter theorist who usually writes more weighty tomes, and Mr. Codor is a professional cartoonist and illustrator.  The book is an entertaining explanation of the laws of thermodynamics, with a particular emphasis on the Second Law, using a humanoid alien, Max (the Demon), as an effective superhero.

The comic does a good job, with nicely illustrated examples, of getting the point across about entropy as counting how many (microscopic) ways there are to do things.  One of Max's powers is the ability to see and track microstates (like the detailed arrangement and trajectory of every air molecule in this room), when mere mortals can only see macrostates (like the average density and temperature).    It also illustrates what we mean by temperature and heat with nice examples (and a not very subtle at all environmental message).   There's history (through the plot device of time travel), action, adventure, and a Bad Guy who is appropriately not nice (and has a connection to history that I was irrationally pleased about guessing before it was revealed).   My kids thought it was good, though my sense is that some aspects were too conceptually detailed for 12 years old and others were a bit too cute for world-weary 15.  Still, a definite good review from a tough crowd, and efforts like this should be applauded - overall I was very impressed.

## Tuesday, November 07, 2017

### Taxes and grad student tuition

As has happened periodically over the last couple of decades (I remember a scare about this when Newt Gingrich's folks ran Congress in the mid-1990s), a tax bill has been put forward in the US House that would treat graduate student tuition waivers like taxable income (roughly speaking).   This is discussed a little bit here, and here.

Here's an example of why this is an ill-informed idea.  Suppose a first-year STEM grad student comes to a US university, and they are supported by, say, departmental fellowship funds or a TA position during that first year.  Their stipend is something like $30K. These days the university waives their graduate tuition - that is, they do not expect the student to pony up tuition funds. At Rice, that tuition is around$45K.  Under the proposed legislation, the student would end up getting taxed as if their income was $75K, when their actual gross pay is$30K.

That would be extremely bad for both graduate students and research universities.  Right off the bat this would create unintended (I presume) economic incentives, for grad students to drop out of their programs, and/or for universities to play funny games with what they say is graduate tuition.

This has been pitched multiple times before, and my hypothesis is that it's put forward by congressional staffers who do not understand graduate school (and/or think that this is the same kind of tuition waiver as when a faculty member's child gets a vastly reduced tuition for attending the parent's employing university).  Because it is glaringly dumb, it has been fixed whenever it's come up before.  In the present environment, the prudent thing to do would be to exercise caution and let legislators know that this is a problem that needs to be fixed.

## Tuesday, October 31, 2017

### Links + coming soon

Real life is a bit busy right now, but I wanted to point out a couple of links and talk about what's coming up.
• I've been looking for ways to think about and discuss topological materials that might be more broadly accessible to non-experts, and I found this paper and videos like this one and this one.  Very cool, and I'm sorry I'd missed it back in '15 when it came out.
• In the experimental literature talking about realizations of Majorana fermions in the solid state, a key signature is a peak in the conductance at zero voltage - that's an indicator that there is a "zero-energy mode" in the system.  There are other ways to get zero-bias peaks, though, and nailing down whether this has the expected properties (magnitude, response to magnetic fields) has been a lingering issue.  This seems to nail down the situation more firmly.
• Discussions about "quantum supremacy" strictly in terms of how many qubits can be simulated on a classical computer right now seem a bit silly to me.  Ok, so IBM managed to simulate a handful of additional qubits (56 rather than 49).  It wouldn't shock me if they could get up to 58 - supercomputers are powerful and programmers can be very clever.  Are we going to get a flurry of news stories every time about how this somehow moves the goalposts for quantum computers?
• I'm hoping to put out a review of Max the Demon and the Entropy of Doom, since I received my beautifully printed copies this past weekend.

## Wednesday, October 25, 2017

### Thoughts after a NSF panel

I just returned from a NSF proposal review panel.  I had written about NSF panels back in the early days of this blog here, back when I may have been snarkier.

• Some things have gotten better.  We can work from our own laptops, and I think we're finally to the point where everyone at these things is computer literate and can use the online review system.  The program officers do a good job making sure that the reviews get in on time (ahead of the meeting).
• Some things remain the same.  I'm still mystified at how few people from top-ranked programs (e.g., Harvard, Stanford, MIT, Cornell, Cal Tech, Berkeley) I see at these.  Maybe I just don't move in the right circles.
• Best quote of the panel:  "When a review of one of my papers or proposals starts with 'Author says' rather than 'The author says', I know that the referee is Russian and I'm in trouble."
• Why does the new NSF headquarters have tighter security screenings that Reagan National Airport?
• The growth of funding costs and eight years of numerically flat budgets has made this process more painful.  Sure looks like morale is not great at the agency.  Really not clear where this is all going to go over the next few years.  There was a lot of gallows humor about having "tax payer advocates" on panels.  (Everyone on the panel is a US taxpayer already, though apparently that doesn't count for anything because we are scientists.)
• NSF is still the most community-driven of the research agencies.
• I cannot overstate the importance of younger scientists going to one of these and seeing how the system works, so you learn how proposals are evaluated.

## Monday, October 23, 2017

### Whither science blogging?

I read yesterday of the impending demise of scienceblogs, a site that has been around since late 2005 in one form or other.  I guess I shouldn't be surprised, since some of its bloggers have shifted to other sites in recent years, such as Ethan Siegel and Chad Orzel, who largely migrated to Forbes, and Rhett Allain, who went to Wired.  Steinn Sigurðsson is going back to his own hosted blog in the wake of this.

I hope this is just indicative of a poor business model at Seed Media, and not a further overall decline in blogging by scientists.  It's wonderful that online magazines like Quanta and Aeon and Nautilus are providing high quality, long-form science writing.  Still, I think everyone benefits when scientists themselves (in addition to professional science journalists) carve out some time to write about their fields.

## Friday, October 20, 2017

### Neutron stars and condensed matter physics

In the wake of the remarkable results reported earlier this week regarding colliding neutron stars, I wanted to write just a little bit about how a condensed matter physics concept is relevant to these seemingly exotic systems.

When you learn high school chemistry, you learn about atomic orbitals, and you learn that electrons "fill up" those orbitals starting with the lowest energy (most deeply bound) states, two electrons of opposite spin per orbital.  (This is a shorthand way of talking about a more detailed picture, involving words like "linear combination of Slater determinants", but that's a detail in this discussion.)  The Pauli principle, the idea that (because electrons are fermions) all the electrons can't just fall down into the lowest energy level, leads to this.  In solid state systems we can apply the same ideas.  In a metal like gold or copper, the density of electrons is high enough that the highest kinetic energy electrons are moving around at ~ 0.5% of the speed of light (!).

If you heat up the electrons in a metal, they get more spread out in energy, with some occupying higher energy levels and some lower energy levels being empty.   To decide whether the metal is really "hot" or "cold", you need a point of comparison, and the energy scale gives you that.  If most of the low energy levels are still filled, the metal is cold.  If the ratio of the thermal energy scale, $k_{\mathrm{B}}T$ to the depth of the lowest energy levels (essentially the Fermi energy, $E_{\mathrm{F}}$ is much less than one, then the electrons are said to be "degenerate".  In common metals, $E_{\mathrm{F}}$ is several eV, corresponding to a temperature of tens of thousands of Kelvin.  That means that even near the melting point of copper, the electrons are effectively very cold.

Believe it or not, a neutron star is a similar system.  If you squeeze a bit more than one solar mass into a sphere 10 km across, the gravitational attraction is so strong that the electrons and protons in the matter are crushed together to form a degenerate ball of neutrons.  Amazingly, by our reasoning above, the neutrons are actually very very cold.  The Fermi energy for those neutrons corresponds to a temperature of nearly $10^{12}$ K.  So, right up until they smashed into each other, those two neutron stars spotted by the LIGO observations were actually incredibly cold, condensed objects.   It's also worth noting that the properties of neutron stars are likely affected by another condensed matter phenomenon, superfluidity.   Just as electrons can pair up and condense into a superconducting state under some circumstances, it is thought that cold, degenerate neutrons can do the same thing, even when "cold" here might mean $5 \times 10^{8}$ K.

## Sunday, October 15, 2017

### Gravitational waves again - should be exciting

There is going to be a big press conference tomorrow, apparently to announce that LIGO/VIRGO has seen an event (binary neutron star collision) directly associated with a gamma ray burst in NGC 4993.  Fun stuff, and apparently the worst-kept secret in science right now.  This may seem off-topic for a condensed matter blog, but there's physics in there which isn't broadly appreciated, and I'll write a bit about it after the announcement.