74 Questions

open_questions_cvjHello from the Aspen Center for Physics. One of the things I wanted to point out to you last month was the 74 questions that Andy Strominger put on the slides of his talk in the last session of the Strings 2014 conference (which, you may recall from earlier posts, I attended). This was one of the “Vision Talks” that ended the sessions, where a number of speakers gave some overview thoughts about work in the field at large.

Andy focused mostly on progress in quantum gravity matters in string theory, and was quite upbeat. He declines (wisely) to make predictions about where the field might be going, instead pointing out (not for the first time) that if you look at the things we’ve made progress on in the last N years, most (if not all) of those things would not have been on anyone’s list of predictions N years ago. (He gave a specific value for N, I just can’t recall what it is, but it does not matter.)

He sent an email to everyone who was either speaking, organising, moderating a session or similarly involved in the conference, asking them to send, off the [...] Click to continue reading this post


It is the 4th of July, and I hope you who are celebrating it have a good time today!

I can’t really let the day pass without sharing with you the episode of Fail Lab in which we examine fireworks and pyrotechnics with an appropriate cautionary note, and a dash of humour. Enjoy it again if you’ve seen it before, and don’t forget to check out all twelve episodes. You can read my discussion of the whole series (excellently made by Patrick Scott) starting here, and there’s more here. Click below for the episode: [...] Click to continue reading this post

It’s Dynamical Cosmological Constant Day!

airline_sketch_28_06_2014As you may know from three previous recent posts on research (here, here, and here), I’ve been thinking and calculating a lot in the area of dynamical cosmological constant – concerning mostly (but not entirely) thermodynamics and quantum gravity. Specifically, the cosmological constant becomes the pressure variable in the thermodynamics. I think it is important, and will teach us something about things like gauge/gravity duality, string theory, black holes, and perhaps even cosmology, but I am not sure what yet. I’ve made some suggestions in recent papers, and computed some interesting things along the way.

Anyway, the larger community has not been following this story much, since: (1) It means a break with some powerful and still very fruitful frameworks where the cosmological constant being fixed is a given – like AdS/CFT – and it is not clear what that means yet, so the motivation is not super-strong; and (2) Let’s be honest, there’s no superstar working on it, so it is not going to get anyone any points. So I’ve been trying to shout about it in my little way from the periphery, as I think it might be useful, and since several people have been doing really good and interesting work on this issue for many years and it is worth more people seeing what they’ve been up to.

So imagine my pleasant surprise when I looked on the listing of new papers on the arXiv for today and saw three (!) papers on the subject, moving things forward in various ways. (They all seem to have noticed some of what I’ve [...] Click to continue reading this post

Strings Talks

20140627-080640-29200119.jpgThe conference is really rather good, with a varied program involving topics and speakers from all over the map. This includes the parallel sessions we had on Wednesday, which were held down at the Institute. Those were a lot of fun, because of the dodging back and forth between different auditoria at the IAS to get to talks of interest. I was chairing one of the sessions, and so did not get to dodge about in the first 90 minutes, and had to miss some interesting talks, but did a little talk-surfing in the second 90 after the break.

It had been many years ago now since I began to talk about there being a need for parallel sessions at strings conferences. Some people would object to them, saying that it would somehow be damaging to the field’s connected nature, where everyone is following many strands and topics in the field. To me that concern was always balanced by the problem of only having a small cluster of people and ideas represented each year due to the constraints of only having five days to present the activity of such a diverse population of researchers in the field. The main objection to having parallel sessions were, to my mind, based on a view of the field left over from when the field was smaller in terms of both people and thriving ideas. I think the conference organizers this year found a way of combining the two models rather well, with the single afternoon of parallel sessions, along with well chosen sets of half hour talks for the main sessions where we all sit together, roughly grouped by themes. There were three one hour big marquee plenary/summary talks. Theses are really useful. If I were to make a change, I’d perhaps have four or five of those, putting the two half hour talks that were displaced into the parallel section.

There is a two hour session of “Vision Talks” this afternoon. Should be interesting to hear what is said. We will perhaps get some good discussion going about where various ideas may be headed. I hope there is a lot of audience participation.

Poster sessions and the “gong show” were also great things to have as part of [...] Click to continue reading this post


swooshWell, I sort of disappeared there for about a week. I got lost in some really interesting physics and had a lot of fun doing it.

I kept walking away, and it kept bringing me back. There’s that fun groove one can get into that other theorists will recognise: You hit an interesting vein where you can calculate interesting results in a particular model, and you just can’t help yourself computing more and more [...] Click to continue reading this post

Stockpiling Notebooks

notebook_supplyAs you know from my writings and sketches, I like to carry a notebook. People often ask me what types I use, or assume that I use the (increasingly fashionable) Moleskine books. I like Moleskine books (the little 3inx5in ones for example), and have used them a lot in the past, but actually I prefer the books by HandBook Journal Co., (made by Global Art Materials). The surface of the paper is more flexible, in my opinion. It has a little more tooth than standard Moleskine, which makes mark-making with pencil much surer, and it also takes wetting better,airline_sketches_9th_july_2013 so you can work with a little wetness as well, such as lots of ink, or watercolour (paint- or pencil-based). That allows for crisp drawings like the one on the right (click for larger view – more about these sketches here), right alongside physics research musings and computations in pen and ink line on the pages shown below on the left (those notes pertain to the paper I discussed here.)

I tend to carry one of the 8.25inx5.5in landscape ones (although I love the 5.5in square ones too). (See more chat about them here.) They allow a good [...] Click to continue reading this post

Honest Time Travel?

On Tuesday I hung out with some of the Screen Junkies folks who you may know from the hilarious “Honest Movie Trailers” web series (seriously, if you’ve not seen any of them, please go right now and have a look). We had a fun chat about time travel in movies, and presenter Hal Rudnick and I bonded over various movies old and new. The final version of the show is up on YouTube (embed below), and I’m bummed that I did not get to meet the other guest, Christina Heinlein (JPL), who seems fun – and is a descendant of, yes, that Heinlein. I love the idea that she works at JPL, helping make possible the space exploration that Robert Heinlein helped inspire us all about in his writing. Anyway, enjoy the short piece (I wish you could see a bunch of the other material too… we really had a great chat about the ins and outs of time travel, but a lot of it inevitably ended up not making the cut…)

I could not resist talking about my view of this (perhaps growing) trend of using time travel as a means of resetting movie franchises (see Star Trek, X-Men…). It’s a great way of repairing writing and other filmmaking wrong turns. Feel free to imagine your own version of this – Star Wars anyone? Another pass at [...] Click to continue reading this post

How I Sometimes Feel

tar_pits_entrapment_eventIn fact, the last several days have felt like this, with regards big decisions about various administrative roles I’ve been asked to consider taking on. It never seems to end, and I am terrible at saying no to as many things as I should. And I have a bad habit of doing things to the best of my ability and hence I get a reputation as the guy to ask to do a task since I did a good job last time, and so it gets me sucked in deeper into the administrative quagmire, and so on and so forth.

Rather like the “entrapment events” that happened in the La Brea Tar Pits so long ago (have a read of what I wrote about those on a field trip to the Page Museum a while back). I was wandering around the LACMA and Tar Pits grounds yesterday evening after a shoot for a show (a fun thing coming that I’ll let you know about shortly) and made a phone call to say, after ten days of [...] Click to continue reading this post

News From the Front XII: The Nuts and Bolts of Enthalpy in Quantum Gravity

So it happened again. I got musing to myself about something and decided to do a quick computation to check it out, and it took me down an interesting rabbit hole, which resulted in me writing a nice little paper at the end of last week that appeared today on the arxiv. I think the physics is really really nice. Let me tell you a bit about it. It is in the same area of ideas that I mentioned last time, concerning that paper I wrote last month. So let me pick up the story there, since I did not really touch on the core of the story. [Note: for non-experts, the following will get somewhat technical and full of terms and ideas that I will not explain. Sorry.]

One of the things that might have struck you (if you’re an expert in the area) from my proposal to make heat engines out of black holes that do real mechanical work like the engines you read about in physics textbooks is that there ought to be no actual mechanical work since there’s no pistons – no pistons changing volumes and so forth. That is (or rather, was) a missing ingredient in the standard thermodynamics of black holes in quantum gravity. Well, that all changed a short few years ago with the work of a number of authors, particularly with the clear suggestion of David Kastor, Sourya Ray, and Jennie Traschen, and work by Brian Dolan, with a fair bit of followup investigations by various other authors including some I’ll mention below. (Update: Two reviews, with different foci, can be found in here and here.) The general idea is that if you allow the cosmological constant \Lambda to be a thermodynamical variable as well (and there is a long history of authors considering this in various contexts), where it naturally acts like a pressure p = -\Lambda/8\pi G, (G is Newton’s constant, and I’m setting various other constants to unity in the usual way) then you naturally include a conjugate to that variable that should be the pressure.

For a simple static black hole like Schwarzschild, the volume turns out to the the naive volume you get by taking the radius of the black hole and forming [...] Click to continue reading this post

Making Marks

Been a while since I got to do some sketching. It is good practice to try to do something every day, but that fell by the wayside a little as far as proper sketches went. It has been busy the last week and a bit, and my subway time has been during very busy times when there’s not enough space to get out pen and paper and sketch a person without becoming a spectacle… and during the moments where I might have caught something, I’ve actually been calculating – working out questions for the final exam in the General Relativity class, and (more recently) doing some computations for a paper I’ll tell you about shortly.

Anyway, when time is short, I sometimes like doing quick sketches with a thicker pen. Stops me from digging into the details too much. In fact, I’m really liking that as a sketch mode these days… You make your lines boldly and you’re stuck with your choices, and so it gets you thinking about what’s globally important carefully before jumping in.


It is great and satisfyingly distracting fun. Anyway, between this and that over the last day or two I did a few quick faces based on some photos I found in a [...] Click to continue reading this post

Commencement Capers…

bromptons_and_robesIt is Commencement day today at USC! In celebration of that I thought I’d post a picture of my colleague Krzysztof Pilch and I, being a bit silly. We each have one of those excellently practical Brompton bikes (splendidly finished in British racing green, of course) you sometimes have read about here, and Krzysztof suggested that we take a picture or two of us in academic robes riding our bikes. Krzysztof had his academic full gear ready because [...] Click to continue reading this post

Advice at Graduation

It is Commencement on Friday, here at USC. Thousands of students will be dressing up in gowns and taking part of the ceremonies marking the ending of their time here at USC and the beginning of the rest of their lives. It’s an exciting time.

Merrill Balassone and a team from USC Media Relations came by my office a few weeks ago to take 15-20 minutes of time to do a prototype of a project on this very subject of commencement. The result was fun, and apparently they used it to build onto in order to make the final short video you can see below. advice_film_stillThey did a great job! It is a group of USC professors and staff** giving brief thoughts to graduating students upon their graduation. You’ll maybe guess what I say in my segment. It is a theme I mention here a lot, as part of my personal war on people being shut out of (or shutting themselves out of) participation in aspects of our society.

The summary of the piece is here and the YouTube video is embedded below: [...] Click to continue reading this post

Old School Writer

posting_stuff…Yeah. Somehow sending proposals and samples of manuscripts around by email does not really feel super-exciting to me. But it is the way things are done now, it seems. But this afternoon, I found myself doing something very old-school, which I rather enjoyed, perhaps because it connected me with writers through the ages: Printing up some special packages (proposal, samples, etc, of the book project), putting them into envelopes and schlepping them down to the post office, getting in line, and [...] Click to continue reading this post

That Time of Year

jacaranda_april_2014Well, it is that time of year. The Jacarandas peaking is one of the many LA markers of the seasons for me. It means that classes will soon be over (in fact they are now) and I’ll be saying goodbye to a group of students, either because a class is over, or because students I’ve taught in earlier classes are graduating and leaving USC. Either way, it is always a time of mixed feelings, and a sense of being in transition in a number of ways. The Spring is already beginning to feel like it is rolling into Summer, and I’m clearing my desk of one set of things and making way for other things.

(Oh, and of course, the other thing that happens this year is that I seem to end up doing a post like this at around this time, right down to within a few days. It usually involves a picture of a Jacaranda tree. See here and look at the list of related posts below.)

I had an extraordinarily good group of students in my Spring class this year. As you may recall it was an undergraduate General Relativity class (see earlier posts on this by searching on that topic). We ended up having a lot of fun with the topic itself, and things were extra good because the students were very [...] Click to continue reading this post

Another Engine

world_engineThis diagram is the cycle for another heat engine (using a black hole as the working substance) that I studied in the recent paper. It is a path made of two constant pressure legs (isobars) and two constant volume legs (isochores) that happen (due to the properties of static black holes) to also be adiabats. See the post.

It got included in the paper as another example where one could compactly write down something useful about the efficiency, since, as it turns out, you can write closed form expressions [...] Click to continue reading this post

A Monday Interview

On Monday 28th April at 8 PM Eastern time (5 PM Pacific) I’ll take part in a live radio interview that you might want to listen to, on a show called Alpha Centauri and Beyond. I guess I’m in the “Beyond” bit? I don’t really know anything about the show except that they like to bring people on to discuss ideas, and when I get a call to come and help sprinkle a bit of science, you know I’m likely to say yes if I can spare the time.

You can see a link to the details here, and you can listen online. As you can see it is advertised as being about me explaining string theory. Well of course that billing is nothing to do with me – I can’t hope to explain any complicated subject like that in the time available – but if asked I will do my best to try and motivate some of the ideas behind the subject. I hope it will be a fun interview and that [...] Click to continue reading this post

News From the Front, XI: Holographic Heat Engines!

Yes, you heard me right. Holographic Heat Engines. I was thinking recently about black holes in universes with a cosmological constant and their thermodynamics. I had an idea, it led to another, then another, then some calculations, and then a couple of days of writing, calculating, and thinking… then a day to cool off and think about other things. Then I came back to it, decided it was still exciting as an idea and so tidied it all up as a paper, made some diagrams, tidied some more, and voila! A paper submitted to the arxiv.

I’m sort of pleased with all of it since it allowed me to combine a subject I think is really fun (although often so bleakly dull when presented at undergraduate level) – heat engines – with contemporary research ideas in quantum gravity and high energy physics. So I get to draw some of the cycles in the p-V plane (graph of pressure vs volume) representing the inner workings of engines of particular designs (just like you might have seen long ago in a physics class yourself) and compute their efficiency for doing mechanical work in exchange for some heat you supply. It is fundamental that you can’t heat_enginedo that with 100% efficiency otherwise you’d violate the second law of thermodynamics – that’s why all engines have to have some exhaust in the form of heat, giving an efficiency represented by a quantity \eta that is less than one, where one is 100% efficient. The diagram on the left illustrates the key pieces all engines must have, no matter what working substance you’re using. The details of the design of the engine are what kind of cycle you taking it through and what the properties (“equation of state”) your working substance has. In the case of a car, for example, the working substance is cleverly mixed up with the source of heat – the air/gasoline mix forms a “working substance” that gets expanded and compressed in various ways (in the green bit of the diagram), but the fact that it also burns releasing heat means it is also the source of the heat that comes into the engine (the flow from the red bit) to be (in part) turned to work, and the remainder flowing out to the blue (exhaust). Very clever.

The cool thing here is that I’m using black holes as the working substance for [...] Click to continue reading this post

Exam Heat

We had a midterm in the undergraduate General Relativity class this week. Midterm II. We’d just come off a batch of lectures on black holes (focussing on Schwarzschild and Kerr), and so it seemed very natural to focus on that as the topic. Schwarzschild is the most basic (vanilla) black hole and Kerr is the case of having rotation for a bit of extra flavour. They are both hugely important in real physics – the former for the basic phenomena and then the latter since most objects out there in the astrophysical realm are actually going to be rotating to some degree (and after gravitational collapse, probably a high degree). So I focussed on those in class.

Screen Shot 2014-04-11 at 14.45.37For the midterm therefore, I got the opportunity to have them discover properties of the (less astrophysically important perhaps) charged black hole – the Reissner-Nordstrøm solution:
 ds^2=-\left(1-\frac{2M}{r}+\frac{Q^2}{r^2}\right)dt^2+\left(1-\frac{2M}{r}+\frac{Q^2}{r^2}\right)^{-1}dr^2+r^2\left(d\theta^2+\sin^2\theta d\phi^2\right)\ ,

…and do a few computations with it analogous to what they did for the other cases in class and in homework. I hope they had fun (like discovering that for a [...] Click to continue reading this post

Festival of Books and CicLAvia

public crossword at festival of booksBy the way, for those of you in the area, don’t forget that the LA Times Festival of Books comes to the USC campus again this month. It is next week – the 12th and 13th April. The book prizes ceremony is the night before, as usual. on the 11th, and as usual there is an interesting selection of finalists in various categories that you can see online here, for example.

(Happily, there is no clash with a CicLAvia this year! – You might remember the craziness last year – The next Ciclavia is this coming Sunday, the 6th, and it is along Wilshire again. Sadly, I will not be able to attend since I must be away on a trip and do not return until the afternoon on Sunday, leaving little time to get on my bike and get down there. Do head there and enjoy it… the Wilshire route is particularly nice.)

The main Book Festival website has a lot of information up about what is [...] Click to continue reading this post

Major Honours

On Friday I had to give the keynote address at the Phi Beta Kappa induction ceremony held here on the USC campus. I did not know what that really was when asked, perhaps because my educational environment as a student was in the UK. (Although for all I know there are such things over there too, but perhaps I did not notice.) After a bit of googling I learned that this is an honours society and it is devoted to excellence in the liberal arts. It is the oldest one of its sort, apparently (founded in 1776), and these days although science was there at the start, the practice is to add “and sciences” when you say liberal arts now. Students who maintain a certain standard of grades through their undergraduate degree in a liberal arts and sciences area are invited to 20140401-093450.jpgbecome members and then there is an induction ceremony. Sadly, no secret handshakes and strange behind the closed doors practices… Well, as far as I know. (In fact, as a thank you for giving the address, I get added to the membership as an honorary member, so perhaps a packet will arrive with my instructions about handshakes and so forth, but I doubt it.)

My speech was to be something about the liberal arts and to celebrate that and to impart some wisdom to the students and their assembled parents and so forth. I was happy to oblige and after letting it stew in background in my head for some time, come Friday morning I sat down at the computer and something nice flowed out through my fingers onto the page. People liked it – a lot, I was later told. I’m still a bit surprised (pleasantly) by that. There may be a story about it later, so I’ll post a link to that when/if it appears.

To my delight I recognised several names in the list for the ceremony. There were in fact five physics majors inducted (is that the right word?) all at the [...] Click to continue reading this post

Talking with Dinosaurs

20140401-095516.jpgThursday’s event at the Natural History Museum went very well. There was a great turnout, and the audience was very enthusiastic. As you can see from the photos*, there were two fierce-looking large dinosaurs in attendance in the audience, but it did not have any effect on the overall time-keeping, and the lectures ran over the allotted time quite a bit.

But people had fun, and the museum staff were very kind and flexible, so that’s ok. I actually learned a lot from Ed Krupp’s talk about the astronomy and astronomical objects along the Silk Road from the Far East to the Middle East especially. Laura Danly gave a talk that was mostly a detailed history the Internet including at least three internet cat videos as illustration (an emphasis that I found unexpected, I’ll admit, since I was expecting more about contemporary astronomy). It was certainly a modern perspective on the Silk Road, as we promised the audience, and it seemed to go down well. The observation opportunity that Laura arranged outside (with the telescopes that were set up in the new gardens) was also well received. Jupiter and its [...] Click to continue reading this post

The Calculus of Gender and Sexuality?

So, I don’t know why, but in addition to the catalogues I get in my work mailbox from publishers of physics books or lab equipment, I’ve started getting a lot about books in the Humanities and related subjects. Is this because those publishers know of my tendency to dabble in other subject? I’ve no idea. In any case, all of those things tend to end up pretty swiftly in the recycling bin nearest the department mailboxes. A suite of lovely new books on teaching Art History is about as valuable to me as a shiny sets of vacuum pumps or electronic controllers. I’ll admit to sometimes looking through and longing for the time I’d need in order to explore such things (vacuum pumps or Art History texts)… but then into the bin they go.

Well, earlier this week a catalogue arrived and one might be forgiven for thinking that they are really trying to get my attention with this one. It is a catalogue of Gender and Sexuality texts from Ashgate, and if the image on the cover is representative (uh, as far as I know it is not!) they’ve really developed some fancy techniques in the field!

Some of the formulae are hilarious! (And I’m trying to understand the, obviously important, inequality right in the middle…) [...] Click to continue reading this post

Under Silk Road Skies

I’m doing a disturbing amount of speechifyin’ this month. One of the occasions is tomorrow, and is open to the general public. Have you been to the Natural History Museum’s “Traveling the Silk Road” exhibition yet? I went to have a look a couple of days ago and it is rather nice. I recommend it. There are even live silk worms!

griffith observatory city view at nightI’ve been coorganizing an event as part of their series of lectures that accompanies the event and I am delighted to announce that I have connected two of the most awesome spaces and institutions in the city for this one. The Griffith Observatory will team up with the Natural History Museum for this one, with a lecture and Q+A session, and then (weather permitting) a bit of stargazing in the new gardens! Please spread the word and come along: [...] Click to continue reading this post

Discovery Coincidence

chatter_sketch_arenaSome of you are wondering what I’m working on while on retreat. Well, actually there’s a nice coincidence here. I’m working on the graphic book that you may have heard me talk about a bit. “The Project” as I sometimes call it. I’ve been doing things on various aspects of it, such as reworking the description of it for various people to look at, writing new bits, and spending a bit of time pulling together various bits of the prototype story I used to start all of this back in 2010. The prototype bits have all of my experimentation and development of style and technique all over them, and so there are pages that needed a bit of rework (to say the least). So, on Monday, [...] Click to continue reading this post

Around Fifteen

While on a hiding retreat in another town or city, I like to seek out a local group that might be doing a “drop in and draw” session. You show up, pay your money, and there’s a safe environment (in a studio, a back room, upstairs of a pub, etc) for a model and artists to work on the wonderful business of capturing the human form in various media. I’m a reasonably private person so I like to keep the anonymity level reasonably high, but it does not only work. People are of course on the watch out to protect the group from perceived problems, so they ask questions. Others are just trying to make friends, and so they ask questions too. I just like to be polite and friendly, share the odd joke or remark, but mostly keep my mouth shut and listen to the various small talk that breaks out during breaks. Most of all, I want to get on with the business of drawing.

sketches_17th_march_2014_smallI went to one on Monday. This time around it was sort of amusing to me at one point when one of the organisers of the group asked me why I’d come down from LA to their small seaside town drawing group and I said I was hiding. I could sense alarm immediately (I can imagine the pictures he might have had in his mind even before I said “hiding”) and so I then went further, by way of reassurance, and said something vague but standard about wanting to get out [...] Click to continue reading this post

Discovery Clarification

I’m actually in hiding and silence for a week. It is Spring Break and I have locked myself away in a seaside town to do some writing, as I did last year. But I must break my silence for a little while. Why? Well there’s been a really great announcement in physics today and while being very happy that it is getting a lot of press attention – and it should since the result is very important and exciting – I’ve been stunned by how confusingly it has been reported in several news reports. So I thought I’d say a few things that might help.

But first, let me acknowledge that there’s a ton of coverage out there and so I don’t need to point to any press articles. I will just point to the press release of the BICEP2 collaboration (yes, that’s what they’re called) here, and urge you once you’ve read that to follow the link within to the wealth of data (images, text, graphs, diagrams) that they provide. It’s fantastically comprehensive, so knock yourself out. The paper is here.

I keep hearing reports saying things like “Scientists have proved the Big Bang”. No. The Big Bang, while an exciting and important result for modern cosmology, is very old news. (You can tell since there’s even a TV comedy named after it.) This is not really about the Big Bang. This is about Inflation, the mechanism that made the universe expand rapidly from super-tiny scales to more macroscopic scales in fractions of a second. (I’ll say more about the super-tiny below).

I also hear (slightly more nuanced) reports about this being the first confirmation of Inflation. That’s a point we can argue about, but I’d say that’s not true either. We’ve had other strong clues that Inflation is correct. One of the key things that pops out of inflation is that it flattens out the curvature of universe a lot, and the various observations that have been made about the Cosmic Microwave Background over the years (the CMB is that radiation left over from when the universe was very young (about 380,000 years old – remember the universe is just under 14 million years old!)) have shown us that the universes is remarkably flat. Another previous exciting result in modern cosmology. Today’s result isn’t the first evidence.

So what is today’s exciting news about then? The clue to the correct [...] Click to continue reading this post