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

Eclipse Progress

eclipse_progress_15_04_2014_cvjDid you catch the eclipse last Monday? It was wonderful. Here’s a little snap I took of the progress (taken with an iPad camera precariously through the lens of a telescope, pointing out of a bedroom window, so not the best arrangement). One of the striking things about looking at the progress of it is just how extra three-dimensional the moon seems as the earth’s shadow slowly covers it. It really makes one’s whole mind and body latch on to the three dimensional reality of the sky – you really feel it, as opposed to just knowing it in your head. That’s sort of hard to explain – and you’re not going to see it in any photo anyone can show – so I imagine you are not really sure what I’m getting at if [...] Click to continue reading this post

Self-Similar Dinner

romanesco_fractal_20_04_2014_2
Eventually, although a bit over-priced in the Hollywood farmer’s market, I do fall for these at least once in the season. As someone whose job and pastimes involve seeing patterns everywhere, how can I not love the romanesco? It’s a fractal! There are structures that repeat themselves on different scales again and again, which is the root of the term “self-similar”. Fractals are wonderful structures in mathematics (that have self-similarity) that I urge you to find out more about if you don’t already know (just google and follow your nose). And [...] Click to continue reading this post

Total Lunar Eclipse!

There is a total eclipse of the moon tonight! It is also at not too inconvenient a time (relatively speaking) if you’re on the West Coast. The eclipse begins at 10:58pm (Pacific) and gets to totality by 12:46am. This is good timing for me since I’d been meaning to set up the telescope and look at the moon recently anyway, and a full moon can be rather bright. Now there’ll be a natural filter in the way, indirectly – the earth!

There’s a special event up at the Griffith Observatory if you are interested in making a party out of it. It starts at 7:00pm and you can see more about the [...] Click to continue reading this post

Participatory Art!

As you know I am a big fan of sketching, and tire easily of the remark people make that they “can’t draw” – an almost meaningless thing society trains most people to think and say, with the result that they miss out on a most wonderful part of life. Sketching is a wonderful way of slowing down and really looking at the world around you and recording your impressions. If you can write you certainly can draw. It is a learned skill, and the most important part of it is learning to look*. But anyway, I was pleased to see this nice way of getting people of all ages involved in sketching for fun at the book festival! So I reached in and grabbed a photo for you.

artists_row_latfob_12th_april_2014 [...] Click to continue reading this post

Young Author Meeting!

20140413-110946.jpgIt is nice to see the variety of authors at a book fair event like this one, and it’s great to see people’s enthusiasm about meeting people who’ve written works they’ve spent a lot of time with. The long lines for signings are remarkable! As you might guess, I’m very much a supporter of the unsung authors doing good work in their own small way, not anywhere near the spotlight. An interesting booth caught my notice as I was wandering… The word “science” caught my eye. Seems that a mother and daughter team wrote a science book to engage children to become involved in science… Hurrah! So Jalen Langie (the daughter, amusingly wearing a lab coat) gets to be [...] Click to continue reading this post

Harmonics Can Make Metals Flux

I’m sitting on the bus, on my way to the LA Times Festival of Books. I’ve opened my notebook to maybe sketch a face or two, but then I spot an algebraic error on a page from a few days ago, so I set about correcting it….(you know, either for those historians who will argue about my intentions while poring over these once-lost manuscripts…. Or more likely for me in a few weeks, likely to get confused by my own blunder-in-haste with a kindergarten level variation.)

20140412-122335.jpgA bearded fellow had boarded the bus and sat next to me while I was doing this. He eventually glances my way, then away, then he does a double take. I’ve been watching him out of the corner of my eye. He starts to speak to me.

Calc or Trig?
Excuse me?
Calc or trig?
Er…. Physics.
What are you studying?
I’m not…studying. It is my research.

Silence from him for a few beats, then:

Into what?
Charged black holes.

I should say at this point that I get this a lot. No matter who I meet out there in the random world, or what they see me writing, the assumption is always that I am taking a class in high school mathematics. Why is that? People, at least guess for some of the time that I might be at least teaching it, even if you can’t imagine people doing research in this area. The grey hairs in my beard are a guide to your assumptions.

Another gripe: if you see someone writing words, and want to engage them in conversation about it, you don’t assume they are practicing the basic structures… Imagine the analogous exchange: Are you practicing joined-up writing madam, or spelling? Neither, I’m writing poetry.

Anyway, back to the conversation. So, as you recall, I said Charged black [...] 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

Wormholes!

“So, you have a choice. We’ve ten minutes of class left. I can either finish early, or…. I can show you that there’s actually a wormhole living in this picture, or can I tell you about Hawking radiation.”

wormhole_sketchThat was the choice I presented the students with after we’d spent some time together exploring the Kruskal-Szekeres extension the the basic black hole solution, in my General Relativity class today. You probably don’t know what all that is, and that’s ok. Suffice to say that you end up with a pretty diagram which looks like two everlasting black holes put together as in a sort of elegant trading card. Or perhaps a neat knot where one black hole is sort of upside down and neatly slots into the other one so that they hug each other into eternity, acting as each others’ past and future. Look it up and see.

Anyway, they went for the wormhole, with a chant “Worm-Hole! Worm-Hole!”. So I constructed the wormhole for them… the Einstein-Rosen bridge, as it is known, ending with the sad news that it is not a real traversable wormhole that [...] Click to continue reading this post

Science Films Galore!

Sorry that it has taken me so long to get to posting the results of the USC Science Film Competition. It has been super-hectic. In addition to the usual things I have to do, I had to give a talk about science education to the Society of Physics Students – that went well, I heard – read and examine another PhD. thesis (twice in one week), do battle with two fronts of vermin attacks on my house, and prep a whole lot of other things I won’t trouble you with… Also, oddly, the time change seems to have left me in a state of exhaustion each day.

Enough with the excuses. What are the results, you ask? And is it true the winner was controversial?!

usc_science_film_showcase_2014_1Well, first and foremost we had a fantastic time celebrating the work of all the students in the competition. About 75 or so people turned up, making all my frantic buying of things in Trader Joe’s and so forth all worth while, and there were two screening sessions separated by a coffee and snacks break. Since there were twelve films this year (a 50% increase!) there were six per session (I curated things so that the sessions were about the same length), which worked rather well. A lot of the films used quite a bit of their 10 minute allowed duration, and so given that I pause between films to give each team a chance to take a bow, it was in danger of being a long evening, and for that I apologize to everyone, but I do think that the students should get a fair amount of individual recognition for their hard work.

Anyway, to cut a long story to medium, the standard was quite high this year, with several good films at the top that were hard to choose between, but I think the 15 judges (from academia and the film industry, with scientists and filmmakers and scientists-turned-filmmakers on both sides) got it right.

The first prize winning film has resulted in raised eyebrows from some, including the filmmakers themselves who apparently were sure that their film would be overlooked due to its content. I think that the judges got it exactly right. It is a fine example of exactly what I’m looking for in this competition- a [...] Click to continue reading this post

Showcase and Awards Today!

science_film_competition_logo_smallJust a reminder: The USC Science Film Competition Showcase and Awards are tonight (March 7th) at 6:00pm. I’ve been tallying up all the judges’ input and have the results in special envelopes to give out tonight. Very exciting. Come along (event information here), and enjoy celebrating all the students’ hard work. There will be twelve films on display!

-cvj Click to continue reading this post

Cloudy with a chance of Physics

I don’t know. That’s a bit of a desperate title. But in exchange, a rather nice cloud formation, don’t you think?

clouds_3_3_2014_1

This was from the sky over Los Angeles yesterday evening (a shot of the sky in the other direction is to the right – click for larger), and my first thought was “what’s the physics behind these beautiful structures?” There’s enough regularity here to expect there to be a mechanism, but I do not know what it is. Some combination of atmospheric conditions like wind speed, clouds_3_3_2014_2temperature, perhaps some layering of different bodies of air, and so forth, resulted in this and I’d love to know more. What factors set the roughly regular size of the structures, their pretty uniform distance apart, etc? (These are typical physicist’s questions, in case you’re [...] Click to continue reading this post

LA Phil Rock Star!

When calling to mind the Los Angeles Philharmonic, everyone’s (and all the posters’) focus is on Gustavo Dudamel, (or, the Dude, as I call him), all unruly hair and visible enthusiasm and so forth, and that’s great. He’s an excellent conductor. However, one of the unsung (as far as I know*) visibly spectacular performers of the LA Philharmonic is the excellent principal viola player whose name I do not know [update: see below*] who puts on the most remarkable physical performance every time I go (and presumably those other times too). Actually, the violist who sits next to her is also remarkable, since she manages without being distracted by her neighbour to maintain a very upright and solid, firmly planted, legs wide stance, in part providing a canvas upon which the viola player I first mentioned can splash bright splashes of movement all over the place! la_phil_sketch_28th_February_2014_smallShe rocks, sways, jerks, and contorts (sometimes even during quiet slow bits)- doing the craziest things with her legs, head, and bow arm, and so much of the time looks like she is about to spectacularly fall off her chair and wipe out at least half the viola section! This is why her colleague right next to her is also remarkable, as she acts as this wonderful un-distractable “straight man” to the physical pyrotechnics helping make them all the more remarkable by contrast. Last night I tried to capture some of the energy of the hyper-energetic viola player in a quick sketch (during [...] Click to continue reading this post

Take Part in the Festival!

I’ve just returned from a rather wonderful two rainy days in Santa Barbara celebrating the work of Joe Polchinski. (See my previous post for more about this, including a few reflections.) It was a combination of high school reunion, group hug (with Joe in the center), and serious reflection about physics, now, back then, and to come. Now the great news is that pretty much everything was recorded on video, and so you can take part in it by settling down in front of your computer (or other device – those of you in the further (but pre-singularity) future can just instruct the appropriate plug-in from [Cyberdine systems ] [Tyrell Corporation] Google to stream directly to the vision centres of your brain) and view the various excellent talks and panel discussions here.

I had the honour of chairing (and contributing to) one of the panel discussions reflecting on D-branes (as I promised last post). The title was “D-Branes: Tools of the Revolution” and it went very well thanks to my three excellent panelists (Greg Moore, Andreas Karch and Samir Mathur) and many members of the gathered audience who contributed to the free-form discussion in the 15 minutes at the end. Have a look at that right along side the really interesting and lively discussion that Steve Shenker chaired at the end of the conference (which sadly I had to miss because I had to get back to LA through the rainstorm for another engagement). The idea there was to speculate a bit about the future of physics and thereby “Planning for Joe’s 90th Birthday“.

Enjoy.

-cvj Click to continue reading this post

Festival of Joe

20140226-214941.jpgEarly evening. Cocktail (made with Hendricks gin, muddled tangerine, and basil…). Roast pork on the way. Old haunt.

Where am I? At Roy’s, in Santa Barbara. I’m here for a two day celebration of the work of Joe Polchinski, one of the giants of my field. It all begins tomorrow, and I am taking the opportunity to have a quiet bit of time in an old haunt. I was a postdoc of Joe’s back in the mid 1990s, just when the world of theoretical physics was waking up to the awesome power of D-branes. D-branes are a special type of dynamical extended object in physics, and Joe had discovered their importance for string theory just around that time. Roy’s opened around that time too, if I recall, and a group of us became regulars, helping it along in those early days when it was smaller than it is now. (That small group included my friend and fellow postdoc Andrew Chamblin, who passed away some years ago.)

A D-braneSo I am here to help celebrate Joe’s work on the occasion of his 60th (hard to believe that number, frankly), and it will be good to see all the people who show up, and of course it’ll be excellent to see Joe. Part of my help in the celebrations is to organize and run a panel about D-branes, which will be on at 11:00 tomorrow. I’ll be reflecting a bit on the good old days when D-branes really broke, and turned out to be the key tool of the Revolution that took place in the field. In lectures and writings from that time and long after I used to refer to them as the Heroes of the Revolution, and in honor of that and of Joe I have named this session D-Branes, Tools of the Revolutionary, or something like that. Joe helped bring about the revolution, and his tools were D-branes, you see.

I was lucky to be here as a postdoc at that time, and happily I had the good sense to be quite sure that it was going to be important to quickly spread the [...] Click to continue reading this post

Introduce a Girl to Engineering Day

Apparently it was Introduce a Girl to Engineering Day yesterday, so some might say I missed it. But as you know, I think that every day should be Introduce a Girl to Engineering Day, so it is not too late! Have a look a website for it I found (here). What can you do? You don’t have to organise a huge event (although feel free to). It can all start small. Maybe for that next gift, consider (if you don’t already) buying your little girl (or someone else’s) a set of LEGO or an electronics kit (or other hands on building toys) instead of the (fill-in-the-blank-standard-girl-toy) everyone else is getting her. Go ahead and make it a pink kit, if you want, since that’s what society seems to want. Who cares what colour it is? Apart from buying, even just chatting a bit with a child about engineering in our lives, and all the people who can (and do) contribute to it would be a great thing to do.

Here’s a short film from our own Viterbi school of engineering:

[...] Click to continue reading this post

Films!

Good News Everyone!

The deadline for the USC Science Film Competition (now in its third year) passed, over the weekend. The good news is that I now have 12 films in the vault (a 50% increase on the two previous years), waiting for the next stage of the competition. They are on a wide range of topics, in a variety of narrative styles, and I’m super-excited to find a block of time and have a look at them. The next stage is judging, and I’ll be assembling the panel over the next day or two and letting them start looking at them and casting their votes.

So keep an eye out for more news soon. The showcase and awards ceremony is on the 7th of March, and I’ll be opening envelopes and giving away prizes with delight, I’m sure. I’ll also be posting films here on the blog for you to look at, once that date has passed.

-cvj Click to continue reading this post

Mass Matters

I was about to do a little post about where we are in the General Relativity class. We’re about to start studying our first full non-trivial solution of Einstein’s equations. Then I had this feeling I’d done it before, so I looked, and indeed the very post I thought I’d do was first posted Feb. 13th 2008. So why not re-post it for your reading pleasure?

_________________________________________________
(First posted 13th Feb. 2008)

Well, only four weeks and change behind us in this course, and… the class (see here and here) is ready to understand this wonderful equation:

the schwarzschild solution

and all that it implies. What is it? It encodes the shape of spacetime around a spherical blob of mass of total mass M. No, don’t worry too much about the details, since this is not a lecture about General Relativity….. it is just nice (I hope) every now and again to get a look at the sorts of things we use in our day to day work. This “warped” spacetime encodes what we interpret as the gravitational field (in the old Newtonian language) due to a spherical (or, to a good approximation, almost spherical) mass. Like the sun, or the earth, or that tennis ball in the corner there*. It is an exact solution [...] Click to continue reading this post

No, That’s the Other Guy…

sam_jackson_tvNo, I’m not Neil deGrasse Tyson. Yes, we both talk about science on TV. Yes, we both happen to be black… but no, we are not the same guy. Also: No, I am not Jim Gates. He also sometimes shows up on TV talking about physics, and he is also black.. but no, he isn’t either me (Clifford) or Neil… He’s Jim.

This attempt at humour is inspired (in part) by real conversations I’ve had (less so in recent years, thank goodness – people are maybe better about googling first?). But mostly it is inspired by this (familiar) sad, funny, and stunningly awkward conversation from Monday* (the first 2 minutes 10 seconds): [...] Click to continue reading this post

Summing Numbers in a Small World

So here’s a slightly weird thing. So there’s been all this excitement over the web about the old old “shocker” that the sum of the positive integers is -1/12. You know, not even an integer, and not even positive. Apparently there have been articles in the New York Times and Slate and goodness knows where else… and I’ve been ignoring it all since I’m tired of what it often leads to: People wilfully using it as a device to manipulate people’s ignorance about subtleties with infinite processes to make the tired point that string theory is somehow wrong since it is based on “funny math”. I called Lawrence Krauss (who should have known better) out about it some years ago when he did that at an event I happened to attend. It’s a bit tedious, not the least because it is actually part of a wonderful field of mathematics that can get misrepresented, and of course because it has nothing to do with string theory.

So I ignored it all. Then some students in my class asked me about it. And I explained why it is interesting and so forth… Then I carried on ignoring it all.

Then a day or two ago a mathematician colleague emailed me to ask what [...] Click to continue reading this post

Straight

In class tomorrow I’ll introduce one of my favourite equations:

<br />
\frac{d^2x^\sigma}{d\tau^2}+\Gamma^\sigma_{\rho\nu}\frac{dx^\rho}{d\tau}\frac{dx^\nu}{d\tau}= 0\ .<br />

… Wait – Where did everyone go?!

Come back! I’m not expecting you to know what it means, I just wanted to talk a bit with it sort of … nearby. If you consider yourself a bit intimidated by mathematics, be assured that it won’t bite. (No more than a piece of sheet music lying nearby will harm someone who has not learned to read music.)

It turns out that it is pretty geometry! In the equation, we’ve the object
<br />
\Gamma^{\sigma}_{\rho\nu}\equiv\frac12 g^{\sigma\mu}\Biggl(\frac{\partial g_{\mu\nu}}{\partial x^\rho}+\frac{\partial g_{\mu\rho}}{\partial x^\nu}-\frac{\partial g_{\rho\nu}}{\partial x^\mu}\Biggr)\ ,<br />
called the “Christoffel symbols”. The set of objects g_{\mu\nu} (the “metric”) actually encode the properties of the space you wish to study (like the plane, or the sphere), and the equation at the top tells you what are the “straight lines” in that space. Well, in the plane (like your desktop) they are straight lines, while in other spaces they are the analogue of straight lines – if you want to go from one point to another point somewhere else in the space and desire to travel along the shortest path to do so, you want to follow such a line. It is called a “geodesic”. The equation is commonly called the geodesic equation.

231px-Longitude_(PSF)You know such lines, intuitively, in a non-trivial example. Next time you look at a globe (wait, does anyone but me look at maps and globes any more? I love them!), you’ll probably see examples of those lines drawn in. They are the “great circles”, the lines of longitude, and the equator. (Image used with permission.)

I just made a class worksheet that guides one through a bit of playing with this equation to get the class excited about [...] Click to continue reading this post

Finally!?

la_clouds_02_02_2014Some rather exciting looking rainclouds, and a strong wind! Will we get some decent rain? Something like a biblical downpour, as promised by these clouds?

[Later:] A few spits of rain, but really nothing. Then back to sunshine again, disappointingly. We need some rain here in Los Angeles! Desperately.

To make the point more clearly, have a look at the site Climatestations.com for data on how we’re doing for rain as compared to the seasonal average. It is very disturbing.

If you look at the graph [...] Click to continue reading this post

Hawking an Old Idea

On the one hand it is good to get members of the general public excited about scientific research, and so having some new excitement about something Stephen Hawking said, driven by gushingly written articles in the press and online, can be good. On the other hand, it is annoying that the thrust of the articles are largely that he’s stunned the world again with a brilliant and unlooked-for idea. People just lap this stuff up, unquestioningly. It is actually an old idea (and in fact one that is being mis-reported – see below). One’s instinct is to just say “Welcome, Stephen, we’ve been waiting for you to join us”, or “Come on in, the water’s lovely”, and just move on, but it seems so unfair. The thing that’s most puzzling in all of this is Hawking’s own paper (which is all of two pages of words – a transcript of a talk he gave in August), which makes no reference at all to (for example) Samir Mathur’s work, which has been explicitly saying essentially the same thing for well over a decade, with a very definite proposal for how it might work. That work has hardly been buried in obscurity. Samir and many other people who have liked his idea have been working out the consequences of the proposal in numerous papers for over a decade and reporting on their results at all the main conferences, and even talking to him about it (I note that Samir was in the audience during the August talk and even politely asked the speaker to compare and contrast the similar-sounding proposals). So it is puzzling that you get no hint from the paper’s citations that this is a well-considered and ongoing idea, even if (perhaps) in detail it may pan out differently from other suggestions.

light cones in  spacetime with a compact mass - a black holeWhat’s the idea?, you ask. Well, it is not, as you might get from most of the articles (somewhat confusingly), that black holes do not exist. It is that the black hole’s event horizon, thought of as a sharp “point of no return” boundary, may not exist. Instead, it is approximation or shorthand for the complicated physics (of both matter and spacetime) that happens in the vicinity of the black hole. Simply put, the horizon arises in classical solutions to classical (i.e. non-quantum) equations (such as in General Relativity) of gravity. (See an earlier post I did about them here, from which came the illustration [...] Click to continue reading this post

Unfinished Meditation

figure_27th_january_2014_1_smallAfter a long weekend of a two-day meeting of an American Physical Society committee (hosted in LA this time, so I did not have to travel far), I decided last night to go and do a drop-in-and-draw session at an art studio, to clear my mind.

The model was excellent, with a smashing hairdo and good body-awareness that made for interesting poses. I was in the mood to disappear and listen to Hendrix for three hours while focusing on the simple task of representing what was in front of me. So I did.

I’m horribly slow again. Lack of regular practice (on full figures), of course. The good news is that I have been able to hold on to some of the more important foundations that allow me to lay things out, and see forms and shapes. But it does mean that I don’t get to get to some of the finishing processes that I intuitively prepare for in the earlier parts of the drawing.

As you know from many posts of mine on the subject (see e.g. here and here) I actually like incomplete drawings where you can see a lot of the process [...] Click to continue reading this post

Morning Flames

sunrise_26_01_2014

I’ve a few things to tell you about from events over the last couple of days, and I want to mention some exciting events to come, but right now I must get on my bike again and head off up the hill in the park to the Griffith Observatory for an early morning meeting. As I was up again before the sun, I got to look out the window and see a wonderful – and rapidly changing – unfolding of the day. Thought I’d share it again*. Quite spectacular!

-cvj

(*See recent posts for other sunrises from recent days). Click to continue reading this post

30 Years…

…but apparently, no black people use Macs. Well, you’d get that impression from Apple’s 30 year celebration video (which I was all excited to watch at first), and from the 30 year timeline on the site (which has one face per timeline). In the video, of course there’s some black people dancing and playing basketball (‘cos, you know, that’s all we can do), but when it comes to images of who’s using the machines and being creative with them… a parade of (often smug) white people and a few asians. Really Apple? Out of 30 people representing the past, present and future of your product that apparently “changed the world”, you can’t find even one black face to pretend to use it for your celebration? And of course, I fall into the trap and link to their site like an idiot for you to look at what I’m talking about. Go for it.

Sigh.

-cvj Click to continue reading this post

Celestial Card Games

celestial_cardsI did not get to read the instructions about the games, but pictured are some cards (apparently from about 1830) for a game set. They have images of stars and planets on them, including one planet called Herschel. This is of course the planet to later be called Uranus. It took a while for the planet’s name to be agreed upon.

These are some of the objects from the Doheny Libary’s collection that will be [...] Click to continue reading this post

When Life Hands You Lemons…

lemons_from_garden_23_01_2014

Accidentally harvested a handful of my precious Meyer lemons from the tree earlier this morning while clearing a branch from a nearby tree. They are delicious and I only get a small number of them each year, so I tend to treat them like gold. Will have to make something special with them…

Yes, also, there’s a metaphor somewhere in there for other things going on, so…

-cvj Click to continue reading this post