So, here we are. Still in existence. Hurrah!
The Large Hadron Collider (image right is courtesy of CERN) started a new phase of experimental work today, colliding particles at double the energy it was working at a few years back when the Higgs was discovered. By time I was making breakfast and checking email, their live blog, etc., this morning, it was clear that (contrary to fears expressed by some) the LHC had not created a black hole that swallowed the earth, nor had it created some sort of strange chunk of new vacuum that condensed that of the entire universe into a new phase. (Or if it did either of those things, the effects are hardly noticeable!!)
As I keep emphasising (actually I’ll be talking about this to a puppet character on a TV show tomorrow too – details later) the LHC (or any of the particle collision experiments we’ve ever done) is not doing anything that Nature does not do routinely right here at earth (and most times way more violently and […] Click to continue reading this post
Here’s some interesting Sunday reading: Frank Close wrote a very nice article for Prospect Magazine on the business of testing scientific theories in Physics. Ideas about multiverses and also string theory are the main subjects under consideration. I recommend it. My own thoughts on the matter? Well, I think most … Click to continue reading this post
Worth a read: This is ‘t Hooft’s summary (link is a pdf) of a very interesting idea/suggestion about scale invariance and its possible role in finding an answer to a number of puzzles in physics. (It is quite short, but think I’ll need to read it several times and mull over it a lot.) It won the top Gravity Research foundation essay prize this year, and there were several other interesting essays in the final list too. See here.
-cvj Click to continue reading this post
There’s an SCSS today, at USC! (Should have mentioned it earlier, but I’ve been snowed under… I hope that the appropriate research groups have been contacted and so forth.) The schedule can be found here along with maps.
-cvj Click to continue reading this post
I just learned of an excellent interview with Edward Witten, one or our field’s grandmasters, or rather: the grandmasters’ grandmaster. I strongly recommend reading it. (This is for technically equipped people working in the field, most likely – I believe that it is not intended for the general public, although you are welcome to read it too!)
There’s a lot of discussion (of among other things like his current work) of that golden period during the 1990s that I had the privilege to work in during my postdoc years (some of them under the guidance of Witten) that remain one of […] Click to continue reading this post
…Or at least, not always the fire you’re looking for. So, as suspected for several months now, the signal seen by BICEP2 experiment and dubbed “a smoking gun” type of direct evidence for cosmic inflation (for which we have lots of strongly suggestive indirect evidence, by the way) is likely an artefact of the effects of galactic dust. I spoke about this in a post a while back, so I won’t repeat myself here. What everyone has been waiting for has been the results of a joint analysis between the BICEP2 people and the ESA’s Planck mission. The Planck satellite, you may recall from reading here or elsewhere, is also designed to carefully study the polarisation of the cosmic microwave background (the earliest light to shine in the universe), and so can (through thorough analysis of the effects of dust that it has measured independently) help rule in or out whether there is a signal. Planck studies essentially the whole sky, not just the patch that BICEP2 was carefully looking at, and one of […] Click to continue reading this post
Yesterday I sneaked on to campus for a few hours. I’m on family leave (as I mentioned earlier) and so I’ve not been going to campus unless I more or less have to. Yesterday was one of those days that I decided was a visit day and so visit I did. I went to say hi to a visitor to the Mathematics Department, Sylvester James Gates Jr., an old friend who I’ve known for many years. He was giving the CAMS (Center for Applied Mathematical Sciences) distinguished lecture with the title “How Attempting To Answer A Physics Question Led Me to Graph Theory, Error-Correcting Codes, Coxeter Algebras, and Algebraic Geometry”. You can see him in action in the picture above.
I was able to visit with Jim for a while (lunch with him and CAMS director Susan Friedlander), and then hear the talk, which was very interesting. I wish he’d had time to say more on all the connections he mentioned in the title, but what he did explain sounded rather interesting. It is all about the long unsolved problem of finding certain kinds of (unconstrained, off-shell) representations of extended supersymmetry. (Supersymmetry is, you may know, a symmetry that […] Click to continue reading this post
Happy New Year! So, it is the second of January. You’ve spent all of the day yesterday recovering from the euphoria (and perhaps revelry) of New Year’s Eve, and so today it is time for the traditional next thing on the new calendar: Planning what you’ll do next New Year’s Eve, of course!
Before doing that however, if you are a research physicist, I’d like to invite you to consider doing something else: Plan your Summer research travel. What I am really trying to do is to make you aware that the end of this month is the deadline for applying to attend the Aspen Center for Physics during some period inside the Summer operating dates Memorial Day (in May) to around Labor Day (September). Now, a lot of people (too many, in my and the opinion of others who care about the ACP) just assume that the place is not for them, for a number of reasons that are really not good ones. So let me address one or two quickly right now.
First, it is not an old boy’s country club. It is for everyone, working in all* fields of physics. Don’t apply and you have zero chance of getting in. Apply and there is […] Click to continue reading this post
Since people were asking for copies of my slides from my colloquium chalkboard-style talk on black holes and the things I call “holographic heat engines” last month at Harvey Mudd College, I decided to export them as a movie. You can find it on YouTube. Link below. It was a 50 minute talk, but all the builds are compressed down to a 6 minute file! I try to keep the bulk of the narrative in my head and speak it with the slides as visual aids (instead of writing everything on the slides as is often the practice) and so I do not know […] Click to continue reading this post
The UCLA group is hosting the next Southern California String Seminar, the long running once a semester (mostly) regional event that roves around the various high energy groups in the region (more here). It is on Friday!
There’s schedule and other information here. The schedule goes something like this: […] Click to continue reading this post
I’m a fan of Chris Nolan’s work so I’ve been looking forward to Interstellar. I’ve also been fascinated by the McConaussance – the transformation of Matthew McConaughey into an actor of considerable stature in a series of excellent films (Mud, Dallas Buyers Club, etc…), so I’ve been doubly interested in seeing how he works in a film under Nolan’s direction. Same for the always amazing Casey Affleck. All quite exciting to see.
But then to my surprise it turns out there’s another reason to be interested. Kip Thorne. Some years ago, at a party when I last saw him, Kip told me that he had been working on some film or other with a major studio, but I did not know of the details. Then I ran into a mutual friend a couple of months ago who said something a long the lines of “Kip’s movie is coming out soon…”, and I learned that it was something to do with Interstellar! But I did not know any details.
Then I got sent* this Wired story, and then** this story, and I finally got around to looking. The Wired story has a lot of interesting detail, including a special film (that I ought to look at at) with interviews and behind the scenes material (the still to the right is a screen shot from it). The film will apparently feature a black hole and a wormhole in some way (I don’t want to know more – I like films to unfold in front of me in the theatre). Kip has been working with the visual effects people to get right exactly how such objects really look, an issue that has not really been fully addressed, it seems. He, like a number of us interested in science and film, is keen to help filmmakers really do a good job of representing some of these fascinating objects as accurately as possible. (Not, in my view, in order to stifle filmmakers’ imagination, as it so often seems when you hear scientists out there pontificating about what’s wrong in one film or another, but because the actual science is so very often far more interesting and full of delights and possibility than a visual effects kluge can be…) So apparently he wrote down […] Click to continue reading this post
I’m on the road. I gave a seminar at the University of Michigan yesterday, and spent the working day chatting with various physicists at the department there, exchanging ideas, catching up on what people are up to, etc. The seminar itself went ok. I’ve been talking about extended gravitational thermodynamics, the subject of all my papers so far this year. I think I paced things a bit poorly (trying to squeeze in results from two papers while at the same time being pedagogical about the basic material since it is not familiar to most), so had to rush at the end, but I got the main points in. Lots of good questions.
At the end of the day, I was pleasantly surprised by the offer of whiskey in the break room. Apparently it is a Friday tradition. I began to wonder, and made some inquiries and found out to my delight that it is a direct decendant of a tradition that I (co-) started back in the mid-90s in Santa Barbara!
It was a long time ago, so I am hazy on who the core people were who regularly kept […] Click to continue reading this post
There has been quite a bit of discussion of the realisation that the exciting announcement made by the BICEP2 experiment back in March (see my post here) was based on erroneous analysis. (In brief, various people began to realise that most, if not all, of what they observed could be explained in terms of something more mundane than quantum spacetime fluctuations in the ultra-early universe – the subtle effects of galactic dust. A recent announcement by another experiment, the Planck team, have quantified that a lot.)
While there has been a bit of press coverage of the more sober realisations (see a nice June post on NPR’s blog here), it is (as with previous such cases) nowhere near as high profile as the initial media blitz of March, for better or worse. I think that “worse” might be the case here, since it is important to communicate to the public (in a healthy way) that science is an ongoing process of discovery, verification, and checking and re-checking by various independent teams and individuals. It is a collective effort, with many voices and the decentralised ever-sceptical scientific process itself, however long it takes, ultimately building and broadening the knowledge base. This self-checking by the community, this reliance on independent confirmation of […] Click to continue reading this post
So while at a hotel somewhere down South for a few days (pen and watercolour pencil sketch on the right), I finally found time to sit and read Graham Farmelo’s book “The Strangest Man”, a biography of Dirac. (It has a longer subtitle as well, but the book is way over in the next room far from my cosy spot…) You may know from reading here (or maybe even have guessed) that if I were to list a few of my favourite 20th century physicists, in terms of the work they did and their approach and temperament, Dirac would be a strong contender for being at the top of the list. I am not a fan of the loudmouth and limelight-seeking school of doing physics that seems all so popular, and I much prefer the approach of quietly chipping away at interesting (not always fashionable) problems to see what might turn up, guided by a mixture of physical intuition, aesthetics, and a bit of pattern-spotting. It works, as Dirac showed time and again.
I’ve read a lot about Dirac over the years, and was, especially in view of the title of the book, a little wary of reading the book when I got it four years ago, as I am not a fan of going for the “weren’t they weird?” approach to biographies of scientists since they serve too […] Click to continue reading this post
I thought I’d mentioned this already, but I could not find anything after a search on the blog so somehow I think I must have forgotten to. It is a cute thing about a certain favourite solution (or class of solutions) of Einstein’s equations that I’ve talked about here before. I’m talking about the Taub-NUT solution (and its cousin, Taub-Bolt). Taub-NUT is sort of interesting for lots of reasons. Many, in fact. One of them concerns it having both mass and another parameter called “nut charge”, . There are several ways to think about what nut charge is, but one curious way is that is is sort of a “magnetic” counterpart to the ordinary mass, which can be thought of as an “electric” quantity.
The language is based on analogy with electromagnetism, where, in the usual […] Click to continue reading this post
Hello 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
As 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
The 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
Today is day one of Strings 2014, this year’s version of the official annual conference about the latest research in string theory. There’s a feeling that there is a buzz of excitement in the air, in part because (I’m guessing): (1) Well, it is the annual conference, you’re going to find out more about what’s been going on in the various corners of the field, and (2) everywhere you look there walks a giant of the field, and (3) more generally, people just like you who “get you”, and whose papers you’ve read that you’ve spent a good portion of your life thinking about, so it would be odd if you were not excited, and (4) it is in Princeton, which is sort of equal to Mount Olympus in our field, where a lot of the giants live, if you’ll permit me to mix metaphors a bit, and (5) apparently this is the largest Strings meeting since Paris in 2004. (I’ve heard that it is maybe 600 people registered, making it the biggest Strings ever?… Not sure.)
I could go on guessing about the buzz felt by others, but instead I’ll mention […] Click to continue reading this post
Well, 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
As 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, 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
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 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 , (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
This 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
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 do 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 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
[Update: Over the months following the announcement, doubt was cast over exactly what BICEP2 saw, and now it seems that the signal announced by BICEP2 is consistent with polarisation produced by galactic dust. See here.]
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
“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.”
That 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
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“.
-cvj Click to continue reading this post
Early 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.)
So 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
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
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.
What’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