Sean Carroll

Blog

  • Explaining Time to Kids

    Don’t forget that the deadline for this year’s Flame Challenge is coming up. Your mission: to explain “Time” to a group of 11-year-olds, who will be sternly judging your work. Get your submissions in by March 1, either video or written (less than 300 words).

    Here’s my attempt. (Just given the likely number of entries, winning seems like a long shot, so I don’t mind encouraging other submissions or giving away all my best lines.) 300 words is hard, and aiming squarely at 11-year-olds who are judging a bunch of submissions is also no easy feat. But it’s good practice. I personally first fell in love with science when I was 10, so 11-year-olds are a great audience to aim at.

    Admittedly the definitions I propose below could be accused of being circular, but without using technical jargon I think it’s appropriate to aim for intuitive understanding rather than perfect rigor.

    Time is not hard to understand! How time works can be tricky, but time itself isn’t that mysterious.

    We live in a world full of stuff. Chairs, trees, planets, stars, all kinds of things. This stuff is spread throughout space–everything has a location somewhere or another. And all this stuff, at various positions in space, happens over and over again, slightly differently each time. Things move, age, transform. Planets orbit stars, animals eat and sleep, people play and fight and think and learn. The universe doesn’t sit still.

    Time is the label we stick on different moments in the life of the world. There is the universe at 2 p.m. July 1st 2013, the universe at 2:01 p.m., and so on. Just like a page number tells you where you are in a book, time tells you when you are in the universe. Moments of time are pages in the book of the universe.

    We can measure time using clocks and calendars—things that repeat themselves in a predictable way. Every time the Earth revolves around the Sun, it rotates around its axis about 365 times. Every time the little hand goes around a clock dial, we can be sure the big hand goes around twelve times.

    Time gets mysterious when we think about past, present, and future. We can remember what happened yesterday, but we can’t remember tomorrow. It seems obvious, but why is it true? Why does everyone – everyone! – get born young, and then grow old? We can choose what to do next in our lives, but we can’t un-choose events in the past, things that have already happened. The past is in the books, but the future remains to be shaped. Let’s hope we choose wisely!

  • Venus and Luna

    Couldn’t resist posting this photograph of the crescent Venus snuggling up to the crescent Moon. Taken by Ivan Eder, Budapest; posted on Facebook by Stars and Constellations; pointed to by Nick Suntzeff. (Update: Peter Simpkin points out that the original can be found here.)

    Venus and Luna

  • Smooth Life

    Chances are you’ve seen Conway’s Game of Life, the checkerboard cellular automaton featuring stable structures, replicators, and all sorts of cool designs. (Plenty of implementations available online.) It’s called “life” because the processes of movement and evolution bear some tangential resemblance to regular organic life, although there are plenty of other reasons to be interested — for example, you can construct a universal computer within the game.

    Now John Baez points us to a version called SmoothLife, in which the evolution looks dramatically more “biological.” (Technical paper by Stefan Rafler here, and a playlist with many videos is here.) Rather than just looking at the nearest neighbor sites on a square grid, SmoothLife integrates over a region in the vicinity of each point, with a specified filter function. As a result, everything looks, well, a lot smoother.

    Generalized Conway Game of Life – SmoothLife3

    While SmoothLife is undeniably more lifelike in appearance, I think the differences between these kinds of simulations and biological life are as important as the similarities. Conway’s original game supports an impressive variety of structures, but it’s not really robust; if you start with a random configuration, chances are good that it will settle down to something boring before too long. My uninformed suspicion is that this is partly due to the fact that cellular automata typically feature irreversible dynamics; you can’t recover the past state from the present. (There are many initial states that evolve to a completely empty grid, for example.) As a result, evolution is not ergodic, exploring a large section of the possible state space; instead, it settles down to some smaller region and stays there. There are some reversible automata, which are quite interesting. To really model actual biology, you would want an automaton that was fundamentally reversible, but in which the system you cared about was coupled to a “low entropy” environment. Don’t know if anyone has attempted anything like that (or whether it would turn out to be interesting).

    While I’m giving away all my wonderful ideas, it might be fun to look at cellular automata on random lattices rather than strict rectilinear grids. If the nodes were connected to a random number of neighbors, you would at least avoid the rigid forty-five-degree-ness of the original Life, but it might be harder to think of interesting evolution rules. While we’re at it, we could imagine automata on random lattices that evolved (randomly!) with time. Then you’d essentially be doing automata in the presence of gravity, since the “spacetime” on which the dynamics occurred would be flexible. (Best of all if you could update the lattice in ways that depended on the states of the cells, so that matter would be affecting the geometry.)

    Musings along these lines make me more sympathetic to the idea that we’re all living in a computer simulation.

  • Summer Institute in Philosophy of Cosmology, Santa Cruz

    This summer UC Santa Cruz will host a Summer Institute in Philosophy of Cosmology, from June 23 to July 15. There will be a great lineup of speakers, not to mention me. The “philosophy of cosmology” isn’t really a recognized intellectual discipline as yet, but some of us are trying to bring it into existence, so it’s an exciting time.

    This is more of a summer school than a conference, so students and postdocs with an interest in the field should certainly think of applying. The deadline for applications is March 15, so don’t wait too long!

  • Higgs Boson Blues

    Almost enough to make me believe in a benevolent force guiding the universe: Nick Cave, on his new album Push the Sky Away, has a song called “Higgs Boson Blues.” (Hat tip to Ian Sample.)

    Okay, don’t expect to hear a lot about spontaneous gauge symmetry breaking or giving mass to chiral fermions. But still:

    Have you ever heard about the Higgs Boson blues
    I’m goin’ down to Geneva baby, gonna teach it to you

    Apparently Cave’s lyrics throughout the album came about from “Googling curiosities, being entranced by exotic Wikipedia entries ‘whether they’re true or not’.”

  • Celebrating Darwin in Congress

    Sometimes the most trivial things can seem, in context, like brave stances. Here is ex-physicist and current New Jersey representative Rush Holt standing up in Congress to say nice things about Charles Darwin.

    In Support of Darwin Day

    Admittedly we’re not talking super-brave here — Princeton and surrounding townships aren’t exactly hotbeds of young-Earth creationism. But it’s sadly true that forthright statements in favor of evolution have become “controversial” among national politicians in this country. Happy to see someone do the right thing.

    (Aside to WordPress/YouTube wonks: there are two ways to embed a YouTube video on the blog, the new “iframe” way and the old way. It seems that the old way means that videos don’t show up on mobile devices, but the new way means that videos don’t show up in the RSS feed. Any wisdoms?)

  • Bookanalia

    The annual Los Angeles Times Festival of Books is always a great event, I highly recommend it to anyone in the area. This year’s edition is on April 20-21. I have a special honor, which really should be reserved for someone older and more distinguished but there you have it: I’ll be presenting the prize for science/technology book of the year. The real honor would be to win the prize, but I’ll take what I can get.

    There was no prospect of winning the prize, even though I did write a book, for the sensible reason that my lovely wife was serving on the panel of judges. That’s the bad news; the good news is that, as the spouse of a judge, you benefit from the constant stream of new books arriving on your doorstep. At least you benefit for a little while. Once the number of new science books from the year hits the triple digits, your response is closer to despair. There are a lot of good books out there. Great if you’re a reader, sobering if you’re an author. It’s kind of shocking that anyone found my humble little book at all.

    books

    One book I can’t help but mentioning, which I don’t think is eligible for the prize since it came out in 2013 rather than 2012 — The Theoretical Minimum: What You Need to Know to Start Doing Physics, by Leonard Susskind and George Hrabovsky.

    minimum Amidst the veritable deluge of science books, Susskind and Hrabovsky have done something simple but radical: they explain introductory physics for real, with all the equations, in a book that is not actually a textbook. This volume (everyone hopes there will be more) covers the principles of classical mechanics, with extraordinary concision but wonderful clarity. The fact that they are trying to explain major concepts rather than cover every detail means they can get much further than a textbook would; a hundred pages in you’re learning about the Principle of Least Action, and not long after that it’s on to Poisson Brackets. If you’re willing to roll up your sleeves and follow the authors along, this is a book from which you can learn a great deal.

    This book, needless to say, is not for everybody. But no book is for everybody; the question should be whether there are enough people in the appropriate niche that a book like this might be commercially viable. The answer is a resounding yes, apparently. Released just a few days ago, The Theoretical Minimum zoomed to #4 on the Amazon.com bestseller rankings, which is truly amazing. (The highest I ever got was around #100, but I’m not jealous!)

    I wonder if now we’ll see a slew of copycat books that throw conventional wisdom to the wind and try to boost sales by having equations on every page. Perhaps not, but readers would certainly benefit. While I am obviously a firm believer in explaining science to as wide an audience as possible, we shouldn’t lose sight of the fact that there is more than one audience out there. Many people might be interested in brushing up on some subject they last took seriously long ago in high school or college, or they might want to fulfill a deferred dream of studying something they regret not taking. The lesson shouldn’t be “equations are okay after all”; it’s “there’s an audience out there for challenging material if it’s presented in an engaging way.”

  • Help Populate the (Solar System’s) Underworld

    Remember Pluto, erstwhile member of the Sun’s retinue of planets? For an object that lacks the dynamical oomph to have cleared its neighborhood, this little dwarf planet sure has accrued an impressive number of satellites. Five of them have been discovered to date, but only three — Charon, Hydra, and Nix — have been given names. The others, laboring under the uninspiring temporary designations P4 and P5, have yet to undergo their official naming ceremonies. So this is your chance to weigh in!

    plutoMOONS

    Not officially, of course. The Nomenclature Working Groups of the International Astronomical Union are unlikely to hand the keys to the Solar System over to the unwashed masses, just so they can end up with celestial objects named “Gaga” and “The Situation.” But they will be consulting with the Hubble Space Telescope discovery team, led by Mark Showalter of the SETI institute. And Showalter has thrown the question open to public input (via 80beats). He is asking folks to vote on a variety of possible names, all drawn from underworld mythology. Your vote won’t be binding on anyone, but who knows? If Alecto storms to the lead, the IAU might just decide that a “hideous, snake-haired monster” is just what the Solar System needs.

  • Virtually Speaking Science

    In a couple of hours (6pm Pacific, 9pm Eastern) I’ll be joining Alan Boyle and Matt Strassler for a chat in Virtually Speaking Science. You can listen along on BlogTalkRadio, or the more adventurous among you can join us in Second Life. After consulting the Twittersphere (and our own inner dialogues), we’ve settled on the topic “Curious things that may or may not be true.” Should be fun.

    341150_10150340110403715_665228063_o

    This is what Jennifer and I would look like if First Life were more like Second. For one thing, apparently we’d be like nine feet tall.

  • Shaken v. Stirred

    Seth MacFarlane will probably do a good job hosting the Oscars, although he’s bound to rub some people the wrong way. Indeed he’s already started, with this little jibe at James Bond.

    Not that anyone really objects to poking fun at Bond, of course (especially during the Brosnan era). But the joke hinges on the idea that real martinis are always shaken, as Bond prefers, rather than stirred. Which is crazy talk. A prescriptive attitude toward food and drink is usually a bad idea — who am I to judge another person’s abiding love for deep-fried Twinkies? — but when it comes to martinis, it becomes time to lay the truth on folks. And the truth is: stirring is clearly preferable to shaking. (I used to be more agnostic on the question, but age has conferred wisdom.)

    The problem is that, while the superiority of stirring is widely accepted amongst the cognoscenti, many silly reasons are put forward therefor. The most common is that shaking “bruises” the gin, as if gin were the kneecaps of a spirited youngster. As far as I know, there is no evidence that this actually happens (corrections welcome). More plausibly, it is claimed that shaking dilutes the martini with water. This does make sense, but it’s not necessarily a bad thing; you would have to shake for a really long time to dilute the liquor noticeably, and a small amount of water can help release the flavors of a spirit. The real reason stirring is better is simple: shaking introduces tiny bubbles into the martini, giving you a cloudy drink. It’s a matter of looks, not of taste; the perfect transparency of an ideal martini can only be attained by stirring. (And any competent stirrer should have no trouble bringing the drink to the appropriate temperature. To wit, very cold indeed.)

    Of course, James Bond prefers a vodka martini, which every right-thinking person recognizes as an abomination. And he wears dive watches with formalwear. So why was anyone ever tempted to follow his lead on anything at all?