Posted tagged ‘Speed of Light’

Somewhere, Doc Is Smiling

December 13, 2011

To the annals of the unbelievably cool, add this:  a camera that can image one trillion frames per second.  That’s fast enough to make a movie of light in motion.

Let me say that again:  this apparatus is sufficiently precise and capable of such extreme slow motion photography that it can make a moving images of light in transit:

My favorite part of the movie itself (as opposed to the ridiculously cool tech and the gorgeous underlying science) is the choice of target, amidst all that ferociously exact equipment.  Yup.  Coke does rule our world.

From the MIT press release linked above, here’s a basic explanation of what’s going on:

The system relies on a recent technology called a streak camera, deployed in a totally unexpected way. The aperture of the streak camera is a narrow slit. Particles of light — photons — enter the camera through the slit and pass through an electric field that deflects them in a direction perpendicular to the slit. Because the electric field is changing very rapidly, it deflects late-arriving photons more than it does early-arriving ones.

The image produced by the camera is thus two-dimensional, but only one of the dimensions — the one corresponding to the direction of the slit — is spatial. The other dimension, corresponding to the degree of deflection, is time. The image thus represents the time of arrival of photons passing through a one-dimensional slice of space…

…But it’s a serious drawback in a video camera. To produce their super-slow-mo videos, Velten, Media Lab Associate Professor Ramesh Raskar and Moungi Bawendi, the Lester Wolfe Professor of Chemistry, must perform the same experiment — such as passing a light pulse through a bottle — over and over, continually repositioning the streak camera to gradually build up a two-dimensional image. Synchronizing the camera and the laser that generates the pulse, so that the timing of every exposure is the same, requires a battery of sophisticated optical equipment and exquisite mechanical control. It takes only a nanosecond — a billionth of a second — for light to scatter through a bottle, but it takes about an hour to collect all the data necessary for the final video. For that reason, Raskar calls the new system “the world’s slowest fastest camera.”

Bonus  trillion fps eye-candy videos here.

And yup, somewhere, Doc Edgerton is one happy camper.



“I knew I was going to take the wrong train….”

September 27, 2011

…”so I left early.”

Thus sayeth that noted neutrino expert Yogi Berra, Bb.D.

Because humankind cannot live by politics alone, here’s a bit of an off-angle reaction to the biggest news in physics since Big Al (as I thought of him through a decade of film-and-book making/writing on the good Dr. Einstein) looked out of his window and wondered what would happen if the roofer he was watching slipped and fell.  Before the poor fellow hit the pavement, of course.

That would be the announcement last Friday that an Italian team of physicists sent a beam of neutrinos from the CERN high energy physics facilty on the Franco-Swiss border through the Alps to a detector in the Italian national physics lab in Gran Sasso, a journey of almost 460 miles (~730 km).  The newsworthy bit was that the experimenters measured the speed with which some 16,000 or so neutrinos covered that distance, and found that it very slightly exceeded the speed of light, “c”  — the canonical limit within Einstein’s special theory of relativity that nothing may exceed.*

The effect detected by the experiment, known as OPERA, was small:  1 part in about 40,000 greater than c.  But any breaking of the light barrier is a huge deal.  If the result stands up, we’re in for a fun ride.  There will be lots of new physics to be found.  Good initial reactions can be found all over the physics blogosphere — try this, or this to get started.

For my part, as someone who’s been observing physics from the outside since I first grew fascinated with Einstein’s work in the late 1980s, I’m reminded a bit of the last decade of the nineteenth century.  In 1894 the (to-be) Nobel laureate A. A. Michelson famously told an audience at the University of Chicago that

The more important fundamental laws and facts of physical science have all been discovered, and these are now so firmly established that the possibility of their ever being supplanted in consequence of new discoveries is exceedingly remote.

Timing is everything:  in  1895, just one year after Michelson gave his speech Wilhelm Röntgen discovered X-rays, and it was off to the races into the 20th century revolutions in physics.

Recently, folks may have been forgiven for feeling at least a little bit of what Michelson did, as by the 1990s, every major relevant experiment over the previous couple of decades had confirmed the details of the Standard Model of particle physics.

That theory is not complete.   It does not encompass General Relativity, Einstein’s theory of gravity, for example, and it has a just the whiff of an ad hoc quality to it.  It has troubled a fair number of observers that the Standard Model comes with a number of dials (parameters) that have to be set by hand, as it were, to make all the sums come out right.

For all that, the theory proved for decades to be astonishingly powerful:  those twenty or so parameters have paid for themselves with hundreds — thousands, really — successful predictions.  But the frustrating bit has been that for many, many years, very clever people have tried and failed  to find something that the Model got wrong that would lead to a more comprehensive picture of reality.  Physics, if not confined to what Michelson quoted a colleague as saying — measurements of the sixth decimal place — seemed to some to be grasping for something to liven up the joint again.†

And then, of course, we got dark matter.  Dark matter has been hanging around for a while — roughly forty years, ever since Vera Rubin first measured motions in distant galaxies that implied the presence of much more mass than could be accounted for by the available luminescent matter —  stars.  We’re still waiting for a definitive understanding of what all that mass is made of.

More recently, dark energy (or a non-zero cosmological constant, if you prefer) appeared on the scene — a yet more challenging observation. Dark energy was first detected by a pair of teams measuring the light from a particular type of supernova. Reporting in 1998 and 1999, they confirmed that the universe is expanding at an accelerating pace — and putting that information into the framework of Big Bang cosmology generated an astonishing number:  about three quarters of the stuff in the universe — the sum of mass and energy present within the cosmos– comes i the form of whatever this dark energy turns out to be.


In other words:  we live in interesting times.  And thankfully, some such circumstances — those outside of politics — are actually interesting as in fun, rather than applying the usual torque that line evokes.

There are huge, significant new problems out there, with at least some real prospect of observational discoveries that could lead to major shifts in our understanding of the cosmos we call home.  This neutrino result would lead to another such shift — if it holds up — and it would thus stand both as an example of virtuoso measurement and as a great big sloppy kiss of an invitation to theorists who will have to rethink special relativity — for a century one of the fundamental principals of existence, a fact of life in the universe so fundamental that any physical result had to conform to it or fail.

To be sure, there’s a good way to go yet before we plunk the leaders of the OPERA team into sedan chairs and bear them off in triumph to Stockholm.  As of four or five days into the era of superluminal neutrinos, no one has found an obvious killing flaw in the work, but it’s a complicated experiment, and confirmation would be so consequential that every physicist I’ve talked to or read has cautioned me not to bet the rent money on it.

(Thanks xkcd)

But even as we wait — probably not too long, as these things go — for another experimental team to reproduce or demolish this initial finding, we can enjoy the one certain decay product of a collision between theoretical physics and the Twitterverse.

That would be neutrino jokes (perhaps an acquired taste).  Hence these, gathered by the L.A. Times.  (h/t @JenLucPiquant).

My favorite (also plumped by regular commenter SiubhanDuinne in a previous thread):

We don’t allow faster than light neutrinos in here, said the bartender. A neutrino walks into a bar.

Yeah.  An acquired taste.

*There is a history of theoretical musings about faster-than-light particles that predates this experiment, but such particles, dubbed tachyons, are understood never to slow to the speed of light.  In this conception, the speed of light is a limit that can be approached from either side — below or above — but never crossed.  So, for those of us in the slow lane, the  cartoon description of the speed of light as a speed limit has been close enough to right to do the job.  We do live in interesting times.

†The “sixth decimal point” statement has earned Michelson a lot of ridicule over the years.  Certainly, it was bad luck indeed to provide such a quotable quote just one year before the gaudy show-stopper of X-rays.  But on reading this paper (pdf) on Michelson’s thinking about measurement, I’m reminded he’s at least partly the victim of a bad rap.  In his 1894 speech he expressly pointed out that two problems pressing on physicists at the time were the “constitution of matter and the ether and the true mechanism of light” — in other words, the questions that lead directly to both relativity and the quantum theory.  (Thanks to Ed Bertschinger for discussing this point with me; he is not to blame for any use I made of his knowledge.)

And though Michelson was clearly wrong in the import of his statement — the “nothing left but the details” suggestion — still, as a master of meticulous experimental technique, he can be credited with a deep, and clearly correct idea:  high precision measurement was and remains the probe through which new phenomena could be discovered.  The neutrino experiment that has prompted all this hullabaloo may indeed be the latest example of the power of experimental acuity to evoke genuinely new insights.

Image:  Joseph Wright of Derby, The Orrery, c. 1766.

Vincent van Gogh, Starry Night over the Rhone, 1888.  (Predictable, I know — but a variation on the usual, and a gorgeous painting).