标签: LIGHT

My chum Jay Dowling manages to find an incredible amount of interesting "stuff" on the Internet. Every day, he sends me a cornucopia of links to general science, physics, astronomy, technology, engineering, etc. sites -- whatever takes his fancy at the time (speaking of time, I don’t know how he finds enough of it). And the thing that appears to have caught Jay's fancy today is a bunch of interesting offerings on Kickstarter.   We start with a drop-dead-gorgeous cathode ray tube (CRT)-based oscilloscope clock that uses a purely analog signal to generate the circles, arcs, and lines that create the characters.     With 17 days to go at the time of this writing, this project has already reached 4X the pledges required to achieve its incredibly modest $1,000 goal. You can get a build-it-yourself kit version for $145; this includes the circuit board and components, but excludes the CRT and enclosure. Alternatively, you can pay more for a fully-assembled model in a plexiglass enclosure. I'm a bit tight on funds at the moment, but I would love to have one of these little beauties here in my office.   Next up, we have a project that would have Sheldon, Leonard, Howard, and Raj on The Big Bang Theory squealing with delight -- a set of highly detailed modular saber parts that let anyone build a beautiful custom light saber with associated electronics.     This is actually a lot tastier than you might imagine. If you watch the Kickstarter video (and who amongst our number could resist), you'll see that this looks like an incredibly versatile system that supports millions of different configurations (is it just me, or is the presenter in the video a doppelganger for Wil Wheaton?). Also, they plan on offering monthly expansion packs, which could keep me busy for years to come. I'm obviously not the only one who loves this stuff because they've achieved more than 8X their original $100,000 goal!   Who amongst us doesn’t drool with desire at the thought of having access to a Star Trek-style holodeck? Well, now we can -- or, at least, our Barbie and Ken dolls can -- with the Holus Interactive Holographic Tabletop Display .     This really does look to be rather spectacular, and I love its creators' sense of humor (the "Holo, World!" at the end made me laugh out loud). I can think of so many things I could do with something like this. The gaming and educational aspects of this device are staggering, and I'm sure that this is only a taste of things to come.   Last, but certainly not least, for this column, have you ever worried about the "shelf-life" of your precious data? When CDs and DVDs first came out, I optimistically thought they would last for a long, long time, but every day I hear talk of doom-and-gloom with respect to the little scamps failing (sad face). If you are concerned about your data, this final Fahrenheit 2451 Kickstarter will be of interest to you because it offers the ability to preserve your most precious memories for thousands of years using a storage medium that resists fire, water, and time.     I'm reminded of the spinning disks ("books") in the original 1960 movie version of The Time Machine by H.G. Wells. On the one hand, the Sapphire Disks featured in this Kickstarter are limited as to the amount of data they can store. On the other hand, it might be nice to preserve photographs of yours truly for the edification and delight of generations to come.   So, out of the four Kickstarters presented above, which one most captures your interest?

Max Maxfield recently offered this challenge: "I still cannot wrap my brain around how mirrors work -- from simple things like why is the angle of incidence equal to the angle of reflection, all the way up to how the photons 'bounce' off the atoms forming the mirror without being scattered to the four winds, as it were."   He's not looking for an easy answer using basic optics or even Maxwell's equations. His question is based on Richard P. Feynman's 1990 book QED: The Strange Theory of Light and Matter (where QED stands for Quantum Electrodynamics). I thought that I would knock out a quick response with a few examples, but this has turned into one of the harder questions I have attempted. Getting to a reasonable answer has made me reset my own understanding.   In fairness to anyone who hasn't read the book, here is a highly condensed summary of how Feynman explains reflection. The idea is to sum components of reflection over all conceivable paths. We want to prove that the angle of incidence is equal to the angle of reflection (AOI=AOR), but we can't start with that assumption. Instead, we have to consider all paths. Feynman does this considering the experiment below -- looking at the various possible paths from the source reflecting off each part of the mirror and ending at the detector.   We sum contributions at the detector by considering each contribution as an amplitude with an associated phase (shown by the arrows below the mirror). We assume the only difference in phase between the paths is due to the lengths of the paths (more on this later), which results in phase shifts between contributions at the detector. The phase shift changes slowly around the center line (at which point AOI=AOR), where the path length varies slowly. The path length (and therefore the phase) changes faster as we move away from the center. When we add these contributions together, they add constructively near the center but increasingly cancel through phase mismatch as we move away from that center. As a result, we obtain a peak around AOI=AOR and very little intensity as we move away from the peak on either side.   All of this is understandable, but what does it have to do with QED? In researching this blog, I first thought Feynman was using creative license to keep his explanation simple. Then I decided he was bending the truth just a bit. Finally, I realized his explanation -- apart from minor details -- is completely accurate and is the most intuitive explanation of QED I can imagine. Thus, the best I can hope for is to add some color to that explanation.   Let's start by saying that we believe photons are real, because we can reduce light intensity until we see single flashes at the detector, and the flashes always have the same intensity for a given frequency of light. So light is quantized, but whatever behavior we invent for this new model, it must still correspond at a macro scale with everything we expect about light behaving as a wave. We also need to double-check what has to be new and what is really just unexpected classical behavior.   An apparent problem emerges in imagining the experiment being performed using a laser as illustrated below.     The light isn't going all over the place, so what gives? In fact, this experiment is a little deceptive. If we look at the mirror from behind the laser, we can see a light spot, which means that light is reflected back toward the laser. This means that, even at the macro level and even for a laser, light is scattered in all directions at reflection. On this point, Feynman's explanation is completely classical, though not the way we normally think about light. Scattering in this way also corresponds with Huygens' principle (1678) that a light wavefront advances by treating each point on the wavefront as a new wavefront, which expands in all directions.   Given this, summing up the paths accounting for phase is also completely classical. That's what you do with waves. There are just two problems. The first is how all this applies to photon "particles"; the second concerns the assumption about phase differences. On the first point, my reading shows two lines of thinking. The most heavily represented is what I'll call the "mystery and imagination" track. Quantum behavior is weird, and we can't really understand what is happening, but the math works. In the meantime, we wrestle with how to imagine a photon particle behaving like a wave. I think most of us are secretly attracted to this track, because it gives us exotic behaviors as fuel for philosophizing about exotic possible causes. Perhaps photons are extended wave packets and behave as waves. Perhaps the universe splits into multiple universes at each event such as reflection, and so on. I'll call the other track "mostly classical." As far as I can tell, it is represented solely by Feynman and a Geneva University theoretician who applied the Feynman path approach to detailed calculations of reflection, refraction, diffraction, and other phenomena in 2005. This paper is quite technical but still worth a read. Though all other authors acknowledge Feynman's genius, it seems that few if any actually use his methods in QED calculations, because they are typically more complex to apply than Schrodinger-based approaches .   The Geneva paper seems to be the first time anyone has documented detailed consequences of the Feynman model. (Feynman didn't record his own calculations for this example.) But before I go there, let's look quickly at the other problem: that phase assumption. Path length is certainly a factor in phase at detection, but what about the phase when a photon starts on one of these paths? If the source is a laser, you can assume phases are equal at creation, but this is not the case for a regular light source. If you assume that amplitude summing (interference) at the detector is between different photons travelling on different paths, path differences still affect the result, but lack of correlation between source phases will lead to random and time-varying (noisy) interference at the detector, which is not what we see.   Back to what the Geneva paper has to say: - Feynman's explanation is more fundamental and more powerful than the Schrodinger approach. Schrodinger can be derived from Feynman, but not vice versa , because Feynman represents correlation between space-time events (between paths), but Schrodinger cannot. - In detailed calculations using the Feynman method applied to photons, all classical behaviors of light as waves emerge as expected. Reflection, in particular, follows Feynman's example. - Photons propagate over macroscopic distances in a completely classical manner. (Heisenberg applies to the creation and detection of a photon and to scattering events, but not to simple propagation.) But we must consider all possible paths in the analysis. - Paths add in the same way that waves add. We add amplitudes with phases to obtain interference at the point of detection. - This brings us to the creation phase issue and the only conceptually difficult requirement of the Feynman method. Different photons have random relative phases at creation, but any given photon is trivially in phase with itself when created. Therefore, to obtain the results we see, interference cannot be between different photons travelling different paths. Each photon individually must travel along all possible paths and (indelicately) interfere only with itself at detection. This is the only way we can avoid that noisy interference between uncorrelated photons, and it is why experiments testing one photon at a time give the same results as for multiple photons at the same time.   I should caution that the 2005 paper is an interpretation, and that it makes predictions of new behaviors that have not yet been tested. But absent counterexamples, I find this interpretation very appealing. It is in complete agreement with Feynman's explanation, and it conserves all classical and intuitive understanding of light behavior based on photons, with just one exception. That exception is a doozy: A photon must travel simultaneously along all possible paths to the point it is detected and resolve itself through self-interference at detection. If we suspend disbelief on this one point, everything else is completely intuitive.   So what do we make of this one difficult point? Travelling simultaneously along all possible paths is definitely neither classical nor intuitive. Perhaps we see a particle travelling along all paths as a projection from a simpler path in something more fundamental than space-time. There are hints of this in a recent article, " A jewel at the heart of quantum physics ," which suggests that the space-time so familiar to us may not be the most basic representation of reality. Whether we will appreciate this as an improvement in intuitive understanding is up for debate.   Bernard Murphy, PhD Chief Technology Officer Atrenta Inc.

Here's another post, in which we pause for a moment to take a deep breath (hold it... hold it... now exhale), slow down, relax, and start winding down in preparation for the weekend. As part of this exercise, I've gathered a few choice diversions for your delectation, delight, pondering, and rumination. This week's humble offerings are as follows: No. 1: Do you think you are having a bad day? Is it as bad as sending eye-watering amounts of electricity surging through your tongue? Sometimes, no matter how horrifying a video is, you just cannot look away. ( Click here to discover more.) No. 2: Unfortunately, Mehdi Sadaghdar—the star of the previous video—just doesn't know when to stop. His videos on how to change an electric light bulb ( click here ) and how to build an electric guitar ( click here ) cannot fail to make you cringe and wince with empathetic pain. No. 3: I don't know about you, but my eyes are still watering from the previous videos. Let's change pace and look at something that makes one gasp in wonder—a 240-year-old clockwork automaton that can write. ( Click here to discover more.) No. 4: Now I feel in the mood for the video equivalent of comfort food. One of my all-time favourite videos is the trick the Improv Everywhere group played in Grand Central Station. Even if you've seen this before, it's always worth another look. ( Click here to discover more.) No. 5: Speaking of improv, another of my all-time favourite videos is the one where over 200 dancers perform "Do, Re, Mi," from The Sound of Music in a Belgian train station. Once again, even if you've already seen this, you need to watch it again, because it's simply impossible to view this all the way through without ending up with a great big beaming smile on your face. ( Click here to discover more.) As usual, if you know of any interesting sites you'd care to share, please comment below.  

Here's another column in which we pause for a moment to take a deep breath (hold it... hold it... now exhale), slow down, relax, and start winding down in preparation for the weekend. As part of this exercise, I've gathered a few choice diversions for your delectation, delight, pondering, and rumination. This week's humble offerings are as follows: No. 1: Let's start with something related to the use of light. My chum with the screen name Antedeluvian (yes, he knows it's the wrong spelling) sent me a link to the most amazing video showing projection mapping onto flat surfaces. The illusion is incredible. You have to keep on reminding yourself that these are just simple flat surfaces you are watching. ( Click here to discover more.) No. 2: Speaking of light and the manipulation thereof, my friend Jay sent me a link to a rather interesting article about a building that has cameras pointing in all directions. The images from the cameras on each side are processed and presented on display panels on the complementary faces. The end result is for the building to appear to be invisible. Hang on, maybe there isn't a building there at all? ( Click here to discover more.) No. 3: Still on the subject of light, I'm sure we all know that photons are massless elementary particles that don't interact with each other and that act as the force carrier for the electromagnetic force. Wait just a minute—did I say massless and don't interact with each other ? Well, it seems that scientists have been able to coerce photons to interact with each other to the extent that they form "photonic molecules" that appear to have mass. I'm still trying to wrap my poor befuddled brain around this one. ( Click here to discover more.) No. 4: I recently wrote a blog about the Fitbit Zip, which counts how many steps you take throughout the day. In a response to this blog, a reader basically called me an idiot (well, I took it that way). Happily, I refuted Truthfinder's assertion as to my mental capabilities in this follow-up blog . I must admit that I was feeling a tad perky when I finished this blog. It reminded me of the French Taunting scene in Monty Python and the Holy Grail, when the Frenchman on the castle ramparts shouts, "Now go away or I shall taunt you a second time!" ( Click here to see this scene.) No. 5: Of course, this immediately reminded me of two classic videos in which the dialogue from Monty Python and the Holy Grail is dubbed over a collage of scenes from the original Star Trek on its "five year mission behind the beyond, behind which no man has gone behind, beyond, before!" LOL. ( Click here and click here to see these compilations.) No. 6: Last but not least for this week, I just saw a rather funny video of Bill Bailey performing the Hokey Cokey in the style of Kraftwerk ( Click here to see this video.) As usual, if you know of any interesting sites you'd care to share, please share them in the comments section.  

My inventor friend Brian LaGrave just directed me to a really interesting project called GravityLight . This is hosted on indiegogo.com , which is similar to Kickstarter.com , the main difference (as far as I can see) being that the folks at indiegogo.com don't take a cut out of the project's funds. According to the project's page, there are currently over 1.5 billion people in the World who have no reliable access to mains electricity; instead, they rely on biomass fuels (mostly kerosene) for lighting once the sun goes down.   As you will discover from the project page, burning fuels like kerosene has tremendous negative effects, including causing lung cancer, eye infections, cataracts, and severe burns from overturned kerosene lamps. The burning of Kerosene for lighting also produces 244 million tonnes of Carbon Dioxide annually. Now, if you were asked to come up with a solution, your knee-jerk reaction (like mine) might be something along the lines of using solar power to charge a battery in the day, and to then use the battery to power a LED-based light in the evening. However, one problem with this solution is that the batteries used in this sort of thing degrade really quickly. Have you ever purchased any of those solar-powered LED lights for your garden pathway? If you have, you'll know what I mean. They look great for the first couple of weeks—then they start to dim and fail—and they end up being a total waste of money. The solution proposed by this project is to use gravity to power the light. The GravityLight is delivered in a bag, which you can subsequently fill with rocks or sand. It then takes only a couple of seconds to lift the bag and hang it on the GravityLight – this mass is used to generate the electricity that powers the light.   The project has already far exceeded its original funding goal and – at the time of this writing – there are still five days left to go. However, the fact that the project has reached its original goal doesn't mean we shouldn't support this effort. Any extra funds can go into research and development to further reduce the cost of the finished product. One can pledge as little as $10. However, for a pledge of $50 you will get your own GravityLight to play with. Having been without power for more than a week myself when tornadoes devastated our area a couple of years ago, I can easily imagine how useful this would be. I know that there are always a lot of demands on everyone's money, but I really do think that this sounds like a good cause. If nothing else, please take the time to visit the GravityLight Project Page , watch the video, read about what they are trying to do, and then maybe you can help to spread the word via your accounts on Facebook, Twirtter, LinkedIn, and so forth.