Photons and electromagnetic waves are hardly topics I choose to think about on a regular basis. Once in a while, I’ll be reminded that it takes 8 minutes for light from the sun to reach the earth, but that’s about it. My father would often say to me when I was a child, looking up to the stars, that I was seeing millions of years into the past. Technically, we see nothing but the past.
Light is both energy and mass at the same time. Light can fall; that’s why black holes are named that way—surrounding light gets sucked inside.
In 2005 it was predicted that there was an attractive and repulsive force component to light. They have since discovered the attractive force, but have only now discovered the repulsive force.
Physics and science in general have become a passion of mine a long time ago. I now find that as time goes by, I am ever more humbled by what we have found out about nature. I recently spoke about my appreciation for Richard Feynman. Some of his lectures on physics have been made available by audio on box sets, which could be purchased at over $150 US. The first time I heard the audio of the lectures at Caltech, I had never heard of the man. To say I was mesmerized would be an understatement. He was an expert at effectively communicating science and knew how to add humor to the material being taught. It helped me begin to gather what was being taught and appreciate its meaning.
I say all this, hoping I still have your attention. If I do, you may be interested in the other discovery I made today.
In the 1960’s, a young man by the name of Bill Gates stumbled on those same lectures and loved them as much as I. Since then, he has purchased the rights to the video of his lectures and has posted them online for free, in what is called Project Tuva. The catch is that you have to download the video player required to see all that is to be seen on the website of Microsoft Research, Silverlight. It is hardly an inconvenience, as it is a 10 second download, and a quicker install, and very much worth your time, if you are interested.
Now you may watch the lectures, in excellent quality, with great extras that are still unobtrusive. I’m not in marketing, but if there was any trick I knew to get people to at least watch the first of the lectures, then I would do it.
If I got a single person to watch even a single lecture by having posted this, it would be worth far more than my time and effort. It just may lead to someone starting think about light a little bit more.
You know what, I think I will give them a listen :)
Posted by Andre Gallant on July 15th, 2009.
Kudos Andrew for some non-astronomy/space Science reporting!
As a scientist though, I feel the need to pop a few bubbles in a few things concerning this blog though.
I believe saying that light can fall is a misrepresentation of what is the physical reality of the effect, “falling” being an erroneous word for this situation. I believe falling refers to the attraction of an “object” (in the most general sense) towards a body of great mass due to classical gravitational attraction that is, the attractive gravitational force. Force being a key word here, if the total force is non zero, a net acceleration is present and we see this as “falling” in the everyday sense (even though you don’t necessarily need acceleration to be falling, in empty space, you do). What general relativity predicted (correctly) was that mass curves space, and this is the source of “gravitational attraction” in the classical sense. But the curvature of space can (and does!) change the trajectory of light, but there is no net attraction (in a classical sense, as with falling) between light and the body. So I would rather say that a the curvature created by a body that has some non-zero mass changes the direction of propagation of light, light doesn’t really fall, as no (fundamental) forces act on light). Anywhom, that’s about as much as I know about this subject and it’s my personal position on that subject. Might just be a play on words.
That’s one.
Posted by Mathieu on July 16th, 2009.
Now, concerning that “attractive/repulsive” light article.
Unfortunately for scientists, the only time journalists report on science discoveries is when it has an attractive (no punch intented) catch phrase to go with it. If you saw the reporting, they do put the words attractive and repulsive in quotation marks. After reading the article that it refers to, I found out that it’s actually very basic physics (in a relative sense), and (thank god), there is currently only 4 fundamental forces in the known universe.
What that article refers to is a mechanical attractive and repulsive force between two waveguides (which are like fiber optics cables, but way smaller) due to induced dipoles in the waveguides created by the light. Let me quote a section of that article :
“Considering two proximate dielectric single-mode waveguides separated by gap g as depicted in Fig. 1a, propagating lightwaves in each waveguide interact through the excitation of dipole oscillations. The optically excited dipoles in one waveguide interact with the evanescent field of the other waveguide and generate a force that is dependent on the separation of the waveguides and the relative phase of the optical modes. When the modes are in phase (psi = 0), the optical force is always attractive; when the modes are out of phase (psi = Pi), the resulting force is repulsive when the separation is larger than a critical value gc , as shown in Fig. 1b.”
So what happens is, when the light is in phase, at every point on both waveguides (which are dielectrics), the electric field of the light creates electric dipoles (i.e. a magnet is a magnetic dipole, it has a “north” and “south” pole). If the light is in phase, the dipoles in both waveguides will be pointing in the same direction, and like magnets, this will cause a mechanical attraction ( because the “south pole” of one waveguide will be closest to the “north pole” of the other. If the light is out of phase, the “south (or north) pole” of one waveguide will be closest to the “south (or north) pole” of the other, and they will repel (as is the case in magnets). There are other little subtleties (as with the Cassimir effect), but that’s the basics of it. One photon cannot (as far as I and most of the scientific community knows) be attracted or repulsed by another photon in empty space (what exactly is a photon in a material is still debated).
Anywhom, thoses were my two cents.
Posted by Mathieu on July 16th, 2009.
I wish you were here to help me wash the walls from my mind being blown away. You make good points and they have been duly noted.
I wish people would call me out more often, how am I supposed to learn otherwise?
Thanks for the comments, Matt!
Posted by Andrew on July 16th, 2009.
Just to add a correction on top of Mathieu’s clarifications. Light has no mass. Energy yes, mass no.
Posted by Gaëtan on July 21st, 2009.