Science-y Stuff

Bullet time for photons

It takes only a billionth of a second (nanosecond), if you can even imagine, for light to travel and scatter through an empty one-liter bottle. However, it took about the good part of an hour to collect all of the data that goes into the final "ultra-fast" video below. Ramesh Raskar, Associate Professor at MIT's Media Lab points out that,

"photons travel at around a million times faster than bullets" (Raskar 2011).

But, because of the high rate of speed that this special camera can operate at, we can most gratefully watch photons moving through space as they travel the length of a one-liter bottle! A laser pulse emits photons and they enter the camera through a slit opening, getting converted into electrons and then are bounced off in another direction by an electric field. It is a rather fascinating thing to note that as the photons bounce around on the inside of objects, their wave-like properties undergo some contrast of interference. The really cool subtle part that might go unnoticed is, that difference between waves can be quantified into visibility by using what is called "incoherent detection methods", or incoherent wave detection. We can see those particles inside objects, like those used for medical imaging. Think of an ultrasound with light. This type of ultra-fast imaging allows us to study how photons travel through the world more precisely. To see a cool experiment done by MIT Media Lab researchers showing a wave traveling at the speed of light, check out the following YouTube video. If you are interested, you can also read more about this experiment directly from the article by Larry Hardesty on the MIT News website.