Science In Real Life

How are you reading this essay? Since the Science In Real Life audiobook hasn’t hit stores yet, you must be absorbing the information through your eyes. That means you’re using light, until such time as the radiation from the hole in the ozone layer gives us all psychic powers. Way back in the Electricity and Magnetism essay, I explained how a light wave is a combined oscillation of electric and magnetic fields. I’m going to take that as a jumping point and start going into some of the basic properties of light as they pertain to how we as organic beings interact with it.

The first thing to note is that the light we can see with our eyes is just a very small slice of the electromagnetic radiation cake. Imagine the bakery screws up your order and sends you an infinitely long line of cake. Off to your left, the low-energy cake represents radio waves, microwaves, and infrared radiation. Right in front of you is a rainbow of visible cake. Then, as you head right, you get ultraviolet, x-rays, and gamma ray cake. Tasty!

Sometimes you will see the electromagnetic spectrum labeled with the various frequencies, other times with the corresponding wavelengths. We can do this because frequency and wavelength are related. Check out this graph here.

( Image credit )

Since a wave is a repeating cycle, we define the wavelength (frequently denoted by the Greek letter λ) as the physical length of one cycle. The number of cycles that pass per unit of time is the frequency, f. How can we relate the two? Imagine instead of abstract cycles, we have bicycles. You’re watching the Tour de France and all of the bikes are going past you single file, in a wheel-to-wheel line. You know that all of the bicycles are 2 meters in length and you see 6 of them go by every second. How fast are they going? In one second, six two-meter bikes go by, for a total distance of 12 meters. Two meters times (6 bikes/1 second) gives 12 meters per second. Quantitatively, frequency and wavelength are related by the speed of the wave: fλ = v.

Much is made of the importance of the speed of light. It is often said that nothing can go faster than the speed of light. Taken at face value, this statement is demonstrably false, since the speed of light is greatly reduced inside matter, and can even be reduced to zero. We have to add the following qualifications: no inertial object (that is, something made of matter like you are) can accelerate to the speed of light in a vacuum or beyond. That “in a vacuum” is crucial – only when light is traveling per nihilo does it attain that magnificent maximum speed.

(Advanced note: That other bit about acceleration is in there because it is acceleration’s peculiar bending of spacetime that runs up against the conservation of energy. If you can figure out a way to propel something at faster than light speed without accelerating it, you will be able to buy and sell Bill Gates six times before breakfast.)

So why is there a maximum speed, and why is it associated with light? That maximum speed is what it is for reasons having nothing to do with the character and behavior of light rays – it is a fundamental limit on the speed of any kind information through space and time (except rumors). Things with rest mass, like your little sister, are restricted to using most of their energy-as-mass to maintain corporeality. A light ray, on the other hand, can blow its whole load of energy-as-energy on extra unleaded liquid Schwartz to blast across the cosmos at 300,000 km per second.

Lastly, I want to briefly address the fundamental nature of light from a quantum mechanics perspective, as specifically pertains to the quantum buzzphrase “wave/particle duality”. Physicists debated for centuries the question “Is light a wave or a particle?” So you can imagine the collective surprise when the answer turned out to be Yes. Depending on what experiment you perform, light rays can be shown to have, undeniably, irrevocably, and incontrovertibly, properties belonging to both wave and particle definitions. “Okay, fine,” you say, “so what is it really?” The answer is it is something else entirely, some entity that can exhibit both behaviors, much like the man who is both Bruce Wayne and Batman. “Okay fine,” you say, “but what IS that, really?” Well, we don’t know. So far, scientists have been content to call it ‘light’, but the search for a more lucid understanding continues.