![]() What was the phenomenon that Planck was working on? And what was his tweak? And what does this have to do with light being a particle? As luck would have it, this small tweak so fundamentally altered the way that scientists view the world that it almost single-handedly ushered in the modern era of physics. However, by making a small tweak to the mathematics describing the phenomenon, a German physicist named Max Planck arrived at a model that correctly described its behavior. So what happened in 1900? It turns out that there was one perfectly ordinary, everyday phenomenon that classical physics was at an utter loss to explain. Einstein’s papers on special relativity weren’t published until 1905, though. “Modern” physics refers to developments after 1900, and includes Einstein’s relativity as well as quantum mechanics. “Classical” physics is the era starting with the discoveries of Newton and Galileo in the 17th century, running all the way up through Maxwell’s work on light and electromagnetism, and ending in 1900. Scientists nowadays divide the history of physics into two eras. Lord Kelvin is alleged to have exclaimed, “There is nothing new to be discovered in physics now,” perhaps vying to get his picture in the dictionary next to the word “hubris.” But it is remarkable that, even today, Maxwell’s equations explain almost everything that there is to observe about light and its interactions with matter.Īlmost: the most exciting word in physics. Combined with the brand-new laws of thermodynamics and a few reformulations of the mechanical laws first introduced by Newton, it looked as if physics were nearing its endgame. Maxwell’s theory also happened to be one of the most successful theories up to that point in history. ![]() ![]() They also predicted that the energy of a beam of light is only determined by its brightness, and is in no way related to its color. Maxwell’s equations, as they’re now imaginatively called, combined electricity and magnetism and showed that light was just made up of waves of both. In fact, a Scottish physicist named James Clerk Maxwell basically codified this intuition into physical law in the mid-1800s, when he formulated his Victorian-era Theory of Everything in a handful of equations. And it’s true brighter lights require more juice: just try powering the Bat signal with a few AAA batteries. Basically, the brighter the light, the more energy it has. Naturally, people thought the main factor was the light’s intensity. Until the 20th century, no one really thought the color of the light had anything at all to do with its energy. Okay, so I kind of fibbed when I said before that it’s a long-established fact that shorter wavelengths of light contain more energy. And you’re probably asking right now: “What does any of this have to do with light being a particle? And, come to think of it, how do we know that shorter wavelengths of light are more energetic, anyway?” I would tell you to stop asking questions faster than I can answer them, but in this case, the answers to the two questions are related in a pretty unexpected way. ![]() Actually, it’s a long-established fact that the shorter the wavelength of light, the more energy the light contains. In it, we mentioned briefly that blue light and red light have different energies, and that blue light is more energetic than red light. In a previous HDWKI, we discussed the Doppler effect as a way to find planets orbiting other stars. I guess I’ll have to try to distract you by changing topics completely. It can spread out, interfere with itself, bend around objects, remember?” Yes, I remember. Most of your arguments in the last post about light had to do with showing how light can’t be a particle. “But Keith,” you say, “I thought you just said that light is a wave. But just in case you chose to spend your teenage years enjoying sunlight and people that exist in real life, a photon is the smallest possible particle of light that you can have. If you’re reading this blog, you probably have a passing familiarity with the word “photon,” even if it’s only in reference to the torpedoes that arm most of the Federation ships on Star Trek. ![]()
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