Einstein won his Nobel prize for explaining the photoelectric effect, one of several strange observations that led to the quantum mechanics revolution. Einstein himself was uncomfortable with the idea that light (electromagnetic radiation) might not be a wave but a particle. The physics luminaries of the day also thought that this strange idea seemed far-fetched, although it was difficult to deny how elegantly it solved the problem. Planck, who first introduced quanta, tried to ignore the implications. Bohr, who made powerful use of quanta to explain the behavior of electrons in atoms, was so uncomfortable with the idea of light being quantum in nature that he proposed breaking the law of conservation of energy.
These stories and more are lively narrated in Manjit Kumar’s Quantum, subtitled “Einstein, Bohr, and the great debate about the nature of reality”. I’m about 40% through the book. Most of the story is not new to me. Over the years, I’ve read much of the history of quantum mechanics and how we have come to our present description of the atom – the fundamental unit of chemistry. Bohr is central to that story, but many others contributed. Reading Kumar’s book reminded me of something I had forgotten: the key role of Arthur Compton’s X-ray scattering experiments in establishing the light-quanta hypothesis into bedrock theory.
Briefly, Compton fired X-rays (short wavelength EM radiation) at various elements and then measured what came out as these X-rays were scattered. It’s somewhat like the famous Rutherford experiment we teach students in introductory chemistry where alpha-particles were fired at a thin layer of gold. Compton discovered that the “secondary X-rays” that resulted from the scattering were at longer wavelengths (and thus lower frequency) than what he started with. Essentially, when EM radiation interacts with matter, some of its energy can be transferred to other forms, and resulting “scattered” radiation has lost that same amount. Energy remains conserved. One photon comes in. A different one comes out, red-shifted in color.
This made me think of magic, line-of-sight, and Harry Potter’s second Triwizard task. I had previously proposed that magic is mediated by electromagnetic radiation. That’s why Hogwarts can’t abide the use of electricity or electronic devices. Too much interference! But if you cast a spell, thereby directing ‘magical energy’ in a particular direction, there might still be interference as it interacts with matter. Since we live in “thin” air, EM radiation easily passes through. It can even “bounce” off solid objects. But could it go awry if there is some “scattering” involved?
If your spell is for destructive purposes, then perhaps it doesn’t matter. You’re just trying to channel EM radiation to break a bunch of chemical bonds and have the object fall apart. Like firing a laser cannon in sci-fi, or cutting something with a lightsaber (in a galaxy far, far away). But what if you need a controlled specific amount of energy aimed at a specific location? To unlock a door perhaps you’d need just the right amount of energy to mechanically disengage the lock. But if air molecules between you and the door interacted with your magical energy, transforming some of the “carrier” EM radiation into different frequencies, maybe that messes up your door-unlocking spell. Maybe that’s why the closer you are to wherever your spell is cast, the more effective it is. This also brings up the possibility of constructing a door-lock that interferes with the standard Alohomora, as Snape does, to prevent break-ins into his dungeon-office. (One must dissuade students up to no good from trying to steal potion ingredients, or in my line of work, lab chemicals.) A suitable material that scatters EM radiation of the Alohomora wavelength should work!
Quantal-light, when behaving like a particle, doesn’t “spread out” like a wave. Does this mean line-of-sight is very important when spellcasting? There seems to be some amount of “aiming” involved during spell-casting especially where doing battle is concerned. You need to point your magic wand in the right direction to be successful – a feature visually emphasized in the Harry Potter movies. But perhaps I’m being too limiting in my emphasis on the physical aspects. Mental energy and imagination are likely to be just as important in directing one’s spell to its desired outcome. And so the adept magician can bend and direct those EM waves in an extra-sensory mind-over-photon way. The Accio summoning spell doesn’t require line of sight; and is useful when you’re summoning an object you can’t necessarily see.
This brings us to the Second Task in Harry Potter and the Goblet of Fire. The action is all underwater. Magic, carried by EM radiation, has to pass through a much denser milieu – lots of water molecules amongst other things! We first see Harry dispatch a grindylow with Relashio. According to the text: “A large bubble issued from his mouth, and his wand, instead of sending sparks at the grindylows, pelted them with what seemed to be a jet of boiling water…” The medium (water) changed the spell’s effects. Nothing much else happens magically. Cedric uses a knife and Harry uses a jagged stone to cut their friends free. Harry then threatens the merpeople with his wand so he can also save Fleur’s sister, but no other magic spells are cast.
I hypothesize that the denser the medium, the more one might expect scattering of EM radiation. Spells cast underwater change in their effects. What about in a dense fog? Light certainly is scattered. Or in driving rain? Lots of opportunity for interference. But let’s get back to fundamentals. Magic may be mediated or carried by EM radiation, but it might or might not be quantal in nature. To interact with matter, the results might be quantal (e.g. the breaking of a chemical bond) but the magic-energy might be a continuous function, and perhaps magic is infinitely divisible. Hmm… I need to learn more magical theory. For now they seem like “rays” of unknown properties. We might have even called them X-rays, except that name is already taken, and thanks to Compton, we learned something fundamental and strange about the nature of reality.
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