Recently, I started learning about quantum mechanics in my degree – finally, the juicy stuff! Waves are acting like particles, particles are acting like waves and light is something noncommittal in between, reminiscent of me flip-flopping between what I should get for dinner. It got me thinking about how our ideas about light have changed throughout history, and how the unquestionable, absolute ideal of science portrayed in media almost disrespects the brilliant murkiness that lies under the surface.

Today we take for granted that neither a wave nor a particle model for light yield a perfect explanation for phenomena we see such as the photoelectric effect and diffraction patterns, and in fact we need different models for different scenarios. But this idea was not easily obtained- Newton’s corpuscular theory of light campaigned for small light particles, and held sway until Young and Fresnel argued for a wave model to explain interference and diffraction^[1].

I remember when I applied to university, I opened my personal statement with some cheesy stuff about being fascinated by the objectivity and absoluteness of Physics. While it’s definitely beautiful to learn about how the universe works, I would say that my perspective on Physics (and science as a whole) has changed with time. Rather than being an infallible description of the way things are, I think it’s more accurate to say it’s our most educated interpretation of what we see. Newtonian gravity is sufficient to predict the orbits of planets, but general relativity is required to explain deviations in Mercury’s orbit. Then in a related vein, there are concepts like Heisenberg’s uncertainty principle which tell us that there are some things we cannot know for sure (beyond some uncertainty) at the same time, namely the simultaneous position and momentum of a particle. There’s some charm in physicists being able to quantify just how much we don’t know, when we don’t know something.

It’s entertaining to consider what will be taken for granted in a few centuries- perhaps the nature of the enigmatic dark energy/dark matter will seem obvious to us. Or perhaps the very concept of them will become outdated like the so-called “luminiferous aether” which was thought to be the medium through which light travelled, before Einstein’s ideas of relativity made the idea of an aether unnecessary.

I’ve no clue what will happen in the future of Physics- so don’t start telling your friends that dark matter is a hoax or that scientists don’t know what they’re talking about! I just find it fun to speculate.

References:

[1] From Huygen’s waves to Einstein’s photons: Weird light

Comptes rendus – Physique, Volume 18, Issue 9-10, p. 498-503, November 2017

Alain Aspect