Don’t waves need a medium to travel through? Isn’t space just essentially empty? I know they’re electromagnetic waves, but what does that mean essentially?
Edit: Thanks for the response guys. From your response I’ve realised there’s no way to explain to a 5 year old how light works!
In: Physics
Light doesn’t have a medium. That was proved in 1887 with the Michelson-Morely experiment.
Light is simultaneously a particle and a wave, but it’s also neither. This debate goes back centuries as to the nature of light. Newton believed it to be a particle. Others believed it to be a wave. It wasn’t until 1801 that the double slit experiment could prove that it was a wave.
When we think of it as a wave, it’s a disturbance in the electromagnetic field. We start with a small electric field, and then as it starts to disappear, that change in the amount of electric field creates a magnetic field. That creation of a magnetic field from nothing means the magnetic field is changing, so that creates an electric field, which then, in turn, creates a magnetic field, and they oscillate until they hit something. All of those interactions between the electric and magnetic fields occur at the speed of causality, which is also known as the speed of light, which is why the wave moves at that’s speed.
When we think of light as a particle, it’s a packet of energy that can’t be divided into smaller pieces, called a photon. This idea was proposed by Max Planck in 1901 as a “mathematical trick” to explain black body radiation to resolve what we call the Ultraviolet Catastrophe. Basically, our models couldn’t explain why hot objects didn’t just radiate away all of their energy at once with very high energy (ultraviolet) light. This “mathematical trick” worked so well that we actually started to consider the idea of light being a particle again.
This then resolved another issue in physics with the photoelectric effect. If we set up the right kind of metal and exposed it to the right kind of light, we could make the metal create electricity, and we had no idea why. The leading theory was that the atoms just soak up the energy until an electron is knocked loose which goes around the circuit as electricity. The only problem was, low energy light, like visible light, it wouldn’t trigger the effect, but ultraviolet light would trigger it, even in small amounts.you could take a light source that produces UV, have the photoelectric effect occur, then place a pane of glass between the light and the metal, which blocks the UV, and the effect stops. Nobody could explain it, but all of the sudden, the quantized light explains it. Only a photon with enough energy to ionize an electron all on its own could cause the photoelectric effect, there was no such thing as absorbing the energy over time.
Jumping back to the “no medium” for a second, this inspired a US patent office worker to theorize that the passage of time changes depending on the way the observer was moving. This led to Einstien’s theories and special and general relativity. Theories that have predicted things we’ve proven to be true over the last century, and found no evidence to the contrary of.
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