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
A few points:
Light isn’t a wave. Light isn’t a particle. Light is something described by quantum mechanics that at times has the properties of both waves and particles, but is neither. As such light doesn’t require a medium.
In the Quantum Field Theory formulation of things, light is an excitation of the electromagnetic field, propagating through space. The EM field permeates all of spacetime.
Space is mostly empty of matter, but it’s still full of fields, the quantum vacuum, and spacetime itself. For example gravitational waves are disturbances in spacetime that propagate as waves.
Light is MODELED as a wave, sometimes. That means we pretend it’s a wave in certain situations and the math works out so that we can make certain predictions. But it is not a wave like water waves, and therefore doesn’t need a medium. In most visualizations, the EM wave is waving itself.
Light is a weird result of electricity creating magnetism and magnetism creating electricity. As light moves the the electricity gets stronger, creating the magnetism, and then the magnetism creates the electricity, with the strength of the two alternating in a wavelike fashion.
At least that’s how I understand it like I’m five.
Yhe photons speed is determined by how fast the electricity can cause the magnetism abd vice -versa, which is why you’ll frequently see people weite that the “speedbof light” is really the “speed of causation” or “speed of information”.
Think of the fundamental forces (including electromagnetism) as properties of space, rather than in it and it makes sense slightly more sense.
It’s still a massive simplification but it’s closer to the truth and tbh is the limit of my ability to visualise what’s going on.
Electromagnetic waves don’t need a medium to travel. Mechanical waves do (water ripples, acoustic shockwave etc.)
It doesn’t need a medium to travel, it’s not actually a wave as others have said. However, you might be interested to know that at one point it was theorized that light traveled through the “ether”. The experiment to disprove this is pretty interesting: https://en.m.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment .
Well if ocean waves move through water then wouldn’t light be the medium?
As Energy moves through water it creates waves or I guess you could say that water can behave as a wave too.
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.
Just wanted to add some cool trivia on the subject since you have your answers.
From the time of the Greek philosophers until the experiments between 1890 and the 1920s showed otherwise, it was thought the empty parts of the Universe were filled with an invisible substance called the ether or aether. The luminiferous ether was the substance waves of light were said to propagate through.
Simple ELI5 answer: Electromagnetism doesn’t require a medium
Complex ELI5 answer: EM *does* require a medium, but that medium is quantum fields which are part and parcel of space itself.
Most complete answer: read about 10 books on quantum electrodynamics and then shrug your shoulders because the minute we understand everything, we understand nothing about physical reality. When you’re utterly confused, that means you finally comprehend the incomprehensibly of it. Paraphrasing Richard Feynman, sometimes it just *is*…
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