Is light realty a wave? I have been reading Richard Feynman’s “QED”, were he seems to make the case light is not wave, but is instead a only a particle, but a particle that we cannot predict the movements of? So is light really a wave? Or just a particle that we cannot predict the movements of, so it appears a like a wave?
Please forgive my grammar mistakes.
It’s a wave and a particle…or it’s neither.
The way I understand it is light can be considered a wave or a particle depending on how you look at it. Do one type of experiment and it is useful to think of it as a particle. Do a different experiment and it is useful to consider it a wave.
In reality it is likely something else we don’t have a definition for that looked at different ways shows different aspects. Consider a pyramid glued to a cube. Looked at one way you see the pyramid, looked at another you see a cube but taken in totality it’s not really a cube or a pyramid. Unfortunately we can’t seem to grasp the ‘bigger’ picture in one go and only see one or the other given aspect.
But is light really a wave? Or just a wave of probability? Meaning you cannot predict the movement of the “particle” light?
As far as we understand it, everything is both really a wave and really a particle… meaning, as Whack-a-Mole described, we probably don’t really understand what’s going on.
Light has particle properties in some experiments (for example, light seems to transfer energy in discreet packets, so it must come in particle form, ie photons).
In other experiments, light is definitely a wave (thin slit interference, for example, where light can be made to interfere with itself–something a pure particle, even one described by a probability wave function, shouldn’t do).
The same can technically be said for everything. For example, Jupiter is technically a wave in some observations… it just has a wavelength much smaller than Jupiter itself, so it generally acts a whole lot more like a particle. You are also a wave (or a collection thereof), you just have a very small wavelength, so you appear to be in one place at any given time.
I’ll let someone else step in with deBroglie info–I don’t have the formulae handy to do the subject justice.
You should read Chronos’s article:
How can light be both a wave and a particle?
And the endless debate in COSR that followed.
Yeah, but I see Chronos’ article in complete contradiction with Feynamen,
Or Feynman.
Major Kong wrote
As one who is impressed with both of these gentlemen (I named my son after one of them; I’ll leave you to guess which one), I’m curious to hear Chronos’s thoughts on this.
Perhaps light is an energy wave that charges latent particles in the “quantuum foam” which then become “photons”.
I’m just speculating of couse.
Kong:
How many wave/particle threads do you need to start on this board, buddy?
Look, light is not a wave or a particle. It’s that simple. In order to understand and predict the behavior of light, we need to assign it certain properties. It appears to behave like a wave in some circumstances and like a particle in others. We are projecting a macroscopic model on something that is below the physical limits of our senses.
Light is Light.
And this goes for any of the various particles described in modern physics. Electrons, or what-have-you.
The thing you have to understand is that very small and very large objects are not like the objects we encounter on a day-to-day basis. Light is like nothing we’re familiar with, and the wave-particle duality is the result of our trying to fit it into categories that it doesn’t belong in.
Consider this old fable:
(NOTE: I did that from memory so no cite and apologies if I mussed it up a bit but I think the sense of it stands)
In the wave/particle duality of light we are essentially the blind men fumbling at different parts of the elephant and grasping at different aspects of it to determine what it is yet unable to grasp the greater reality of the elephant in its entirety.
“At the speed light travels, it’s a good thing it don’t weigh much.” - Hollywood George, c. 1969.
Maxwell’s equations like Newton’s laws are excellent approximations, but when you get into things like black body radiation, the photoelectric effect, Compton scattering etc. they cease to cut the mustard.
First Planck and then Einstein discovered that in order to explain these phenomenon you had to posit that only discrete amounts of energy equal to integer values of h*f (Planck’s constant times the frequency) could be exchanged with resonators (matter). And thus was born quantum mechanics.
You can relate light quanta to an electromagnetic wave by considering that the probability per unit time that a photon will be detected in any small volume is proportional to the square of the amplitude of the wave’s electric field vector.
But if I am reading Feynman correctly, he seems to be saying that photons (light) are particles. And all their behavior can be described treating them as particles. It is just in the macroscopic world the “paths” of the particles will cancel out all but one path, which isn’t true for photons, electrons, etc. But photons are definitely particles.
The idea that I’ve settled on is that thinking of it as a “probability wave” is most comfortable for me. The photon (or electron, or Jupiter, or whatever particle) exists as a probability wave between the times when we observe it as a particle. Is this generally correct? If it’s not, do I miss out on anything by thinking this way?
It’s just a metaphor. A classical particle is something whose behavior can be explained by Newton’s laws. Photons are definitely not classical particles. You can think of photons as particles with some wave-like attributes such as phase and interference, which is what Feynman is doing. It’s equally correct to think of them as waves with some particle-like attributes (quantization). The truth is that neither analogy/metaphor is perfect.
Why is it so hard to accept that classical/macroscopic ideas like “particles” and “waves” do not apply to photons and subatomic particles? It’s like debating whether SUVs are trucks or cars. You are trying to apply outdated classification schemes to newly discovered (or invented) things, and it’s not going to work.
I like the SUV analogy, scr4.