# Light, Wave or Particle?

Ratzinger said:
But E(r,t) is not a quantum wave function, or is it? On the other hand I saw in my quantum text that it's interpreted just like that. Then I read here on physicsforums it's all wrong, it's ripples in quantum fields.
Could someone explain the relationship photon-quantum wave-classical EM wave?
thankyouverymuch
The probability density is given by the square of that field. In that sense you can think of it as the wave function.

Pete

da_willem said:
'Wavicles' propagate like waves but exchange momentum and energy like particles.
I beg to differ . In my opinion wavicles do not propagate like waves. According to the Free Dictionary a wave in Physics is: "A disturbance traveling through a medium by which energy is transferred from one particle of the medium to another without causing any permanent displacement of the medium itself." Don't alll waves spread out in at least 2 dimensions for water waves and 3 dimensions for sound waves. But wavicles do not appear to spread out at all. Also a wavicle does not tranvel in a medium really. The space continuum is physical but not really a medium. That is why I don't like to call light a wave, because it confuses people to say it is a wave when it doesn't act at all like waves in a medium. Light is more like a vibration or occilation than it is a wave.

Ben Wiens said:
I beg to differ . In my opinion wavicles do not propagate like waves. According to the Free Dictionary a wave in Physics is: "A disturbance traveling through a medium by which energy is transferred from one particle of the medium to another without causing any permanent displacement of the medium itself." Don't alll waves spread out in at least 2 dimensions for water waves and 3 dimensions for sound waves. But wavicles do not appear to spread out at all. Also a wavicle does not tranvel in a medium really. The space continuum is physical but not really a medium. That is why I don't like to call light a wave, because it confuses people to say it is a wave when it doesn't act at all like waves in a medium. Light is more like a vibration or occilation than it is a wave.
It is a very special wave indeed, there is no disturbance of a medium as we are acquainted with from our experience with waves. But it's behaviour is described by a wave-equation just like any other wave. In this case it is not some displacement of a medium that satisfies the wave equation but the particles wavefunction [itex]\psi (\vec{x},t)[/tex] satisfying [itex]|\psi (\vec{x},t)|^2= p(\vec{x},t)[/tex] with p the probablility density of finding the particle.

The wave equation is of course the Scrödinger equation; for a free particle:

$$i\hbar \frac{\partial \psi}{\partial t} = \frac{\hbar ^2}{2m} \nabla ^2 \psi$$

The time-dependence of a particle with definite energy E is

$$\psi \propto e^{-i\frac{E}{\hbar} t}$$

so $$\frac{\partial \psi}{\partial t} = -i\frac{E}{\hbar} \psi$$

substituting in the Schrödinger equation leaves us with

$$\frac{2m}{E} \frac{\partial^2 \psi}{\partial t^2} = \nabla ^2 \psi$$

Unmistakably a wave-equation for a particle with phase velocity [itex]v=\sqrt{\frac{E}{2m}}[/tex]

da_willem said:
It is a very special wave indeed...with p the probablility density of finding the particle.
I agree, if a photon can be called a wave at all, it is a very special type of wave as you say. By the way how big is a photon, or "special wave"? By big I mean how far away from the center of the "particle" or "wave" is it able to cause an effect. How far to each side and forward and backwards? Does this depend on the frequency or energy of the photon?

I haven't read the whole thread, but I've had the same views upon this for a long time already. My idea basically is that Light (and of course all em ray thingeys) is neither particle nor ray (oh, how poetic), but something other having properties from both.