Question about light (wave-particle duality)?

Question

Someone please set the record straight for me: Is light simultaneously a particle and a wave, or sometimes a particle and sometimes a wave?

How can light be a wave if there is no medium in space? Light travels from the Sun to Earth through empty space (no medium). Don't all waves require a medium to propogate through? Or has it got to with space not being a true vacuum? Or is it because of some kind of electromagnetic field? I can understand light being considered a particle, but how so a wave?

I'm only taking Physics C: Mechanics so we don't study any of this. It's just out of curiosity.

Thanks for answering.

Answer 1

Light is simultaneously acts as a particle and a wave.



It needs no medium (other than possibly free space -- which has an energy associated with it) to travel. If you have an electron and move it back and forth, it will create an electromagnetic wave. It is caused by the acceleration of charged particles.



It is also the charged particle (primarily electrons) that interact with the em wave. It is this interaction that allows us to see. This is how the sun's rays warm us. This is how we get radio waves.



The funny thing is that the interactions can only occur in discrete amounts of energy (quantum). This interaction creates a particle-like effect. You have a packet of energy received at a fixed (within uncertainty rules) place in time and space. This is called a collapse of the wave function. The wave is now a particle.



The funnier thing is that matter acts the same way. It is really just discrete waves that continuously interact with other waves creating a particle-like effect.



Trying to understand this is more mind-blowing than any legal or illegal drug. lol.



[And this doesn't even get into virtual photons which are used to explain the attaction between charged non-accelerating particle]

Answer 2

First of all, light *is* an electromagnetic field. It is the interaction between the electric and magnetic parts that allow the light to propagate in a vacuum.



Next, light, like all things at the quantum level is both a particle and a wave. More specifically, it is a probability wave where the probability is of detection of a particle. The wave nature shows up in things like interference fringes and diffraction patterns. There is also a wavelength and frequency associated with it. However, if the intensity is very low, only individual photons will be detected. Even still, the interference patterns will build up over time.



I'd should point out that electrons have this same property of being both a wave and a particle. We typically think of electrons as particles, but they also show interference patterns with constructive and destructive interference. This actually shows an underlying unity in ALL fundamental particles: they all show both wave and particle properties with the wave being a probability wave.

Answer 3

Particles of light propagate in wave form .Each particle supplies energy to the next for movement. No medium is required

Answer 4

A fundamental law of quantum mechanics:

The only way to really understand quantum mechanics is to stop trying to understand it in terms of things you understand and just do the math and work out the consequences.



Light is not a particle nor is it a wave. As one author (Gribbin I think) put it, it is a slithy tove. All quantum mechanical objects are slithy toves. Electrons, photons, whatever. Calling them by a nonsense name is better than muddying your head with loose analogies.



So what is light? It is a disturbance in the electromagnetic field. The electromagnetic field fills all of space. There is no medium. According to the laws of quantum field theory, disturbances in the field only come in discrete chunks which we call photons. These photons are particle-like in that they come in chunks. They are wave like in that their propagation obeys a differential equation that produces wave-like phenomena such as interference and diffraction. But really they're just slithy toves.

Answer 5

Sometimes light behave like wave (Young's experiment) and sometimes it behave like stream of particles - photons (photoelectric effect or Compton effect).



We can't consider that it is only particle or wave. We can only use these both types of description of light to explain phenomenons easier. It would be really difficult to explain for example Young experiment using particle character of light.



Light is electromagnetic wave - it can spread in vacuum. Only mechanical waves can not go through vacuum. For example acoustic waves.

Answer 6

As Richard Feynman said:



I am going to tell you what nature behaves like. If you will simply admit that maybe she does behave like this, you will find her a delightful, entrancing thing. Do not keep saying to yourself, if you can possibly avoid it, ‘but how can it be like that?’ because you will get ‘down the drain,’ into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that.

Answer 7

Of Interest:



http://en.wikipedia.org/wiki/Aether_theories





[I don't Have a Very Good Understanding of It Either. It Simply is.]