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Is light fundamentally a wave or a particle?

forbes.com

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Re: Is light fundamentally a wave or a particle?

#11

Post by jjbinx007 »

effie wrote: post #7
witherk wrote: post #4

Wave particle duality used to stress me out before I read Feynman talk about it. "Things on a very small scale behave like nothing that you have any direct experience about. They do not behave like waves, they do not behave like particles, they do not behave like clouds, or billiard balls, or weights on springs, or like anything that you have ever seen..... There is one lucky break, however—electrons behave just like…

Single beam of electrons diffracts like single beam of light, but otherwise electrons behave very differently than light: two electron beams interfere with each other, while two light beams do not.

Am I right that thinking of everything as waves isn't a bad mental model?

If everything is a field, then light is simply a three dimensional wave in that field. This makes the double slit experiment seem much easier to grasp:

A single photon (which is a wave with a discreet amount of energy) travels through both slits at the same time. This causes the wave to interfere with itself and when it hits the wall it registers as a single point, as the photon must always be a discreet quantum of energy.

To me, this makes intuitive sense and removes a lot of the mystery and confusion that gets invoked whenever pop-sci writers explain the experiment. They tend to say something along the lines of: photons are like billiard balls, so they can only go through one slit or the other, but if you don't detect which slit it goes through it seems to go through both.

Am I close to what's actually going on, or am I way off?

Re: Is light fundamentally a wave or a particle?

#14

Post by danbruc »

beojan wrote: post #9
effie wrote: post #7

Earlier quoted context omitted.

Single beam of electrons diffracts like single beam of light, but otherwise electrons behave very differently than light: two electron beams interfere with each other, while two light beams do not.

Two coherent beams of light will absolutely interfere.

I think that was meant to mean that the two beams interact. Two crossing light beams will pass right through each other without much happening while two electron beams will interact. But this is because electrons are charged and photons are not. On careful inspection and with high energy photons one would also notice an interaction between two light beams due to photon photon scattering [1]. But one could reasonably call this a kind of distraction due to different charges of different particles. Ignoring those makes photons and electrons behave identical in respect to the phenomena discussed in the article.

[1] https://en.wikipedia.org/wiki/Two-photon_physics

Re: Is light fundamentally a wave or a particle?

#15

Post by harshitaneja »

jjbinx007 wrote: post #11
effie wrote: post #7

Earlier quoted context omitted.

Single beam of electrons diffracts like single beam of light, but otherwise electrons behave very differently than light: two electron beams interfere with each other, while two light beams do not.

Am I right that thinking of everything as waves isn't a bad mental model? If everything is a field, then light is simply a three dimensional wave in that field. This makes the double slit experiment seem much easier to grasp: A single photon (which is a wave with a discreet amount of energy) travels through both slits at the same time. This causes the wave to interfere with itself and when it hits the wall it registe…

The problem with treating everything as a wave is that all these entities can only exist at certain energies. So the field is quantized.

Re: Is light fundamentally a wave or a particle?

#16

Post by danbruc »

bhaak wrote: post #12

Why not both?

It is both, or probably even better neither. Elementary particles are not classical particles and they are not classical waves. They are things that behave similar to classical particles in some circumstances and similar to classical waves in others, but they are neither. But as humans have no experience with such things in the macroscopic world, as we lack intuition for them, we desperately want them to be either or the other in order to comprehend them. Ironically this desire is probably what makes them actually more incomprehensible.

Re: Is light fundamentally a wave or a particle?

#17

Post by ahartmetz »

beojan wrote: post #9
effie wrote: post #7

Earlier quoted context omitted.

Single beam of electrons diffracts like single beam of light, but otherwise electrons behave very differently than light: two electron beams interfere with each other, while two light beams do not.

Two coherent beams of light will absolutely interfere.

Electron beams interfere in ways that light beams don't, though. If they cross in vacuum, they deflect each other due to the electric charge carried by electrons. Light beams can only deflect each other in media with non-linear response to electromagnetic fields, i.e. the response to one beam modifies the response to the other beam.

Re: Is light fundamentally a wave or a particle?

#19

Post by simonh »

effie wrote: post #7
witherk wrote: post #4

Wave particle duality used to stress me out before I read Feynman talk about it. "Things on a very small scale behave like nothing that you have any direct experience about. They do not behave like waves, they do not behave like particles, they do not behave like clouds, or billiard balls, or weights on springs, or like anything that you have ever seen..... There is one lucky break, however—electrons behave just like…

Single beam of electrons diffracts like single beam of light, but otherwise electrons behave very differently than light: two electron beams interfere with each other, while two light beams do not.

Well yes one has charge and the other doesn't, they aren't literally the same thing so are different QED. The point is the rules are the same.

Re: Is light fundamentally a wave or a particle?

#20

Post by klodolph »

jjbinx007 wrote: post #11
effie wrote: post #7

Earlier quoted context omitted.

Single beam of electrons diffracts like single beam of light, but otherwise electrons behave very differently than light: two electron beams interfere with each other, while two light beams do not.

Am I right that thinking of everything as waves isn't a bad mental model? If everything is a field, then light is simply a three dimensional wave in that field. This makes the double slit experiment seem much easier to grasp: A single photon (which is a wave with a discreet amount of energy) travels through both slits at the same time. This causes the wave to interfere with itself and when it hits the wall it registe…

If you want to think about it, I suggest that you keep a “library” of classic experiments in your head.

There are experiments that show that light is not a particle (in the classical sense) and other experiments that show that light is not a wave (in the classical sense). Quantum mechanics is the result of trying to find a theory consistent with both sets of experiments.

Originally, the double slit experiment was seen as proof that the wave theory is correct. So if you want to challenge your wave theory, look to different experiments. Wave theory of light was predominant from the mid-19th century to the emergence of quantum mechanics in the early 20th century, so I would focus on science from the early 20th century, such as the ultraviolet catastrophe and the photoelectric effect.

Consider the photoelectric effect. If light were a wave that carried energy, this wouldn’t explain why an equal amount of energy has a different effect depending on its wavelength. The quantum explanation is that one packet of light contains a different amount of energy, which depends on wavelength. “Light is a wave” kind of falls apart as a theory, because it is unable to explain this.

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