How can light be a wave and particle at the same time?

[gronk]

TL;DR

How light can be a wave and particle at the same time.

I don't even have enough education in physics to even be considered a novice. And this might be a 'duh' observation. To begin with consider that we don't properly conceive what light really is. We define it in ways that we can work with it. What we define could just be like shining a flashlight on something and defining it by it's shadow. But if you rotate the object 90 degrees and shine the flashlight on it, it's shadow looks completely different.

 

[Matterwave]

The "light is both a particle and a wave" description is a rather outdated and non-precise description of our understanding of light.

In certain experiments like the single or double slit diffraction experiment we see wave-like behavior in that light diffracts. Diffraction is something we describe with wave mechanics.

In other experiments like photoelectric effect experiments light is shown to come in basic "quanta" and exhibits particle-like behavior.

The above two statements don't necessarily imply "light is both a particle and a wave".

 

[jeffn1]

My impression is, at a quantum level, all fundamental "particles" are really waves. According to Quantum Field Theory, all fundamental particles are merely excitations of their underlying quantum field.

But, I tend to think there is a better case for viewing fundamental particles as "particles" when they are not massless (electrons, etc.).

Photons have no mass and (as a result) travel at the speed of light. But, as a I understand it, the photons are only emitted and absorbed in packets (quanta). So, this has a "particle-like"characteristic to it.

That's my simplistic view, for what it is worth.

 

[PeterDonis]

My impression is, at a quantum level, all fundamental "particles" are really waves.

No, they're not...

According to Quantum Field Theory, all fundamental particles are merely excitations of their underlying quantum field.

Yes, but a quantum field is not a wave. It's a quantum field.

I tend to think there is a better case for viewing fundamental particles as "particles" when they are not massless (electrons, etc.).

Your next sentence contradicts this:

Photons have no mass and (as a result) travel at the speed of light. But, as a I understand it, the photons are only emitted and absorbed in packets (quanta). So, this has a "particle-like"characteristic to it.

Yes, and it's the same "particle-like characteristic" that leads us to call electrons, etc., particles.

 

[PeroK]

My impression is, at a quantum level, all fundamental "particles" are really waves.

The electron and the photon are particles, by definition. They are defined by their generic properties, as per the standard model of particle physics.

An instance of an electron or photon also has dynamic properties (energy, momentum, angular momentum and specific spin/polarisation). These dynamic properties may be described or encapsulated by a wave-function or the quantum-field equivalent.

In modern, mathematical physics it's important to treat things as they are defined and not according to some a priori expectation of what something should be. Confusion is sown by popular science writers, who promote "wave-particle duality" as a sublime mystery, rather than a historical footnote that was clarified about one hundred years ago.

There is a certain parallel in the history of mathematics, where mathematicians wasted their lives trying to prove that a straight line was more than its definition implied. A line is what it's defined to be. And if it doesn't meet someone's expectations of what a line should be, then that is their problem!

 

[haruspex]

I have a suspicion that some respondents are reading the thread title as "How can light be a wave and particle at the same time" instead of "How light can be a wave and particle at the same time".
As I read it, the OP is suggesting that whether it behaves like a wave (as we experience waves at the macro level) or as a particle (ditto) depends what question you ask of it. That's true, but I don’t see that the flashlight analogy is, ahem, illuminating.

 

[Herman Trivilino]

To begin with consider that we don't properly conceive what light really is. We define it in ways that we can work with it.

Well, we create models. That's physics. Describe and predict the way Nature behaves using models.

What we define could just be like shining a flashlight on something and defining it by it's shadow.

No, because we have additional observations and evidence other than just the shadow.

But if you rotate the object 90 degrees and shine the flashlight on it, it's shadow looks completely different.

Yup. Like that!

The model of light as a wave gained traction with the work of Maxwell and others. Later, photons as a model gained traction. We now know that only when we have large collections of photons the wave properties appear.

 

[PeterDonis]

I have a suspicion that some respondents are reading the thread title as "How can light be a wave and particle at the same time"

Which is a perfectly reasonable reading since it's what the thread title actually says, word for word.

instead of "How light can be a wave and particle at the same time".

I'm not sure I see the difference. Either way the question is not really well posed; light is not a wave and a particle at the same time. It's neither. It's a quantum field.

 

[haruspex]

Which is a perfectly reasonable reading since it's what the thread title actually says, word for word.

You're right - I was looking at the first line of the body of the post, the bit to the right of the"TL;DR". I just assumed the title was the same.
So the puzzle is, which did @gronk mean?

I'm not sure I see the difference. Either way the question is not really well posed; light is not a wave and a particle at the same time. It's neither. It's a quantum field.

The difference is that "how can it be" is asking for an explanation whereas "how it can be" is offering one. The rest of post #1 fits better with offering than asking.

 

[jeffn1]

Which is a perfectly reasonable reading since it's what the thread title actually says, word for word.


I'm not sure I see the difference. Either way the question is not really well posed; light is not a wave and a particle at the same time. It's neither. It's a quantum field.

Is light "a quantum field" or is it more accurate to say it is an "excitation in a quantum field"? (Specifically, the electromagnetic field).

 

[PeterDonis]

The rest of post #1 fits better with offering than asking.

To the extent it's offering something, the issues with what it's offering have already been pointed out. Again, either way the issue is not really well posed.

 

[PeterDonis]

Is light "a quantum field" or is it more accurate to say it is an "excitation in a quantum field"? (Specifically, the electromagnetic field).

It depends on what you want to use the term "light" to refer to. That's a question about words, not physics. I was, of course, using it to refer to the quantum field. But you could also use it to refer to, for example, a dot on a detector screen in an experiment with a very low intensity light source that leads us to use to term "photon". Most physicists would say the dot is caused by an excitation in the quantum field, that then interacts with the matter in the detector screen.

 

[bhobba]

Because it's neither.

It's a disturbance in a quantum field that pervades all space.

For the gory technical details:
https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3211&context=physics_facpub

Thanks
Bill