# What's the nature of light?

#### Asexperia

Registered Senior Member
Is light a wave or a particle ?
Light isn't a wave nor particle.
Light behaves like a wave or a particle depending on the experiment being carried out.

Studying I have learned that:
Photon has no mass, is electromagnetic in nature and its energy increases with frequency.

Do you have a question or something you want to discuss? This is a discussion forum, remember.

Do you have a question or something you want to discuss? This is a discussion forum, remember.

OK, I have 3 questions.

1- What's the vehavior of light when it travels through space?

2- What would it happen if a ray of light freezes or stops?

3- What's the frequency of the radiated heat?

OK, I have 3 questions.

1- What's the vehavior of light when it travels through space?
Pretty broad question. What kind of behavior are you asking about? It follows a geodesic, which is curved in the presence of mass.

2- What would it happen if a ray of light freezes or stops?
It can't. Unless the photons get absorbed.

3- What's the frequency of the radiated heat?

I have a question that I think is relevant.

When an object, like a bell or something, makes a sound - the sound wave travels from the object in all directions. When I light a match in a dark room, light travels from the match in all directions. But suppose I had a light source that could emit a single photon. Which direction does the photon travel? Or does it disperse in all directions, like the sound wave from the bell?

For example, when We heat ourselves with a bonfire.

I have a question that I think is relevant.

When an object, like a bell or something, makes a sound - the sound wave travels from the object in all directions. When I light a match in a dark room, light travels from the match in all directions. But suppose I had a light source that could emit a single photon. Which direction does the photon travel? Or does it disperse in all directions, like the sound wave from the bell?
Light behaves like a wave or a particle depending on the experiment being carried out.
A photon is a quanta of an electromagnetic field
https://en.wikipedia.org/wiki/Photon
photon is a type of elementary particle. It is the quantum of the electromagnetic field including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force (even when static via virtual particles).
Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles. For example, a single photon may be refracted by a lens and exhibit wave interference with itself, and it can behave as a particle with definite and finite measurable position or momentum, though not both at the same time as per Heisenberg's uncertainty principle.

When an object, like a bell or something, makes a sound - the sound wave travels from the object in all directions. When I light a match in a dark room, light travels from the match in all directions. But suppose I had a light source that could emit a single photon. Which direction does the photon travel? Or does it disperse in all directions, like the sound wave from the bell?
A light bulb that emits light in all directions emits individual photons in random directions. Since there are billions and trillions of them, the distribution ends up being very uniform in all directions.

If you could dim down the bulb to the point where it was only emitting a few photons per second, or something like that, then you'd notice that each photon is emitted in a random direction.

More advanced answer: Of course, the above assumes you're using some kind of detector (camera or screen or wall or your eye, or whatever) to actually detect the photons and deduce their directions of travel. Quantum mechanically speaking, each individual photon is actually emitted in all directions simultaneously. It doesn't have a particular direction until something detects it, at which point the wavefunction collapses.

Quantum mechanically speaking, each individual photon is actually emitted in all directions simultaneously. It doesn't have a particular direction until something detects it, at which point the wavefunction collapses.
So the previous answer is correct?quantum mechanically speaking?
A photon is a quanta of an electromagnetic field
https://en.wikipedia.org/wiki/Photon
photon is a type of elementary particle. It is the quantum of the electromagnetic field including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force (even when static via virtual particles).
Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles. For example, a single photon may be refracted by a lens and exhibit wave interference with itself, and it can behave as a particle with definite and finite measurable position or momentum, though not both at the same time as per Heisenberg's uncertainty principle.

For example, when We heat ourselves with a bonfire.
What does that have to do with the other questions? This is not a coherent thought.

So the previous answer is correct?quantum mechanically speaking?
Well, you said something correct about what photons are, but you didn't actually answer the question that was asked.

A photon is a quanta of an electromagnetic field
https://en.wikipedia.org/wiki/Photon
photon is a type of elementary particle. It is the quantum of the electromagnetic field including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force (even when static via virtual particles).
Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles. For example, a single photon may be refracted by a lens and exhibit wave interference with itself, and it can behave as a particle with definite and finite measurable position or momentum, though not both at the same time as per Heisenberg's uncertainty principle.
Thanks - but I can read wikipedia too. Doesn't really help me visualize the answer to my "thought experiment".
A light bulb that emits light in all directions emits individual photons in random directions. Since there are billions and trillions of them, the distribution ends up being very uniform in all directions.

If you could dim down the bulb to the point where it was only emitting a few photons per second, or something like that, then you'd notice that each photon is emitted in a random direction.

More advanced answer: Of course, the above assumes you're using some kind of detector (camera or screen or wall or your eye, or whatever) to actually detect the photons and deduce their directions of travel. Quantum mechanically speaking, each individual photon is actually emitted in all directions simultaneously. It doesn't have a particular direction until something detects it, at which point the wavefunction collapses.
This is better.

So am I basically asking a restatement of the double slit experiment?

If I set up a single detector, will it always detect the photon? Or will it only occasionally detect it?

EDIT: I know in my bell example above, that the sound is actually an energy wave travelling through a medium. There is no sound "particle", it's the air molecules bumping into each other than carries the wave. I'm having a harder time visualizing this with light as it doesn't require a medium. (Unless spacetime counts as a "medium".)

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If I set up a single detector, will it always detect the photon? Or will it only occasionally detect it?
Photon[s].

It will detect a few photons. A bigger detector will intercept more photons over time.

Each photon that is emitted will essentially expand as a wave, but will only be detected at a single point, and there, the wave collapses.

What does that have to do with the other questions?

The radiated heat are infrared waves.

The radiated heat are infrared waves.
Yes.
This is unrelated to your other questions.

If you have other questions, ask.

Is light a wave or a particle ?
Light isn't a wave nor particle.
Light behaves like a wave or a particle depending on the experiment being carried out.
Your last line is most correct.

Light is neither exclusively particle nor wave. It has both particle-like properties and wave-like properties. Depending on how we choose to detect it will determine which properties we see.

Well, you said something correct about what photons are, but you didn't actually answer the question that was asked.
The third choice in the OP, which I gave gives the answer...
Light behaves like a wave or a particle depending on the experiment being carried out.
Which is the same as ....
Quantum mechanically speaking, each individual photon is actually emitted in all directions simultaneously. It doesn't have a particular direction until something detects it, at which point the wavefunction collapses.
correct?

So am I basically asking a restatement of the double slit experiment?
Really, we don't need that level of complexity to explain what's going on here. It's easier just to assume that for a light source emitting light in all directions, individual photons are like particles that are emitted in random directions. So, what you'll find at the microscopic level is that the intensity of the light isn't adjustable continuously, but rather it adjusts in "steps" equivalent to the energy of one photon. In other words, it is quantised. If light was just a wave, then we'd expect the intensity to vary in a continuous way.

If I set up a single detector, will it always detect the photon? Or will it only occasionally detect it?
Only occasionally, assuming your detector only covers one portion of the spherical surface surrounding the light source.

EDIT: I know in my bell example above, that the sound is actually an energy wave travelling through a medium. There is no sound "particle", it's the air molecules bumping into each other than carries the wave. I'm having a harder time visualizing this with light as it doesn't require a medium. (Unless spacetime counts as a "medium".)
In the sound wave the intensity of sound is determined by the maximum distance that each air molecule is displaced from its equilibrium position as the wave goes past. With light, the intensity is determined by the maximum amount by which the value of the electric or magnetic field at a given point in space varies as the wave goes past. That's the wave picture. In the particle picture, the intensity is determined by how many photons go past that point in space every second.

It's easier just to assume that for a light source emitting light in all directions, individual photons are like particles that are emitted in random directions. So, what you'll find at the microscopic level is that the intensity of the light isn't adjustable continuously, but rather it adjusts in "steps" equivalent to the energy of one photon. In other words, it is quantised. If light was just a wave, then we'd expect the intensity to vary in a continuous way.
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Noice!