# Which force is responsible for light's reflection in a surface?

• fbs7
In summary, the photon is being absorbed by the atoms in the table and then, somehow, another photon is (magically) re-emitted at the same exact angle that it arrived.
fbs7
I think I understand how electromagnetic force works, so I predict that if I take a big, big, long flat table, charge that table with a big negative electric voltage (say -500kV), then I shoot an electron at that table at an angle, then the electron will be repulsed by the charge, will make a nice little parabola and then shoot out at an outbound angle equal to the inbound angle, all the while following a nice smooth trajectory. If you watch that from a billion km away, the parabola part becomes very small and the electron will just seem to bounce off the the table - but it actually never touches it.

Now, instead of an electron, if you remove the electric charge from the table and shoot a ping-pong ball at the table, it will also seem to bounce off the table at the same angle, but it's actually not touching it either. I understand that electromagnetic repulsion between the ping pong atoms and the table atoms will act exactly the same way (although with a different formula, as that's repulsion between atoms, and is quantum level rather than classical), so the force here is also electromagnetic.

Then if my table is a mirror and I shoot a ray of light... which force is responsible for the photon emerging at the same exact angle at the other side? It can't be electromagnetism, as light does not interact. The only things I know a photon can do is to follow a straight line (bent by gravity), be absorbed by a particle and be emitted by a particle... so is the photon being absorbed by the atoms in the table and then, somehow, another photon is (magically) re-emitted at the same exact angle that it arrived?

Hi FBs7. I'm going to have to let someone else give you a more detailed explanation, but let me help clear one thing up in your reasoning - I know this, cause I do it all the time!

Light / electromagnetic radiation is not a photon and it's not a wave; it's not even both. It's something else, but can be modeled in some situations as if it were a discrete "particle" of light; and in other situations as if it were a wave. And in others as a fluctuation in a field. It's why the 2-slit experiment is such a brain-bender!

My guess is that the explanation to your question is going to come down to picking the right model for the job. Now I'll stand aside and let someone who actually understands this better step in

Understood - thank you!

Now, that's a good point... does light, as a wave, obey the 4 basic forces (electromagnetic, weak -- or electroweak, strong and gravity)? Hmm... I always assumed it did, but I don't really understand this duality thing... maybe the wave equation itself will lead to the reflection in the same angle thing? Hmmm...

fbs7 said:
so is the photon being absorbed by the atoms in the table and then, somehow, another photon is (magically) re-emitted at the same exact angle that it arrived?

That is certainly one way to look at it, without the magic.

Do you understand how reflection works classically? It's a prerequisite to understanding what happens quantum mechanically.

Hmm... that's a good question.

I remember going through Fermat to prove the angles of reflection and refraction, but I remember ever since then (it was physics I in college, I think, like 35 years ago) it seemed to be something taken out of the hat. I think it goes like this (if I remember it right): light goes from point A, reflects on point B, reaches an unknown point C; then, something about light makes it prefer to take the lowest time from A to C, therefore (obviously said my teacher) makes it so that the angle BC must be the same as the angle AB. Similar thing for refraction.

The thing with that line of thought is that it assumes that light reflects, but never explained why light reflects. Now, back in college we didn't have quantum physics (it was engineering college), but much later on I learned a little bit about the 4 forces thingie, and light absorption/emission, but neither one seems to provide much insight on why light reflects on something. From this absorption/emission thingie I'd expect light to be absorbed and re-emitted, like heat, that is, scattered all over the place instead of following the nice straight path, which for some reason will always make the smallest time from point A to B to C.

Get a copy of Feynman's little book, "QED The Strange Theory of Light and Matter." Don't worry, it is a popular exposition, not a textbook on quantum field theory.

## 1. What is the force responsible for light's reflection in a surface?

The force responsible for light's reflection in a surface is the electromagnetic force. This force is responsible for the interaction between charged particles, such as electrons, and is responsible for the behavior of light.

## 2. How does the electromagnetic force cause light to reflect?

When light hits a surface, the electromagnetic force causes the electrons in the surface material to vibrate. This vibration creates an electric field, which in turn creates a magnetic field. These fields interact with the incoming light, causing it to change direction and reflect off the surface.

## 3. Does the type of surface affect light's reflection?

Yes, the type of surface can affect light's reflection. Smooth, polished surfaces tend to reflect light more evenly and at a consistent angle, while rough, uneven surfaces may scatter light in different directions.

## 4. Can other forces also play a role in light's reflection?

Yes, other forces such as gravity and surface tension can also affect light's reflection, but the electromagnetic force is the primary force responsible for light's reflection in a surface.

## 5. Is light's reflection always the same on every surface?

No, light's reflection can vary depending on the properties of the surface, such as its smoothness, color, and angle. Additionally, the angle and intensity of the incoming light can also affect how it reflects off a surface.

• Optics
Replies
15
Views
2K
• Optics
Replies
5
Views
1K
• Optics
Replies
2
Views
11K
• Optics
Replies
26
Views
4K
• Quantum Physics
Replies
14
Views
3K
• Optics
Replies
2
Views
3K
• Optics
Replies
4
Views
1K
• Optics
Replies
28
Views
3K
• Optics
Replies
5
Views
2K
• Electromagnetism
Replies
8
Views
2K