# Laser and Mirror Thought Experiment

• ChrisisC
In summary, the property of light that allows it to be seen in a mirror is its ability to scatter or reflect off of surfaces, such as the mirror in the bathroom experiment. While photons are individual packets of energy in an electromagnetic wave, they are not necessary to explain the reflection of light in this scenario. The laser beam is well collimated and the scattered light is what is visible in the mirror.
ChrisisC
I have a thought experiment that i need a answer to. In my experiment, I am in a bathroom with a mirror along one wall. I also have a laser that emits a single file line of photons. The laser is attached to the ceiling and emits a line of photons parallel to the mirror. What property of light makes it so i can see the photons in the mirror? A normal laser that doesn't emit just a single file of photons can be seen reflected in a mirror while it's pointed parallel to the mirror. So how is this possible? How do the photons get out of the line if the laser and reflect off the mirror to my retina? How do the photons go in a different direction than the laser is emitting them? I hope i presented my question in a answerable manner, and please excuse my lack of knowledge.

ChrisisC said:
I also have a laser that emits a single file line of photons.
There is no such thing. A laser doesn't emit a stream of photons, whether "in single file" or not, it emits light, which is to say electromagnetic radiation. The light interacts with and is scattered by the mirror, and you see the scattered light.

Photons only come into the picture if you do detailed quantum mechanical calculations (which are completely unnecessary for this problem) of exactly how the light is scattered by the mirror.

Nugatory said:
There is no such thing. A laser doesn't emit a stream of photons, whether "in single file" or not, it emits light, which is to say electromagnetic radiation. The light interacts with and is scattered by the mirror, and you see the scattered light.

Photons only come into the picture if you do detailed quantum mechanical calculations (which are completely unnecessary for this problem) of exactly how the light is scattered by the mirror.

Precisely my question, HOW does the EM radiation get emitted from the laser and actually travel to he mirror to be reflected? Wouldn't the light wave be traveling parallel to the mirror? The light wave would have to hit the mirror, meaning it's not parallel to the mirror anymore, right?

ChrisisC said:
HOW does the EM radiation get emitted from the laser and actually travel to he mirror to be reflected?
It gets scattered or reflected off something else first. A laser beam in vacuum is not visible.

ChrisisC said:
And aren't photons EM radiation? photons are individual packets of energy of a EM wave, right?
Yes, but they don't behave the way you describe. To correctly describe photons you need to use QFT.

But as @Nugatory says, that is unnecessary for this problem. All you need to do is say that your laser beam is well collimated and then talk about the scattering of the beam. There is no need to bring in photons

Last edited:
davenn
Dale said:
It gets scattered or reflected off something else first. A laser beam in vacuum is not visible.

Ah, that's a very valuable piece of information I was not aware of. Thank you!

ChrisisC said:
Ah, that's a very valuable piece of information I was not aware of. Thank you!

## 1. What is a laser and mirror thought experiment?

A laser and mirror thought experiment is a theoretical scenario that explores the behavior of light and reflections using a laser beam and mirrors. It is often used as a teaching tool in physics to help understand concepts such as reflection and refraction of light.

## 2. How does the laser and mirror thought experiment work?

In this thought experiment, a laser beam is directed at a mirror and the resulting reflections are observed. The laser beam is coherent, meaning that all the light waves are in phase with each other. As the light hits the mirror, it reflects off at an angle equal to the angle of incidence. The reflections continue until the laser beam is interrupted or absorbed.

## 3. What can we learn from the laser and mirror thought experiment?

This thought experiment can help us understand how light behaves when it reflects off a surface. It also demonstrates the principle of the Law of Reflection, which states that the angle of incidence is equal to the angle of reflection. Additionally, it can be used to study the properties of mirrors and the effects of different surfaces on the reflection of light.

## 4. Can the laser and mirror thought experiment be applied in real-life situations?

Yes, this thought experiment can be applied in real-life situations. For example, it can be used in the development and testing of laser technology, such as laser cutting and engraving. It can also be used in the design and construction of optical devices, such as telescopes and cameras.

## 5. Are there any limitations to the laser and mirror thought experiment?

One limitation of this thought experiment is that it only considers ideal conditions, such as perfectly reflecting surfaces and a coherent laser beam. In reality, there may be imperfections in the mirrors and the laser beam may not be completely coherent, which can affect the results. Additionally, this thought experiment does not take into account other factors that may influence the behavior of light, such as diffraction and interference.

• Optics
Replies
6
Views
885
• Optics
Replies
26
Views
4K
• Special and General Relativity
Replies
26
Views
605
• Optics
Replies
17
Views
2K
• Quantum Physics
Replies
2
Views
389
• Optics
Replies
9
Views
1K
• Optics
Replies
8
Views
1K
• Optics
Replies
8
Views
2K
• Quantum Physics
Replies
16
Views
2K
• Atomic and Condensed Matter
Replies
10
Views
2K