Photons as a wave traveling in a vacuum

In summary: The wave picture is not the only way to view light. As you know, light can also be thought of as a stream of particles, called photons. However, this particle picture is not as intuitive and easy to understand as the wave picture. It is only when we get to the quantum level that the particle nature of light becomes apparent.So in summary, light can be thought of as both a wave and a particle. The wave picture is more intuitive and easy to understand, while the particle picture is only necessary at the quantum level. The properties of light can be explained by its interaction with electric and magnetic fields, as described by Maxwell's equations.
  • #1
Mr. Gus
1
0
I'm extremely uber layman, so forgive me for any ignorance or stupidity and my excessive use of the word "so".

I'm failing to understand either what light is or how it can travel through space (or both). I read that light is photons, and photons are particles that have no mass, and are a wave. So my understanding of that is that photons are not so much physical substance as they are energy that effect some aspect of physical substance.

So if it was a wave as in sound, it causes vibrations in the air of our atmosphere. A literal wave or ripple comes from vibrations of the surrounding water. So if photons as a "wave" are directly analogous to sound or a ripple in a pond in how they work, then that means that there is some sort of medium or atmosphere that they are effecting, and it is this effect on whatever medium or atmosphere that exists that we are measuring and referring to as photons and light.

So if this above is more or less correct, and space is really an empty vacuum apart from the odd rocks and debris, how does light get transmitted by nothing for millions or billions of years? Is there really something there that is transmitting light waves? Or is light really a physical something that is just moving really fast, and my lack of a proper scientific physics-based understanding of what mass really is is messing me up?
 
Science news on Phys.org
  • #2
Mr. Gus said:
I'm extremely uber layman, so forgive me for any ignorance or stupidity and my excessive use of the word "so".

I'm failing to understand either what light is or how it can travel through space (or both). I read that light is photons, and photons are particles that have no mass, and are a wave. So my understanding of that is that photons are not so much physical substance as they are energy that effect some aspect of physical substance.

So if it was a wave as in sound, it causes vibrations in the air of our atmosphere. A literal wave or ripple comes from vibrations of the surrounding water. So if photons as a "wave" are directly analogous to sound or a ripple in a pond in how they work, then that means that there is some sort of medium or atmosphere that they are effecting, and it is this effect on whatever medium or atmosphere that exists that we are measuring and referring to as photons and light.

So if this above is more or less correct, and space is really an empty vacuum apart from the odd rocks and debris, how does light get transmitted by nothing for millions or billions of years? Is there really something there that is transmitting light waves? Or is light really a physical something that is just moving really fast, and my lack of a proper scientific physics-based understanding of what mass really is is messing me up?

Photons are particles - tiny indivisible objects that can be counted. In this respect they are not much different from other known particles, like electrons, protons, etc. Photons have zero mass, but this is not that important. Rules of relativistic quantum mechanics permit existence of massless particles.

As all other particles, photons obey Rules of Quantum Mechanics. These rules basically say that propagation of particles in space is (to a certain degree) random. Generally, it is not possible to predict at which point in space the photon will be found if we decided to measure its position. Such a prediction can be done only probabilistically. Quantum mechanics provides rules for calculating these probabilities. According to these rules, the probability distribution should be obtained as a square of photon's wavefunction, which obeys a wave equation. This is where all wave properties of photons (diffraction, interference, etc.) come from.

The wavefunction should not be imagined as some kind of "substance" propagating in space. Actually, wavefunctions are just mathematical abstractions, whose only purpose is in assisting our calculations of probabilities of observed physical events (like detection of photons at a certain position in space). Since wavefunctions are not material "substances", there is no point to invent any "medium" for their propagation.

Eugene.
 
  • #3
Mr. Gus said:
I'm extremely uber layman, so forgive me for any ignorance or stupidity and my excessive use of the word "so".

I'm failing to understand either what light is or how it can travel through space (or both). I read that light is photons...

everybody just loves to jump into the whole "photon" discussion, don't they.

you might rather start off by thinking about the old ho-hum description of light as an electromagnetic wave... since that's how light, as we normally experience it--I.e., the stuff that goes into your eye that you actually see--is most conveniently described.

a charged particle gives off an electric field which puts forces on other charged particles, it the charged particle shakes and shimmies about then the electric field shakes a bit too, and if the shaking is in such a way that a wave can be produced (like the way that electrons in an antenna shake) then the shaking of the electric field can propagate out like a wave--it is a wave--an electric field wave, and that's light.

I admit that the above is a little vague, and if you really want to understand light you have to understand Maxwell's four equations which I have cutely unified into one equation for you (forgive me, I couldn't resist, I still a bit tipsy... gaussian units btw):

[tex]
(\nabla\cdot\vec E-4\pi\rho)^2+(\nabla\cdot\vec B)^2+(\nabla\times\vec B-4\pi \frac{\vec j}{c}-\frac{\partial \vec E}{c\partial t})^2+(\nabla\times E-\frac{\partial B}{c\partial t})^2=0
[/tex]

cheerz
 
  • #4
olgranpappy said:
a charged particle gives off an electric field which puts forces on other charged particles, it the charged particle shakes and shimmies about then the electric field shakes a bit too, and if the shaking is in such a way that a wave can be produced (like the way that electrons in an antenna shake) then the shaking of the electric field can propagate out like a wave--it is a wave--an electric field wave, and that's light.

This continuous electromagnetic wave representation does a good job at explaining properties of high intensity light, which we experience in our everyday life. What about extremely low intensity light consisting of one or two photons? How can you reconcile its apparently discrete nature with your continuous wave description?

Obviously, your classical electromagnetic wave description is not valid in the low-intensity regime anymore. It should be replaced by a quantum theory. However, we know that the two-slit interference picture has exactly the same shape whether it was created by a high-intensity lightbulb or by photons released one-by-one. If we accept your logic, we should conclude that the same effect (interference) is described by two completely different theories in the high-intensity and low-intensity regimes. In the high intensity regime, the interference is due to vector addition of vectors E and B from different parts of the wave. In the low intensity regime, the interference is due to addition of complex wavefunction amplitudes.

It is more economical to have a single theory for all intensity levels. The quantum approach is general enough to cover both (high and low) limits. Then the question is: how classical vectors E and B are expressed through the quantum photon wavefunction? I don't have a good answer for this question yet.

Eugene.
 
  • #5
meopemuk said:
This continuous electromagnetic wave representation does a good job at explaining properties of high intensity light, which we experience in our everyday life. What about extremely low intensity light consisting of one or two photons? ...

well, the OP asked about "light" which commonly refers to photons en masse and at eV scale energies...

Obviously, your classical electromagnetic wave description...

Oh, I wouldn't call it "my" description. It belongs to men much greater than I.


Then the question is: how classical vectors E and B are expressed through the quantum photon wavefunction? I don't have a good answer for this question yet.

nor I. Something to do with coherent states, etc, maybe...

certainly I can write down a free-field expression for an electric field operator E and then consider expectation values
[tex]
<E>
[/tex]

Cheers.
 

1. What is a photon?

A photon is a fundamental particle that makes up light. It is considered both a wave and a particle, and has no mass.

2. How does a photon travel in a vacuum?

A photon travels in a vacuum as an electromagnetic wave, with an oscillating electric and magnetic field perpendicular to each other. This wave travels at the speed of light.

3. Can photons be affected by gravity?

Yes, photons can be affected by gravity as they have energy and mass. This means they can be bent by massive objects, such as stars or black holes.

4. Can photons be destroyed?

No, photons cannot be destroyed. They can only change form or be absorbed by matter, releasing their energy.

5. How do photons interact with matter?

When a photon encounters matter, it can either be absorbed, reflected, or transmitted. The way it interacts depends on the properties of the material, such as its density and atomic structure.

Similar threads

Replies
4
Views
661
Replies
4
Views
9K
Replies
4
Views
2K
  • Optics
Replies
4
Views
1K
Replies
5
Views
5K
Replies
3
Views
684
  • Quantum Physics
Replies
17
Views
1K
Replies
78
Views
3K
Replies
6
Views
1K
Replies
16
Views
1K
Back
Top