# B Why waves of light don't hit each other?

1. Mar 5, 2016

### aiop

How do waves interact, What happens when two waves with the same frequency and wave length hit each other. Would the resultant change if it was lets say an X-ray hitting an Gama-ray. That is if waves can even hit each other.

2. Mar 5, 2016

### Ranvir

No, they interfere, if that's what you want to call hitting. Do light waves scatter each other? I don't really know.

3. Mar 5, 2016

### Staff: Mentor

The waves simply overlap, with the total electromagnetic field being the sum of all the waves. If the waves have the same frequency, this can lead to regions of constructive and destructive interference, like in the double slit experiment.

Note that the same behavior is observed for other kinds of waves, like sound waves or waves at the surface of water.

For a very high intensity of light, photon-photon scattering is possible, but it has not yet been observed.

4. Mar 5, 2016

### aiop

But how can the waves simply over lap as well on water.
So if when describing light in waves they over lap, what about when describing light as a photon with particle light properties do they go straight through each other.

5. Mar 5, 2016

### 256bits

What is your envision of a photon?

6. Mar 5, 2016

### Staff: Mentor

Why not?
Light is not made out of billard balls.
Photons do not even have a well-defined position.

7. Mar 5, 2016

### aiop

like a wave of water that also can have particle like properties. not sure how to tie that part in to the image though, How could light with particle like properties just go through each other... i don't understand how that could be possible.

8. Mar 5, 2016

### aiop

But how can two different waves for example move through each other they don't have mass but are made out of energy and energy of two different levels if lets say a Gama-ray and a X-ray hit each other would they not have some reaction. When for example hot air moves through cold air they do react by transferring energy and that is just a matter of a difference in energy. so what makes light so special?

9. Mar 5, 2016

### Drakkith

Staff Emeritus
Light isn't a particle like a dust grain is a particle. It is not composed of solid pieces. It is simply alternating electric and magnetic fields. The "particle" property of light is that it interacts in discrete chunks of energy. There's literally no physical particles to imagine here, as you might imagine a water wave.

10. Mar 5, 2016

### aiop

But when imagining water to be like a light wave i run into a problem. Water waves go up and down because of gravity's pull so why would a light wave go up and down if light does not have mass. I know its alternating electric and magnetic fields but why would they behave as a wave with out something to pull the waves making them waves and to cause them to alternate. How do light waves alternate?

11. Mar 5, 2016

### Drakkith

Staff Emeritus
They don't go up and down. The electric and magnetic fields alternate in polarity and magnitude as the wave travels. As for why, well that's a consequence of electrodynamics and is not something easily explained without getting into the math.

12. Mar 7, 2016

### HallsofIvy

Haven't you ever watched water waves cross each other? Where "peaks" cross "peaks" the heights add, where "troughs" cross "troughs" they subtract but once they have passed on each leaves the other untouched.

13. Mar 8, 2016

### Passionate Eng

___________
then, how could photoelectric phenomenon be explained?

14. Mar 8, 2016

### phinds

You don't seem to have really read the post you are responding to. I'll repeat the significant part, relative to your question "The "particle" property of light is that it interacts in discrete chunks of energy."

15. Mar 8, 2016

### Drakkith

Staff Emeritus
Let's say that an EM wave with a wavelength of 198.6 nm interacts with the metal and transfers 1 joule of energy to the metal over the course of one second. If we were to look very closely, we would find that this energy was transferred to the metal in 1018 individual "bundles" or "chunks". Each of these bundles contained 10-19 joules of energy, no more no less. All of the energy was contained within these bundles and any EM wave with a wavelength of 198.6 nm would have a quantity of energy that is a multiple of 10-19 joules. These bundles are called photons.