# Tag Info

## New answers tagged photons

Accepted

### Energy of photons in perfect mirror box with FRW metric

If the box has a fixed size, then the energy of the photons will be conserved. If the box is expanding or contracting, then the photons will lose or gain energy, respectively. Thermodynamically, the ...
• 6,449
1 vote

### Why can't thin clouds form rainbows?

You only see a bright, first-order rainbow when you are looking toward rain or mist and the Sun is behind you. Also, You said, "Sunlight easily passes through thin layers of cloud." That ...
• 15.2k
1 vote

### Why can't thin clouds form rainbows?

Clouds are complicated. There are lots of different types of clouds, which may be composed of spherical or non-spherical water droplets, with uniform or non-uniform sizes; planar or columnar ice ...
• 91.5k

### Energy of photons in perfect mirror box with FRW metric

Great question. Thing to note is that expansion of the universe is inertial, scale factor is not constant. Scale factor inside your box is 0. So no, your photons don't lose energy and all mass is ...

### If the probability of a point (photon) hitting another point (electron) is zero why do they interact?

Elementary particles are point-like in the sense that they can get arbitrary close to each other. They are not point-like in the sense their position is a point in space. Their position is spread out ...

• 358k

### Is a photon truly massless?

The correct version of your syllogism is: $E=mc^2$ for a particle at rest. For a photon, $E>0$. For a photon, $m=0$. The correct conclusion is that a photon can never be at rest.
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### Is a photon truly massless?

Light has inertia: it takes a force to change the direction in which they travel, and if you have a box with light bouncing around inside of it, it takes more force to change the speed of the box than ...
• 14k

### Photonic black holes

For the sake of argument, let us simplistically take the photon energy $E=hf$, and see what kind of black hole we get. The Schwarzschild radius of a given parcel of energy $E$, which has an equivalent ...
• 9,500

### Photonic black holes

"According to electromagnetic theory, the rest mass of photon in free space is zero and also photon has non-zero rest mass, as well as wavelength-dependent. The very recent experiment revealed ...

### Why does radiation of small wavelength interact with small objects?

Your bullet analogy applies in the sense that the bullet is analogous to the macroscopic thermal "damage" caused by lower frequency, longer wavelength microwave radiation, while the higher ...
• 73.7k

### Photonic black holes

A photon in a box has mass and pressure. Put it in an impossibly small box and it'll theoretically make a black hole.
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### The speed of a QM particle

Mass particles can travel at any speed (so long as it is less than that of light) depending on how much energy was invested in accelerating them.
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### How is light interference explained with photons?

Now, if we model light as collections of photons, how is light interference explained? It is explained the same as classically. Classically there is an electromagnetic field that obeys Maxwell’s ...
• 103k

### How is light interference explained with photons?

Feynmans PI basically says if we consider many paths (like in a computer simulation) the sum/phase squared info shows paths that are full wavelength multiples are preferred (more probable). This ...
• 2,699
Accepted

### Why does the up and anti-up quark combine into a pion and not a photon?

Particle annihilation occurs when a particle meets its corresponding antiparticle, converting their mass-energy into two photons. This is a useful oversimplification. Even electron-positron pairs, ...
• 91.5k
For a first-generation quark-antiquark pair (up-antiup or down-antidown) to have a high probability to form a neutral π meson ($π^0$) these conditions must be satisfied : Color charges should be such ...