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3 votes
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 ...
Sten's user avatar
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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 ...
Solomon Slow's user avatar
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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 ...
rob's user avatar
  • 91.5k
0 votes

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 ...
Alien from future's user avatar
0 votes

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 ...
Alien from future's user avatar
0 votes

Is Bell's Theorem Wrong?

People tend to overcomplicate this. When we have two entangled polarised photons and pass them through polarising analysers (A and B) the correlation probability is given by $$p = \cos^2(\theta_A - \...
KDP's user avatar
  • 6,132
-1 votes

What makes an electron jump down to lower energy level?

Because the electron’s electric charge is opposite to the charge of the nucleus (protons), so they are attracted to each other and, since there is at least another possible solution to the Schrödinger ...
Stefania's user avatar
1 vote

Energy and momentum conservation for photon absorption

As you point out, not all of the energy of the photon goes into exciting the electron, Similarly when stationary atom emits a photon, some of the electon level enenrgy goes into the recoil kinetic ...
mike stone's user avatar
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0 votes

What are some good resources for learning photonics?

I suggest reading the paper "The concept of the photon" by M. Scully and M. Sargent. Yariv, "Quantum Electronics," and "Optical Electronics," are excellent. I also ...
0 votes

Good book on quantum photonics and applications

I suggest reading the paper "The concept of the photon" by M. Scully and M. Sargent. This is a good start. Then, I recommend reviewing your classical EM stuff and being very comfortable with ...
6 votes

Could a single gamma ray photon break the Schwinger limit? If so, at what energy?

Consider an electorn-positron collision, and the subsequent production if photons. It is known that there must be at least two photons produced. This is because momentum must be conserved. In the ...
CompassBearer's user avatar
4 votes

Does photocurrent depend on intensity or on number of photons?

The current depends on the number of photons with high enough frequency(energy). 1 radio photon and 1 gamma photon will give you 1 electron, because gamma photon has enough energy to expell an ...
Alien from future's user avatar
5 votes
Accepted

Does photocurrent depend on intensity or on number of photons?

You have it right. You can idealize it as each photon kicks off one electron. (It might be really that each photon kicks off one avalanche.) So current is proportional to number of photons. If the ...
mmesser314's user avatar
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-2 votes

Can photons interact with one another?

Most of the time they interact by changing a medium which changes the properties that the photon sees. But another possibility is HOM interference, in which the possible outcomes of the different ...
Steven Sagona's user avatar
3 votes

Can photons interact with one another?

Photons can interact with each other. However, the interaction is very weak in the vacuum. I'm not sure this can be explained using a simple explanation from wave-particle duality. The full ...
Josh Newey's user avatar
0 votes

Is a photon truly massless?

Mass is not an inherent property of energy. It is a property energy can have, but does not always have. Specially, confined energy has associated mass, while free energy does not. A freely traveling ...
RC_23's user avatar
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5 votes

Is a photon truly massless?

I like pictures, and the relevant picture is: You can ignore the formulae, they are just high school trig, tho, so nothing prohibitive. (The do look bad, though, I think it's because they are crammed ...
JEB's user avatar
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11 votes

Is a photon truly massless?

Although everyone has heard of the famous equation: $$ E = mc^2 \tag{1} $$ few realise that this is a special case and applies only in limited circumstances. Specifically it applies only to a massive ...
John Rennie's user avatar
9 votes

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.
WillO's user avatar
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6 votes

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 ...
g s's user avatar
  • 14k
3 votes

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 ...
RC_23's user avatar
  • 9,500
-1 votes

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 ...
Ritzthephysibeast's user avatar
0 votes

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 ...
Bob D's user avatar
  • 73.7k
-2 votes

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.
John Doty's user avatar
  • 21.8k
0 votes

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.
niels nielsen's user avatar
2 votes

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 ...
Dale's user avatar
  • 103k
-1 votes

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 ...
PhysicsDave's user avatar
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2 votes
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, ...
rob's user avatar
  • 91.5k
0 votes

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

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 ...
Robin's user avatar
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