The photon is the quantum of the electromagnetic four-potential, and therefore the massless bosonic particle associated with the electromagnetic force, commonly also called the "particle of light". Use this tag for questions about the quantum-mechanical understanding of light and/or electromagnetic ...

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Photons straight into black hole

What happens to a photon shot straight into a black hole? Does it gain infinite momentum before it crosses the horizon? If it has a finite momentum going in, then it would seem that a photon of the ...
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Photon emission and absorption by atomic electrons

Assume a photon is produced by an atomic electron making a transition down from a certain energy level to another. Can that photon only be absorbed by another atomic electron making exactly the ...
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114 views

Suppose a light wave with wavelength 3m. What happens if one tries to contain that wave within a 1m container?

Suppose a light wave with wavelength 3m. What happens if one tries to contain that wave within a 1m container? If I'm going about this entirely the wrong way or have wrong conceptions about light ...
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Intuitive understanding of wavelength

Light is described as having wavelength. I can somewhat understand this in connection with for example the double slit experiment, that photons interact spatially in a wave like manner. But can the ...
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Optical Bloch Oscillation

I have a doubt about how the optical Bloch oscillations happen in a 1D photonic crystal. I try to explain: in a photonic crystal with discrete translational symmetry in one direction I superimpose a ...
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156 views

If a photon's emission is detected is it real or virtual?

I understand that one can measure a single photon being absorbed using a photomultiplier tube or CCD. Can one measure a single photon being emitted by monitoring the current through an LED or the ...
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86 views

What is the significance of the difference in the eigenvalue equations of Bloch functions for electrons vs photons?

any text on photonic crystals will highlight the almost perfect analogy between electrons in a periodic potential and photons in a periodic dielectric. The analogies are: $$V(\vec r + \vec R) = ...
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Comparing predictions and reality for the gravitational attraction due to light beams

While doing some on-the-side reading, I stumbled across this question: Do two beams of light attract each other in general theory of relativity?. Great question and a great, easily understandable ...
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What happens to a photon when it enters a black hole?

The photon has a mass of 0, but it has energy because of its motion. When it is sucked into the black hole and becomes a singularity, it loses its energy because it is no longer moving. It is not ...
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113 views

Can a wave exist on the “face” of a wave?

It would seem that this would be possible with waves in water. What about other waves Clarification: Given a wave starting from a point of impact, in water, at: Time 0:00 and xyz 0,0,0 and the ...
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311 views

Sign in the photon propagator

The Klein Gordon propagator is given (I use Peskin and Schroeder's conventions, if it matters...), \begin{equation} \frac{ i }{ p ^2 - m ^2 + i \epsilon } \end{equation} The photon propagator ...
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Can we expect the discovery of something that moves faster than light/photons?

As our knowledge on M-Theory improves in the times ahead which may unfold some warped dimension, can we expect the discovery of something that moves faster than light/photons?
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If photons don't have mass, how can they accelerate objects? [duplicate]

As far as I know photons don't have mass but they do have momentum ($p=mv$). Scientists say that if we put a shiny (reflective) shield of large radius in the vacuum of space, then light from sun will ...
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551 views

where does the photon go after scattering?

My question is about photo electric but it could be applied to other daily routine phenomenon. As we know rest mass of photon is zero. When a photon strikes the ...
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43 views

Relection of light [duplicate]

If I recall my physics correctly, and it was a long time ago, when a photon strikes a reflecting surface that specific photon is not what is reflected--rather the photon excites an electron which ...
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300 views

Do photons and cosmic rays radiate energy through gravitational waves? If not, why not?

Due to the mass-energy equivalence, both matter and EM radiation bend spacetime, and both are capable of forming singularities (black hole, white hole/kugelblitz). In light of this, why do photons ...
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256 views

Orbital angular momentum of photon

People talk about orbital angular momentum (OAM) of photons. Is there some physical example that cannot be explained without assuming that photons have non-zero OAM? Does different photons have ...
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152 views

The speed of light as it approaches a massive body

No matter how fast you go, you will aways perceive the speed of light as constant. Taking that as a fact, the special relativity theory was formulated. Now, for what I understand about general ...
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is a single photon a wave? Is it a wave packet?

How could it split and interfere? How could a wave packet, with many frequencies, be a photon with one freq.? Thank you very much.
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What Causes the Noise Floor of Modern CCDs?

CCDs are getting pretty good these days, but all systems are subject to noise. A typical value for a CCD seems to be 20 electrons RMS per pixel. This article from qsimaging.com says CCD Read ...
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How is a photon emission energy balance maintained?

How is a photon emission energy balance maintained ? If an electron is in motion across space at 260,000 kilometers per second, and it releases a photon in that same direction of travel, the photon ...
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210 views

How far does a Photon's field Extend?

I read the related answer to whether photons have size, and the answer seemed to be it depends. If a Photon, or a rather an E&M wave has a magnetic and electric field, should things be able to ...
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889 views

How do electrons and photons interact?

Two electrons, or an electron and a proton, interact with each other because of the Coulomb potential, which can also be seen in the Schrödinger equation (which is the equation that describes the ...
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219 views

Atomic Physics: stimulated emission

I'm studying a chapter about atomic physics right now but there's thing I just don't seem to understand. When stimulated emission occurs, there's an incoming photon which stimulates the atom to go an ...
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Can we observe diffraction even if the slit size is tending to zero?

According to Huygens principle, if we consider any point of the primary wave fronts, each point is the source of secondary disturbance. If the point size we consider tends to zero, the number of ...
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Why can TV broadcasts send such large amounts of data(photorealism) and a PC cant

Firstly I think I am right in saying that TV broadcast are sent via electromagnetic waves which means they are sent via photons, how is that even possible? And then the main questions, how can you ...
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What is the energy distribution of light if it has an infinite length?

What is the energy distribution of light if it has an infinite length? I have read in one of the answers here on phys.SE that light has actually an infinite length. But then what is the energy ...
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how photons are said to be in momentum if they are considered to have no mass and no charge? [duplicate]

According to quantum theory,Einstein said that light waves have small packets called photons and they are said to have no mass and charge but having energy E=hv and they behave has both particle and ...
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48 views

What is the nature of Young's Double Slit Experiment with detectors?

If a detector is kept at the two slits the fringes disappear. But, when the detectors are removes do the fringes come up immediately without any significant time lag? Can there be a way to switch on ...
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138 views

Why photon-electron energy transfer can't occur in steps or does it?

The process of exchange of energy between a photon and an electron only occur after a specific energy called work-function of the material. Thus, the energy transferred is quantised due to the fact ...
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Do photons feel gravity of approaching objects only?

I have read that photons while travelling near massive objects such as the sun experience gravitational pull which is why we see some stars at different positions than they are when seen towards the ...
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2k views

What force particle mediates electric fields and magnetic fields?

The force carrier for magnetic fields and electric fields are supposedly photons. I don't get it: 1) Wouldn't that mean that a charged particle (e.g. an electron or even a polarized H2O molecule) ...
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55 views

Dual photon in d=3

In some papers (such as http://arxiv.org/abs/hep-th/9910184 and http://arxiv.org/find/all/1/all:+AND+kapustin+AND+topological+disorder/0/1/0/all/0/1) I am reading it is always referred at "the dual ...
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Does a photon instantaneously gain $c$ speed when emitted from an electron?

An excited electron looses energy in the form of radiations. The radiation constitutes photons which move at a speed $c$. But, is the process of conversion of the energy of the electron into the ...
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289 views

Degrees of freedom of the photon in $d=n$

It is well known that in ordinary $4$ dimension, the photon has on shell only two physical degrees of freedom. Physically this means its elicity is either $\lambda=+1$ or $\lambda=-1$ but cannot ...
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Polarisation of light is a wave concept or applicable to photons as well?

I have a very fundamental question. We explain polarisation of light assuming wave nature of light. Is it still valid if we assume light as photons? Or in other words, polarisation is a wave concept ...
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180 views

Why is photon annihilation associated with the POSITIVE frequency component of the electric field?

I'm reading Glauber's paper "The quantum theory of optical coherence". In his work he does not introduce the annihilation and creation operators, but he refers instead to the positive and negative ...
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Collision between a photon and a massive particle

Just a small question regarding collisions. Imagine a head-on collision between a photon and a particle with mass that moves with a non-relativistic speed, the particle was on its ground state, ...
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Do two photons traveling in opposite directions emit gravitational waves?

Do two photons traveling in opposite directions emit gravitational waves? If so, does it mean that any volume filled with photon gas will eventually degrade into graviton gas? In other words, if flat ...
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Does the photon emitted by an electron falling to a lower energy level have a direction?

When an electron falls from an energy state to a lower one, electromagnetic radiation is emitted. Is this equally emitted in all directions (as a spherical wave) and can we only give it a direction ...
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93 views

Photon number conservation during scattering

I was reading this writeup on the Kompaneets equation and the Sunyaev-Zel'dovich effect. On page 3, section 2 the author states There is no way to increase the mean energy of a planckian ...
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102 views

Is it feasible to transfer energy from power stations to communities via photons instead of electrons?

Electrical wires are relatively inefficient in transferring energy--especially when the place of production is quite far from communities. Would it be possible to transfer that energy via photons? I ...
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93 views

Quantum eraser double slit experiment

In the quantum eraser double slit experiment, does the photon (or wavefunction) pass through one slit or both slits when different polarizers are placed over the slits?
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The nature of the probability distribution for the energy of a photon released via stimulated emission

The vanilla description of stimulated emission (e.g. in the context of an inverted population laser gain medium) says that a photon with some state vector specifying its energy / polarization / ...
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Didn't Newton's Corpuscular theory fail to explain reflection?

In 1637 Descartes gave the corpuscular model of light and derived Snell's law. This Corpuscular model of light was further developed by Isaac Newton in his famous book entitled OPTICKS and because of ...
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Why do light disappears the moment we switch off the source (inside the wooden box)?

I am failing to explain why light won't remain inside the wooden box in the following situation. I considered a wooden box closed from all the sides, with a bulb inside it. If we switch on the bulb, ...
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How is the probability of intersystem crossing influenced by small differences in energy levels?

Say I have some dye molecule in some low level triplet state, e.g. $T_1$, and it's decaying slowly to the ground state via phosphorescence. However, there are also events where the dye in the $T_1$ ...
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139 views

How to smooth the spectrum of a light source?

Could somebody please tell me if there's a reasonably cheap substance or device can I use to smooth the spectrum of a light source? For example, if the spectrum has spikes as in the blue graph below, ...
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What is the relation between electromagnetic wave and photon?

At the end of this nice video, she says that electromagnetic wave is a chain reaction of electric and magnetic fields creating each other so the chain of wave moves forward. I wonder where the photon ...