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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How can absorption spectra form if atoms can't remain in an excited state?

I have been tasked to write a research paper on stars. However, I know very little about physics in general. I am learning about how we can glean information about stars by analyzing the light that ...
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1answer
165 views

Why does light not slow down?

Clearly light bounces off of things, going really really fast. I'm curious to understand how light interacts with matter in order to bounce without: Applying force to the object Losing speed So my ...
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966 views

Is a photon technically a set of two particles?

When looking at the classification of massless particles, one finds that there is the (half-integer) quantum number "helicity" $h$. For every possible $h$ there is a certain particle kind. In the case ...
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Number of different wavelengths in the visible spectrum reaching Earth

I recognize the visible wavelengths of light extend from approximately 400 - 700 nm. But how many different wavelengths exist in that range? 300 ? 30,000 ? (400.01 - 699.99) If it's completely ...
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49 views

Relation between number of photons and energy?

Please can anyone explain it. If number of photons are increased will it increase the providing energy. Suppose, we are sending a limited number of photons each carrying energy. We have a energy ...
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1answer
47 views

Does light have a gravitational pull? [duplicate]

I understand that everything with mass does have a gravitational pull no matter how small the object, which means even a grain of sand has a gravitational pull. But light is something that exists, ...
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69 views

What is the speed of a Photon? [duplicate]

How fast does a Photon travel through space? And is gravity able to influence a Photon's path?
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27 views

where does the kinetic energy of electron revolving in nucleus go when photoelectric effect takes place?

we all have been studying that when photon is incident on alkali metal surface, photo currents are created due to ejection of electron after exceeding the work function.but the electron do have ...
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84 views

How can a photon have a frequency but not a phase?

When a single photon is emitted as a result of relaxation of an electronic energy level, it (the field) is clearly in a Fock state because it has a well-defined number of quanta. By the uncertainty ...
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22 views

Calculation of energy deposit of photon beam

Let's say I shoot a 1 MeV photon beam onto a volume. I want to know the ratio of deposited dose per path length for different materials (water and air) at a certain position (e.g. x=0) in the volume. ...
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2answers
25 views

Laser beam sensed by scattering

Can a laser beam, whether it is a IR laser or of the visible to human eye spectrum, be seen/sensed by an electronic eye like a photosensor/photodetector, not human eye, if the beam is just in air? For ...
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17 views

Gamma photon excitation of electron

Can a single high energy photon excite more than one electron in an atom?
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129 views

How hot is your photon?

This question comes from my answer to the question Can a cubic meter of space at absolute zero have any object with mass inside? and the related discussion under it. To summarize, I stated that the ...
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1answer
43 views

Can someone reconcile the Boltzmann transport equation with the Maxwell equations for photons/light?

Having taking courses in both physics and nuclear engineering, I've noticed that the two fields tend to describe photons/light in two different settings. In nuclear engineering, the radiative ...
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3answers
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Do Photons Move in a Wave Like Pattern [duplicate]

In many pieces of literature, light is said to travel like a "wave". Does this mean the light literally propagates through space like a wave as in up and down and so on or does light move linearly ...
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0answers
27 views

The path that light travels [duplicate]

This is a question that has puzzled me for some time. As a star emits light, the light travels away from the star. If you were to pick any spot on the star and draw a line extending outwards and then ...
2
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3answers
64 views

Laser beam photon counting

I'd like to know if devices exist that are able to detect the single photon missing out of a normal laser beam. I am aware of the fact that single photon counters do exist, but I'd like to ask some ...
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2answers
46 views

How can solar sails be maneuvered?

Photons from the Sun are always radial to it and hence solar sails can only travel radially. Any techniques related to maneuvering?
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1answer
49 views

Under what conditions would photons interact to create pair production? [closed]

I understand that two photons colliding can result in pair production but under what conditions would this happen? Would the photons have to be in a superconductive state or is it just by chance, as ...
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2answers
448 views

Is there anything that could attract and trap a photon?

Is there any particle or anything that could attract and trap light or photon particle? Can anti photon particle attract photons and trap them ?
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2answers
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What would influence two or many photons to collide and create an electron-positron fermion pair?

If there were billions of photons around in nothing - no gravity, no electromagnetic fields, etc., what (if anything) would cause the photons to interact in a way that would cause a collision ...
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2answers
109 views

Explain the notion of light/electromagnetic waves/photons to a non-physicist

A non-physicist asked me about special relativity. My explanations naturally were based on gedankenexperiments involving light. This forced the question: "What is light? It is particles, isn't? Or is ...
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2answers
83 views

Are the photons released by trees the same generated by the sun?

According to Feynman in this youtube video the photons that are released when a tree burns are sort of those that were trapped during photosynthesis. Are these the exact same photons produced by the ...
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1answer
64 views

What happens when two photons collide? [duplicate]

From a little research done it seems as though they would create subatomic particles (maybe electrons?)If so, would photon collisions technically create matter? Is this a widely thought of theory?
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1answer
67 views

What is the total matter equivalent of the Sun's output per year?

Say we can collect all the energy from the sun's output and all the particles from the solar wind. If we had an energy to mass converter and turned everything into say, carbon, how many kilograms of ...
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63 views

Can photons “stop time”?

If traveling past the speed of light causes time to reverse than does traveling in time make time "stop"? If not then how do photons/mass-less particles experience time, if at all.
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2answers
83 views

What would be the photon's effective mass in Newton's Law of Gravitation?

If we equalize the force from the Newton's Law of Gravitation to Force on a photon in a gravitional field (I don't know if there is an equation for it). What would be the photon's effective mass? (I ...
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40 views

If 2 photons collided head on, what would happen? [duplicate]

If 2 photons, in perfect synch (frequency, amplitude, etc. were all equal) and they collided head on, what would happen? Would they pass right through each other? Would they interfere, then go back to ...
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47 views

How does electron excitation work for the Bohr model with non hydrogen atoms?

I've seen a lot of explanations of electron excitation by photons in the Bohr model but they all use a hydrogen atom which only has one electron. How does the excitation work for atoms with more ...
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2answers
66 views

Is colour a purely quantum effect?

If the colour of an object is determined by the wave-lengths of light that is absorbs and reflects (?) then can colour be described as a purely quantum effect (i.e. without quantum effects an objects ...
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1answer
44 views

Why photons are having energy when they are massless? [duplicate]

As per the Einstein equation $E=mc^2$, the energy of the particle is depends on the mass of the particle. Or else in other terms the energy is proportional to the mass. If the photons are having zero ...
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4answers
236 views

How can we prove that a photon is absorbed only once?

When I first heard about the photons and the double-slit experiment my immediate thought was the following: Alright, energy is not absorbed continuously but in discrete units, photons, but nature ...
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1answer
74 views

Calculation of the efficiency of a Carnot engine for photon gas

I am working on a problem considering the Carnot cycle for a photon gas. The cycle has two isothermic processes at $T_{H}$ and $T_{C}$ and two adiabatic processes. The entropy of the photon gas is ...
3
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1answer
483 views

Width of a photon. And its length

Everyone is always talking about photon's wavelength. But what about its dimensions? What is length and width of it? And does it even have a point to think about such things? Or those dimensions are ...
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96 views

How can a single photon or electron create a small visible dot on a photosensitive plate?

The photon or electron is just one subatomic particle, but if it hits the film and creates a dot visible to the human eye (btw, modern technology can do this), then the dot must be a collection of ...
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121 views

Slower than light photons in vacuum?

This report on the BBC site suggests that optical photons have been prepared that travel slower than c in vacuum. How is this possible?
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Can photons travel through space independent of time?

I read an article about advanced photons and they stated that photons traveled back in time to hit an electron. Can photons really travel back in time and if so, how?
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32 views

Intuitive model to show difference between photon energy and light intensity?

What would be a good (intuitive, easily comprehensible) model to explain the quantum nature of light insofar as there is a fundamental difference between intensity and photon energy? One example (not ...
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1answer
251 views

Can very high power laser beams self focus in vacuum?

I first recall reading about such an effect in a SF story entitled "Rails Across the Galaxy" which involved self focusing laser beams. And in a science paper here
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Are there any theoretical limits on the energy of a photon?

Is there any lower or upper limits on the energy of a photon? i.e. does the mathematical framework we currently use for Quantum Mechanics blow up when a photon surpasses a certain upper limit of ...
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59 views

Combination of 2 photons in opposite phase

We can explain conservation of energy in interference phenomena by saying that there is redistribution of energy. However if only 2 photons in opposite phase "combine" then how can we explain ...
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40 views

What happens when light is reflected from a surface moving in a medium with a huge refractive index?

Imagine a mirror is moving away from a light source in a substance through which the speed of light is very slow -- so slow that the speed of the mirror is close to being the same as the speed of the ...
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3answers
62 views

What are high energy photons?

I have often read the term High Energy photons, does this mean that there do exist photons with low energy? Aren't they supposed to have constant energy according to $E= h\nu$?
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I want to know why light even moves at all.

Never mind in a vacuum, why and how does light even move at all? What propels it?
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If two photons collide, does the resulting particle have zero velocity?

If two photons traveling in opposite directions along the same line collide, will the resulting particle have a velocity of zero relative to the rest of time space in the instant of the collision?
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1answer
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Increasing the efficiency of photovoltaic power cells

Given that solar cells use one or more semiconductor materials to convert light to electricity, and that the efficiency of that conversion is dependent on the material and the wavelength of the light, ...
3
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1answer
88 views

In how many possible ways can a photon be emitted?

I am currently studying atomic physics, and I encountered the question above. I am posting this question because I can't afford to move on with even the tiniest bit of uncertainty in my understanding ...
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1k views

Do we really not know why atoms 'decide' to produce a photon?

I was watching the Cosmos documentary where Neil deGrasse Tyson explained how certain energy photons get absorbed by an atom, which causes the electrons of that atom to climb into a higher energy ...
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2answers
147 views

What is the frequency of a single photon? [duplicate]

What frequency means for a single photon?