The photon (Greek: φῶς, phōs, light) is a type of elementary particle. It is the quantum of the electromagnetic field including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always move at the speed of light in vacuum, 299792458 m/s (or about 186,282 mi/s). The photon belongs to the class of bosons.
Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, their behavior featuring properties of both waves and particles. The modern photon concept originated during the first two decades of the 20th century with the work of Albert Einstein, who built upon the research of Max Planck. While trying to explain how matter and electromagnetic radiation could be in thermal equilibrium with one another, Planck proposed that the energy stored within a material object should be regarded as composed of an integer number of discrete, equal-sized parts. To explain the photoelectric effect, Einstein introduced the idea that light itself is made of discrete units of energy. In 1926, Gilbert N. Lewis popularized the term photon for these energy units. Subsequently, many other experiments validated Einstein's approach.In the Standard Model of particle physics, photons and other elementary particles are described as a necessary consequence of physical laws having a certain symmetry at every point in spacetime. The intrinsic properties of particles, such as charge, mass, and spin, are determined by this gauge symmetry. The photon concept has led to momentous advances in experimental and theoretical physics, including lasers, Bose–Einstein condensation, quantum field theory, and the probabilistic interpretation of quantum mechanics. It has been applied to photochemistry, high-resolution microscopy, and measurements of molecular distances. Recently, photons have been studied as elements of quantum computers, and for applications in optical imaging and optical communication such as quantum cryptography.
Hello,
I've been running into some frustrating issues with my MCNP deck. Photons are getting lost which is terminating the run file prematurely. When consulting the output file there seems to be some sort of geometry issue, but there are no fatal errors that I can see so I'm lost on how to...
I have heard it suggested that the random scatter of photons passing through a single slit can be explained by appealing to the HUP. The slit constrains the particle in the Y direction introducing an uncertainty in the Y momentum. A simple calculation leads to a formula which is at least...
Hello! i need help in such case. I want to simulate the interaction of gamma photons with only oxygen (O) atoms in MCNP, while am using the material card for silicon dioxide (SiO2). Which card shall I use to get the photon interacted with only the oxygen component separately. Thanks for help.
My understanding is (was) that "virtual particles" is a computational concept used in perturbation calculations in QFT e.g. in Feynman diagrams. This understanding is in conflict with the following note in Quantum Field Theory for the Gifted Amateur by Tom Lancaster and Stephen J. Blundell:
and...
Before boost we have
Then using the Lorentz boost:
I want to calculate:
I tried multiplying the matrices together but I never get the stated answer which should be:
I was reading this paper (https://academic.oup.com/mnras/article/288/2/387/960778) where they analysed how CMB radiation is affected by evolving voids in an expanding spacetime (particularly through the Rees-Sciama effect and the integrated Sachs-Wolfe effect).
This effect predicts that photons...
In the Delayd Choice experiment, it seems as if the photon kan "knows" what is going to happen before it happens, at least thats one interpretation of the results. Is maybe the fact that the photon, traveling at speed C, maybe relevant? It does not "experience" time? It would be nice to hear...
I have been working for some time on designing an experiment and have gotten stuck on one particular aspect. I would greatly appreciate any advice that can be offered. I'm using SPDC to produce two polarization-entangled photons. Through the course of the experiment I know that one of the...
Recently saw this video.
"Why No One Knows If Photons Really Are Massless: What if they Aren't?"
Arvin Ash
He says photons need not be massless, but they must be quite light nonetheless. He separates speed of light from speed of causality. Is it true that we can't know its mass below a...
IE = KZ(Em – E)
where IE is the intensity of photons with energy E, Z is the atomic number of the target, Em is the maximum photon energy, and K is a constant. As pointed out earlier, the maximum possible energy that a bremsstrahlung photon can have is equal to the energy of the incident...
if matter and anti-matter meet, they annihilate each other. Gravitons are anti-photons and photons are anti-gravitons. They MUST meet in immesurable quantities in our universe. Yet gravity exists, and light exists in our known universe. This denies the annihilation necessity. And annihilation...
I am a new user of MCNP and I am trying to generate photons in ZnS:Ag through electrons as my source particle. My simulation as it is now creates photons however they are not right. For example ZnS:Ag should create a lot of photons with energy of around 3.1eV. However I see a spike around 4.8eV...
In this video how are the entangled photons later used and actually identified as an entangled pair amongst billions of others.
Also does he really mean the photon is split or is the quantised energy split with half frequencies?
Not directly from the core, but a trajectory that goes to the event horizon, and gets corrected to a perfect, perpendicular bisector path by the gravity of the core, when it reaches the event horizon.
Would they escape the event horizon, since they have to always move at c? On this trajectory...
Hello everyone!
I don't know where to look for information - maybe here it will work :)
Is there a generator of entangled photons with fixed polarization?
If not, is it theoretically possible to build or is it against the laws of physics.
I need this knowledge for further computer...
The effective mass density of photons in a vacuum ##\rho^{vac}_M## is related to the photon energy density ##\rho^{vac}_E## by
$$\rho^{vac}_M=\frac{\rho^{vac}_E}{c^2}.$$
Is it true that the mass density of photons inside a medium of refractive index ##n##, ##\rho^n_M##, with phase velocity...
Now if two different time durations are measured for one and the same event by two different observers, for example T+1 and T-1 seconds. Is the speed of passage then (T x c)/(T+1) and (T x c)/(T-1) respectively? So not c?
You may be wondering…, and yes, there is an example of it!
Hi
Would you explain to me what is the q^ and how they are related to completeness.How can i solve this exercise?It is from "Quarks and leptons An Introductory course in Modern Particle Physics" of Halzen and Alan D.Martin.Also, can you point me to a useful bibliography?
Consider a source emitting a beam of photons. These photons pass through x thickness of material. The attenuation coefficient of the beam \mu is known.
We can write this formula
If I'm not wrong, this formula tells us the number of photons that passed through the material of thickness x...
In some cases, photons can be produced in "back to back" (BTB) conditions. For example, electron-positron annihilation produces two photons, each at 0.511 MeV, with equal and opposite momentum. Or pretty close, up to the original velocities of the electron and positron.
Start with a source of...
Recently I've stumbled across a preprint in which the author describes a photon is a wave packet and even suggests a transverse extent.
I find it strange, as my understanding so far has been that a photon (and the EM field as such) is a construct used to model certain observed interactions...
(Beginner) - W.o. going into particle/wave duality, we know the resultant image came ONLY through something going through this nano opening we left uncovered. We also see that the resultant image still neatly shows diff. colors. But ALL the objects reflecting are sending different colors...
Hi Pfs,
consider a pair of maximally entangled photons where the total momentum is null and the same thing for the total angular momentum.
I suppose that this pair is like an universe: nothing outside the pair acts on it except maybe a device for the measurement of these two properties (no local...
What kind of imaging system could be used to see without photons? I ask because I was watching a video and the furthest we can see back is Redshift Z~1090 which is the CMB. We can’t see the universe before the first stars formed or the Big Bang itself. My first guess would be some kind of dark...
So, I have a question.
The time dilation formula is:
t = t₀ • 1 / √(1 - v²/c²)
Let's take a photon that travels at c. In my opinion, for a photon "clock doesn't tick" and its life is just a moment.
But when we calculate time dilation by this formula, then c over c is 1 and the root of 1 minus...
In classical physics we know photon emits when electron move from higher to lower state but in nuclear fusion photon emits when neutron turn into proton. Is both correct?
The integrated Sachs-Wolfe effect occurs when a photon goes through a gravitational potential that changes due to spacetime expansion (presumably caused by dark energy). For that reason, a photon going through a gravitational well would gain energy (blueshift) when entering and it would lose...
while the photon travels at light speed and a neutrino travel at just below light speed why then are photons stopped by an object and the neutrino can past through?
In Kaur, M., Singh, M. Quantum double-double-slit experiment with momentum entangled photons. Sci Rep 10, 11427 (2020). https://doi.org/10.1038/s41598-020-68181-1 and in C. K. Hong and T. G. Noh, "Two-photon double-slit interference experiment," J. Opt. Soc. Am. B 15, 1192-1197 (1998) it is...
What is it of the photon that gets polarized from a quantum mechanical perspective? In the classical perspective it is often thought that it is the oscillating electric field that gets polarized. But in the quantum case: Is it the de Broglie wave function? Or is it the spin and in case it is the...
I am not sure if this is the way to ask questions here but having nobody to ask and little time, i hope i can get a fast reply here.
So since the scaler the universe above us i.e. bigger than us is so huge and we aren't even sure about it further than sight (acc to my book), isn't it just like...
Since high frequency photons have more relativistic mass, should we expect them to bend more than lower frequency lights when traveling through a gravitational field, thus produce a rainbow effect? But we don't seem to experience rainbow effects with star light.
Hello,
I have a little problem understanding Young's slit experiment with single photons :
I have understood for a long time that each photon impact on the screen corresponds to a photon sent by the source, and that, if we don't try to find out by which path the photon has passed, of course...
why is the result not like a movie screen where you are projecting 300 films at the same time, over each other ?
(I would get it, if each object only sent one discrete beam, the next object another one, and so on, but it is a cone, of equally strong photons, being projected everywhere, into your...
I can understand how ##\phi (x)|0\rangle## represents the wavefunction of a single boson localised near ##x##.I don't understand how the same logic appies to ##A^{\mu}(x)|0\rangle## and ##\psi |0\rangle##. Both of these operators return a four component wavefunction when operated on the vaccuum...
I found out about this interesting paper through a Tweet by Steven Thomson.
https://arxiv.org/abs/2108.05169
https://www.nature.com/articles/s41467-022-31608-6
Relativistic Bohmian trajectories of photons via weak measurements
Joshua Foo, Estelle Asmodelle, Austin P. Lund, Timothy C. Ralph...
I saw that we can talk about the light as particles (photons ) or as an electromagnetic wave , the question is that do we represent other electromagnetic waves (like microwaves or radio waves ) as particles (like we do with light ) ?
[Moderator's note: thread spun off from previous thread due to topic/level change.]
This [Ed.: the claim that photons have a "path"] is a misconception of quantum theory already for massive particles. It's even more severely misleading for massless quanta of spin ##\geq 1##, which do not even...
(My multipart question is from a very naive perspective, so sorry if it is rife with misunderstandings. Please answer conceptually, with as few & as simple equations as possible. I think that all of the answers to these questions should be understandable to a high schooler, though maybe the...
As I understand it, photons are subject to the same time and space distortions under SR as anything else, which is why they don't perceive time or space, since they travel at the speed of light. To an outside observer, then, they should appear stationary, immobile at their moment of creation...
Hi there. I am attempting to do calculations for my own project, the question being what is the attenuation necessary to reduce the number of photons in a beam to single-photon levels. N approximately 1 or 2.
The laser in question is a 650nm 5mW laser.
I have solved the energy per photon...
I was reading Diagrammatica by Veltman and he treats the photon field as a massive vector boson in which gauge invariance is disappeared and the propagator has a different expression than in massless photon. After some googling, I found that this is one way to formulate QED which has the...
P=mv *momentum equals mass X velocity.
Light particles or "photons" are said to be "massless". And yet they have
momentum. How is that possible? (p.s. I used to know the answer)
Hello, I am a student who started studying MCNP. I'm not used to writing in English, so I'd appreciate it if you could understand even if there were grammatical errors in my thread.
I want to check the energy of gamma rays from neutrons reacting with matter. So, I wrote this in the content of...
Tentatively, I ask in this forum for a qualitative pointer to what end effects one might expect when a gamma energy photon energizes an atom of a substance, and causes fluorescence. It relates to a practical endeavour about using a PIN diode as an X-ray detector, where the device considered...
Can someone please explain the four classes of fundamental particles? (Just the basics) I came here because I never learned any chem or physics in school so please explain like I’m five :)