Photon Definition and 1000 Threads

In relativity, momentum of a body is given by ##p=mv/\sqrt{1-v^2/c^2}##, but if mass is exactly zero and velocity is exactly ##c##, how is the photon momentum even defined? I don't think this problem can be resolved by simply stating the other formula relating energy to momentum, since it was...

Let's say that we're sending a collimated beam of EM radiation through a slit that's 3 cm wide, and it diffracts and forms a clear interference pattern on a screen, with the bands of brightness and darkness, or of high and low intensities. And next, we reduce the intensity of the beam until it...

Are there any kind of observed and experimentally verified processes or mechanisms where photon emission occurs and which are directly cause by spacetime expansion in some way?

This is just a curiosity to me. My interest is from the position of a layman (as you will see from my description below). In the double slit experiment it shows a wave passing through both slits and interfering with itself to create an interference pattern. This is how I understand it... From...

When a photon is absorbed, electrons move from a lower energy level to a higher energy level, so my answer is a, b, c, and f. I don't understand why the solution is b, c, d, e. Can electrons in this case move from a higher to lower energy level? Thank you.

I can't find the anwer on this anywhere, so I hope I may ask it here. My question: In a standard double slit experiment, according to the Many Worlds Interpretation, does the photon create different worlds with different impact locations of the photon? So, without measuring which way...

Hi PF. I desire deeper understanding of fundamental physics, and quantum mechanics can be a challenge for me (compared to other topics in physics). I read in the intro of the physics textbook chapter that QM explains many phenomena, e.g. why copper conducts electricity and glass does not. In...

Is this known in QFT or is this "spontaneous".

In a double slit experiment with one photon sent at a time, the wave function Ψ of the photon reaching the screen is a superposition of Ψ1 (photon going through first slit) and Ψ2 (photon going through second slit). At the screen, Ψ1 and Ψ2 interfere (i.e. the photon interferes with itself)...

While this was inspired by another thread, I think the question is different enough that it can be asked separately. It's also more suited to this forum than the forum where the question that inspired this one was asked. Wiki gives four possible interactions for interactions of gamma rays with...

In the video above we can see the wave like patterns. The microscope on the video, used on the experiment, has a low quality and a low magnification. If anyone has a scientific article or a video source for such experiment with low magnification but with a high quality of definition it would be...

I've been reading Computer Graphics: Principles and Practice by Folly and I've encountered the following paragraph in chapter 1.5. I haven't understood how he got to the result in the following calculation, that if there exists a single 100W light bulb, emitting an order of ## 10^{12} ##...

(0:00 / 0:42) photon going light-speed blender simulation I have no idea how a mathematician would translate this example into an equation. Every time I've worked with soft bodies I seem to run short of mathematicians buddies. Regardless of the mathematics of continuous object deformation, this...

I have come across an old formula from my notes and I have no reference for it but it is using truncated digits in its formula to calculate the redshift for decoupling. The formula is nearly as accurate as the observed data from Planck 2018. So I would like to figure out the derivation of those...

How does the polarization of a photon impact the state change of an electron that absorbs it? Presumably the change of an electrons state (including spin) differs based on the polarization of the photon it absorbs.

Are photons left- and right-handed? If so, does the handedness change when a photon is reflected? Is there any other way the handedness can change? -- Jeff, in Minneapolis

Hi everyone, background for my question is here: and https://www.researchgate.net/publication/45424433_Direct_generation_of_photon_triplets_using_cascaded_photon-pair_sources: My question is whether it's possible to determine if two photons are entangled without using a coincidence counter...

We know that as speed increases, time slows, and at the speed of light time apparently ceases. Imagine a hypothetical hitch-hiker sitting on a photon and speeding through the universe at -- well, the speed of light. If time has stopped for him (her?), what is his experience of his journey? Are...

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...

I am aware that one usually starts from the Maxwell equations and then derives the masslessness of a photon. But can one do it the other way round? The action of photon would be ##S = \hbar \int \nu (1 - \dot{x}^2) \mbox{d}t##, where ##\nu## is the frequency acting as a Lagrange multiplier...

If I look at the photon propagator <A_mu (x) A^nu(0) > in momentum space, as I understand it I am to compute this by summing up all the self-energy diagrams of the photon, which look like: photon -> stuff -> photon In particular, since the photon shares the same quantum numbers as the Z, you...

What diameter does a photon have? Does it vary and if so within what range?

If you have γ+γ→γ+γ what would the Feynman diagram look like (time-ordering implied). I think it will be a square with four photons on each vertex but is this all there is to it or am I missing something?

Why we know that average speed of a single photon(in point particle view) equal the speed of EM wave?If average speed of a single photon smaller than c then there exist massive photons?

I was just reading on this forum (and other sources) about the relationship between photon spin and the polarization of light. From what I have gathered, photon spin corresponds to circular polarization: +1 and -1 spins correspond to right and left helical polarizations. So I have a few...

We know that we can not cut a single photon into many photons. So that there must be a single color for a single photon?Because if a single photon has many color then it will be dispersed through prism(so a single photon would be cut into many photons(?))

I was taught that photons ( non-ionizing at least) never interact. So Its really bugging me that most info on faraday effect invokes B field as the cause of ( for example) rotation effects. Since EM-waves (IE Photons) themselves propagate a (oscillating) Magnetic field through infinite space...

Summary:: Hello I am a writer and presently working on treatment for a science-fiction story. So I am not a scientist, just a neophyte interested in science and wanting to write a fiction that would not be too far-fetched and that would make some sense for everyone, including the scientific...

This is from Problem 7.45 of Thermal Physics by Daniel Schroeder.

Could someone ell me if photon has mass? How can light have its direction changed by massive bodies?

A photon often travels billions of years (Gyr) through the CMB photon gas (410 photons per cubic centimeter) to reach us. Does it travel freely? Let’s share our thoughts about this. For discussion purpose, let’s assume the photon has a wavelength of 500 nm, close to the peak of the solar...

When a photon travels through space it is spreading out like a fan while in its superposition (except that it is spreading also vertically in addition to horizontally). So, what happens if for instance the right outer edge of the photon's superposition is captured by the gravity of a black hole...

I have been developing a SPAD based photometer having a 10 ns deadtime, near-zero dark counts, near-zero afterpulsing, and that is temperature independent (within a reasonable range). It works well with photon level pulsed optical signals, (10ns to several microsecond pulse widths at rates up...

Hi Guys ! Previous question was to determine the energy of photon with wavelength = 820nm I found that E = 2.42x10^-19 J = 1.51 ev using the equation E=hc/wavelength - I tried to solve the above problem with various equations but all failed. The closest equation i tried is...

During time evolution of one photon with vacuum state with hamiltonian as a^†b+b^†a, the answer is cos(t/ℏ)|0,1⟩+isin(t/ℏ)|1,0⟩. But i don't know how to do calculation to get this answer. Can someone please help me? I tried to do this calculation: |0⟩|1⟩(t)=e−iHtℏ|0⟩|1⟩...

But then I learned a photon can be split into two or even three photons (red-shifted, energy is conserved), and also photon can lose energy and still be a photon (Raman effect, inelastic scattering). Now, I am not sure what it means when it is said photons are quanta of light (smallest unit of...

Bumped into this video after admiring the falling cat by @A.T. As an experimental physicist, indeed experienced a little of the 'hole in the brain' phenomenon!

I would like to know, how can we be sure this is not due to the influence/impact/interference of our measurement, not necessarily the intrinsic nature of photons? In most reference books, it seems it is a given and it is not discussed

If the answer is Yes, then I would ask, if the mirror absorbs a portion of the energy of the photon, so the photon should simply stop existing because we cannot have a smaller package of light than a photon. If the answer is No, then I would ask why a beam of light (which is made of a big...

The information I have are the following: ##p^\mu=(E, p, 0, 0)## ##p'^\mu=(E', p'\cos\beta, -p'\sin\beta,0)## ##k^\mu=\tilde{E}(1, \cos\alpha, \sin\alpha, 0)## Where: ##E=\sqrt{M^2+p^2}## ##E'=\sqrt{m^2+p'^2}## Using the conservation of the four-momentum ##p^\mu=p'^\mu+k^\mu##...

Hi. As i understand in double slit experiment photon can arrive at slits through different paths (longer and shorter) and it would still show interference pattern. My question is - if there was some path cutting device in a way of photon (on longest path after length that photon arrive at...

In Theoretical Minimum: Quantum mechanics, Leonard Susskind describes an electron in the higher energy spin state in a magnetic field radiates a photon of energy ##\hbarγ|B_0|## and flips into the lower energy spin state. I am wondering if this photon is related to the "virutal photon" that...

Optical photon is produced e.g. during deexcitation of atom, carrying energy, momentum and angular momentum difference. So how is this energy distributed in space - what is the shape and size of single photon? Looking for literature, I have found started by Geoffrey Hunter, here is one of...

I have calculated the Christoffel symbols for the above given metric, but I don't understand how to calculate a photon's four-momentum using this information. I believe it has something to do with the null geodesic equation but I can't understand how to put that information into the problem...

E=hf

I understand that any accelerating charged particle will emit a photon. But I do not understand how the rate of acceleration relates to the photon that is emitted. For example: If a proton is falling to Earth in a vacuum at 9.8 m/s^2, then what are the characteristics of the photon that will be...

Suppose we receive a cosmic microwave background (CMB) photon from space. According to the Big Bang model, this photon became free to travel when the universe was about 0.38 million years (Myr) old. At that time, it was about 42 million light years (Mly) away from our location. Because of the...

I've attached a picture of a table in Sean Carroll's The Particle at the End of the Universe. It says that photons don't "feel" electromagnetism, but gluons feel the strong force, the W and Z bosons feel the weak force, and gravitons feel gravitation. How is this so? (I have no formal quantum...

Wikipedia: "When a photon has about the right amount of energy to change the energy state of a system (usually an electron changing orbitals), the photon is absorbed." What happens if a somewhat higher energy photon arrives?