Photon Definition and 1000 Threads

hi, recently i have been struggling with the concept if photon exists without traveling at velocity c ? i knew c is constant only when it travels trough space and when it travels through other medium with refractive indexes it does not exist at all .. is it true ? how do scientists define why...

Homework Statement A particle of mass m is at rest in the lab frame. The particle discharge a photon with energy 1/2mc^2 to the direction of x+. A spaceship is moving at v = 0.8c in the direction x+ (in the same direction the photon is moving). What is the total energy of the particle after it...

Homework Statement The question I have is simple enough: at what energy do an electron and a photon have the same wavelength? Homework Equations I know that for a photon, λ=\frac{hc}{E} and for an electron, λ=\frac{hc}{\sqrt{E^{2}-mc^{2}}} The Attempt at a Solution I can't just equate...

So I know that a linearly polarized photon is in a state ψ = cos(θ)\left|x\right\rangle + sin(θ)\left|y\right\rangle What if θ depends on time maybe something like θ\equiv\frac{E_{0}t}{\hbar}? The polarization is linear at any time t, it rotates as time passes? Isn't that circular...

Gravity effects the energy of a photon per the equation GM/c^2r. I understand that a photon traveling on a crash course with a black hole will be blue shifted according to the hole's mass, however I'm a little confused as to what happens when a photon simply passes nearby a massive object. For...

A photon is emitted and then absorbed. And since a photon travels at the speed of light, time does not exist. So that should mean that a photon is in either a state of emission or a state of absorption. Doesn't that make a photon a type of bit? Furthermore - if there is no time involved...

Hi yall, I have a few questions in regards to EM radiation and photon density, or energy density; not sure what exactly the correct term would be here. (1) Anyway, first off, excluding the possibility that a black hole would form, is there anything that would limit EM radiation energy density...

Is it possible, in theory, that the physical entity electron e(-) and its charged opposite positron e(+) both obtained their respective electric charges by simultaneous capture, by a more fundamental quantum entity (call it FQE), of a quantum of photon with zero rest mass having equal amounts of...

the wiki article on vector meson dominance says "hadronic components of the physical photons". How can a photon have hadronic photon components? Could someone please enlighten me?

Hi all, What is the relation between RAMAN Intensity and Energy of the photon and/or bond stregth and/or bond energy? Is there any equation or sth explain it easily? If you can explain it in a simple way, I will appreciate. Thanks

Hi, i have a question about SR. would happen if two bodies were moving away from each other at exactly .50c, and one body emitted a beam of light the opposite way it was traveling just as the other was passing? I know that simultanety is relative, but what if someone moving on the body that...

Good morning everyone ! I've been reading discussions on PF for a long time, but here I'm stuck on a little problem that really annoys me and I couldn't find answer anywhere, so I guess it was time to register. :> I've been focusing on quantum electrodynamics for a couple of weeks now as part...

hi all, I have a couple of questions. is there a limit to how much energy can be stored in a photon? And why does the spectrum only go to gamma rays? And what is the higest observed energy and what made it ? Thanx in advance

I'm studying spontaneous emission and I'm in trouble to understand the following: In a hydrogen atom we have distinct energy levels with different energy values associated to them. E1 = -13,6 eV E2 = -3,4 eV E3 = -1,51 eV To go from the first to the second energy level we need a photon...

I found the explanation of the radiation here, in the document of the Purcell Simplified: http://physics.weber.edu/schroeder/mrr/MRRtalk.html I like it, however I'm ucertain how to fit this to the light, as photon. Am I thinking correctly, that this figure fits also the case when a...

If I reach the speed of light which is 300 00 km/s the time will stop! and if I travel faster then light i'll travel to the past (Please Correct me if I'm wrong) I read that the Neutrino is faster then photon (light) so how can be this possible ?! Because if it is really faster than light that...

Homework Statement Consider a nucleus which is initially at rest and in an excited state with energy Ei. It then decays to a lower energy state with energy Ef by emitting a gamma-ray photon. Show that the energy of the photon is approximately given by Eγ≈ΔE−(ΔE)^2/(2mc^2) where ΔE = Ei - Ef...

I recently learned that a free electron can't absorb a photon and derived it by showing it would be impossible to conserve both momentum and energy if that were the case. It seems like the same argument would extend to other fundamental particles. Is it true that no free fundamental particle can...

Hi all, What is the highest frequency photon ever seen, whether in nature or the lab? This is based on an earlier post of mine, but I think has merit as its own post. Since E=hf, there is no maximum freq or energy of a photon, it seems, on a max freq of a photon. It seems that such high...

I understand that electromagnetic radiation is a photon. But one thing that is continuing to bug me is the question how does a photon, which is defined as a particle not a wave, have a wavelength? Do photons travel as packets in some sort of a compression type wave similar to sound?

I heard Neil deGrasse Tyson talk about the life of a photon that was emitted from the Sun and hit oneself. He said that its entire life was an instant. I hope I'm not misquoting or misunderstanding what he said. With that in mind, does that instant take into account the thousand of years...

Good evening fellas, I'm in a bit of a conundrum: lately I've been considering a 2D array of atoms and the interactions that may arise when studied with photon beams. Up until now, I was using in 3D systems, but when I switched to 2D, I got some unexpected intensity at the boundary of the...

can a photon have a perfectly smooth orbit? say for e.g. you have a photon orbiting a point, if its wavelength were to become twice the diameter of its orbit then would the wave not become a replica of the orbit offset by the amplitude? similarly say the amplitude is the radius of the...

Does it make sense to talk about the amplitude of a photon? In my mind, the amplitude of the photon is the maximum strength that the electric and magnetic field gets as they oscillate. If you were to change the amplitude of a photon (say increase), then the maximum strength of the e&m fields...

Part 1: Homework Statement Use two coupled-wave equations for the Raman amplification process depicted to the right to show that for every photon at Stokes frequency omega_s created (destroyed) one photon in the laser pump field omega_L is destroyed (created). I have the coupled-wave...

I think I understand this only up to a point. 1. Photon spin is quantized to be +1 or -1 and these represent left- and right-hand circular polarization. 2. A photon can have a superposition of 2 spin states in any proportion. 3. Having probability amplitude of 0.5 of spin 1 and 0.5 of spin -1...

Hey everyone, This is my first time posting on PF! I want to model the photons ejected from a blackbody source at temperature T. The question I want answered is: given a photon is detected, what is the probability of the photon having a wavelength λ? This amounts to just attaining the...

Hello. I know that light exerts pressure. My question is how can light exert some kind of a force? If it exerts a force, it means that there has to be a change in momentum but light clearly can't go slower and it doesn't change its wave length after the bounce. If it is able to move a solar...

...a mass? not matter how fast it hits an object, it doesn't have mass. F=ma. (explain without any equations or without too many equations.)

Homework Statement There's an elastic collision between a photon of energy E and an atom in an excited state. After the collision, the energy of the photon is still E but its direction changed of angle of 180° and the atom is now going back with velocity Bc. If the atom is in his ground state...

Homework Statement Hello everybody , a/There's an elastic collision between a photon of energy E and an electron at rest. After the collision, the energy of the photon is E/2 and propagates in a direction making an angle theta=60° with the initial direction. Find E. What kind of photon is this...

Hi all! I have been told that if an unpolarized photon hits an electron in a Thomson scattering the outcoming photon will be polarized because of the electron's spin. I didn't understand what it means, nor do I get how an electron reacts to an unpolarized photon: in Classical Electrodynamics...

Hi guys, I'm constantly bothered by one assumption in my textbook..it says that the photon emitted by the accelerating electron boiled off from the cathode colliding into the anode, has E=hf neglecting the work function, since its negligible. I'm curious whether it's E=hf plus or minus the work...

I am a beginner to QFT and I try to plot the Feynman diagram for the photon self-energy. Following Mandl-Shaw book (page 109 Eq. 7.22) \int d^4x_1 d^4x_2 (-1)\mathrm{Tr}(iS_F(x_2-x_1)\gamma A^-(x_1) iS_F(x_1-x_2) \gamma A^+(x_2)) but when I try to convert it to momentum space I get \int...

Let a monochromatic plane wave impinge on a collector of area A, delivering power P. Let the average photon rate of arrival on the collector be B. Now make the collector move toward the source at velocity v. By the Doppler effect, the frequency, and hence the energy, of the photons will...

When electromagnetic waves of different frequencies interact, they give rise to secondary wave structures called envelopes in which individual waveforms form at the rear and die out at the front. These envelopes are called groups and they travel with a velocity called group velocity and the...

My question is as follows: A photon clock (two 100% reflective mirrors exactly parallel and photons whizzing in between) actually possible. My question is made assuming we could get the mirrors exactly parallel. So really, I suppose my question is: Are 100% reflective mirrors possible to make...

Homework Statement An electron of wavelength 1.74 \times 10^{-10} m strikes an atom of ionized helium (He+). What is the wavelength (m) of the light corresponding to the line in the emission spectrum with the smallest energy transition? Homework Equations Kinetic Energy...

Hello PF people, Homework Statement In a Compton scattering event, after the collision, the Photon has an energy of 0.12 MeV and the Electron has an energy of 0.04 MeV. Find the following: i) The Wavelength of the photon before the collision. ii) The scattering angle for the photon...

Homework Statement In special conditions, it is possible to measure the energy of a gamma ray photon to 1 part in 10^15. For a photon energy of 50 keV, estimate the maximum lifetime that could be determined be a direct measurement of the spread of photon energy. Homework Equations...

Say it has xnm wavelenght. It hits an atom that reflects it, then another different atom absorbs it, why? Also what determines if particles like free neutrons or some hadrons will absorb a particular wavelenght? Why does gold absorb all wavelength except yellow and why does it also seem...

Is it possible a single photon to be seen by using any existing scientific equipment? I mean seen , after it is caught and enlarged on a photo or computer monitor, the way we can see a very small object. I mean a photon directly , not a picture of effect it may produce when interact with the...

The photon, "time" and entropy (ignore original title, in fact id appreciate if a mod would change it. It was not my intention to have a conversation about time, lol!) Can we view a closed system of just photons, as ever, or usually, being subject to entropy (defined by the whole 2nd law...

on a visible spectrum scale what are the numbers for the colors of ROYGBIV? for example is violet 400-500nm and red is 700-800nm? how about the other colors? If the energy of a photon is 2.63 x 10^-19 J, how can we tell what color this is? i was looking at this electromagnetic spectrum and it...

Time in the "reference frame" of the photon and as well curved spac Hi there! I understand the tendency of physicists to stick to the math, and the logic itself, and to often avoid attempting to conceptualize a process or law, but that's kinda the opposite of what I'd like to do here. I...

Imagine that an excited hydrogen atom in the symmetric 2s state emits a photon. We use a birefringent crystal to split the photon into vertical and horizontal components. Is the phase relation between these components random or is it the same for every photon emitted by a similarly excited...

If a photon does not experience space-time does that mean it cannot "degrade/fray"? Is there a way to reconcile the, say, eight minutes, time the photon (approx) took to travel from sun to Earth with the zero time that passed in the (frame of reference of) photon? Where was the photon, in a...

What is a photon? Does it have mass?(if no then why it has momentum) it travels with speed of light? Has it some wavelength associated with it,that can be calculated by De Broglie wave equation?

So firstly, the book supplies the answer of \Delta\lambda = \frac{h}{2mc} I use energy and momentum conservation. I say the total energy is that of the incoming photon, which is then changed to energy of the photon released, and kinetic energy of the atom, from the recoil. I say the same...

we know that particle having rest mass cannot reach speed of light,c. but if we apply results of special relativity to a photon,then it seems that for a photon 1)there is no time and 2)length is contracted to zero. 1) so does that...