Photons Definition and 1000 Threads

First off, I must ask if the reflection of a photon is truly an elastic collision; is it? If it is, then wouldn't that mean that there is perpetual momentum? And if that is true, then can't this momentum be converted into perpetual energy? Apparently, they have successfully trapped a...

Hello all, I am asking this question in the context of general relativity. In general relativity the stress-energy tensor is related to the spacetime metric through the Einstein field equations. The production of a curved spacetime is what creates what we call gravitation. For example a...

Homework Statement A ray of photons coming from a laser with a wavelenght of 589.59nm meets a ray of sodium atoms (A=23) coming from the opposite direction. What is the maximum speed the sodium atoms can have in order to absorb photons? The Attempt at a Solution I thought about...

I am currently capturing and analyzing spectra. My analysis software includes allowances for Doppler shifts resulting from relative radial motion between source and observer, and also Earth’s rotation. Results are accurate . The basic introduction to the Doppler effect generally starts with...

Hi guys, I'm new to this forum... I was just reading the link given below,posted by ZapperZ, describing as how photons propagate in the form of phonons in medium like glass... https://www.physicsforums.com/showthread.php?p=899393#post899393 and a question it struck to me, In the last...

I am working on Weinberg, Cosmology book. I am currently reading Chapter 6. At the last paragraph of Page 257, Weinberg said these equations take a simple hydrodynamic form for cold dark matter and ..., but for calculations of high accuracy it is necessary to use the Boltzmann equations of...

Entangled photon-pairs are being produced in labs with 'Spontaneous Parametric Down Conversion' apparatus. While in the core of our sun gamma photons are being produced through nuclear fusion which then down-converted into myriad of low-energy photons. Is it possible that those myriad of...

Homework Statement The problem is taken from A Modern Approach to Quantum Mechanics by Townsend, and is stated as follows: The answer given in the back of the book is 0.12, though I have not managed to get this result. Homework Equations Classically, light traveling through a crystal...

For outside observer, an object falling into black hole seems to freeze at event horizon and never cross the boundary and proceed inside the black hole. This is of course not the case in the falling objects own reference frame. Depending on the size of the black hole, a falling object may not...

I am learning quantum mechanics from Feynman Lectures on Physics. Where he says that amplitude of alternatives that can't be distinguished interfere with each other. I am trying to understand some simple phenomenons using this principle. My query is, when photons of different energy come from...

Okay, so when a photon travels near an electron orbiting some atom, the electron then absorbs the photon (given that it has enough energy) and causes the electron to jump up an energy level. My question is what happens when a photon has a little more than enough energy to bump up the electron...

I have heard that photons do not have any mass which is why they travel at the speed of light. However consider the following thought experiment. You are box in space accelerating at 1 G. From your perspective, you are in a gravitational field of 1G. If you shine a light from one wall of the...

Now another question , We have two types of charges , positive and negative ones. The field between them (electric field) is said to be also positive and negative , but the particle that mediates the electric and electromagnetic field is photon which has no charge.(chargeless) Now the...

I've been thinking about this for a while. I believe I have some misconceptions about light. Let's say we have a photon that is emitted from some atom as it de-exictes. It has definite momentum since it is of a specific energy. Where is it located? Let's ignore the issue of trying to pin down...

If we have twin photons moving in the opposite direction. For the first photon we can pass it through a polarizer that will either output a photon with vertical polarization or a photon with horizontal polarization. after this experiment we now know what will the other unobserved photon...

Relativity says photons have energy E=pc. Classical physics says E=1/2 pv. There seems to be a factor of 2 missing in one case or the other or does the energy formula change as the speed of light is reached? There must be a simple explanation but I have not found it yet. I did not know where...

I was reading a book called "Hyperspace", by Michio Kaku, and there he gave a sort of introduction to general relativity. Well its not at all technical, just for reading and knowing... There he claimed that space is curved because light rays will take a bent path inside an accelerating...

Since this is my first post on this forum, I would like to start by saying: Hello everyone! :smile: Now let's get straight down to business: Over the past few months, I have been doing quite a bit of research in terms of physics, and have had the following questions pop up. I've...

My goal is to build a software program that simulates the function of the eye. As I (barely) understand things, a single photon can bounce off an object and enter my eye. Q1 - Does the photon determine the color? If not, what determines the color of that single wave/particle? Q2 - How...

If something is traveling at the speed of light, its time stops to a relative outsider. But photons (basically light) are traveling at the speed of light... So does that mean that to me the photons are stationary? But if they are stationary, then they're not being reflected off an object and...

Hey all, my first post here. I'm 17 years old and am taking physics at A level. (Just finished my end of year exam today) So the understanding I have of light is that it is the oscillation of an electric field and of a magnetic field perpendicular to each other. I've come to the conclusion...

Homework Statement So we have a source (OP) that emits single photons of a constant wavelength and angular frequency. The photons hit a 50-50 beam splitter, and are then reflected in the mirrors. Where is says (L) ou (SP) (yay for studying in French!) there is a beam splitter. What I...

Hi! I'm not sure this is exactly the right subforum, but here goes: Homework Statement So we have a source (OP) that emits single photons of a constant wavelength and angular frequency. The photons hit a 50-50 beam splitter, and are then reflected in the mirrors. Where is says (L)...

Hello, I have a question that i'd like to ask, but the wording is a little tricky, so I hope you can get the gist of what I'm trying to describe. I was thinking about the thought experiment that is often used to describe relative motion - a light clock on a train passing through a station...

This isn't a homework question, though it kind of relates to a practical I did recently. Sorry if it's posted in the wrong section! So, why are only 2 photons formed from positron-electron annihilation at rest? I understand why you can't have just one, as then you won't get conservation of...

My general question is: can high energy photons convert into many lower energy photons? Could the reverse reaction occur spontaneously? Let's say we have a single photon that was emitted from a distant supernova. We detect it here on Earth. The photon hasn't converted into multiple lower...

does every electromagnetic radiation consist of photon?

Greetings people of Physics, I was just having a think about E=MC2 (as is common with people these days... probably) and if we assumed that a random photon had an energy of 3 Joules, and we rearranged E=MC2 to work out the mass (M=E/C2), it would mean that our photon has a mass of...

For every one billion anti-matters in the universe, there needs only one billion and one matter particle counter-parts to create the universe today. Don't we also know that they annihilate into photons? Following that logic, can't we assume 2billion/(2billion+1) is the percentage of...

If energy is kept constant and intensity of photons is increased, will the threshold frequency be lowered? I ask because I'd like to understand this graph - http://www.flickr.com/photos/coachrobbo/3909285882/ "lower intensity same frequency" causes stopping voltage to be lowered, thus...

So i am taking the MOOC of Galitski et al on Exploring Quantum Physics. I like it. But i keep running into some difficulty with my understanding of what it means to quantize a static EM (or E or M) field: Is the field made up of photons? If so, are they somehow moving at the speed of...

Hello i have a little clarification to make for myself with the help of you:) So we know that electricity moves so fast through the wires because the charge is being "pushed" by the EM force which is mediated by the photon. Now AC systems no matter what the frequency have real photons...

I understand that in GR mass is considered a distorting of space-time. If you had a teleporter which transmitted an object's energy perfectly as photons to be reconfigured at a perfect reciever at the destination location, whilst in transit as a (very high energy) light pulse, would the same...

Hi guys, This is probably a basic and therefore stupid question, but hey, I'm new. When a photon hits an atom, it's energy is 'absorbed' and the electron (if we use hydrogen as an example) jumps up an orbit. It then naturally wants to loose this energy to settle back into it's ground state...

Homework Statement A typical incandescent light bulb emits ~3x10^18 visible-light photons per second. Your eye, when it is fully dark adapted, can barely see the light from an incandescent light bulb 10 km away. How many photons per second are incident at the image point on your retina...

Although it is well known that a series of individual photons will build up an interference pattern in a double slit setup, there have been few (if any) experiments where such a pattern is built up by sending photons through one at a time. Here is a great experiment from one of the top quantum...

Homework Statement The diagram is attached. Photons are being beamed with momentum \rho_{0} and mass m at a slit of width A Estimate the uncertainty \Delta p_{y} emerging from A Sketch spot size at B as a function of slit width using the uncertainty principle Determine minimum spot size...

It is often said that the photon is the long range force carrier like the static force between electrons. Let's say we have two electrons galaxy apart, wouldn't the virtual particles have to travel long distances and "virtually" become real. And isn't the first sentence is wrong anyway since...

A) I want to understand electricity in terms of quantum theory. as I understand photons are the carriers of EM energy so how do photons trasfer energy from electric company or battery through a wire. and the connection to electron movement (do electrons from one atom bum into another...

Homework Statement \rho(\lambda)d\lambda=\frac{8(\pi)hc}{\lambda^{5}}\frac{d\lambda}{e^{hc/(\lambda)KT}-1} What does this represent? Calculate the number of photons per unit volume in a blackbody from \lambda to d\lambda Homework Equations N/A The Attempt at a Solution I...

We know electric current travels around 200000 km/s.. Yet electrons are moving way much slower, just acting as a medium for the transportation of the energy. Can same principle apply for light? Although the energy flows at 300000 km/s the photons may actually not? Like, the energy traveling...

Hi all - thank you for this forum - it's proving very helpful: Am I correct in thinking that if we measure a period of time that light travels, that in the case of red vs blue light: 1) Both will travel at the same speed in a vacuum? 2) More blue photons will arrive than red (given...

The photon as I understand it is a massless particle that "must" travel at the speed of light. However I do not understand the idea that a photon is also the carrier of the em force. If there is a simple ball of static charge and a test charge comes near do photons exchange between the two...

Me and my teacher have been arguing, whether photons have or don't have mass. I say that it's impossible for photons to have mass, but my teacher says that we can calculate the photons mass. So my question is, can photons have mass?

As an atmospheric physics major I am familiar with electromagnetic radiation in the atmosphere and what dictates what wavelength objects will emit at. When observing radiation in the atmosphere it is always thought of as a wave, whether it be longwave or shortwave. Recently though I have been...

I am wondering about photons having mass. The new thing on all the space shows is the sailing through space with a sail that harnesses photons as a ship harnesses wind. They did an experiment and the photons exerted a force on the sail. Am I wrong to think that E=mc^2 (E can not be 0 so M can...

Hello, New to this forum. Very fascinated with physics. Started as a fascination with waveforms, sound, acoustics, and quickly spiraled into an infinite fascination with physics in general, specially particle physics at a quantum level and general relativity at a cosmic level and nuclear...

NOT including the prediction capabilities of the particular math equations of GR or SR. In particular, hard evidence such as, or close to; here's an electron, because we measured it directly, or saw it in an electron microscope. Or here's a cell under a microscope. Or this is a brain scan/MRI...

Hi all, If we have any setup that causes diffraction with light, such as a single slit, and count the number of photons detected at a certain point behind this slit, is it true that we can determine this count as follows: 1. Consider each point in the slits a new wave source, and calculate...

I imagine this gets asked a lot but I'm looking for an in depth explanation since none of the others I've found are detailed enough. I understand that p = mv is not applicable near the speed of light and I think (but am unsure) that the correct equation to use is e = pc. Assuming that e =...