What is Photons: Definition and 1000 Discussions

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.

View More On Wikipedia.org
Recent contents Top users
  1. X

    Optical Noise Photons: Calculate Sun's Ambient Light for Detector Simulation

    I need this information for a simulation I am working on that involves optical photon detectors. Specifically, I need a rough figure for how many photons a photon detector would register per second if I were to place it in ambient light from the sun. I realize that this number depends on the...
  2. PhysicsKid0123

    "Topological" properties of photons?

    I was wondering, how does a photon look like? What does it look like? I'm taking modern physics at the moment and I'm able to calculate lots of things quite well. Like DeBroglie wavelengths, I'm able to utilize the Schrodinger equation and the Heisenberg uncertainty principle and what not but I...
  3. Bendelson

    Massless photons? Is everything light?

    Are photons massless? They have energy and can be affected by gravity, so don't they have mass? I've heard plenty of people say that photons are massless, does this just mean that they have negligible mass? Also, if only light/photons can move at the speed of light, then wouldn't everything be...
  4. J

    Explaining the Paradox of Measuring Photons from the Sun

    Imagine a stream of photons moving from the sun to the Earth (A, B, C, D, E, F, G, etc.). Now imagine 2 different men measuring the speed of the photons, and (somehow) recording which photon is hitting them. They are in the same position, but one is traveling 1/2 the speed of light (relative...
  5. jerromyjon

    Does Relativity Support the Masslessness of Photons?

    From what I understand Einstein was the person who decided length contraction would indeed occur in the vector of velocity, more so as you approach c. If it were possible to accelerate a particle to c, would the length would become 0? If the length were to become zero, would the notion of mass...
  6. J

    Light photons, color and energies of molecules.

    Hi, so I'm a first year neuroscience student at Carelton University in Canada. I had a little bit of a "revelation" with this topic recently after I understood it a bit better and I think this is really interesting. (If I understand it correctly!) We're learning about Kekule structures...
  7. Godparicle

    Do photons pass through each other?

    If I am not wrong, Feynman is claiming that photons can pass through each other. Isn't it? This thread is started with the interest of the thread "Does electron has definite path?": https://www.physicsforums.com/threads/does-electron-has-definite-path.780047/page-2#post-4905563
  8. G

    Electromagnetic radiation and photons

    Why is light viewed as both wave energy and particle motion, whereas other forms of electromagnetic radiation is only seen as waves? Light is just a small part of the spectrum, so, surely all electromagnetic radiation should be viewed in the same way.
  9. jk22

    Polarization, Bell, and spin of photons

    i have the following questions: Bell inequalities use spin 1/2 matrices and experiments use photons. Is then the electric field horizontal or vertical after the measurement with a polarizer in other words can we assimilate the orientation of the field with a vector in the hilbert space ? How...
  10. R

    Number Density of Photons (Cosmology)

    Homework Statement Given the maximum possible number density of stars in the present universe, assume that they have been radiating light for 10 billion years at a solar rate of ##3.9 \times 10^{26} \ W##. Photons emitted all have a restframe wavelength of 500 nm. Find a crude upper bound for...
  11. Dadface

    Quantum Imaging with Undetected Photons arXiv:1401.4318(quant phy)

    Hello all, I have been looking at the arXiv account of the quantum imaging experiment but there are certain features of the theory I am trying to get a better understanding of. The main thing at the moment is the relationship between the signal and idler photons. Consider those idlers that are...
  12. J

    What if photons were not particles at all?

    I was always thought that photons were electromagnetic wave-particles. What if they were only EM waves and not particles at all. You are probably going to ask. What about polarization? And if there were 2 spaces intertwined at 90 degree angle. You probably have played with polarized glass and...
  13. C

    Why does photons of a given frequency satisfy the Boltzmann distribution?

    A mode of frequency ##\nu## has energy ##E_n = h \nu##. In terms of photons, the interpretation that I have read several places, is that this correspond to ##n## photons of energy ##h \nu##. Furthermore, it is stated that the probabilty of finding ##n## photons at frequency ##\nu## is given by...
  14. Spinnor

    Can 3 photons bunch, Hanbury Brown and Twiss effect?

    Could we split the beam of light in the Hanbury Brown and Twiss effect setup into 3 equal beams each, with each beam having a detector, and measure three photons arriving at nearly the same time at all three detectors? Thanks for any help!
  15. johann1301

    Gravity Between Photons: Exploring the Possibility

    Is there gravity between two photons?
  16. C

    Methods of keeping photons entangled for extended periods?

    Greetings, I am interested in conducting a retro-causality experiment to send a bit of data back in time. I would like to delay how long it takes one of a pair of entangled photons to reach a part of the experiment for an extended period of time such as an hour. What ways are there to keep...
  17. T

    Are Photons Particles or Waves?

    When the light from a distant star comes to our eyes...as the photons transverse the distance...are they traveling as a particle or as a wave? ie Are we being bombarded by millions of photon bullets or millions of waves? tex
  18. H

    Exploring the Speed of Neutrinos vs. Photons

    hello everyone I have a question , that is like a story " I talking with my friend about Neutrino and ... " I had written about it at wikipedia and they said that the speed of Neutrino not more than Photons , but I had read that they are faster than Photons speed. which one is true?! I am...
  19. M

    Photons interacting with multiple matter particles

    Everyone learns the picture associated with e.g. the Balmer series in Hydrogen: a photon with a precise energy flies in and is absorbed by an electron which is excited into a higher energy state, which then decays to the ground state, re-radiating a photon of that precise frequency. If we...
  20. H

    De Broglie wavelength - model for comparing photons and electrons

    Hello, I'm thinking about the wavelength of a freely propagating photon vs. a freely propagating electron. For the photon, we have the classical picture of oscillating E and B fields perpendicular to the direction of propagation, and we call the wavelength of the photon, which can be...
  21. A

    Can two photons be at the same place at the same time?

    Since photons are bosons and do not follow the pauli exclusion principle, does this mean that two photons can be at the same place at the same time? Is it meaningful to talk about a photon 'colliding' with another photon? I mean, suppose we send two photons of the same color towards each...
  22. L

    Exploring the Potential of Photon-Based Currents

    The photon is the force carrier of the electromagnetic force, I'm not talking about photonics but hasn't the effect of every electric current dc or ac ever been due to photons acting only? In theory couldn't we have an electron-less current due to only photons but still with the same effects?
  23. microsansfil

    Quantum imaging with undetected photons

    Hello, Schrödinger's Picture: Researchers Take An Image Without Ever Detecting Light which speaks about the article from nature Quantum imaging with undetected photons" Normally by the entangled it is not possible to transfer information :rolleyes: Patrick
  24. P

    Interaction of photons with charged particles

    Can someone please tell me the name of the theory describing the interaction of photons with charged particles eg electrons, protons? Can you also suggest a good introductory web page describing that theory at First Year University level for self study? Better still, a good VIDEO lecture on...
  25. R

    Capability of gas to absorb & emit photons

    Which gases have to capability to absorb light and emit photons of equal frequency?
  26. R

    Atoms Absorbing Light & Emitting Photons: The Gas Experiment

    If a gas is bombarded with light will the atoms absorb the light and emit photons of an equal energy level?
  27. A

    Do photons bounce into each other?

    if photons bounce into each other at a frequent rate, and photons bouncing off of each other may result in large change in direction of motion... then why don't we see "junk" photons? photons that enter our eye not because they bounced off a surface, but instead bounces off of another photon?
  28. RUTA

    "Asking photons where they've been" -- the DFBV experiment

    Here's an experiment using weak measurements on photons in a "nested interferometer." They conclude: In conclusion, we have performed direct measurements which shed new light on the question: Where were the photons passing through an interferometer? The main results are presented in Fig. 2B...
  29. anorlunda

    Are Photons Capable of Traveling Faster Than Light?

    In Feynman's famous book QED, he repeatedly reminds us that we must include the possibilities of photons traveling faster than light and slower than light to get the right answers. At least for short distances, short times. For longer distances, longer times, those possibilities cancel and the...
  30. K

    Why photons can't go any slower than the speed of light?

    Why photons can't go any slower than the speed of light, in vacuum? Or if they could, then why they don't?
  31. T

    Pair Production by two photons : energy range of the electron created

    Hi all, I'm currently studying pair production by two photons (a high-energy one traveling in a isotropic field of low-energy ones), and I'm trying to understand the energy range of the electron created by this phenomenon. For this, I'm studying an old paper from Aharonian 1983...
  32. cbram

    Number of photons in photoelectric effect

    Does the intensity of light mean increase no. of photons?
  33. E

    Waveform of Photons: Current Thinking & Analysis

    What is the current thinking about the waveform of photons? How can finite signals in the time domain produce a discrete frequency response in the frequency domain? As anyone who has worked with signal analysis remembers, the Fourier transforms of time signals in the real world always produce...
  34. X

    Must photons be absorbed or emitted one by one?

    Good evening. Usually we say that during light-matter interaction, energy of light should be transferred piece by piece, rather than continuously, with each piece equals hbar*ω. But in photon echo experiment, we say atoms are excited into a "superposition state" of ground state and 1st...
  35. R

    Exploring the Resonant Frequency and Optimal Energy of Light Oscillations

    Is there a resonant frequency of light? I was just wondering because the higher the frequency of light, the higher the energy. Or is there an optimal frequency?
  36. B

    DTQE idler photons fall into a Black Hole- interference at d0?

    Experiment: Imagine the dalayed time quantum eraser experiment, except the pair of "idler" photons(which would normally pass onto the detectors d1,d2,d3,d4) instead fall into a black hole. Would d0 detect interference or not? It seems commonly accepted that the information of...
  37. DrChinese

    Can single photons be made coherent through entanglement and manipulation?

    I thought that it would be possible to get a single photon to a double slit which would be sufficiently coherent to create an interference pattern. You would use entangled photon pairs, which I realize is not coherent light to start with. And use the Alice stream to herald the Bob stream. But...
  38. T

    Young's Slits and "one-at-a-time" photons

    Hi Everyone There is a problem that I have with understanding what happens when photons are emitted "one-at-a-time" in the Young's Slits experiment. However, I think I may have come up with a solution to this problem and would be very grateful for your thoughts. Let's say a single photon...
  39. T

    Do all photons have the same electric field

    I deliberately wrote that heading not quite accurate, as a photon is more of a probability thing, and so might not have an electric field at all. But what I'm getting at is, we know a photon doesn't have a well defined amplitude, but it does have a frequency. So what I wan't to know regarding...
  40. DiracPool

    Relative velocities of particles and photons

    According to my understanding of SR, a light photon traveling at c, of course, relative to me "experiences" no time. In other words, it is not traveling through, at least, the time dimension I am traveling through. A neutrino, say, moving close to c does, but it is traveling very slowly...
  41. WannabeNewton

    Boltzmann equation for photons

    Hi there. I have a couple of questions regarding the derivation of the Boltzmann equation in Dodelson for photons when given scalar overdensity perturbations to the FRW metric. To start with, let ##\Theta(\vec{x})## denote the temperature perturbations to the Bose-Einstein distribution of the...
  42. kini.Amith

    How does Compton scattering suggest photons?

    I have seen many 'photoelectric effect vs compton effect' Questions in this and other forums, but i am still not convinced. I can see how photoelectric effect points to the particle nature of light. But i don't see how compton effect as a separate experiment is needed to confirm this. The only...
  43. X

    Question about SPDC (Making entangled photons)

    Hello everyone, I have a question about the process of spontaneous parametric down conversion (or SPDC). This process is used to create two entangled photons in the visible regime by shining a laser through a beta-barium borate (BBO) nonlinear crystal. My question is, can this process be...
  44. B

    Photons -- where am I going wrong?

    I'll describe what I "think" a photon is and once any misunderstanding I have has been corrected then any problems I have following the correction should probably be ignored as I will have to re-evaluate from that point. So here goes. Its an electromagnetic wave that's emitted from an atom...
  45. A

    A Descriptive Explanation of Photons required

    What actually are photons, means are they packets of energy or some sort of matter.
  46. I

    Speed of 2 photons traveling in opposite directions

    If two photons ( A and B ) are traveling in opposite directions from a point in a vacuum will the relative speed of photon A to photon B be grater then C?
  47. G

    Understanding Photons: The Role of Energy and Momentum in their Existence

    i have read that existence of photons as a mass less particles came from the energy momentum equation. E^2 = (mc^2)^2 + (pc)^2 and that since when m = 0, there is still an energy = pc but, sunce momentum defined as m*v, and mass is absolute quantity, then why that m = 0 which we were...
  48. J

    Why do sparks radiate photons?

    Hello there, I am an undergrad physics student. Electric sparks are used to ignite fuel. However, why do electric sparks release more heat than electricity conducted through a wire? And what influences the amount of heat radiated from an electric spark? Why do some sparks radiate a lot...
  49. H

    Relation between photons and EM wave frequency

    Do individual photons have some attributes which relate to EM wave frequency? In other words, is there any difference in photons composing a red and blue beam of light?
  50. N

    Coherence time of parametrically downconverted entangled photons

    What is the coherence time for a pair of entangled photons produced in a nonlinear crystal? Is it related to coherence time of the pump photon? Also, if we say that the coherence time of the two photons is T, then does it mean that the two photons can interfere with each other even if their...
Back
Top