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.

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  1. S

    Photons and charged particles and dark matter

    Are photons capable of interacting with particles with no charge. And if not, is it possible that that's the reason dark matter has so far eluded detection: because it has no charge?
  2. S

    Applications of Trapped Photons

    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...
  3. J

    Should photons be considered massless?

    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...
  4. H

    Maximum speed for absorbing photons?

    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...
  5. P

    Photons and the Doppler effect

    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...
  6. N

    Why some photons are absorbed while propagating through glass

    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...
  7. W

    Hydrodynamical description of photons

    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...
  8. R

    Possibility of million entangled photons

    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...
  9. B

    Polarisation of photons exiting a birefringent crystal

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  10. Ookke

    Will photons fry an object falling into black hole?

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  11. Ahmed Abdullah

    Do photons of different energy interfere with each other?

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  12. L

    Electrons Absorbing Photons - Extra Energy

    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...
  13. R

    Do photons have mass experiment?

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  14. Crazymechanic

    Electric field , photons, charge

    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...
  15. W

    Where is a Photon? Understanding Light and Momentum

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  16. T

    EPR experiment with twin photons then interference experiment

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  17. P

    Energy of photons vs classical physics energy

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  18. deep838

    Photons Affected by Pseudo Forces | Hyperspace by Michio Kaku

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  19. C

    Photons, Antimatter- My unsolved Questions

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  20. I

    Photons Impact on the Visual Process

    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...
  21. G

    Speed of photons and its effect on us

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  22. S

    Electromagnetic radiation and photons

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  23. P

    Beam splitter with single photons

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  24. P

    Single photons traversing a beam splitter

    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)...
  25. L

    Photon Mass and Momentum: Train Experiment

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  26. phosgene

    Why 2 photons are formed from positron-electron annihilation at rest

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  27. E

    Can UV photons spontaneously convert into IR photons, and vice versa?

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  28. S

    Does Electromagnetic Radiation Contain Photons?

    does every electromagnetic radiation consist of photon?
  29. A

    Do Photons Have Mass According to E=MC2?

    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...
  30. G

    Why we have 4-5% matter, given most m/anti-m annihilate to photons

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  31. T

    Does intensity of photons affect threshold frequency?

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  32. J

    Is a static EM field made of photons? Do they move at c?

    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...
  33. Crazymechanic

    Are DC circuits similar to AC circuits during switch on/off?

    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...
  34. B

    Do photons warp space like the equivalent energy as mass would?

    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...
  35. J

    What happens to 'unabsorbed' photons?

    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...
  36. R

    Find Photons per second on the eye from a source a distance away

    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...
  37. DrChinese

    Double-slit interference pattern measurement with entangled photons

    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...
  38. T

    Photons Moving Through a Single Slit (Uncertainty)

    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...
  39. F

    Virtual photons and long range force carrier

    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...
  40. K

    Photons and electrons and electricity.

    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...
  41. T

    Photons per Unit Volume (Quantum)

    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...
  42. E

    Virtual Particles and Photons

    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...
  43. B

    Photons, speed and energy - Beginners concept question

    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...
  44. M

    How photons and static em feilds work

    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...
  45. medgalis

    Can Photons Have Mass? Debate & Answer

    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?
  46. J

    Seeing colors: photons vs waves

    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...
  47. C

    Is the Mass of a Photon Affected by its Energy?

    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...
  48. S

    Photons effected by gravity of a Blackhole?

    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...
  49. C

    Regular empirical evidence of curved space or massless photons?

    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...
  50. G

    Diffraction of individual photons

    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...
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