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. C

    B Exploring the Concept of Time for Photons

    Do photons, I'm not sure how to express this, "experience" time? Since they move at the speed of light does time not exist for them? If time does not exist, how is it possible for anything to happen to them. If interacting with matter requires a change in their condition, how can a change in...
  2. S

    Number of photons emitted by a laser

    P.t = nhf n/t = P/(hf) = 1.25 × 10^16 Something wrong with my working or I just pick (E) as answer? Thanks
  3. G

    B Eddington's 1919 Eclipse: Photon Deviation & Redshift

    Hi all, I've been wondering: Thinking of Arthur Eddington's relativistic oriented 1919 eclipse observation, would the photon deviation due to the Sun's gravitational imposition have caused the photons to exhibit a qualitative redshift due to the time photons had spent within the Sun's...
  4. R

    I What is the Invariant Mass of Two Perpendicular Photons?

    I think since Esystem=(PsystemC)^2 + (Minvariant C^2)^2. Then the invariant mass of the system should be zero, but I am hesitated with this is it always the case that photon that travels perpendicular to each other have zero invariant mass
  5. P

    A moving pi-meson decaying into 2 photons - finding their energy

    I've tried using gammamc^{2} = E1 + E2 but how do i find gamma?? If i try to use the kinetic energy then I just get gammamv^2 = 1gev but i don't know v? very confused
  6. S

    I Trying to Generate Entangled Photons

    I've been trying to generate entangled photons using KTP laser pointer that normally produces green light at 532 nm. I was hoping that after removing the IR filter, I could add a reflective coating (right now the coating I have is a glittery metallic green nail polish) to reflect the green light...
  7. A

    I Does p=mc Apply To Photons? | A.P. French's Special Relativity

    In A.P. French's Special Relativity, the author said the following, As I understand, photons are massless, so I don't think the last equation above applies to photons, but then, when deriving it, he used an equation proper to photons (##E=pc##). So in which context is ##m=p/c## valid?
  8. Saptarshi Sarkar

    I Effects of photons having a finite mass

    Few days back, our college professor told us that if a photon were to have a finite mass, then the Coulomb potential between two stationary charges separated by a distance r would be strictly zero beyond some distance. He told us that it was due to the reason that photon is the elementary...
  9. H

    B Backscattering of photons in dim = 1

    Hi PF i am reading a book written by L Tarassov about the Young slits experiment there is a source of photons in the middle behind the slits. when the electron passes thru one slit the photon is detected by a camera near this slit or another near the other slit. there is a probablité thar the...
  10. Saptarshi Sarkar

    I Speed of Light in Inertial Ref Frames: Photon Perspective

    According to the 2nd postulate of Special Relativity, speed of light in vacuum is the same in all inertial reference frames. If I take a beam of photons and see the other photons in the beam from a frame of reference of a single photon, do they look stationary or moving at the speed of light...
  11. I

    B Do photons bunch up at an interface? Can they lase (laze?)

    If the light slows at an interface, what happens to the photons coming in after the slowed ones? Can these cohere with the leading (slowed) ones and create what amounts to a FEL?
  12. J

    I Thermal photons emission inside a material

    in the inside of the material is heat also can transferred by radiation?
  13. dom489

    How can I increase the wavelength of light photons?

    Summary:: need to increase the wavelength of light. I am an intro physics student working on a project and need to increase the wavelength of photons. I only have visible light sources available but need to have an emission of a wavelength larger than 1mm. is there a way to shift wavelength...
  14. Maslova

    B Position of a particle and photons

    Once I have read that we can’t know a actual position of a particle because to see the particle we need to send photons and when we send photons it colides with the particle and change it’s position. Is this true?
  15. Sophrosyne

    B The nature of virtual photons in quantum electrodynamics

    In quantum electrodynamics, the energy exchange between two charged particles is called a virtual photon, allowing the exchange of quanta of energy between the two charged particles. But these are not the traditional photons of electromagnetic waves. They apparently just arise from the equations...
  16. Alfredo Tifi

    I What if a body loses 86,6% of its mass as couples of gamma photons?

    After emitting two photons (or any other kind of energy) in the direction of motion and in the opposite direction, the velocity of the body (a big charged and unstable particle) remains unchanged, while the kinetic energy decreases. This entails a decrement of the rest mass, or of the inertia of...
  17. R

    B Can photons of visible light lose energy and become sub-visible?

    Let me clarify this by a thought experiment: Imagine, a heated, red-hot (emitting only monochromatic red light) metal bar is brought inside a dark room. The room is practically insulated and the metal bar is glowing in the dark - emitting 'red photons' of visible light. Eventually, the bar...
  18. D

    I QED question: Photons absorbed and emitted by electrons

    According to QED photons can be absorbed or emitted by electrons, and this process results in em forces via virtual photons. What determines the emitted photon frequency, and are they fully absorbed by electrons assuming photons are discrete and must be in quantized packets? How fast are...
  19. B

    A Late Photons from the Early Universe?

    It has been reported [http://www.astro.yale.edu/larson/papers/SciAm04.pdf, https://www.scientificamerican.com/article/the-first-stars-in-the-un/] that scientists have observed spectra of radiation emitted by quasars that date from about 900 million years after the big bang. Others have observed...
  20. P

    B How Can Photons Contribute Mass to a Container?

    My question comes from reading the wikipedia page on mass-energy equivalence. The statement would seem to be contradictory: So photons contribute to the energy (and therefore mass) of the container; but photons are massless - that is, they have 0 rest mass. But doesn't this mean that we're...
  21. S

    Do photons of different energies interact with each other?

    According to this link photons can interact with each other through the creation of other particles. My questions are do they have to have the same wavelength to be able to interact with one another? Is there a threshold where they start to interact with each other?
  22. E

    B Photons as bullets at 10 trillion FPS (frames per second)

    The following extraordinary experiment from Caltech highlights the 'classical' behaviour of light(photons) traveling through medium. It vindicates the notion that photons(at least from our limiting human perspective) do behave the same way as other quanta(much like ordinary 'matter' - chairs...
  23. J

    B Photon Continuity in Double-Slit Experiment

    In the double-slit experiment, is there experimental evidence that a photon detected passing a slit always results in one and one only screen point?.
  24. V

    I Who did this experiment with photons?

    This is the phenomenon of a photon simultaneously exist in many different spaces, experiment show that space does not exist and the distance is not real. This experiment bring a lot of sense in quantum research. I want to review again but forgotten the name of person that did it.
  25. E

    Shift in wavelength of photons from the Sun using energy argument

    I came across a question recently which involved calculating the change in wavelength of a photon between being emitted from the surface of the sun and arriving at the Earth. The method that was implied involved calculating the GPE's of the photon (assuming the photon to have a mass h/[c...
  26. J

    B Why do photons only interact with charged particles?

    Why do photons only interact with charged particles?
  27. W

    I How electrons absorb or emit photons

    Hi, I am aware that the reason why objects have color is an old subject. However I come across two claims which sound like they are in contrast to each other. On one hand I read that the photons with specific frequency in incoming light are absorbed (i.e. have enough energy to move an electron...
  28. D

    A Soft photons and the ETH interpretation of QM

    As the thread on Jürg Fröhlich's paper on the "ETH interpretation" of QM has been closed, I want to consider here a specific point. Fröhlich points out that this interpretation requires the inclusion of massless particles and I think this is the key to getting a physical understanding...
  29. I

    Exploring the Relationship Between Photons and Vibration in Light Transmission

    Are photons vibration or is vibration the transport medium for light? In what kind of medium are photons more transferrable?
  30. PeterDonis

    I Gravitational Mass of a Ball of Photons: Concept Q10.4 in Gen Relativity

    This is based on "Concept Question 10.4" in Andrew Hamilton's General Relativity, Black Holes, and Cosmology. I have modified the question somewhat in order to focus on what seem to me to be the key issues. Suppose we have a spherically symmetric ball of stress-energy surrounded by vacuum. More...
  31. F

    I How to Determine a Photon's Wavefunction After it Collapses?

    Suppose one measures the position of a photon without destroying it. From my understanding, the wavefunction of the photon should collapse, and will return to a more spread out state over time. How would one calculate this, specifically the rate at which the wavefunction spreads out from the center?
  32. B

    B Exploring the Nature of Photons: Position, Speed, and Emission/Absorption

    Just wondering... If photons do not have a position operator - is it because theory math does not provide it, or because theory math forbids it? - how is speed (the difference between two positions divided by time) determined? - are emission and absorption inferred from measuring energy...
  33. M

    B Total % of Photons Redshifted While Moving Away From a Black Hole?

    Suppose a black hole with a radius equal to the radius of the observable universe exists and a fleet of coasting spacecraft are moving directly away from the black hole (along a similar vector) at very close to the speed of light with an amount of kinetic energy A with respect to the...
  34. jim421616

    I Can Compton scattering increase the energy of photons?

    I've read (in Hagai Netzer's book The Physics and Evolution of Active Galactic Nuclei) that "Comptonization in the [black hole's accretion] disk atmosphere can increase the energy of some photons..." I thought Compton scattering could only decrease a photon's energy. What am I missing?
  35. Y

    I What will eventually happen to all EM waves / photons?

    I'm not an expert in this matter, and at best only aware of some superficial facts and a layman's understanding of them. So please forgive me for any ignorant mistakes in my thoughts, and kindly point them out to me. Going by the Lambda-CDM model, the expansion of the Universe will eventually...
  36. P

    The attractive force of photons on other photons & matter

    Summary: massless particles (or at least photons) are attracted to other photons and to matter, but which is most attractive, and why ... Summary: massless particles (or at least photons) are attracted to other photons and to matter, but which is most attractive, and why ... I am really...
  37. Joseph1785

    B Do Entangled Photons React to possible Photon-Photon Collisions?

    Summary: The limitations of engagement and possible results of the Breit-Wheeler theory collider in relation. *You will need to read the article for this to make sense Upon reading an article "Scientists discover how to turn light into matter after 80-year quest" I had a thought, How will...
  38. W

    I Are EM fields clouds of photons?

    Personally, I have trouble visualizing a flock of birds without the birds. I have the same trouble trying to visualize an EM field without the photons. More than once, I have been hounded off of the ham radio forums for mentioning the word "photon". As one ham radio operator put it, "We don't...
  39. R

    The Mystery of Photons Inside Electrons: Where Do They Come From?

    we know that when a electron lost its energy , it will emit photon , but why electron have a photon inside ? does it already exit in a electron from the beginning or it comes from environment ? if comes from environment , where does photon come from?
  40. S

    If photons can't escape a black hole, how come gravitons can?

    It would seem that they both must observe the laws of General Relativity.
  41. liroj

    Measuring Wavelength of Photons: Precision & Variation

    How precise can a wavelength of photons be measured and how much can it vary? For example, 300nm, 300.1nm, 300,11nm, 300.111 etc... What is the limit up to which we can measure it or is there a point where there is no variation anymore - something like a "quantum" of wavelength? Hope you...
  42. T

    I Looking for more accurate energy-momentum transformations for photons

    Photons deviate from the above energy-momentum transformations under certain circumstances while still in flat space-time, I'm wondering what set of transformations would more accurately describe them over as wide a range of circumstances as possible, still in flat space-time, I've searched and...
  43. P

    Finding the unitary matrix for a beam splitter

    Hello, I have some trouble understanding how to construct the matrix for the beam splitter (in a Mach-Zehnder interferometer). I started with deciding my input and output states for the photon. I then use Borns rule, which I have attached below: To get the following for the state space...
  44. fluidistic

    A Photons through transparent materials, what's going on?

    I have read, heard and seen texts and youtube videos about the slowing down of light through matter, and also about why some materials are transparent. I am satisfied with the explanation of the slowing down of photons through matter, but not the explanation of why materials are transparent. I...
  45. M

    I Do Photons Decay? QED Predictions & Measurements

    QED predicts photon-photon scattering, via a fourth-order Feynman diagram with four external photon legs connected to an electron loop. It seems to me that the same diagram should also predict a process where a single incoming photon decays spontaneously into three photons. This is not forbidden...
  46. H

    How can I calculate the number of photons with this data?

    The problem says: A radio station emits electromagnetic wave with a frequency of 100MHz (102*106 Hz). a)What's the energy of this radiation's/glow's photon? (Solved, i found 6,63*10-26 J) b)Compare your calculation with the energy of another visible radiation/glow, with a wavelength of 600nm...
  47. S

    I Microwave photons and microwave oven doors

    Photons are point-like particles with no size, but they have different frequencies. Photons with certain frequencies (like microwave photons) can not pass through the holes of the mesh on a microwave oven, so this confuses me. Photons seem to act like they have size at low frequencies. I have...
  48. J

    B Entangled Photons: Adam Becker's QM Book "What is Real?

    I'm reading Adam Becker's QM book "What is Real?" At one point he says: "The single wave function shared by the two entangled photons guarantees that they will always behave in the same manner when encountering two polarizers with parallel axes. It does not specify what they will do. But merely...
  49. B

    Photons and solar wind/plasma interaction?

    Can the suns photons accelerate the plasma/solar wind away from the sun? or is there no interaction between them?
  50. R

    Chemical structure vs excitation frequency (photons)

    Is there a text, or set of texts, on how to predict what frequency of photon is released when a particular molecule is brought to an excited state and then relaxes? So for example if you were to put, say, benzene into an electrical tube and excite it what frequency would be released and more...
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