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. J

    When photons hit metals, does the electron created go in a random direction?

    Some metals generate electrons when photons hit them, If so then what direction will the electron go into, will it be random and the uncertainty principle and quantum randomness. Or will it go in a direction relative to the point of impact from the photon, So if you shot a photon at an atom...
  2. L

    Can photovoltaic cells capture gamma photons?

    I am by no means well versed in nuclear power, but from my limited exposure I have gathered that a very large portion of nuclear energy (and antimatter) is expressed in high energy gamma radiation. All forms of electromagnetic radiation are expressed as photons, correct? Taking the concept of...
  3. B

    Are photons massless or practically massless

    Title says it all. Also, do photons in a vacuum travel in a straight line? I find that kind of strange. Also, are gluons massless or practically massless? How are gluons detected?
  4. G

    Do Photons Have Mass? Exploring the Particle

    photon is a particle. then how come it does not have mass?
  5. P

    What Happens to the Photons in Destructive Interference?

    I know about the law of conservation of energy, and I understand interference effects conceptually, but when I put the two together I'm a little confused. I know that the energy of light must simply by transformed in destructive interference...but where does it go and how? If the...
  6. C

    Photons vs neutrinos energy ratio

    What is the ratio of energy contained in photons vs energy contained in neutrions in the present universe? Also, how is that ratio changing with time? Thanks.
  7. M

    Medical Photons vs. Protons in Radiotherapy - Why photons?

    Something has been bugging me ever since I learned about Bragg's peak (and how it compares to x-ray attenuation) a few years ago... I understand there are probably advantages that photon therapy has over proton therapy, but what are they? Cost? Feasibility? Probably a dumb question, but...
  8. S

    Photons vs. Neutrinos in electromagnetic fields

    I have been wondering why photons can't go through matter and electromagnetic fields mostly unaffected while neutrinos can. Neither of them have an electric charge as a particle, and the basic description I see about neutrinos is always that "they are unaffected because they have zero electric...
  9. xaratustra

    Charged particle and virtual photons

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  10. J

    What if photons had an electric charge?

    What would happen if all photons had (slight) electric charge? Would we just not be able to see? Or would we not exist at all? Why? If they were negatively charged, would they repel electrons and attracts to the nucleus of an atom? What consequence would this have?
  11. S

    CMb Photons: Finite or Infinite?

    Is there a known quantity of CMb phtons? Presumably we can only receive a finite amount in our detectors, but is that due to the fininite distance to our comsic horizon? But if the universe were infinite would it have emitted an infinite amount of photons from the CMb/ Would everyplace in the...
  12. M

    Question regarding photons and mass

    Sorry if this is a noob question or if it has been answered before or if I'm just misunderstanding the physics involved but this has been keeping me up at night and it'd be nice to have it resolved. If E=MCsquared implies that greater energy equates to greater mass in a particle, how is it...
  13. G

    Vibration of Photons: Do Photons Oscillate?

    Do photons vibrate or oscillate in any way?
  14. I

    Splitting photons are entangled?

    I'm sorry if this is a silly question and please forgive me but, if you split photons into two by any medium or matter can it entangle photons? Do the photons have to go through a beta barium borate crystal or any other crystals? Are there any alternatives to split photons? Please provide good...
  15. I

    Do you have to use a Beta-barium borate crystal in order to entangle photons?

    im just curious and i just want to know, do you need a Beta-barium borate crystal to entangle photons? are there any alternatives? can you use sodium chloride crystals as a possible option? what makes a Beta-barium borate so special and different from any other crystals? please provide good info...
  16. P

    Extremely High Energy Photons?

    I was wondering whether it was possible for an extremely high energy photon to exist, or if there's a limit to the energy in just one photon. And I'm talking REALLY high energy here. Like twice the energy of, say, the gamma rays released in a supernova. If this is possible, what is that photon...
  17. A

    Photon & Lighting: What Happens After Production?

    Hello everyone! It's pouring with rain and the thunder is roaring. I was sitting outside watching the lighting and I had a strange thought come to me, the lighting is producing photons correct? What happends to photons after they are produced? Do they keep on moving through things just not...
  18. M

    Can Electrons Absorb Photons With Different Energy Levels?

    For electrons in some atom to absorb a photon having some amount of energy, must this energy be (exactly) equal to the difference between the two energy levels?, can't it be absorbed when its energy is more than that difference? Because in the case of (exact-equality), it would be hard for an...
  19. J

    Using the Double Slit Experiment & encoding photons with binary data

    My name is Joe Fiero. Ever since I was a little kid, I loved science, especially science fiction. Sliders, Back to the future, Star Trek. I never had a chance to get a degree in the things I loved the most because I came from a poor family... which has lead me to a path of self education and...
  20. N

    Photons, what makes them a act like a wave?

    If photons exist relatively unbounded by time, then does this mean they're outside of time, or experiencing past/present/future all in the same instance? Does this imply that they can match the quantum state of any pair photon/electron within some range, which is based on the charge of the...
  21. S

    Does a modulated electromagnetic wave contain photons of different energy?

    Hi Guys, I have a doubt. When we think of a modulated wave, consider frequency modulation for example, does the wave contain photos of gradually changing energy (or frequency)?
  22. T

    Assistance with Massive Photons Homework | 3rd & 4th Part Help

    Homework Statement This is my problem: (5th part is not needed) The problem is I took a bit too complicated course for me and I don't know how to solve this. Specially I need help with 3rd and 4th parts. I will very much appreciate the help. Thank you in advance.
  23. E

    How is the wave function of a photon described in quantum field theory?

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  24. N

    Photons observed on photographic plate - but not in eyes? Why?

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  25. StevieTNZ

    Number of Photons In Each Section

    Hi there, How can I find out how many photons would land in each areas, for the following patterns: http://www.bbk.ac.uk/tpru/BasilHiley/QuantEraserLight.pdf - page two's image (screen B) How many photons make up 'eraser no photon' pattern, and where each is. Likewise for the 'eraser yes...
  26. T

    Transparency of the sun to extremely long wavelength photons

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  27. Y

    Can photons provide information about color and distance?

    I was wondering, well basically if photons carry information about themselves that is interpreted by our brain? I ask because I was thinking about things like color and distance. Correct me if I'm wrong but we see different colors because of the way the molecules or elements that make up an...
  28. S

    Can anybody explain the modulation of radio waves in terms of photons?

    Hi All, I wonder if the modulation of RF waves (Amplitude Modulation, Frequency Modulation, and Phase Modulation) can be explained in terms of photons. Thanks, Srini
  29. Vorde

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    How does the exchange of virtual photons result in an attractive force (for example between a proton and electron)?
  30. J

    What is a Rest Frame and How Does it Relate to Photons and the Speed of Light?

    This has been discussed in a number of threads and in FAQs. I was wondering what constituted a rest frame as nothing in the universe is at rest, if you work the figures out we are moving at around 2.5% c. In another thread I found out that at rest simply meant not accelerating. This means...
  31. D

    What factors influence the direction of emitted photons from an atom?

    Hi sorry my english I am french. :) So I was wondering what's the direction of light? I understand light is composed of photons and those are released when electrons change orbit. But if 10 000 photons are released what direction will they take and why ? Tell me if I am wrong about some...
  32. S

    Photons radiated by free electron?

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  33. C

    Continuous EM fields vs. fixed freq photons

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  34. M

    Why exactly do electrons emit photons?

    When electrons gain enough energy to move out to a higher energy orbit then back to their ground state, why do they release a photon? Also, what exactly is 'electromagnetic' about light?
  35. F

    How can infrared photons impart energy

    And still be re-emitted at the same wavelength, even after being absorbed? I imagine visible colors, to hit a dark colored surface and become absorbed. In that process some of the object's electrons (I believe the outer shell) become energetic or is raised higher. To achieve equilibrium, it...
  36. S

    Explain phase change of an EMW in terms of photons.

    Hi Guys, I have a question. Can we attempt to explain the phase change of a carrier wave in terms of photons? For example consider GPS signal. It is BPSK modulated, in which phase change of 180 degrees happens for multiple of 1540 cycles of the carrier. How is the phase information...
  37. D

    Do Photons Experience Changes in Potential Fields?

    Are photons effected by traveling through electric or gravitational potential differences? If so, how so?
  38. D

    Photons from black body spectra

    Hi, I don't quite understand which are the fundamental processes for production of photons that are emitted by a "black body". Usually this is explained by considering a cavity in thermodynamic equilibrium but I am not interested in this. I am looking for a more practical description of this...
  39. C

    Mass of trapped photons vs. Mass of potential energy

    I've understood for a while that a black hole is made more massive simply by shining light on it; the energy of the photons "goes towards" (for lack of a more informed/accurate term) the mass of the black hole. Also, a couple weeks back, someone on the forums said that if one had a container...
  40. I

    Behavior of Photons During Reflection.

    Which of the following is consistent with experiment/observation. When light is reflected off of a material, what happens to the photon? A. Is it absorbed by the electron or lattice and then re-emitted? OR B. Does it somehow just reflect/bounce off the electron/lattice? Kind of...
  41. P

    Photon Mass: My Irresistible Urge to Draw

    I had an irresitible urge to draw this...
  42. M

    A question on Virtual Photons, and QED

    Quantum Electro Dynamics, the quantum theory of the photon, describes the photons interaction with electrons and this is what I beleived created the electromagnetic field. However recently I've heard a disscusion that virtual photons and their interaction with electrons and the polarization of...
  43. P

    Photon Decay: Can High Energy Photons Transform?

    I was recently wondering about this. A very high energy photon cannot transform into any collection of particles with mass without interacting with another photon or particle, else it is trivial to show energy/momentum cannot be conserved. Interacting with another photon allows...
  44. P

    Special Relativity - Distance between photons

    Homework Statement (Not homework, just a textbook question I'm confused about) Two photons travel along the x-axis of S, with a constant distance L between them. Prove that in S' (moving at velocity v w.r.t S) the distance between these photons is L\sqrt{\frac{c+v}{c-v}} Homework...
  45. Y

    Understanding Photon Velocity: Impact on Mass and Life Span Explained

    I am posting this under the belief that velocity affects mass and time, if my understanding is incorrect please correct it. If a photon is traveling at C then theoretically does it have an increased mass compared to a photon that is "at rest"? And if a photon is moving at C then does it...
  46. I

    Visualizing Photons: Wavefunctions, Frequency, and More

    Hello again, After asking for a better way to visualize electrons around a nucleus (and receiving one - thank you alxm), I am now left wondering about photons. How should I go about visualizing them? I have heard that they have a wavefunction, just like electrons do, but I would like to...
  47. A

    Do Photons Influence Gravitational Fields?

    Do photons contribute to the gravity? Are there any experimental results like two parallel laser beams attracting each other?
  48. E

    Do photons interact with neutrons?

    Quick question: photons do not interact with other photons photons do interact with electrons photons do interact with protons (I think) so do they intereact with neutrons? How could you tell, if the energy state of the neutron changed from absorbing a photon?
  49. S

    Do Photons Relax? | Physics of Mass & Energy

    imagine a photon (travelling with the speed of light) is moving straight towards a huge mass say 10^10 Msun. what will happen to its speed/energy as it comes closer to it?
  50. Spinnor

    How is energy shared in plasma between particles and photons?

    Suppose I had some plasma in box with walls that allowed nothing thru, photons, plasma, energy. Now heat the plasma and maintain some temperature T (ignore the difficulty in heating the plasma with the above walls, just assume you can). An approximation to this might be some small region of the...
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