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. entropy1

    Depiction of distribution of photons over time

    I have a question about photons and the Schrödinger equation. Photons behave like particles but also as waves. I understand that this can be described by the Schrödinger equation as a photon having a certain probability to be somewhere. If I understand this correctly, I take it that there are...
  2. B

    Could photons be 2D objects in String Theory?

    String Theory speculates that extra dimensions may exist. Obviously, it would be difficult to describe or imagine that, but is it possible that there are objects or particles that exist observing LESS dimensions. For example, photons travel at c meaning that time travels infinitely slow in for...
  3. U

    Redshift effect And photon energy loss

    I've been searching around the web to figure out why photons shift towards the longer wavelengths as they travel from stars and other light sources but I haven't figured out why they loose energy as they travel ( and after reading some web pages I was told that they don't even loose the energy...
  4. ZapperZ

    Do Photons Move Slower in a Solid Medium? - Comments

    ZapperZ submitted a new PF Insights post Do Photons Move Slower in a Solid Medium? Continue reading the Original PF Insights Post.
  5. B

    About photons and it's quality

    The photons get absorbed according to quantum theory by an electron for Instance in an atom form this phenomenon can anyone explain me reflection ,refraction and scattering of light in photon point of view and not by wavetheory
  6. ayush solanki

    Why are photons affected by gravity?

    Photons are massless,so why does it get affected by gravity?and are neutrinos affected by gravity too?thank you.
  7. T

    Light if energy density of photons were constant

    Homework Statement At what rate would stars have to be producing light (how many photons per second per solar mass start) in order for the energy density of photons in the universe be constant? Assume current values of cosmological parameters. Do it for current time. Homework Equations e =...
  8. Malaxus

    Is it possible for photons to display in the center of room?

    Is it possible for photons to center themselves in mid-air in the center of a room, multiplying and change directions while still being somewhat centered in the room? I have tried looking this up in Google, but all I got were articles which I did not have enough time to read. If this is the...
  9. J

    Energy of Photons: An Exploration

    I was wondering about the amount of energy in Photons. Do they all have the same amount of energy? Or do they have a base amount which can increase depending on frequency or some other parameter? Also, I have read that photon photon collisions can yield positrons and electrons, both positrons...
  10. F

    A Thought Experiment: Photons Passing through Detectors

    Pretend we have a multi-slitted grating whose slits are infinitesimally small. We On each slit is a detector. If we shine (UPDATE) light monochromatic light through the grating, what distribution pattern occurs on the screen past the grating? I understand the train of thought to a slight...
  11. phoenixthoth

    Photons and nonstandard analysis

    Hi PF contributors, Have there been attempts to apply nonstandard analysis to the behavior of photons? For instance, considering the mass of a photon to be infinitesimal. I'm guessing the answer is yes so if you could provide references, I would be much obliged. phoenixthoth
  12. TheDarkness

    Can Virtual Particles Have Infinite and Negative Acceleration?

    Hypothetically, a particle p of mass M is sitting at velocity v. Assuming M = 0, and the vi of p is 0 m/s, 0 seconds passes and vf 100 m/s is reached. Since time t is 0, acceleration cannot exist, as no t has passed between the vi and vf states. And, knowing that a = (vf - vi)/ Δt, a = (100 -...
  13. C

    Electron-positron creation from colliding photons

    Homework Statement Consider two photons, one with energy ε1 = 2MeV traveling to the right, and the other with energy ε2 = 3MeV moving tot he left. The two photons collide head-on and produce a positron-electron pair. Suppose the the electron and positron move along the same axis as the photons...
  14. DaniV

    Photons acceleration in refraction

    In transparent matirials it is known that when light going through it ,photones speed in the matirial would be smaller than in a vaccum. When the light refractioning, the photones transfer from one transparent media to another (for example- Vaccum to water). The photones during the process...
  15. J

    Are photons really particles or just a misconception?

    Hello everyone, thanks for reading I'll explain my question. At first, light was described as electromagnetic waves, until Einstein proposed the photoelectric effect and thus creating the concept of photon, a particle of light with momentum and energy, but no mass. It could explain why the...
  16. B

    Exploring the Age of Photons: My First Post

    My first Post :) I understand photons are are not going to age. But they still have a time in which they are created. Maybe this is known and I am just late. While learning about photons, right away I got he question if we can measure its born date.I mean everything decays right? So we should...
  17. ZapperZ

    Do Photons have Mass? - Comments

    ZapperZ submitted a new PF Insights post Do Photons have Mass? Continue reading the Original PF Insights Post.
  18. J

    Which photons pass through a circular annulus?

    Passing light through a circular sieve: Well, actually, let’s think about radar or microwaves with a wavelength of order a centimeter or two, so you can tailor your aperture, say by etching a silver screen on glass. If you have a reflective metal screen, and you cut a long narrow rectangle in...
  19. desta41

    Do just electrons emit photons?

    Do just electrons emit photons/radiation. Or do atoms and molecules emit photons as well? Just can't get a clear answer on this. And if atoms and/or molecules also emit photons, can you please explain what causes them to?
  20. G

    Question about quantum superposition in CMB photons

    Hi, CMB photons reaching our telescopes have traveled for over 13 billion years without interacting with anything. If I understand correctly, from the event of the photon emission, its wavefunction gradually spreads, encompassing more and more possible states for the photon, coexisting in...
  21. Christian Grey

    Why photons reflect off glass?

    Why photon reflects and refracts through glass? Some photons pass through glass and some reflects.I know this is due to energy levels of electrons of glass, an incoming photon is unable to excite the electron to a different energy orbit. But I want to know, if an incoming photon is unable to...
  22. C

    How we are still able to detect CMB photons?

    This might be a silly question. But recently I got to know about CMB(cosmic microwave background) and this question is nagging me. During CMB , the universe was pretty small compared to now, so our current point of existence in space would have been very near the CMB, 13.7 bill yrs ago. So the...
  23. bcrowell

    Will all matter be converted to photons?

    bcrowell submitted a new PF Insights post Will All Matter Be Converted to Photons? Continue reading the Original PF Insights Post.
  24. A

    B Why does light travels in all directions?

    My understanding of time, gravity and speed of light: Earth revolves around the Sun. Sun revolves around Milky Way centre. Milky Way also keeps moving. All these movements are caused by gravity. Thus, all that what is formed by fermions (particles causing mass) has been affected by gravity...
  25. P

    What actually happens when the black hole takes the photons

    We all know from the relativity, that even the light gets into the black hole, so gravitation-gravitons(what is actually graviton?)are stronger than photons in this case!?
  26. Dry

    Expansion is a compounded error based on a wrong assumption?

    I accept that what I write below will be unpopular and argued with vehemently, however I think it should be considered with an open mind and recognised for the sense that it has. Originally the concept of an expanding universe (and therefore by extrapolation the concept of the Big Bang that...
  27. Docon

    Why Photons Can't Explain Dark Matter

    In general photons are not candidate for dark matter. From the other hand stars constantly change matter into radiations (photons among them). And we can not measure radiation that does not hit us (although we can try to calculate it because radiation from star goes with same intensity in each...
  28. allybee

    I have always wondered if Photons are magnetic and if so are

    I have always wondered if Photons are magnetic and if so are they affected by the geomagnetic field around the earth
  29. nathan mcgrath

    How can photons be used to manipulate matter and create fire?

    Hi people. I'm currently well into my 4th novel, 'The Atlas of Elegance.' it's a book about magic - but a kind of magic based around physics, in particular quantum and astrophysics. The main characters in the story have the ability to control matter at a sub-atomic and quantum level. I'm using...
  30. CjCastro

    Photons and Space-Time Expansion

    Hello all! I apologize if this question has been asked already, anyways I have a conceptual question, let me see if I can explain it properly. So we know that the universe is expanding at a rapid rate, very rapid in fact, space and time itself is expanding; and we also know the maximum speed...
  31. A

    Does universe expansion separate photons, traveling parallel?

    I understand that the force of gravity prevents galaxies from expanding, as space increases. However, I question if universal expansion separates photons (electromagnetism), as they are traveling along parallel paths (Would the normal distance between them increase over time)? Thank you.
  32. P

    Can a beam of photons accelerate an atom or object?

    Not quite sure how to ask this, but here goes: I think I understand how a photon impacting an atom can increase the energy level of an electron in the atom. When I read about "light pressure", I thought, is there a way for, say, a stream of photons to accelerate an atom by continually impacting...
  33. S

    Relativity: Massless particles and photons

    I f a particle starts moving with the velocity of light it becomes massless.But practically a massless particle has no existence.Again one of the main constituents of light is photon,then is it a massless particle?But I know electron has the least mass in this world and photon is heavier than...
  34. QuantumKangaroo

    Difference between Photons and the Higgs Boson?

    I'm new to quantum physics, and this might be a stupid question. What is the difference between Photons and the Higgs Boson? I know that neither of them interact with the Higgs field. And that when CERN found the Higgs Boson, it decayed into other particles INCLUDING photons. So what's the...
  35. rumborak

    Arbitrarily changing EM fields and their photons

    This started with me trying to read up how static electric/magnetic fields are described with photons, but it quickly evolved into the realization that I don't really know how the photonic viewpoint describes *any* changing EM field that isn't a neat monochromatic wave. Some sites mention...
  36. rw11

    Photons to energize rhodopsin & trigger a nerve impulse

    I am wondering how many photons must be captured by a rhodopsin molecule to energize it, and also to trigger a nerve impulse to the brain or to deeper in the eyes neural system?
  37. Suraj Nehra

    Do Photons Have Mass? Physics Forums FAQ

    I read the FAQ about photons not having mass: https://www.physicsforums.com/threads/do-photons-have-mass.511175/ But De-Broglie's equation says that wavelength=Plank constant / mass x velocity i.e. λ=h/mv inserting values in the above relation we find the mass of a photon having certain wavelength
  38. S

    Photons from two sources versus one source

    Assume that we are given a big black box with two windows. Each window emits a laser beam. All our best measurement techniques show that the two beams have the same wavelength and have near-perfect mutual coherence (or as good as the self coherence of each output beam). Is it possible to tell...
  39. J

    Entangled photons and their Parents

    I am curious if photons are quantized because their 'parent' particles are quantized, and the photons are entangled with their parents. In other words, if you were to have two entangled particles emit a photon(s) that is entangled in energy somehow, do they emit a single photon, two photons...
  40. deansatch

    If probability wave is true wouldn't there be flickering?

    I've been reading up a lot on the double slit experiment recently (and I'm no physicist at all). Although I haven't really seen the experiment done with my own eyes, from the demonstrations on youtube it seems as though the pattern when shining a laser through the slits is constant and solid...
  41. A

    Photons emitted by heated objects

    Hello everyone, I have a question. Electrons jumps up the energy level by absorbing a photon and down releasing it, giving off a characteristic spectrum. Then, are the photons released when an object is been heated up due to intermolecular forces, since they are of a full spectrum? Is the...
  42. R

    Photons striking a camera sensor?

    I am curious as to roughly how many photons strike a camera sensor (e.g. a DSLR) in dim light, where the camera can form an image? Also how many photons are hitting a photosite for it to be triggered? and... how many photons have to hit a human rod (or cone) cell for it to be triggered and...
  43. J

    Photons and transparency....who's right?

    All, I have read as much as I can find online regarding this topic and there are so many conflicting answers that it is insane. First, many sources identify photons vibrating the electrons in a transparent material in such a way that the net effect is to pass the photons out the other end of...
  44. tg85

    Spin-parity of two photons

    I am trying to understand how charmonium states can be produced in electron-positron collisions, and which quantum numbers are possible for each process. I am having trouble understanding the quantum numbers that are possible for the two-photon process, e+e- → e+e- γγ → e+e- cc̅. I have read in...
  45. H

    Would synthesis of Acetylcholine make photons?

    the Neurotransmitter Acetylcholine (ACh) has 1 less electron for its Nitrogen (N), I think it gives it to Chlorine (Cl) so when an electron in one energy orbit goes into a new atom at a different energy orbit, would the difference of energy level (the Photon) radiate outward? After all the...
  46. S

    Is it possible to charge photons?

    I was wondering if there is any way to electrically charge photons?
  47. H

    I have a quick question about Photons

    When an electron passes from one atom to another is a photon emitted?
  48. T

    Distances for classical objects vs. photons

    Good afternoon all, A few days ago, I had been reading a book on general relativity and cosmology by Dr. Brian Greene, in which something was written that I found to be very profound. (At least, from the standpoint of my own ignorance on the subject.) I was wondering if any professionals could...
  49. G

    CMB photons, why are they still around?

    10 billion years ago, photons emitted at the surface of last scattering were being absorbed by whatever stuff was around. Those atoms would absorb those photons and release other photons, but these would not be primordial photons from the CMB anymore but photons emitted at a later time by the...
  50. Prashan Shan

    Do virtual photons explain this phenomenon?

    ok. this may sound stupid, first of all i asked this question because i have a doubt that "if a photon can see things around it will it be able to see its own reflection if it aproaches towards a mirror?" so i played a video of light being reflected in a mirror in slow motion and paused the...
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