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. Pattarasak

    I Measurement of the mean value of the number of photons?

    Hi everyone, I do experiment in field of quantum optics and I want to calculate the mean of the number of photons (MNP). In the most of papers, MNP can be calculated by using average power which is measured by power meter. But my power meter is defective. For now, I have only the avalanche...
  2. T

    Wave Particle Duality For Electrons and Photons

    Homework Statement Discuss the concept of the wave-particle duality for electrons and photons and include an equation which connects the wave like and particle like properties. Homework EquationsThe Attempt at a Solution So I am having trouble with how to word this question and generally...
  3. K

    B Exactly why FTLC is impossible with entangled photons?

    It’s written almost all physics books and courses that entangled photons can’t be used for faster than light communication. The question about used entangled photons to communicate faster than light has been discussed before, but I didn’t get exactly why faster than light communication with...
  4. T

    Photons in Fiber Optics V Solar Sails

    Solar sails use the push of photons on a mirror. Would it work to use the push of photons in the atoms in fiber optic cables so the question is would there be push and how much on 1 mile of a space train 50 feet wide with 1 foot thick of fiber optics. Here's how I think it would be nearly...
  5. K

    B Why do scientists claim that there's true randomness?

    When we look at the cars on the road, it appears like where they are driving is random, their directions appear as random. But the drivers don't drive into random directions. It appears random to us because we don't know the thoughts and intentions of the drivers. If we knew almost everything...
  6. Z

    B Single photons and expanding spheres of light

    This question has been bothering me for decades: Imagine a point source in space that emits one photon per second. Would the photon expand in a globe in all directions until it strikes an object or would the photon shoot off in a random direction? Suppose you have one target ten meters away...
  7. B

    I Work Out Number of Photons in Vacuum

    given a complete vacume.(Excluding the photons) given a volume. given a temprature. given a wavelenth. work out the number of photons in the vacume?
  8. W

    Understanding Image Formation: Exploring the Role of Photons and Detectors

    General question regarding how images are formed. As you move your eye "detector" around a illuminated room. The is image of let's say "a book" is in every position in the room at a given time correct--even before you "look" at it? The photons reflected off the book have formed an image of the...
  9. Adiater

    I Double-Slit Interference w/ Separate Sources

    If you have two similar coherent sources which are separated from each other by a barrier. Now one source sends particles one by one into one slit and the other sends particles into the other in a double slit interference experiment. Now, the photons are always undistinguishable, so they should...
  10. gmalcolm77

    I Photon Frequency: Can a Photon Change Color?

    Can a photon ever change frequency? What I mean is, can say a photon of red light ever become a photon of green or yellow light?
  11. R

    I Why don't we ever hear about low-frequency photons?

    We're told that all electromagnetic radiation consists of photons. But you never hear them mentioned when discussing low-frequency radio waves. Why not? I get that, due to the low frequencies, the energy of each individual photon would be very small, so there must be lots and lots of them flying...
  12. F

    I How can electrostatic fields be composed of photons?

    I know little about QED, QCD, and whatever the corresponding theory for the weak force is, and of course virtually nothing about the quantized theory of the gravitational force, which mostly doesn’t exist, so the following arguments and questions may be somewhat wrongly based where they refer...
  13. K

    I Thought experiment: Photons in a box

    Consider a box whose walls are mirrors. Suppose we trap a bunch (yes, it's vague) of photons inside the box. They will not escape, or assume that a major part of them will not escape the box. Now suppose we have a way of decreasing the size of the box at our will, but possibly obeying the laws...
  14. H

    Number of Photons inside a Laser Cavity

    << Mentor Note -- thread moved from the technical forums, so no Homework Help Template is shown >> Let's say you have a laser cavity with two mirrors at either end, one is considered 100% reflective, the other 99.9%, so that a wave beam is emitted through this lower reflectivity mirror. I know...
  15. P

    B Photons, mass, and black holes

    If photons are light particles, and they lack mass, how is it possible that they are affected by gravitational pull from a black hole? Super sorry if this has been asked / answered before, I couldn't find it on this forum if it has... Caveat No.2: My physics knowledge was limited to high school...
  16. slow

    Exploring the Behavior of Parallel Photons in a Vacuum

    Hi. Maybe you can help me understand something. Two identical photons travel parallel in a vacuum. I want the lines of their trajectories to be as close to each other as possible. 1. If each photon could observe the other, what would it detect? 2. Is there a minimum separation necessary to...
  17. C

    I Time Delay on Multiple Photons when travelling from one plac

    I'm trying to understand the time delay induced on each photon when several individual photons travel in an open space from a sender to a receiver for example in the application of Quantum Key Distribution. So what I understand so far is light(photon) travel around 299,792 km (186,282 miles) per...
  18. E

    I What's the interval between photons in stimulated emission?

    What's the interval between photons in stimulated emission? In stimulated emission one photon induces the emission of a second photon whose coherence length, energy, polarisation and direction of travel are all identical to its own. There must be a delay between the two photons, see below, so...
  19. J

    Reasoning for photon having no mass

    Other than relativity is there any theory, proof, experiment, etc. that tells us a photon has no mass? i.e. Is the concept of zero mass solely derived from relativity
  20. F

    B What happens to virtual photons when an EMF is extinguished?

    Let's say I feed the same electrical signal into the opposed windings of a contrawound toroidal coil, and that this results in their individual electromagnetic fields cancelling to "zero". Can someone explain what in turn happens to the virtual photons associated with those canceled fields? For...
  21. Dadface

    I Spontaneous parametric down conversion photons

    When I look at certain experiments involving entangled photons generated by spdc, for example quantum eraser experiments, it seems to me that each observed pair of entangled photons is propagated in a horizontal plane. However, aren't the entangled photons generated randomly in all planes...
  22. T

    What is light exactly? Electromagnetic wave or photons?

    When why sey that light is electromagnetic wave i understand this. But what i do not understand is where photons come into picture ? can somebody explain me the relationship between those two . My knowledge in this respect is not great so I would ask that the answers be adjusted .
  23. F

    I Is the Existence of Photons Proven by Modern Quantum Optics?

    from wiki "Although the photoelectric effect and Compton scattering strongly suggest the existence of the photon, it might alternatively be explained by a mere quantization of emission; more definitive evidence of the quantum nature of radiation is now taken up into modern quantum optics as in...
  24. Pushoam

    The effect on a photocurrent of reducing the frequency of photons

    Homework Statement Homework EquationsThe Attempt at a Solution As frequency is decreased to threshold, no. of emitted electrons will remain same, but their maximum kinetic energy will decrease. So, the current should decrease slowly. For frequency less than the threshold frequency, no...
  25. ISamson

    B Light, Photons, Waves, Particles: Wave-Particle Duality....

    Me and my friend have recently (half a year ago) had a huge debate, between ourselves, about the wave-particle duality. We took sides in light being a particle or a wave. I was for particle he was for waves. At the end of a hot-filled week of arguing, the debate ended up with the acceptance of...
  26. Kara386

    Roughly estimate the probability that 2 photons are from Higgs

    Homework Statement Make a very rough estimate of the probability that two high energy photons with an invariant mass of 126GeV are decay products of the Higgs. Use information found elsewhere (so I need to find this info preferably on the internet). Homework EquationsThe Attempt at a Solution...
  27. MichPod

    I Modified double-slit experiment - two photons

    On the following link https://physics.stackexchange.com/questions/183961/modified-double-slit-experiment-two-electron-sources-instead-of-two-slits there is a discussion of the modification of double-slit experiments where two electrons sources are put in place of the slits. The conclusion is -...
  28. J

    The relation between photons and waves

    Hi everyone! Sorry for the bad English! Please, I learned that a wave is something the photons "surf" on, like, in one electromagnetic wave, can have many photons. So, is this true? Like, I though that one gamma ray and an infrared photon would ride different waves... More: the light from the...
  29. SunRay-dvsh

    A Why light beams attract or repel each other even when they don't have charge

    Hi, Can someone please explain as to why light beams attract or repel each other even when they don't have charge. Seems like it behaves like two current carrying parallel wires. There is very little material about this which goes completely above the head. Thanks
  30. S

    B Decoding Dark Photons: Gauge Symmetry in the Dark Matter Sector

    If there were dark photons in the dark matter sector.. should it be described by gauge symmetry.. in other words.. should the dark photons be gauge bosons? or nongauge bosons just like the higgs?
  31. F

    I Measurement of a particle's position using photons

    I've read that a particle's position can be measured by firing a photon at it, but how does one actually determine the position of the particle by doing this? What is the maths behind it (is it calculated from momentum conservation)? Furthermore, I've read that increasing the energy of the...
  32. S

    Problem about momentum uncertainty

    Homework Statement According to the Big Bang model of cosmology, the universe has been expanding since some initial time (call it t = 0) when the temperature was infinite. At early times, the temperature T scales as t^1/2 . The current temperature is about 3K. Consider the part of space which...
  33. Buckethead

    B Why do photons allow Doppler shift

    If we (a detector) are moving toward a star that emits a single photon (due to its distance) and that photon hits our detector, it will be blue shifted. My question is why. If the color of a photon is a reflection of its energy level and since the speed of the photon is always coming at us at...
  34. F

    I Exploring the Existence of RF Photons in NMR Spectroscopy: A Scientific Analysis

    Some will claim that RF energy being composed of photons can only be accepted on faith because there is no experimental evidence and there probably will be no experimental evidence due to the comparatively long wavelenghts of RF waves. But the technique of NMR (nuclear magnetic resonance)...
  35. itoero

    I Entanglement-questions photons

    Photons contain kinetic energy. When you entangle photons, do you change the properties of the kinetic energy which forms the wave energy? Kinetic energy is proportional to temperature... Kinetic energy is also proportional to relativistic mass.(in Special Relativity) So is the mass of...
  36. T

    I Interpretation of photons having zero spin

    What is the interpretation of the fact that photons have spin zero? Does it has do to with the fact that their proper time variation is zero? Or let's go a bit deeper into the math. If it's possible to write down an eigenvalue equation for photons as it is possible for electrons, then we should...
  37. weezy

    I Why do people keep saying photons are timeless?

    If you search for "does a photon experience time", almost every other link says that they travel at the speed of light and so STR tells us that its clock doesn't tick at all. However why do they use the arguments for special relativity which was developed for massive particles moving close to...
  38. R

    B How does force transfer through an object microscopically?

    I heard that you can never really touch anything. I also heard from an article that the reason why your butt doesn't fall through your chair is due to forces. Here is a short excerpt: "Cracking like lightning through the void, all the specks of electrons and the specks of nuclei are constantly...
  39. K

    I Does the wave function shorten when approaching light speed?

    Relative to the observer, objects shorten when approaching the speed of light exponentially. Does this rule also apply to the wave function? Does this rule also apply to massless particles like Photons? Or am I just simply forgetting something?
  40. C

    I If electromagnetic waves propagate, do photons as well?

    In classical physics, EM waves propagate this is one of the main features of all waves in general. Usually for mechanical waves the elements (like molecules) that vibrate do some little motion. For example a string can move up and down, but the waves travel further through propagation. The...
  41. T

    How are photons able to carry messages?

    I'm having trouble understanding how simple particles can be received and then with that information translated into a song on the radio or a program on television. Any help?
    • Timvanhoomissen
    • Thread
    • Tags
      Photons
    • Replies: 8
    • Forum: Optics
  42. T

    I Are photons from the CMB being emitted from beyond our cosmological horizon?

    Is there more to our universe than what we can observe? If so, does that mean that photons from the CMB are traveling towards us from beyond our cosmological horizon?
  43. C

    A Generalizing distinguishability of photons on HOM dip?

    Hello all. I am trying to determine what is the effect of having photons that are distinguishable undergoing a quantum interference process. To do that, I try to generalize the Hong-Ou-Mandel effect, and try to determine what are the terms that appear as a function of the product of the creation...
  44. C

    B Can Mirrored Solar Arrays Create a Continuous Ion Channel for Energy Transfer?

    If one was to create an array of X amount of mirrors tracking the sun and shining on a targeted spot in the sky to create ions at specific elevations similar to a ladder, could this cause an ion column to create a continuous charge of energy from the upper atmosphere to hit the ground? Lets...
  45. O

    B Why don't emission/loss of virtual photons lower a charge's energy?

    Hello all, I came to know that electric(electromagnetic in general) force between charge particles is mediated by photons. At first I just wondered what are photons doing here? I mean till what I know is that photons bundels of energy for em radiation and that they are massless but have...
  46. lawlieto

    I Are any electrons ejected below the threshold frequency?

    I've been reading about the photoelectric effect, and something got me thinking. If the frequency of light shone onto the metal is below the threshold frequency, no electrons are liberated from the surface of the metal, since electrons absorb quanta of energy, so if that light is shone for a...
  47. E

    I Can Photons travel faster than c?

    I've looked up this question on the web, and I've gotten seeming conflicting answers. According to Feynman's path integral - to find the probability of a photon being at A at time 1 and B at time 2 can be determined by taking an integral of the photon traveling over all possible paths. I...
  48. Strange design

    Infrared radiation from friction

    Hello all, I was driving down the road yesterday, and I realized that I don't really have a solid grasp on how frictional forces cause infrared radiation. Can anyone explain, or direct me to a resource that explains, how this happens at the atomic level? I am thinking that the work done...
  49. C

    A Simple way to create entangled photon pairs?

    Two photons arrive at a hypothetical 50:50 Beam-Splitter with no phase shift between reflected and transmitted modes. One enters the Left side and the other the Bottom side of the BS as shown in Fig.1 of the link below: https://drive.google.com/open?id=0B5JsDLKoUSA5emk5Qk9nUHVIelE Each photon...
  50. Grinkle

    B Can Photons be in a Stable Orbit? GR Analysis

    Does GR allow for photons to be in a stable orbit around a massive body?
Back
Top