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. V

    Wavelength of Photons: 3-2 Transition

    Homework Statement Between which energy levels are the photons in this line transitioning? Wavelength= 660 * 10^-9 m Change in energy = 3.01 * 10^-9 A. 4 and 2 B. 3 and 2 C. 3 and 1 D. 2 and 1 Homework Equations...
  2. Prashan Shan

    What are the different forms of Virtual Photons?

    1).Virtual Photons forms in pairs like particles and anti particles? or 2).by borrowing energy from future? or 3) in both ways?
  3. mss90

    Melting ice - how many photons?

    Homework Statement how many photons (lambda=620*10^-9) must be absorbed to melt 2kg block of ice at 0deg into water at 0deg? and on average, how many H2O molecules does one photon convert from the ice phase to water phase? Homework Equations E=hc/lambda The Attempt at a Solution I have no idea...
  4. S

    Interaction mechanisms of photons and electrons with matter

    Hello everyone, I would like to ask a couple of questions related with the interaction mechanisms of photons and electrons with matter. Through searching about this subject, I have concluded that they both have different penetration depth and different interaction mechanisms. But apart from...
  5. F

    Rate of Lyman Alpha photons emitted....

    First off, I'm not sure if this question should go here or in the homework section. It is an astronomy homework question BUT there are only physics subtopics and did not want to post it in the wrong section. Let me know if it should be moved to there! Homework Statement Consider a nebula...
  6. bcrowell

    Emitting two photons in a single transition?

    A student asked me a question last night that stumped me. Suppose we have an atom in its first excited state A, and it's going to decay electromagnetically to the ground state B, losing energy E. We would expect this to occur through the emission of a photon with energy E. But what prevents it...
  7. P

    Do Photons Experience Time? Exploring Time Dilation & Redshift

    I've often heard the speed of light and time dilation related from the standpoint of a particle as being in constant motion at the speed of light with the vector rotated slightly off the temporal dimension and toward any combination of the three spatial dimensions. Does this mean photons...
  8. Eddie Sines

    What are the benefits of using superconductors for energy conversion?

    New member here, would love to talk about superconductors, photons and electrons and energy conversion. Feel free drop drop me a question.
  9. E

    Why photons don't interact with the Higg's field

    hi every one i am only 14 so can we please try and make answers in such a way that i will understand them. i am wondering as to why photons do not interact with the higes field many thanks Evenus1
  10. H

    If photons have no charge then how

    do they deflect / accelerate electrons in an antenna? For an electron to accelerate it has to experience an electric field or changing magnetic field. What I can tell from the standard model a photon carries no charge = no electric field. Further a classic EM wave is defined by an E vector...
  11. ryanuser

    Splitting Gamma-Ray Photons: Is It Possible?

    Is there a way to split gamma-ray photons into less energetic photons? And is the opposite possible, by combining low energy photons into a high energy one?
  12. M

    How Does Light-Matter Interaction Challenge Classical and Quantum Views?

    I have just started reading about a classical electromagnetic treatment of light-matter interaction (beginning with dispersion relations, and then moving on to the standard phenomena - reflection, refraction, etc.). The discussion begins with a forewarning that light is not 'continuous' as the...
  13. Mohan Nivas

    Understanding the Sun's Role in Warming the Earth

    The sun radiates its energy in all directions by emitting photons. As the photons travel as electromagnetic waves it reaches the earth. The photons collide with atoms and molecules in the atmosphere due the collision the energy of photons are emitted as heat. The atmosphere is thus heated and it...
  14. CAH

    WHY can't electrons absorb photons of any energy?

    hey! So oribital electrons can only absorb photons if they are the exact amount of energy between energy levels unless it is more than the ionisation energy. But why can't they? Couldn't they just emit the extra energy or 'keep' it? Thanks :smile:
  15. CAH

    Photons emitted between energy levels?

    See photo attachment! (question 1(b) and see answer on mark scheme underneath) How can three photons be emitted? Either the electron drops down from 3 to 1 and skips 2 emitting one big 12.1 eV photon OR it falls down in step emitting two photons 1.9eV and 10.2eV. How can it emit more energy...
  16. CAH

    Electrons absorb exact energy photons so how is Ek possible

    Hello! I've read that electrons can only absorb photons of exactly the right amount of energy to move to a higher energy level, if its to little or too much then it doesn't absorb it at all, so my question: How can electrons be liberated from an atom with Kinetic energy when they can't absorb...
  17. P

    Static field from ensemble of photons

    Hi, In QED it is stated that an EM field can be written as a sum of quantized oscillators (the photons). In "classical" Electrodynamics, it can also be shown that the EM field decomposes into normal modes. But both the quantized oscillators (in the Heisenberg picture) and the classical normal...
  18. K

    Photons per second from lightbulb

    Homework Statement [/B] If 5 percent of the power of a 100 W bulb is radiated in the visible spectrum, how many visible photons are radiated per second? Homework Equations E=hf=hc/λ The Attempt at a Solution I know how to solve this, I just wanted to make sure. I will take 5 W or J/s as the...
  19. B

    Photoelectric current: why does it decrease?

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  20. P

    Creating Matter from Photons: Proton-Antiproton Bias?

    Given sufficient energy a proton/antiproton pair can be created from photons in the laboratory. Does the (apparently) slight bias exhibited in the big bang apply to the laboratory? In other words, the universe is seemingly not made of antimatter, only "matter." Pushing this idea further, is...
  21. L

    Photons -- can they have mass and travel at c?

    Hi everyone, many (sigh), many years ago, when I was in high school, I recall a little discussion we had with some classmates, which I gave little thought to at the time, but thinking back to it now, could never really figure out. It was about relativity. The story was that nothing could reach...
  22. S

    Measuring properties of entangled photons

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  23. N

    What chem reactn gives the highest rate of photons emssn/t ?

    I was trying to google it, but coudn't find any specific answer. Oxidation of Magnesium, for example, emits a lot of light. Is there a table of reactions by high much light they create ? What chemical reaction emits the highest number of photons per unit per time ? Thank you.
  24. Muthumanimaran

    Why do photons seem to defy the effects of time?

    As we know light travels very very large distances from far far away galaxy reaches our eyes, why it is timeless, I mean particles like muon disintegrates in time but photon does not why?
  25. A

    Why must an electron-positron collision produce gamma rays?

    Or, more specifically, what determinates the frequency of the photons emitted by a such a collision. I know that the number of photons produced depends on the spin and energy states of the initial particles.
  26. Shri13

    Photonic vacuum and atomic stability

    Hi friends, this is my third post of my curiosity. :woot: First of all a photonic vacuum (as defined by me) is a region of space where there doesn't exist any type of photons or EM radiations ( those too which are beyond the detection of our present tech... i.e. including each and every...
  27. Shri13

    Curiosity for existence of Anti- photons?

    Hello friends! I am a newbie here. I love quantum physics very much... especially the standard model of fundamental particles, QED, QCD, etc. I have an urge to create my own theory on space quanta (that's for another time...) but my main question is: Does anti-particle of a photon exist (i.e...
  28. S

    Whether Photons Do In Fact Age

    Hi I was posting on io9 on a thread that asked "what scientific fact transformed the way you view the world?" I posted I got that from Brian Greene in The Elegant Universe. Someone responded challenging me with. I'm really having a hard time making sense of his reasoning and why gravity...
  29. C

    Uncovering the Mysteries of Photons: Energy, Illumination, and Mass - FAQs

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  30. C

    Statistical mechanics: Total number of photons in a cavity

    Homework Statement Show that the number of photons in equlibrium at tempertaure t in a cavity of volume V is, N=[2.404 V (t/ħc^3]/Pi^2 The total number of photons is the sum of the average number of photons over all modes n->∑<s> Homework Equations n=Sqrt[nx^2+ny^2+nz^2] ωn=(n Pi c)/L...
  31. lukestar

    About "Light", need better understanding of it.

    Is there different types of light/particles of light? because all of these lights are different how it works, laser light, light from flash light, sun light. Why does flash light only illuminate only less area/more area depending on how much volts the battery is and a sun illuminates a whole...
  32. C

    Spins on electrons versus photons

    Suppose you measure the spin of an electron with a sensor oriented in the +z direction and find that the spin is up (aligned with the sensor). Now if you immediately measure the spin of the electon with a sensor oriented in the -z direction, you are guaranteed that it will be down (oppositely...
  33. ShayanJ

    Photoelectric effect without photons

    Recently I've seen claims here on PF(from some highly trusted members), that photoelectric effect can be described without using the photon concept and so can't be a demonstration of the quantized nature of light. This demonstration is only provided by more advanced experiments. After that, I...
  34. S

    Relativity & Photons: Exploring the Paradox

    Hi! First sorry my little bad english :-) My question is... A photon leaves the surface of the sun. It needs approx 8 mins to reach the Earth. Or we can say - in the notion of relativity - that the Earth needs 8 mins to reach the photon. BUT! Photons moving at c. And if we solve the Lorentz...
  35. 1

    What Are Photons? Effects of Electric Charges

    Are photons the things which are constantly emitted from electric charges in all directions, which then interact with other electric charges, or are photons something else? If photons are constantly emitted from electric charges in all directions, and photons are particles, as the ring of...
  36. Domenico94

    Solar panels and optical parametric oscillator

    Hi everyone. On these days, by watching solar panels and similar stuff, I just thought about it, and why they take such a wide surface to produce energy, and why their output is often low, as we all know. By navigating here on the internet, I've just seen a device called OPO (Optical...
  37. N

    Photons Travelling at Less than c in "free space"

    BBC has a small article on how Prof Daniele Faccio of Heriot-Watt University and Prof Miles Padgett of Glasgow slowed a photon to less than c in "free space", which I pressume to mean a vacuum. Done by "changing the photon's shape" via some medium. When the photon returned to "free space" it...
  38. teetar

    Photons = Wavelike, Particle-like, or Both?

    I've heard that basically photons can exhibit wave-like or particle-like based on what kind of experiment you perform to prove one or the other. However, are they hence both waves and particles at the same time? I'm not sure if this is a proper question, or if I'm misunderstanding something, but...
  39. E

    Do Photons Have Mass Despite General Relativity?

    I am knew only in year 9 but am doing some research on photons and was wondering how they have a mass of 0 as I thought every thing had to have a mass to be within the realms of reality or general relativity. but I might just be wrong and if so could you explain it to me simply why and the...
  40. Invutil

    Are photons imaginary particles?

    Since an electron generated a negative charge around itself and can push other electrons around itself, waves can travel through electrons. These are electromagnetic waves. But quantum theory proposes that the pushes between electrons happen in discrete packets. Electromagnetic packets called...
  41. M

    If photons have no mass,why would black holes attract light?

    If photons have no mass, why would black holes attract light? I was told that photons have no mass. However I thought that black holes are called "black" because no light can go escape the gravity force in their vicinity. I somehow think that, if light is just photons, then it should not be...
  42. S

    Quantum imaging with undetected photons - adding of states

    I have a question concerning the paper "Quantum imaging with undetected photons". http://arxiv.org/abs/1401.4318 In the schematic (Fig. 1) a photon (idler) is created at NL1 and passing the object at O to be reflected further to NL2. It is then stated in the paper "By reflection at dichroic...
  43. N

    Reading of planets billions of light years away

    We can see galaxies/planets light years away determine their composition such such as if they have water et cetera. My question is if light takes billions of years to reach us from there how is that we can determine such things? Is the speed at which a telescope can zoom faster than the speed at...
  44. R

    Do Photons Experience Time?

    It's my understanding (I might be talking senescence) that as an object approaches the speed of lights time starts to slow down, and if it achieves the speed of light time would stop. Do photons experience time?
  45. P

    Creating radiowave entangled photons

    I would like to create entangled photons at radiowave frequencies. To do this I thought it might help to understand as much details as possible how entangled photons are created by parametric down-conversion. Since the down-conversion doesn't happen often, what are the special conditions? Are...
  46. J

    How can I sort photons by spin?

    I want to split a photon beam with no net angular momentum into two beams in both of which the sum of photon spins is not zero.
  47. Ontophobe

    Do Photons Conserve Angular Momentum?

    Do photons obey the conservation law of angular momentum?
  48. O

    Does Electrical or Magnetic field attract photons?

    I have heard that photons are attracted by gravity. Does this apply to electrical or magnetic fields?
  49. V

    Lorentz-Invariance of Photons travelling parallel to each other

    Homework Statement Show the Lorentz-Invariance of the following spatial statement: Two photons are traveling parallel to each other. The relative position vector of the two photons is orthogonal to the velocity and has length d. Homework Equations / The attempt at a solution[/B] The first...
  50. V

    Why does recombination in PN junctions release photons?

    In a pure crystal structure of some semiconductor compound each molecule is usually bound to other four by covalent bonds, in other words each of the four valence electrons of each molecule is in a covalent bond with another molecule. At 0K all electrons remain in these covalent bonds, but as...
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