What is Massless: Definition and 293 Discussions

In particle physics, a massless particle is an elementary particle whose invariant mass is zero. The two known massless particles are both gauge bosons: the photon (carrier of electromagnetism) and the gluon (carrier of the strong force). However, gluons are never observed as free particles, since they are confined within hadrons. Neutrinos were originally thought to be massless. However, because neutrinos change flavor as they travel, at least two of the types of neutrinos must have mass. The discovery of this phenomenon, known as neutrino oscillation, led to Canadian scientist Arthur B. McDonald and Japanese scientist Takaaki Kajita sharing the 2015 Nobel prize in physics.

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  1. V

    Can something massless be stationary ?

    Hello to all, something came up in another forum and I would like to ask the following question ; In outer space, or anywhere outside a confined physics experiment, can something massless be stationary ? Regards, VE
  2. M

    Massless Particles: Can Photons Travel Faster than Light?

    Hey, well I've just been having a discussion with someone this minute, about traveling at the speed of light. We said that for something to travel at the speed of light, the partcile will need to be massless, but when I looked it up, I found that a particle has to have mass? Does a photon have a...
  3. Phrak

    Charged Massless Waves in Maxwells Equations?

    Hello. This is a first post for me. Do Maxwell's equations alone allow for propagating waves in charge/current (\phi,s[/B]J)? I was rather struck dumb by this question out of the blue. I've never seen it addressed, denyed or confirmed. Schematically the electric and magnetic fields are...
  4. W

    Why massless particles must travel at c

    Homework Statement give a logical argument for why a particle with m0 = 0 with nonzero energy has to move with a speed equal to c. Homework Equations The Attempt at a Solution I attempted using the momentum equation but I always get a multiplication by 0 which doesn't make sense...
  5. K

    Two Blocks, Massless Rope. Pulley

    Homework Statement The two blocks, m1 = 3.3 kg and m2 = 4.2, in the figure below are connected by a massless rope that passes over a pulley. The pulley is 12 cm in diameter and has a mass of 2.0 kg. As the pulley turns, friction at the axle exerts a torque of magnitude 0.35 Nm. If the blocks...
  6. S

    Normal frequencies of 2 pendula connected with a massless rigid rod

    Homework Statement I need to figure out the normal frequencies (or eigenfrequencies) of a system of two simple pendula (call them A and B), connected with by a massless rigid rod at an arbitrary distance from the pivot point or the mass. That is, the pendula are not connected at their masses...
  7. J

    Two masses on an inclined plane with a massless pulley

    Homework Statement A block of mass m resting on a 20 degree slope. The block has coefficients of friction mu_s =0.80 and mu_k =0.50 with the surface. It is connected via a massless string over a massless, frictionless pulley to a hanging block of mass 2.0 kg. What is the minimum mass m that...
  8. B

    Finding the energy and momenta of massless particles

    Homework Statement A pion spontaneously decays into a muon and an antineutrino according to pion^1- => muon^1- +antineutrino.. Current experimental evidence indicates that the mass m of the antineutrino is no greater than about 190 keV and may , in fact, be zero. Assuming that the pion decays...
  9. L

    Massless strings force problem

    help me! Homework Statement Three blocks on a frictionless surface are connected by massless strings, with M1 = 1.80 kg, M2 = 2.80 kg, and M3 = 3.70 kg. Due to the force F acting on M3, as shown, the system accelerates to the right. Given that T1 is 2.70 N, calculate T2 Homework...
  10. T

    The Irony of the Higgs Mechanism: Giving Mass to the Massless?

    Forgive if I'm being sarcastic, but I just read on the Higgs mechanism, giving mass to the fermions and bosons. But at the same time, Higgs itself has mass? Isn't that abit irony?
  11. B

    Massless photons is a hard concept to grasp

    how can an elementary particle like a photon be massless? How can physicist measure and detect a photon if the don't know its inherent properties? I know a photon travels at the speed of light , but wouldn't you have to know a particle mass , in order to know its speed? Or are physicists...
  12. T

    Fermions: Massless? Higgs & LEP Results Explained

    I read that fermions really should be massless when you write down the Lagrangian, as it violates the gauge symmetry. It's the Higgs coupled to them that give them their masses. I was so shocked. I have only learned QED and abit of QCD Lagrangian, and the fermions did have masses in the...
  13. C

    Is Light a Massless Energy or a State of Matter?

    Light is known a as some kind of energy that is being radiated; and energy is known as the fundamental source for any work. In addition, energy is known to be massless and so is light. Also light is the result of proton particles traveling in a very high speed known as the speed of light, which...
  14. R

    Is the momentum of a massive particle traveling at the speed of light zero?

    I know this isn't a deep discussion and the thread will be short but this question has been bothering me for a while and I hope the moderators won't terminate it. Are photons the only massless particles that travel at the speed of light? Diagrams of the standard model do not reveal the...
  15. R

    Do all massless particles travel at the speed of light?

    I know photons have no mass but are there other particles that have no mass and if so can they travel at the speed of light? Thanks RAD
  16. D

    How Do You Calculate the Frequency of Oscillation for a Massless Spring?

    Homework Statement A massless spring hangs from the ceiling with a small object attached to its lower end. The object is initially held at rest in a position yi such that the spring is at its rest length. The object is then released from yi and oscillates up and down, with its lowest...
  17. L

    Where can I find massless string for physics experiments?

    Hi, I am new to the forum. lol. I came here because in my physics class, many of the experiments call for massless string. Does anyone know where I could purchase some? I understand it is harder to come by, but I am willing to pay extra. Thanks a bunch
  18. L

    Understanding the Massless Photon

    (I hope I've chosen the right sub-forum for this question...) Hi folks - I've recently joined here to see if people who are more knowledgeable than me can help me understand some physics issues I have struggled with for a long time. My current question is a pretty basic one about how it is...
  19. L

    Forces on massless particles

    do massless particles not feel forces - other than gravity? The only massless particles I know are photons and neutrinos. Photons feel gravity, but other than that, once a photon is created, is its energy fixed? Laura
  20. S

    Understanding Massless Quarks in QCD and the Nambu-Jona-Lasinio Model

    I've been doing some reading on QCD, and I keep running into the notion of "massless quarks". Are they massless in the sense that if you look at E = \pm \sqrt{p^2 + m^2} the p^2 term dominates and E \sim p or is this something completely different?
  21. N

    Do massless particles always have momentum in the direction of travel?

    I'm not sure this is the right forum, but I wanted to ask the following (possibly bizarre) question: Is it implicitly assumed that zero rest mass particles have momentum in the same direction as they travel?
  22. F

    Rotating on a small platform attached by massless rods to a pivot

    I recall my teacher explaining this concept in class, but he did not go over how we would solve these types of problems: Bob the monkey (20 kg) is on a small platform (2 kg), which is attached by massless rods (R = 3m) to a frictionless pivot, and initially at rest...
  23. F

    Masses hanging on massless meter stick problem

    Two masses (mA = 3 kg, mB = 6 kg) are attached to a (massless) meter stick, at the 0 and 75 cm marks, respectively. a. Now, if mass B was removed, how much force would need to be exerted at the 100 cm mark in order to keep the meter stick level? b. Now, if mass B was removed, and no...
  24. F

    Angular acceleration problem - masses on massless rod

    A 3 kg mass and a 4 kg mass are attached to either end of a 3 m long massless rod. If the system is rotated about the center of mass by a force of 7 N acting on the 4 kg mass, (perpendicular to the rod), what will the size of the angular acceleration of the system be? I used angular...
  25. L

    Perspective of Massless objects

    Hey all! New to the forums here, and I must say, I've been greatly enjoying all the reading. Just three quick questions to ask... If one were able to have the 'perspective' or viewpoint of light, then they would see time as non-existent correct? They could go anywhere whenever and time...
  26. W

    Massive and massless quark renormalization in QCD

    In modify minimal subtract sheme,using dimension regulation, I calculate the the renormalization constant of massive quark and massless quark,get the same result.But in some papers,they are different. Is there a review or any book on MS renormalization,that giving all the self energy and...
  27. P

    Massless Charged Particles: Fact or Fiction?

    I've been studying the Yang-Mills theory, which predicted the existence of massless charged particles. That theory was later proven to be wrong, but it made me wonder nevertheless - can there ever be massless charged particles? And if such particle exists, how will it behave? How will it...
  28. C

    Electron Mass: A Fundamental Property or a Complex Concept?

    It was my understanding (however my understandings are wrong 99.9% of the time) that a electron was massless, and that it took the form of a wave that collapsed into a specfic point when it was "located" however, I was told that I am my friends AP physics class, there are told to use the...
  29. S

    Static Equilibrium of massless rope

    A uniform sphere of mass m and radius r is held in place by a massless rope attached to a frictionless wall a distance L above the Centre of the sphere. Find the tension in the rope and the force on the sphere from the wall. I tried to get a picture, but it is apparently too big to host...
  30. C

    Do electrons really have zero mass?

    Electrons are "massless"? Why are electrons described as "massless". It seems to me that they would have to have mass. Are they truly massless or is this the same kind of aproximation that is made with ideal gas laws?
  31. ZapperZ

    Massless electrons behave relativistically

    "Massless" electrons behave relativistically This is just one of a zoo of examples from condensed matter where relativistic forms manifest themselves via condensed matter phenomena. http://physicsweb.org/articles/news/9/11/6/1 Just imagine. One could have a benchtop demo of QCD! Zz.
  32. I

    Massless particle revolving in a circle

    Given: A massless particle revolving in a circle with a rotational velocity = (2+sin(a)) To Find: Y-axis acceleration Method #1 (from rotational acceleration) Y-axis acceleration = (2+sin(a))(cos(a))^2 Method #2 (from Y-axis velocity) Y-axis acceleration =...
  33. A

    Period of Oscillation of Mass on Massless Rod with Springs

    A mass m is attached to a massless rod of length L to make a pendulum. In addition, when the rod is vertical, two relaxed springs with constants k1 and k2 are attached on either side of the mass to walls. What is the period of oscillation. I started by writing the potential energy as a...
  34. M

    Tunnel-effect possible for massless particles?

    For the tunnel-effect, the relation between the transmissioncoefficent T and length of the barriere L is: T=e^{-2KL} in which: K=\sqrt{\frac{2m(U_0-E)}{\frac{h}{2\pi}^2}} Now, the tunnel-effect is possible for light right? But light means m=0, meaning K=0, meaningT=1! I must be...
  35. F

    Kinetic energy of massless spring

    Alright I'm having a little trouble on this one... One end of a massless spring is welded to a flat surface; the other end points upward. A mass of 2.0kg is set on top of the spring. The spring is then compressed by hand so that the end of the spring is 42cm lower than the position of the...
  36. G

    Massless Strings: How Particles Vary in Mass

    how is it that some strings have mass (spin 1/2 particles) while others have no mass at all (spin 2 particles and force carrying particles)? all strings are the same, its just how they move and vibrate that they change from particle to particle, but wouldn't this mean that all strings either...
  37. K

    Gravity and massless particles?

    I'm sure this is a very newbie-level question, but how is it that massless particles and light are affected by gravity? I've been reading about the 'ghost condensate' theory, and the latest article in New Scientist that says these massless 'ghost' particles should have been sucked up by black...
  38. S

    Is Light Massless? Understanding the Nature of Photons

    Does light is massless ?
  39. C

    Neurinos are massless paricles

    I've heard that it is thought that Neurinos are massless paricles, but I'm now hearing that they have kinetic energy. Can something with no mass have kinetic energy?
  40. H

    Massless Particle? - Exploring Photon & Gravity

    "Massless" Particle? What is meant by a massless particle? I know that a photon is massless and travels at the speed of light. Then how is it that a black hole ( or gravity) can affect it? I thought that gravity affects only objects with mass.
  41. P

    Light Speed: Massless Particles, Unchangeable Velocity

    Where does the speed of light (~300000km/sec in vacuum) come from Is this the rotational speed of an electron. Up to Einstein a photon has no mass once it is in movement. Is the absence of mass the reason why speed of light cannot be modified ?
  42. S

    A massless, frictionless pulley is suspended from a rigid rod

    A massless, frictionless pulley is suspended from a rigid rod. Two masses, m (50 kg) and M (60 kg), are suspended on either side of the pulley, respectively, by a light, inextendable cord. Determine the accelerations of the masses. I drew the force diagrams of both; there is an upward...
  43. T

    Boundary Problem: Massless String with Knot of Mass 'm' at z=0

    So I have a wave incident on a boundary problem. The incidence is normal and the boundary is a knot of mass 'm' at z = 0, with the wave coming from minus infinity. The problem is that the string on the other side is massless, and I can't figure out exactly how that effects the boundary...
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