Massless Definition and 293 Threads

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. I

    Light has mass, and it travels at the Speed of light, so a massless object .

    Light has mass, and it travels at the Speed of light, so a massless object... I'm new to this entire field, and I know I'm probably wrong, and someone has already debunked this years ago, and if so, please either 1. correct me or 2.Add something. Since Photons have mass and when they comein...
  2. M

    How to detect nteraction between two massless particles?

    What equipment one can use to detect interaction between two massless particles, such a photons? Is that even possible? If it is possible, I guess the only thing that one will be able to measure is the difference in energy between particles.
  3. K

    Are Photons Massless? | Inquiry & Confusion

    This is just a random inquiry that's confusing me. I remember hearing at one point that the reason no object could travel at the speed of light is that an object with mass going at the speed of light would require an infinite amount of energy to get moving that fast. And that photons could do it...
  4. Q

    Solving a Frictionless Massless Pulley Problem

    Homework Statement A frictionless, massless pulley is attached to the ceiling, in a gravity field of 9.81 m/s2. Mass M2 is greater than mass m1. The quantities T1, T2, T3 and g are magnitudes. The Attempt at a Solution The Options are Greater than, Less than, Equal To T1 is...
  5. R

    How come massless photon has energy

    I don't much about it.. but according to Einstein's equation that E=MC squared which suggests that the mass is also a factor, therefore in theory that photon suppose not to have any energy but however... photon travels through the space without stoping..just like infinity.. does photon ever...
  6. P

    Why do massless objects travel at c?

    Why do photons, gluons, and all massless particles move at c? and will this fail if the Equivalence principle is disproved?
  7. FeDeX_LaTeX

    Exploring the Hypothetical Graviton: Is It Truly Massless?

    I was just reading a Wikipedia article about a hypothetical particle known as the graviton. It stated that it was massless -- but how is this possible? I thought that every particle has to have a mass.
  8. K

    How is Energy Defined for a Massless Particle?

    Homework Statement Show that if mass = 0, then E=pc and u=c. Homework Equations E^2 = (pc)^2 + (mc^2)^2 B = u/c = pc/E The Attempt at a Solution I understand that if m=0, then E^2=(pc)^2 => E=pc. But isn't p = Ymu? then: E^2 = (Ymuc)^2 + (mc^2)^2 Plugging in m=0 sets E=0... It seems...
  9. F

    Massless Particles and the algebra involved

    Homework Statement The positive pion decays into a muon and a neutrino. The pion has rest mass m=140 MeV/c^2, the muon has m=106 MeV/c^2 while the neutrino is about m=0 (assume it is). Assuming the original pion was at rest, use conservation of energy and momentum to show that the speed of the...
  10. H

    Exerting forces on massless objects

    Hi, I'm pretty sure that you must have a mass inorder to exert a force on something (at least from what I know). But can you exert a force on something that is massless? :S You can right? Because when we talk about massless springs and cords, things are exerting forces on them.. but then if you...
  11. P

    Massless Limit of Massive Field Theory: Right or Wrong?

    If I take the massless limit of a massive field theory (e.g. considering cross-sections or other observables), do I always obtain the "right" massless theory?
  12. C

    Massless Particles: Speed of Light & Gravitons

    Do all massless particles travel away from you at the speed of light regardless of you speed . i know light does , does this include gravitons .
  13. matt_crouch

    Massless Particles: Carrying Momentum?

    In my lecture this morning i was told that charged particles interact by the exchange of virtual photons and that they serve as carriers of momentum and force. But it says that a photon is a boson with spin number 1, massless and zero charge. The question is basically how can a massless...
  14. J

    Calculating Max Compression of Massless Hookslaw Spring

    Homework Statement A massless hooksw law spring has a unstretched length of L, when a mass m is ploaced on it, and slowly lowered until the mass is at rest, the spring is queezed to a length of x. the mass is then dropped on the spring from a height of h, use energ methods what is the...
  15. haushofer

    Non-relativistic limit of Klein Gordon (and massless limits)

    Hi, I have a conceptual question about taking non-relativistic (NR) limits of the Klein-Gordon equation, inspired by Zee's book on QFT (chapter III.5) So we have a complex scalar field with the equation of motion (\partial^2 + m^2 ) \phi = 0 Then we consider the fact that \phi \sim...
  16. R

    Exploring Flavor Symmetry Breaking in Massless Quarks

    If you model the quarks as massless, there should be no flavor mixing, because flavor mixing is achieved through the CKM matrix, which is a mass matrix. However, if quarks are massless, there ought to be an axial flavor symmetry, but there isn't. So to reconcile this, we must spontaneously...
  17. S

    Massless photon infinite speed?

    massless photon...infinite speed? ok here's the deal, a photon is massless its mass is 0 and f=ma then why is the speed of light not infinite
  18. M

    Massless Particles: Gauge Bosons, Photons & Gluons

    in what way are gauge bosons ,photons and gluons massless? please explain the significance of the massless nature,i mean every particle is supposed to have mass?
  19. N

    Massless representations of the Poincare group

    Never mind, I answered my own question...
  20. C

    Velocity of mass connected to a fixed rotating wheel with a massless string

    Homework Statement A mass of 0.8kg is attached to a massless string that passes over a pulley and is wrapped around a wheel of radius 0.5m, and rotational inertia 1.0 kgm^2. The wheel can rotate freely. The mass is initially held stationary at a height of 1.5m above the ground. When the mass...
  21. N

    The Pauli-Lubanski vector for massless particles

    Does anyone know how to prove that W^2 = 0 for massless particles, where W is the Pauli-Lubanski vector W^\mu = \frac{1}{2} \epsilon^{\mu \nu \rho \sigma} M_{\rho \sigma} P_\nu ?? The books I have either give no proof, or they rely on the expression obtained in the massive case...
  22. C

    Exploring the Physics of Massless Objects Traveling Faster Than c

    As I understand it (I don't study physics) any object with mass gets heavier and heavier as it accelerates, so it never reaches c. 'Light' has no mass, but can be regarded as essentially a fluctuation in the electric/magnetic field? From the definition of c^2=1/epsilon0/mu0, I interpreted...
  23. O

    Why masons can be massless but their composite quark and antiquark both massive?

    How masons can be massless while their composites quark (q) and antiquark (\bar{q}) are both massive? Is there any clear physical scenario to understand this?
  24. Spinnor

    Massive and massless modes of the anchored string.

    An anchored string is a simple modification of a vibrating string. We imagine a sideways restoring force applied to a vibrating string. The sideways force per unit length is proportional to the displacement of the string. This additional force gives the string the the same dispersion curve as...
  25. J

    Bound states of massless fermions

    If I look at the energy of the hydrogen atom, the energy is proportional to the mass of the electron (or more precisely, the reduced mass). Does this mean that without a Higgs mechanism, there are no bound states of the hydrogen atom? (Or is it just an artifact of a non-relativistic theory that...
  26. P

    Two blocks on a frictionless horizontal surface connected by a massless string

    Homework Statement Two blocks on a frictionless horizontal surface are connected together by a massless string. A second massless string is attached to the block of mass m2, as shown. Suppose you pull on this second string with a horizontal force directed to the right. Determine the ratio...
  27. V

    How can something be massless?

    I am confused about a problem that has arose from my reading of the forums. If something is massless, then how can it exist? I was taught that all objects in the universe have mass, however small, so how can photons and gluons have no mass?
  28. H

    Massless boson vs massive boson

    Hi, this might sound stupid, but I have a question. why does massless bosons, such as photon, gluon have an infinite range where w and z bosons have finite ranges??
  29. S

    Are There Any Massless Charged Particles and How is Particle Charge Calculated?

    I have the below doubts related to charge and mass.. Why charge always comes with mass? Why there are no massless charged particles? what prohibits it? Is there any theory that prohibits it Or still to find one? How charge of a particle is calculated?
  30. E

    Is there any exp. evid that massless photons cuves spacetime?

    Is there any experimental or observationa evidence that massless photons warp spacetime? Of course I know that in GR everything that has energy curves spacetime, including massless particles, but what-if this is wrong, and that particles must have mass to act as a "charge" for gravity? what...
  31. C

    Can massless quarks form massive hadrons?

    It is clear that the mass of the valence quarks is only a small fraction of the mass of the hadrons (for example, the proton). However, I wonder if it would be possible to get massive protons in QCD if the quarks were truly massless. On one hand, for massless quarks, the pions, as...
  32. R

    Inclined plane with massless, frictionless winch

    A 100 kg box is pulled up an inclined plane by a massless, frictionless winch to which it is attached by a massless rope. The plane makes an angle of 45° with respect to the horizontal. The coefficient of friction between the box and the plane is μ = 0.25 (with μs = μk). The winch has a radius...
  33. K

    Tension with a with a massless rope

    Hi... I have a little assignment where I'm not quite sure, what would be the correct answer... A massless pulley, is mounted to the ceiling with a massless rope. Over the pulley runs another massles rope, with a box with mass m in one end and a box with mass 2*m in the other. Q1) In...
  34. G

    Massless strings/pulleys: Finding the magnitude of the Force

    Homework Statement A massless string runs around two massless, frictionless pulleys, as shown in the figure below. An object with mass m = 10.3 kg hangs from one pulley. A force F is exerted on the free end of the string. What is the magnitude of the force F if the object is lifted at a...
  35. I

    Contact Forces with a Massless String

    Homework Statement Three blocks of equal mass (m = 0.88kg) are placed in a row onto a rough ramp (μ=0.77) whose angle of inclination is 35 (degrees). Each block is connected to the other by a massless string. Suppose you pull upwards on the top block with a force of 34.9N. Answer the...
  36. P

    How is Tension Distributed in a Massless Pulley System?

    A small man is sitting in a bosun chair that dangles from a massless rope, which runs over a massless frictionless pulley and back down to the mans hand. The combined mass of the man and the chair is 95kg. with what force magnitude must the man pull on the rope if he is to rise? Heres a link...
  37. L

    Calculating Tension in a Massless Cable for a Moon Orbit

    Homework Statement Suppose the moon were held in its orbit not by gravity but by the tension in a massless cable. You are given that the period of the moon's orbit is T = 27.3 days, the mean distance from the Earth to the moon is R = 3.85 x 10^8 m, and the mass of the moon is M = 7.35 x 10^22...
  38. M

    Massless Particles: At Rest & Why?

    Can we find massless particles at rest? and why?
  39. M

    Does massless particles experience gravity

    From Newtonian theory massless particles wouldn't experience force of gravity. Then from General relativity prospective gravity is ripples in space time due to a massive body so other objects move in the straight path in this curved space-time hence this objects appears to move in a...
  40. jtbell

    Why are massless photons affected by gravity?

    In general relativity, gravitation is a manifestation of the curvature of spacetime. The motion of all objects is affected by this curvature, regardless of whether they have mass or not. Light follows geodesic paths in spacetime, which are straight lines in flat spacetime, and curved paths in...
  41. L

    Massless free field equation -> Maxwell's eqn.

    Massless free field equation --> Maxwell's eqn. The massless free field equation is supposed to turn into the empty space Maxwell's equations for spin 1 (like a photon). But, in the book I'm using, Roger Penrose's "The Road to Reality", there seems to be a typo, because it's not quite...
  42. Z

    Why are Photons Massless? Zach's Questions

    I do not understand how photons are massless. I understand why they need to be massless, because if they had mass, you could accelerate them a little more and they would be going faster than the speed of light, but as a massless particle, you can't accelerate them, so that makes sense...
  43. Orion1

    Massless Schrödinger equation

    A massless particle situated in a 1D infinite square well with momentum only in the direction of quantum confinement (the x direction): E_t \psi (x) = \hbar \omega \psi (x) = i \hbar \frac{\partial}{\partial t} \psi (x) p(x) \psi(x) = \hbar k_x \psi (x) = -i \hbar \frac{\partial}{\partial x}...
  44. A

    NET Force on Massless Body: Acceleration & Spring Force

    What happens when the NET force on a massless body is 0. I mean what will be the acceleration , if any? Also if we pull a massless spring, from one side with a force F1 and from the other side a force F2, what will be the spring force?
  45. C

    Is U(1)xU(1) a valid electroweak theory with massive photons?

    The Higgs mechanism can give gauge bosons mass. However, in the electroweak theory, only W and Z get masses, not the photon. Is there any fundamental reason why the photon should remain massless? Considering the experimental limit of the photon mass (2. 10^-16 eV), is there any theory that...
  46. arivero

    Can Witten's Trick Apply to Any Number of Extra Dimensions?

    I have remembered Witten had a trick to see massless particles in 4+n dimensions as if it were massive particles in 4 dimensions. Does the trick works for any number of extra dimensions? Or only for 4+n=10?
  47. F

    Determining Min. Charge States of Yukawa's Particle & Why Gluons are Massless

    Hi, i am kind stuck on this question as i don't know what equation to use. doesn't seem to be in any books. By considering possible interactions between protons and neutrons, determine the minimum number of charge states of yukawa's particle. Also why is the interquark force of finite...
  48. X

    Massless Universe: Examining the Behaviour & Mass of Our Universe

    How would a universe with a total mass of zero behave? By comparing the expected result for a zero mass universe, can we be sure that our universe has total mass?
  49. R

    RS 1, massless scalar field, and sep of vars.

    Hey, this is rather involved but I hope someone can help me out. I am reading http://arxiv.org/abs/0704.3626 ( the casimir force in randall sundrum models) and am trying to get from equation 2.1 : g^{\mu\nu}\partial_\mu\partial_\nu\Phi+e^{2ky}\partial_y(e^{-4ky}\partial_y\Phi)=0 to...
  50. I

    Proving Massless Particle's Speed: 0.5c

    Homework Statement Massless Particles A neutral pion traveling along the x-axis decays into two photons, one being ejected exactly forward and the other exactly backward. The first photon has three times the energy of the second. Prove that the original pion had speed 0.5c. Homework...
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