Massless Definition and 285 Threads

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...

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...

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...

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?

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 .

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...

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...

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...

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...

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

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?

Never mind, I answered my own question...

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...

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...

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...

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?

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...

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...

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...

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?

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??

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?

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...

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...

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...

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...

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...

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...

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...

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...

Can we find massless particles at rest? and why?

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...

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...

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...

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...

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}...

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?

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...

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?

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...

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?

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...

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...

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

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...

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...

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...

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...

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...

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...