Massless Definition and 293 Threads

I have wondered how a photon could be massless, given E=mc2. I have seen explanations involving treatment of the situation through consideration of momentum. It seems to me my own explanation is valid, and I ask for comments. Actually E= m’c2 =gmc2, where g=1/sq rt{(1/[1-(v2/c2)]}. Photons...

Are there any other things/objects in our universe that are massless other than Gluons and Photons? I guess energy is massless, but it's not so much a thing, more-so a property.

So according to QFT, fundamental particles are just excitations in their underlying fields. So the photon would correspond to an oscillation of the EM field. But it takes energy to excite this field. And E=mc^2. So therefore the photon should have some mass. Energy was put into create it. That...

Homework Statement We're working in 2-d Anti-de Sitter space with metric: \begin{eqnarray*}ds^2 = \frac{1}{z^2}(-dt^2 + dz^2)\end{eqnarray*} with 0<=z. The solution is: \begin{eqnarray*}z^2 = (t+c)^2 + B\end{eqnarray*} And we've been asked to plot this (I think its a parabola with minima at...

Homework Statement I need to gauge the symmetry: \phi \rightarrow \phi + a(x) for the Lagrangian: L=\partial_\mu\phi\partial^\mu\phi Homework EquationsThe Attempt at a Solution We did this in class for the Dirac equation with a phase transformation and I understood the method, but...

Physical polarization vectors are transverse, ##p\cdot{\epsilon}=0##, where ##p## is the momentum of a photon and ##\epsilon## is a polarization vector. Physical polarization vectors are unchanged under a gauge transformation ##\epsilon + a\cdot{p}=\epsilon##, where ##a## is some arbitrary...

What is the moment of inertia of massless (ideal) pulley that has a string attached to its center and a mass m attached to that string? If this pulley were hanging from a massless rope that was attached on one side to the cieling and the other side had a tension of mg, what would be the...

since gluons are massless, shouldn't glueballs also be massless? is there any possibility gluons acquire mas by interacting with other gluons, not higgs?

Hello! Could anybody help me? My wondering seems so trivial, but I can't skip it. They say that since u and d quarks are much lighter than QCD scale(~200MeV), in reality we can consider the QCD Lagrangian has an approximate global chiral symmetry with respect to these two flavors. At first, it...

< Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown > Problem Statement: Case 1: Mass is m; Cross sectional area is uniform A. What will be the stress in the middle section. Case 2: Bar is massless; What will be the stress in the middle section...

Just finished reading Sean Carroll's "The Higgs Boson and Beyond". I would be grateful if someone could explain how gravity, which I understand to be a function of mass, can interact with massless particles as evidenced by the phenomenon of gravitational lensing. I understand that gravity is a...

Homework Statement A box of textbooks at unknown mass rests on a loading ramp that makes an angle α = 16o with the horizontal. The coefficient of static friction is 0.30, and kinetic friction is 0.25. Then the box is released. (a) Will it start sliding down the ramp? (a) Find the normal force...

If a metric admits a Killing vector field ##V ## it is possible to define conserved quantities: ## V^{\mu} u_{\mu}=const## where ## u^{\mu}## is the 4 velocity of a particle. For example, Schwarzschild metric admits a timelike Killing vector field. This means that the quantity ##g_{\mu 0}...

I think I have never seen a force equation for massless particles, I wonder if such thing exist or if not why not?

(I think) I know that massless particles can only exist traveling at c, but I find it somehow counter-intuitive (like many other real things... :D ) Would anyone please be so kind to confirm that, for instance, a gamma photon generated by the radioactive decay of a stationary isotope is already...

Homework Statement So, a string with length L and a mass of M is given tension T. Find the frequencies of the smallest three modes of transverse motion. Then compare with a massless string with the same tension and length, but there are 3 masses of M/3 equally spaced. So this is problem #1...

Photon have the same size as an electron(i think) but no mass. Gluons also. WHY

QUOTE: "In 1929, physicist Oskar Klein[1] obtained a surprising result by applying the Dirac equation to the familiar problem of electron scattering from a potential barrier. In nonrelativistic quantum mechanics, electron tunneling into a barrier is observed, with exponential damping. However...

Homework Statement The double Atwood machine has frictionless, massless pulleys and cords. Determine (a) the acceleration of masses ma, mb, and mc, and (b) the tensions Fta and Ftc in the cords. Homework Equations F=ma The Attempt at a Solution So I drew free body diagrams for the mass A...

Consider a ##j## point all massive leg one loop polygonal Feynman diagram ##P## representing some scattering process cut on a particular mass channel ##s_i##. Invoking the relevant Feynman rules and proceeding with the integration via dimensional regularisation for example gives me an expression...

The main obstacle to FTL is that mass increases with velocity and in the book of my imagination there is a blank spot on how to nullify the mass of a star ship. I can't help but think the answer is hidden somewhere in Albert's equation E=MC2.

Is higgs boson massless? Photon is massless , is photon get mass when interract with water?

since a massless spin 2 field when perturbatively quantized gives rise to gravitons, which couple to everything and is identical to gravitation, is spacetime itself massless spin 2 field? do virtual graviton exchange also modify time and space?

(Note: The title would better describe the subject if written like this: "2 blocks on a horizontal frictionless surface connected by a massless string vs. pulley system")Hello, I have a problem regarding pulling two blocks of different masses connected by a string horizontally with opposing...

Are massless particles always their own anti-particle? Thanks in advance.

I f a particle starts moving with the velocity of light it becomes massless.But practically a massless particle has no existence.Again one of the main constituents of light is photon,then is it a massless particle?But I know electron has the least mass in this world and photon is heavier than...

may i ask you something? if there is any wrong excuse me. according to mass-energy equation mass &energy are not different but two forms of the same. photon ,graviton... are the mass less particles but photon is a form of energy. can you explain why photon is massless?

is defined or not? Thanks.

Is it possible to have a free massless scalar field in 1+1 spacetime and then add another field of the right type which interacts with some adjustable strength with the massless field to give mass to the massless field? Is there a Higgs-like mechanism in 1+1 spacetime? Thanks for any help!

I am pulling a rope and that rope is pulling another body which is attached to rope. The force applied by me on the rope will be equal to the force applied by rope on that body if 1. The rope can't increase in length due to force, or 2. if the rope is massless. I understand the reason behind...

The speed of light is a parameter that attaches itself to what exactly, an inertial frame of reference or a massless particle moving therein?IH

If we take one end of a mass-less string and pull it with force F, would the string have any tension in it? Would it have any tension when we pull it with force F from both the ends?

i'm still wondering, i know a bit of quantum mechanics and general relativity. well... very very little, if photon is a particle, it must be "something" right? i mean, something that exist in this space and time. why is "something" that "exist" don't have a mass? what is it consist of? or...

I think I have read that massless fermionic states can be used (as a basis?) to build up massive fermionic states. Is that true? If so, could you please give me a very short outline of how this is done, or maybe better, a mathematical statement that "says" the same thing? Thanks for any help!

Homework Statement Consider a situation I'm curious why is that the massless pulley's acceleration is just the avarage of acceleration of m1 and that of m2? ab=(a1+a2)/2 Homework Equations Forces acting on pulley are Tc-2Ta=0 (because pulley is massless, force can't give it acceleration)...

It looks to me like all the massless particles so far discovered may be force bearing particles, there being 3 of them. Am I right? If so can it be said that forces propagate at the speed of light whilst what we might think of a tangible particles cannot? I did post this question on another...

Suppose we have a massless complex field in 3+1 spacetime where E^2 = P^2. Suppose that the only excitations that are possible are those that in some rest frame consist of an excitation of a pair of states p1 and p2 such that p1 = -p2 and ιp1ι = ιp2ι = mc^2 = (+or-)E, and the pair of states p1...

Can a Massless Photon create Mass? Is Electrostatic Induction a form of “Mass Transfer through the process of Absorption”? A new star is created. The star generates massive Magnetic Fields. What happens to the hydrogen particles, Nebula, when they are influenced by the Magnetic Field? If the...

Are photons massless? They have energy and can be affected by gravity, so don't they have mass? I've heard plenty of people say that photons are massless, does this just mean that they have negligible mass? Also, if only light/photons can move at the speed of light, then wouldn't everything be...

Homework Statement A simple pendulum of length ##b## and bob with mass ##m## is attached to a massless support moving vertically upward with constant acceleration ##a##. Determine (a) the equations of motion and (b) the period for small oscillations. 2. Formulas ##U = mgh## ##T = (1/2)mv^2...

From what I understand Einstein was the person who decided length contraction would indeed occur in the vector of velocity, more so as you approach c. If it were possible to accelerate a particle to c, would the length would become 0? If the length were to become zero, would the notion of mass...

I was reading Schwartz's qft book. I saw the proof of ward identity taking pair annihilation as an example. he claimed he didn't assume that photon is massless in this derivation. but i have confusion with this statement. gauge invariance is a fact related to massless particles. now he has...

Homework Statement Homework Equations f_spring = k(x_near - x_far) The Attempt at a Solution a. FBD: The force goes through the nodes, and the sum of the forces must be 0 because the nodes are massless. Therefore, kx_1 = x(t) So x_1(t) = x(t)/k b. FBD: For this system, the parallel...

Let us imagine that there is a Massless spring with fixed at one end. Unloaded length = L Spring constant: = k Mass = 0The spring is at static Equilibrium Force: F Displacement: d F = k d, elongated length: L+d If I remove F, what will happen ? 1. Spring return to...

For a massive particle, say, an electron, we can use a spin vector ##\vec{S}## to denote its spin state, and the corresponding covariant four vector ##S^\mu##. And we have ##P \cdot S = 0## in the particle rest frame, so it holds in any frame for it is an Lorentz scalor. But, what if the...

Mass-less particles travel at the speed of light. If such a particle has an intrinsic spin, the DIRECTION of the spin angular momentum vector must be in the same direction as the linear motion of the particle. Why exactly is that? Thanks in advance.

Please note that I neither hypothesize the existence of such particle, nor know any evidence of it. This is purely a what-if scenario. So, my questions are: 1)Is there any law or whatsoever that forbid the existence of a massless particle that possesses charge? 2)If such particle exist, how...

Three Bosons: the Photon, the Gluon, and the Graviton are all massless Bosons; they all travel at the speed of light and therefore have no interaction with the Higgs field. How is it possible to differentiate between these three particles being that the Photon is a Majorana Fermion and therefore...

Does modern physics allow for the existence of massless fermions?

If a theory is spontaneously broken, you usually make calculations by expanding the field about the ground-state expectation value \nu , so that you define a new field \rho such that \phi=\nu+\rho such that \langle \rho \rangle =0 . What if you just calculate perturbation theory with \phi...