Massless particles Definition and 51 Threads

Coleman ("Quantum Field Theory Lectures of Sidney Coleman", p. 400) states: "Spin is a concept that applies only to particles with mass, because only for a particle of non-zero mass can we Lorentz transform to its rest frame and there compute its angular momentum, which is its spin. For a...

I feel like if something is massless it should be able to travel infinitely fast with any amount of energy. When you have something with mass, you would need an infinite amount of energy to push it infinitely fast, but if the thing you’re pushing is massless, you should be able to push it with a...

I am just reading Carroll's textbook on GR, where at the end of chapter 7.4 Gravitational Wave Solutions he discuss how rotational symmetries in polarization modes are related to spin of massless particles. He then explains that we could expect associated spin-2 particles to gravity - gravitons...

Would it be correct to represent the energy of massless particles before electroweak symmetry breaking as ##E = cp##, just as we do with photons post-symmetry breaking?

Before electroweak symmetry breaking, there were massless particles. Can these massless particles be seen in terms of energy momentum relation ##E = ##c##p##?

Most of the mass of matter comes from energy of strong force interactions between quarks. However the quarks still have intrinsic mass. Other particles have no intrinsic mass but still have energy. So according to mass-energy equivalence, these particles should still have effectively mass, to my...

Summary: massless particles (or at least photons) are attracted to other photons and to matter, but which is most attractive, and why ... Summary: massless particles (or at least photons) are attracted to other photons and to matter, but which is most attractive, and why ... I am really...

How could electrically charged particles be massless before the symmetry breaking? Wouldn't the energy stored in the electric field contribute to particles mass?

Poorly phrased but here goes - I'm trying to understand some of the SpaceTime videos on youtube, specifically the massless mirrored box and how the mass (ie resistance to acceleration) is a function of the change in momentum of the contained (constrained) photons. It makes sense but raises a...

If gravitational force is caused by a particle (tensor boson) which is massless and so travels at c, why doesn't matter ever exhaust, or even seem to reduce, its supply of these particles?

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...

If a photon does not experience time, how can it change? Without change, how can it have frequency?

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...

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?

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

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...

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.

Hello, I am a game developer working on a science fiction video game. The game is intended to be vaguely scientifically plausible and I'd love some advice from someone with a greater knowledge of physics than me! In the game, you have a futuristic device that creates cubes of "energy"...

I was hoping someone could help me with a simple physics question I've been mulling over, I've failed to find an answer using online queries, I suspect my line of inquiry is flawed in some way. I would be grateful if someone could confirm if I've understood this correctly: Particles without...

Salutations, question: ~wikipedia. I'm assuming that's because (correct me if I'm wrong) those particles would travel at c and you could not overtake them so their chirality and helicity are equal.But if a photon was coming towards you then zoomed past you surely the chirality would change...

First of all, i need to say that i have read various threads posted by other users in physicsforum who have asked the same question. However, I still don't have a clear picture of why massless particles must travel at c. Personally, I have came up with an explanation which is rather simple...

Hello, would you be able to recommend a book on introduction to relativity? A one that does a thorough comparison on the physics of massive vs. massless particles If the book is a popular read (low on math), that would still be quite okay. I am familiar with "Why does E=mc2" by...

I know physical bodies with mass cause gravitation. But do massless particles, like photons, also cause gravitation ? I know they're affected by gravity, but would a cloud of photons bend space by itself? Thank you

do all mass less particles travel at the speed of light?

On "why massless particles move at the speed of light" It has come up a few times whether you can derive that massless particles must go the speed of light, strictly using SR. Bcrowell proposed a way that some argued against. I have a different tack for consideration. I recently derived...

I have taken down in my notes that for massless particles the formula by DeBrogle becomes E = pc, where p is momentum and c is the speed of light. But what I don't understand is how you can calculate momentum without mass? I thought momentum was mass times velocity? The specific example I...

Why do massless particles have only two degrees of freedom, i.e. the two helicity states. Why do massless spin-j particles do not have 2j+1 degrees of freedom like the massive particles? thanks

Anything that is massless must follow null geodesics. Why is this?

Homework Statement A pion at rest decays into a muon and an antineutrino. The mass of the antineutrino is zero, find the energies and momenta of the muon and antineutrino. Mass of the pion is 139.57 MeV/c^2 and the mass of the muon is 105.66 MeV/c^2 Homework Equations pion -> muon +...

Are there any reactions in that require the interaction of massless particles or am I right in thinking this is impossible? Thanks

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.

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...

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...

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?

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...

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...

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?

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...

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 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...

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...

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

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

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?

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...