energy, mass, and the speed of light question

[gebreab]

Imagine two particles going the speed of light. Would this mean they have equal energy? Will they have to have a mass of 0?

 

Also does mass come from the fact that a particle has slowed down slower than the speed of light? Does its energy level matter?

 

If one particle is traveling speed of light, and particle 2 is traveling 1\2 speed of light, does particle 2 have 1\2 the energy?

 

In the end my question is does the energy and speed determine mass. Is this in proportion? Is speed proportional to energy? Does being heavy and low energy have to mean you go slow through space?

If a particle slows to half speed of light, does it lose half its energy? Does it gain in mass in proportion?

 

Thank you just wondering what mass and energy really are.

[D H]

Imagine two particles going the speed of light. Would this mean they have equal energy? Will they have to have a mass of 0?

 

No, they don't necessarily have equal energy. Yes, they have an intrinsic mass of 0.

 

 

Also does mass come from the fact that a particle has slowed down slower than the speed of light? Does its energy level matter? If one particle is traveling speed of light, and particle 2 is traveling 1\2 speed of light, does particle 2 have 1\2 the energy?

 

No, no, and no. Massless particles always travel at c. Massive particles always travel at less than c.

[gebreab]

OK thanks. I got another question! If a particle has to have 0 mass to go speed of light, does he have to have a certain energy? Is it a set value? Can it be 0. If energy doesn't give speed than what does?

 

Thanks for any insight

[Markus Hanke]

OK thanks. I got another question! If a particle has to have 0 mass to go speed of light, does he have to have a certain energy? Is it a set value? Can it be 0.

 

Particles travelling at the speed of light have always done so - massless particles cannot accelerate or decelerate, therefore no "minimum" energy is required. On the other hand a particle with zero rest mass and zero total energy would not be physically meaningful, since such an entity could not interact with its surroundings; for all intents and purposes it wouldn't physically exist at all.

 

If energy doesn't give speed than what does?

 

What "gives" speed is technically acceleration, which boils down to the expenditure of energy. The difference between massive and massless particles in that regard is that the former can experience acceleration, whereas the latter can't. Ultimately the reason for this is the geometry of space-time itself; massless particles always move along so-called null geodesics in space-time, which implies ( maths omitted here ) that they cannot experience acceleration and thus always propagate at exactly the speed of light.

 

[gebreab]

Thanks! I know its more complicated than this, but can i look at the speed of light as if it is a default speed, but something happened to particles with mass that slow them down?

 

Thanks for the patience and helpful answers, I appreciate it.

[e.brand]

Good question George, You said " particles of light " so you are talking about Photons. I always thought that Photons are exceptions to the rule ( more Velocity = more Mass ) meaning as you know, the faster something goes the more mass it gains.

 

The photon is the gauge boson or electromagnetism (1.) and therefore all other quantum numbers of the photon (such as lepton number: baryon number, and flavour quantum numbers) are zero. (2.)

 

 

(1.) Role as gauge boson and polarization section 5.1 inAitchison, I.J.R.; Hey, A.J.G. (1993). Gauge Theories in Particle Physics. IOP Publishin: ISBN 0-85274-328-9

 

(2.) See p.31 inAmsler, C.; et al. (2008). "Review of Particle Physics". Physics Letters B 667: 11340. Bibcode: 2008PhLB..667....1P doi:10.1016/j.physletb.2008.07.018

 

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The energy and momentum of a photon depend only on its frequency (ν) or inversely, its wavelength (λ):

 

 

 

where k is the wave vector (where the wave number k = |k| = 2π/λ), ω = 2πν is the angular frequency, and ħ = h/2π is the reduced Planck constant. (3.)

 

(3.) Davison E. Soper, Electromagnetic radiation is made of photons, Institute of Theoretical Science, University of Oregon

 

 

 

Since p points in the direction of the photon's propagation, the magnitude of the momentum is

 

 

 

 

 

Also as a gauge field, i.e., as a field that results from requiring that a gauge symmetry holds independently at every position in space time. (4.)

 

( 4.) Ryder, L.H. (1996). Quantum field theory (2nd ed.). Cambridge University Press. ISBN 0-521-47814-6.

 

For the electromagnetic field, this gauge symmetry is the Abelian U (1) symmetry of a complex number, which reflects the ability to vary the phase of a complex number without affecting observable or real valued functions made from it, such as the energy or the Lagrangian.

 

 

The quanta of an Abelian gauge field must be massless, uncharged bosons, as long as the symmetry is not broken; hence, the photon is predicted to be mass less, and to have zero electric charge.

 

I guess this is my round a bout way of saying, I am not sure but my guess would be no, I think the there would be no change in energy, but their would be a change in Velocity. So that means I have no idea, LOL. I would like to know one way or another, again good question.

[gebreab]

Thanks for the reply, I was trying to get a different picture of the universe. I have always seen it as static, or not moving. But now I am thinking everything is moving at blinding speeds right? So maybe the default speed of things is to go really fast, like the speed of light. And all the things that we see, like planets stars, are just a few things that happen to be traveling slower than the norm, perhaps because we gained mass or something, maybe in the higgs field, the new theory they are talking about.

[Delbert]

I understand that according to Richard Feynman what we call a photon travelling from A to B , is in fact a myriad of interactions. Possibly to the point that a photon doesn't exist (although I don't think he actually said that). Such that a photon is possibly nothing more than an event at the source and then an event at the destination.

 

After all, with the two slit experiment the photon apparently travels thought both slits to get to the destination! And doubtless, if we provided even more slits, it would travel through all of them as well to get to the destination.

 

With that in mind it seems a contradiction to experimental evidence to visualise two such particles 'travelling' together - or even travelling!