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I'm sorry if this is a dumb question but physics is not really my area. I've been listening to the CBC Massey lectures by physicist Neil Turok, which I quite like. Anyway, when he talks about mass increasing at higher speeds, how does that happen? Is there actually an increase in the amount of matter or atoms or particles? Or does it just take more force to accelerate it? I had always thought that mass and matter were the same thing.

I'm sorry if this is a dumb question ...

I vote that it's actually inertia which increases, not mass.

How does mass increase at higher speeds?

Quote from: a_dark_knight on 05/12/2012 06:14:51I vote that it's actually inertia which increases, not mass.These are not independant things. Mass is the measure of something's inertia.

Quote from: cheryl j on 27/11/2012 18:32:17How does mass increase at higher speeds?It doesn't.

These are not independant things. Mass is the measure of something's inertia.

That's a really good point Dark Relativistic mass and 'gravity' are not the same. But if we use 'energy' as our measure then?

Hi Cheryl J; having worked through this thread I find myself wondering if your original question was answered. I think it may have been, but that could be because I had my own pre-conceived idea as to what it should be.I would be fascinated to know your thoughts.

Quote from: Bill S on 08/12/2012 17:05:45Hi Cheryl J; having worked through this thread I find myself wondering if your original question was answered. I think it may have been, but that could be because I had my own pre-conceived idea as to what it should be.I would be fascinated to know your thoughts.I think I'm more confused than ever.

okay, what about that weird meter stick thought experiment where different observers pass it going different relative speeds. Does the meter stick really become shorter as the observers approach the speed of light. Is there "less" of the meter stick? Because in this experiment it doesn't sound like the meter stick's mass, matter, or inertia has changed at all, the observers are different.

Let's take a example that gives us a totally new, and well earned, headache

Consider yourself heating up a gram of some, very, temperature resistant metal. You've weighted it before but after it gets heated you weight it again, finding it to weight more.

One way to describe it might be to consider the particles making the material accelerating inside the metal as they gain 'energy' from heat, moving agitatedly.

Can we then discuss those particles as gaining a relativistic mass, or not?

Do you remember when I showed that a system of 2 photons with opposite velocities has non zero invariant mass?

[quote = JP] If you understand mass as a measure of the "resistance" of something to being pushed faster, then it does increase as the speed increases.

Quote from: lightarrow on 12/12/2012 15:15:54Do you remember when I showed that a system of 2 photons with opposite velocities has non zero invariant mass? If the two photons are somehow bound together, the pair would act like a particle.

Since we're in the mainstream forum I'll refrain from speculating on what force or field could conceivable bind a pair of photons together.

A change in relative velocity, dv, of the center of the pair

(whether they're bound or not) is equivalent to looking at the pair from a different reference frame, having velocity dv relative to the center of the pair. SR gives the ratio of the pair's energy and momentum in the two reference frames. At non-relativistic speeds, the momentum ratio for a given velocity difference is the mass of the pair. That's what inertial mass is ... M = dp/dv. I don't accept the claim that a photon has no mass.

A bound pair of photons (if there is such a thing) would have a rest mass.

What type of mass does the "m" represent in the good old E=mc^{2}?

How do you define the centre in a system of two photons?

Quote from: lightarrow on 13/12/2012 15:27:49How do you define the centre in a system of two photons? Tough question! [] Next, consider a reference frame moving in the +x direction at .866 c relative to the first reference frame. Gamma = 2; so in this reference frame, the photon moving in the +x direction has energy E'_{1}= E/2, and the other photon has energy E'_{2} = 2E. Do I have that correct?

Quote from: Phractality on 14/12/2012 00:35:27Quote from: lightarrow on 13/12/2012 15:27:49How do you define the centre in a system of two photons? Tough question! Next, consider a reference frame moving in the +x direction at .866 c relative to the first reference frame. Gamma = 2; so in this reference frame, the photon moving in the +x direction has energy E'_{1}= E/2, and the other photon has energy E'_{2} = 2E. Do I have that correct? No. In the first case: E' = sqrt[(1-beta)/(1+beta)] = sqrt[(1-sqrt(3)/2)/(1+sqrt(3)/2)] = 2 - sqrt(3) ~ 0.268E; in the second case: E' = sqrt[(1+beta)/(1-beta)] = sqrt[(1+sqrt(3)/2)/(1-sqrt(3)/2)] = 2 + sqrt(3) ~ 3.73E.

Quote from: lightarrow on 13/12/2012 15:27:49How do you define the centre in a system of two photons? Tough question! Next, consider a reference frame moving in the +x direction at .866 c relative to the first reference frame. Gamma = 2; so in this reference frame, the photon moving in the +x direction has energy E'_{1}= E/2, and the other photon has energy E'_{2} = 2E. Do I have that correct?

Thanks for the correction. I had a feeling I got it wrong. I know how to do the math, but the math corner of my brain was in full revolt. I'm wondering, now, if I should consider the center of the two-photons to be the center of energy; equivalent to center of mass. Applying inverse square law to the energy of each photon to get a ratio of each photon's distance from the center. My brain hurts; maybe I'll just play solitaire, instead.

You can't localize a photon, so you can't do that.

I'm not a Higgs expert, but from what I understand it won't be too revolutionary to have found the standard Higgs. This is because it's been part of the Standard Model for a while (since the 1960s, I think) and people have spent a lot of time thinking about its implications. If we find the standard Higgs particle, it validates the model, but doesn't introduce new physics.

Yor_on, here's the same question, but in a slightly more extreme form: If you have a box made of perfect mirrors and you inject some light into it, the box's energy has now increased. If it's sitting still next to you, its mass increases (by E=mc^{2}, which holds for stationary objects). So clearly its mass, measured at rest, went up. Since invariant mass is supposed to not change with reference frame, and the rest frame is a reference frame, its invariant mass also went up. Additionally, if you try to push it, you'll find its inertial mass went up. But photons individually have no mass? How did it gain mass?

To what I've learned from physics, photons dont have mass, but they do have impulse. Photons can 'push' things when something absorbs or reflects it. The mirrors reflect the photons. So when you push the box and accelerate it a bit, photons push harder against the side you push. So you feel resistance. Even so photons are following the spacetime curve of gravity, so they tend to move more down then up in the box. So more photons reflect to the bottom then to the top of the box. This way the box feels heavier.My question is, does this increased mass you feel, because of the 'impulse pressure' (or whatever you call it), also generate gravity?

But mass creates a gravitational field. Whereas inertia doesn't, in my opinion.

That's the distinction I'm referring to.

Mass also implies the amount of "stuff" …

So does that mean that things moving near the speed of light have a larger gravitational field than they would otherwise?

But that doesn't count for uniformly moving bodies Pete, right?

Or do you mean that it is strictly observer dependent, and so needs two bodies in relative motion versus each other?

But that way 'gravity' would 'fluctuate' with what observer we have in relative motion, relative what body's gravitational field he measures.

My thought has been, and still is, that uniform motion no matter its speed, as measured relative something else, has no effect on the gravitational field surrounding it?

Physicists like to find the smallest common nominator for things, and when we (they) talk about mass then that should be 'mass-energy'.

But photons individually have no mass? How did it gain mass?

Quote from: bizerl on 12/12/2012 23:52:34What type of mass does the "m" represent in the good old E=mc^{2}?Invariant mass (the one sometimes also called "rest" mass or "proper" mass).