And without mass, there would be no stars, no planets and no atoms?

Without mass try defining momentum and kinetic energy. Now write down the Scroedinger eq. which is why this is not so crazy

[Well, this amounts to "without mass the laws of physics are different. Or, restarted, "if the laws of physics are different then the laws of physics are different". That's true, but trivially so -W]

Yes without mass particles travel at the speed of light.
Now the thing is, MOST of the mass of a proton, say, doesn't come from Higss mechanism, but rather from the mass equivalence of binding energy of the quarks and gluons.

But if you take away the Higgs mechanism the Standard Model doesn't work so you can make up what you want now.... you are already counterfactual (good to be able to say that).

Tree forest facts mass. . . . Yep

> Yes without mass particles travel at the speed of light.

Yep, without rest mass. But then they gain mass, any mass:

mc^2 = hf

with f the frequency.

(Trying to imagine a hydrogen atom made up of a massless proton and a massless electron, orbiting each other at the speed of light... yes that package would have a (rest) mass and its centre of mass would not itself travel at c. I think :-)

[Ah, now you're giving them mass via relativity. Quite how SR or GR is supposed to interact with Higgs stuff I don't know - everyone has been very quiet about that -W]

William, what rock have you been sleeping under? Of course this stuff is relativistic. The full 4-D monty. You could get away with forgetting about GR, but SR is part of the fabric where the standard model has lived for the last, eh, half century or so :-)

BTW after more thinking I now see that my massless-particles atom likely wouldn't work... it would be metastable. Perhaps that's what was meant with 'atoms cannot exist'.

The Higgs gives the fundamental particles in the Standard Model their *rest* masses.

(Particle physicists often don't use the "relativistic mass" concept because half the time they're using a system of units where the speed of light is 1, so "energy" is already a perfectly good word for that: E=mc^2 is so fundamental it fades into the background. When they say "mass" they mean rest mass, or, in other words, the energy a particle has even when it's standing still.)

And, yes, a particle with no rest mass travels at the speed of light. To first approximation, at least: quantum field theory introduces all sorts of semantically tricky wrinkles having to do with virtual particles and off-shell amplitudes.

If it weren't for the masses given by the Higgs to quarks and leptons, nuclei would behave completely differently and atoms as we know them really wouldn't exist.

...It is worth saying, though, that 99% of your mass doesn't come from the Higgs at all, it comes from energy associated with quark-gluon interactions. The quark masses in the Standard Model that come from the Higgs are only a small portion of the proton and neutron masses.

A massless particle at rest has no energy. Therefore, in SR, massless particles at rest don't exist. A massless particle traveling at less than c will be at rest in some inertial frame. Therefore, massless particles with v < c don't exist in SR.

Besides the particle's mass, we also have some of the rates at which it decays into other particles, and those rates are consistent with a standard model Higgs boson. In some circles, what we have so far is known as the "disaster scenario": a standard model Higgs and no surprises. No Higgs at all would give more hints.

Objection! My comment is very moderate, it has no need to await moderation. It merely needs to have its moderation recognized.

[You'll need to talk to my software guv, not me -W]

Without mass try defining momentum and kinetic energy.

This step is actually quite easy. Photons carry momentum and energy--that's the principle behind a solar sail.

Quite how SR or GR is supposed to interact with Higgs stuff I don't know - everyone has been very quiet about that -W

As Martin pointed out upthread, the theory intrinsically includes special relativity. SR was developed precisely in order to make classical electrodynamics self-consistent and, as theoretical physicists say, manifestly covariant (i.e., any inertial frame of reference is as good as any other). Einstein's paper on SR was called "On the electrodynamics of moving bodies."

GR is another matter. There is no shame in your not knowing how GR and the Higgs work together, because nobody else knows, either (which is one reason people have been quiet about that). There is a branch of physics called string theory which has been working on that problem for about three decades, so far without obvious success.

"... photons have momentum without having mass ..."
http://www.physlink.com/education/askexperts/ae270.cfm

Not knowing a whole lot about this, having been told that Higgs particles give other particles mass, I might have imagined that Higgs give the quark-gluon interaction its mass as well. (How? Would Higgs give it its energy? Or would Higgs give energy its mass?) Apparently not so - thanks for clearing that up for me.

>"but they only know the mass so far, not any other properties?"

Well they know it decays in 5 different ways each as predicted by SM theory. The branching rates to each of these decay channels are within error limits so far consistent with SM but error bars are wide: eg decay to gamma gamma is currently nearly twice rate expected. If this nearly twice holds up rather than being a fluctuation that reverts to SM branching ratio then this may offer possible ways forward rather than HEP being stuck.

http://blog.vixra.org/2012/06/29/whats-the-deal-with-h-%e2%86%92-ww/