Source
r/Physics•
decatron

What does it mean for the mass of a particle to be dependent of the energy?

Question

I'm reading this statement:

At sufficiently high energies, all particles of the standard models are massless. Only after the electroweak phase transition do particles receive their masses through the Higgs mechanism.

I should probably know this, but I can't wrap my head around an elementary particle having anything other than constant mass. How should I think of this, either formally or intuitively?

Posted Oct 23, 2014, 8:21 AM UTC

4430
aroberge•

You are in a field full of mud. The longer you stay at one spot, the more you sink and it becomes incredibly difficult to extract your feet from the mud. You manage to do so and walk. The faster you walk (and the higher your kinectic energy), the less your feet sink in the mud and the less the mud slows you down. If you run fast enough, you actually feel like you are running on solid ground, and the mud has no apparent slowing down effect.

Like all analogies, the one above is not a faithful representation of what is happening with elementary particles interacting with the Higgs field. It is just meant to give you an intuitive idea of how interactions can vary with energy, and how apparent inertia (resistance to change of state of motion, more commonly called mass) can be lowered when the energy increases.

40
ZachGaliFatCactus•

Æther theory reborn in a backwards sort of way.

4
PostPostModernism•

I've been thinking about this for awhile as I learn more about field theories. Is the only real difference between old school aether explanations and current field theories like EM fields, Higgs fields, etc. that aether was presumed to be a physical substance?

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B-80•

Aether (in the classical sense as a substance embedded in space) comes equipped with the notion of a reference frame where the aether is stationary (which you could probably call a consequence of presuming it "to be a physical substance"). GR/SR shows us that this way of thinking can not be correct as it separates space and time.

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rantonels•

This makes it look like a faster particle interacts less with the higgs, which is wrong.

1
aroberge•

Of course it is "wrong"; like I said, it is not a faithful representation. The OP was asking about some intuitive idea so that he or she could wrap their head around the fact that elementary particles could have a mass that depends on their energy.

Perhaps you can come up with a better analogy.

2
LasseMyyry•

Sidebar posting rules seem to indicate this question would be more suited to r/askscience. Anyway, since their FAQ doesn't seem to include this, some quick points:

  • In the Standard Model, thinking about independent particles hanging in space doesn't always work. Everything is about fields, and how they interact : particles are just well defined ripples in those fields.

  • Personally found Prof. Matt Strassler's physics blog to be insightful. Directly related to your question is his If The Higg's Field Were Zero

  • In that view, most particles with mass are not that elementary. Like electron being mixture of electron-left & electron-right. The particle keeps flip-flopping between left and right due Higg's field : this interaction gives it intrinsic energy, which we measure as rest mass and inertia.

17
sickofthisshit•

I must admit ignorance about the standard model and the Higgs mechanism, but I think I understand enough to clarify one point. When you say "elementary" particle, it is not in the sense that an electron is composite, but rather that what you see is not a pure eigenstate but rather is dressed by interactions. This is quite similar to condensed matter, where the electron-like quasiparticles have different effective mass, but relatively energetic electrons act free.

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outerspacepotatoman9String theory•

Personally I think questions that involve RG flow are probably sophisticated enough to warrant threads in this subreddit.

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Ostrololo•

High energy in this context means high temperature. Just like water undergoes a phase transition to ice as temperature decreases, so does the Higgs field. At high temperature, the Higgs field is "off" and doesn't confer mass to elementary particles. Once the temperature gets low enough, the Higgs field suddenly gets turned "on" (just like how water suddenly turns to ice) and those particles gain mass.

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outerspacepotatoman9String theory•

My advice would be not to focus so much on the particles themselves. Don't think of a single particle with a nonconstant mass. Instead, think about the fact that what we really want to do is come up with a description of physics, in this case in the form of a QFT. It turns out that we need to use different descriptions at different energies. So, what we really have is a continuous family of theories that, in this particular case, have similar particles but with different masses.

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[deleted]•

[deleted]

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taedas•

So many questions.

Is there a critical temperature when mass turns off? Or is it continuous?

How does this relate to special relativity? Which says mass increases as you travel faster through space.

1
rantonels•

Mass in general does not turn on or off. It is the higgs vev contribution to mass of fermions and weak bosons that switches on/off with the electroweak symmetry breaking. There is a precise temperature for this, it's around the TeV scale, and I reckon it could be a sharp transition, but I'm guessing. It really depends on the temperature dependence of the effective higgs potential, of which I only have an intuitive understanding.

3
John_Hasler•

In this usage "mass" refers only to rest mass.

2
taedas•

So the rest mass decreases but effective mass increases.

What depends on rest mass and not effective mass?

1
elelias•

This is a very different question that relates e and m through e=mc^2.

What this means is that, if the lowest possible state of energy, which is called "vacuum" were a lot higher, then the lowest possible energy of the Higgs field would not induce the spontaneous breaking of the symmetry that the field has.

Since the universe cooled below that critic temperature, in every single point of space-time the Higgs field acquired a so-called "vacuum expectation value". By doing so, the otherwise massless particles now have to move through a vacuum that interacts with them and slows them down, therefore giving rise to a "mass" term.

Does that answer your question?

1
tangerinelion•

Just an aside, but can we stop with the e=mc^2 thing? It's wrong. There's a factor of gamma in there, unless you want to talk about the ever so outdated and non-physical "relativistic mass." Only in the case that kinetic energy is zero is gamma 1, and then e=mc^2 is correct.

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rantonels•

You should formally think of this as the m^2 parameter in the Lagrangian being scale-dependent. (Trivially, since it arises from dynamical effects).

Think in terms of quantum fields, not particles.

Also you shouldn't really think of the energy of a single particle, rather you should consider something like typical energies involved in interactions or even better thermal energy of the QFT.

You can't simply Lorentz-boost a muon up to ten TeV then expect it to look massless, you need to thermalize the higgs above phase transition temperature.

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aroberge•

Another way to gain some intuition about this is to consider the motion of a particle (not elementary particle ... say, a small metal ball) moving through liquid helium. Above the critical temperature, the ball will experience some drag which you can think of as increasing its mass/inertia. Below the critical temperature, helium becomes superfluid and its viscosity is zero, and the previously mentioned drag will disappear.

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[deleted]•

[deleted]

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decatronOP•

Thanks, but this isn't related to my question at all.

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glesialo•

e=m.c^2

m=e/c^2

-12
indigo121Undergraduate•

That equation is only valid for rest energy and mass

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glesialo•

As I understand it, energy supplied to a moving particle increases its speed and mass. The more its speed nears 'c', the higher percentage of supplied energy goes to increase the particle's mass.

I used to work in electron microscopy: faster electrons have higher mass.

1
decatronOP•

When I (and the majority of the professional physics community) say "mass", I mean rest mass.

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taedas•

This is what I learned too but op is saying as energy increases mass decreases.

I want equations for both of these models.

2
taedas•

E^2 =m^2 c^4 + p^2 c^2

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peteroh9Undergraduate•

You need to type spaces

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OCDyslexicParticle physics•

I like his version better

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peteroh9Undergraduate•

Honestly, I did too.

1
taedas•

Thank you should be fix now

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