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Author Topic:   A Higgs Question
Percy
Member
Posts: 22392
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.3


Message 1 of 24 (457084)
02-21-2008 1:31 PM


The Large Hadron Collider (LHC at Wikipedia) is expected to finally answer the question of whether the Higgs boson (HB at Wikipedia) really exists. If it exists then it lends further confirmation to the standard model, which would probably disappoint most particle physicists. If it doesn't exist at any of the energies that theory says are possible then we know the standard model is incomplete, which we were pretty sure of anyway, but it would mean we'd finally identified one of the very borders between known and unknown where the standard model finally stops working. Particle physicists would find this very exciting.
The LHC will be able to produce the high energies necessary to produce the Higgs, which will exist for only an instant before decaying into a spray of lighter particles. Particle detectors built into the LHC will detect this spray and from it attempt to infer the existence of the Higgs.
The Higgs is highly intriguing to physicists because it is theorized to be the mediating particle of gravity. Just as light is transmitted by photons, gravity is theorized to be transmitted by exchanges of Higgs bosons. The Higgs field, supposedly generated by the motion of Higgs bosons just as electromagnetic fields are generated by the motion of photons, is what is thought to give matter mass.
But if the Higgs boson, unlike the photon, is highly unstable and decays almost instantly into lighter particles, how can it be the mediator of anything like gravity. A Higgs boson from our sun would take eight minutes to get here, far too long a journey for it to survive.
What's more, given that the Higgs is a massive particle it couldn't possibly move at anything like light speed, and so it couldn't possibly mediate the force of gravity at the speed of light.
Given these seeming contradictions, obviously I'm misunderstanding something somewhere. Can someone explain these things? Thanks!
--Percy
Edited by Percy, : Spelling and grammar.
Edited by Adminnemooseus, : Do stuff I suggested in message 2.

Replies to this message:
 Message 2 by Adminnemooseus, posted 02-21-2008 9:37 PM Percy has not replied
 Message 4 by fgarb, posted 02-22-2008 1:35 AM Percy has not replied
 Message 5 by cavediver, posted 02-22-2008 6:02 AM Percy has replied
 Message 16 by kalimero, posted 02-26-2008 5:15 PM Percy has not replied

  
Adminnemooseus
Administrator
Posts: 3974
Joined: 09-26-2002


Message 2 of 24 (457249)
02-21-2008 9:37 PM
Reply to: Message 1 by Percy
02-21-2008 1:31 PM


The abbreviation/acronym police in action
What's a LHC? Is it like LSD? LDS? PBS? PBR? BGR?
A link to this LHC might also be a nice thing (and what's this "Google" everyone keeps talking about?).
To the "Big Bang and Cosmology" I presume?
Input from other admins welcome.
Adminnemooseus

This message is a reply to:
 Message 1 by Percy, posted 02-21-2008 1:31 PM Percy has not replied

  
Adminnemooseus
Administrator
Posts: 3974
Joined: 09-26-2002


Message 3 of 24 (457258)
02-21-2008 10:53 PM


Thread moved here from the Proposed New Topics forum.

  
fgarb
Member (Idle past 5391 days)
Posts: 98
From: Naperville, IL
Joined: 11-08-2007


Message 4 of 24 (457265)
02-22-2008 1:35 AM
Reply to: Message 1 by Percy
02-21-2008 1:31 PM


Percy writes:
The Higgs is highly intriguing to physicists because it is theorized to be the mediating particle of gravity. Just as light is transmitted by photons, gravity is theorized to be transmitted by exchanges of Higgs bosons.
The higgs particle actually is not expected to mediate gravity. That's what the graviton supposedly does (another theorized particle which is much less likely to be experimentally observed in the near future). Rather, there is a theory called the higgs mechanism, which was put forth to explain why other particles have mass. A necessary consequence of this mechanism is the existence of a new spinless particle called the higgs boson. It works out to be the case that the stronger this boson interacts with other particles, the greater their mass, and massless particles would have no interaction at all with the higgs boson.
There's no good way to explain how this all works without delving into a lot of nasty math. Briefly, the higgs mechanism assumes a higgs field which has a potential energy that is only at its minimum when the field is not at its equilibrium value. If you assume that the field settles into one of its minimum energy states, that breaks a symmetry which produces masses for other particles and creates an observable higgs boson.
Percy writes:
But if the Higgs boson, unlike the photon, is highly unstable and decays almost instantly into lighter particles, how can it be the mediator of anything like gravity. A Higgs boson from our sun would take eight minutes to get here, far too long a journey for it to survive.
It's true that the higgs boson would decay extremely quickly. But it's the higgs mechanism that supposedly creates mass for other elementary particles, not the higgs particle itself, so that's not a problem.
Percy writes:
The Large Hadron Collider (LHC at Wikipedia) is expected to finally answer the question of whether the Higgs boson (HB at Wikipedia) really exists.
Just to put in a plug for an American experiment, the Tevatron collider at fermilab is putting a lot of effort into searching for the higgs right now. Depending on the mass of the higgs, there's a quite good chance that it has already produced some higgs particles, there just isn't enough data yet for anyone to be sure. Right now the race is on for the tevatron to gather enough stats to discover or rule out the higgs before the LHC gets up and running.
Percy writes:
If it exists then it lends further confirmation to the standard model, which would probably disappoint most particle physicists.
Maybe. There are other theories besides the standard model which predict the presence of one or more higgs particles. The simplist form of supersymmetry, for example, predicts five different higgs particles with different masses and charges. I think I remember reading that some kind of supersymmetry must be correct for string theory to be true, so it would be very interesting if multiple higgs were discovered and their properties were consistent with supersymmetry rather than the standard model.

This message is a reply to:
 Message 1 by Percy, posted 02-21-2008 1:31 PM Percy has not replied

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 5 of 24 (457276)
02-22-2008 6:02 AM
Reply to: Message 1 by Percy
02-21-2008 1:31 PM


fgarb has answered your main points so I'll just add a bit of my own.
As explained, the Higgs boson, and the entire Higgs field in general, has nothing to do with gravitation - or at least no more than any of the other quantum fields. Remember, space-time curvature is generated by mass/energy, where-as the Higgs mechanism produces effective rest-mass. The photon has zero rest-mass but it still has energy and hence still couples to space-time curvature.
The mystery is not why do fundemental particles (electron, quark, etc) have rest-mass, but why do they have such a small, yet non-zero rest-mass? We were talking about Planck Energy yesterday - well that is equivalent to a Planck Mass. That is the natural scale for the rest-mass of quantum excitations (particles) So, particles should really have masses of zero, 1 PM, 2 PM, 3PM, etc. The problem is that 1PM is HUGE. It is 2.176 10^-8 kg !!! The observed rest-mass of the electron is 9.109 10^-31 kg !!! Something is very wrong here. The elctron mass should be zero, or 22 orders of magnitude larger than its observed value.
This is a signal that the electron rest-mass is not fundemental but is an effective rest-mass generated by some mechanism... now, it is possible that each particle type has its own mechanism for generating its own effective rest-mass. But it is much more parsimonious that there is one extra field with just one mechanism that is responsible for all of the particles rest-masses: the Higss mechanism is our favourite method. Essentially, all of the known particles have zero rest-mass, but have an induced rest-mass caused by interactions with the Higss field.
The Higgs field, supposedly generated by the motion of Higgs bosons just as electromagnetic fields are generated by the motion of photons...
Wrong way round - the Higgs bosons are ripples in the Higgs field, just as photons are ripples in the em fields.

This message is a reply to:
 Message 1 by Percy, posted 02-21-2008 1:31 PM Percy has replied

Replies to this message:
 Message 6 by Percy, posted 02-22-2008 7:41 AM cavediver has replied

  
Percy
Member
Posts: 22392
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.3


Message 6 of 24 (457282)
02-22-2008 7:41 AM
Reply to: Message 5 by cavediver
02-22-2008 6:02 AM


To Fqarb and Cavediver,
Thanks for the explanations, much appreciated. Let me explore what I sort of get and what I sort of don't.
I somehow confounded the Higgs boson/Higgs field with gravity when they're actually theorized to be the responsible for giving mass to particles. A particle's mass is a function of how strongly it interacts with the Higgs field.
Do I have it right that there are theorized to be two contributors to rest mass, one a function of quantum excitations, the other a result of interaction with the Higgs field?
Stepping out on a limb, since mass is responsible for the shape of space time, then how strongly particles interact with the Higgs field governs the shape of space time, and so in some way should be related to the exchange of gravitons, if they exist.
Cavediver says that photons and Higgs bosons are actually ripples in fields, but what is a field, EM or Higgs, made of if not of the particles that, uh, transmit (?) the field? Oh, wait a minute, could the field be thought of as some kind of probability function for finding the appropriate particle at any particular point in space/time? If so then I get it, sort of, kind of.
Sometimes I feel like I'm getting glimpses of what I miss due to not understanding the math and having to rely upon analogies and visualizations.
--Percy
Edited by Percy, : Grammar fix in last para.

This message is a reply to:
 Message 5 by cavediver, posted 02-22-2008 6:02 AM cavediver has replied

Replies to this message:
 Message 7 by Son Goku, posted 02-22-2008 8:26 AM Percy has not replied
 Message 8 by cavediver, posted 02-22-2008 8:36 AM Percy has replied

  
Son Goku
Inactive Member


Message 7 of 24 (457286)
02-22-2008 8:26 AM
Reply to: Message 6 by Percy
02-22-2008 7:41 AM


Fields
This is a very difficult thing to explain. A quantum field is a very unusual object and there are at least four (five?) different ways of conceiving of what it is. Strangely enough, the most mathematical approach is usually the easiest to explain.
You could consider the field as the collection (set of) probabilities to measure a value for some physical quantity in a given region of spacetime. A simple example is "the probability to measure an energy of 0.0004 Joules in Seattle between 1 A.M. in the mourning and 2 P.M". The probability (or what the field really gives is the square root of a probability) is a complex number and the field is the set of all such complex numbers for any given quantity, time and location.
There are also rules for relating the probabilities for measuring things as viewed by different observers. So if I'm measuring some quanitity A, the rules can tell me the corresponding quantity B that a guy moving at half the speed of light might measure. However usually the rule is quite complicated and can be broken down into simpler individual algorithms.
Particles are simply a collection of observables that transform in a very simple way, their rules don't break down any further.
(I'm aware that this is a very empirical way of visualising things, but I just thought I'd put it out there as I'm sure cavediver will give a more physical one)
Edited by Son Goku, : Addition

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cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 8 of 24 (457287)
02-22-2008 8:36 AM
Reply to: Message 6 by Percy
02-22-2008 7:41 AM


Do I have it right that there are theorized to be two contributors to rest mass, one a function of quantum excitations, the other a result of interaction with the Higgs field?
Yes, though we only ever see the zero quantum excitation contribution as anything above that is far too large.
Stepping out on a limb, since mass is responsible for the shape of space time, then how strongly particles interact with the Higgs field governs the shape of space time, and so in some way should be related to the exchange of gravitons, if they exist.
No. You are confusing mass and rest-mass. Rest-mass makes almost negligible contribution to the observed mass in the Universe. The rest-mass of the quarks in a proton is about 6 MeV. The mass of the proton is 938 MeV. All that extra mass is just the binding energy of the zero rest-mass gluons.
what is a field, EM or Higgs, made of
They're not made of anything - they are fundemental. In grand unification, there is just one quantum field, and in a full theory of quantum gravity, that field is unified with space-time. So there is only the space-time: a balloon with ripples running over its surface.
The only description/explanation of the fields is the mathematics of algebraic topology - and this is where it appears that the mathematics is the actual substratum upon which the 'physics' rests. It is at this level of understanding that theoretical physicists start to become pseudo-Platonic.
Edited by cavediver, : No reason given.

This message is a reply to:
 Message 6 by Percy, posted 02-22-2008 7:41 AM Percy has replied

Replies to this message:
 Message 9 by fgarb, posted 02-22-2008 10:07 AM cavediver has replied
 Message 13 by Percy, posted 02-25-2008 10:51 AM cavediver has replied

  
fgarb
Member (Idle past 5391 days)
Posts: 98
From: Naperville, IL
Joined: 11-08-2007


Message 9 of 24 (457290)
02-22-2008 10:07 AM
Reply to: Message 8 by cavediver
02-22-2008 8:36 AM


Hi cavediver,
cavediver writes:
Percy writes:
Stepping out on a limb, since mass is responsible for the shape of space time, then how strongly particles interact with the Higgs field governs the shape of space time, and so in some way should be related to the exchange of gravitons, if they exist.
No. You are confusing mass and rest-mass. Rest-mass makes almost negligible contribution to the observed mass in the Universe. The rest-mass of the quarks in a proton is about 6 MeV. The mass of the proton is 938 MeV. All that extra mass is just the binding energy of the zero rest-mass gluons.
Are you saying that the higgs mechanism would have no gravitational effect at all, or that it would just be small compared to effects from binding energy? To phrase it another way, if the lifetimes of much heavier particles were long enough that many of them were still around from the big bang, would the higgs mechanism then dominate gravitation? I should admit up front that I have never taken a GR course.
Also, am I correct that you and Son Goku are cosmologists? If I may ask my own question, I am curious about how the Tevatron and the LHC are viewed within cosmology circles. Does anyone expect much useful data to come out of them, or would you need collisions of much higher energy (closer to the Plank scale) to test most cosmological theories?

This message is a reply to:
 Message 8 by cavediver, posted 02-22-2008 8:36 AM cavediver has replied

Replies to this message:
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cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 10 of 24 (457292)
02-22-2008 10:28 AM
Reply to: Message 9 by fgarb
02-22-2008 10:07 AM


Hi fgarb,
Are you saying that the higgs mechanism would have no gravitational effect at all, or that it would just be small compared to effects from binding energy?
It would just be small. Having said that, I'm completely ignoring dark matter. It's quite possible that the majority of the mass of dark matter comes from the Higgs mechanism, via WIMPs.
if the lifetimes of much heavier particles were long enough that many of them were still around from the big bang, would the higgs mechanism then dominate gravitation?
I'm not sure - I don't know how the binding energies would scale with the heavier generations of particles. A TTB baryon will be incredibly heavy just from the Higgs assocaited mass of the Ts and B, but what the lowest energy stsate of this configuration is, I don't know. It may be many times even this huge quark rest-mass.

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Replies to this message:
 Message 11 by Modulous, posted 02-22-2008 10:48 AM cavediver has replied

  
Modulous
Member
Posts: 7801
From: Manchester, UK
Joined: 05-01-2005


Message 11 of 24 (457293)
02-22-2008 10:48 AM
Reply to: Message 10 by cavediver
02-22-2008 10:28 AM


So what you are saying is that at the singular timeless energy there was no mass, but complex intelligence which had compressed itself into an unbounded energy out of nothing that created the Higgs to give everything mass and somehow this singular timeless complex intelligence was able to overcome gravity to expand the universe? Sorry, this thread is reaching a dozen posts and was completely rational. It just didn't look right to me.
I'm not going to waste a post though:
It's quite possible that the majority of the mass of dark matter comes from the Higgs mechanism, via WIMPs.
So if the majority of mass of dark matter comes from MACHOs, then you'd predict that the Higgs mechanism would only have a small gravitational effect compared with the effects of binding energy? Did that even make sense? I've written variations on the question and deleted them so often - I'm not even sure if I know what I'm trying to ask. Perhaps you can help me out?

This message is a reply to:
 Message 10 by cavediver, posted 02-22-2008 10:28 AM cavediver has replied

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cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 12 of 24 (457297)
02-22-2008 11:13 AM
Reply to: Message 11 by Modulous
02-22-2008 10:48 AM


Sorry, this thread is reaching a dozen posts and was completely rational
And may it long remain a safe haven for those of a truly inquisitive mind...
So if the majority of mass of dark matter comes from MACHOs, then you'd predict that the Higgs mechanism would only have a small gravitational effect compared with the effects of binding energy? Did that even make sense? I've written variations on the question and deleted them so often - I'm not even sure if I know what I'm trying to ask. Perhaps you can help me out?
That sounds right - MACHOs are made up of standard baryonic matter (protons and neutrons bound into nuclei) so binding energy will vastly dominate rest-mass in terms of contribution to space-time curvature.

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Percy
Member
Posts: 22392
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.3


Message 13 of 24 (457758)
02-25-2008 10:51 AM
Reply to: Message 8 by cavediver
02-22-2008 8:36 AM


Had to think about this for a while. Thanks to both you and Son Goku.
So a unified quantum field (which we don't really have a good model for yet?) includes what we call the electromagnetic field and the Higg's field? And different particles interact with this field in different ways? There's a mass-type response to the field, and there's an electromagnetic-type response to the field, and would it also be correct to say there are strong and weak responses to the field?
--Percy

This message is a reply to:
 Message 8 by cavediver, posted 02-22-2008 8:36 AM cavediver has replied

Replies to this message:
 Message 14 by Son Goku, posted 02-25-2008 11:26 AM Percy has not replied
 Message 15 by cavediver, posted 02-25-2008 12:44 PM Percy has not replied

  
Son Goku
Inactive Member


Message 14 of 24 (457761)
02-25-2008 11:26 AM
Reply to: Message 13 by Percy
02-25-2008 10:51 AM


Fields 2
Just to say something that could be confusing, particles do not interact with fields. Rather fields interact with fields. For instance, electrons are really just quanta or lumps of the Dirac field and photons are quanta or lumps of the electromagnetic field. Really all that happens is that the Dirac field interacts with the electromagnetic field. However photons are gregarious and hence tend to build up into a large scale classical field. Where as electrons exclude one and other and hence never build up into a classical field, which is why we think of them as particles.
I'm sure you've heard that electrons repulse each other by emitting photons, however equally photons can repulse each other by emitting electrons (this is called box scattering).
Basically particles are just as much a field as the electromagnetic field, since they are bits of a field.
Your post is mainly about unification and I have an explanation on the way, but my points above will be a prerequisite to any explanation so it's best to get them out of the way.

This message is a reply to:
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cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 15 of 24 (457767)
02-25-2008 12:44 PM
Reply to: Message 13 by Percy
02-25-2008 10:51 AM


As SG points out, what you call matter particles are just excitations in another layer of the universal field. At today's energy scale, the different layers of this field appear as separate fields, overlying each other. And that is the sum total of existence - a bunch of overlapping 4d fields. Mass, energy and even distance are all just descriptions of the states of these fields.

This message is a reply to:
 Message 13 by Percy, posted 02-25-2008 10:51 AM Percy has not replied

  
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