You asked questions about the LHC (and in particular, the believed discovery of the Higgs Boson) of physicist Giovanni Organtini. Organtini has responded (answers below), and written a brief introduction to explain what the Higgs boson is and how it provides mass to other particles:
"The Higgs mechanism was introduced to explain the fact that experimentally particles have mass. In fact, without the Higgs mechanism, the equations of motion for particles can only be written for massless particles. The actual mechanism is rather difficult to understand without a solid Quantum Field Theory background, but can be understood as follows: most of you know that particles gain some energy when they interact with a field. As an example, consider a book on a table. Since the book is subject to the earth's gravitational field, it has some potential energy that transforms into kinetic energy if it is free to fall. The potential energy depends on the mass of the book and on the intensity of the gravitational field. With the introduction of Special Relativity, however, we have to add an extra term to the energy of the book depending on its mass only (the famous E=mc^2). Introducing a special field (the Higgs field), we can turn this term into something similar to the gravitational potential energy, i.e. something that contributes to the energy of the book because it interacts with a field. The mass of a particle, then, is nothing but its potential energy in the Higgs field. The Higgs field is auto-interacting, i.e. it interacts with itself, as the electric and magnetic fields do. As the electromagnetic field can, the Higgs field can also propagate through space, but since it's auto-interacting, it gains some energy from itself, as the book gains energy from the interaction with it, resulting in the appearance of a mass for such a field, that becomes observable as a particle called the Higgs boson. You can find a more formal, yet simple, explanation of the mechanism here." Read on for his answers to reader questions.Why is Higgs so elusive?
This may sound really dumb but the answers to the dumbest questions are sometimes the most interesting :) I understand that the Higgs is responsible for giving mass to all the other particles, then it must be *everywhere*. Why is it so difficult to detect? Why does it take such a staggeringly powerful supercollider to find what ought to be as common as the electron or proton?
Giovanni Organtini: The Higgs boson is unstable: once produced, it suddenly decays into pairs of particles. As a result, it cannot be found in ordinary matter as protons or electrons. It must be produced and observed soon after. In order to produce new massive particles, we are used to smashing other particles together. It happens that the energy E of the collision can "materialize" into particles, provided that E>=mc^2, where m is the sum of all the particles produced in the collision.
The Higgs boson mass is about 125 times the proton mass: it is quite heavy, in fact! The higher the mass of the particle to be produced, the higher must be the energy of the collision. Moreover, it turns out that protons are not elementary particles: they are composed of quarks and gluons, collectively called 'partons'. It is the collision between partons that produces the Higgs bosons. Partons carry only a fraction of the total energy of the proton. Then, we had to build a very high energy collider to produce such a Higgs boson, such that the collision between two partons happens with enough energy to create a Higgs boson.
There are other limitations, too: the production of a Higgs boson, even if the energy of the collision is enough, is a rare process, much rarer than the production of other particles like those we already know. The collider, then, must not be just powerful in terms of energy; it must also be 'luminous' enough, i.e. it must produce billions of collisions, such that the expected number of Higgs bosons produced is large enough to be distinguished from background.
"Also, I can't help but to visualize particles as something like billiard balls while I'm aware they're only mathematical abstractions from our point of view and that experiments like the double-slit experiment refute the billiard-ball model... is there a way to visualize the Higgs to make the answer to my previous question easier to understand?"
Actually, from the mathematical point of view, there is no such a distinction between particles and fields. Both are represented in the same way. In fact, in quantum mechanics, there are neither particles, nor fields, as we imagine them. The 'objects' behave like fields in certain conditions and like particles in different conditions.
This may sound frustrating to some people, but you have to consider that physics relies on experiments. We cannot tell the Universe how it should work: it's just the opposite! Despite the fact that we cannot figure out what a particle that behave like a field is, experiments tell us that, in our Universe, sometimes particles behave like fields. That's all! There is no reason for Nature to work as we would like it. Nature works irrespective of our ability to imagine how it works.
In my opinion the best image you can have of a Higgs boson produced at LHC is just like a billiard ball, in fact.
Energy to mass conversion?
This is an IT worker question, not a particle physicist question, so hopefully it's an easy one. How does the Higgs boson come into play when photons, which have a tiny amount of mass, are spontaneously created when a substance like metal gets hot. Is it a direct energy to mass conversion?
GO: Photons do not have a tiny amount of mass. They are massless, as they do not interact with the Higgs field. When a metal gets hot, it's because you provide some heat — that is, a form of energy. You can always convert energy into particles (and vice versa) provided the total energy (i.e. including the rest energy mc^2) is conserved. As far as the metal glow, it gets colder, since the energy accumulated during heating is released in form of photons. There is no need for a Higgs boson in this case. Even this is not the case, energy to mass conversion is a common practice in high energy physics and is predicted by Einstein's Special Relativity. Each time we make two particles collide, they often produce new particles as a result of materialization of the energy of the collision.
The question, however, is interesting to discuss another feature. Despite that photons do not couple with the Higgs bosons, the latter were identified because of their decay into two photons. It may happen in quantum mechanics that a pair of particles 'annihilate' into photons. In this case, the Higgs bosons decay into a pair of quarks or vector bosons, that in turn annihilate producing two photons.
Is it higgsy?
What success or failure factors can/should/will be used to determine whether or not the new particle is actually the higgs, or something else unexpected?
GO: We currently have just a measurement of the mass of this new particle. We also know, from its decays, that it must have spin-0 or spin-2. In order to be reasonably sure that this new particle is in fact a Higgs boson we must precisely measure its spin and we also have to observe and measure the predicted decays.
To complete this task we need a lot more statistics. It will take years, probably, to obtain enough precision.
That said, assuming that the new particle behaves exactly like a Higgs boson in its decays, there is in principle no guarantee that it is the Higgs boson, in the sense that all these measurements do not prove that the observed particle is the one that gives rise to the existence of mass! However, I cannot believe that we observed a particle that behaves exactly as predicted for a Higgs boson that is, in fact, something very different!
Analogies to magnetic and electric fields?
One press report discussed the idea that the Higgs field might have the same transient existence that the aether did in Electro-Magnetic theory. Do you think there is a field that will interact with the Higgs field to produce an energy transmission function similar to that described by Maxwell's equations?
GO: The Higgs field interacts with itself and as such is able to propagate more or less as electromagnetic waves. The only difference with respect to the e.m. field is that the latter is massless and propagates to infinite distances, while the Higgs field gets mass and materializes into a Higgs boson. Due to its finite mass, it cannot propagate too far, in fact. Actually a Higgs boson decays into matter particles in tiny fractions of a second.
Higgs and the Ether?
The likely Higgs discovery would seem to validate Quantum field theory. Would this then be best described as an ether, only instead of matter traveling through the ether, matter is a manifestation of the ether (fields) itself? Would this also than mean that the motion of matter is not a physical movement of a "particle" but instead the transfer of the "excitement" of a field from one spot of the field to another?
GO: That is an intriguing question. I am personally convinced that there could be some relationship between the Higgs mechanism, inertia and the fact that the speed of light is finite, mostly because the Higgs field is a scalar field (I do not want to enter into details, here, but this is the first observed spin-0 elementary particle). In my opinion what physicists called Ether could in fact be something related to the Higgs boson. It must be said that there is no coherent formulation of this. It's just a guess I make (and not very popular among other physicists).
As already said, there is no difference between a particle that moves and what you called an excitement of a field from one spot to another, in quantum mechanics. Both are the same thing.
And what, if any, implications does this discovery have for unifying gravity or other areas of physics?
GO: It is hard to say. Despite the Higgs hypothesis was formulated some 50 years ago, no convincing theory emerged yet, unifying gravity and other forces. In fact it is not yet clear why the inertial mass (the one provided by the Higgs boson) is equal to the gravitational mass (the source of gravity).
Inertial mass vs. gravitational mass?
The Higgs boson is famously associated with how particles acquire a 'mass.' But mass is, in itself, an interesting property. As I understand it, the Higgs boson is only associated with inertial mass. If this is so, do you expect gravitational mass and inertial mass to be always the same? If so, would you speculate on the mechanism that ensures this is true?
GO: In fact the Higgs boson provides inertial mass to particles. As far as we know inertial mass is something fundamentally different with respect to the gravitational mass: the first is responsible for inertia; the second is the source of the gravitational field. We have no idea about why the two masses are numerically equal. We do not believe in coincidences. There must be a reason for that, but we could not yet figure out it.
If you want me to speculate, I can imagine that gravity comes into play because the Universe tends to remain stable. The Higgs mechanism predicts that an empty Universe is unstable, while a Universe with some amount of the Higgs field is stable, because its energy is lower than an empty Universe. We call this condition the vacuum condition (i.e. vacuum does not correspond to 'empty', but to 'minimum energy'). What I imagine is that there should be some mechanism according to which fluctuations of the vacuum produces Higgs bosons that must interact in such a way that the energy of the Universe is conserved. And this may generate gravity. Though, again, I have not a coherent formulation of such a principle.
Applying the discovery in engineering & tech?
Dr. Joe Incandela of UC Santa Barbara and CMS director said recently of the CERN Higgs results: "This is so far out on a limb, I have no idea where it will be applied, we're talking about something we have no idea what the implications are and [they] may not be directly applied for centuries." My questions: Do you agree that the direct application of the findings are as nebulous and abstract as he describes?Please discuss the implications of your answer and how they relate to the economic choices of how humans use their scientific resources.
GO: I completely agree with the above statements. Note that most important revolutions in technology and economy came much later with respect to a fundamental scientific discovery: we can use cell phones and WiFi because of Maxwell equations, GPS because of Relativity and all the electronics is an application of quantum mechanics. None of these discoveries were done having in mind any application. Moreover, no major breakthrough in technology or economy was achieved thanks to applied research. That is, in fact, a very good reason to support our activities.
That said, even if we cannot imagine possible direct applications of the Higgs bosons, we can for sure imagine possible applications of the technologies developed in order to detect it: large scale superconduction can save lot of money and energy savings, computing techniques needed to analyze LHC data are driving the birth of cloud computing, the detectors developed for these experiments can be used in different ways in medicine and industry. The past generation of experiments already generated some interesting spin-off: the new detectors for mammography, much more compact and precise with respect to the past, were developed for LEP experiments. Also the research on composite materials received a boost from our needs and are nowadays used to realize helicopters. Last, but not least, the world wide web as we know it today, is a CERN spin-off, developed to keep hundreds of physicists around the world updated about what was going on at CERN.
The future of the Higgs?
While I know it is rather early to comment, what do you think the future applications of today's research into Higgs Boson will be? Don't be afraid to be a little bit sky-high. I for one am already fantasizing about space ships propelled by manipulation of the Higgs field on a local scale. I'm only asking because, a century ago the electron was discovered and nobody was quite sure what to do with it. And it runs the world.
GO: As I said above, I cannot figure out any direct application of the Higgs boson itself. However I can imagine the birth of new techniques in manufacturing, energy production and transport, medicine and computing inspired by the technologies that we had to develop to discover the Higgs boson.
However, I don't want to escape the question and, being *very* sky-high, I can imagine that if we were able to isolate a region from the Higgs field (much as we use Faraday cages, i.e. metal boxes, to protect circuits from electromagnetic interferences), we can turn all the particles inside the region massless. You can imagine by yourself what this implies, for transportation, storage, etc.
What are the next incremental follow-ons?
I heard they may want to check several other decay paths for energy resonances. I also heard there could be a family of Higgs bosons, so we may look for others?
GO: There are plenty of questions to which we need to provide answers, in fact. First of all we have to search for all the predicted decay paths for the observed resonance. There are theories predicting the existence of two or more Higgs bosons, and we need to discriminate between them. Some theory predicts charge Higgses, too. Moreover, even if the resonance is a standard Higgs boson, we are still left with the questions 'why different particles have different mass?' and 'why the masses are those observed?', just to be on the subject.
Needless to say that with the discovery of the Higgs boson we still have the problem to explain the estimated mass and energy of the Universe. With the known particles we can explain less than 10% of the mass of the Universe. There must be other weakly interacting particles (called dark matter) providing the missing energy, that we have not yet discovered.
Significance of Higgs Boson mass?
As I understand it, a Higgs Boson compatible with the standard model could have been found at a range of different masses, and the search for it has involved searching the possible mass range until it was either discovered or not. Assuming that this new discovery is indeed the Higgs Boson as predicted and compatible with the standard model, what is the significance of the particular mass that it has been found to have? Are there any macro-scale predictions that depend on its mass?
It means that with this mass, a Higgs boson can be accommodated in any 'reasonable' theory. In other words, the Higgs boson has the observed mass because it cannot have any other mass. Any other mass would cause the Universe to behave differently at different scales. This is an important fact. If something similar is proven for other fundamental constants, we can get rid (at least partially) of the (in)famous anthropic principle: the world is as we observe it because, whatever the initial conditions, it must necessarily evolve in the current state!
The Best of the Worst Science Reporting?
In regards to the Higgs Boson, what's the stupidest thing you've seen in the press? Has anything in particular made you really laugh or groan? Has the reporting been overly irresponsible for this discovery process or just the same old press that you're used to?
GO: Incredibly enough, for this discovery I didn't find something particularly funny in the press. As I am a bit conceited :-) I can attribute the merit to our communication teams, that in fact did a great job this time.
The nickname given to that particle (the 'God' particle) makes me laugh a bit. But in this case the one responsible for this is a physicist: Prof. Leon Lederman, who gave this title to a book of his about the Higgs boson. According to what can be read, in fact it was the publisher that chose that title, but manifestly Prof. Lederman must have agreed. In this case journalists just used that nickname, which obviously sounds appealing.
by Michael Woodhams
Had the superconducting supercollider (SSC) been completed in the USA in the 1990s, would it have found this particle? Even with a 20 year technology advantage, LHC has taken some time to get there.
GO: The plan for the SSC was to achieve a higher energy with respect to the one planned for LHC. In fact we are still using LHC at half of its maximum energy, for safety reasons. Hence, in principle, SSC would have found it.
However, a discovery like that is not just a matter of energy and luminosity. The possibility to find the Higgs boson is strongly related to the available computing and networking technologies that evolve much faster than detector's technology.
Use of military tech in physics?
How do you feel about the fact that a large portion of the CMS was built by recycling military hardware? Do you see it as a sign that the world is finally moving towards peace and that large scientific projects like the LHC are helping it along that path; Or do you find it disappointing that it was the only option to acquire the necessary materials?
GO: I am happy with the fact that a portion (not so large, in fact) of the CMS was built by recycling material, irrespective of its provenance. I believe that we should learn recycling much more than what we do now, not only in building detectors (on the other hand we build a new detector like CMS every 15-20 years). Then I don't see why I should be disappointed. Recycling should not be seen as a last resort to exploit when money is lacking; its should be regarded as an opportunity for the whole of mankind.
The fact that, to build CMS, weapons were destroyed, well, is exciting! The less weapons on earth, the better the life for humans. I'm glad to be part of an experiment who helped in making weapons disappear.
Since you're a fan of free software, why don't we see more open data efforts in particle physics? I see headlines like this and they're kind of a turn-off. Aside from this super-confusing applet I haven't been able to find torrents of the data available on these tests. Why is that? I mean, as a software developer there is a legitimate effort of folks writing open source software and then there's a legitimate effort of people using that software to accomplish many things and everyone deserves credit. So why are particle physicists so keen on being the collectors and (at least initially) the sole keepers of their data? It would seem to make sense to me that people should be rewarded based on their collection of data and how meticulous and well they do that while any group can consume and derive results from said data. I understand the process has gotten more open but why so slowly? Why not torrent your data to whoever wants it immediately after you get it?
GO: Let me first state here that I'm in favor of open data, whatever they come from. Then, I will support any action to make more and more public our data, too.
There is, in fact, some reluctance to make scientific data public, also by scientists that use and promote open source software. I believe that this attitude has sociological bases and with time will vanish, as is happening with software.
That said, not only particle physicists tend to keep their data. As far as I know, in most scientific projects data (at least raw data) can be accessed only by those who collected them. The only exception I know is in astrophysics where, however, there is an initial period in which only the principle investigator's team can look at data collected by telescopes or satellites. This is comprehensible since who had a brilliant idea about how to make some observation, want to keep for himself the right to publish the result that, in few cases, can be straightforward to obtain once you have the data.
It must be said that in particle physics this is not the case. And in particular for LHC. Data are extremely complex and it is not at all easy to extract interesting signals from it. You must also consider that we produce of the order of 1 to 5 PB of data per year and it is impossible for anyone not owning a large computer centre to download even a small portion of them. You should also consider that the physicists working on these experiments already saturate all the available resources (in terms, e.g., of bandwidth, storage and CPU) and, of course, we do not want to reduce our quota of resources just to make data public.
Thanks to Dr. Organtini for these answers. Do you have ideas for leads for more Slashdot interviews? They're welcome at firstname.lastname@example.org!