tugs on Pasta’s labcoat
My question had two parts, you only answered one: half grade.
Part two was whether what you do is what you were thinking of doing when you were in college (I mean starting undergrad).
If I can extend this a bit: the people who specifically study quantum physics are interested in the basic phenomena, essentially independent of application. Someone doing post-doc research in QM may be modeling the entanglement interactions between a system of four electrons, or investigating a means to falsify some particular interpretation of the ontology behind QM, and so forth. Basically, it involves a lot of thought experiments involving highly simplified and constrained “quantum” systems and some math that looks suspiciously like a bored child’s doodling.
Particle physicists, on the other hand, use QM is a predictive tool, but they’re more interested in what sort of particles are going to pop out of a high energy impact, how fast and into what products they will decay or recombine, and how that explains other phenomena observed by experimenters and astronomers. So their work involves less constrained systems of higher energy or real world interactions that are generally too complex to model in a strictly analytical fashion; they end up using a lot of numerical approximation methods (like the stochastic Monte Carlo simulation method mentioned below), or trying to renormalize their interactions in order to get some kind of valid approximation that lets them tune up their model or reveal a more fundamental interaction.
In analogy relating to automobiles, a QM theorist would be the guy trying to tune combustion in the cylinder in order to get a little more power out of the engine; the particle guy is taking the published information about combustion in different cylinder/fuel injector configurations and using that to design a more efficient engine and powertrain. And the experimenter is the guy who hops in the car, revs it up to the redline, drops the clutch, and immediately runs into an embankment, after which he climbs out and complains that the ****ing steering response is too stiff.
To the o.p.: what research area or program would be your ideal area of career focus?
Stranger
So I was in Dallas with an undergrad physics degree back when the Supercollider went bust, leaving us with a partial hole in the ground. How much further along do you think we’d be if it had been completed?
Also, those stories about the future “sabotaging” the LHC–does anyone in the community take that at all seriously, or was that the press just taking either a crackpot or whimsical comment too seriously?
In reference to the SCSC did they really spend a billion dollars to dig the hole and then another billion to fill it up again? Would the SCSC have been a better machine then the LHC?
It’s closer to US$2B to build the tunnels, some labs, and some preliminary equipment. The tunnel was about 1/4 complete at the time the program was canceled, and are still there, not filled in except for water leakage through the rock.
The SSC would have developed energies at ~40 TeV, compared to ~14 TeV for the LHC. The amount of energy isn’t the only factor in how useful the system is, of course; the LHC has some additional luminosity capacity (the particle flux through the target) and measurement capabilities that wouldn’t have been available to the SSC at the time it was being constructed, but the maximum energy output does limit the masses of particles that can be developed from it. The LHC can generate particles of masses that are only at the low range of estimates for the Higgs boson, so if we are lucky and it does occur at the lower mass we might see it (or rather, the resulting interactions from it, as it wouldn’t exist for long enough to be measured) but we’d have a better chance with the SSC. However, given that the LHC is a truly international (predominately European) program it will likely offer more opportunities to more programs around the world. A capability upgrade proposal (the Super Large Hadron Collider) has been proposed but I don’t believe it has received any funding.
Stranger
Are there any concepts or topics in physics that are generally accepted and taught as being a certain way, but you personally have a hunch that they are wrong, and there’s really something else going on?
You rock, **Pasta **- thanks for your thoughtful answers. You, too, Stranger, as always…
I look forward to tracking this thread.
There was an article in the New Yorker about an “outsider” physicist/mathemetician/thinker who had combined some approach to manifold space to superstring theory. Do you know of the article and did it cause any buzz or ripple for you insiders? It seemed to suggest that this approach was outside standard thinking but could be so whacked-out that it could turn out to be true…
This is really a kind of stupid question, but can you explain photons? I’ve studied just enough quantum mechanics to know that it’s way beyond my capabilities. I know that photons effectively are light. Light is a wave. But photons are also particles (and whether it behaves like a wave or a particle is dependent on…something?). But photons also have no mass.
What the hell are photons made of? How can something which has no mass - and therefore, I’d imagine, shouldn’t be able to exist as a physical particle - effect and be effected by things?
Also, I recall a freaky demonstration in my “quantum mechanics for non-technical people” (don’t ask) in which we aimed a laser though the center of an electromagnet, and put a polarized lens at the end. We then oriented the lens so that it blocked the laser. We then turned on the electromagnet, which somehow changed the polarization of the laser, and our little red dot reappeared on the wall, past the lens. Can you offer an explanation for dummies who forget things as to how this is anything but witchcraft?
If the LHC were to create a stable black hole, would it grow slowly, quickly or not at all? Please don’t assume that I’m a crazy person that thinks the LHC will lead to the destruction of the earth.
Are you interested in astronomy and astrophysics? If so, would you say that’s a natural outgrowth of your interest in particle physics, or vice versa? Or, could you be interested in particle physics with no particular interest in stuff going on “out there?”
Who are your top 10 favorite physicists?
I don’t really have a set of favorite physicists, sorry!
Are you an atheist
Yes
Is Ed Whitten the smartest physicist alive?
I don’t think there is really an answer to this one. He’s pretty good at what he does, to be sure, but “smartness” isn’t really a one-dimensional scale on which you can sort everyone. (It would be like asking, “Is Kasparov the best board game player in the world?”)
tugs on Pasta’s labcoat… My question had two parts, you only answered one: half grade. Part two was whether what you do is what you were thinking of doing when you were in college (I mean starting undergrad).
Oops!
I think you never really know what you’re getting into until you start down the road, and if you don’t like it, I guess you leave the field. (Many do.) I majored in physics, and knew I liked the material, and knew I was an experimentalist at heart, but that is still a far cry from internalizing what physicists actual do. And, prior to specializing in a particular subfield, you can’t really say anyway, because it can be quite different field to field. A friend of mine who does atomic physics is working on schemes to measure magnetic fields to better than one-part-per-billion, so he (for example) spends a lot of time worrying about stray fields and he doesn’t do any heavy computing. In my current work, I couldn’t care less about ambient magnetic conditions, and I often keep thousands of CPUs toasty for weeks at a time. Yet, we’re both doing frontier physics research. (Incidentally, my friend actually has his experiment set up in a local arboretum to keep away from buildings, and he can’t take data anytime the subway passes by – several blocks away.)
**To the o.p.: what research area or program would be your ideal area of career focus? **
When looking at research topics, I ask: can l answer a fundamental question? Is there a “reasonable” chance of finding something brand new? A lot of research involves measuring some basically understood quantity a little better. An example would be measuring the decay rate of some rare radioisotope. There’s no reason to think that the answer will be surprising, but it would be good to know it anyway, since that isotope might, say, lead to backgrounds in some other experiment. I’m really glad there are folks doing that sort of research, but it doesn’t really get me too excited.
The “environment” of the topic matters to me, too. I made a conscious decision not to go the LHC route, as I do not think I would be as happy working on a 3000-person collaboration, complete with beaurocray and so big that it would be impossible to follow every aspect of the experiment. (There would be too many “black boxes” for my taste. I prefer knowing what every electronics board does and what every software package does, from start to final answer.)
So, neutrinos and dark matter are what I’m looking to do for the next decade or so. After that, we’ll see. (There’s a pretty good chance that the landscape of particle physics will be very different in ten years.)
How much further along do you think we’d be if the SSC had been completed?
About a decade. Stranger is correct that the machines do differ, but it would be a pretty good estimate to say that wherever we are in ten years, we would have been there already if the SSC went to completion. (The U.S. itself would have been even farther along, since the world focus would point here instead of to CERN. Many American physics departments have empty hallways where current LHC grad students and postdocs might otherwise have stationed themselves.)
Also, those stories about the future “sabotaging” the LHC–does anyone in the community take that at all seriously, or was that the press just taking either a crackpot or whimsical comment too seriously?
Whimsy. No one takes the idea seriously.
Are there any concepts or topics in physics that are generally accepted and taught as being a certain way, but you personally have a hunch that they are wrong, and there’s really something else going on?
Oh, that’s a good one. Physicists are (or, at least, should be) natural skeptics, so anything getting taught formally would be either well-vetted or appropriated caveated. On the non-formal side, though, there are commonly adopted physical assumptions or analytical techniques that can permeate a particular subfield. Most of these are solid, so that’s okay, but not all are. I might try to pick out a few examples later.
**There was an article in the New Yorker about an “outsider” physicist/mathemetician/thinker who had combined some approach to manifold space to superstring theory. Do you know of the article and did it cause any buzz or ripple for you insiders? It seemed to suggest that this approach was outside standard thinking but could be so whacked-out that it could turn out to be true… **
I suspect that this is the theory you’re talking about. It’s clever enough, but isn’t really revolutionizing anybody’s thinking, and it always struck me as more of a human-interest story than a physics-breakthrough story.
This is really a kind of stupid question, but can you explain photons? I’ve studied just enough quantum mechanics to know that it’s way beyond my capabilities. I know that photons effectively are light. Light is a wave. But photons are also particles (and whether it behaves like a wave or a particle is dependent on…something?). But photons also have no mass.
Far from a stupid question!
In non-physics English, a “particle” is a chunk of stuff that you can look at, maybe touch, maybe move; and a “wave” is a ripple on the water or a density fluctuation traveling through a packed concert crowd. Is a photon a particle or a wave? The usual pop-science answer is that a photon is both a particle and a wave, but I much prefer my answer:
A photon is neither a particle nor a wave. It is a _____. Unfortunately, physics never produced a good single word to put in that blank space, so we use things like “particle” or “wave” or “wave packet” or “field”. The bottom line is that a photon is what a photon is, and all these other words should be taken as linguistic conveniences and not as any real means of explanation.
So, what is it, then? Let’s go back to the concert crowd. For visualization purposes, here’s the sort of crowd I’m thinking of: a crowd.
If some big dude decided to ram into the edge of the crowd, you would be able to watch the disturbance propagate across the scene, as each person bumped into the next. A little pocket of annoyance would make it’s way from one side of the crowd to the other.
Two things to notice about the disturbance…
(1) It has wave properties. If another dude sent another disturbance across the crowd at right angles to the first one, the people at the crossing point would get double the annoyance as the two waves constructively interfered. And, for the most part, the waves would continue propagating in their original directions after that. (Humans being rather non-ideal oscillators, this analogy isn’t perfect, of course.)
(2) The disturbance has a location. You could point and say, “Look at those annoyed people there.” So you’ve got some well-defined, spatially localized thing (a “packet of annoyance”) that moves around but also has wave-like properties.
Now imagine that Nature has decided that when two annoyance packets cross paths, there is a chance that they will interact and transform into, say, happiness packets that also propagate out. Our mood packets now come in multiple varieties and have:
(a) defined positions
(b) wave-like properties
(c) interaction dynamics
but they are still just abstract objects existing on top of some medium (the crowd). A photon has all of the above, but it also…
(d) doesn’t live on top of some medium.
It exists in its own right. Nothing you ever come across in normal life (baseballs, dust, …) has all of these properties, so using words like “particle” or “wave” can cause trouble.
So, to summarize: a photon is a thing that has the above properties, but we don’t have a good word for it, so we highjack the word “particle” (or something else). These things-we-shall-call-particles also carry extra properties (mass, electric charge, spin, …) that relate to their propagation through space and/or their interactions with other particles. Some of these characteristics may be absent (such as mass for the photon).
How can something which has no mass - and therefore, I’d imagine, shouldn’t be able to exist as a physical particle - affect and be affected by things?
The mass of a particle just describes the minimum amount of energy it can ever have (namely, when it is stationary). Mass is relevant for many things, to be sure, but a particle can exist without mass and a particle can interact without mass (since interactions are determined particle properties other than mass.)
Also, I recall a freaky demonstration in my “quantum mechanics for non-technical people” (don’t ask) in which we aimed a laser though the center of an electromagnet, and put a polarized lens at the end. We then oriented the lens so that it blocked the laser. We then turned on the electromagnet, which somehow changed the polarization of the laser, and our little red dot reappeared on the wall, past the lens. Can you offer an explanation for dummies who forget things as to how this is anything but witchcraft?
Do you have any further details? I do not see how the magnet could affect the laser’s polarization (assuming the field did not affect the laser source itself or the polarizer.) Did the laser light pass though some transparent medium inside the magnet, or was it empty space (well, maybe air)?
If the LHC were to create a stable black hole, would it grow slowly, quickly or not at all? Please don’t assume that I’m a crazy person that thinks the LHC will lead to the destruction of the earth.
The first clause causes trouble, since we have no working theory about what a stable black hole with a few-TeV of energy would do. Everything we know about black holes says that a few-TeV black hole would decay quickly. (One could hopefully then measure the decay products to infer something about the black hole’s properties.)
If you can make a stable black hole with the LHC, we know only that it won’t cause any harm since there would already have been bazillions made on earth by nature in the past four billion years or so. The prevailaing feeling, though, is that you can’t make a stable black hole at these energies at all.
Are you interested in astronomy and astrophysics? If so, would you say that’s a natural outgrowth of your interest in particle physics, or vice versa? Or, could you be interested in particle physics with no particular interest in stuff going on “out there?”
Everyone’s different, with varying cross interests. I’m very interested in cosmology, and also astrophysics insofar as it ties to particle physics or cosmology. I have a general scientist’s interest in astronomy, but only at the same level as the next topic (condensed matter, biophysics, …).
There is a lot of overlap between particle physics, cosmology, and certain aspects of astrophysics. The early universe was a terrific particle physics experiment…
Does this mean that it’s possible that unstable black holes are created all the time but we just haven’t detected them?
As a geek, I approve of this “Ask the…” thread 
Thanks Pasta!
Can’t believe people are lost for words talking to you at parties…if I was lucky enough to corner a particle physicist at a party, he’d have to call the cops.
So, questions:
[ul]
[li]what do you think is going on with Entanglement, really? (since we know it’s not hidden variables)[/li][li]what is energy (or mass)? (maybe a question for the philosophers)[/li][li]if the Higgs boson is (hypothetically) responsible for giving mass to other particles, how can it make sense to talk of it having mass itself?[/li][/ul]
Does this mean that it’s possible that unstable black holes are created all the time but we just haven’t detected them?
Yup. Protons (and miscellany) from deep space are constantly bombarding earth, and the energy range of these extends wayyyy beyond what the LHC can do. These high-energy particles hit the earth and make whatever they wanna make.
What do you think is going on with Entanglement, really? (since we know it’s not hidden variables)
I have no particular insight here, to be honest. Neither entanglement nor non-locality bothers me. If the way nature works is that two spacelike-separated particles can have their properties set by just observing one of them, I’m okay with that. Hidden variables and other underlying dynamics are usually introduced just to get around the need for non-locality, but I say: who are we to tell nature that she can’t have non-locality? Of course, if we did uncover a deeper dynamic, that would be exciting. But, to me, the strongest motivation for such ideas is classical prejudice, and it seems that quantum mechanics is elegant enough without these.
Of course, if nature starts trying to pull any causality violation, I might start getting a bit miffed. I’m getting too old to retrain my intuition that much.
What is energy (or mass)? (maybe a question for the philosophers)
I think Feynman said it pretty well:
There is a theorem (Noether’s theorem) that says that such a conserved quantity must exist if the laws of physics do not vary with time. This conserved quantity happens to relate to the masses of things, the relative motions of things, and the forces between things.
The “motion” part is special, since you can change your reference frame and cause the system you’re observing to have more or less total energy, as measured by you. But the lowest energy you can ever get to is when the system is at rest in your reference frame. The energy of the system at that point is called its “mass”, and you can’t get any lower. If the system is a single particle, you say that that’s the mass of the particle.
Note that a system consisting of two massless photons heading in opposite directions will always have some energy. If you try to pick a reference frame that reduces the energy of one photon, the other photon will have more energy in that reference frame. Thus, this system has non-zero mass (i.e., a minimim energy that can’t be reference-frame’d away), even though the constituent particles are individually massless.
Thus, the term “mass” is a bit muddy linguistically. Since the properties of individual particles are often important in particle physics, “mass” is usually disambiguated in the field. If someone says, “Photons have no mass,” they would be interpreted as saying that individual photons have no mass. If they intended to indicate that a particular system of photons had no mass, they would have said, “Those photons have zero invariant mass,” or “That system of photons has no mass.” This ambiguity does not arise in, say, general relativity, since one is always talking about the mass of the system there.
Your next question relates to this…
If the Higgs boson is (hypothetically) responsible for giving mass to other particles, how can it make sense to talk of it having mass itself?
This is another reason why “mass” requires careful use in particle physics, since another definition of mass could be, “How strong is the coupling (i.e., interaction strength) between particle X and the Higgs?” (Although, this usage would be in very specialized contexts, so it isn’t really a big issue.)
Anyway, the idea is that all of space has some Higgs “essence” in it that can’t be gotten rid of. Particles interact with this ubiquitous Higgs-ness, and these interactions manifest as particle masses. The Higgs can interact with its own essence, so it, too, has mass.
You might say, “If there’s a bit of Higgs-ness everywhere, why don’t we look for that?” Well, the only manifestation of it would be that particles have mass, and we already knew that. It isn’t that there are actual Higgs particles everywhere. It’s just that the answer to the question “What’s the expected value of the Higgs field right here?” is not zero, even though there is no full-on Higgs particle there. (A “field” is a mathematical construct that represents particles in the formulation of the Standard Model.)
So, one can interpret the math as:
The Higgs field has a non-zero value everywhere in space, and anything that can interact with the Higgs will feel this, and this interaction looks like mass. Also, the Higgs can interact with itself, so it, too, has mass.
Now, all this questions about the meaning of intrinsic physical properties, the universe and everything are interesting but…
Here we have a bunch of brilliant minds working for months on end, maybe in a frickin’ cave, long hours and fastidiously methodical work. SO, what kind of practical jokes do particle physicist pull on each other?
Also when (or if) you watched the movie Angels and Demons, did you:
A- Sprain your eyeballs due to continuous rolling motion.
B- Felt compelled to strangle the nearest Hollywood screen writer.
C- Had to be escorted out of the theater, still cursing the stupid “God Particle”.
D- All of the above.
Hehe… The only one I can think of off hand: a researcher who routinely left his keys in his jacket in his office during lunch did so as expected one day. So, a few of us grabbed the keys, headed to the nearest hardware store, and made a copy of his car key. Then, each day, one of us would go out and turn his car around in its spot. (So, if he pulled in straight, he would find it backed in in the evening.) From a 10th floor window, we could secretly watch him going to his car. The first day, he really looked befuddled. The effect wore off pretty fast though, only last three days or so.
Not very scandalous, and not really field-specific, but I guess it’s something…
I haven’t seen it, and I seriously doubt I ever will.
Ah, OK. I was kind of hopping the sentence would continue with a “put them in the cyclotron…” or something along those lines.
Once again, all sorts of Thank You. I love your explanatory approach and writing style. And yes, that article on Lisi was the one I was referring to from the New Yorker. It read like a human-interest story to me as well; I was trying to understand if there was traction in the underlying science to make the human-interest aspect important or if it was a puff piece.
As for the quote above, I understand how, based on the concept of a medium like Michaelson-Morley’s ether, your statement is true. The rejection of ether is at the fundamental heart of modern physics, to my limited knowledge. But can it be said that there is kind of a medium through which a photon propagates - namely the stuff of reality? I don’t wanna inject imprecise, trippy notions in a science-and-data-based discussion so if I am way off base, please just shut this down. But is my frail understanding that, as light travels away from us at, well, the speed of light (c) regardless of how fast we are going, it is in fact, alternating between light energy and magnetic field energy? I recall getting this visual while reading E=mc^2 by Bodanis - in explaining why time, mass, length, etc. all vary in the face of the constancy of c, he describes how a wave of light basically propagates through *reality *- I am sure I am relating this incorrectly because as I re-read this post is feels ether-ish and that is not what I am going for…its almost like light’s existence and movement is the foundational characteristic of physical reality as we know it…
…is there something in all that to comment on and clarify or am I just in a muddle??
Excellent answer…thanks Pasta. I’ve read all the popular science books on these topics (Brian Greene etc.) but it’s good to hear from someone who currently works in the field.
Regarding the Higgs Boson – does that mean that some theoretical alien race, who discovered things in a different order to us, might not have a concept of “mass”? Instead, they would merely think of things “interacting with the Higgs field”, just like we don’t usually think of “magnetism” as a property of something that is ferromagnetic but isn’t magnetized, but merely a result of it interacting with magnetic field?
Regarding the pranks question: I heard a story along these lines, but not quite a prank. A research physicist was having problems with his computer monitor – odd color blobs and distortions. He called in the IT guys to take a look; after checking everything out, that started looking around…and realized his office was next to an experimental Tokamak reactor. Sounds urban-legendy to me, but funny.