First collisions at the LHC with unprecedented Energy! (Ask a particle physisicist)

[JuliaL]

Vell, ve can't all be der virst violinists in der orkestra.
Some ov us gots to push der vind tru der tuba!

After 6 years of medical practice, I thought it might be amusing to take a course in ethics as distribution credits towards an engineering degree.
It was fun, but I wasn't impressed with the rigor.
Math isn't as flexible.  But when it's right it's right.

BTW, is there a 'Particle physics math for dummies?"
I did well in the engineering math courses, though it's been a while.

I strongly disagree with the idea that math isn't poetic. I find the crystalline elegance with which it describes many things, to be among the most poetic things I know.


Concerning particle maths for dummies, when my field theory text book comes out this fall (which is aimed at advanced undergrad and beginning grad students) I have actually considered doing something like that - kind of a popular science book with extra maths sections.

I think, if you check carefully, that I wrote, not that math wasn't poetic, but that it wasn't as flexible.
(don't you love quick editing?)

In your writing, please do address the greater audience.
I'm sure you'll have no lack of volunteers to check for comprehensibility (raises and waves hand with enthusiasm.)

[JuliaL]

Higher number body systems can sometimes be treated in perturbation theory, i.e. a systematic approximation. Newton did not understand this, but Laplace and colleagues did, and this is how they finally were able to fully describe the solar system including the effects planets have on each other.

It is very easy to find scenarios where all analytic description fails and all we can do is try and run a computer simulation, which is also always an approximation.

The equations of motion of the standard model have not been solved exactly analytically either, and need to be treated e.g. with such a perturbation theory.
In fact, Feynman diagrams are exactly that - a graphic representation of a systematic approximation taking more and morr virtual particle effects into account.

I remember, way back in the previous century, when I was taking fluid mechanics, the navier stokes equation was the thing only it couldn't be solved for real bodies and so was sort of a lovely theory with no real applications.
Then came computational fluid dynamics which was nothing but approximations but which could be implemented and now we've got things like spaceship one where really complex dynamics can be simulated and prototyping is minimized if not eliminated.

Sounds like your perturbation methodologies are something like that.

But Julia, here's a follow up question to your idea, how do you measure the accuracy of a theory? How accurate is newtonian physics? I can contemplate situations where it fails with arbitrary severity - just go close enough to the speed of light.

I'm going to take that as a rhetorical (answer optional) question. Otherwise you're really asking the wrong person.
I get stuck on figuring out whether or not motion exists.
How about 'accurate enough?'

[Pyrrho]

Higher number body systems can sometimes be treated in perturbation theory, i.e. a systematic approximation. Newton did not understand this, but Laplace and colleagues did, and this is how they finally were able to fully describe the solar system including the effects planets have on each other.

It is very easy to find scenarios where all analytic description fails and all we can do is try and run a computer simulation, which is also always an approximation.

The equations of motion of the standard model have not been solved exactly analytically either, and need to be treated e.g. with such a perturbation theory.
In fact, Feynman diagrams are exactly that - a graphic representation of a systematic approximation taking more and morr virtual particle effects into account.

But Julia, here's a follow up question to your idea, how do you measure the accuracy of a theory? How accurate is newtonian physics? I can contemplate situations where it fails with arbitrary severity - just go close enough to the speed of light.

Isn't Newtonian physics "good enough," as long as one stays away from very fast things and very tiny things?  Or in other words, isn't Newtonian physics adequate for anything a regular person is going to need?

[Pyrrho]

Of course as a big disclaimer, I have not been a very important figure in the grand scheme of particle theory, but I would say that I have done some good work and a very decent grasp of the physics and a pretty broad range of expertise. I say that to emphasize that I am not necessarily the gold standard by which to judge expertise in theoretical physics, and to establish that I am not suffering from delusions of grandeur. That being said, I have, just recently, read articles in a respectable journal by professional philosophers concerning my field of study, and have been less than impressed. One guy who is a chair of philosophy of physics, was going on and on about how physicists are misled because how can we possibly advance the field if we don't really know what particles really are and so on. To me it read like someone who doesn't understand the maths desperately trying to tell us that we do not know what we are doing or talking about, because we don't rigidly formulate our theories in a language he understands (because it is arguably impossible). What makes me angry about this is, in his desperate attempt to stay relevant despite not fully understanding the theory, the guy besmirches the reputation of the field. This is not the first time I encountered this kind of lameness. I signed up for the philosophy working group of the german physical society and went to the first meeting, and that was the last one I went to.

There are fortunate examples to the contrary. I know a former colleague of my phd advisor who changed carreers and does intriguing philosophy of physics, addressing questions such as in which sense successive scientific theories improve, and whether they might converge to something that can be called Truth. This guy is good enough to be able to talk about such topics without inducing fatal eyeroll in experts of the field. Not everyone is. You have to have training in some variety of quantum physics, or be really good, not to make a complete ass of yourself when attempting this kind of discussion.

I'd say that people doing philosophy of science professionally without having in depth training in at least one field they address, or better yet research experience, run a high risk of producing work that working scientists perceive as highly embarassing, and there are plenty examples.

Generally,

I was pretty sure you would be more gentle in expressing this than I was, and you have not disappointed.  It pleases me that we are in agreement on this (though you may not like the association).  The fact that even I, who am no scientist, can recognize that they are generally idiots, who do not understand science, is really damning criticism of them.

I do have a question:  What would finish the sentence you started at the end of your post, which is quoted in full above?

[Alex K]

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Higher number body systems can sometimes be treated in perturbation theory, i.e. a systematic approximation. Newton did not understand this, but Laplace and colleagues did, and this is how they finally were able to fully describe the solar system including the effects planets have on each other.

It is very easy to find scenarios where all analytic description fails and all we can do is try and run a computer simulation, which is also always an approximation.

The equations of motion of the standard model have not been solved exactly analytically either, and need to be treated e.g. with such a perturbation theory.
In fact, Feynman diagrams are exactly that - a graphic representation of a systematic approximation taking more and morr virtual particle effects into account.

But Julia, here's a follow up question to your idea, how do you measure the accuracy of a theory? How accurate is newtonian physics? I can contemplate situations where it fails with arbitrary severity - just go close enough to the speed of light.

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Isn't Newtonian physics "good enough," as long as one stays away from very fast things and very tiny things?  Or in other words, isn't Newtonian physics adequate for anything a regular person is going to need?

Yes, although I'd like to take this opportunity to point out that it is not necessarily smallness which marks the transition into the quantum regime. If that were the case, we would expect a constant of nature which has units of length or time or energy which sets such a scale. But we don't (the Planck scale would satisy those criteria but it does not appear in quantum mechanics). The constant of nature which marks the transition to the quantum regime is Planck's constant which has units of Energy*time. In other words, quantum phenomena becone important whenever the energy transfer in some process times the time span it occupies are below this tiny constant. There is no fixed length below which "quantum" starts.

But I digress. Yes, Newton is good enough for low speeds if you don't measure too accurately. If you are doing GPS or are otherwise messing with atomic clocks, you may find yourself forced to use relativity at relatively low speeds. What is troubling is that the description of the world in classical mechanics, relativity and quantum mechanics differs so widely that it is not clear in which sense the *explanations* converge towards something. That is an issue for philosophers.

[JuliaL]

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Isn't Newtonian physics "good enough," as long as one stays away from very fast things and very tiny things?  Or in other words, isn't Newtonian physics adequate for anything a regular person is going to need?

Yes, although I'd like to take this opportunity to point out that it is not necessarily smallness which marks the transition into the quantum regime. If that were the case, we would expect a constant of nature which has units of length or time or energy which sets such a scale. But we don't (the Planck scale would satisy those criteria but it does not appear in quantum mechanics).

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The constant of nature which marks the transition to the quantum regime is Planck's constant which has units of Energy*time. In other words, quantum phenomena becone important whenever the energy transfer in some process times the time span it occupies are below this tiny constant. There is no fixed length below which "quantum" starts

Am I correct in interpreting this to mean that an event involving a relatively large energy (or equivalent mass)  could show quantum characteristics if it took place over a short enough time?
Do you get extra credit for things that make less sense?

[Alex K]

You are correct. And it would mean that quantum phenomena that involve very very little energy transfer can have long duration. Bose Einstein condensates come to mind. This is just arguing from very general principles without having thought about the detailed examples too much.

[Alex K]

What I say above is just my standard opinion which I have voiced many times IRL

I .do have a question:  What would finish the sentence you started at the end of your post, which is quoted in full above?

Generally, I think that good philosophy of physics is important, because we do want more from our science than a black box of equations which reproduces certain experiments - because as David Deutsch rightly asks in "fabric of reality" (*), what would we have gained in understanding over someone who merely executes the experiment, if we did limit ourselves to such a concept of science as a predictive black box. We want more from our science - we want it to provide intuitions, explanations, we have a natural urge to see truth in our theories. To what extent we can have this and what it means, those are, in my opinion, questions of philosophy, not science, and questions one would not want to do without.

(*) I may be paraphrasing...

[JuliaL]

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What I say above is just my standard opinion which I have voiced many times IRL

I .do have a question:  What would finish the sentence you started at the end of your post, which is quoted in full above?

Generally, I think that good philosophy of physics is important, because we do want more from our science than a black box of equations which reproduces certain experiments - because as David Deutsch rightly asks in "fabric of reality" (*), what would we have gained in understanding over someone who merely executes the experiment, if we did limit ourselves to such a concept of science as a predictive black box.

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We want more from our science - we want it to provide intuitions, explanations, we have a natural urge to see truth in our theories.

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To what extent we can have this and what it means, those are, in my opinion, questions of philosophy, not science, and questions one would not want to do without.

(*) I may be paraphrasing...

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In my opinion it is impossible to keep people from indulging in and expounding on their own intuitions and explanations, often when they have the confidence but lack the background to do so with authority.  In these circumstances it is all the more important for those with the appropriate credentials as experimentalists or theorists to establish a voice and act positively to restrain the less disciplined.

[pocaracas]

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What I say above is just my standard opinion which I have voiced many times IRL





Generally, I think that good philosophy of physics is important, because we do want more from our science than a black box of equations which reproduces certain experiments - because as David Deutsch rightly asks in "fabric of reality" (*), what would we have gained in understanding over someone who merely executes the experiment, if we did limit ourselves to such a concept of science as a predictive black box.

---

We want more from our science - we want it to provide intuitions, explanations, we have a natural urge to see truth in our theories.

---

To what extent we can have this and what it means, those are, in my opinion, questions of philosophy, not science, and questions one would not want to do without.

(*) I may be paraphrasing...

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In my opinion it is impossible to keep people from indulging in and expounding on their own intuitions and explanations, often when they have the confidence but lack the background to do so with authority.  In these circumstances it is all the more important for those with the appropriate credentials as experimentalists or theorists to establish a voice and act positively to restrain the less disciplined.

LOL.... they can't. they're nerds.

And that's why the Higgs became known as the god particle, Cosmic expansion became the Big Bang and... luckily, most everything else is incomprehensible to journalists....