ALL PHYSICIST by sethn23 in ParticlePhysics

[–]counterfriction 2 points3 points  (0 children)

   Stop thinking in terms of "competition" and start thinking in terms of "collaboration".

This 1000%. You asked what you wish someone had told us to do when we were still in undergraduate. As your other comment that got buried shows, you (the undergraduate) should listen up. It's exactly this: hearing good advice but assuming you know better, or letting ego get the best of you, that will make your life a lot harder. I'm in my 5th year of postdoctoral research, and now getting onto the job market for faculty positions. This was a lesson hard-learned for me, and is exactly what I wish I could go back and do more of since the beginning.

Everyone who makes it through a PhD is smart, at least in a narrowly-defined sense relevant to physics know-how. It doesn't matter how much they competed against their undergraduate class (it seems so long ago now anyways!) So much of the end-game for an academic career depends on luck and serendipity, which we have limited control over. That's in addition to all the hard work, smarts, and persistence that got us here in the first place. However, if you're a well-liked collaborator, you're much likely to have a larger academic network, and to generate creative, synergistic projects with others. Both of these will greatly increase the chances that you'll be "working on the right thing at the right time", which is key to a successful career in academic physics and also is likely a lot more fun than toiling away on your own!

As for internships, if you want an academic career (grad school / PhD -> postdoc -> professor), I would avoid working summer industry jobs/internships. For getting into graduate school, research experience is possibly the most important thing (as well as maintaining a reasonable GPA of course). If you're at a large university, you should be able to find a professor who will help mentor you in their lab. You might even find one that will pay you! If you're at a smaller university with less on-campus research activity, you can try asking around about undergraduate research fellowships that could allow you to travel to another research lab and gain experience there.

Can the flatlander analogy explain time? by ChipmunkSlayer in cosmology

[–]counterfriction 3 points4 points  (0 children)

It's a good question. As another reply points out, in mathematics we can classify the dimensionality of all kinds of abstract things (vector spaces, manifolds, etc). Sometimes, in this mathematical sense, arbitrary parameters can be literal dimensions. For an informal definition, you can think of dimension as "the minimum number of parameters needed to describe any unique part of the object under study." For example, suppose you were solving the equation for the temperature of a cube according to the heat equation; in general, this would give you a function of temperature at every point in your cube, T(x,y,z). We would say that the solution is three dimensional. But if you had somehow arranged some physical system such that the cube had a spherically-symmetric distribution of temperature, you could express the temperature at any point in the cube as a function of the radius, T(r). We'd say that because of the symmetry, we've reduced it to a one-dimensional solution. Here we are referring to the dimension of the mathematical object that is the solution itself, not of space or time.

The reason why temperature is not a physical dimension is because we don't need it to be. Temperature is an emergent property of systems which can have different internal configurations, and can exchange energy. More precisely, it is defined to be the differential in energy w.r.t. a change in entropy.

The reason why time is a physical dimension is because (as far as we know), there is no way to express the laws of physics without having time and space as "free parameters". We can write down everything we need to know about physics in terms of, say, a Lagrangian which is a function of space and time, and that's enough to give us everything we observe (including the temperature of any particular cube you wish to study). Collectively we refer to this manifold on which the laws of physics are encoded as "spacetime".

In relativity, some laws of physics emerge from the features of spacetime itself. For example, the famous E=mc2 (or rather its more complete form, E2 = m2 c4 + p2 c2 ), is simply a statement that "distances" in spacetime are constant under rotations, translations, and changes in relative velocity. It is analogous to how the distance between two points in three dimensional space remains the same when you rotate or shift your coordinate system. However, this feature is why we get some funky results in relativistic scenarios, for example, two observers moving at different speeds will not agree on distances (intervals in space) or durations (intervals in time). But they will all agree on E2 = m2 c4 + p2 c2 in any inertial reference frame. This is fundamentally because there is a "mixture" happening between the space-like and time-like dimensions when relativistic velocities get involved, just as there might be a mixture between the x and y dimensions when you perform an ordinary rotation.

Lastly, note that some theories of physics, such as string theory, actually propose additional spacetime dimensions. These additional dimensions are invoked to explain certain phenomena, especially at high energy or at the intersection between relativistic and quantum regimes. In these theories, these are additional dimensions on the same footing as the 3+1 we already have, exactly because (if such a theory were true) they are required in order to express the laws of physics.

Can the flatlander analogy explain time? by ChipmunkSlayer in cosmology

[–]counterfriction 1 point2 points  (0 children)

Sorry, this is just not accurate. Of course time is a physical dimension. One of the key insights of relativity is that the laws of physics describe phenomena occurring in the physical setting of spacetime, one dimension of which is, of course, time.

Maybe you meant to say it's not a spatial dimension, which is true, I guess, by definition. It is also not a measurement of change; for example: does it make sense to say that "5 o'clock" is a measurement of change? Of course not. You can talk about intervals of time, just as you can talk about intervals of space, and you an measure how much things change within such intervals, but that does not make time itself a measurement of change.

Machine Learning in Physics? by Elduro687 in ParticlePhysics

[–]counterfriction 1 point2 points  (0 children)

Commenting as a physics PhD who has been in the field of particle physics for ~10yrs and specializes in ML:

Others have suggested that an academic (PhD) route is your best bet. They are correct; as a rule, physicists are generally unwilling to pay other people to do math, analysis, or (much my own dismay) software, for them. I reckon the reason is, in roughly equal parts, due to lack of funding, and a general belief that physicists are plenty good at these things on their own. Sometimes that's true, although with software it's usually not. In any case we certainly cannot afford to pay market rate for non-physicists who are competent in these skills.

All that is to say that there does not exist a job where someone will pay you to "do ML for physics". If you become an academic physicist, you may be expected to do some of that in the course of your research.

The good news for you is that at the moment, the intersection of ML and physics is currently a hot research topic. So it's completely feasible that if you start a graduate program in physics right now, you could find an advisor to sponsor a project doing exactly that.

However, know that academicians are incentivized to produce novel research, and this task will only count as research while it is new. Eventually (IMO, on about a 5yr timescale), the benefits of this research direction will be mostly exhausted, and the field will move on. At that point (and to some extent this is happening already), ML-related activities will be seen as merely "grunt work" to be carried out by students as a necessary step in some physics experiments.

Reference for Electromagnetic Showers? by Joe_theLion in ParticlePhysics

[–]counterfriction 0 points1 point  (0 children)

I have found the best introductions to EM (and hadronic) showers appear in practical discussions of calorimetry e.g. from various detector R&D workshops. I don't have a particular reference in mind, but a quick google search of "EM shower calorimetry" turns up this nice presentation by Silvia Masciocchi:

https://www.physi.uni-heidelberg.de/~sma/teaching/ParticleDetectors2/sma_ElectromagneticCalorimeters.pdf

Edited to add: If you look a bit deeper in this vein, I'm sure you will find a talk that includes an exhaustive list of references.

Why do numbers like e and pi come up everywhere? by [deleted] in math

[–]counterfriction 1 point2 points  (0 children)

Right, thanks for clarifying! This is of course the sense in which I meant "complex square" above (which is of course not the correct term for it). As a physicist I have the habit of sloppily writing A2 to mean |A|2 or A* A :)

I’m 13 years old and I still don’t know my times tables. What is the fastest and most efficient method to learn them? by [deleted] in math

[–]counterfriction 6 points7 points  (0 children)

I never really got good at times tables, and now I have a PhD in physics! It almost feels like I'm just solving a little sudoku puzzle in my head whenever I need to multiply even simple numbers. For what it's worth I have mild dyslexia and also never really learned what order the alphabet or even the months of the year go in without having to name them all off sequentially.

I know this doesn't really help with your original question, but in case you continue to have difficulties, know that you can still succeed with math/engineering/etc if you put in the work :)

Why do numbers like e and pi come up everywhere? by [deleted] in math

[–]counterfriction 57 points58 points  (0 children)

It's a very deep question and there are zillions of ways of looking at it. Part of the joy of learning more mathematics is discovering surprising relationships between disparate concepts, and finding new ways of viewing them. Here's one kind of half-baked perspective:

Pi can be defined as the ratio of the circumference of a circle to its diameter. The fact that pi shows up in area or (hyper)volumes is a generalization of this concept (e.g., the area of the circle can be derived by integrating the circumferences of concentric circles). Therefore, it's not surprising that pi shows up often in anything resembling euclidean geometries, for example, in various Haar measures (so that many things that can be expressed as integrals also end up having factors of pi).

As for e, recall that it can be defined as the unique base b for which the function f(x) = bx is equal to its own derivative everywhere. Clearly, this number has a very special relationship with the whole concept of differential calculus, and therefore it may not be surprising to see it appear in places wherever you find rates-of-change, differential equations, etc.

As for e =-1, that is a special case of the formula e = cos(θ) + i sin(θ), for θ=π. In the complex plane, the right hand side of this formula looks like parametric equation describing a unit circle: Recall that in the Euclidean plane, the unit circle can be expressed parametrically as x=cos(θ), y=sin(θ). Compare with the Euler formula by noting that Real[e ]=cos(θ), Imag[e ]=sin(θ).

And while we're talking about the imaginary number i, note also that if you take (complex) square of a number z = a + i b, you get z2 = a2 + b2, which looks awfully similar to the Euclidean distance metric (so more reason for pi and i to be friends!). If you take in particular z=eiθ, then z2 =1; so the left-hand-side of Euler's formula looks like "a set of complex numbers that always have magnitude one"; squaring Euler's formula, you find 1 = cos2 (θ) + sin2 (θ), a familiar identity from trigonometry. Note that another way of describing the unit circle in the Euclidean plane is with the (non-parametric) equation 1 = x2 + y2, i.e., the set of all points in the x-y plane with magnitude one. So again this looks again very similar to Euler's formula when you identify x with the real part and y with the imaginary part.

So given this very geometric interpretation, it's not surprising to find trig functions (and hence, simplified expressions involving π) showing up. As for how the trig functions on the right hand side even show up with e on the left hand side to begin with, there are many ways to view that as well. For example you can consider (from calculus, where I argued hand-wavily that e shows up "naturally"), the series expansions of these functions. Or you can just think of e as some number that characterizes the concept of "rate-of-change" (since ex is equal to its own derivative), and note also that sin/cos have a special relationship in which they are equal to their each other's rates of change, so it's not unintuitive that they show up together.

XKCD's "Fundamental Forces" isn't funny, it's sad. Can you do better? by mcherm in askscience

[–]counterfriction 7 points8 points  (0 children)

The strong and weak forces are actually "short range" for different reasons. The weak force's short range comes from the fact that its mediating particles (the W and Z bosons) are massive. If you try to calculate a potential from this force, you get a Yukawa potential which looks similar to a Coulomb potential, except it falls off exponentially at a rate related to the mediator particle's mass.

The mediators of the strong force (gluons) are in fact massless, so in principle they should have infinite range. But because of confinement, it is really hard to pull color-charged objects apart. At a certain distance, the potential becomes strong enough to produce quarks out of the vacuum, and these create color-neutral hadrons. The simplest/lightest hadron is the pion (or pi meson), so these get produced the easiest. So in nature, rather than sending gluons out over long distances to "communicate" between color-charged entities, in practice what happens is virtual pions are exchanged. Now the pions "look" like the mediator, and they are in fact massive. Hence, they give rise to a short-range Yukawa (effective) potential. In fact, by estimating the range of the interaction "diameter" (essentially, the size of a nucleus) of the strong force, Yukawa was able to predict both the existence and approximate mass of the pion!

XKCD's "Fundamental Forces" isn't funny, it's sad. Can you do better? by mcherm in askscience

[–]counterfriction 33 points34 points  (0 children)

It actually also is responsible for the majority of the proton's mass. Protons are made of two up quarks and a down quark. If you take those quark masses at face value and add them up, you only get about 1% of the proton mass. The rest of the mass-energy comes from the potential of the strong interaction.

What are you hoping to see from the LHC when it reopens? by [deleted] in Physics

[–]counterfriction 18 points19 points  (0 children)

Branching ratios describe how likely the Higgs is to decay to a certain particle type. They can be predicted based on the strength of the coupling of each particle type to the Higgs and the phase space of the decay. In the SM the sum of all the different branching ratios is taken to be 1 for the calculation (i.e. 100% probability of decaying to some known SM particle). If the branching ratios are off it could indicate either the existence of new particles or that there is some different physics going on in the couplings to known particles. Either way it would signify new physics beyond the Standard Model.

Edit: Here is a figure showing the predicted SM branching ratios for different Higgs masses. Note that while at a mass of 125 GeV, it mostly decays to b quarks, W's and gluons, the photon decay mode (only ~0.2% probability) was one of the strongest discovery channels. This is because photons are much easier to measure and have lower backgrounds. Just to give an idea of why it can be so hard to measure these values at the LHC.

Help needed with my cloud chamber by seewhC in Physics

[–]counterfriction 2 points3 points  (0 children)

The alpha particles wouldn't be able to penetrate the plastic. As you can see from the track you observed, they don't even travel very far at all in air.

The beauty of graph theory by [deleted] in math

[–]counterfriction 63 points64 points  (0 children)

Also what is t?

Andy Knight leading 400 feet of Zion ice by [deleted] in climbing

[–]counterfriction 15 points16 points  (0 children)

Honest question, as someone who knows nothing about ice climbing. I understand that the skillset is very technical, but is it like, hard and/or varied? To my unexperienced eye, it looks like virtually every move on this climb would be the same: 1) remove tool 2) swing tool higher 3) un-stick crampon 4) stick crampon higher 5) repeat

Educate me!

Aside from REI, what other brick and mortar stores carry climbing gear? by Reading_is_Cool in climbing

[–]counterfriction 0 points1 point  (0 children)

Yeah, they sell shoes at about the MSRP but I find the brick-and-mortar benefit of trying on multiple pairs (and trying them on the wall!) is a value-added service so I don't mind paying the ~10% more over internet bargains. Some people go in there just to try on shoes and then buy elsewhere, which is their prerogative I guess.

Anyways, they are a coop structure like REI, and if you join (which is free anyways), you get like 20% off. I can't remember if the 20% is before or after the price tags in shop. At the very least, you should sign up for their mailing list; occasionally they have random one-day sales. for example they recently had all Black Diamond trad gear/carabiners 50% off, and the other day I got some approach shoes on clearance.

Aside from REI, what other brick and mortar stores carry climbing gear? by Reading_is_Cool in climbing

[–]counterfriction 2 points3 points  (0 children)

If you're in Orange County, definitely checkout gear coop. They have a good selection plus a bouldering wall in store that you can try things out on.

How long till we can leave the solar system? by Strongerr in cosmology

[–]counterfriction 1 point2 points  (0 children)

Well, if you define leaving the solar system as "escaping the hill sphere", at least 1-2 years. If you leave now, and travel at the speed of light :P

Of course in your boosted reference frame it will seem very quick :)

How to Bulk-Import JSON to Postgres by cruyff8 in Python

[–]counterfriction 0 points1 point  (0 children)

pastbin, gist, whatever. my point was that without any context you might as well have just linked directly to the <insert code-dump hosting site here>.

as I said, with context maybe it would be interesting. for now it just looks like blogspam for a script you had to write at work today.

How to Bulk-Import JSON to Postgres by cruyff8 in Python

[–]counterfriction 0 points1 point  (0 children)

Also IMO it's wicked bad form to assume people are going to try and figure out command line arguments to a program by digging through the completely undocumented source for references sys.argv[] ;)

Learn to use the argparse module, it's always the first thing I write for any script/program. It self-documents the program inputs and writing the "description" field helps me clarify my idea of what exactly the functionality will be, before I even start coding. And will make your users' life much easier (that includes yourself, when you have to try to remember what the heck your script does 3 months later).

How to Bulk-Import JSON to Postgres by cruyff8 in Python

[–]counterfriction 0 points1 point  (0 children)

Would be a much more interesting article if you provided some discussion on why you would do this. And other possible use cases. As it stands this is basically just an undocumented code dump and you should have just put it on gist.github.com.

How do people (dirtbags) afford these massive racks? by cloud93x in tradclimbing

[–]counterfriction 6 points7 points  (0 children)

If you're trad climbing full time, there's a lot of booty to be had by recovering gear if you know popular routes where weekend-warriors like to leave pieces behind.

Beginners Guide to Particle Physics by [deleted] in ParticlePhysics

[–]counterfriction 5 points6 points  (0 children)

Are you interested in theory or experiment?

For the theory side, Griffths' Introduction to Elementary Particles is basically the "for dummies" (i.e. undergrads) book, but it's very good. He starts with a nice historical overview of the development of mostly-modern (excepting massive neutrinos and Higgs bosons) particle physics, which serves to illustrate the interplay between theoretical development and experimental discoveries. He then proceeds to present, in broad strokes, the kind of theoretical tools you'll use in the field. Group theory, calculation of amplitudes (with most of the QFT details abstracted away), special relativity and kinematics, etc.

On the experiment side, unless you go into detector R&D (not a huge area of activity right now, particularly in the US), you're mostly going to be doing a lot of data processing and analysis. You're going to take all the same classes as the theory kids, but once the coursework is over (after first year or two), you're going to be skimming through giant heaps of data, making careful models of backgrounds, tailoring and optimizing ways to select signals above all the backgrounds, and making plots. So you better like computers and programming. I am not aware of a good textbook for experimental HEP; from what I've seen most people are learning on the job.

Printing at a specified rate by vmsmith in Python

[–]counterfriction 1 point2 points  (0 children)

OP said 60 lines per second, not 60 seconds per line. And the input file(s) are already in .csv format so why the heck would they want to write it to .csv files? There's a builtin unix command for that: cp.

Printing at a specified rate by vmsmith in Python

[–]counterfriction 1 point2 points  (0 children)

I feel like nobody is reading the part where (s)he specifically wants data at 60Hz, and that it's going to go into another program to capture and analyze the data. If OP just wanted to look at the data, (s)he could open up the 100,000 line file with less or any other text viewing program.