# Tag Info

31

As a computational physicist working in materials/condensed matter, I'm either highly biased or well-placed to comment on this. Physics, in practice, is divided into three overlapping approaches: experimental, theoretical, and computational. (The highest impact research papers usually include a combined effort from all three.) If you plan to go into ...

18

I think perhaps some of the other answers are taking computer science to be synonymous with computation. I guess that this is perhaps not what you mean, but rather theoretical computer science. There is obviously a huge overlap with quantum information processing of which I think you are already well aware, so I will ignore that. Much of physics (including ...

13

Programming is immensely useful in any branch of physics. I don't know where the notion that programming is not useful at CERN comes from (? Home of the ROOT package, and the internet? Really? TeraGrid, eh? 1 GB/s of data from the detectors at the LHC won't analyze themselves!), but you may wish to revisit your research on that matter. I can say that in ...

13

Starting from 90nm tech processes we've started to see sad signs of stagnation: 1) Most of delay in logic circuits is in interconnect, not transistors 2) Most of energy dissipated is due to quantum tunneling, not transistor switching. By far. 3) As consequence of #2 - transistor gate width scaling has significantly slowed down, as well as dielectric width ...

11

I can't really know why your professor used C++, but there are several reasons why you would: Performance: Scientific computations might require top-notch performance. C++ allows for very low level control over the hardware and has many possibilities for micro-optimization while still providing high-level abstraction. Of course, this is also the reason ...

10

You are asking two questions. I am only going to address one of them: Can the Church-Turing hypothesis be deduced from other fundamental law of physics? There are two fundamental theories of physics that account for nearly all experiments and observations performed to date: general relativity and the Standard Model. If we could simulate these theories ...

10

EDIT: This answer is specifically from the perspective of very computationally oriented fields like theoretical plasma physics. Most physicists can program, and in fact many are rather good programmers. It would be difficult to work in modern physics without being able to program. Unfortunately, many are also not terribly good programmers (I've read many a ...

10

Programming is extremely important in almost every area of physics. Not every physicist has to be an expert programmer, but many are, and virtually all physicists are at least competent programmers. In most experiments, the process of data analysis is complex enough to require some programming. More importantly, in many situations, the best (or only) way of ...

10

Crank-Nicholson method is effectively the average of forward (explicit) Euler $\psi(x,t+dt)=\psi(x,t) - i*H \psi(x,t)*dt$ and backward (implicit) Euler method $\psi(x,t+dt)=\psi(x,t) - i*H \psi(x,t+dt)*dt$ The backward component makes Crank-Nicholson method stable. The forward component makes it more accurate, but prone to oscillations. If you want to ...

8

You don't need a really big computer. Peter LePage used to do talks where he'd ask the audience fro a "random" number as the beginning of the talk (but not 7, 17, 42, or 69 'cause he'd already done those) and start a simulation on one screen with that number as a seed. Then he'd give a talk on how to speed up LQCD calculations on the other screen while his ...

8

this is a broad, complex, somewhat tricky question with many angles that an entire survey or book could be written on but unfortunately it seems one hasnt yet. heres a "grab bag" of some deep parallels noticed over the years that such a book might cover & "research leads" for further inquiry. Modelling and simulation. as computing capability has ...

7

But the most glaring is that it is quite clear that the moment you introduce anything less than zero latency (speed of gravity). The entire system falls apart, planets fly off, everything dissipates. Newton himself didn't quite like the instantaneous action at a distance as implied by his law of gravitation. The only saving grace is that it worked. ...

6

If you look at the Laplacian: $$\nabla^2=\frac{1}{r}\,\frac{\partial}{\partial r}\left(r\frac{\partial}{\partial r}\right)+\frac1{r^2}\frac{\partial^2}{\partial\phi^2}$$ you can clearly see that this diverges at $r=0$ so discretization of this should also diverge. There are three solutions to remedying the divergent feature that I can think of: Choose a ...

6

Standard Monte Carlo samples the canonical (NVT) ensemble. So it maintains constant temperature but the potential energy is free to fluctuate - both up and down. This will only seem odd if you incorrectly imagine the equilibrium state of a system to correspond to that with the minimum energy. The equilibrium state is actually determined by the minimum free ...

6

What you want to do is change the wave equation into a Klein-Gordon equation: $$\frac {1}{c^2} \frac{\partial^2 \psi}{\partial t^2} - \nabla^2 \psi + \alpha^2 \psi = 0,$$ where $\alpha$ is a constant of appropriate dimension and usually (in quantum theory) given by $$\alpha=\frac {m c}{\hbar}.$$ Inserting an ansatz of the form \psi=e^{i(kx-\omega ...

6

"They" are probably talking about symplectic integrators. Most numerical integrators for (partial) differential equations do not specifically consider the energy of the system; they are generic integrators capable of solving any set of DEs, and not all DE's have a concept like "energy". When these are applied to a classical dynamics problem concerning ...

6

The first thing that comes to mind is that the speed of light limits the rate at which different components of a computer, or even a single chip, can communicate with each other. For example, if you have, say, 10 cm of wire running between your motherboard and hard drive, it will necessarily take a minimum of about a third of a nanosecond to fetch data from ...

6

While not strictly lattice QCD, Michael Creutz' 30 year old lattice gauge papers have very simple C implementations (!). For example, look at this paper, which gives a very readable explanation of lattice gauge simulations, with source code: http://latticeguy.net/mypubs/pub165.pdf The source code is also available here: http://thy.phy.bnl.gov/~creutz/z2/ ...

6

Some of the SDSS images in JPEG format (for example those served by the SDSS DAS) have sections of the FITS headers of the corresponding data images embedded in them. I expect that other projects have done similar things, but I am not aware of any uniformity in how it is done. For the most part, the image formats you list were really not intended for ...

6

When you think of a physical parameter which is "uncomputable", what precisely do you mean? For us to know that it is uncomputable, it has to arise somehow, on theoretical grounds, from e.g. a compu­tational process which is equivalent to the Halting Problem of theoretical computer science; so that we could not compute it from first principles. ...

5

Programming is a skill that some physicists need and others do not. Ditto for knowing your way around a mill or a lathe. Ditto for digital electronics, or contour integrals, or writing popularizations, or vacuum systems.

5

Overlap fermion approach may be the answer (I think for U(1) gauge symmetry only). Ounce a theory is defined on a lattice, it can be simulated by a computer that we already have. Here is a review on overlap fermion approach: Tata lectures on overlap fermions arXiv:1103.4588 R. Narayanan Overlap formalism deals with the construction of chiral gauge ...

5

Color forces are not like electromagnetic ones. There exist no unbound color carrying particles analogous to the electron, because the forces increase with the distance rather than decrease and collective effects appear only within nuclei through residuals of the colored forces which attract the nucleons and hold them in the nuclei. Collective effects ...

5

Computational quantum chemistry is one. Researchers in pharmaceutics use computational quantum chemistry programs to model the interactions of small molecules (drugs or fragments of drugs) with proteins/DNA and predict whether or not the designed drug may or may not be effective for its purpose. They can do that before having to spend time and money ...

5

You are asking quite a few questions, so let me try to go step by step. First, an area law is a very special property among quantum states: If you pick a random state, it will have almost maximal entropy (i.e. a volume rather than an area scaling). So essentially any state would be a counterexample ;-) On the other hand, ground states appearing in nature ...

5

I would argue that this maybe due to the way you calculate your autocorrelation. An autocorrelation like that straight line is the result of a large square signal. The Ising model has a phase transition at the critical temperature. Above it, it's disordered; below it, it becomes ordered, which means that the magnetization stops flipping back and forth. This ...

5

As I commented, I would think that any 3D hydrodynamics code would work. The basics of hydrodynamics can be summed up in the following five equations: \begin{eqnarray} \frac{\partial \rho}{\partial t}+\nabla\cdot\rho\mathbf{v}=0 \tag{1} \\ \frac{\partial \rho\mathbf{v}}{\partial t}+\nabla\cdot\left[\rho\mathbf{v}\otimes\mathbf{v}+P\mathbb ...

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