Hot answers tagged computational-physics
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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 ...
11
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 ...
10
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 ...
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 ...
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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 ...
7
You are right about exact results, these depend on your definition of "exact". The best definition of an exact is if you have a fast algorithm to calculate the result in a reasonable time. The faster the algorithm, the more exact the result.
For Helium atoms, the answer is yes--- you can use the variational method to produce a result to as good a precision ...
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 ...
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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 ...
6
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 ...
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
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 ...
4
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/
...
4
As Georg says, there are a set of dimensionless numbers that control which physics are important under which conditions. To the set he suggested I'll add the Grashof number
There are existing treatment of pipes embedded in a bulk medium (because this problem comes up over and over again...), and they are very complete if the pipe is either horizontal or ...
4
Mark Eichenlaub's answer is 100% correct, but you can also do it without changing reference frames, and I think it's probably easier that way. Here's how I would set it up.
Suppose that you've determined that two objects are going to collide within the next time step. Determine the positions of the two objects at the moment of collision. Draw a line ...
4
To write down Dirac's equation over curved spacetime, first express the geometry in terms of vierbeins and spin connections. Spinor bundles are vector bundles over spacetime transforming locally under the local Lorentz gauge group. Using the spin connection, we can write down covariant derivatives for sections of the spinor bundle. To get the Dirac operator, ...
4
You can't define QED as a strict continuum limit of a "lattice QED" simply because pure QED is inconsistent at extremely short distance scales.
The fine-structure constant "runs" and at energies of the form $\exp(137 C)$ times mass of the electron, where $C$ is a number of order one and $137$ stands for the inverse fine-structure constant, the coupling ...
4
An addition to the above answers: I believe there are a couple of ways modern physicists use computers. On the most theoretical level, people use computer algebra systems (CAS) to do lengthy calculations completely or to check results. If you're into theory, you can think of software packages to do tensor manipulations in GR or software that calculates ...
4
What they show in the paper is that, for $\beta>2$, there are no solutions with the given asymptotic form as $r\to 0$ unless we assume $\alpha>0$. I think you can go further and show that there are no nonsingular solutions for $\beta>2,\alpha<0$, but I'm not sure.
What does this mean physically? Well, when we have a potential with a ...
4
I think the real answer is that when it comes to nanorobots, the materials we're using readily oxidise. Put them out of a vaccum and they're toast the instant they come into contact with the atomosphere.
Biology manages to deal with this by using a different material set, and encapsulating everything pretty well so that the environment doesn't damage cell ...
4
The main question is how do you map the CA to reality? You need to say how you describe an experimental situation in terms of the CA variables. If the map is such that an atom is described by a local clump of automata variables, and a far-away atom is described by another local clump of automata variables far away, it is flat out impossible to reproduce ...
4
After a bit of research, I believe the most robust solution that I could find is the 'Astronomy Visualization Metadata (AVM) standard for astronomical imagery', which uses Adobe's XMP standard to embed the metadata as RDF. XMP can be embedded in PDF, JPEG, JPEG 2000, GIF, PNG, TIFF, PS, EPS and audio and other non-image formats.
Other potential candidates ...
4
A technique is to perform a supercell calculation where in the calculation is performed over several cells instead of a single unit cell. The desired change is made to a single cell within this larger structure. This does make your change periodic, but if the supercell is large enough, then the change can be made essentially local. This method has been used ...
4
This is the basis of a pretty common set of techniques to find ground state properties. The hard part is writing down the matrix and multiplying it against trial wavefunctions in a large many-body basis. The projection intuition itself is not enough, but it turns out we can use:
Projector Quantum Monte Carlo (there's a lot of literature on this, but see for ...
4
If you're very close to the loop, there is a small range of theta that provides almost all of the field. When you're randomly choosing points, a relatively small fraction of those points will happen to be in that crucial range. This will amplify the random sampling error. In other words, the closer you get to the loop, the larger the number of sample points ...
4
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 ...
3
I'm making this an answer because its too long to be a comment but its just an expansion of the things already stated in comments:
Non-normalizable states: The Schroedinger equation has an infinity of solutions but almost all of them do not have a finite norm ($\int|\psi(x)|^2dx$ is not finite). These are not phyiscally acceptable, since there would not be ...
3
I recently did something like this, in order to simulate a system of two masses connected by a spring. Those masses lay horizontally on a frictionless plane. One of these masses got an initial impulse and thereafter the system was left alone. While the entire system (the controid to be precies) moves with constant velocity, the two masses are oscillating, ...
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