All Questions
Tagged with numerics or computational-physics
1,932 questions
119
votes
2
answers
7k
views
Is it necessary to consume energy to perform computation?
As far as I know, today most of the computers are made from semiconductor devices, so the energy consumed all turns into the heat emitted into space.
But I wonder, is it necessary to consume energy ...
- 1,243
53
votes
2
answers
2k
views
Can we infer the existence of periodic solutions to the three-body problem from numerical evidence?
I recently found out about the discovery of 13 beautiful periodic solutions to the three-body problem, described in the paper
Three Classes of Newtonian Three-Body Planar Periodic Orbits. Milovan ...
- 135k
39
votes
1
answer
2k
views
Can lightning be used to solve NP-complete problems?
I'm a MS/BS computer science guy who is wondering about why lightning can't (or can?) be used to solve NP complete problems efficiently, but I don't understand the physics behind lightning, so I'm ...
- 525
35
votes
5
answers
7k
views
How were the Navier-Stokes equations found in the first place if we can't solve them?
I was reading up on the Clay Institute's Millenium prizes in mathematics.
And I noticed the Navier-Stokes equations were described as minimally understood.
As far as I was taught in physics a few ...
- 826
35
votes
1
answer
2k
views
Intuition for when the replica trick should work and why it works
I am a graduate student in mathematics working in probability (without a very good background in physics honestly) and I've started to see arguments based on computations derived from the replica ...
- 593
32
votes
1
answer
11k
views
Software for calculating Feynman Diagrams
Is there a software (open source preferred) where I would input something like "Ingoing: a fermion $(p1, s1)$ and a photon $(p2, s2)$. Output: A fermion $(k1, r1)$ and a photon $(k2, r2)$" and I would ...
29
votes
6
answers
6k
views
Is there any aspect of an explosion resulting from a nuclear weapon test that cannot be simulated using super computers?
This Washington Post news article states that with the advent of computer simulation of nuclear tests, live tests are no longer needed.
Generally speaking there are 3 aspects of an explosion ...
- 415
25
votes
9
answers
4k
views
How does a particle know how to behave? [duplicate]
How does a particle know it should behave in such and such manner?
As a person, I can set mass is so and so, charge is so and so - then set up equation to solve its equation of motion but who ...
- 221
23
votes
5
answers
8k
views
How do computers "solve" the three-body-problem?
I've done a bit of research, and have learned that computers "solve" the three-body-problem by using "Numerical methods for ordinary differential equations", but I can't really find anything about it ...
- 613
23
votes
3
answers
5k
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Programming in physics [closed]
How important is programming in physics?
I am studying physics at university and these first years there is actually no approach (as it is understandable) to what working in physics is like. Now, I ...
- 451
21
votes
5
answers
4k
views
Home-made lattice calculation?
The topic of Lattice QCD or Lattice gauge theory or even Lattice field theory is quite old now. And the main reason for the interest in the topic is the ability to calculate nonperturbative stuff on a ...
- 20.2k
20
votes
4
answers
7k
views
How efficient is a desktop computer?
As I understand it (and admittedly it's a weak grasp), a computer processes information irreversibly (AND gates, for example), and therefore has some minimum entropy increase associated with its ...
- 53.7k
19
votes
5
answers
7k
views
What do theoretical physicists need from computer scientists?
I recently co-authored a paper (not online yet unfortunately) with some chemists that essentially provided answers to the question, "What do chemists need from computer scientists?" This included the ...
Aaron Sterling
19
votes
2
answers
2k
views
How can one obtain the metric tensor numerically?
I am self-studying General Relativity.
Is there a method for obtaining the metric tensor exterior to a specified mass distribution numerically? In the simplest case of a spherical mass this should ...
- 1,741
19
votes
2
answers
5k
views
How many qubits are needed for useful computation?
Seeing the news about 14 entangled states today @ Innsbruck:
I haven't found a clear guide online to how many qubits we are aiming for a first practical quantum computer,
e.g.
Factorization,
Search ...
- 319
18
votes
8
answers
6k
views
Software for physics calculations [closed]
What is some good free software for doing physics calculations?
I'm mainly interested in symbolic computation (something like Mathematica, but free).
18
votes
3
answers
13k
views
Why is the pressure gradient zero at a wall?
It's accepted to impose a zero pressure gradient normal to a wall when solving the Navier-Stokes equation. Is there any mathematical reasoning for that? Which pressure (static pressure, total pressure....
- 331
18
votes
3
answers
20k
views
Numerical solution to Schrödinger equation - eigenvalues
This is my first question on here. I'm trying to numerically solve the Schrödinger equation for the Woods-Saxon Potential and find the energy eigenvalues and eigenfunctions but I am confused about how ...
- 189
17
votes
3
answers
3k
views
Why do we still use perturbation theory, when we have advanced numerical methods and fast computers?
If my question sounds ignorant or even insulting, I apologise. I may be completely wrong, since I'm not a theoretical physicist.
So, I understand why perturbation theory was originally used in ...
- 553
17
votes
1
answer
10k
views
Solving Schrödinger's equation with Crank-Nicolson method
I am trying to numerically solve Schrödinger's equation with Cayley's expansion ($\hbar=1$)
$$\psi(x,t+\Delta t)=e^{-i H\Delta t}\psi(x,t)\approx\frac{1-\frac{1}{2}i H\Delta t}{1+\frac{1}{2}i H\Delta ...
- 575
17
votes
3
answers
4k
views
Correct way to write the eigenvector of a diagonalized hamiltonian in second quantization
I am studying diagonalization of a quadratic bosonic Hamiltonian of the type:
$$ H = \displaystyle\sum_{<i,j>} A_{ij} a_i^\dagger a_j + \frac{1}{2}\displaystyle\sum_{<i,j>} [B_{ij} a_i^\...
- 504
16
votes
5
answers
22k
views
How useful is programming in physics? [closed]
I have been wondering recently how useful programming is to a physicist. It seems fairly useful (simulations are a lot cheaper than the actual thing in many cases) in some areas (say space programs), ...
- 189
16
votes
1
answer
5k
views
Why do we use the imaginary time evolution in simulations of some quantum system?
I realize that the imaginary evolution could help us to find the ground state for a system.
However, I very puzzled why it works, and what the principle is back up there?
I have done some searching on ...
- 185
15
votes
3
answers
3k
views
How are physics and computer science getting united? [closed]
How is theoretical computer science getting united with physics? Phenomena like Quantum Computing uses Quantum Mechanics to be able to compute things, how are computers helping not just to model our ...
- 1,586
15
votes
3
answers
3k
views
Can we fully simulate molecular physics?
Is our knowledge of physics complete enough to achieve fully natural simulations of molecular interactions in a computer simulation? How far off are we?
Reason for question: I wonder how far we are ...
- 253
15
votes
1
answer
1k
views
Why isn't the Gear predictor-corrector algorithm for integration of the equations of motion symplectic?
Okumura et al., J. Chem. Phys. 2007 states that the Gear predictor-corrector integration scheme, used in particular in some molecular dynamics packages for the dynamics of rigid bodies using ...
- 1,809
15
votes
3
answers
1k
views
Why don't hexapods gallop?
I haven't observed any terrestrial hexapods that gallop like agile tetrapods(cheetahs/horses). Instead, I've observed that all of them scuttle which constrains their maximum velocity. And after ...
user29305
15
votes
5
answers
4k
views
How do I determine equilibration in a Monte Carlo $NVT $ simulation?
I'm running an NVT (constant number of particles, volume and temperature) Monte Carlo simulation (Metropolis algorithm) of particles in two dimensions interacting via Lennard-Jonse potential $$U = 4\...
- 685
14
votes
2
answers
2k
views
Why Does Lattice QCD Use Heavier Than Physical Masses For Calculations?
It is common place (e.g. here), for Lattice QCD calculations to be computed using reference masses (such as the pion mass) which are greater that the physical values of those quantities.
Sometimes, ...
- 3,967
14
votes
7
answers
2k
views
Binary Black Hole Solution of General Relativity?
This is rather a technical question for experts in General Relativity. An accessible link would be an accepable answer, although any additional discussion is welcome.
GR has well known solutions ...
- 4,763
14
votes
3
answers
2k
views
Does quantum mechanics allow you to simulate chemical reactions in software?
I'm a software developer interested in learning quantum mechanics to simulate chemistry. I know it's a very difficult topic, so I consider it a long term "someday/maybe" goal, and I’m not sure it's ...
- 463
14
votes
3
answers
1k
views
Has the Landauer Limit really been overturned? What was wrong with the original analysis?
This news, summarizing results from
M. López-Suárez et al. Sub-$k_B T$ micro-electromechanical irreversible logic gate, Nature Commun. 7, 12068 (2016).
Makes the claim that
It clearly shows that ...
- 5,337
14
votes
3
answers
4k
views
What limitations are there in measuring physical properties accurately?
In a StackOverflow answer, I attempted to explain why a 32-bit float was perfectly adequate for representing the questioner's weight measurement:
Physical properties are inaccurately measured anyway:
...
- 281
14
votes
1
answer
3k
views
What is the status of applying numerical analysis to QM/QFT problems [closed]
This is something I don't ever seem to hear about, except regarding QCD ("lattice QCD"). What about QED? Is numerical integration always inferior to hand-calculating Feynman diagrams in perturbation ...
- 7,488
13
votes
12
answers
3k
views
Is there an equivalent of computation of physical processes in nature? [closed]
I was watching a waterfall in the Austrian Alps. There were thousands of water droplets falling down, splattering on the stones below. I thought - how does nature find out so quickly where each ...
- 179
13
votes
2
answers
17k
views
Superconducting gap, temperature dependence: how to calculate this integral?
Tinkham (page 63) states that the temperature dependence of the gap energy of a superconductor $\Delta(T)$ can be calculated using the following integral:
How can this actually be carried out? I am ...
- 235
13
votes
2
answers
1k
views
What is meant exactly by "renormalization" in condensed matter physics, specifically in density matrix renormalization group (DMRG)?
I first encountered the concept of renormalization in the context of statistical physics. Here, the renormalization "group" is a set of transformations of the system such that the Hamiltonian $H(J,\...
- 4,776
13
votes
7
answers
2k
views
Numerical simulation of the double-slit experiment including watching the electrons
The double-slit "thought experiment" described by Feynman in Lectures on Physics Volume 3 section I-6 Watching the electrons consists in firing electrons through a double-slit to observe the ...
user130529
13
votes
3
answers
1k
views
Why do we need Gauss' laws for electricity and magnetism?
The source of an electromagnetic field is a distribution of electric charge, $\rho$, and a current, with current density $\mathbf{J}$. Considering only Faraday's law and Ampere-Maxwell's law:
$$
\...
- 625
12
votes
6
answers
22k
views
How is computer science and physics related? [closed]
Not sure if this is a 'real' question, but what is the relationship between physics and computer science? A lot of physicists are also computer scientists and vice versa. My professor has a PhD in ...
- 1,158
12
votes
1
answer
1k
views
Difficulty of numerically solving Einstein equations
The most recent episode of Sean Carroll's podcast is an interview with Kip Thorne, in which it is stated that until somewhat recently it was unclear that it would ever be possible to simulate the ...
- 375
12
votes
1
answer
6k
views
Tight binding model in a magnetic field
The standard way to treat a tight binding method in a magnetic is to replace the hopping matrix element:
$t_{i,j}\rightarrow e^{i\int_i^j\mathbf{A(x)}.d\mathbf{x}}$
the so called "Peierls ...
- 173
12
votes
5
answers
2k
views
Basic mechanics problems, unsolvable by brute-force numerical integration
I'm looking for simple problems in theoretical mechanics that are impossible or unreasonably difficult to solve by means of "brute-force" numerical integration of Newton or Euler-lagrange equations.
...
12
votes
2
answers
248
views
Numerical Analysis of Elliptic PDEs
I am looking for an elementary reference regarding issues of stability in numerical analysis of non-linear elliptic PDEs, particularly using the finite difference method (but something more ...
user566
12
votes
2
answers
751
views
How do you simulate chiral gauge theories on a computer?
David Tong and Lubos Motl have argued that our universe can't possibly be a digital computer simulation because chiral gauge theories can't be discretized, and the Standard Model is a chiral gauge ...
- 121
12
votes
1
answer
3k
views
What programming languages would be helpful for a physicist to know? [closed]
From the vantage point of a physicist and the kind of problems he would like a computer program to solve, what are the essential programming languages that a physicist should know.
I know C++ and I ...
11
votes
1
answer
1k
views
Is the common formulation for (Ising Model) Monte Carlo simulations a bit off?
A common [Ising Model] Monte Carlo simulation repeats the following algorithm:
randomly pick a [flip] event
compute change in energy $\Delta E$
if new energy is lower than old energy, accept the ...
- 133
11
votes
1
answer
5k
views
Connection between bond-dimension of a matrix product state and entanglement
The bond dimension is the dimension of the truncated matrix product state (MPS). Let us assume that I am simulating some many-body system with high entanglement via the density matrix renormalization ...
- 2,695
11
votes
4
answers
9k
views
Why is the canonical ($NVT$) ensemble often used for (classical) molecular dynamics (MD) simulations?
Molecular dynamics (MD) simulation is a common approach to the (classical) many-body problem. It relies on integration of Newton's equations of motion to simulate the trajectories of many (e.g., ~1,...
- 1,163