# Tagged Questions

DO NOT USE THIS TAG just because the question requires a computation!

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### A question about ultimate computation capability

If we consider the physical limit of computational capability of a system with average energy $E$, then (1) According to Margolus and Levitin, a quantum system with average energy $E$ takes time at ...
5k views

### Calculating displacement amplitude of ultrasonic power transducer

I am not a physicist, but my current project drives me to some physics-related computations, hence seeking help. I have some ultrasonic transducers, 5938D-25LBPZT, for which very limited information ...
1k 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 ...
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### The simulation hypothesis and the halting problem [closed]

I have a basic knowledge of classical and quantum information which isn't remotely enough to make me an expert on the subject. That being said, reading some questions about the simulation hypothesis ...
187 views

### Is the universe a Turing machine?

Reading about Computable numbers I wondered if there is any physical experiment that returns non-computable numbers or if there is any physical theory that needs non-computable numbers. Because if ...
3k views

### Software for physics calculations

What is some good free software for doing physics calculations? I'm mainly interested in symbolic computation (something like Mathematica, but free).
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### How much computation can be performed in given time using given energy inside a ball of given volume?

Landauer principle asserts that there are physical limits on computation given finite free energy (although there are ways around it). $E=hc/\lambda$ provides a lower limit on the amount of energy ...
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### Classical Computation without NOT [closed]

Is it possible to do universal classical computation using bits and 2-bit gates when you cannot perform a NOT operation on a single bit (hence cant do CNOT and so on). If yes, what are the possible ...
328 views

### Computations using light

I recently found out about analog computers. They really intrigue me. I've seen a few videos on how mechanical computers work. I also know that there are electric analog computers too (I have no clue ...
470 views

### Does the universe follow a general physical and computational principle of evolution?

Evolution is a principle in biology, whereby organisms evolve their ability to replicate and multiply in numbers over successive generations. From a computational point of view, the organisms employ a ...
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### Can Black Holes Maintain Data Entropy When Formed By a Data Storage System?

It's been shown that black holes don't destroy information. There's a little-known scenario in computer science (Specifically AI) where an advanced civilization creates an artificial intelligence that ...
278 views

### In what way are the Mathematical universe hypothesis and A New Kind of Science connected

The Mathematical universe hypothesis, mainly by Max Tegmark and A new Kind of Science, mainly by Stephen Wolfram both claim (as least as I understand it) that at its innermost core reality is ...
441 views

### Computation theory and the simulation argument

Can physical states be treated as information (strings over some alphabet)? If (1) is true, isn't this a trivial conclusion that the universe can be simulated by a Turing machine or a cellular ...
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### Is there a physical system that emulates mathematical cellular automata?

Theoretical cellular automata have been proposed as models for many physical phenomena from music to quantum mechanics. My question concerns the reverse: Is there a simple physical system that ...
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### Construct classical computer using classical light

Quantum light (i.e. photons), linear optics, adaptive measurements and feed forward can be used to build an efficient universal quantum computer. ref: Knill et. al. 2001. Clearly the above resources ...
147 views

### Why are some variables summed infinitesimally and others aren't?

This is something that has been bothering me and I hope the title kind of makes sense. It may be a stupid question but please be gentle. My question is, let's say we have current: $$I=\frac{dq}{dt}$$ ...
101 views

### Are the laws of physics bound by the same performance bounds algorithms are bound by?

Consider the problem of finding the convex hull for $n$ points on a plane. No constant time algorithms exist to solve it. Now say you represent the points as poles of equal height that you hammer ...
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### New coordinates in terms of old from Jacobian— Software? [duplicate]

Fellow geometry enthusiasts: I am studying a particular geometry and I would like to change from one set of coordinates to a new set that makes the metric unimodular (i.e. it's determinant is one). ...
904 views

### live Kp index data

I need to create an online service displaying latest Kp index. Where I can take the data? The data should be in machine-readable format, i.e. text files, XML, or CGI gateways, for instance. No ...
133 views

### Dimensions of wave equation

If you take the homogenous wave equation: $$-\Delta_x u(x,t) + \frac{1}{c^2} \frac{\partial^2 u}{\partial^2 t} (x,t) \ = \ 0 \ \ \mathrm{in} \ \Omega \times (0, \infty),$$ with some proper initial- ...
322 views

### Simulation of fluid flow using Euler equation

I have been looking on Euler's equations for a while and can't grasp one thing. Suppose we have initial system state with volumes of fluid "hanging" in air (time is frozen and equal to zero), each of ...
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### How much computer power would we need to model every physical aspect of the universe [closed]

So I know there are equations that give you the total energy in the Universe(Friedman). So about if we we to simulate every single interaction from neurons to physical forces, strong and weak, ...
355 views

### Can the quantum eraser experiment result indicate a 'computed universe'?

The quantum eraser experiment tells us that a photon shot at two slits is a wave, unless you measure which slit is taken and you do not destroy the measurement result. I've found this very similar to ...
354 views

### An explanation for the Landauer's principle

Has anyone understood the Landauer's principle? What is the current status? In specific, is there a theoretical derivation of the Landauer's Principle?(not the heuristic one based on Salizard's ...
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### How physical objects (e.g. Earth and Apple) are aware and do computation about each other? [closed]

For example, in Issac Newton's famous story, how Earth and Apple are aware that they are at distance r of each other? How they can compute their movements?! Above ...
455 views

### Is it wasteful to use a heating element, instead of doing useful work?

Consider a computer CPU consuming electrical energy to perform calculations and consequently emitting heat. Assumption: That a CPU consuming x Watts of power, emits the same amount of heat as an ...
1k views

### What is the next step beyond quantum computation?

Assuming we develop quantum computers one day, what would be theoretically the next step? Would it be string-theory based computers? How would these computers differ performance-wise (ie what can they ...
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### Yutsis graphs in quantum theory

Cubic Yutsis graphs appear in the context of the quantum theory of angular momenta. The recognition of these graphs is NP-complete. Is there any implication to quantum physics if recognition of ...
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### Reference-request: Computational science and physics [closed]

I'm interested in the following question: Is Nature computable at it's most fundamental level? Can anyone suggest any works (books, papers / articles, reviews) related to the above question? (I'...
2k 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 ...
595 views

### Quantum XOR: How do you generalize it?

Consider the classical XOR Gate: Given a 2 bit system: $G = [u_1, u_2]$ $$XOR(G) = (u_1 + u_2) \ mod \ 2$$ Is the following a good generalizaiton of a Quantum XOR Gate: Given a 2-qubit system: \$...
3k 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 ...
398 views

### Computability of physics

As far as I understand a Universal Quantum Simulator can simulate any quantum system and thus anything that exists in the universe. Also, a quantum computer can implement such a quantum simulator. ...
4k 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 ...
743 views

### How is acceleration computed in the leap-frog algorithm in computer simulations of particles?

I am reading the book Computer Simulation of Liquids by Allen and Tildesley (here is another link). On page 80, the authors describe the leap-frog algorithm, which is used extensively in molecular ...
109 views

### buiding circuits from color superconductors

caveat: the sort of exotic matter engineering in here is currently beyond the reach of our technology, but, that having been said: Has their been any research on building models of these sorts of ...
454 views

### Why can't we set the lattice spacing 'a' in lattice QCD?

My question is to do with lattice QCD. In the lattice action there is a parameter, 'a', the lattice spacing in physical units. However, if we want to generate a configuration with a certain lattice ...
2k views

### how does human brain compare to a modern CPU in energy per bit?

Can someone compare the energy efficiency of human brain as a computer ? What is the energy in joules / flop ? may be some reasonable assumptions on the computational load of common tasks such as ...
210 views

### Churchâ€“Turing Thesis

Can the Churchâ€“Turing Thesis be proved assuming classical mechanics, how is the proof or disproof? Edited: I was looking for a proof of "everything computable by a device obeying CM is computable by ...
2k 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 ...
393 views

### How to simulate a crashing wave? [closed]

I'd like to create a very rough animation of a wave crashing on a beach. I'm guessing it would have to be a particle simulator, where you code in the forces between the particles and then integrate ...
3k 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 ...
4k views

### Physics and Computer Science

Not sure if this is a 'real' question, but what is the relation between physics and computer science? A lot of physicists are also computer scientists and vice versa. My professor has a PhD in Physics ...