Questions tagged [discrete]

Discrete means as opposed to continuous. For instance, people may ask questions about discrete electric charges, discrete spacetime, discrete energies, etc. If discretization is vital/essential to the question, then tag it with this tag.

526 questions
Filter by
Sorted by
Tagged with
31 views

Can we describe 4 dimensional spinors on an 8 dimensional manifold?

I was reading about models of space-time, in particular where it is modelled as a mesh and that it becomes smooth 4D space-time in the limit as the cell sizes go to zero. (An example of this, is what ...
• 6,068
36 views

Ising model correlation function in the high temperature limit

I'm reading the book 'Gauge Fields and Strings' by A. Polyakov and I don't understand his derivation of the correlation function of the Ising model in the high temperature limit. I don't really ...
2k views

When we say a rigid body is a system of particles, what exactly are 'particles' here?

In Newtonian mechanics, a particle (in my knowledge) is a point-like mass with no shape and size, deformation, rotation and internal movements, which is an idealized model of an object which does have ...
1 vote
33 views

Propagator for a single particle in 1D in Polyakov's Gauge Fields and Strings

I was reading the book 'Gauge Fields and Strings' by A. Polyakov and I don't understand a step in the 1D single particle propagator derivation.. The part I don't understand is Eq. (1.2). for the ...
1 vote
18 views

How do I approximate an angular acceleration vector from a history of orientations?

A rigid body is simulated to move in six degrees of freedom. At every past timestep, I know its displacement vectors $x^{GLOB}$ in the global coordinate frame, as well as 3x3 matrices $R$ that ...
• 257
79 views

Are there any significant integer constants that are not unitless? [closed]

When it comes to meaningful integer constants, the only ones I can come to think of (except zero) are unitless, for example 1 (the multiplicative identity), 2 (the base of the binary system), 10 (the ...
• 418
36 views

Does the quantisation of energy apply to everything? [duplicate]

Radiation is quantised according to Planck, so that's out of the question. However, I have seen many simplifications that claim Planck introduced quantised energy. Period. Has Planck really done that? ...
• 335
49 views

Discrete Spectrum vs Continuous Spectrum and Bounded, Scattering States

Apolgies in advance if this is a confusing ramble and multitude of questions, I'm not quite sure how to articulate myself. I am currently reading up on quantum mechanics and seem to have confused ...
1 vote
68 views

How to understand crystal momentum, its relation to translational symmetry, Noether theorem, and to symmetry breaking/Landau-Ginzburg theory?

This question continues from my another question How to understand critical points of the Brillouin zone, (in)direct bands of transition-metal dichalcogenides?, and is related to Is crystal momentum ...
47 views

Quantization of Electric Charge and Cutting Spheres

Say you have a metallic sphere that holds a charge $Q$ uniformly. If we cut the sphere into two equal halves, each half of the sphere will hold a charge of $Q/2$. Also, electric charge is quantized. ...
20 views

Can finite element analysis predict whether flow is turbulent?

Finite Element Analysis in Simulation Software to predict the Reynold's number are computed using the formula$=pVD/u$ or there is a finite element method for this? I was just wondering whether it ...
1 vote
52 views

• 13
59 views

Microstate and Phase space

Pathria, Statistical mechanics, 4ed,pg32-33 "The microstate of a given classical system, at any time, may be defined by specifying the instantaneous positions and momenta of all the particles ...
• 698
45 views

Is charge not quantized fundamentally and that is why we haven't come across magnetic monopole?

If protons are getting charged from quarks.. then the charge in quarks is fractional and not quantized. Does this mean that the charge we see is not fundamental? And the charges in quarks are just ...
81 views

Is time continuous or discontinuous? [duplicate]

As I notice I sometimes feel as if time is discontinuous it’s like a comic book where each act is planned out and the main character just comes there. Please give an explanation and correct me if I am ...
• 21
1 vote
89 views

• 1,149
1 vote
123 views

Aren't we crossing infinity? [duplicate]

Couldn't there be infinitely small time units? When a second passes, aren't we passing infinite units of time? When we walk across a room, aren't we passing an infinite amount of small length units? ...
• 181
1 vote
71 views

Solving the 1d Schroedinger Equation numerically. How to get complex phases?

There is a nice method that lets you solve the Schroedinger Equation in 1d numerically, by discretizing space. Tranforming the Eigenfunction problem into an eigenvector problem with a finite-...
105 views

Confusion about $U(1)$ representations and charge quantisation in the context of gauge theory

In a gauge theory, the fields transform under representations of the gauge group. When studying a special unitary group $SU(n)$, I've usually thought of the elements of a representation as being the ...
79 views

Franck-Hertz experiment

In the Franck-Hertz experiment why are the peaks much sharper than the troughs? Also our data analysis suggested that the distance between the peaks is smaller (nearer to $4.9 \$ eV ) than the ...
• 79
78 views

Why the thermal radiation spectrum is continuous?

Why do photons within one body have different energies in a thermal radiation spectrum? Does it have to do with different modes of vibrations or phonons (for solid states)? In other words, is the ...
• 11
71 views

Discrete Fourier transform intuition

I'm given a signal $$x(t)=\cos(200\pi t)$$ which is sampled at $t=n/400$ instance, for $n=0,1,2,..,7$ I've to comment on $X$, the 8 point discrete Fourier transform. Just multiplying by the DFT matrix ...
79 views

Conservation of charge and quantisation of charge

How does the idea of conservation of charge relate to the quantisation of charge.
1 vote
92 views

Quantization of the Berry Phase

Let's consider the Aharanov-Bohm effect. Following Girvin & Yang, an infinitely long, very thin flux tube running along the $\hat z$ axis is surrounded by a strong potential barrier preventing ...
• 123
48 views

What are some references on discrete symmetries (CMT)

I'm a condensed matter theorist, and find that others in the field are very literate in consequences of breaking discrete symmetries. For example, there are a number of statements which often float ...
72 views

Apart from quantum mechanical systems, how you will accept that energies are quantized? [duplicate]

Why energies are quantized at quantum scale? Apart from quantum mechanical calculations, how you will accept that energies are quantized?
• 413
82 views

Is anything truly continuous? [closed]

Is any 'continuous' thing (fluids, light, time, etc...) truly continuous? Or is it really batch but at just such a high frequency that it appears to us as continuous? I.e. it appears to me that the ...
• 454
22 views

Can an electron jump to a higher orbit with an energy that is only a little less than the theoretical requirment? [duplicate]

I understand that electrons can possess only discrete amounts of energy so if an electron in an atom has to jump from a lower orbit to a higher orbit it will require a discrete amount of energy to the ...
• 183
87 views

Planck's quantum theory

Recently came across Planck's theory, $E = h\nu$. It means that at any frequency, there is given energy. But I also saw that, $E$ can be $0, h\nu, 2h\nu, 3h\nu,...$. How is it possible that energy can ...
• 31
152 views

Is using traditional continuous calculus appropriate to study discrete Nature events such as quantum physics? [duplicate]

I was wondering why traditional calculus is used for studying quantum physics considering that there seems to be no continuum at quantum scale but discrete. For example, differential equations ...
• 409
196 views

Could wavefunction values be quantized?

According to standard quantum mechanics, Hilbert space is defined over the complex numbers, and amplitudes in a superposition can take on values with arbitrarily small magnitude. This probably does ...
• 3,691
151 views

Asymmetric potential well and discrete energy levels

Let us consider an asymmetric potential, which is piecewise defined as $V_1$ for $x<0$, $0$ when $0<x<a$ and $V_2$ for $x>a$, together with the condition $V_1 > V_2 >0$. In the first ...
90 views

Do electromagnetic fields propagate continuously? [duplicate]

Having learned about plancks constant it is easy to mentally assign a grid-like structure to reality, almost starting to think of it as being pixellated in a way. This raises the question in me though ...
• 11