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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 the [tag:discrete] tag.

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2answers
63 views

Is the whole electromagnetic spectrum made of quanta?

My question is probably stupid (and maybe has already been answered on other posts), but I just started investigating quantum physics and I am struggling to understand the real meaning of "quantum". ...
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2answers
1k views

Why light coming from distant stars is not discrete? [duplicate]

Imaging the light racing out from distant sun, as beam of light shoots aways is a circular pattern (spherical actually), remembering that, light comes in photons or packets of energy. so how come is ...
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1answer
62 views

Where exactly does energy quantisation come in for light?

Planck quantised the energy of light in order to solve the black body radiation problem. However, I am confused as to exactly what he quantised. On one hand, I have seen that he quantised the energy ...
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0answers
38 views

Discrete time evolution in a non-Euclidean space?

The time independent schrödinger equation can be written as $$i\frac{\partial \psi}{ \partial t}=H\psi$$ if we consider the case of a 1D particle we can evolve it in time by discretising the ...
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0answers
23 views

Is there a “smallest unit of time”? [duplicate]

I am aware of the planck-length, being the smallest unit of space. I was wondering if there was such a thing as the smallest, undividable unit of time, something like 1 x 10 to the power of -35 ...
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0answers
46 views

Can Noether's theorem be applied to cyclic time symmetries? [duplicate]

Noether's theorem relates continuous symmetries in the time evolution of a system to a conserved value. Many conserved values, such as conservation of momentum, can be described via this theorem. I'...
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1answer
44 views

Is the answer to the question “How many moments in time exist between any two particular moments?”, infinitely many? [duplicate]

This question is related to Xeno's paradox, and to the discrete/continuous time debate, but it comes from a slightly different angle. If the answer is infinitely many, why would this not be a ...
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0answers
24 views

Geometrical way to view discretization of energy in quantum mechanics. How commutation relation implies discreteness?

The relation from which discreteness in eigenvalue of the energy of bound state arises is $[x, p]=i\hbar$ followed by the rule that wavefunction should be normalizable. So my question is there a ...
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1answer
50 views

Would any continuous model of the universe have/be based on hypercomputational laws?

I've read that when Turing-Church thesis is applied to the universe and physics, one of the three interpretations that we can use and is defended by some important physicists is that: "The universe ...
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1answer
58 views

Discretization of Hamiltonian with first derivative

In a particular 1D system, the Hamiltonian can be writen as $$H=\mathrm{i}\left(f(r)\frac{\partial}{\partial r}+\frac{1}{2}f'(r)\right)\; ,$$ wher $\mathrm{i}$ is the imaginary unit, and $f(r)$ is a ...
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3answers
154 views

Superposition principle forbids quantisation?

Apparently bound states in quantum mechanics require energy states to be discrete. That means energy in such systems is quantized, right? However, say that we have a superposition of energy ...
3
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1answer
105 views

Is entropy quantized in Loop Quantum Gravity?

From the Beckenstein-Hawking formula, we know that entropy is proportional to the area of the event horizon of a black-hole: $S\propto A$. From Loop Quantum Gravity, we know that length, area and ...
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3answers
93 views

Quantization of electrons' angular momentum in atoms and molecules

It is known that the Schrödinger's equation of the electron's wave function in atoms can be solved analitically only when a single electron is present (the "hydrogenlike atom"). In that case, the ...
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1answer
42 views

How to Find Jerk from Discrete Velocity Data?

I have measured the velocity of an object at discrete intervals. I want to find the corresponding acceleration and jerk of the object. How do I do this with discrete values rather than continuous ...
1
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1answer
86 views

Is space continuous? [duplicate]

Take a particle, it has a position $(x, y, z)$ maybe it is $(0.231, 8.962, 10.567)$. Is there a maximum precision to this? Is the space discrete or continuous? If it is discrete, how thin the ...
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1answer
19 views

What is the flux $\Phi$ enclosed by cyclotron orbit, which can express the quantization rule?

Suppose an electron (mass $m$, charge $e$) in the xy-plane with $B=(0,0,B)$ (The classical EOM result in circular orbit). Using the Bohr-Sommerfeld quantization rule we can find that $E_n = (n+1/2)\...
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0answers
64 views

Compactness and Quantization

So I was thinking today about when observables become "quantized", and came to the conclusion that every instance of quantization I've ever come across has come about from solving the Schrödinger ...
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3answers
64 views

What are wave-functions in QM. corresponding to?

I was learning about a particle trapped in a double well potential $$V(0) = \infty, V(x1)=\infty$$ which can be described by $\psi_n$ for n=0,1,...,$\infty$ with corresponding Energies $E_n$. Just ...
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0answers
18 views

Aggregation phenomena : How to get from a discrete to a continuous point of view

I'm studying a diffusion limited aggregation phenomenon. The $N$ particles diffuse in a box and when there is a contact they stick with a probability $p$, and let's say to simplify $p=1$. Meaning that ...
2
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1answer
53 views

Minimal Requirements for Space and Time

I read recently that to consider the Planck length of less than 1.6 x 10 exp -34 meters the smallest unit that can manifest 4 coordinate space time to be incorrect in its interpretation. The reason ...
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0answers
25 views

Is it possible to define background independent fluid dynamics equations?

Imagine a lake, and you measured the distance from each molecule to it's neighbours for molecules to within say 3 molecular radii. Taking this data you could reconstruct the positions of the ...
4
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4answers
132 views

Is it possible to have non-integral multiple of $e$ as charge?

We have 2 similar balls. On one ball there is charge $e$ and on other no charge. I connect the balls using a metal wire. We know that the charge gets shared until they have the same charges. Thus we ...
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0answers
93 views

Why any theory of spacetime atoms would be wrong from start? What about causal sets?

After watching this public talk by Nina Arkani-Hamed titled "The doom of spacetime", I can't fully understand what he said in the answer to an audience question about gravity. He said we can't simply ...
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0answers
106 views

Can Probability be quantized? [duplicate]

There are conjectures that quantities like space, time, energy, etc. are quantized and can only get some discrete values. I was wondering if there is any relationship in physics that interrelates ...
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2answers
49 views

IQHE, quantized conductance, and zeeman splitting

I've been trying to understand IQHE by reading these lecture notes by David Tong. Mainly, I was trying to understand the quantized hall resistivity in terms of the number of Landau levels crossing ...
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0answers
23 views

Does our universe has a limited decimal precision? [duplicate]

This question may be a bit strange but I was wondering if our universe has a kind of limit in precision. For example: A particle can be in coordinates a or ...
3
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4answers
101 views

In $E=hf$, can $f$ assume any positive value? (Beginner) [duplicate]

The energy of photon is given by the equation $E=hf$, where $h=$ Planck's constant, and f=frequency of radiation. Is f quantized, or can it assume any value? If it can assume any value, then wouldn'...
4
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2answers
113 views

Why position and momentum operators are both continuous spectrum while angular momentum is discrete? [duplicate]

We know that position $\hat{r}$ and momentum $\hat{p}$ are both continuous spectrum operators, i.e. $$\hat{r}|r'\rangle=r'|r'\rangle, \quad \hat{p}|p'\rangle=p'|p'\rangle.$$ But the angular operator $\...
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3answers
105 views

What was shocking in Einstein's partcile theory of light?

I know that when Einstein proposed the particle theory of light it was revolutionary and shocking for most of physicists and it took years to accept that view. Particle theory had been proposed in the ...
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2answers
84 views

Do we know, or at least have a strong argument for the fact that for a given time interval, we can always find a smaller time interval? [duplicate]

Motivation: In Biology, when, for example, biologists try to model the population dynamics of a population, they say: Let $N: \mathbb{R}^{nn} \to \mathbb{R}^{nn}$ be a function that represents ...
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2answers
67 views

Could spacetime have crystalline properties?

Space-time is currently modeled as a continuous manifold. However, space-time shares many features in general relativity that mimic a fluid-like thing. Fluids are certain states of matter and under ...
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0answers
65 views

Non-vanishing matrix elements in QFT after discretization

In QFT, introducing the lattice size $L$ implies that the momentum of plane wave solutions is discretized as $$\vec{p}_\vec{n} = \dfrac{2\pi}{L}\vec{n}\quad,\qquad \vec{n}\in\mathbb{Z}^D$$ I would ...
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2answers
342 views

Is Bohmian mechanics wrong in the case that space and time are quantized?

Bohmian mechanics assumes that particle trajectories are continuous. Also, it claims the random outcome of certain experiments (like the double-slit experiment) to be due to the random initial ...
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0answers
17 views

Why the eigenvalues of hamiltonian are discrete in bounded systems (only discrete energy levels)? [duplicate]

In one dimensional motion the general potential is given as in the figure above When energy is between V min and V 1 the energy levels are discrete like in the potential barrier and well example or ...
2
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2answers
175 views

Why atom has the straight discrete energy levels? [duplicate]

Interaction between a nucleus and electrons is in gravity(not considering) and electrostatics. Due to electrostatics nucleus attracts electrons. The force that describes this process is $$F=k\dfrac{...
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0answers
21 views

Pairwise additivity of numerical potentials

Surely this is a trivial problem, but I'm very much confused on how to approach so please bear with me. Say I have a two-dimensional evenly-spaced 16x16 grid centered at the point (x1,y1). I also ...
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1answer
136 views

Is any particle's energy quantized?

In the above picture, the author is trying to summarize the correlation between particle and wave packet. In doing so, he assumes that frequency is related to energy as: $E=h\nu$. Is this apparent ...
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1answer
34 views

What is a finite cellular automaton?

I found this paper: https://arxiv.org/abs/1606.08764 There, it is said "We realize constant-space quantum computation by measure-many two-way quantum finite automata" What are "finite automata"? ...
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0answers
81 views

Is simulating quantum field theoretical equations in the continuous limit the same as simulating really quantum continuous processes?

At the end of this article: https://hal.archives-ouvertes.fr/hal-00542373/document it is said that: "For example, several works simulate quantum field theoretical equations in the continuous limit of ...
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0answers
72 views

Are there any proved consistent quantum continuous cellular automata/game of life model?

There are quantum cellular automata (continuous game of life, which is a type of cellular automata): https://hal.archives-ouvertes.fr/hal-00542373/document There are continuous cellular automata (...
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1answer
80 views

Mechanism for light generation

Is all observable light caused by electrons dropping to a lower discrete energy level while bound in an atom? If so, how can a continuum of frequencies be generated? Is the thermal radiation ...
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3answers
125 views

Quantum mechanics calculations - must they always output a rational number?

If space is quantized, and particles are quantized, then the chance of a particle showing up in a specific unit of space must be a rational fraction? Could a quantum mechanics calculation ever output ...
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0answers
126 views

Is the universe a lattice?

My understanding is that cause and effect create a partial order of events in the universe (and that relatively prevents anything stronger). My understanding is also that it’s generally useless to ...
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2answers
48 views

Quantisation of States in QM

In the orthodox interpretation, the eigenvalues are the only measurable values of the corresponding operation, i.e., if the total energy of a particle is measured, the only numbers (as outcomes) are ...
3
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3answers
122 views

Is there a basic/elementary mass in the universe? [duplicate]

When speaking about electrical charges, it seems every particle either has a charge $+1$ or $-1$, in units of the electron charge. Therefore, we have a fundamental charge. But what about mass? Is ...
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0answers
52 views

Why is $x(t) = \frac {x_n + x_{n+1}}{2}$ when proving the Euler-Lagrange Equation?

When proving the Euler-Lagrange Equation for a single degree of freedom, we replace continuous time with stroboscopic time. We replace $$\dot x=\frac{x_{n+1}-x_n}{\Delta t}$$ but why do we replace $$...
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0answers
18 views

How to obtain boundary effects in the eigenmode analysis of a discretized WLC?

I'm currently working on the eigenmodes of a worm-like chain (WLC) polymer in the discretized version. We have the overdamped Langevin equation $\zeta\dot{r}(s,t)=-\kappa r''''(s,t)+\xi(s,t)$ for a ...
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0answers
33 views

Why are physical systems continuous?

To my (very limited) knowledge, physical systems (fluids, for example) can't have jump discontinuities. Why? Which fundamental laws can this be derived from, if any? This question is related to ...
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0answers
37 views

DFT of a non-continuous discrete time series

I am looking for a periodic signal in a time series $x_i, \quad i=1, \, ...,\, N-1 , \, N , \, N+P , \, N+P+1 , \, ... , \, N+P+M$ where $P$ is an unkwnown gap in time, for which I have no ...
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1answer
266 views

Is light a discrete or continuous phenomena?

Image a light bulb. In it the filament with a simple metallic composition, copper or other metals. At the precise instant, say $t=0$, where the first copper atom will be shining. In which direction ...