# Questions tagged [randomness]

Randomness covers questions having to do with the concept of randomness in physical processes and questions about determinism vs indeterminism or interpretations thereof. Question related to concepts of probability may also use this tag.

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### Finding the correlation matrix and mean value of Gaussian random matrix $A$ from expectation value of $e^A$ and $e^A ⊗ e^A$

I have a random matrix $A$ with Gaussian distribution. and I know value of $E(e^A)$ and $E(e^A \otimes e^A)$. are there any way to find Gaussian function? both numeric and analytic ways are helpful. P....
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### Feynman's random walk (6.3)

In chapter 6 of volume 1 of the Feynman lectures on physics, Feynman's elaborates on the random walk. https://www.feynmanlectures.caltech.edu/I_06.html Amidst his lecture, he says this: The expected ...
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### Classical unpredictability

Consider, a box with $N$ particles each of mass $m$, arranged at time $t=0$ to be moving parallel to the $x$-direction, with mean velocity v and mean distance l. The particles are spheres of mean ...
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### Feynman's random walk (6-3)

How does Feynman get to $D^2_{N-1}$? The expected value of $D^2_N$ for $N>1$ can be obtained from $D_{N−1}$. If, after $N−1$ steps, we have $D_{N−1}$, then after $N$ steps we have $D_N=D_{N−1}+1$ ...
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### Why does a collection of radioactive atoms show predictable behaviour while a single one is highly random?

Well, we know that it is impossible to say exactly when a radioactive atom will go on decay. It is a random process. My question is why then a collection of them decays in a predictable nature (...
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### Fundamentally random physical phenomena

I read on Wikipedia: Quantum mechanics predicts that certain physical phenomena, such as the nuclear decay of atoms, are fundamentally random and cannot, in principle, be predicted. What does that ...
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### How does quantum theory allow a rock to turn suddenly into a duck? [closed]

Quantum theory does not allow a rock to turn suddenly into a duck. It does not allow any other bizarre transformation to happen either. This idea is a myth perpetuated by people who misunderstand ...
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### Applications of the Gaussian unitary ensemble

It is well known that the pair correlation function of the zeros of the Riemann zeta function reproduces the correlation function of the random matrices from the Gaussian unitary ensemble (GUE). ...
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### Quantum: Is it possible to determine the past knowing the present?

Due to quantum randomicity, it's impossible to determine the future knowing the present. But is it possible to determine the past knowing the present? As far as I understand, it is impossible because ...
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### Why do chaotic numbers improve evolutionary algorithms such as genetic algorithm?

I have implemented a genetic algorithm to solve a problem. In the process of genetic algorithm, instead of random numbers, I have used the chaotic numbers generated by the logistics map. The genetic ...
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### What is the reason that Quantum Mechanics is random?

We know quantum mechanics gives a random result when we observe a particle that's in a superposition, but why is it random? One of the explanations I've heard is that because light comes with those ...
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### What is a probabilistic physical theory?

What do we mean when we say that we have a probabilistic theory of some phenomenon? Of course, we know from experience that probabilistic theories "work", in the sense that they can (somehow)...
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I read in some papers such as this one about Boltzmann brains. Now I have seen many arguments against the fact that we are Boltzmann brains, see for example here (if I remember correclty Feynman said ...
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### Do physicists accept true randomness in nature? [duplicate]

I am not a physicist but I've started studying the subject and noticed that terms like "random", "randomness", "randomly" are widely used when talking about nature. For example, random movement of ...
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### How can we prove that pure randomness exists?

I want to know does real randomness ( no cause-effect law ), really exists? And if it exists how can we prove it? because saying something doesn't have a cause is akin to saying we don't know the ...
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### Why do we have different probability densities in the forward and backward Fokker-Planck equations?

For a system involving randomness, we can find a probability distribution $\rho$ that obeys the forward Fokker-Planck equation: \begin{align} \partial_t \rho + \nabla (\vec b \rho) &= D \nabla^2 \...
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### explanation of random motion of multiple pendulums

is there an explanation of random motion of multiple pendulums , it seems to be 'orderly chaos'. example : https://www.youtube.com/watch?v=1M8ciWSgc_k
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### On uniformly randomly choosing a pure quantum state [closed]

If I have a Hilbert space $\mathcal{H}_A$, how can one uniformly randomly choose a pure quantum state in this space? I believe the answer is to take the state $\vert 0\rangle$ and apply a random ...
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### How can we interpret a system in which the probability distribution obeys the forward and the backward Fokker-Planck equation simultaneously?

For a system involving randomness, there is no longer a unique derivative and hence no longer a unique definition of velocity. But for the forward (Ito) derivative, we can find a probability ...
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### If 1 photon hits 1 atom, will the departing angle be deterministic?

Consider a single photon fired towards a single atom. After interacting with the atom, the photon heads away from the atom (assume no absorption). Is the angle at which the photon departs ...
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### Is throwing dice a stochastic or a deterministic process?

As far as I understand it a stochastic process is a mathematically defined concept as a collection of random variables which describe outcomes of repeated events while a deterministic process is ...
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### How to introduce dimensionality in a dimensionless framework?

This question is an extension of this one. I have been told that to introduce dimensionality in a dimensionless quantity I need to multiply with suitable parameters. For instance, for velocity I have ...
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### A case where entanglement leads to correlation in decay time

Half-lives of unstable or metastable states are typically known, but specific decay times are inherently uncertain. On the other hand, quantum entanglement leads to correlations between inherently ...
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### How to deal with motion on a 2-D lattice in terms of dimension?

I am reading a paper titled: Random walks of molecular motors arising from diffusional encounters with immobilized filaments. There the authors consider the molecular motor moving on a 1-D protein ...