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.

Filter by
Sorted by
Tagged with
-1
votes
0answers
20 views

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....
-1
votes
0answers
33 views

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 ...
0
votes
1answer
55 views

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 ...
-1
votes
1answer
59 views

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 $D_N=D_{N−1}+1$ ...
22
votes
9answers
5k views

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 (...
2
votes
3answers
89 views

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 ...
-3
votes
3answers
122 views

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 ...
0
votes
1answer
42 views

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). ...
3
votes
2answers
137 views

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 ...
2
votes
1answer
54 views

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 ...
44
votes
8answers
6k views

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 ...
2
votes
3answers
125 views

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)...
0
votes
0answers
35 views

Confusion about Boltzmann brains

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 ...
0
votes
1answer
65 views

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 ...
1
vote
1answer
71 views

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 ...
0
votes
0answers
15 views

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 \...
0
votes
1answer
26 views

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
1
vote
1answer
59 views

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 ...
1
vote
0answers
40 views

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 ...
0
votes
1answer
33 views

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 ...
1
vote
0answers
17 views

Why is the continuity equation only valid for the flux velocity but not for the osmotic velocity?

The continuity equation $$ \partial_t \rho + \nabla (\vec v \rho) = 0 , $$ can be derived from the Fokker-Planck equations for the forward- and backward velocity ($b,b^\star)$: $$ \partial_t \...
2
votes
2answers
68 views

What's the meaning of a continuity equation with $\nabla^2 \rho$ on the right-hand side?

I stumbled upon a continuity equation with a $\nabla^2$ term on the right-hand side: $$ \partial_t \rho + \nabla (\vec b \rho) = D \nabla^2 \rho , $$ where $b$ denotes the forward velocity and $D$...
1
vote
1answer
63 views

Doesn't the Many Worlds interpretation of Quantum Mechanics rail to remove randomness?

In the Copenhagen Interpretation, the observed state of a particle is random. In the Many Worlds interpretation, the all possible observed state of a particle are true, an the universe "splits". But ...
3
votes
1answer
47 views

Do we know when a particle has a tangled pair?

By looking at a particle alone, can we tell if it has a tangled pair somewhere in the universe? Moreover when measuring the spin of a electron, we can't predict it, unless we know the spin value of ...
1
vote
0answers
24 views

Can we have a Non-Gaussian Likelihood and which are the conditions or examples?

I am working on Fisher formalism and MCMC method. It seems that Fisher formalisme assumes that posterior is always Gaussian. So if I find with MCMC a gaussian posterior, I validate the results of ...
1
vote
1answer
59 views

Variance of Simulated Langevin Equation

I simulated (by Matlab) the Langevin equation for optical-trapped particle in very short time "steps" And I got this white noise figure.. The question is how I can calculate the variance (or in ...
0
votes
0answers
53 views

Are there systems in classical mechanics that are provably non-deterministic? [duplicate]

N body problems mostly don't admit any algebraic solutions although they can be solved numerically at least in principle. Determinism basically is the claim that given any system and its initial ...
0
votes
0answers
20 views

What's the meaning of the osmotic velocity?

To describe a random-walking particle, we can use the stochastic differential equation \begin{equation} dx(t)= b\Big(x(t),t \Big) dt + dw(t) , \end{equation} which is also known as the Langevin ...
1
vote
0answers
26 views

Why is the osmotic force virtual?

In Einstein's treatment of Brownian motion he argues that (in equilibrium) there is an "osmotic pressure force" $\vec O$ that counterbalances the effect of gravity $\vec K$. This allows him to derive ...
6
votes
2answers
79 views

What effect stabilizes chaos by randomness?

Reading the book Antifragile-Nassim Nicholas Taleb, I encountered the following paragraph. And ironically, the so-called chaotic systems, those experiencing a brand of variations called chaos, can ...
-1
votes
1answer
39 views

Generating random change in photon frequency $\Delta \nu$ from angle-averaged isotropic redistribution function

I am implementing the Monte Carlo Simulation Code for the case of photons being scattered by electrons. The paper I'm referring (Hillier 1991, Appendix B) suggests that after each scattering, the ...
2
votes
1answer
99 views

Does exist a (truly) stochastic but causal physical process?

I wonder if it is possible for causality to be held, but not determinism. Does any real-world example exist? If yes, please explain how does that satisfy causality and not determinism. (for example, ...
0
votes
0answers
59 views

Random fields in physics - how do they work?

I'm trying to get an intuitive understanding of what random fields are. Wikipedia's article gives a formal definition (which is in very mathematical language), but also says various much more ...
-1
votes
1answer
62 views

Building realistic simulation using differential equations [closed]

I am building simulation using differential equations to model the motion of a damped vertical spring-mass system. I wish to use this simulation to extract data. For example, I am trying to find the ...
0
votes
1answer
66 views

Brownian Motion

I’m currently interested in learning some topics about the Brownian motion and the random walk (in general, from a pure statistical and probabilistic way). For that, I would like to ask you if you ...
1
vote
0answers
42 views

Origin of Quantum Randomness

I'm in the process of developing a Quantum Random Number Generators (QRNG) for cryptographic applications. I have a basic understanding of quantum physics from my A-Levels and some additional research ...
1
vote
1answer
33 views

Is every emitted particle in a one-particle double slit experiment the same?

Lately, I was thinking about the one-particle version of the double slit experiment, e.g. in which an electron or a buckyball is emmited. The precise description of what I mean can be found here. ...
0
votes
1answer
135 views

Could quantum randomness be transformed into classical, macroscale randomness?

If measurements of quantum phenomena can show results that are truly random wouldn't it be possible to establish a macroscale-dependence on such a non-statistical result and thereby introduce ...
14
votes
5answers
3k views

What triggers a nuclear decay?

I am not a physicist but I have been wondering about this: I understand that the decay of a nucleus is a random event and one cannot predict exactly when it will happen for a particular nucleus. ...
2
votes
2answers
121 views

Flipping a coin with same initial conditions

Today, in my physics class my teacher was talking about how we can never predict the outcome of a coin flip. So I thought: Will the outcome of a coin flip be the same if we do not change the initial ...
2
votes
1answer
62 views

Randomly stopped dynamics of $x(t)$: How can I find $\text{var}\{ x(t) \}$?

Consider the simple dynamical equation $$ \dot{x}(t) = u H(t-\tau),$$ where the timescale $\tau$ is an exponentially distributed random variable $\tau \sim \omega \exp\{\omega \tau\}$ and $H(t) = 1-\...
0
votes
2answers
43 views

Can a perfectly symmetrical round bead dropped into a perfectly level Galton Board indefinitely balance on a peg?

Probability implies that "The Galton Board consists of a vertical board with interleaved rows of pegs. Beads are dropped from the top and, when the device is level, bounce either left or right as they ...
2
votes
1answer
103 views

Quantum Mechanics - How do we know that the observed locations of electrons are random? [duplicate]

How do we know that the observed location of a electron (or any quantum object) is purely random (there is no way to predict it) within the probability-function instead of normal randomness (we don't ...
2
votes
0answers
254 views

What is the Spectral Form Factor?

In many papers in Random Matrix Theory [1-3] related to quantum chaos (and, in particular, to the SYK model) they analytically continuate the partition function of the system $Z(\beta)$ into $Z(\beta +...
26
votes
5answers
5k views

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 ...
1
vote
0answers
32 views

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 ...
0
votes
0answers
33 views

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 ...
1
vote
1answer
28 views

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 ...
0
votes
0answers
82 views

Is the “probabilistic nature of quantum mechanics” and quantum randomness the same?

Digital Physics are a branch of hypotheses about the fundamental physics of our universe. They basically describe the universe as an analogy to a computer and defend that everything in the universe is ...
-1
votes
2answers
184 views

If the universe is random, why does it contain structure? [closed]

Ive read that the scientific community agrees on that the universe works in a non deterministic way. However, because we have some kind of structure in the universe I assume (from a super novice ...