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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92
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7answers
45k views

Is the universe fundamentally deterministic?

I'm not sure if this is the right place to ask this question. I realise that this maybe a borderline philosophical question at this point in time, therefore feel free to close this question if you ...
58
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9answers
5k views

Is the uncertainty principle a property of elementary particles or a result of our measurement tools?

In many physics divulgation books I've read, this seems to be a commonly accepted point of view (I'm making this quote up, as I don't remember the exact words, but this should give you an idea): ...
49
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7answers
6k views

Are random errors necessarily Gaussian?

I have seen random errors being defined as those which average to 0 as the number of measurements goes to infinity, and that the error is equally likely to be positive or negative. This only requires ...
34
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5answers
6k views

Why do all the atoms of a radioactive substance not decay at the same time?

Why does the substance decay at a rate which is proportional to the amount of the substance at that moment? As all atoms are in hurry to become a stable atom and as their decay do not depend on any ...
26
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2answers
3k views

Could the randomness of quantum mechanics be the result of unseen factors? [duplicate]

The possibility of randomness in physics doesnt particularly bother me, but contemplating the possibility that quarks might be made up of something even smaller, just in general, leads me to think ...
25
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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 ...
25
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6answers
3k views

Quantum random numbers from a laser — simplest setup?

I'm a software / maths guy who would like to build a physical setup for generating quantum random numbers. I have no physics background, so bear with me. Background The project is for a public ...
24
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9answers
6k views

What exactly is deterministic in Schrödinger's equation?

I have read the following on Wikipedia but I can't understand it: In quantum mechanics, the Schrödinger equation, which describes the continuous time evolution of a system's wave function, is ...
14
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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. ...
11
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4answers
808 views

What is an interpretation of quantum mechanics?

In the sense of "Copenhagen Interpretation", what exactly is an interpretation? What purpose does an interpretation serve? Can an interpretation be tested or even be correct or incorrect independent ...
10
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2answers
2k views

Why does the Stern–Gerlach quantum spin experiment conflict with classical mechanics?

My understanding of the Stern–Gerlach experiment is that neutral (0 total charge) particles are sent through a non-homogeneous magnetic field, with the expectation that the field will push that ...
9
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2answers
697 views

Schrodinger's “What is life ” book quote: : The laws of physics are statistical in nature [closed]

In the book What is life? by Erwin Schrodinger, he says that the laws of physics are statistical in nature. Today, thanks to the ingenious work of biologists, mainly of geneticists, during ...
9
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4answers
511 views

Is there a mathematical basis for Born rule?

Wave function determines complex amplitudes to possible measurement outcomes. The Born Rule states that the probability of obtaining some measurement outcome is equal to the square of the ...
7
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3answers
529 views

True randomness? [duplicate]

I am a physics high-school student so my knowledge is not very deep on the subject. We started learnning about quantum mechanics and on some processes that my teacher described as random. I began to ...
6
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2answers
593 views

“Randomness” versus “uncertainty”

Highly rated PhysicsSE contributor @CuriousOne regularly makes the following claim about quantum mechanics (e.g. here): There is no randomness in quantum mechanics, there is only uncertainty. I ...
5
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4answers
23k views

Is radioactive decay spontaneous or random?

When it comes to radioactive decay, what is the difference between random and spontaneous? For example, when the count rate of a radioactive isotope is measured, the readings fluctuate. Is this a ...
5
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1answer
372 views

How do we know that radioactive decay is memoryless?

Let $\tau$ be the random variable that describes the lifetime of a given particle. It seems to conform to common-sense that $\mathbf{P}(\tau>t+s|\tau>s)=\mathbf{P}(\tau>t)$, as it would be ...
5
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1answer
4k views

True randomness via Radioactive decay [duplicate]

Is radioactive decay able to be used for true randomness? And do we know if radioactive decay is truly random? Edit. Here is a example true random number generator made using radioactive decay. http:/...
5
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1answer
259 views

Randomness and Thermodynamics

I am currently reading The road to reality by Roger Penrose. In chapter 27 he discusses time symmetry in dynamic evolution. He defines the Second Law of thermodynamics the following way: Heat flows ...
4
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3answers
381 views

How do we know that certain quantum effects are random?

I was looking at a website that claims to generate random numbers from observation of quantum effects. This lead me to question how we know that the numbers are truly random. When we observe a ...
4
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3answers
3k views

Difference between “Random motion” and “Brownian motion”?

I know "Random motion" is non-deterministic unpredictable motion of a particle. But it seems "Brownian motion" has some form of determinism as we can predict the pattern created by path taken by ...
4
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1answer
3k views

What exactly is entropy? Why is it measure of randomness? [duplicate]

What exactly is entropy? Why is it measure of randomness? I have been told Entropy is measure of randomness and it increases everytime randomness increases. What is Randomness? Randomness in what? ...
3
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3answers
991 views

Is quantum mechanics truly probabilistic?

Probability arises inherently from a lack of information. For example, if I were to take a ball out of a bag with 3 yellow and 2 white balls, I would have a 0.6 probability of getting a yellow and a 0....
3
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3answers
2k views

How do particles “know” when to decay?

So, as I understand it, in a substance that is made of radioactive elements, the half-life tells us how long until the half of those atoms decay into their next atom [is there a name for that: the ...
3
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3answers
1k views

How do we know that nuclear decay is truly random and spontaneous?

Nuclear decay is said to be random and spontaneous but how do we know for certain, that it is not just a lack of understanding of some other unknown force. Doesn't everything in the universe just ...
3
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3answers
171 views

Is there a mechanism for randomness?

I couldn't think where to post this, so I decided physics is the closest to answering this. Apologies for my amateur understanding of QM (0 understanding of QFT), I learn on free time by internet, so ...
3
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2answers
150 views

How does one understand the connection between symmetry and randomness?

In this famous book Physics from symmetry the author Jakob Schwichtenberg tells us all the existing physics can be derived by the symmetry of nature.In my opinion, the intuitive thing I can recall ...
3
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3answers
161 views

How can we certify that the randomness in the measurement outcomes is not due to randomness in the state preparation?

According to the theory of quantum mechanics, if a spin state is prepared along axis "x", and then measured along axis "z", then the result of the spin projection is probabilistic: half of the times ...
3
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2answers
62 views

What is the minimal discrete model of wave propagations?

If one takes the step size of an $n$-dimensional symmetric random walk to be infinitesimal, then the transition probability becomes the heat kernel. Thus, symmetric random walks are discrete, or ...
3
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1answer
531 views

What do we mean by “typical state”?

My question is somehow simple, but not trivial. I'm reading many articles about the ER=EPR correspondence. There are some articles which study this proposal from a field theory point of view (one ...
3
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1answer
80 views

Introducing Randomness into Lagrangian Mechanics

Let's say at $t_o$ we have a ball rolling along a (rigid) tight rope. Is there anyway that we can solve for the trajectory of the ball knowing that at some $ t' $ there will be a random constraint ...
2
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2answers
104 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
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5answers
422 views

Could the universe be accurately simulated with an infinitely powerful computer? [duplicate]

This would mean that every event happens because of what has hapened before it and there is no randomness factor. At a microscopic level, the motion of atoms is a result of the motion of other atoms ...
2
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2answers
162 views

Is Quantum Mechanics Compatible with Conservation of Information?

What is exactly the law of conservation of information? In quantum mechanics we have truly random outcomes in experiments, but doesn't this randomness mean that new information is produced and the law ...
2
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1answer
433 views

Deterministic universe for dummies [duplicate]

Is there a general consensus about whether the universe is deterministic? Is it still up in the air? I have attempted to read other physics.stackexchange answers and do some independent research, but ...
2
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2answers
626 views

Why isn't the universe uniform? [duplicate]

I always have a question in my mind when I think about the big bang. It is that if the universe has expanded from a tiny singularity by an explosion to the universe of today, why didn't it expand into ...
2
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1answer
57 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-\...
2
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1answer
182 views

The entropy of lottery drawing machines

Suppose we have a fair lottery drawing machine where you have a container of numbered balls that is rotated many times such that interaction of the balls with themselves and the container produces a ...
2
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2answers
87 views

Randomly initializing ensemble of particles in “toy” computer model

I'm programming a "toy" model, and want to intialize the $(\mbox{positions},\mbox{momenta})$ of an ensemble of particles in three-space, using a uniform (pseudo) random number generator. But I'm a ...
2
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1answer
161 views

Is there $\frac{1}{f^{0.5}}$ noise?

I've heard of $\frac{1}{f^0}$ noise (white noise), $\frac{1}{f}$ (pink, or sometimes tan noise), and $\frac{1}{f^2}$ (brown noise). But why no $\frac{1}{f^{0.5}}$ or $\frac{1}{f^{\pi-2}}$ noise. Do ...
2
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2answers
199 views

Is there even something like true randomness?

So a few months ago a research team did the following experiment: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.060401 They shot lasers at certain detectors trying to detect the spin ...
2
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1answer
57 views

Does quantum randomness allow extreme deviations like Gaussian randomness does?

{ I am explaining things as I know it. Please feel free to correct as necessary. } As I have understood it, Gaussian randomness forms a predictable pattern when sample size is very high. If we take ...
2
votes
1answer
109 views

Feynman's random walk: How does he get $⟨D^2_N⟩=N$?

In Feynman's lectures, section 6.3, I follow most of his argument about a random walk, but I miss one step. To summarize, he's discussing a one-dimensional random walk (eg, determined by coin flips), ...
2
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2answers
682 views

Can string theory get rid of randomness in quantum processes?

I am not a physicist, but I am very much into popular science, especially string theory. I would like to know if it is conceivable that string theory might be able to get rid of the randomness ...
2
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0answers
236 views

Temperature as the independent variable of Lagrangian

I was thinking about applications of the Lagrangian and I started to toy with some ideas and tried to come up with interesting twists. Immediately I thought it would be interesting to use temperature ...
2
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0answers
2k views

Are radioactive decays truly random? [duplicate]

By truly random I mean that IF we knew the position and velocity of every particle in radioactive isotope, could we predict when the decay would happen?
2
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1answer
93 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 ...
1
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3answers
88 views

What happens to a radioactive material's atom when it disintegrates?

Suppose you initial had radioactive $2^n$ atoms (where $n$ is an integer). Now after a number of halflives the number of left out atoms becomes 1. Now what will happen to it will it disintegrate and ...
1
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1answer
161 views

Generalizing a Gaussian distribution

Perhaps this a nonsensical question but hear me out. I have a random variable $x$ whose moments I can calculate. The first moment $<x>$ is zero and the second $<x^2> = X^2$ is something ...
1
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3answers
106 views

Is wave function collapse the only source of 'randomness' in QM? What about field fluctuations? Are these two even distinct?

Basically I want to know the validity of the statement, "All randomness originates from wave function collapse" or maybe "The only true random event is the collapse of wavefunctions" This seemed to ...