Questions tagged [information]
Add this Tag for questions on information theory applied to physics, especially in the fields of statistical mechanics and thermodynamics, the black hole information paradox, complexity of dynamical and physical systems and questions to do with whether information is conserved by physical systems. Use the tag quantum information if your question is to do with information theoretic concepts applied to quantum states.
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Is the optimal POVM of a mixed state the same as the optimal POVM of the pure states in its ensemble?
If I have a mixed state, where each pure state in the ensemble has the same optimal POVM (by optimal I mean POVM for which the classical Fisher information is the same as the quantum Fisher ...
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The connection between entropy in physics and information theory [duplicate]
In physics, there is a version entropy which is defined as $S = k_B \ln W$ while in information theory it is defined as $H(X) = -\sum_{x} p(x) \log p(x)$. Why does entropy have different units in ...
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Does the master equation break down for negative times?
I'm studying stochastic dynamics and have encountered the framework of the master equation for the study of continuous time Markov processes. First, I'll state some general definitions and then say ...
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Information conserved applied to time
So it's said that information in the universe is conserved. So does that also mean that anything that happened in the past is also conserved and can be accessed?
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The difference between classical and quantum entropies
The von Neumann entropy $-\mathrm{Tr}(\rho\ \log\rho)$ of a quantum thermal state with $\rho=\frac{1}{Z}e^{-\beta H}$ gives the thermal entropy, see e.g. this question.
The von Neumann entropy is a ...
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Does a shredded book contain more or less information (or the same) than the original book
If I shred a book into numerous pieces, and scatter them, so that the original text is completely unreadable, then for me, as a reader, the book has lost all its information. Its entropy has greatly ...
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Can, in theory, information escape an event horizon via a specialized setup?
Can, in theory, information escape an event horizon via a specialized setup?
Specifically, send a beam of photons to be barely—just barely—inside the event horizon, then wait for hawking radiation to ...
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Communication via entanglement [duplicate]
For years now i have in my haed a thought experiment for information exchange via quantum entanglement. And i am aware that something must be wrong with it but i can't figure out what it is.
The ...
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(Generalized) Jarzynski equality
Sagawa and Ueda ref, generalized the Jarzynski equality in the presence of a feedback control, leading to the following equation:
$$ \langle e^{-\beta(W-\Delta F)-I} \rangle = 1.$$
Can I interpret ...
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How information of accelerated charged particle travels, if photon is absorbed?
There is an electrostatic field around the electrically-charged particle (particle is the source of that field).
When the particle accelerates, it emits photon.
Photon travels at finite speed.
...
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Which theory can resolve black hole information paradox?
I am new, not have expert level knowledge.
But I have studied about black hole information paradox. The black hole doesn't kept any information which passes event horizon. Which can break physics.
Is ...
user375123
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Is the informational approach to thermodynamics generally accepted as "correct"?
This question is about the "ontology" as it were of statistical mechanics. In my limited reading of (equilibrium) statistical mechanics texts, I have encountered two viewpoints for what is &...
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Faster than light communication by entangled photons [duplicate]
Faster than light communication is not possible. If I measure the polarization of an entangled photon and it turns out to be right circularly polarized. In that instant, dont I know that someone ...
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How much information is in a hydrogen atom?
How much information is contained in a hydrogen atom (a bound electron and proton) at room temperature?
There are bounds that set limits on the amount of mass/energy that can exist in a given region ...
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Mutual information between energy levels
I have the following partition function
$$Z(\beta_1,\beta_2) = Z(\beta_1)Z(\beta_2) +Z(\beta_1,\beta_2)_c$$
Thus, I have a non-zero mutual information $I(Z(\beta_1);Z(\beta_2)) = S(Z(\beta_1))+S(Z(\...
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The Journey of an Electromagnetic Wave Exiting a Router
I'm learning a bit of how WiFi works under the hood, and have a basic grasp of the general process.
First, you make an internet request. Your computer then sends out a WiFi signal which your router ...
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What information is gained when just one single half of an entangled photon pair is detected, following its transmission through a polarizer?
My admittedly limited understanding of QM is that it is a matter of probabilities whether or not a photon is (re)transmitted through a polarising filter and that these are a function of the relative ...
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Shannon's information theory on open systems
A university professor on Library and information science told me that he considers Shannon's information theory too limited since it doesn't apply to open systems.
I couldn't find info to back up ...
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How can entanglement entropy be quantified between lattices of differing structures?
Suppose there are two 1 dimensional particle lattices, both with differing distances between particles and not necessarily the same number of particles. Each particle exists in a superposition of spin ...
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References on Information Conservation and Hamiltonian Mechanics for Undergraduate Presentation
As an undergraduate physics student, I am currently working on a presentation focused on applications of Hamiltonian mechanics. Specifically, I am interested in exploring the relationship between ...
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Entropy expressions for Bose-Einstein and Fermi-Dirac statistics
We are all familiar with the Boltzmann-Gibbs-Shannon entropy formula:
$H_{\text{BGS}} = -\sum_{k}p_{k}\log{p_{k}}$
In information theory, this can be interpreted as the expectation value of the "...
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Information theory in classical mechanics
I've only ever heard about information theory being used in stuff related to probability distributions, which makes sense because information and entropy are related. However, I'm having trouble ...
user367128
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Why are CT scans much smaller than the raw data?
I'm not too familiar with CT, but I worked with medical CT images long ago, and recall that the raw data, recorded by the scanner was way bigger than the 3D image itself (Both were 16-bit TIFF files, ...
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Landauer limit - cost to avoid changing a bit already equal to desired value
If I have a bit and I do not know what the current value is, is it possible to use less energy than $E_b = k_b T \ln(2)$ so that if the bit value is already equal to what you want, you don't waste ...
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Correlation and thermodynamics [closed]
I have two systems that are correlated, their energy levels are not independent: $\rho(E_1,E_2) \ne \rho(E_1)\rho(E_2)$.
So I wanted to quantify the amount of dependence they have, I used the mutual ...
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Why isn't correlation in the description of entangled states just a sign of model information redundancy? [closed]
Two entangled particles are described (modeled) such that there may be a correlation between parts of the model. That is, measuring one of the pair provides information about the other. Why isn't ...
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Landauer's principle debunked?! "Information entropy and thermal entropy: apples and oranges"
I was asking a question about sustainability of reversible computers against entropy. I referenced Landauer's principle to frame my question and someone told me in the comments that Landauer's ...
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"Information Catastrophe" and measuring density of planets?
In the article https://arxiv.org/pdf/2009.01937.pdf the term "Information catastrophe" is explained. Suppose the later proposed experiment by this author https://aip.scitation.org/doi/10....
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Relativity, communication and reference frames [closed]
Quick question here.
Does communication in special relativity involve sending signals from contrasting reference frames? I gather reference frames aren't really physical things, they're mathematical ...
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What is meant by: "each particle in the observable universe contains 1.509 bits?"
What do physicists generally mean by particles "storing" bits and the idea that information is neither created nor destroyed?
Example:
"We determined that each particle in the ...
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Correlation between mutual information and thermodynamic entropy
Does a system having a lower thermodynamic entropy imply that there is greater mutual information between the variables associated with its constituent parts? I.e., in a lower entropy system, any one ...
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Does Maxwell's demon include the knowledge of the experimenter?
We know Leo Szilard was right when he said the demon would need to expend energy to know which molecules are hot or cold, and there has been experiments that have converted information to energy using ...
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Why black hole erase information
It is usually said that according to the no hair theorem, black holes erase the information enter them which reduce the entropy and imply the so called "information paradox".
The problem is ...
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Maximum Entropy Principle with inequality constraints
It is well known that, maximizing the entropy of the joint distribution $P(x_1,...,x_n)$ of a random vector $(X_1,...,X_n)$ subject to equality constraints for the mean vector ($\mu$) and the variance ...
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Does the holographic principle allow realistically-sized universe simulation?
I was reading about the holographic principle and a question came up to my mind which I can't find an answer to. My understanding is that the holographic principle states that the description volume ...
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How are Shannon's non-physical entropy and physical entropy related?
Suppose there is a die manufacturer. This facility has a dice machine which is in charge of producing new dice by casting their faces in molds made out of some special material, so in a way, it has a ...
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How is $S=\frac{A}{4G}$ not manifestly a solution to the black hole information paradox?
If we take the black hole entropy $S=\frac{A}{4G}$ as given and let the black hole evaporate, the area of the black hole decreases, so the entropy of the black hole decreases. The entropy should tell ...
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How can storing a bit of information require less mass than an electron?
The prefixes ronna-, ronto-, quetta- and quecto- were adopted recently to mean $10^{27}, 10^{-27}, 10^{30}$ and $10^{-30}.$ According to The Guardian, "An electron weighs about a rontogram, and a ...
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Nonlocality of a bug on movie screen
I am currently learning quantum mechanics using Griffiths. In the appendix, he goes to talk about EPR and Bell's inequality, and that experimental verification of Bell's inequality rejects the "...
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Loss of information
Let's say we have a perfectly flat cylinder. It stands on a perfectly flat table. We make it spin for one minute on the table with no more pressure than the weight of the cylinder itself. We can agree ...
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Role of information in physics [duplicate]
The fact that information is preserved is often stated as a fundamental fact in physics.
Not being a physicist I do not understand how information enters physics at all. What is it an attribute of? ...
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Why are physicists surprised that the information of a black hole is proportional to its boundary? #2
Inspired by Why are physicists surprised that the information of a black hole is proportional to its boundary?
Intuitively, one of two things must happen to information that enters a black hole: ...
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Entropy as extractable useful work vs. statistical entropy
Statistical (Boltzmann) entropy of a (thermodynamic) system is defined as
(The logarithm of) the amount of microstates corresponding to the (thermodynamic) macrostate of the system.
So, in way of ...
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Entropy in a chess game [closed]
For entropy to be correct, i mean, that increases over time, in a chess game, there should be more options as game time goes on. But it's the opposite. Why?
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Accounting for computation time in Counterfactual Computers
After researching some stuff about Turing Machines and Automaton Theory I stumbled upon the concept of "counterfactual computers". Having little experience with quantum physics (and usually ...
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Is it possible for the universe to return to the exact current state if information cannot be lost?
My understanding is that, if information in the universe cannot be lost, it will always be possible (in principle) to tell which prior state of the universe has led to the current state. Is this true ...
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Does a random number generator have real entropy?
In thermodynamics, entropy is defined for gases. Of course, my laptop is not a gas. However, it contains a random number generator and I have seen the word ‘entropy’ being used in this context. Is ...
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Is there a universal conservation of information theory?
Specifically, is there a working theory from a perspective that relates cosmic expansion (recession?), the increasing total potential information density of the Universe (based on the simplified idea ...
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Relation between entropy and information [duplicate]
Lack of information is entropy.
But entropy has dimension and information has no dimension. Then how do we relate these two terms..
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Maximum information transmission rate using an electrical wire
Suppose that we're trying to transmit information at a distance $ L $ using an electrical wire made out of a material with known properties. The circuit setup is as follows: there's a wire that's ...
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