1. Quantum Alchemy

    I How does Classical Physics explain Quantum Entanglement?

    As a Computer Programmer, it's hard to wrap my head around Quantum Entanglement and non locality being explained in the context of Classical Physics. In other words, if the universe at it's core is physical where does Quantum Entanglement fit within a physical picture of reality? There's been...
  2. jackmiller2003

    I Time Delay Information Transfer with Entangled Particles

    Hello, my name is Jack and I'm a year 11 student in Australia. After listening to, and reading some information regarding quantum entanglement, I'm still a little unsure about the solution to a thought experiment: Let's say that I create a situation in which multiple pairs of particles are...
  3. S

    I "It from Bit" and the multiverse?

    Did physicist John Archibald Wheeler propose the existence of multiple universes through his "It from Bit" or "Participatory Universe Principle" or "Law without Law and Pregeometry"? Is the multiverse related to Wheeler's ideas? I've been told that It can produce multiple universes, obviously...
  4. H

    A Irreversible processes. Heat equation, diffusion equation

    Both the heat equation and the diffusion equation describe processes which are irreversible, because the equations have an odd time derivative. But how can these equations describe the real world when we know that all processes in nature are reversible, information is always conserved? But these...
  5. entropy1

    B Is the Universe information?

    Is the problem with interpretations of quantum mechanics that one can describe the universe consisting of "stuff" that exists ontologically in different but conflicting ways, so that the universe can really only be described informationally instead of ontologically? That is: does the universe...
  6. nomadreid

    I Uncertainty: balance of two aspects?

    There are two aspects of uncertainty (a) how far different from the situation where all possibilities are of equal probability (b) how spread out the values are. In discussions about (Shannon) entropy and information, the first aspect is emphasized, whereas in discussions about the standard...
  7. S

    A Could information in a boundary be modified once encoded?

    Could information in a boundary be modified once encoded in holographic principle? There are models of universes where holographic principle has a different correspondence (there is absolutely no reason to assume that this would hold true for all possible universes. You could have a universe...
  8. H

    A Information and successive measurments

    Suppose you measure the spin of an electron along some axis, we get the result +1 with probability 0.5 and -1 with probability 0.5. The average information we receive is 1 bit of information. Now if we rotate our apparatus 90 degrees and make a new measurement, we will as before get the value +1...
  9. anorlunda

    Insights How to Better Define Information in Physics - Comments

    Greg Bernhardt submitted a new PF Insights post How to Better Define Information in Physics Continue reading the Original PF Insights Post.
  10. Danny Boy

    A Defining Krauss operators with normal distribution

    I am interested in defining Krauss operators which allow you to define quantum measurements peaked at some basis state. To this end I am considering the Normal Distribution. Consider a finite set of basis states ##\{ |x \rangle\}_x## and a set of quantum measurement operators of the form $$A_C =...
  11. O

    I Nearly Perfect Efficiency - 2nd Law of Thermodynamics

    Recently read this article on Physorg: My questions are: 1. If "converting" information into energy requires a system (the demon I suppose) having a photodiode, processor, laser (light trap) all expending energy in order to cause the conversion...
  12. Danny Boy

    A Von Neumann Entropy of a joint state

    Definition 1 The von Neumann entropy of a density matrix is given by $$S(\rho) := - Tr[\rho ln \rho] = H[\lambda (\rho)] $$ where ##H[\lambda (\rho)]## is the Shannon entropy of the set of probabilities ##\lambda (\rho)## (which are eigenvalues of the density operator ##\rho##). Definition 2 If...
  13. entropy1

    B Information transfer using entanglement?

    I split this off a separate thread in response to a post of @Nugatory . The matter was about the (im)possibility of transfering information using entanglement. This is a basic thread, so I keep it simple: There are two particles/detectors, A and B. The particles are in the singlet state. My...
  14. Nim

    I Why Is There No SI Unit For Information?

    Why is the quantity "information" missing from the SI system? Also, if they did add it, do you think it would be added as a base unit or dimensionless derived unit?
  15. J

    Cosmology Book on Black Holes, Strings, AdS/CFT

    Hello, I would really like a book like Susskind's "An Introduction To Black Holes, Information And The String Theory Revolution: The Holographic Universe" but not so condensed. If you have anything to suggest please do so. Also, if you know of any book that contains any part of the above book in...
  16. AlexSH

    I Conservation of Information and indeterminism?

    I just recently learned about Leonard Susskind's work on conservation of information. From what I've read and from his lectures, conservation of information and the holographic principle are based on the reversibility of physical laws. Reversibility in turn implies determinism, so if...
  17. K

    A How to calculate the Wigner function for an entangled state

    I'm trying to calculate a Wigner Function of an entangled state, and I'm not quite sure how to proceed. I have created this state by sending in vacuum and a squeezed state into a 50/50 BS, where the output state has a density operator: $$\rho_{34}=S_{3}S_{4}S_{34}|00\rangle_{34}\langle...
  18. Radu Mitroi

    B What percentage of the universe do we know

    Hello. First of all, I must say that I'm new to this forum, so I apologize if I'm posting in the wrong section. I'm a 17 year old with not that much knowledge about physics, so if what I'm talking about makes no sense or is completely stupid, just let me know. A couple of days ago I asked...
  19. entropy1

    B Measurement and the creation/loss of information

    If we measure, say, the polarisation of a photon, the polarisation state of the photon collapses along the eigenvector of the observable corresponding to the measurement. This may seem as a loss of information of the original polarisation (for it is now collapsed into another value). However...
  20. E

    A Information contained in minimum value of truncated distribution

    Suppose that a given population is endowed with a pair of characteristics T and K. Let's think of these characteristics as random variables (T,K)∼BiNormal((μT,μS),(σT,σS),ρ) I observe the realisations of T for a sample consisting of those individuals with K<a, where the selection threshold a...
  21. V

    Help understanding Shannon entropy

    Hi I'm having some trouble understanding Shannon entropy and its relation to "computer" bits (zeros and ones). Shannon entropy of a random variable is (assume b=2 so that we work in bits) and everywhere I've read says it is "the number of bits on the average required to describe the random...
  22. J

    I Is there anti-Information?

    Is there any theory that says anti-information exists? If there is anti-matter, would that matter carry information to annihilate the regular matter's information saying its a certain type of matter and turn it into energy? Could anti-matter just be regular matter with anti-information.
  23. Abel Cavaşi

    The informational paradox of rectilinear motion

    If the torsion of the straight line is undefined what happens with the information about the torsion? It is known (, that the information conserved in a system can be nor created...
  24. AngularMomentum

    Presentation about Roger Bacon (rainbows)

    I need to give a presentation about roger bacon (the guy who said that rainbows form at a 42 degree angle). It's hard to find information about his study of rainbows so if anyone knows something about it I'll be grateful.
  25. G

    How is information lost if nothing passes the event horizon?

    Hi. From an outside observer's view, any object approaching the event horizon of a black hole appears to slow down and never quite pass through the horizon. So information about those objects can always be retrieved (if you correct for the redshift). So what actually is the information paradox...
  26. BillTre

    Hello Forum

    I'm a biologist interested in physics. Biology is undergoing several revolutionary changes, but physics is interesting too! I am interested in the physical aspects of information processing in biological entities, things like: genetic control systems, information transmission through...
  27. G

    Relationship between energy, information and dark energy

    Hi. I have no significant pure physics or math education or work experience (retired corporate analyst) but I was wondering what experts here might think about the relations between energy, dark energy and information. My understanding is that dark energy is the expansion of space, with space...
  28. T

    EPR paradox and time of collapse

    According to the EPR-paradox, if we have a pair of two entangled spin-1/2 fermions A and B and measure z-component of A, B collapses immediately as well(i'm using these letters for both particles and their observers). The 'canonical' solution is then to state that it is not possible to transfer...
  29. G

    Problems solvable by thermodynamics of information

    Hello, I need to work on the thermodynamics theory of information, but I can't find real applications aside from the resolution of the maxwell's demon and the szilard engine. I would need more applications... Any idea?
  30. Z

    Information Theory (very basic)

    I am reading a book called 'quantum processes systems and information' and in the beggining a basic idea of information is set out in the following way. If information is coded in 'bits', each of which have two possible states, then the number of possible different messages/'values' that can be...