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Gerard ’t Hooft, Theoretical Physics as a Challenge

Gerard ’t Hooft, Theoretical Physics as a Challenge
by Gerard 't Hooft Note: This web site will soon be removed from its present address. An updated and renewed version is available at: This is a web site for young students - and anyone else - who are (like me) thrilled by the challenges posed by real science, and who are - like me - determined to use their brains to discover new things about the physical world that we are living in. It so often happens that I receive mail - well-intended but totally useless - by amateur physicists who believe to have solved the world. It should be possible, these days, to collect all knowledge you need from the internet. I can tell you of my own experiences. Theoretical Physics is like a sky scraper. Note that this site NOT meant to be very pedagogical. Languages:English is a prerequisite. French, German, Spanish and Italian may be useful too, but they are not at all necessary. Return to List Now, first things first : Algebraic equations. Related:  Quantum Mechanics

[nanocursus] De EPR-Paradox, het experiment van Bell en waarom het heelal waarschijnlijk niet gedetermineerd is - Cursussen en FAQ's - Wetenschapsforum De EPR-Paradox, het experiment van Bell en waarom het heelal waarschijnlijk niet gedetermineerd isDe EPR-paradoxDe EPR-paradox komt eigenlijk neer op de vraag of er toeval is in het heelal. Volgens de kwantumtheorie wel, daar gebeuren dingen die enkel van het toeval afhangen. 3 wetenschappers waren het daar echter niet mee eens: Einstein, Podolsky en Rosen. Daarom bedachten ze een paradox die aantoonde dat het heelal echt niet van het toeval kon afhangen. "Als het heelal echt toevallig is", zo zeiden ze, "dan komen wij de EPR-paradox uit. Om de EPR-paradox helemaal uit te leggen is echter moeilijk, ik snap het zelf niet helemaal, denk ik. Het experiment van Bell Het experiment kan op 2 manieren uitgelegd worden:1) Je kunt het volledige experiment begrijpen zonder iets van kwantummechanica af te weten. Verborgen inhoud uitleg met kwantumtheorie dicht laten.OF2) Je kunt meteen erbij lezen waarom de kwantumtheorie de metingen wel verklaart! open klikken. Stelling 1) De wet van Malus zegt dat

A Double Slit Quantum Eraser Experiment A Double-Slit Quantum Eraser Experiment This web-page was created as an assignment for PHY 566, taught by Prof. Luis Orozco at Stony Brook University in the fall semester of 2002. The following describes work done by S. This experiment uses the phenomena of interference, produced by light incident on a double slit, to investigate the quantum mechanical principle of complementarity between the wave and particle characteristics of light. A Peculiarity about Quantum Mechanics Interference Any wave in nature is capable of producing interference. Interference and photons Quantum mechanics governs all phenomena on the atomic scale. Mathematically the quantum description is not any different from the classical wave interference description. A single photon cannot of course make a whole interference pattern on a screen by itself. Formation of the interference pattern. Which Way? It is difficult at this point to not be tempted to ask, which way does the photon really go? Experimental Investigation

quantum mechanics - Interference and which-path information So, to be clear, my understanding of your setup is that you are doing SPDC in a noncollinear geometry, so you get photons entangled in transverse momentum, and you basically want to get the momentum of one photon from the other, by studying the wall. To get interference, the momentum change must be indistinguishable in principle, not just practically. How could this happen? Well, the wall itself is also a quantum object, so if its two possible momenta from the photon are both within the uncertainty of its total momentum, it is not possible to distinguish the two cases. In the case of this setup, really what you are suggesting is a quantum eraser experiment, in a way. To compare this with a typical quantum eraser experiment, look here for example. (edit: this analysis is incorrect; see comments) edit2: from the comments: There is no inconsistency between what I am saying and what they are, but I have to be very careful to be clear about what I mean by 'decoherence,' and by 'environment.'

Bell's Theorem with Easy Math Bell's Theorem with Easy Math By David R. Schneider IntroductionAuthor's note: This article is based on Bell's Theorem (2). I have reformulated the presentation to make it a little easier to follow if your math skills are a little rusty. Bell's Theorem is the most famous legacy of the late great J.S. No physical theory of local Hidden Variables can ever reproduce all of the predictions of Quantum Mechanics. If you are unfamiliar with the math of Bell's Theorem, or have previously found it difficult to comprehend... then perhaps this paper can help. History In 1935, Albert Einstein collaborated with Boris Podolsky and Nathan Rosen to publish a paper which is now simply referred to by the initials of its three authors: EPR (1). EPR provided a proof that says in essence: either there are Hidden Variables, OR particle attributes (such as position, velocity, energy, polarization, etc.) are not real and defined until they are observed. Or not! Proof a. b. c. We're done! d.

Entangled In the Past: “Experimental delayed-choice entanglement swapping” – Uncertain Principles Enough slagging of beloved popularizers– how about some hard-core physics. The second of three extremely cool papers published last week is this Nature Physics paper from the Zeilinger group in Vienna, producers of many awesome papers about quantum mechanics. Ordinarily, this would be a hard paper to write up, becase Nature Physics are utter bastards, but happily, it’s freely available on the arxiv, and all comments and figures are based on that version. You’re just obsessed with Zeilinger, aren’t you? Oh, OK, that sounds– Wait, what? The vertical axis represents time, moving into the future as you go up. Since these photons went into much longer fibers (104m vs. 7m), though, the entangling measurement is made after the two photons whose states are being entangled have had their polarizations measured– about 520 ns after they were produced. OK, that’s just weird. Wait, how does that work? That’s… Why would you do that? So when they do this, what do they see? OK. Yes, that’s the problem.

Local hidden variable theory The term "hidden variable theory" is used in the interpretation of quantum mechanics. It refers to all types of the theory that attempt to account for the probabilistic features of quantum mechanics by the mechanism of underlying inaccessible variables. A local hidden variable theory has the added requirement of being consistent with local realism, requiring that distant events be independent, ruling out instantaneous (i.e. faster-than-light) interactions between separate events. The mathematical implications of a local hidden variable theory in regard to the phenomenon of quantum entanglement were explored by physicist John S Bell. The theory of quantum entanglement predicts that separated particles can briefly share common properties and respond to certain types of measurement as if they were a single particle. Local hidden variables and the Bell tests[edit] where is the probability of detection of particle with hidden variable by detector , set in direction , and similarly , for particle .

HyperPhysics Concepts About HyperPhysics Rationale for Development HyperPhysics is an exploration environment for concepts in physics which employs concept maps and other linking strategies to facilitate smooth navigation. For the most part, it is laid out in small segments or "cards", true to its original development in HyperCard. The entire environment is interconnected with thousands of links, reminiscent of a neural network. Part of the intent for this exploration environment is to provide many opportunities for numerical exploration in the form of active formuli and standard problems implemented in Javascript. New content for HyperPhysics will be posted as it is developed. A resource that was initiated as a resource for local high school physics teachers whom I had taught has expanded into an intensively used website worldwide. CD or DVD versions have been sent to 86 countries to date, and translations into German, Italian, Chinese, and Español have been licensed and are underway. HyperPhysics (©C.R.

EPR, Bell & Aspect: The Original References EPR, Bell & Aspect: The Original References (in PDF Format) By David R. Schneider NOTE: Please feel free to link to this page or the PDF files. This page contains references to the key original papers on the longstanding debate about the completeness of Quantum Mechanics (QM), particularly Bell's Theorem. What do they say? Does this settle the matter? Seeing the originals of these three papers is - to me - very exciting as they expose the power of human ideas. 1. The first was the paper written in 1935 by Albert Einstein and two others, Rosen and Podolsky. As per usual, Einstein cut to the heart of the matter. • For the complete EPR paper in PDF (Acrobat Reader) format:EPR.pdf (4 pages, 300k) 2. The second was the paper written in 1964 by J.S. • For the complete Bell paper in PDF (Acrobat Reader) format:Bell_Compact.pdf (6 pages, 500k) Or download a larger file, but containing better resolution: Bell.pdf (6 pages, 5 megabytes) 3. Other helpful links on the EPR Paradox: