{"page":"\u003clink rel=\"stylesheet\" href=\"https://lessonplanet.com/assets/packs/css/resources-c03aa079.css\" /\u003e\n\u003clink rel=\"stylesheet\" href=\"https://lessonplanet.com/assets/packs/css/lp_boclips_stylesheets-517835be.css\" media=\"all\" /\u003e\n\u003cdiv data-title='Copenhagen vs. Many Worlds: Two Views of Quantum Mechanics Explained' data-url='/boclips/videos/689565b4f85aec7d1d07d045' data-video-url='/boclips/videos/689565b4f85aec7d1d07d045' id='bo_player_modal'\u003e\n\u003cdiv class='boclips-resource-page modal-dialog panel-container'\u003e\n\u003cdiv class='react-notifications-root'\u003e\u003c/div\u003e\n\u003cdiv class='rp-header'\u003e\n\u003cdiv class='rp-type'\u003e\n\u003ci aria-hidden='true' class='fai fa-regular fa-circle-play'\u003e\u003c/i\u003e\nVideo\n\u003c/div\u003e\n\u003ch1 class='rp-title' id='video-title'\u003e\nCopenhagen vs. Many Worlds: Two Views of Quantum Mechanics Explained\n\u003c/h1\u003e\n\u003cdiv class='rp-actions'\u003e\n\u003cdiv class='mr-1'\u003e\n\u003ca class=\"btn btn-success\" data-posthog-event=\"Signup: LP Signup Activity\" data-posthog-location=\"body_link_boclips\" data-remote=\"true\" href=\"/subscription/new\"\u003e\u003cspan\u003e\u003cspan\u003eGet Free Access\u003c/span\u003e\u003cspan class=\"\"\u003e for 10 Days\u003c/span\u003e\u003cspan\u003e!\u003c/span\u003e\u003c/span\u003e\u003c/a\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv class='rp-body'\u003e\n\u003cdiv class='rp-info'\u003e\n\u003cdiv aria-label='Hide resource details' class='rp-hide-info' role='button' tabindex='0'\u003e\u0026times;\u003c/div\u003e\n\u003ci aria-label='Expand resource details' class='rp-expand-info fai fa-solid fa-up-right-and-down-left-from-center' role='button' tabindex='0'\u003e\u003c/i\u003e\n\u003ci aria-label='Compress resource details' class='rp-compress-info fai fa-solid fa-down-left-and-up-right-to-center' role='button' tabindex='0'\u003e\u003c/i\u003e\n\u003cdiv class='rp-rating'\u003e\n\u003cspan class='resource-pool'\u003e\n\u003cspan class='pool-label'\u003ePublisher:\u003c/span\u003e\n\u003cspan class='pool-name'\u003e\n\u003cspan class='text'\u003e\u003ca data-publisher-id=\"30356011\" href=\"/search?publisher_ids%5B%5D=30356011\"\u003eCurated Video\u003c/a\u003e\u003c/span\u003e\n\u003c/span\u003e\n\u003c/span\u003e\n\u003c/div\u003e\n\u003cdiv class='rp-description'\u003e\n\u003cspan class='short-description'\u003ePhysicists know how to use the equations of quantum mechanics to predict things, but don't really understand what is fundamentally going on. The primary challenge is that according to the equations of QM, all particles exist in a state...\u003c/span\u003e\n\u003cspan class='full-description hide'\u003ePhysicists know how to use the equations of quantum mechanics to predict things, but don't really understand what is fundamentally going on. \u003cbr/\u003e\u003cbr/\u003eThe primary challenge is that according to the equations of QM, all particles exist in a state of superposition. In fact, before it is measured, the particle is said to be in many states at once. \u003cbr/\u003e\u003cbr/\u003eHow does one explain the transition from the behavior of objects at quantum scales to their classical behavior upon measurement? The various interpretations of quantum mechanics are attempts to explain this transition. \u003cbr/\u003e\u003cbr/\u003eThe standard is the Copenhagen interpretation because if was devised in Copenhagen, Denmark by Niels Bohr and Werner Heisenberg. This is taught to most students in college. But even a majority of physicists do not agree that this is the correct interpretation. There is no single interpretation that has a consensus agreement. \u003cbr/\u003e\u003cbr/\u003eMost interpretations focus on the Schrodinger equation and the wavefunction to explain quantum behavior. This equation was developed by Irish-Austrian physicist Erwin Schrodinger in 1926. It contains a wave function, represented by the Greek letter psi. \u003cbr/\u003e\u003cbr/\u003eGerman physicist Max Born formulated the interpretation of psi, which is that the square of the norm of  psi is the probability of finding a particle in any one particular state if we were to measure it. \u003cbr/\u003e\u003cbr/\u003eThe concept of measurement was introduced to explain what we actually see when we make an observation. \u003cbr/\u003e\u003cbr/\u003eThe fact is that even if it were possible for us to directly observe quantum particles, we would never see them being in superposition, we would only observe them being in one state or another. \u003cbr/\u003e\u003cbr/\u003eLet’s look at this in terms of the famous Schrodinger’s cat experiment. We have a box with 4 things in it, cat, a radioactive source, a detector with hammer attached and a vial of poison gas.\u003cbr/\u003e\u003cbr/\u003eIf the detector detects radiation, the hammer will smash the vial of gas and the cat will die. If no detection, the cat will stay alive. \u003cbr/\u003e\u003cbr/\u003eIf we look at this from the quantum mechanical point of view, there are two possibilities for the wave function of this system - cat dead or cat alive. Both are in superposition.\u003cbr/\u003e\u003cbr/\u003eIn the Copenhagen interpretation, as soon as you open the box to make an observation, one of the probabilities comes true, and the other probability disappears. The wave function \"collapses\" as the result of a measurement by an observer or apparatus external to the quantum system. A measurement is an interaction of the quantum system with a classical system, which can be the observer.  \u003cbr/\u003e\u003cbr/\u003eThe problem with this interpretation it doesn’t explain how this collapse happens - what is the mechanism? This is the measurement problem. Bohr might have said it just fits the data, so we know collapse occurs. \u003cbr/\u003e\u003cbr/\u003eAn alternative, the many worlds interpretation of the same event would be that no collapse occurs, but that two different worlds with two different results exist simultaneously.\u003cbr/\u003e\u003cbr/\u003eThis interpretation was formulated by Hugh Everett in 1957 as a graduate student at Princeton University. Some say this is the simplest interpretation of quantum mechanics because it introduces no other assumptions, other than the Schrodinger equation.\u003cbr/\u003e\u003cbr/\u003eThe distinction that the many worlds interpretation makes vs. the Copenhagen interpretation is that it says, the observer is also a quantum system, and is entangled with the cat. Both the cat and observer are part of the same wave function. So the reality where the cat is alive, is but one world. But there is another reality the cat is dead. Both worlds exist. You just happen to find yourself in one of them.\u003cbr/\u003e \u003cbr/\u003eWhy do we find ourselves in only one branch? Everettians say it is due to decoherence. \u003cbr/\u003e\u003cbr/\u003eQuantum decoherence is the physical process that is used to describe how quantum states transition to the one state that we experience. The key realization is that in reality, you have more than just you and the cat entangled. Both will also be entangled with their environment because THAT is also a quantum system. The environment inside the box for a cat that is alive will be different than the environment for a cat that is dead. \u003cbr/\u003e\u003cbr/\u003eBecause the entanglement with the environment now enters the picture, the coherent superpositon between you and the cat is broken. The Schrodinger equation says that the two parts of the wave function above are perpendicular to each other, that have no connection to each other. 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