{"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='How Quantum Mechanics Shapes Reality and the Arrow of Time' data-url='/boclips/videos/689566edf5a33cc1b5ec9c56' data-video-url='/boclips/videos/689566edf5a33cc1b5ec9c56' 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\nHow Quantum Mechanics Shapes Reality and the Arrow of Time\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'\u003eHow does the indeterminate world of quantum mechanics, where the future isn’t fixed, become the classical predictable real world we experience? Quantum researchers argue about it even today. It's really all about time, and the boundary...\u003c/span\u003e\n\u003cspan class='full-description hide'\u003eHow does the indeterminate world of quantum mechanics, where the future isn’t fixed, become the classical predictable real world we experience? Quantum researchers argue about it even today. It's really all about time, and the boundary between the past and future. \u003cbr/\u003e\u003cbr/\u003eQuantum mechanics insist that the spin of particle has neither one direction or the other until we look. The very act of looking forces the universe to make a choice. \u003cbr/\u003e\u003cbr/\u003eAll the variables that characterize the properties of an elementary particles, such as its position and momentum, are encoded in a mathematical expression called a wave function. It is just a sum of the states that the particle could be found in. This is called a superposition. \u003cbr/\u003e\u003cbr/\u003eBy itself, the wave function doesn’t have any intuitive meaning. But the square of the wave function gives us the probability of finding that quantum object in any particular place. Prior to measurement, quantum mechanics doesn’t really tell us anything about a particle. We know this is true because particles interfere with each other prior to measurement as in the double slit experiment. \u003cbr/\u003e\u003cbr/\u003eIn our macro world, we never see this superposition. So quantum physicists have to add in this transition from quantum to classical step by hand, as something extra to quantum mechanics, ThisIt is often called the “collapse” of the wave function, and was first introduced by the Hungarian mathematical physicist John von Neumann. \u003cbr/\u003e\u003cbr/\u003eA better description of this is decoherence. This is how it works: The quantum state of a particle becomes mixed up – or entangled – with the states of the atoms in the environment. If the particle is in a superposition, this superposition then spreads to the atoms it interacts with. The come these entangled particles interact with, the farther this entanglement spreads until it spreads all across the universe. This leads to decoherence, because not the original particle becomes unrecognizable. \u003cbr/\u003e\u003cbr/\u003eBut the problem with decoherence is that in theory there is no end tot he entanglement or spreading of this quantumness. So in principle the superposed state of the original particle could be reconstituted if we could keep track of all the entanglement of all the particles. \u003cbr/\u003e\u003cbr/\u003eBut this would be like reversing time. Experiments in “recoherence” has been done however.  This would mean undoing the measurement, and erasing any information we gained about it. \u003cbr/\u003e\u003cbr/\u003eSo here’s the question: Is there ever a point where the measurement process switches from being fully reversible in principle by this sort of recoherence, and becomes irreversible? Is there a point of no return?\u003cbr/\u003e\u003cbr/\u003eQuantum experts don’t agree about this. As long as the process is reversible, it’s still quantum. It’s only when it becomes irreversible that it becomes classical – and it’s only then that we can truly say “what happened” - when reality becomes real.\u003cbr/\u003e\u003cbr/\u003ePhysicist Lee Smolin has suggested that this is in fact what distinguishes the past from the present. The past is classical. The present is quantum. What separates them is whether they are reversible or not, whether they have become known or not. Quantum mechanics may link knowledge, information, and time. \u003cbr/\u003e\u003cbr/\u003eAccording to Smolin, It’s the change from a quantum, indefinite present to a classical, definite past that defines the very arrow of time itself, pointing it always in the forwardin one direction as the quantum present constantly churns out a classical past. \u003cbr/\u003e\u003cbr/\u003eThe past goes away. It is already known. But the future is all possibility. We can never go back – we can’t change the past. In fact, the past no longer really exists at all. “Once something is definite”, says Smolin, “its job is done and it is gone.”\u003cbr/\u003e#decoherence\u003cbr/\u003e#quantummechanics\u003cbr/\u003eBut what happens to all those futures that aren’t selected by the decohering present? Where do those alternative possible futures go? Do they pop up in an alternative universe? 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