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eilishbillie987
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06 Apr 2019, 7:18 pm

eilishbillie987
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Joined: 1 Apr 2019
Age: 31
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06 Apr 2019, 7:20 pm

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Fnord
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06 Apr 2019, 9:02 pm

MIT Article: No, scientists didn’t just “reverse time” with a quantum computer

Amazing headlines about time machines are a long way off the mark, sadly.

Quote:
So if they didn’t invent time travel, what did these scientists actually do? Think about pressing rewind on a video. That "reverses the flow of time," in a way. If you’ve never seen it before, it’s kind of neat. It might let you see things -- like steam flowing back into a tea kettle or Humpty Dumpty spontaneously assembling from a jumble of broken pieces -- that appear to "reverse the arrow of time." The paper in question describes a quantum-computing version of such a video running in reverse.


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eilishbillie987
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Joined: 1 Apr 2019
Age: 31
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06 Apr 2019, 11:12 pm

"In other words, take two tokens of a nomologically reversible process type, say A and B, and let B be the actively time reversed process of A, then this interpretation claims that A and B causally develop in the same direction of time. So, according to this view, neither incoming, contracting electromagnetic waves nor the decrease of entropy would count as examples of backward causation as long as such processes involve ordinary types of matter, i.e., matter that possesses positive mass and/or energy pointing, in relation to our normal time sense, towards the future. The notion of backward causation should instead be applied to matter of a different type, particles that appear to have, according to usual conventions, negative mass and/or energy pointing, in relation to our normal time sense, towards the future but positive mass and/or energy pointing towards the past. Such advanced matter, if it exists, should be distinguished from both ordinary retarded matter as well as tachyons by always being described with respect to our time sense in terms of negative mass and energy stretching forward in time. A consequence is that a world in which advanced matter exists together with retarded matter, and where advanced matter is able to interact directly with the same amount of retarded matter, both would, in case they actually did interact, annihilate without leaving any trace of energy. "


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