Re: Retiring the universe
On 16 Jan 2014, at 17:30, Gabriel Bodeen wrote: Amanda Gefter wrote: More importantly, it could offer us a better conceptual grasp of quantum mechanics. Quantum mechanics defies understanding because it allows things to hover in superpositions of mutually exclusive states, like when a photon goes through this slit and that slit, or when a cat is simultaneously dead and alive. It balks at our Boolean logic, it laughs at the law of the excluded middle. Worse, when we actually observe something, the superposition vanishes and a single reality miraculously unfurls. Well, a common error: quantum logic (and reality) does obey to the excluded middle. That is why you can havean intuitionist quantum logic (like the comp QL related to Bp Dt p, for those who know a bit of AUDA). Then the author here (Amanda Gefter) seems to believe in the collapse, or in one reality. But I tend to think that the collapse idea is a retired idea since the beginning. It is like the danger of cannabis: a rumor spread by some authorities, but which has never made much sense. Doubting the universe? It is like God, it is an idea to much fuzzy to be doubted. But of course, comp encourages (to say the least) a different approach to it, and to physics. So the text of Amanda is not so bad with that (comp) respect. Bruno http://iridia.ulb.ac.be/~marchal/ -- You received this message because you are subscribed to the Google Groups Everything List group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/groups/opt_out.
Re: Retiring the universe
On 16 Jan 2014, at 19:40, LizR wrote: I must admit I thought the MWI had already retired the universe. Hmm... Physicists replace it with a multiverse, which is a new form of a Universe. But with comp even the multiverse might need to retire, at least as a fundamental primitive reality. It is still an inside approximation of something *very* much bigger, itself being just an aspect of something still *very* much bigger (and more theological than physical, even if arithmetical). Bruno -- You received this message because you are subscribed to the Google Groups Everything List group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/groups/opt_out. http://iridia.ulb.ac.be/~marchal/ -- You received this message because you are subscribed to the Google Groups Everything List group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/groups/opt_out.
Retiring the universe
If any of you haven't seen it, you will likely be quite interesting the The Edge's list of responses to this year's question, What scientific idea is ready for retirement? Some of the answers are fascinating, some are absurd, and some are confusing. Take a look! http://www.edge.org/responses/what-scientific-idea-is-ready-for-retirement My favorite comes from Amanda Gefter. I'll reproduce it below. (Hopefully that counts as fair use.) -- Amanda Gefter Consultant, New Scientist; Founding Editor, CultureLab *The* Universe Physics has a time-honored tradition of laughing in the face of our most basic intuitions. Einstein's relativity forced us to retire our notions of absolute space and time, while quantum mechanics forced us to retire our notions of pretty much everything else. Still, one stubborn idea has stood steadfast through it all: the universe. Sure, our picture of the universe has evolved over the years—its history dynamic, its origin inflating, its expansion accelerating. It has even been downgraded to just one in a multiverse of infinite universes forever divided by event horizons. But still we've clung to the belief that here, as residents in the Milky Way, we all live in a single spacetime, our shared corner of the cosmos—our universe. In recent years, however, the concept of a single, shared spacetime has sent physics spiraling into paradox. The first sign that something was amiss came from Stephen Hawking's landmark work in the 1970s showing that black holes radiate and evaporate, disappearing from the universe and purportedly taking some quantum information with them. Quantum mechanics, however, is predicated upon the principle that information can never be lost. Here was the conundrum. Once information falls into a black hole, it can't climb back out without traveling faster than light and violating relativity. Therefore, the only way to save it is to show that it never fell into the black hole in the first place. From the point of view of an accelerated observer who remains outside the black hole, that's not hard to do. Thanks to relativistic effects, from his vantage point, the information stretches and slows as it approaches the black hole, then burns to scrambled ash in the heat of the Hawking radiation before it ever crosses the horizon. It's a different story, however, for the inertial, infalling observer, who plunges into the black hole, passing through the horizon without noticing any weird relativistic effects or Hawking radiation, courtesy of Einstein's equivalence principle. For him, information better fall into the black hole, or relativity is in trouble. In other words, in order to uphold all the laws of physics, one copy of the bit of information has to remain outside the black hole while its clone falls inside. Oh, and one last thing—quantum mechanics forbids cloning. Leonard Susskind eventually solved the information paradox by insisting that we restrict our description of the world to either the region of spacetime outside the black hole's horizon or to the interior of the black hole. Either one is consistent—it's only when you talk about both that you violate the laws of physics. This horizon complementarity, as it became known, tells us that the inside and outside of the black hole are not part and parcel of a single universe. They are *two* universes, but not in the same breath. Horizon complementarity kept paradox at bay until last year, when the physics community was shaken up by a new conundrum more harrowing still— the so-called firewall paradox. Here, our two observers find themselves with contradictory quantum descriptions of a single bit of information, but now the contradiction occurs while both observers are still outside the horizon, before the inertial observer falls in. That is, it occurs while they're still supposedly in the same universe. Physicists are beginning to think that the best solution to the firewall paradox may be to adopt strong complementarity—that is, to restrict our descriptions not merely to spacetime regions separated by horizons, but to the reference frames of individual observers, wherever they are. As if each observer has his or her own universe*.* Ordinary horizon complementarity had already undermined the possibility of a multiverse. If you violate physics by describing two regions separated by a horizon, imagine what happens when you describe *infinite* regions separated by *infinite *horizons! Now, strong complementarity is undermining the possibility of a single, shared universe. On glance, you'd think it would create its own kind of multiverse, but it doesn't. Yes, there are multiple observers, and yes, any observer's universe is as good as any other. But if you want to stay on the right side of the laws of physics, you can only talk about one at a time. Which means, really, that only one *exists* at a time. It's cosmic solipsism.
Re: Retiring the universe
I must admit I thought the MWI had already retired the universe. -- You received this message because you are subscribed to the Google Groups Everything List group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/groups/opt_out.
Re: Retiring the universe
On 1/16/2014 8:30 AM, Gabriel Bodeen wrote: Leonard Susskind eventually solved the information paradox by insisting that we restrict our description of the world to either the region of spacetime outside the black hole's horizon or to the interior of the black hole. Either one is consistent—it's only when you talk about both that you violate the laws of physics. This horizon complementarity, as it became known, tells us that the inside and outside of the black hole are not part and parcel of a single universe. They are /two/ universes, but not in the same breath. First, Susskind's horizon complementarity is far from accepted as a solution and has various problems. Second, the inside of a black hole is not separate from the outside. Stuff from the outside goes in all the time and the problem Susskind is trying to solve is to explain how it can also come out via Hawking radiation. Brent -- You received this message because you are subscribed to the Google Groups Everything List group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/groups/opt_out.
