tag:blogger.com,1999:blog-5592542.post7257969838282889597..comments2024-03-18T17:28:44.693-07:00Comments on Rondam Ramblings: Parallel universes and the arrow of timeRonhttp://www.blogger.com/profile/11752242624438232184noreply@blogger.comBlogger25125tag:blogger.com,1999:blog-5592542.post-76415351462380626312018-04-21T11:31:07.455-07:002018-04-21T11:31:07.455-07:00That would have been technically correct, but I do...<i>That would have been technically correct, but I don't think it would have made the underlying issues any clearer.</i><br /><br />It would have made a big difference: in all of the cases where the traveler's worldline is timelike (interval getting smaller and smaller, but not zero), you can't even make the argument that the "origin" and "destination" are Peter Donishttps://www.blogger.com/profile/09122769947782402203noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-40920183676088172952018-04-21T10:01:49.013-07:002018-04-21T10:01:49.013-07:00> This is not correct. The correct statement is...> This is not correct. The correct statement is that there is no such thing as a "reference frame" for a "traveler" moving at the speed of light<br /><br />Cut me a little slack, will you? I'm writing for a (mostly) lay audience. I could have said that the apparent distance travelled and the apparent time elapsed in the traveller's reference frame both approach Ronhttps://www.blogger.com/profile/11752242624438232184noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-82624189781620469882018-04-20T23:18:47.276-07:002018-04-20T23:18:47.276-07:00I'm coming to this article late, via a link fr...I'm coming to this article late, via a link from a discussion on Hacker News. I wanted to comment on some of the physics discussed in the article.<br /><br /><i>A trip from earth to pluto at the speed of light is indistinguishable (to the traveller) from a trip from pluto to earth at the speed of light. Both consist simply of being at earth and pluto (and everywhere in between) at the same Peter Donishttps://www.blogger.com/profile/09122769947782402203noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-2943741232873947992014-10-21T10:03:33.725-07:002014-10-21T10:03:33.725-07:00> You can't always retrodict a classical tr...> You can't always retrodict a classical trajectory for <i>quantum particles</i>. But that is hardly surprising, since quantum particles don't <i>have</i> trajectories because they aren't classical entities.<br /><br />What makes the difference between quantum particles and classical particles, other than that the latter are 'observed' [with sufficient frequency]?<br /><br Lukehttps://www.blogger.com/profile/18395549142176242491noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-41668046152498102792014-10-21T09:57:33.760-07:002014-10-21T09:57:33.760-07:00> you can't always retrodict a classical tr...> you can't always retrodict a classical trajectory<br /><br />You can't always retrodict a classical trajectory <i>for quantum particles</i>. But that is hardly surprising, since quantum particles don't <i>have</i> trajectories because they aren't classical entities.<br />Ronhttps://www.blogger.com/profile/11752242624438232184noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-42610463370368385432014-10-21T01:10:41.813-07:002014-10-21T01:10:41.813-07:00> Yes. That is what is meant by "classical...> Yes. That is what is meant by "classical correlation."<br /><br />According to <a href="http://physics.stackexchange.com/questions/4040/weak-measurement-and-hardys-paradox/4043#4043" rel="nofollow">Luboš Motl on "Weak measurement and Hardy's paradox"</a>, you can't always retrodict a classical trajectory. I wonder if that messes with anything... (Woot for QM Lukehttps://www.blogger.com/profile/18395549142176242491noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-19232281044986510492014-10-20T20:40:55.469-07:002014-10-20T20:40:55.469-07:00> must there be only one possible past for any ...> must there be only one possible past for any given moment?<br /><br />Yes. That is what is meant by "classical correlation."<br /><br />> could not this current configuration of the universe have been arrived at via multiple pasts?<br /><br />No.<br /><br />> Perhaps your reverse-o-matic ray could send you back on one of many pasts<br /><br />Not by reversing entanglements.Ronhttps://www.blogger.com/profile/11752242624438232184noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-13589318103249908562014-10-20T19:53:07.029-07:002014-10-20T19:53:07.029-07:00Hmmm...random question that occurs to me while thi...Hmmm...random question that occurs to me while thinking of the flow of time and the universe and the symmetry of things: must there be only one possible past for any given moment?<br /><br />Just as the current instant leads to one of multiple and exponentially increasing numbers of possible futures, could not this current configuration of the universe have been arrived at via multiple pasts?<br cobyhttps://www.blogger.com/profile/04042136876169040477noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-529735787445735032014-10-15T17:16:57.645-07:002014-10-15T17:16:57.645-07:00We're safe. From the abstract of http://arxiv....We're safe. From the abstract of http://arxiv.org/abs/1206.6224:<br /><br />"Causal loops are avoided by this anticipation remaining encrypted until the final outcomes enable to decipher it."<br /><br /><irony>Whew.</irony><br /><br />And since you asked:<br /><br />> As to what constitutes 'ethical'—well that depends on whether you think there is a Platonic Ronhttps://www.blogger.com/profile/11752242624438232184noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-81553257532277565472014-10-15T17:02:29.309-07:002014-10-15T17:02:29.309-07:00Homer Simpson on Time Travel Risks<a href="https://www.youtube.com/watch?v=v1IKioDLEh8" rel="nofollow">Homer Simpson on Time Travel Risks</a>Publiushttps://www.blogger.com/profile/00647613579979908182noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-46237531345801543812014-10-15T17:01:26.174-07:002014-10-15T17:01:26.174-07:00> And today there is no law against time travel...> And today there is no law against time travel.<br /><br />Fine, but there remains my point that we are far from being able to get <i>reliable messages</i> via the method pioneered by Aharonov, if indeed his method works. And so, your original scenario that you claim would not be 'cheating' <i>perhaps cannot yet happen</i>. The closer it gets to realistically happening, I claim the Lukehttps://www.blogger.com/profile/18395549142176242491noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-33068246721172276142014-10-15T16:51:46.344-07:002014-10-15T16:51:46.344-07:00> Well, your original statement contained '...> Well, your original statement contained 'would':<br /><br />English is a fluid language and the meanings of words depend on their context. My statement:<br /><br />"This wouldn't be cheating, and it wouldn't be interfering."<br /><br />Your statement:<br /><br />"restrictions would likely be placed on it"<br /><br />My statement is an assessment, yours isRonhttps://www.blogger.com/profile/11752242624438232184noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-5205700634571025082014-10-15T16:06:03.991-07:002014-10-15T16:06:03.991-07:00> I don't. That doesn't change the fact...> I don't. That doesn't change the fact that as far as we know right now FTL is impossible.<br /><br />I simply prefer to say: "We don't yet know how FTL, or FTLI, would work." It is very close to what you said, but also different. Also, for fun: <a href="http://en.wikipedia.org/wiki/Alcubierre_drive" rel="nofollow">Alcubierre drive</a>. Cheating for the win!<br /><br />&Lukehttps://www.blogger.com/profile/18395549142176242491noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-78670254560875202162014-10-15T13:55:54.477-07:002014-10-15T13:55:54.477-07:00> Too many 'laws' have been found to b...> Too many 'laws' have been found to be only approximations. Why expect this one to be any different?<br /><br />I don't. That doesn't change the fact that as far as we know right now FTL is impossible.<br /><br />> restrictions would likely be placed on it. Do you really disagree with this?<br /><br />No. But "would be placed" is not the same as "have beenRonhttps://www.blogger.com/profile/11752242624438232184noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-19596735478089924992014-10-15T12:48:49.645-07:002014-10-15T12:48:49.645-07:00> We don't know anything for sure. But It w...> We don't know anything for sure. But It would falsify relativity, so we know it as surely as we know anything.<br /><br />Meh, I much prefer to say that relativity might be falsifiable, but that would involve moving to quite a different regime than where we seem to spend most of our time. Too many 'laws' have been found to be only approximations. Why expect this one to be any Lukehttps://www.blogger.com/profile/18395549142176242491noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-3932427617596210482014-10-15T12:38:14.501-07:002014-10-15T12:38:14.501-07:00> Do we know, for sure, that FTL communication ...> Do we know, for sure, that FTL communication is impossible?<br /><br />We don't know anything for sure. But It would falsify relativity, so we know it as surely as we know anything.<br /><br />> Back to the Future Part II<br />> Star Trek Voyager<br />> Star Trek Enterprise<br /><br />If you are seriously suggesting that science fiction is a reliable guide to ethics then you Ronhttps://www.blogger.com/profile/11752242624438232184noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-33768535549571696242014-10-15T12:08:12.782-07:002014-10-15T12:08:12.782-07:00> If Copenhagen is true (and specifically, if w...> If Copenhagen is true (and specifically, if wave-function collapse is a real, physical phenomenon) then this can be used to produce faster-than-light communication. See http://www.flownet.com/ron/QM.pdf<br /><br />Do we know, for sure, that FTL communication is impossible? That seems rather a big guess that lots of physicists have confidence in, but which hasn't been tested extensively. Lukehttps://www.blogger.com/profile/18395549142176242491noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-17891363783833014382014-10-15T11:41:00.005-07:002014-10-15T11:41:00.005-07:00> What experiment falsified Copenhagen, or what...> What experiment falsified Copenhagen, or what contradiction was found within it?<br /><br />If Copenhagen is true (and specifically, if wave-function collapse is a real, physical phenomenon) then this can be used to produce faster-than-light communication. See http://www.flownet.com/ron/QM.pdf<br /><br />> Would you be a bit more specific? For example, does this critically depend on all Ronhttps://www.blogger.com/profile/11752242624438232184noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-42220367125149560092014-10-15T11:14:52.189-07:002014-10-15T11:14:52.189-07:00> No. Most of them are *equivalent*, different ...> No. Most of them are *equivalent*, different ways of saying the same thing. (Copenhagen is demonstrably false, however.)<br /><br />What experiment falsified Copenhagen, or what contradiction was found within it? <a href="http://en.wikipedia.org/wiki/Copenhagen_interpretation#Acceptance_among_physicists" rel="nofollow">Copenhagen interpretation § Acceptance among physicists</a> has:<br /><brLukehttps://www.blogger.com/profile/18395549142176242491noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-91111573504890054922014-10-15T10:54:00.505-07:002014-10-15T10:54:00.505-07:00> Wait, this sounds you're saying that we n...> Wait, this sounds you're saying that we now know that the vast majority of interpretations at Interpretations of quantum mechanics are false; is that the case?<br /><br />No. Most of them are *equivalent*, different ways of saying the same thing. (Copenhagen is demonstrably false, however.)<br /><br />> What would falsify the "static" claim?<br /><br />You'd have to Ronhttps://www.blogger.com/profile/11752242624438232184noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-65989684116756348882014-10-15T10:39:25.261-07:002014-10-15T10:39:25.261-07:00@Ron:
> Well, it's a story that is consist...@Ron:<br /><br />> Well, it's a story that is consistent with the current state of scientific understanding of our universe. Furthermore, it's the *only* story (AFAIK, and modulo minor variations on the theme, like multiple-worlds) that has this property.<br /><br />Wait, this sounds you're saying that we now know that the vast majority of interpretations at <a href="http://Lukehttps://www.blogger.com/profile/18395549142176242491noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-48131121555644643262014-10-15T10:25:52.705-07:002014-10-15T10:25:52.705-07:00@ErnestO: Thanks for the kind words!
> Your fo...@ErnestO: Thanks for the kind words!<br /><br />> Your focus on remembering the past is confusing me a bit<br /><br />Yeah, I was afraid of that. I was going to talk about this explicitly but I had already spent three days composing that post and it was already getting too long.<br /><br />When I talk about "remembering" what I'm not talking about *consciously* remembering. I&#Ronhttps://www.blogger.com/profile/11752242624438232184noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-59760818218318039022014-10-14T18:56:17.762-07:002014-10-14T18:56:17.762-07:00> But in fact you do not travel through time, b...> But in fact you do not travel through time, because at root there is no you, and there is no time. There is only the wavefunction, from which you emerge as an approximation.<br /><br />Is this necessarily true, or dependent on particular metaphysical assumptions? I'm reminded of the <a href="http://en.wikipedia.org/wiki/Growing_block_universe" rel="nofollow">growing block universe</a> Lukehttps://www.blogger.com/profile/18395549142176242491noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-19177244334605529082014-10-14T15:35:51.923-07:002014-10-14T15:35:51.923-07:00Nice connection between memory, and the arrow of t...Nice connection between memory, and the arrow of time. Maybe we travel backwards in time, regularly! LOL.<br /><br />I've heard it before, but I still love this line: "Everything is always moving at the speed of light through space-time." And the followup: "When you move faster through space you move slower through time." I think that clearly distinguishes people who &Don Geddishttps://www.blogger.com/profile/04214642122689048677noreply@blogger.comtag:blogger.com,1999:blog-5592542.post-27625393573637572562014-10-14T15:04:38.384-07:002014-10-14T15:04:38.384-07:00First, I love your blog. :-)
I really enjoyed wh...First, I love your blog. :-)<br /><br />I really enjoyed what you have written here, and I think I follow what you are saying, but I'm a bit confused. I'm very much an amateur with this stuff, and am not sure how to best express these things.<br /><br />Your focus on remembering the past is confusing me a bit, since any given person will forget many things from the past, or even ErnestOhttps://www.blogger.com/profile/13491058613470971173noreply@blogger.com