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Is Time Travel (going backwards) Possible?
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<blockquote data-quote="freyar" data-source="post: 6052123" data-attributes="member: 40227"><p>I'll agree with Umbran as far as he goes on this, but I'd also add that there's probably nothing to do even with quantum time travel in this result. Specifically, this experiment looks at a type of particle known as a "B0," which has the unusual (but not unheard of) ability to change into its own antiparticle. <em>Now I'm going to oversimplify grossly.</em> What BaBar did <em>more or less</em> is measure the speed at which B0 turns into its antiparticle compared to the speed at which the antiparticle turns back. There are really a lot of technical details that make that not quite right, but the gist is that the two speeds are different. So the one reaction is not the same speed if you run it forwards vs backwards in time. This is called time-reversal violation, and it's been expected for a long time. In fact, it's probably been measured before with other types of particles, but those earlier measurements have some more errors. So there's really nothing about going back in time; it's about whether two reverse processes happen at the same speed going forward in time.</p><p></p><p>Another point to make is that there is actually always (mathematically proven) a way to reverse a process and get the same speed. This is called CPT because it involves reversing the time (T) (ie, the order of the process), parity (P) (which is reversing all the spatial motion), and charge (C) (turning all particles to their antiparticles). If you do that, you get two equal speeds; if not, well, you'll (1) have to subject your results to incredibly intense scrutiny and (2) win fame, fortune, and a Nobel prize if you're right (but you're probably not <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite2" alt=";)" title="Wink ;)" loading="lazy" data-shortname=";)" />). </p><p></p><p>There's a reasonably nice not-too-technical explanation <a href="http://blogs.discovermagazine.com/cosmicvariance/2012/11/20/time-reversal-violation-is-not-the-arrow-of-time/#more-9085" target="_blank">here</a>.</p></blockquote><p></p>
[QUOTE="freyar, post: 6052123, member: 40227"] I'll agree with Umbran as far as he goes on this, but I'd also add that there's probably nothing to do even with quantum time travel in this result. Specifically, this experiment looks at a type of particle known as a "B0," which has the unusual (but not unheard of) ability to change into its own antiparticle. [I]Now I'm going to oversimplify grossly.[/I] What BaBar did [I]more or less[/I] is measure the speed at which B0 turns into its antiparticle compared to the speed at which the antiparticle turns back. There are really a lot of technical details that make that not quite right, but the gist is that the two speeds are different. So the one reaction is not the same speed if you run it forwards vs backwards in time. This is called time-reversal violation, and it's been expected for a long time. In fact, it's probably been measured before with other types of particles, but those earlier measurements have some more errors. So there's really nothing about going back in time; it's about whether two reverse processes happen at the same speed going forward in time. Another point to make is that there is actually always (mathematically proven) a way to reverse a process and get the same speed. This is called CPT because it involves reversing the time (T) (ie, the order of the process), parity (P) (which is reversing all the spatial motion), and charge (C) (turning all particles to their antiparticles). If you do that, you get two equal speeds; if not, well, you'll (1) have to subject your results to incredibly intense scrutiny and (2) win fame, fortune, and a Nobel prize if you're right (but you're probably not ;)). There's a reasonably nice not-too-technical explanation [url=http://blogs.discovermagazine.com/cosmicvariance/2012/11/20/time-reversal-violation-is-not-the-arrow-of-time/#more-9085]here[/url]. [/QUOTE]
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