Category: Quantum Mechanics

Temporal Paradoxes Talk Done: World Safe for Grandfathers

Had a very good time at NASA’s Goddard Space Center doing my talk Temporal Paradoxes.  Nice crowd; lots of good questions.  NASA’s audio-visual support was first rate, as you would expect, and the talk should be up on their site in a bit.  I’ll post a link here when that happens.

I’d like to thank Brent Warner & his colleagues for their warm welcome & all the feedback during the talk.  Brent tells me he particularly liked the quote from an Astounding Science Fiction reader (1933):

“Why pick on grandfather? It seems that the only way to prove that time travel is impossible is to cite a case of killing one’s own grandfather. This incessant murdering of harmless ancestors must stop. Let’s see some wide-awake fan make up some other method of disproving the theory”*

As I say in the talk, if the current literature is on target, the grandfather & other paradoxes are cancelled out by interference by the time machine’s wave function with itself.

Brent & his NASA colleagues were kind enough to provide lunch & a fascinating tool of the facilities:  they manage the Hubble & are working on the James Webb.  Huge rooms with vast devices for subjecting equipment to high G’s, vacuum, heat, noise, vibration, & every other insult that it will need to be able to withstand during launch or in space:  gives one a real sense of just how hard it is to get this stuff to work!

*as quoted by Paul Nahin in his Time Machines: time travel in physics, metaphysics, and science fiction

Temporal Paradoxes Talk Online

I had a lot of fun putting my NASA talk Temporal Paradoxes together.  The feedback I got from the assembled multitude at the Radnor Library last week was extremely helpful, leading to a near complete rework of the talk, in the interests of making it clearer.   Thanks!

The pdf & keynote versions are now online.

Practice Run Thru on Temporal Paradox Talk

I’m doing a practice run thru on my Temporal Paradoxes talk at NASA.

The run thru will be at the Winsor room at the Radnor Memorial Library on March 12 at 2pm.  This is a few hundred feet from the main intersection in Wayne, PA.

The talk is basically the Physics Of Paradox talk, but more focused on the physics than the science fiction (tho in this area it can be hard to tell them apart) & with animations.

Since this is a complete redo of the talk, I’m hoping to get feedback on timing & clarity & focus & such like!

Please come!  And criticize!

Thanks!

— John Ashmead

The Physics of Paradox — Followup

Gave the Physics of Paradox talk at the Library of Congress Thursday (10/21/2010) & then again at Capclave Saturday (10/23/2010).   Good audiences both times, lots of good questions.  At Capclave talk was standing room only & Brent Warner, from the Goddard Space Center has asked if I would be interested in doing it there this spring.

I made some changes to the talk over the weekend, in response to audience feedback & further reflection.  The latest version is now up as Keynote (for Mac users), PowerPoint (for PC users), PDF in slides-only and also annotated forms.

I’d like to thank Dick Ladson, Walt Mankowski, Bruce Bloom, Shelley Handen, Ed & Marguerite Rutkowski, & of course Ferne Welch for their feedback at the dry run, which improved it immensely.  And I would like to thank Nathan Evans of the Library of Congress & Colleen Cahill of Capclave (& as it happens the Library of Congress) for having me.  Lots of fun!

Physics of Paradox

This talk — scheduled for the Library of Congress & for Capclave next week — is now up.

It was a lot of fun to put together:  I discuss time in relativity & quantum mechanics, kinds of time, some possible time machines, the three kinds of paradox (grandfather, bootstrap, & freewill), the Hawking & Novikov consistency conditions for avoiding paradox, some ways to implement those conditions, paradox noise, what the world might look like if paradox avoiding time travel were possible, and of course why this is likely.

I’ve got the talk on line as Keynote (for Mac users), PowerPoint (for PC users), PDF in slides-only and also annotated forms.

I’m doing a practice run on the talk in two days at the Radnor Memorial Library in the Winsor room from 6pm to 8pm (when we have to be out).  I start the actual talk about 6:30pm.  This is a dry run (well more of a wet run really) for the talks next week.

If you are not too far from Wayne, PA & have an interest in time & paradox (but then if not why are you reading these words?) please feel free to come!

Time and quantum mechanics at the Chestnut Hill Book Festival

Spoke at noon yesterday (July 10th, 2010) at the Chestnut Hill Book Festival; in spite of heavy rain a nice crowd.
This was my Balticon Time & Quantum Mechanics talk, adjusted for a general (rather than a science fictional) audience.  I covered over a hundred years of physics in less than an hour — a lot — but the audience survived & even seemed to prosper, asking some good questions!
I’ve uploaded the power point and keynote versions of the talk so you can see the animations of the double slit experiment, if you have power point and/or keynote.  You may have to tell your browser how to handle .ppt and/or .key files, for all parts to work with maximum smoothness. I’ve also uploaded the pdf and html versions.
The references — several asked after them — are on slide 36.  Enjoy!
I’d like to thank Oz Fontecchio for organizing this, Ferne Welch for moral & practical support, Bob Rossberg (sp?) for critical help on the AV, & the Chestnut Hill Book Festival for providing the venue!

Time & quantum mechanics talk done

Did the talk Saturday evening as planned.  Very sophisticated audience: almost everyone there had heard of the double slit experiment!

The talk went over well:  audience enthusiastic; lots of good questions.  Post talk I was asked if I would do similar presentations for Capclave & for the Library of Congress.  Leaning in favor.

I think that to really get across quantum mechanics, especially in a short time, nothing beats animations; the animations of the single & double slit were probably the most effective bits.  In future talks I shall be more animated.

The animations were courtesy of Bernd Thaller’s Advanced Visual Quantum Mechanics. He provides a useful kit of Mathematica functions for building such; looks a good starting point.

I’ve uploaded the power point & keynote versions of the talk so you can see the animations of the double slit experiment, if you have power point and/or keynote.  You may have to tell your browser how to handle .ppt and/or .key files, for all parts to work with maximum smoothness.

The pdf & html versions are still present, of course.  These are the talk as delivered, slightly different from the version previously posted (I added several more slides on the quantum eraser).

On the nature of time & quantum mechanics

… there are known knowns: there are things we know we know.  We also know there are known unknowns: that is to say we know there are some things we do not know.  But there are also unknown unknowns — the ones we don’t know we don’t know.” — Donald Rumsfeld.

I’m doing a popular talk on “The Nature of Time & Quantum Mechanics” tomorrow at Balticon. I’m deliberately not including anything from my paper “Quantum Time“.

Instead I look at a couple of areas at the intersection of time & quantum mechanics.  There are too many such areas for one talk. In accordance with my father’s rule of three (you can only get three points across in any one talk) I selected three of them, one from each of Donald Rumsfeld’s categories.

  1. The delayed choice quantum eraser.  I find this amazing:  if you try to see which slit the particle went thru in the double slit experiment, it becomes a single slit experiment.  But if you do something that should tell you which slit it went thru — and then deliberately erase your knowledge — the single slit experiment turns back to a double slit experiment & we recover the interference pattern.  And this is the case even if we do the probe/erase after the particle has gone thru the two slits!  Weird  but well understood & tested.
  2. The time symmetric formalism of Aharonov, Bergmann, & Lebowitz.  They formulated quantum mechanics in a time symmetric way, demonstrating that it is not essentially asymmetric in time.  It’s just usually drawn that way, as Jessica Qubit might put it.  There has been some speculation that their formalism could imply retro causation.  I doubt it myself but this would be a known unknown.
  3. The competition between the inflationary universe model & the ekpyrotic (cyclic) model of the universe.  The inflationary model now has a bit of competition in the ekpyrotic model of Steinhardt & Turok (see their book Endless Universe for a popular treatment).  Colliding branes, bouncing universes, & decaying dark energy oh my!  We have no idea what about the start, expansion, & finish of the universe we don’t know.  We don’t even know if the terms start & finish make sense, universe-wise.

I’ve put the slides for the talk up as a pdf & as html.

Dissertation complete

I’ve finished re-checking the dissertation:  629 equations, 188 references, 110 pages, 83 input files, 48 lists, 36 footnotes, 28 quotes, 17 figures, 6 chapters (counting the appendix), 5 requirements, 1 idea.  It should be up on the physics archive in a day or two.

A Typology of Quantum Gravities – Followup on Quantum Gravity Panel

Catherine Asaro, Jay Wile, & I had a good crowd for our quantum gravity panel at Philcon: I was impressed that that many people (perhaps 40 or 50) wanted to hear about a relatively esoteric subject. Esoteric but hot: there are (right now) 663 papers on the physics archive with quantum gravity in the title, in just the last five years!
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