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.

I can no other answer make, but, thanks, and thanks.

Lately it appears to me what a long, strange trip it’s been.
— Robert Hunter of the Grateful Dead
We are all travellers in the wilderness of the world, and the best we can find in our travels is an honest friend.
— Robert Louis Stephenson
I thank my long time friend Jonathan Smith for invaluable encouragement, guidance, and practical assistance.
I thank the anonymous reviewer who pointed out that I was using time used in multiple senses in an earlier work.
I thank Ferne Cohen Welch for extraordinary moral and practical support.
I thank Linda Marie Kalb and Diane Dugan for their long and ongoing moral and practical support.
I thank my brothers Graham and Gaylord Ashmead and my brother-in-law Steve Robinson for continued encouragement.
I thank Oz Fontecchio, Bruce Bloom, Shelley Handin, and Lee and Diane Weinstein for listening to a perhaps baroque take on free will and determinism. I thank Arthur Tansky for many helpful conversations and some proofreading. I thank Chris Kalb for suggesting the title.
I thank John Cramer, Robert Forward, and Catherine Asaro for helpful conversations (and for writing some fine SF novels). I thank Connie Willis for several entertaining conversations about wormhole physics, closed causal loops and the like (and also for writing several fine SF stories).
I thank Stewart Personick for many constructive discussions. I thank Matt Riesen for suggesting the use of Rydberg atoms. I thank Terry the Physicist for useful thoughts on tunneling and for generally hammering the ideas here. I thank Andy Love for some useful experimental suggestions, especially the frame mixing idea. I thank Dave Kratz for helpful conversations. I thank Paul Nahin for some useful email. I thank Jay Wile for some necessary sarcasm.
I thank John Myers and others at QUIST and DARPA for useful conversations.I thank the participants at the third Feynman festival for many good discussions, including Gary Bowson, Fred Herz, Y. S. Kim, Marilyn Noz, A. Vourdas, and others. I thank Howard Brandt for his suggestion of internal decoherence.
I thank the participants at The Clock and The Quantum Conference at the Perimeter Institute for many good discussions, including J. Barbour, L. Vaidman, R. Tumulka, S. Weinstein, J. Vaccaro, R. Penrose, H. Price, and L. Smolin.
I thank the participants at the Third International Conference on the Nature and Ontology of Spacetime for many good discussions, including V. Petkov, W. Unruh, J. Ferret, H. Brown, and O. Maroney.
I thank the participants at the fourth Feynman festival for many good discussions, including N. Gisin, J. Peřina, Y. S. Kim, L. Skála, A. Vourdas, A. Khrennikov, A Zeilinger, J. H. Samson, and H. Yadsan-Appleby.
I thank the librarians of Bryn Mawr College, Haverford College, and the University of Pennsylvania for their unflagging helpfulness. I thank Mark West and Ashleigh Thomas for help getting set up at the University of Pennsylvania.
I thank countless other friends and acquaintances, not otherwise acknowledged, for listening to and often contributing to the ideas here.
I acknowledge a considerable intellectual debt to Yakir Aharonov, Julian Barbour, Paul Nahin, Huw Price, L. S. Schulman, Victor J. Stenger, and Dieter Zeh.
I thank Balticon for having me speak on this.  And I thank Chris Heimark and the other members of my Macintosh Programming SIG for inviting a talk on quantum time.
Finally, I thank the six German students at the Cafe Destiny in Olomouc who over a round of excellent Czech beer helped push this to its final form.
And of course, none of the above are in any way responsible for any errors of commission or omission in this work.

Finally

Quantum Time now up on the physics archive.

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.

Now drops shoe the 3rd …

Give me the child. Through dangers untold and hardships unnumbered, I have fought my way here to the castle beyond the Goblin City to take back the child that you have stolen. For my will is as strong as yours, and my kingdom is as great…

Or, less poetically, I have (finally) finished checking the calculations in my dissertation.  The checked version is up & I hope to have it uploaded to the physics archive by the end of the weekend.

The Other Shoe Drops

I’ve just finished the cross checks on my dissertation “Quantum Time“.

The dissertation asks “what happens if measurements in the time dimension are fuzzy, just as we know they are in the space dimensions”?  Another way to put this is “what if particles are spread out in time, not just fixed in the present instant, but extending a bit into future and past”?

The question is motivated by relativity:  From relativity we know that time and space are interchangeable.  Even if a particle should happen to be flat in one frame, with no extension into past or future, in another frame it will have such an extension.  Therefore it is simplest to assume any particle is always extended a bit in time, just not so much that we notice it.

But to work out specific predictions from this is tricky:  how do you give an experimentalist something to chew on?

I was able to work out the rules for this by rewriting quantum mechanics in a way that doesn’t favor space over time.  But even with that part done, it was still tricky to apply these rules to specific experimental cases and be confident that I had used the rules consistently and correctly.

Eventually what I hit on is a set of principles (aside from being as careful as possible about the algebra!):  when the extension in time goes to zero, we should get exactly the standard result.  And every experiment should morph smoothly into its neighbors.  For instance, if we are working on a double slit experiment, and we separate the two gates far enough, the results should look like those for two separated single gates.

I’ve spent the last two months working on this & as of yesterday the analysis seems complete.

In general, of course, everything gets fuzzier in time.  If you send a particle through a “chopper”, a gate in time, then the pattern it leaves in time at the detector will be more spread out if time is fuzzy.

There were some surprises of course.  For instance, the classic double slit experiment normally produces an oscillating comb-like pattern at the detector.  If time is fuzzy, not only does each tooth of the comb get wider (we knew that was coming) but the teeth get more spread out.  And shorter.  So there are three different effects to look for.

All three effects are subtle, so it is possible that the effects of quantum time have already been seen, but racked up to experimental noise.

I’m letting the latest version of the paper cool off for a week, then giving it a quick double check & submitting it to the physics archive next weekend.

“Morlet wavelets in quantum mechanics” updated

The announcement the world has been waiting for can now be made:  the paper “Morlet wavelets in quantum mechanics” has been updated.  The latest version has a much clearer explanation of the point, a number of errors corrected, and some stylistic infelicities eliminated.

This version has been uploaded to the physics archive.

Abstract:

Wavelets offer significant advantages for the analysis of problems in quantum mechanics. Because wavelets are localized in both time and frequency they avoid certain subtle but potentially fatal conceptual errors that can result from the use of plane wave or delta function decomposition. Morlet wavelets are particularly well-suited for this work: as Gaussians, they have a simple analytic form and they work well with Feynman path integrals. To take full advantage of Morlet wavelets we need an explicit form for the inverse Morlet transform and a manifestly covariant form for the four-dimensional Morlet wavelet. We supply both here.

Paradox Noise

saberhagen - after the fact “YOUR ONLY CHANCE LIES IN PREVENTING THE ASSASSINATION OF PRESIDENT ABRAHAM LINCOLN . . .”

“What?”

A burst of audio and visual static reduced reception to unintelligible noise. Then the paradox-generated interference was gone again, as suddenly as it had come.

” . . . Fourteenth of April at Ford’s Theater –” blast, crackle.

“. . . you must be within two meters of the President . . . just before the bullet smashes into Lincoln’s brain. Your total window of opportunity will be three seconds.”

– Fred Saberhagen’s After the Fact


If the block universe view is correct, if time is “nothing but” a space dimension, then we should be able to travel in it. Leaving aside the fact that we don’t quite yet know how to do this (but see some of the books under references) shouldn’t time travel be forbidden by the paradoxes it would otherwise make inevitable?  There are three kinds of paradox to consider:

Three kinds of paradox

Grandfather paradox

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.

– 1933 letter to Astounding Stories, as quoted in Nahin’s Time Machines: Time Travel in Physics, Metaphysics, and Science Fiction

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Quantum time talk today

December 12th, 2009

One of the members of my Macintosh programming SIG asked me if for today’s meeting I would talk about Quantum Time, which I was, of course, happy to do.  There is nothing like explaining something to a bunch of intelligent listeners for getting it straight in your own head.  And if you can get across some of the wonder & the weird that is modern physics, that’s even better!

I’ve got the slides online (see under talks).  Summary:
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