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.


Quantum Time now up on the physics archive.

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