Sunday, January 21, 2018

Weyl and Quasiparticles

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Jim and Randy discuss quasiparticles recently found in condensed matter systems that mirror particles theorized nearly a hundred years ago, but never found in the vacuum. Weyl particles are massless fermions, and once it was hoped that neutrinos would turn out to be this kind of particle, and Majorana fermions have real-valued wave functions and therefore many strange and possibly useful properties.

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Notes:

1. The papers we read for this program:
2.  Popular papers we may have read:
3. Original Papers:
4. I was wrong.  "Weyl" rhymes with "pile," not with "pail."

5. Please visit and comment on our subreddit, and if you can help us keep this going by contributing to our Patreon, we'd be grateful.

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Wednesday, January 10, 2018

The Origin of Inertia

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Randy tells Jim about a scheme that uses Mach's Principle - the idea that there is a preferred background frame with respect to the fixed stars - to explain the origin of inertia. Why exactly does an object in motion stay in motion?

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Notes:

1. The papers we read for this program:

2. In addition, Randy sent me a lot of blog and other forum posts for background:


3. Our discussion on Gravitoelectromagnetism..

4. Our discussion of Aharonov and Rohrlich's Quantum Paradoxes, nine of the ten recorded episodes. I don't think we get into the retrocausal part of it.

5. Please visit and comment on our subreddit, and if you can help us keep this going by contributing to our Patreon, we'd be grateful.

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Thursday, December 21, 2017

Exoplanets

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Episode 19 - Exoplanets has been lost. We continue with our original numbering as we attempt to fix it.

Go to Episode 20 - Time Crystals for the next episode.

Please visit and comment on our subreddit, and if you can help us keep this going by contributing to our Patreon, we'd be grateful.

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Time Crystals



Jim talks to Randy about structures that are periodic in time like crystals are periodic in space. This idea came from Frank Wilczek in 2012, and was realized just recently, providing an extraordinary turn-around time from theory to observation.

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Notes:

1. The papers we read for this program:

2. Our subreddit.

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The following post was made to the arXiv_plus subreddit about these papers:

This was an interesting one. Frank Wilczek hypothesized, here, that there would be structures that were periodic in time the way crystals are periodic in space. The wave functions, in time, would be similar to the Bloch functions of condensed matter. The character of the wave functions would be a little like solitons, with an attractive nonlinearity balanced by uncertainty-related dispersion. His original model was to look at coupled superconducting rings. The coupling would repeatedly and periodically reproduce the same state.

In Discrete time crystals: rigidity, criticality, and realizations, Yao, et al., showed that the ground state wave function cannot have the periodicity required -- but an excited state could. What you would need to do is produce a Hamiltonian that did three things, successively: orient the system, order the system, and finally randomly disorder it.

Two groups wasted no time at all producing these excited "time crystals," simultaneously publishing in Nature about a year ago. One group looked at what I'd think of as a very artificial system, a few optically-trapped, ultra-cold atoms. In this case each of the effects was programmed by laser interactions. The other group used a real crystal: diamond with nitrogen vacancies at room temperature.

Both groups successfully reproduced the phenomena of Yao's paper. The nature of the Hamiltonians, if I'm free to interpret them, is a successive Zeeman interaction to align the spins of the atoms, an exchange term like the Heisenberg Hamiltonian, and a diffusion term.

There is some similarity to spin echos here, but the effects are much more coherent.

Wednesday, December 6, 2017

The 2T Physics of Itzhak Bars

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Randy tells Jim about a theory that complements other theories of fundamental physics based upon a phase space symmetry between the 4-position and the 4-momentum of a particle. The upshot of the theory is that there should be a second time dimension and a fourth space dimension, both macroscopic in extent, and the physics we see are 4D projections from the larger 6D space-time.

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Notes:

1. The papers we read for this program:
  • A two Time Universe?, by Tom Siegfried on phys.org. This is a popular article on the theory.
  • The Standard Model as a 2T Physics Theory, Itzhak Bars. AIP Conference Proceedings 903, 550 (2006) [arXiv]
  • Gravity in 2T Physics, Itzhak Bars, Physical Review D77, 125027 (2008) [arXiv]

2. Itzhak Bars lecture on 2T Physics.

3. Extra Dimensions in Space and Time, a book containing a longer, less technical (almost popular) description of 2T physics by Itzhak Bars. That takes up about half the book, the other half is John Terning discussing more traditional extra dimensions in string theory. My review on PhysicsFM is here.

4. Please visit and comment on our subreddit, and if you can help us keep this going by contributing to our Patreon, we'd be grateful.

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Friday, November 24, 2017

The Physics of Time Travel

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Recorded: 2017/04/02 Published: 2017/11/23
Randy and Jim try to get their heads around how time relates to relativity. Of particular interest is Kurt Goedel's 1949 solution to the field equations that shows closed time-like null geodesics (paths followed by massless particles moving at the speed of light). The subject focuses mainly of some implications of general relativity that obey our intuition locally, but not globally.

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Notes:

1. The papers we read for this program:
  • An Example of a New Type of Cosmological Solutions of Einstein's Field Equations of Gravitation, Kurt Godel (Rev Mod Phys 21 447 (1949)
  • Cauchy Problem in Spacetimes with Closed Timelike Curves, Physical Review D 42, 1915 (1990)
  • Closed Timelike Curves, Bryan W. Roberts
  • Is Physics Consistent with Closed Timelike Curves? John L. Fiedman, Annals of the New York Academy of Sciences
  • Chronology Protection Conjecture, S. W. Hawking, Physical Review D 46, 603 (1992)
  • Time Travel and Time Machines, Chris Smeenk and Christian Wuthrich, Oxford Handbook of Time (Oxford)


2. Related episodes of Physics Frontiers:


3. Books related to this podcast:


4. James Gleick's Google talk on time travel, and Time Travel: A History, the book it's based on.

5. I dropped about 7 minutes of my recording, which from Randy's comments included a brief discussion of positive probability of backward causation in the Compton effect's path integral formulation. I did include his overview of "Time Travel and Time Machines," after the end of the show which is a philosopher's take on the issue.

6. Our subreddit.

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Monday, November 6, 2017

Stochastic Resonance Energy Harvesting

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Recorded: 2017/03/05 Published: 2017/10/21

Randy tells Jim about ways in which external vibrations can be used to do useful work in large-scale devices. These processes look at have happens when bistable systems (e.g., a bent cantilever) are subjected to random forcing from the environment.

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Notes:

1. The papers we read for this program:
  • A Piezomagnetoelastic Structure for Broadband Energy Harvesting (APL2009)
  • A Review of the Recent Research on Vibration Energy Harvesting via Bistable Systems (2013)
  • An Application of Stochastic Resonance for Energy harvesting (JSV2014)
  • An Experimental Study of Stochastic Resonance in a Bistable Mechancial Systems (2012)
  • Bistable Vibration Energy Harvesters (2012)
  • Feasibility of Energy harvesting Using Stocahstic Resonance (2014)
  • Towards Broadband Vibration-Based Energy Harvesting

2. Past and future shows:


3. Bing Crosby, Ac-cent-tchu-ate the Positive:

4. Our subreddit.

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