Thursday, February 8, 2018

Dark Energy



Randy helps Jim get a handle on dark energy. Why do we need it? Why do we want to believe in it now, but didn't earlier? How many different things could it be? What does it have to do with you? How close are we to knowing anything about it?

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Notes:

1. The papers we read for this program:
  • Carroll, S., "Dark Energy and the Preposterous Universe." [arXiv]
  • Turner, M., "Dark Energy and the New Cosmology." [arXiv]
  • Zwicky, F., "On the Masses of Nebulae and Clusters of Nebulae." Astrophys. J.  86, 217 (1937) [web]
  • Holsclaw, T., Alam, U., Sanso, B, Lee, H., Heitmann, K., Habib, S. and Higdon, D., "New Constraints on the Time-Variation of the Dark Energy Equation of State from Current Supernova Data." [web]
2.I'll review Oyvind Gron's book, Lecture Notes on the General Theory of Relativity soon. I've been meaning to for a couple of months now.

3. Previous Episodes Referenced:
4.If you or Dragan Hejdukovic wants to supply us with the background energy that would be predicted from virtual gravitational dipoles, please leave us a nice comment with smilies.

5. Our subreddit.

Sunday, January 21, 2018

Weyl and Quasiparticles



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. Our subreddit.

Wednesday, January 10, 2018

The Origin of Inertia



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. Our subreddit.

Thursday, December 21, 2017

Exoplanets

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.

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.

Wednesday, December 6, 2017

The 2T Physics of Itzhak Bars



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. Our subreddit.

Friday, November 24, 2017

The Physics of Time Travel



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. Kurt Goedel's On Formally Undecidable Propositions of Principa Mathematica and Related Systems, which I jabber on a little too much about in the podcast.

3. A World Without Time: The Forgotten Legacy of Goedel and Einstein by Palle Yourgrau, a popular book on this subject I read a long time ago and I misplaced.

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.