New Thoughts About The Universe
23rd - 25th July 2009
The Bosworth Hall Hotel, Warwickshire, UK
Supported by a mini-grant from the Foundational Questions Institute.
Participants:
- Martin Bucher
- Rob Crittenden
- Pedro Ferreira
- Gary Gibbons
- Steven Gratton
- Adrian Kent
- Antony Lewis
- Jonathan Oppenheim
- Andrew Pontzen
- Paul Saffin
- Marcus Werner
Programme:
Thursday 23rd July
- 12 noon-1pm: Arrive and tea/coffee (inc. guests) outside Thornley Suite
- 1pm-2pm: Lunch outside Thornley Suite
- Check-in
- 2:15pm: Welcome
- 2:30pm: Rate Equations and Quantum Mechanics (MB)
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- 3:00pm: Interpretations of Quantum Mechanics Intro/Review (AP)
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- 3:15pm: Tea/Coffee
- 3:30pm: The Nature of Time Intro/Review (SG)
- 5pm: Tea/coffee
- 5:15pm: Compressibility of Descriptions of Nature (AK)
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- 6pm: Close
- From 7pm: Meet in Hotel Bar for Pre-Dinner Drinks
- 7:30pm: Dinner in Redmoor Room
Friday 24th July
- 7:30-9am: Breakfast in Jenny's Restaurant
- 9am: Area Metrics (MW)
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- Magnetic fields (AL)
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- Vacuum Energy (PS)
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- 10:45am: Tea/Coffee
- 11am: Dark Energy (PF)
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- 1-2pm: Lunch
- 2pm: Walk around Bosworth Park
- 3:15pm: Tea/Coffee
- 3:30pm: Non-unitarity and Cosmology (JO)
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- Simulating the universe (AP)
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- 5pm: Tea/Coffee
- CMB non-gaussianities (AL)
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- Scale-dependent bias (RC)
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- 6pm: Close
- From 7pm: Meet in Hotel Bar for Pre-Dinner Drinks
- 7:30pm: Dinner in Redmoor Room
Saturday 25th July
Topics and Preparatory Material:
- Area Metrics (MW): The area metric is a fairly new concept in differential geometry developed
by Frederic Schuller et al., which appears to emerge naturally in the
context of electromagnetism and string theory. It is a potentially
interesting approach to modified theories of gravity from a geometric point
of view, with applications to accelerating cosmology. A comprehensive
introduction can be found, e.g., in Punzi, Schuller and Wohlfarth: "Area
metric gravity and accelerating cosmology," JHEP 02 (2007), 030. See the abstract here.
- Non-unitarity and Cosmology (JO): I don't really take a position on whether the laws of evolution are
unitary or not, but I think it's important to explore the options,
especially in light of the black-hole information puzzle (i.e. can pure
states evolve into mixed states). Surprisingly little research has been
done in this area even though there doesn't appear to be anything which
rules out non-unitary evolution except for taste. In order for such
theories to be causal and conserve momentum, they turn out to create
long-range correlations over space-like distances. It is perhaps
counter-intuitive that the creation of correlations over space-like
distances doesn't violate causality/Lorentz invariance. Are there
cosmological implications? Does this allow for solutions to the horizon
problem other than via inflation? Refs:
[1] Fundamental destruction of information and conservation laws, JO &
B.Reznik arxiv.org/abs/0902.2361,
[2] Difficulties for the Evolution of Pure States Into Mixed States.
Banks, Susskind, Peskin
http://www-spires.slac.stanford.edu/spires/find/hep/www?irn=1135198,
[3] Evolution laws taking pure states to mixed states in quantum field
theory, Unruh and Wald, http://prola.aps.org/abstract/PRD/v52/i4/p2176_1.
- The Compressibility of Descriptions of Nature (AK):
What we normally think of as fundamentally probabilistic theories
(in particular, qm) may better be understood as statements about the
algorithmic compressibility of our best possible current description
of nature. This explains how and why we can and do confirm or falsify
"one-world" theories, in which experiments have single unpredictable
outcomes. However, nothing analogous works for "many-worlds" theories,
which suggests that they may simply not be confirmable or falsifiable. See arXiv:0905.0624 and refs therein (in particular papers by
Greaves-Myrvold and Wallace on Everett and decision theory).
- Rate Equations vs Quantum Mechanics (MB)
- Quasi-Newtonian Cosmological Computer Simulations: Could they be the wrong approach? (AP)
Newtonian gravity is observationally relevant only insofar as it constitutes
a good approximation to general relativity. But quasi-Newtonian gravity
(Newtonian gravity with periodic, rather than asymptotic, boundary
conditions on its potential) is used almost exclusively by cosmologists to
understand the non-linear evolution of structure in the Universe. A
systematic comparison between fluid cosmologies in the two theories may be
obtained by constructing gauge-invariant covariant theories of perturbations
on homogeneous background for each case (e.g. Ellis & Bruni 1989, Ellis
1990, Ellis & van Elst 1998 -- the last of these is a very useful
pedagogical review). These explain much more succinctly than in the Bardeen
approach how it is that quasi-Newtonian theories remain rather good
approximations on large scales. However, there are unanswered questions --
in particular the unphysical restriction on the Weyl tensor that the
periodic Newtonian theory imposes (e.g. Ellis & Dunsby 1997). Further,
cosmological simulations do not perfectly evolve the Newtonian fluid
equations but must discretized in a manner which, to my knowledge, has not
had its convergence properties studied mathematically (only rather
schematically through running individual simulations with different
resolutions). How worried should we be about these problems?
- Interpretations of Quantum Mechanics (AP)
- The Anthropic Principle and Bayesian Evidence (RC):
See hep-th/0407213 by Smolin,
math/0608592 by Neal,
astro-ph/0607227 by Starkman and Trotta,
0704.2630 by Hartle and Srednicki and
0901.2414 by Ellis and Smolin.
- Scale dependent bias from non-Gaussianity (RC):
See the paper by Dalal, Phys.Rev.D77:123514,2008 (or arxiv 0710.4560).
- A democracy of measures in eternal inflation (SG):
There has been much activity recently in the search for a suitable measure for eternal inflation. Motivated by recent work obtaining sensible results out of the much-maligned proper time measure, one might speculate that the difficulties might be more to do with some of the questions being asked as opposed to the measures themselves and that we might eventually need to become comfortable with a multitude of measures in eternal inflation.
- The Nature of Time (SG):
The Foundational Questions Institute recently ran an essay contest on "The Nature of Time". It might be interesting for us to take a look at some of the winners of that contest and have a discussion on this perennial topic. See here, perhaps in particular the first few essays.
- Why do humans perceive a classical 3D universe with occasional irregular "quantum jumps"? (SG): This may well be a "lo-fi" version of AK's question above! Could it be that we perceive a point moving in 3N-dimensional configuration space rather than a 3N-dimensional function on the configuration space simply because it is so much easier and still gets the answer basically right for predictions most of the time? Are the "quantum jumps" simply us discarding our model for a new one when it fails to be useful/tenable for us anymore? Is it the simple form of the interaction potential amongst degrees of freedom that encourages us to see a 3D universe with N particles rather than a 1D universe with 3N particles?
- If Not Dark Energy, Then What? (PF): There are all these possibilities
like backreaction, modified gravity, large voids but the question is, are we
being exhaustive? Are we missing
any possibility? See 0907.4109.
- What Would Make Us Give Up On Dark Matter? (PF)
- Understanding the cosmological constant (PS)
Following on from work by Volovik gr-qc/0604062 there
has been a series of papers trying to understand the cosmological constant
using thermodynamic arguments. In particular, Klinkhamer and Volovik have
constructed a rather general framework to analyze the thermodynamics of
the quantum vacuum 0711.3170 and have also studied
the dynamics of particular examples 0806.2805 which
indicates that the trans-Planckian modes conspire in such a way as to
cancel the large vacuum fluctuations of the sub-Planckian modes.
(Perhaps see also 0905.1919 and 0811.4337.)
- Are Boltzmann Brains Real Observers? (AL/SG) See 0802.0233.
- Are credences the same as probabilities? (AL)
- Are big universes a priori more likely? (AL)
- Were magnetic fields primordial? (AL)
- Can large scale modes explain CMB anomalies? (AL)
- Are there reasonable physical models with zero bispectrum but large
trispectrum? (AL)
Practical Details
The event starts at 12 noon on the Thursday with arriving tea/coffee outside the Thornley Suite and will formally finish at 12 noon on the Saturday, after departing tea/coffee at 11:45am. Guests are invited to join us here as we introduce ourselves/say goodbye.
A large table for delegates (and guests to sit with us if they wish to) has been reserved in Jenny's Restaraunt from 7:30am - 9am on the Friday and Saturday mornings.
Buffet lunches will be provided for delegates on the Thursday and Friday, at 1pm, outside the Thornley Suite.
The main discussions will be held in the Thornley Suite at the hotel, starting at 2pm on the Thursday and at 9am on the Friday and Saturday.
Our evening dinners will be in the Redmoor Room at the hotel, starting at 7:30pm.
Wi-fi is available throughout all hotel bedrooms and function suites.
The hotel homepage is www.hotelbosworthhall.co.uk. Driving details are available there, and the nearest big railway station is Leicester. Hopefully we can organise shared rides to/from Cambridge.
