Search Talks

A very general way of describing the abstract structure of quantum theory is to say that the set of observables on a quantum system form a C*-algebra.  A natural question is then, why should this be the case - why can observables be added and multiplied together to form any algebra, let alone of the special C* variety?  I will present recent work with Markus Mueller and Howard Barnum, showing that the closest algebraic cousins to standard quantum theory, namely the Jordan-algebras, can be characterized by three principles having an informational flavour, namely: (1) a generalized spectral decomposition, (2) a high degree of symmetry, and (3) a requirement on conditioning on the results of observations.   I'll then discuss alternatives to the third principle, as well as the possibility of dropping it as a way of searching for natural post-quantum theories.

There is evidence for a 130 GeV gamma-ray line at the Galactic Center in the Fermi Large Area Telescope data. Dark matter candidates that explain this feature should also annihilate to Standard Model particles, resulting in a continuous spectrum of photons. To study this continuum, we analyze the Fermi data down to 5 GeV, restricted to the inner 3 degrees of the Galaxy. We place a strong bound on the ratio of continuum photons to monochromatic line photons that is independent of uncertainties in the dark matter density profile. Neutralino dark matter is excluded by the derived constraints.

Tidal stripping of dark matter from subhalos falling into the Milky Way produces narrow, cold tidal streams as well as more spatially extended ``debris flows'' in the form of shells, sheets, and plumes.Here we focus on the debris flow in the Via Lactea II simulation, and show that this incompletely phase-mixed material exhibits distinctive high velocity behavior. Unlike tidal streams, which may not necessarily intersect the Earth's location, debris flow is spatially uniform at 8 kpc and thus guaranteed to be present in the dark matter flux incident on direct detection experiments. At Earth-frame speeds greater than 450 km/s, debris flow comprises more than half of the dark matter at the Sun's location, and up to 80% at even higher speeds. Therefore, debris flow is most important for experiments that are particularly sensitive to the high speed tail of the dark matter distribution, such as searches for light or inelastic dark matter or experiments with directional sensitivity. We show that debris flow yields a distinctive recoil energy spectrum and a broadening of the distribution of incidence direction.

We discuss the shortcomings of Einstein gravity at both the classical and quantum levels. We discuss the motivation for replacing Einstein gravity by conformal gravity. We show how the conformal gravity theory is able to naturally solve the quantum gravity problem, the vacuum zero-point energy problem, the vacuum zero-point pressure problem, the cosmological constant problem, and the dark matter problem. Central to its viability as aquantum theory is that the conformal theory is both renormalizable and unitary, with unitarity being obtained because the theory is a PTsymmetric rather than a Hermitian theory. We show that in the conformal theory there can be no a priori classical curvature, with all curvature having to result from quantization. In the conformal theory gravity requires no independent quantization of its own, with it being quantized solely by virtue of its being coupled to a quantized matter source. In the absence of quantum mechanics then there would thus be no gravity, with it being the desire to start with a classical gravity theory and then quantize it
that has prevented the construction of a sensible quantum gravity theory. We show that the macroscopic classical theory that results from the quantum conformal theory incorporates global physics effects coming from the material outside of galaxies (viz. the rest of theuniverse), global physics effects that are found to provide for a detailed accounting of a comprehensive set of 138
galactic rotation curves with no adjustable parameters other than galactic mass to light ratios, and with the need for no dark matter whatsoever. With these global effects eliminating the need for dark matter, we see that invoking dark matter in galaxies could potentially be nothing more than an attempt to describe global physics effects in purely local galactic terms.

The world's most ambitious scientific experiment is buried 100 meters underground, straddling Switzerland and France.  A billion times every minute, the Large Hadron Collider (LHC) slams together protons, while four giant detectors watch closely.

 So how does the Large Hadron Collider work?  Why can slamming tiny particles into each other provide clues about the nature of all space and time?  What mysteries are physicists trying to solve with data from the LHC, and what is the Higgs anyway?  What might we learn next? How does the cutting edge of particle physics relate to the world around us, from the patterns of stars in the sky to the fact that they shine at all?

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
 


So how
does the Large Hadron Collider work?  Why
can slamming tiny particles into each other provide clues about the nature of
all space and time?  What mysteries are
physicists trying to solve with data from the LHC, and what is the Higgs
anyway?  What might we learn next? How
does the cutting edge of particle physics relate to the world around us, from
the patterns of stars in the sky to the fact that they shine at all?

Just as there is a
difference between knowing how to *drive* a car and understanding its
functioning well enough to fix it when it breaks down, so too is there a
difference between knowing how to *use* quantum theory to make
predictions and understanding what it says about the world well enough to see
how it might fail or how it might be usefully generalized. The field of quantum
foundations seeks to achieve such a deeper understanding. In particular, it
seeks to determine the correct interpretation of quantum theory and to find the
principles underlying it, questions for which there is still no consensus among
researchers.  In this talk, I’ll discuss some of the interpretational
problems of quantum theory and several of the most prominent proposals for how
to overcome these problems.  The list includes introducing hidden
variables that we must necessarily remain uncertain of, changing the rules of
logic, and positing the existence of an infinite number of parallel worlds.