192 research outputs found
Drawing with Complex Numbers
It is not commonly realized that the algebra of complex numbers can be used
in an elegant way to represent the images of ordinary 3-dimensional figures,
orthographically projected to the plane. We describe these ideas here, both
using simple geometry and setting them in a broader context.Comment: 14 pages, 5 figure
La Cohomologie des Figures Imposibles
On explique ici le lien étroit entre certains types de figures impossibles et la notion mathématique de cohomologie en relation avec la tripoutre et avec un autre type de figures impossibles lié au cube de Necker.The close relationship between certain types of impossible figure and the mathematical idea of cohomology is explained in relation to the tribar and to another type of impossible figure related to the Necker cube.Peer Reviewe
Exploring the unification of quantum theory and general relativity with a Bose-Einstein condensate
Despite almost a century's worth of study, it is still unclear how general
relativity (GR) and quantum theory (QT) should be unified into a consistent
theory. The conventional approach is to retain the foundational principles of
QT, such as the superposition principle, and modify GR. This is referred to as
`quantizing gravity', resulting in a theory of `quantum gravity'. The opposite
approach is `gravitizing QT' where we attempt to keep the principles of GR,
such as the equivalence principle, and consider how this leads to modifications
of QT. What we are most lacking in understanding which route to take, if
either, is experimental guidance. Here we consider using a Bose-Einstein
condensate (BEC) to search for clues. In particular, we study how a single BEC
in a superposition of two locations could test a gravitizing QT proposal where
wavefunction collapse emerges from a unified theory as an objective process,
resolving the measurement problem of QT. Such a modification to QT due to
general relativistic principles is testable near the Planck mass scale, which
is much closer to experiments than the Planck length scale where quantum,
general relativistic effects are traditionally anticipated in quantum gravity
theories. Furthermore, experimental tests of this proposal should be simpler to
perform than recently suggested experiments that would test the quantizing
gravity approach in the Newtonian gravity limit by searching for entanglement
between two massive systems that are both in a superposition of two locations.Comment: 51 pages, 10 figure
Polarization modes for strong-field gravitational waves
Strong-field gravitational plane waves are often represented in either the
Rosen or Brinkmann forms. These forms are related by a coordinate
transformation, so they should describe essentially the same physics, but the
two forms treat polarization states quite differently. Both deal well with
linear polarizations, but there is a qualitative difference in the way they
deal with circular, elliptic, and more general polarization states. In this
article we will describe a general algorithm for constructing arbitrary
polarization states in the Rosen form.Comment: 4 pages. Prepared for the proceedings of ERE2010 (Granada, Spain
Stephen Hawking
Tributes poured in on Wednesday to, the brightest star in the firmament of science, whose insights shaped modern cosmology and inspired global audiences in the millions. He died at the age of 76 in the early hours of Wednesday morning. In a statement that confirmed his death at home in Cambridge, Hawking’s children said: “We are deeply saddened that our beloved father passed away today. He was a great scientist and an extraordinary man whose work and legacy will live on for many years. His courage and persistence with his brilliance and humour inspired people across the world
On Conformal Infinity and Compactifications of the Minkowski Space
Using the standard Cayley transform and elementary tools it is reiterated
that the conformal compactification of the Minkowski space involves not only
the "cone at infinity" but also the 2-sphere that is at the base of this cone.
We represent this 2-sphere by two additionally marked points on the Penrose
diagram for the compactified Minkowski space. Lacks and omissions in the
existing literature are described, Penrose diagrams are derived for both,
simple compactification and its double covering space, which is discussed in
some detail using both the U(2) approach and the exterior and Clifford algebra
methods. Using the Hodge * operator twistors (i.e. vectors of the
pseudo-Hermitian space H_{2,2}) are realized as spinors (i.e., vectors of a
faithful irreducible representation of the even Clifford algebra) for the
conformal group SO(4,2)/Z_2. Killing vector fields corresponding to the left
action of U(2) on itself are explicitly calculated. Isotropic cones and
corresponding projective quadrics in H_{p,q} are also discussed. Applications
to flat conformal structures, including the normal Cartan connection and
conformal development has been discussed in some detail.Comment: 38 pages, 8 figures, late
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