8,471 research outputs found
Time and Spacetime: The Crystallizing Block Universe
The nature of the future is completely different from the nature of the past.
When quantum effects are significant, the future shows all the signs of quantum
weirdness, including duality, uncertainty, and entanglement. With the passage
of time, after the time-irreversible process of state-vector reduction has
taken place, the past emerges, with the previous quantum uncertainty replaced
by the classical certainty of definite particle identities and states. The
present time is where this transition largely takes place, but the process does
not take place uniformly: Evidence from delayed choice and related experiments
shows that isolated patches of quantum indeterminacy remain, and that their
transition from probability to certainty only takes place later. Thus, when
quantum effects are significant, the picture of a classical Evolving Block
Universe (`EBU') cedes place to one of a Crystallizing Block Universe (`CBU'),
which reflects this quantum transition from indeterminacy to certainty, while
nevertheless resembling the EBU on large enough scales.Comment: 25 Pages. 3 figure
Context, spacetime loops, and the interpretation of quantum mechanics
Three postulates are discussed: first that well-defined properties cannot be
assigned to an isolated system, secondly that quantum unitary evolution is
atemporal, and thirdly that some physical processes are never reversed. It is
argued that these give useful insight into quantum behaviour. The first
postulate emphasizes the fundamental role in physics of interactions and
correlations, as opposed to internal properties of systems. Statements about
physical interactions can only be framed in a context of further interactions.
This undermines the possibility of objectivity in physics. However, quantum
mechanics retains objectivity through the combination of the second and third
postulates. A rule is given for determining the circumstances in which physical
evolution is non-unitary. This rule appeals to the absence of spacetime loops
in the future evolution of a set of interacting systems. A single universe
undergoing non-unitary evolution is a viable interpretation.Comment: 19 pages. For special issue of J.Phys.A, "The Quantum Universe", on
the occasion of 70th birthday of Professor Giancarlo Ghirard
A delayed choice quantum eraser explained by the transactional interpretation of quantum mechanics
This paper explains the delayed choice quantum eraser of Kim et al. in terms
of the transactional interpretation of quantum mechanics by John Cramer. It is
kept deliberately mathematically simple to help explain the transactional
technique. The emphasis is on a clear understanding of how the instantaneous
"collapse" of the wave function due to a measurement at a specific time and
place may be reinterpreted as a gradual collapse over the entire path of the
photon and over the entire transit time from slit to detector. This is made
possible by the use of a retarded offer wave, which is thought to travel from
the slits (or rather the small region within the parametric crystal where
down-conversion takes place) to the detector and an advanced counter wave
traveling backward in time from the detector to the slits. The point here is to
make clear how simple the Cramer transactional picture is and how much more
intuitive the collapse of the wave function becomes if viewed in this way. Also
any confusion about possible retro-causal signaling is put to rest. A delayed
choice quantum eraser does not require any sort of backward in time
communication. This paper makes the point that it is preferable to use the
Transactional Interpretation (TI) over the usual Copenhagen Interpretation (CI)
for a more intuitive understanding of the quantum eraser delayed choice
experiment. Both methods give exactly the same end results and can be used
interchangeably.Comment: 24 pages 4 figures, fifth draf
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