2 research outputs found
Echoes in classical dynamical systems
Echoes arise when external manipulations to a system induce a reversal of its
time evolution that leads to a more or less perfect recovery of the initial
state. We discuss the accuracy with which a cloud of trajectories returns to
the initial state in classical dynamical systems that are exposed to additive
noise and small differences in the equations of motion for forward and backward
evolution. The cases of integrable and chaotic motion and small or large noise
are studied in some detail and many different dynamical laws are identified.
Experimental tests in 2-d flows that show chaotic advection are proposed.Comment: to be published in J. Phys.
Twisting of light around rotating black holes
Kerr black holes are among the most intriguing predictions of Einstein's
general relativity theory. These rotating massive astrophysical objects drag
and intermix their surrounding space and time, deflecting and phase-modifying
light emitted nearby them. We have found that this leads to a new relativistic
effect that imposes orbital angular momentum onto such light. Numerical
experiments, based on the integration of the null geodesic equations of light
from orbiting point-like sources in the Kerr black hole equatorial plane to an
asymptotic observer, indeed identify the phase change and wavefront warping and
predict the associated light-beam orbital angular momentum spectra. Setting up
the best existing telescopes properly, it should be possible to detect and
measure this twisted light, thus allowing a direct observational demonstration
of the existence of rotating black holes. Since non-rotating objects are more
an exception than a rule in the Universe, our findings are of fundamental
importance.Comment: Article: 18 pages (11 pages in form of an Appendix). Total number of
figures: