The standard quantum mechanics does not forbid time-travel. However, some alternative formulations (based on the so called “rigged Hilbert space”) include irreversibility as a fundamental principle: a quantum particle that decays cannot travel back in time.
There are not direct evidences of the irreversibility of decay processes, but the new quantum mechanics predicts that the decay rates are quantized.
If one observes the quantization of the decay rates, one can claim to have provided experimental support to the irreversible formulation of quantum mechanics.
In simple terms, one can claim that time-travel is not possible at the quantum level (…and also at the classical level).
Silvia Gentilini, Maria Chiara Braidotti, Giulia Marcucci, Eugenio Del Re, and Claudio Conti simulated in the laboratory one of the simplest models of the irreversible quantum mechanics, that follows an original proposal of Glauber. A laser beam emulates a quantum particle in a reversed harmonic oscillator, as a result the first experimental evidence of the quantization of decay time is reported in a paper published in Scientific Reports.
(reprint from the former complexlight.org website)
Marco Ornigotti, Claudio Conti and Alex Szameit develop a rigorous theory of propagation invariant “X-wave” pulses with orbital angular momentum. These new photon states form and propagate in quadratic and cubic nonlinear media, and represent a novel tool for quantum information and entanglement. X-waves also allow a new 3D+1 representation of the propagation of light in nonlinear media as a spinning quantum fluid.
The fact that solitons may have a role in quantum gravity is intriguing.
In a paper in ArXiv, by Leone Di Mauro Villari, Giulia Marcucci, Maria Chiara Braidotti (all of them top complexlight students), and CC, a toy model concerning Hawking radiation by moving black holes is proposed.
Within a simple one-dimensional theory, based on solitons of the Sine-Gordon equation, the authors claim that Hawking emission may be extracted by the concomitant observation of gravitational and electromagnetic waves emitted by colliding black holes. The effect is due to the black-hole-velocity dependent emission spectrum (figure above), which results into an electromagnetic frequency chirp detected by the observer.
The fact that black holes are solitons is not very well known. Abdus Salam and others outlined this issue several years ago. Stephen Hawking predicted that Black Holes evaporate, and this is a quantum effect on classical gravity governed by the highly nonlinear Einstein-Hilbert equations.
Leone Villari, Ewan Wright, Fabio Biancalana and Claudio Conti report on the possibility that all types of classical solitons may evaporate in the quantum regime. A paper in the arXiv contains the theory on the exact quantization of the nonlinear Schroedinger equation: solitons emit a blackbody radiation spectrum at a temperature given by the same formula of Hawking!
This result is intriguing. On one hand, because it represents the first theoretical prediction of the Hawking radiation in a fully nonlinear quantum field theory. The standard Hawking theory relies on the quantization of a linear field in a curved background. The theory may hence provide insights for a true quantum gravity based on the complete quantization of the Einstein-Hilbert equations.
On the other hand, the result is also important because the Hawking radiation from a quantum soliton may furnish a novel highly tunable quantum source with many possible applications.