A new analysis published on the arXiv preprint server by scientists V. Vilasini of ETH Zurich in Switzerland and Roger Colbeck of the University of York in the UK shows that causal loops do not stay in the field of theory , but could actually occur in more theoretical universes than previously expected. And it could be that also in ours.
What is a casual loop?
A causal loop is a classic time travel puzzle. To explain it simply, if you send information to the past, for example, you give the German scientist Albert Einstein the formula E=mc ² before he theorizes it himself, then he publishes it and you, for your part, look it up in a textbook and you find it as such, with him as its creator, you would create a situation where the information has no true origin. The new research paper shows that this type of causal loop is possible in more theoretical universes than previously thought.
In theoretical universes where this is possible , there is no need to resort to physics that breaks the precept that something must move faster than the speed of light in order to, say, send messages back in time (such as as many science fiction books, series and movies show us).
Physicists have found that causal loops, where two events separated in time paradoxically influence each other, are allowed in many theoretical universes, some of which share characteristics with our own.
Causal loops do not necessarily lead to dramatic paradoxes, but they do show that both the past and the future can be correlated in counterintuitive ways.
Will it be the same for our universe too?
Referencia: Impossibility of superluminal signalling in Minkowski space-time does not rule out causal loops
V. Vilasini, Roger Colbeck
Causality is fundamental to science, but it appears in several different forms. One is relativistic causality, which is tied to a space-time structure and forbids signalling outside the future. A second is an operational notion of causation that considers the flow of information between physical systems and interventions on them. In an associated paper, we propose a framework for characterising when a causal model can coexist with relativistic principles such as no superluminal signalling, while allowing for cyclic and non-classical causal influences and the possibility of causation without signalling. In a theory without superluminal causation, both superluminal signalling and causal loops are not possible in Minkowski space-time. Here we demonstrate that if we only forbid superluminal signalling, superluminal causation remains possible and show the mathematical possibility of causal loops that can be embedded in a Minkowski space-time without leading to superluminal signalling. The existence of such loops in the given space-time could in principle be operationally verified using interventions. This establishes that the physical principle of no superluminal signalling is not by itself sufficient to rule out causal loops between Minkowski space-time events. Interestingly, the conditions required to rule out causal loops in a space-time depend on the dimension. Whether such loops are possible in three spatial dimensions remains an important open question.
Comments:
4+4 pages. This work is based on the framework of arXiv:2109.12128, which is an update of the relevant parts of VV’s PhD thesis arXiv:2102.02393
Subjects:
Quantum Physics (quant-ph)
Cite as:
arXiv:2206.12887 [quant-ph]
(or arXiv:2206.12887v1 [quant-ph] for this version)
https://doi.org/10.48550/arXiv.2206.12887
