As of October 2026, can anything reliably send messages back? What do experts say?

"Proposed constructs such as Gödel's rotating universe, the Tipler cylinder, traversable wormholes, and the inner regions of Kerr black holes all theoretically allow CTCs-but only under unphysical assumptions such as infinite mass, negative energy, or cosmological rotation."

"Bell felt that the cure would be worse than the disease – he thought that this kind of “retrocausality” would conflict with free will, and with assumptions fundamental to the practice of science. (He said that when he tried to think about retrocausality, he “lapsed into fatalism”)."

"The chronology protection conjecture is a hypothesis first proposed by Stephen Hawking that laws of physics beyond those of standard general relativity prevent time travel ⁠ ‍ —   even when the latter theory states that it should be possible (such as in scenarios where faster than light travel is allowed)."

"Initial attempts to apply semiclassical gravity to the traversable wormhole time machine indicated that at exactly the moment that wormhole would first allow for closed timelike curves, quantum vacuum fluctuations build up and drive the energy density to infinity in the region of the wormholes."

"However, in 1997 a general proof was found demonstrating that according to semiclassical gravity, the energy of the quantum field (more precisely, the expectation value of the quantum stress-energy tensor) must always be either infinite or undefined on the horizon itself."

"Stephen Hawking conjectured that not only would the pileup of vacuum fluctuations still succeed in destroying the wormhole in quantum gravity, but also that the laws of physics would ultimately prevent any type of time machine from forming; this is the chronology protection conjecture."

"A definite theoretical decision on the status of the chronology protection conjecture would require a full theory of quantum gravity [ 13 ] as opposed to semiclassical methods."

"Semiclassical approaches to incorporating quantum effects into general relativity seem to show that the chronology protection conjecture postulated by physicist Stephen Hawking fails to prevent the formation of such rings"

"Matt Visser feels that there are reasons to think the semiclassical approach is unreliable here, and that a full theory of quantum gravity will likely uphold chronology protection."

"a Roman ring (proposed by Matt Visser in 1997 [ 1 ] and named after the Roman arch , a concept proposed by Mike Morris and Kip Thorne in 1988 and named after physicist Tom Roman ) [ 2 ] is a configuration of wormholes"

"Some physicists have presented arguments to suggest that a theory of quantum gravity (which would incorporate both theories) would eliminate those solutions in general relativity that allow for backward time travel (see: Chronology protection conjecture ) and thus make the Alcubierre drive invalid."

"beware: in relativity, any method to travel faster than light can in principle be used to travel back in time (a time machine)". In the next slide, he brings up the chronology protection conjecture and writes: "The conjecture has not been proven (it wouldn't be a conjecture if it had), but there are good arguments in its favor based on quantum field theory. The conjecture does not prohibit faster-"

"a 2025 follow-up by Achintya Sajeendran and Ralph modified the rotation profile so that some of these curves become spatially circular geodesics, which a freely falling particle could enter and leave from an ordinary flat region of spacetime; the authors present the construction as a theoretical model rather than a physically realisable one."

"Calculations by physicist Allen Everett show that warp bubbles could be used to create closed timelike curves in general relativity, meaning that the theory predicts that they could be used for backwards time travel ."

"A 2022 study by Carlos Barceló, Valentin Boyanov, Luis Garay, Eduardo Martín-Martínez and Jose Manuel Sánchez Velázquez re-examined this argument and found that in 2+1 and higher dimensions the locations at which infinite blueshift occurs are generically isolated points, so that the total energy accumulated need not diverge; the authors suggested that suitable choices of bubble shape and trajector"

"are nothing but clever deceptions."

"an efficient real-time prediction of an unpredictable future sentiment is impossible and affirmed it"

"ein Superdeterminismus (alles ist seit Anbeginn vorherbestimmt, keine Retrokausalität) zutrifft."

"verbally suggesting that the PSE is merely a “quantum delusion.” That is, it really appears, yet retrospectively only."

"No scientist now goes beyond the conclusion that something of the nature of ESP prob probably - ably probably can exist in certain persons if not in everybody"

"The findings are currently theoretical but could be tested experimentally"

"Using computer simulations, García-Pintos and his colleagues found that by knowing the original state of a quantum system and the outcome after a measurement is made, they could reverse the arrow of time"

"Die seriöse Wissenschaft erkennt die Parapsychologie als wissenschaftliche Disziplin gemeinhin nicht an und betrachtet sie als Pseudowissenschaft ."

"Creating these Hamiltonians in practice would require perfect measurements without information loss, says Murch, who was not involved in the study."

"This makes it unlikely that experimental research alone will be successful in the long run demonstrating PSI effects."

"Dennoch ist es der Parapsychologie bislang nicht gelungen, die Existenz der von ihr untersuchten Phänomene zweifelsfrei nachzuweisen, trotz des Einsatzes von auch in anderen Bereichen der Wissenschaft wie der Psychologie und der Medizin verwendeter Methoden."

"But the efficiency with which they collect that returning light to see how the system changes is only about 50 percent, he says, which means some details are fuzzy."

"None of the two experiments was significant."

"Präkognition : Empfangen oder wahrnehmen von Informationen zukünftiger Ereignisse, bevor diese eintreten und ohne dass sie aus den Möglichkeiten der Vergangenheit oder Gegenwart extrapoliert werden können."

"We discuss the controversial status of precognition and other anomalous effects collectively known as psi."

"Gutachter kritisieren, dass scheinbar erfolgreiche Versuchsergebnisse in der Psi-Forschung eher auf ungenauen Versuchsdurchführungen, schlecht ausgebildeten Forschern und methodischen Fehlern beruhen als auf echten Psi-Effekten."

"Moreover, it cannot be verified on each particle alone (only on pairs) and cannot be used for teleportation."

"However, this entanglement is of subtle kind since both the pre- and post-selected states were not entangled in the first place."

"We thus understand that quantum correlations underlie almost any experiment, but are only visible upon post-selection and grouping of similar results."