A
Roman ring, in theoretical
physicsPhysics is a natural science; it is the study of matter and its motion through spacetime and all that derives from these, such as energy and force...
, is a configuration of
wormholeIn physics, a wormhole is a hypothetical topological feature of spacetime that is fundamentally a 'shortcut' through space and time. Spacetime can be viewed as a 2D surface that, when 'folded' over, allows the formation of a wormhole bridge. A wormhole has at least two mouths that are connected...
s where for each individual wormhole the
timeTime is a component of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify the motions of objects...
difference across its mouths is such that it may not allow a
closed timelike curveIn a Lorentzian manifold, a closed timelike curve is a worldline of a material particle in spacetime that is "closed," returning to its starting point...
(CTC), or 'closed-time loop'. If these wormholes and their mouths are arranged in a suitable configuration, a closed time loop will be again possible.
A
Roman ring, in theoretical
physicsPhysics is a natural science; it is the study of matter and its motion through spacetime and all that derives from these, such as energy and force...
, is a configuration of
wormholeIn physics, a wormhole is a hypothetical topological feature of spacetime that is fundamentally a 'shortcut' through space and time. Spacetime can be viewed as a 2D surface that, when 'folded' over, allows the formation of a wormhole bridge. A wormhole has at least two mouths that are connected...
s where for each individual wormhole the
timeTime is a component of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify the motions of objects...
difference across its mouths is such that it may not allow a
closed timelike curveIn a Lorentzian manifold, a closed timelike curve is a worldline of a material particle in spacetime that is "closed," returning to its starting point...
(CTC), or 'closed-time loop'. If these wormholes and their mouths are arranged in a suitable configuration, a closed time loop will be again possible.
For example, an
EarthEarth is the third planet from the Sun. It is the fifth largest of the eight planets in the solar system, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density...
-
MoonThe Moon is Earth's only natural satellite and the fifth largest satellite in the Solar System. The average centre-to-centre distance from the Earth to the Moon is , about thirty times the diameter of the Earth. The common centre of mass of the system is located at about —a quarter the Earth's...
wormhole whose far end is 0.5 seconds in the "
pastThe relativity of simultaneity is the concept that simultaneity is not absolute, but dependent on the observer . That is, according to the special theory of relativity, it is impossible to say in an absolute sense whether two events occur at the same time if those events are separated in space...
" will not violate
causalityCausality is the relationship between an event and a second event , where the second event is a direct consequence of the first....
, since
informationInformation as a concept has many meanings, from everyday usage to technical settings. The concept of information is closely related to notions of constraint, communication, control, data, form, instruction, knowledge, meaning, mental stimulus, pattern, perception, and representation.The English...
sent to the far end via the wormhole and back through normal space will still arrive back on Earth (-0.5 + 1) = 0.5 seconds after it was transmitted; but an additional wormhole in the other direction will allow information to arrive back on Earth 1 second
before it was transmitted.
SemiclassicalSemiclassical gravity is the approximation to the theory of quantum gravity in which one treats matter fields as being quantum and the gravitational field as being classical....
approaches to incorporating quantum effects into general relativity seem to show that the
chronology protection conjectureThe chronology protection conjecture is a conjecture by the physicist Professor Stephen Hawking that the laws of physics are such as to prevent time travel on all but sub-microscopic scales...
postulated by physicist
Stephen HawkingStephen William Hawking, CH, CBE, FRS, FRSA is a British theoretical physicist. He is known for his contributions to the fields of cosmology and quantum gravity, especially in the context of black holes...
fails to prevent the formation of such rings, although some experts such as
Matt VisserMatt Visser is a mathematics Professor at Victoria University of Wellington.Some of his research interests include General Relativity, Quantum Field Theory and Cosmology....
feel that there are reasons to think the semiclassical approach is unreliable here, and that a full theory of
quantum gravityQuantum gravity is the field of theoretical physics attempting to unify quantum mechanics with general relativity in a self-consistent manner, or more precisely, to formulate a self-consistent theory which reduces to ordinary quantum mechanics in the limit of weak gravity and which reduces to...
will likely uphold chronology protection.