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The theoretical study of time travel generally follows the laws of general relativity. Quantum mechanics requires physicists to solve equations describing how probabilities behave along closed timelike curves (CTCs), which are theoretical loops in spacetime that might make it possible to travel through time. [1] [2] [3] [4]
For instance, an object located at position p at time t 0 can only move to locations within p + c(t 1 − t 0) by time t 1. This is commonly represented on a graph with physical locations along the horizontal axis and time running vertically, with units of for time and ct for space.
A tautochrone curve or isochrone curve (from Ancient Greek ταὐτό ' same ' ἴσος ' equal ' and χρόνος ' time ') is the curve for which the time taken by an object sliding without friction in uniform gravity to its lowest point is independent of its starting point on the curve.
past-directed if, for every point in the curve, the tangent vector is past-directed. These definitions only apply to causal (chronological or null) curves because only timelike or null tangent vectors can be assigned an orientation with respect to time. A closed timelike curve is a closed curve which is everywhere future-directed timelike (or ...
The curve of fastest descent is not a straight or polygonal line (blue) but a cycloid (red).. In physics and mathematics, a brachistochrone curve (from Ancient Greek βράχιστος χρόνος (brákhistos khrónos) ' shortest time '), [1] or curve of fastest descent, is the one lying on the plane between a point A and a lower point B, where B is not directly below A, on which a bead ...
The vertical direction indicates time, while the horizontal indicates distance, the dashed line is the spacetime of the observer. The small dots are specific events in spacetime. Note how the momentarily co-moving inertial frame changes when the observer accelerates. time-like curves, with a speed less than the speed of light. These curves must ...
The problem of time is central to these theoretical attempts. It remains unclear how time is related to quantum probability, whether time is fundamental or a consequence of processes, and whether time is approximate, among other issues. Different theories try different answers to the questions but no clear solution has emerged. [6]
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).