To wear as a pendant, a simple 4mm-thick cord works well.
Time travelMain article: Time travel
The theory of general relativity predicts that if traversable wormholes exist, they can also alter the speed of time. They could allow time travel
This would be accomplished by accelerating one end of the wormhole to a high velocity relative to the other, and then sometime later bringing it back; relativistic time dilation
would result in the accelerated wormhole mouth aging less than the stationary one as seen by an external observer, similar to what is seen in the twin paradox
. However, time connects differently through the wormhole than outside it, so that synchronized clocks
at each mouth will remain synchronized to someone traveling through the wormhole itself, no matter how the mouths move around.
This means that anything which entered the accelerated wormhole mouth would exit the stationary one at a point in time prior to its entry.
For example, consider two clocks at both mouths both showing the date as 2000. After being taken on a trip at relativistic velocities, the accelerated mouth is brought back to the same region as the stationary mouth with the accelerated mouth's clock reading 2004 while the stationary mouth's clock read 2012. A traveler who entered the accelerated mouth at this moment would exit the stationary mouth when its clock also read 2004, in the same region but now eight years in the past. Such a configuration of wormholes would allow for a particle's world line
to form a closed loop in spacetime, known as a closed timelike curve
. An object traveling through a wormhole could carry energy or charge from one time to another, but this would not violate conservation of energy or charge in each time, because the energy/charge of the wormhole mouth itself would change to compensate for the object that fell into it or emerged from it.
It is thought that it may not be possible to convert a wormhole into a time machine in this manner; the predictions are made in the context of general relativity, but general relativity does not include quantum effects. Analyses using the semiclassical
approach to incorporating quantum effects into general relativity have sometimes indicated that a feedback loop of virtual particles
would circulate through the wormhole and pile up on themselves, driving the energy density in the region very high and possibly destroying it before any information could be passed through it, in keeping with the chronology protection conjecture
. The debate on this matter is described by Kip S. Thorne
in the book Black Holes and Time Warps
, and a more technical discussion can be found in The quantum physics of chronology protection
by Matt Visser
There is also the Roman ring
, which is a configuration of more than one wormhole. This ring seems to allow a closed time loop with stable wormholes when analyzed using semiclassical gravity, although without a full theory of quantum gravity
it is uncertain whether the semiclassical approach is reliable in this case.