Wormholes and Time Travel
Shortcut Through Spacetime
A short-cut through space time that exists because of the general
relativity. Traveling through a wormhole is faster than traveling at the
speed of light, which allows the possibility of time travel.
|General Relativity: Wormholes and Time Travel
Shortcut Through Spacetime - If Traversable Wormholes Exist, They Could Allow Time Travel
In physics and fiction, a wormhole is a hypothetical topological feature of spacetime that would be, fundamentally, a "shortcut" through spacetime.
A proposed time-travel machine using a traversable wormhole would (hypothetically) work in the following way:
One end of the wormhole is accelerated to some significant fraction of the speed of light, perhaps with some advanced propulsion system, and then brought back to the point of origin.
Alternatively, another way is to take one entrance of the wormhole and move it to within the gravitational field of an object that has higher gravity than the other entrance, and then return it to a position near the other entrance.
For both of these methods, time dilation causes the end of the wormhole that has been moved to have aged less than the stationary end, as seen by an external observer; however, time connects differently through the wormhole than outside it, so that synchronized clocks at either end of the wormhole will always remain synchronized as seen by an observer passing through the wormhole, no matter how the two ends move around.
This means that an observer entering the accelerated end would exit the stationary end when the stationary end was the same age that the accelerated end had been at the moment before entry; for example, if prior to entering the wormhole the observer noted that a clock at the accelerated end read a date of 2007 while a clock at the stationary end read 2012, then the observer would exit the stationary end when its clock also read 2007, a trip backwards in time as seen by other observers outside.
significant limitation of such a time machine is that it is only
possible to go as far back in time as the initial creation of the
machine; in essence, it is more of a path through time than it is a
device that itself moves through time, and it would not allow the
technology itself to be moved backwards in time.
This could provide an
alternative explanation for Hawking's observation: a time machine will
be built someday, but has not yet been built, so the tourists from the
future cannot reach this far back in time.
Albert Einstein Worm Hole
Is time travel possible?
According to current theories on the nature of wormholes, construction of a traversable wormhole would require the existence of a substance with negative energy (often referred to as "exotic matter").
More technically, the wormhole spacetime requires a distribution of energy that violates various energy conditions, such as the null energy condition along with the weak, strong, and dominant energy conditions.
However, it is known that quantum effects can lead to small measurable violations of the null energy condition, and many physicists believe that the required negative energy may actually be possible due to the Casimir effect in quantum physics.
Although early calculations suggested a very large amount of negative energy would be required, later calculations showed that the amount of negative energy can be made arbitrarily small.
In 1993, Matt Visser argued that the two mouths of a wormhole with such an induced clock difference could not be brought together without inducing quantum field and gravitational effects that would either make the wormhole collapse or the two mouths repel each other. Because of this, the two mouths could not be brought close enough for causality violation to take place.
However, in a 1997 paper, Visser hypothesized that a complex "Roman ring" (named after Tom Roman) configuration of an N number of wormholes arranged in a symmetric polygon could still act as a time machine, although he concludes that this is more likely a flaw in classical quantum gravity theory rather than proof that causality violation is possible.
Einstein's Theory of Relativity says that time travel is perfectly
possible — if you're going forward.
Finding a way to travel backwards
requires breaking the speed of light, which so far seems impossible.
But now, strange-but-true phenomena such as quantum non-locality, where
particles instantly teleport across vast distances, may give us a way to
make the dream of traveling back and forth through time a reality.
into a time machine and rewrite history, bring loved ones back to life,
control our destinies. But if we succeed, what are the consequences of
such freedom? Will we get trapped in a plethora of paradoxes and
multiple universes that will destroy the fabric of the universe?
A wormhole is, in theory, much like a tunnel with two ends each in separate points in spacetime.
There is no observational evidence for wormholes, but on a theoretical level there are valid solutions to the equations of the theory of general relativity which contain wormholes.
Time travel to the past is theoretically allowed using the following methods:
The first type of wormhole solution discovered was the Schwarzschild wormhole which would be present in the Schwarzschild metric describing an eternal black hole, but it was found that this type of wormhole would collapse too quickly for anything to cross from one end to the other.
- Travelling faster than the speed of light
- The use of cosmic strings and black holes
- Wormholes and Alcubierre drive
Wormholes which could actually be crossed, known as traversable wormholes, would only be possible if exotic matter with negative energy density could be used to stabilize them (many physicists such as Stephen Hawking, Kip Thorne, and others believe that the Casimir effect is evidence that negative energy densities are possible in nature).
Physicists have also not found any natural process which would be predicted to form a wormhole naturally in the context of general relativity, although the quantum foam hypothesis is sometimes used to suggest that tiny wormholes might appear and disappear spontaneously at the Planck scale.
It has also been proposed that if a tiny wormhole held open by a negative-mass cosmic string had appeared around the time of the Big Bang, it could have been inflated to macroscopic size by cosmic inflation.
The American theoretical physicist John Archibald Wheeler coined the term wormhole in 1957; however, in 1921, the German mathematician Hermann Weyl already had proposed the wormhole theory, in connection with mass analysis of electromagnetic field energy.