If traversable wormholes exist, they could allow time travel. 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, or become "younger", 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.
One 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; [24] : It is more of a path through time rather than it is a device that itself moves through time, and it would not allow the technology itself to be moved backward in time.
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, [6] : and many physicists believe that the required negative energy may actually be possible due to the Casimir effect in quantum physics. In , 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, [42] or otherwise prevent information from passing through the wormhole.
However, in a 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.
A possible resolution to the paradoxes resulting from wormhole-enabled time travel rests on the many-worlds interpretation of quantum mechanics. In David Deutsch showed that quantum theory is fully consistent in the sense that the so-called density matrix can be made free of discontinuities in spacetimes with closed timelike curves.
A particle returning from the future does not return to its universe of origination but to a parallel universe. This suggests that a wormhole time machine with an exceedingly short time jump is a theoretical bridge between contemporaneous parallel universes. Because a wormhole time-machine introduces a type of nonlinearity into quantum theory, this sort of communication between parallel universes is consistent with Joseph Polchinski 's proposal of an Everett phone [49] named after Hugh Everett in Steven Weinberg 's formulation of nonlinear quantum mechanics.
The possibility of communication between parallel universes has been dubbed interuniversal travel. For a simplified notion of a wormhole, space can be visualized as a two-dimensional 2D surface. In this case, a wormhole would appear as a hole in that surface, lead into a 3D tube the inside surface of a cylinder , then re-emerge at another location on the 2D surface with a hole similar to the entrance. An actual wormhole would be analogous to this, but with the spatial dimensions raised by one.
For example, instead of circular holes on a 2D plane , the entry and exit points could be visualized as spheres in 3D space. Another way to imagine wormholes is to take a sheet of paper and draw two somewhat distant points on one side of the paper.
The sheet of paper represents a plane in the spacetime continuum , and the two points represent a distance to be traveled, however theoretically a wormhole could connect these two points by folding that plane so the points are touching.
In this way it would be much easier to traverse the distance since the two points are now touching. Theories of wormhole metrics describe the spacetime geometry of a wormhole and serve as theoretical models for time travel. An example of a traversable wormhole metric is the following: [52]. One type of non-traversable wormhole metric is the Schwarzschild solution see the first diagram :. The original Einstein—Rosen bridge was described in an article published in July For the combined field, gravity and electricity, Einstein and Rosen derived the following Schwarzschild static spherically symmetric solution.
Wormholes are a common element in science fiction because they allow interstellar, intergalactic, and sometimes even interuniversal travel within human lifetime scales. In fiction, wormholes have also served as a method for time travel.
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For more detailed instructions and a video demonstration see this page. The two entrances could then be brought together, but then one of the entrances would be in the past of the other, according to MIT physicist Andrew Friedman. To travel back in time, you'd simply walk through one end. When you exited the wormhole, you would be in your own past. There is currently no known way to construct a wormhole, and wormholes are purely hypothetical.
Although exotic matter is unlikely to exist, there may be another way to stabilize wormholes: negative energy. The vacuum of space-time is filled with quantum fields, the fundamental quantum building blocks that give rise to the forces and particles that we experience, and these quantum fields have an intrinsic amount of energy. It's possible to construct scenarios in which the quantum energy in a particular region is lower than its surroundings, making that energy negative at a local level. Such negative energy exists in the real world in the form of the Casimir effect, in which the negative quantum energies between two parallel metal plates cause the plates to attract, according to University of California, Riverside mathematician John Baez.
But no one knows if this negative quantum energy can be used to stabilize a wormhole. It may not even be the "right" kind of negative energy, since it's only negative relative to its surroundings, not in an absolute way. Wormholes might occur naturally at microscopic scales in the quantum foam , the roiling nature of space-time at the very tiniest of scales due to those same quantum energies. In that case, wormholes might be popping in and out of existence constantly. But again, it's not clear how to "scale up" those wormholes to sizes big enough for you to walk through, and keep them stable.
Paul M. He regularly appears on TV and podcasts, including "Ask a Spaceman. Live Science.
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