Friday, February 6, 2015

Wormholes and the Potential for Time Travel

Nearly every person at some point in his or her life has encountered the idea of time travel. Whether in movies, comics, novels, or TV shows, the concept of time travel is pervasive in popular culture. In all likelihood, you have spent nights falling asleep to questions like “is time travel possible” and “what would time travel be like?” For a long time, these questions only existed in the realm of imagination and science fiction. However, now there is scientific reason to believe that time travel may some day, albeit some day a very long time from now, be possible. The discovery that wormholes, which are essentially short cuts through spacetime, are allowed under Einstein’s Theory of General Relativity has given a scientific backbone to the idea of time travel. Wormholes exist in regions of spacetime that are bent so that two distant points come in very close contact and become connected via a tunnel, or wormhole, through “hyperspace” (an imagined space that exists outside of spacetime). If someone were to be able to move through a wormhole, they would actually be moving faster than the speed of light, since it would take light longer to travel through spacetime between the two points than for an individual to pass through the wormhole. Furthermore, if one opening of the wormhole were sped up to nearly the speed of light time would slow down at that opening, and once the opening came to a stop again it would have experienced less time than the opening that was always stationary. This, essentially, would permit the wormhole to act as a time machine. Since time is connected between the two sides of the wormhole, someone who entered the side of the wormhole that had been accelerated (and had experienced less time) would leave the stationary side at that same time (i.e. some time that was in the stationary side’s past); conversely, if someone entered the stationary side (which had experienced more time), they would exit the accelerated side at that same time as well (i.e. some time that is in the accelerated side’s future).

The concept of wormholes and their potential for time travel was first introduced in 1916 when Ludwig Flamm found a solution to Albert Einstein’s field equations that allowed for such an occurrence in nature. It was Einstein and Nathan Rosen, however, who in the 1930s first studied the idea of wormholes intensively. The “Einstein-Rosen Bridges” that the scientists modeled would be in existence only briefly. In fact, “the wormhole throat would flicker in and out of existence so quickly that nothing – not even light – would have time to get through” (Toomey). The gravity of the wormhole would be so great that it would accelerate radiation, causing the wormhole to nearly instantly collapse on itself, and making any kind of transversal impossible. After Einstein and Rosen studied wormholes and had obtained these findings, wormholes did not receive very much attention within the field of astrophysics.

In 1988, with the publication of “Wormholes, Time Machines and the Weak Energy Condition”, Kip Thorne and Mike Morris reignited interest in wormholes and time travel. Thorne and Morris presented a situation in which a wormhole could remain open, therefore permitting time travel. Thorne and Morris showed that if a type of “exotic matter,” which has a negative energy and exhibits a repulsive force, was placed in the throat of the wormhole, then the throat could be held open for longer periods of time, allowing passage through the wormhole and time travel. Essentially what Thorne and Morris had done was “turn science fiction into science” (Toomey). Since this 1988 paper, research has been done that has further changed the perception of wormholes. Physicist Matt Visser has illustrated using string theory that a traversable wormhole could exist without exotic matter, in which it is held open by negative mass cosmic strings.

While many types of wormholes have been hypothesized, there remains no evidence for their actual existence. There is evidence of objects in the cosmos collapsing in on themselves to form black holes, but not wormholes. While it is speculated that small wormholes may exist in the 'quantum foam' with throats less than 10-30 centimeters across, the most compelling evidence for them remains that their existence is allowed by the equations of general relativity. As Matt Visser has stated, the evidence for wormholes comes from the fact that “even though wormhole physics is speculative, the fundamental underlying physical theories, those of general relativity and quantum mechanics, are both well tested and generally accepted.” So as of today wormholes are entirely theoretical, and therefore the possibility of time travel is very distant. If we ever get to jump in a wormhole and travel through time and space like members of the USS Enterprise, it certainly will not happen for a very long time.

The New Time Travelers, by David Toomey
Black Holes, Wormholes, and Time Machines, by Jim Al-Khalili
“Time Travel and Wormholes: Physicist Kip Thorne's Wildest Theories,” by Calla Cofield
“What is a Wormhole?” by Nola Redd
“Wormholes”, by Dr. David Anderson
- Zachary Ettensohn