by Paige Harriss AP Physics 1 student
“A civilized man…can go up against gravitation in a balloon, and why should he not hope that ultimately he may be able to stop or accelerate his drift along the Time-Dimension, or even turn about and travel the other way?” H.G. Wells encapsulated popular interest in time travel through this quote and others in his novel The Time Machine written in 1895. Believed to be the first novel written about time travel, The Time Machine has been in print continuously since its initial publication and reveals our national intrigue in this extraordinary concept. More recently, time travel has been studied by physicists as a plausible theory – one that may or may not be within the bounds of modern physics. Albert Einstein, Nathan Rosen, and later Kip Thorne contributed to the idea of a black hole providing a portal to the past. Other recent theories also support the idea of time travel; however, an opposing viewpoint based on the grandfather paradox refutes the notion entirely.
The theory of a black hole providing a mode of time travel has long been suggested. Black holes have the ability to bend the space and time surrounding them to the point of breaking, creating a small rip. In 1935 Nathan Rosen and Albert Einstein theorized that this small rip could connect to a rip in another black hole, creating a bridge; the Einstein-Rosen bridge, that would provide a passage through which a time traveler could be transported into another dimension. However, there are disparages with the bridge. Too small for even an atom to fit through, these “wormholes” are unusable for a time traveler, and close so quickly even light would not have the ability to pass through to the other side. In the 1980s, Kip Thorne elaborated on the Einstein-Rosen bridge and theorized a way to use anti-gravity to hold the portal open long enough for a person to pass through. Anti-gravity, pushing apart the space around the wormhole, would be channeled in large amounts to hold the portal open. To supply these large reserves of anti-gravity energy, Thorne hypothesized the Casimir effect; that two metal plates in close proximity could eventually generate enough negative energy to hold open the portal. Lastly, to create a true time portal, Thorne theorized a way to desynchronize the two black holes so that time would run differently in each. By containing one of the holes in negative energy and somehow transporting it around the universe at the speed of light, the two holes would desynchronize, with one black hole existing in a different era than the other, but in the same location. True time travel would thus be achieved. Although one of the first extensive approaches toward time travel put forth, this elaborate theory has been doubted by some physicists.
Numerous alternative approaches have permeated modern time travelling physics research. In 1991 Princeton astrophysicist J. Richard Gott proposed the idea of a shoestring. These cosmic strings, formed since close to the beginning of the universe, would pass each other in anti-parallel directions, running at the speed of light. A time traveler would thus be able to wait nearby and enter in between these strings which have twisted space-time due to their infinitely long and incredibly dense structure. Edward Witten is at present developing his super-string theory, while Stephen Hawking has even proposed lining up infinite parallel universes to achieve time travel. It seems that even if such theories prove viable, the mathematics behind each is nearly impossible to solve. Physicist Michio Kaku, commenting on the superstring theory, stated, “At present, superstring theory is the leading candidate for such a theory (in fact, it is the only candidate; it really has no rivals at all). But superstring theory…is still too difficult to solve completely. The theory is well-defined, but no one on earth is smart enough to solve it.” Theories abound, and deeply committed physicists are convinced that eventually the mystery will be solved, though perhaps, not in their lifetime. There are also those who reject all propositions of time travel, doubting the possibility that even a future generation might find the key to a parallel universe.
The Grandfather Paradox presents an argument silencing any notion of time travel. Described as early as 1931 in various science fiction novels including Ancestral Voices by Nathaniel Schachner, published in 1933, and Future Times Three by René Barjavel in 1943, this paradox seems irreconcilable with the notion of travelling through time. The Grandfather Paradox presents the idea that if a person were able to travel to the past and then kill his/her parents, then that person would never have been born and thus it would be impossible to travel back in time in the first place. There have been responses to this paradox, such as the idea that the individual “would fail for some commonplace reason…her gun might jam, a noise might distract her, she might slip on a banana peel…” or that travelling in the past “merely creates a parallel universe.” So we are changing someone else’s past by saving, perhaps, Abraham Lincoln from being assassinated at the Ford Theater, but our Lincoln is still dead. A concrete answer to this fundamental complexity still has not been established. Clearly, modern mathematics must be more advanced before we are able to answer such paradoxes, or the disparagement between quantum mechanics and gravitational relativity; the fact that they “dominate in disparate domains, and…seem to converge only in enormously dense, quantum-size black holes,” must be resolved.
Even with the abundance of theories including the Einstein-Rosen bridge and superstring theory, numerous paradoxes still remain unanswered. The Grandfather Paradox will continue to discourage many from the seemingly irrational research of time travel, and, even in the event that time travel becomes possible, many will question the morality of attempting to change events of the past. However, current research on the topic has become more plausible, and it is clear that “our heirs, whatever or whoever they may be, will explore space and time to degrees we cannot currently fathom…creating new melodies in the music of time.”
Kaku, Michio. “The Physics of Time Travel.” Explorations in Science Official Website of Dr Michio Kaku RSS. N.p., n.d. Web. 17 Apr. 2016.
Koks, Don. “What Is the Casimir Effect?” The Casimir Effect. N.p., 2002. Web. 17 Apr. 2016.
Moyer, Michael. “The Physics of Time Travel.” Popular Science. Bonnier Corporation, 19 Feb. 2002. Web. 17 Apr. 2016.
Person, and Annalee Newitz. “Are We about to Reconcile Gravity with Quantum Mechanics?” Io9. I09, 07 Nov. 2013. Web. 17 Apr. 2016.
Pickover, Clifford. “Traveling Through Time.” PBS. PBS, 12 Oct. 1999. Web. 17 Apr. 2016.
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