I originally posted this on my old website in November 2002.
I wrote this report for my Technical Composition class during my Freshman year at MSOE. I was actually curious to do a casual investigation into the possibility of time travel into the past ever becoming a reality, and figure I might as well do it for a grade. I was somewhat surprised by what I was able to find on the subject, without needing a full understanding of quantum physics and the associated complex mathematics. As it stands, I think it is at least a good basic introduction to the concept of relativity.
The Possibilities of Time Travel
By Robert West
Introduction
Time travel has been a dream of people ever since H. G. Wells wrote The Time Machine and a dream of scientists since Einstein created his theory of relativity and suggested that it might actually be possible. But is it possible?
Purpose
The purpose of this report is to analyze the possibility of traveling through time, either to the future or into the past, and determine if it is a goal worth pursuing.
Scope
This report will cover the following areas:
- Einstein’s Theory of Relativity & how it relates to time
- The possibility of traveling into the future
- The possibility of traveling into the past
- Experiments with the speed of light
- What is preventing further experimentation
Limitations of Research
Research on this topic was limited because almost all data on time travel is theoretical, and the mathematics and quantum physics involved in time travel theories is too advanced for anyone without a degree in physics to fully understand. Also, time travel has not been seriously studied until very recently, and therefore books on the subject are difficult to find. Many scientists have avoided time travel so their colleagues would not think less of them for considering it. Stephen Hawking has said, “A physicist working on the possibility of travel into the past has to be careful not to be labeled a crank, or accused of wasting public money on science-fiction fantasy” (“Time Travel”).
Data and Analysis
The Relative Nature of Time
Before Einstein’s theory of relativity, time was thought to be a constant throughout the universe. Einstein changed that by saying that time is relative. As an object’s speed increases, time slows down around it. A common example of this theory involves two twins. One twin takes off in a space ship and travels for a year at a speed near the speed of light, while the other twin stays on earth. When the first twin returns to earth a year later, the second twin has aged ten years (Davies) (“Time Travel”). In this way, according to Einstein, time travel into the future is possible. Speed is not the only way to change the speed of time. Gravity also affects time. Einstein’s general theory of relativity states that time and space curve in relation to the mass and density of nearby objects. An object’s mass and density determine its gravitational pull. Objects with greater gravitational pull curve time and space more. Time flows faster for GPS satellites in orbit than for us on earth, due to decreased gravitational forces. The mass of the earth has less gravitational affect on the satellites then it does on up because they are farther away. Within a black hole, where gravity is believed to be strong enough to crush any object to the subatomic level, scientists believe time stops completely (Davies).
Traveling To The Future
Does Einstein’s theory work? Will we ever travel to the future? Actually, people do it all the time. Airline passengers travel into the future every trip, but only by a fraction of a second, because their speed is only slightly higher then that of people standing on the earth. A 1971 experiment by Joe Hafele and Richard Keating proved this. They flew an atomic clock around the world and then compared it to one that had stayed on earth. The clock from the plane was off by 40 billionths of a second (“Time Travel”)
As for traveling hundreds or thousands of years into the future, we will have to wait until high-speed space travel becomes a reality. The time differential will become a fact of life for space explorers, as they will end up going into the future during every trip. But even though travel into the future is possible, we still have to worry about going back to the past.
Going Back in Time
Einstein’s theory of relativity shows us how to go into the future, but it avoids the concept of going backwards in time. Einstein never says that it is possible, but he never says that it is not either. The difference between going into the future and going back in time is that while you can use speed or gravity to change how fast time flows, it is still moving forward. To go back in time, you have to make time move backwards. The debate over time travel has divided scientists into two groups. One group believes it is impossible to travel into the past. The other group believes it is theoretically possible and has several possible theories for how it might be accomplished.
Theories
The Cylinder Theory
One possibility for traveling into the past suggests that a massive cylinder, rotating at half the speed of light, could provide a way into the past if it were infinitely long and dense enough, and if a spaceship could circle it (Stone). The density and speed of the rotating cylinder would curve time around it, so by circling it in a spacecraft, one could possibly travel back through time (See Appendix A). Just creating a cylinder large enough for the first theory would take far more resources then we could ever hope to create. Then it would have to be rotated at half the speed of light, a speed we are nowhere near achieving.
The Cosmic String Theory
Another theory, devised by Princeton astrophysics professor J. Richard Gott III, involves cosmic strings. Cosmic strings are theoretical strings of high energy incredibly thin and incredibly long. If a large enough loop of a cosmic string could be found and made to contract, the resulting density of the energy could be great enough to provide a way into the past (See Appendix B). Cosmic strings, however, like wormholes, are only theoretical and have never been observed. Gott himself admits that cosmic strings have never been discovered, and that a trip backwards one year would require a string with half the energy of an entire galaxy. Not only that, but the gravitational forces could create a black hole, making access to the gravitational forces needed for the trip inaccessible (Gott).
The Wormhole Theory
A third theory involves wormholes. In theory, a wormhole is a black hole that connects two distant points in space, due to the fact that a massive enough object with enough density could curve space and time enough for two distant points to connect, via the wormhole. According to physicists at Caltech, if one end of the wormhole moves at near the speed of light while the other stays in one place, the fixed end will connect to a time earlier than the moving end (See Appendix C). Such a wormhole has not been discovered, and the energy needed to create one artificially would be enormous. Still, this theory is the most probable, but it is still unlikely anytime in the foreseeable future. Wormholes have been created, but their openings are microscopic and only stay open for a fraction of a second. To keep a wormhole open large enough and long enough to enter requires negative density, which can be created by holding two electrically conducting plates incredibly close together in a vacuum. Negative density has been created in a laboratory on a small scale, but to create the negative density needed for the wormhole would require plates with mass over 200 times greater than the sun (Gott).
Exceeding The Speed Of Light
Einstein believed nothing could ever exceed the speed of light. Most scientists have agreed that the speed of light is the “speed-limit” of the universe, although some scientists still wondered what would happen if something did break the “speed-limit.” An experiment performed by the NEC Research Institute in Princeton New Jersey provides the strongest evidence for time travel into the past. This experiment involved sending a laser beam through a glass cylinder filled with cesium gas. The beam of light traveled 310 times as far as it could have at the speed of light, and actually exited the gas chamber before it entered it, ending up 20 meters past the chamber before it even entered it. The beam actually went back in time, proving that at least light can exceed the “speed-limit,” and go back in time. The scientists who performed the experiment claim that it is still impossible for any object with mass to exceed the speed of light, but the experiment still opens up many possibilities (Chandler).
Another experiment found a similar result with microwaves. Professor Guenter Nimtz split a single microwave signal in two directions, sending one half through the air and the other half into a barrier. An oscilloscope showed that a small part of the signal sent toward the barrier went through it and ended up ahead of the signal traveling at the speed of light. This is due to quantum tunneling, which based on the idea that, at the subatomic level, everything is based on probability and that something that might be impossible for us can happen on the subatomic scale. This is how some particles can appear on the other side of the barrier. Raymond Chiao has confirmed Nimtz’s results with experiments of his own. In his laboratory he has found that a single photon can travel at 1.7 times the speed of light with quantum tunneling (“Time Travel”).
Despite having similar results, Nimtz and Chiao disagree on what they mean. Nimtz believes he could send a message back through time with quantum tunneling. Chiao says he couldn’t. Chiao believes that because of the randomness that occurs at the subatomic level, the signal would not be a signal after traveling through the quantum tunnel. Both Chiao and Nimtz insist they are correct, but neither can fully prove the other wrong. Still, both their experiments show that the speed of light can be exceeded, leaving the possibility sending a message to the past, if not going there personally (“Time Travel”).
Conclusions and Recommendations
Reasons We Can’t Travel Through Time
No theory for time travel can even be tested for many years, possibly centuries or even millennia. Going to the future is possible, but making a trip of any significance requires speeds we can only dream of today. As we develop faster modes of travel, experimentation will become more possible. But any significant experiments will not be possible until speeds approach the speed of light. All experiments for travel into the past depend on either theoretical stellar phenomena, massive constructions in space, or a combination of the two. None of them violate the theory of relativity; therefore all of them could theoretically work if the circumstances needed for them could be created. However, all of the theories would require massive amounts of energy and materials. Because of this, many scientists believe time travel will remain a dream. Also, Stephen Hawking claims that an attempt to travel backwards in time would produce a buildup of energy that would tear space apart, however there is no evidence to support this (Stone). Physicists who believe in time travel have found theoretical loopholes for every argument presented by the opposite side, so the debate remains unresolved.
Conclusions
Time travel into the future is clearly possible, and will become a problem as space travel reaches higher speeds, as there will be no way to get back to the past after a long journey at high speeds. Traveling into the future is not a matter that needs additional study. It has been proven to be possible, and it will become more of a reality for coming generations as space exploration reaches speeds where the time differential becomes significant.
As for time travel into the past, it may be theoretically possible. Astronomer Carl Sagan says of time travel, “Right now we are in one of those classic, wonderfully provocative moments in science where we just don’t know” (“Time Travel”). I would have to agree with him. It has been discovered that light can travel backwards through time if it exceeds the speed of light, and several theories have been proposed to send matter back through time. However, the energy needed to test any theory will not be available any time in the foreseeable future. Time travel into the past, while it seems to be possible in theory, will have to remain a dream, possibly for millennia, until our technology becomes advanced enough to experiment with matter. Someday, we may know for sure, but that day is many years off.
Recommendations
As a result of this analysis, I recommend the following:
- Any experimentation regarding time travel should be put on hold until we achieve technology that is affected by time’s relative properties, such as the ability to travel at speeds near the speed of light.
- Upon achieving this technological advancement, experimentation with time should begin in order to determine if time travel into the past is possible.
Time travel is a dream that may someday become reality, however it is clear that no one alive today will see any significant trips into either the future or the past. Despite the fact that it remains out of reach, it leaves scientists with a goal that stimulates the imagination and reminds them that anything might be possible. While I do not think it is something today’s scientists should be concerned with, it is something that mankind should research when the time is right.
Appendices
Appendix A: Diagram of the Cylinder Theory
Appendix B: Diagram of the Cosmic String Theory
Appendix C: Diagram of the Wormhole Theory
Works Cited
Chandler, David L. “Speed of Light may not be the Last Word.” Boston Globe 20 Jul. 2000: Online. Proquest. 18 Jan. 2001.
Davies, Paul. “Star warps.” Forbes 30 Nov. 1998: Online. Proquest. 18 Jan. 2001
Gott III, J. Richard. “Will We Travel Back (or Forward) in Time?” Time 155.14 (10 Apr. 2000): MAS Online Plus. Online. EBSCO. 18 Jan. 2001.
Stone, Brad. “From here to there: The Physics of time travel.” Newsweek 16 Mar. 1998: Online. Proquest. 18 Jan. 2001
“Time Travel.” Nova. PBS. WGBH, Boston. 12 Oct. 1999. Transcript.
© Robert D. West: 2001, 2003.
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