Running head: How To Build A Time Machine: An article review
How To Build A Time Machine: An article review
Ronald Marish
Embry Riddle Aeronautical University
August, 2010

Abstract
This paper will review an article published in Scientific American’s September 2002 issue by physicist Paul Davies, “How To Build A Time Machine.” Topics included will be theory, application, and potential paradoxes which are involved in time travel. Also covered will be some methods by which human civilization could successfully achieve travel through time, some of which are more commonplace than most would think.
How To Build A Time Machine: An article review

Paul Davies is a well know figure in the physics community, who has authored many papers, books, and magazine articles. He is currently a physics professor at Arizona State University, who received his PhD in 1970 from the University College of London. In his article, “How To Build A Time Machine”, which was published in 20021, Davies discusses not only the possibilities of time travel becoming a reality, but also the methods by which we could achieve such a feat.
To understand time travel, one must first understand time. Considered the fourth dimension, time can be described in a number of ways, each with different meanings ranging from the clinically scientific to the purely philosophical. No particular definition is more accurate than another, but each can be applied uniquely to different theories about time. For this discussion, we will use Dictionary.com’s2 number one entry which defines time as “the system of those sequential relations that any event has to any other, as past, present, or future; indefinite and continuous duration regarded as that in which events succeed one another.”
We all already know that we can move forward in time. In fact we do it all day every day. We do not need to gaze at the second hand of a watch as it ticks by to know that we are moving forward in time, we simply know this because of the experiences we have inside of our brains. Our consciousness always moves in one direction, what we call forward, and we experience a moment or a thought very briefly before it is no longer a thought, but a memory. We can easily remember a thought or experience from a moment ago, but we cannot, despite great effort, remember a thought or experience from a few moments in the future. That is because for us, it has not occurred yet. This sets the stage for a consistently forward arrow of time, which all those in this universe experience, though at times at different rates relative to one another, yet still forward.
It is possible, and within our current technological grasp, to change the rate at which time passes relative to something or someone else. In fact, every time we step on an airplane we move through time faster than those on the ground. Another example, time in a rapidly moving spaceship passes at a faster rate when compared to time in a non moving spaceship or to someone stationary on earth (as in the Twin Paradox). To be precise, it is not the movement of the ship which changes the passage of time (because we can never be sure which ship is actually moving, just that they are moving away from each other) but the acceleration that the rapidly moving ship endures to get moving fast. This effect is called time dilation. Time dilation also occurs as a result of large gravitational fields.
An interesting correlation must be drawn here, and that is that acceleration and gravity are in many ways the same force. The effects of either are indistinguishable from one another, not only by humans, but by sub atomic particles as well. If you were standing in a closed box with no windows, you would not be able to tell the difference (neither by your own perception, nor by carrying out experiments) between being accelerated at 1g in any direction in space or whether you were stationary on the surface of the earth3. It is no surprise therefore to learn that large gravitational fields also change the speed at which time passes for an object in the field relative to an object outside that field.
So far we have established that it is possible to increase the rate at which time passes relative to someone else. This could effectively be called traveling into the future, or forward time travel. More specifically, we should call this time traveling into someone else’s future, because we would only be skipping ahead relative to their passage of time. Would then, it be possible to travel the opposite direction, and venture into our own past or the past of others? As Paul Davies states in his paper, this is quite a bit more problematic.
If the universe was rotating, reverse time travel could be possible. As the rotation drug space (and time) around with it, it would theoretically create a closed time loop, enabling someone to travel a great distance and reach their own past. We have now found out that the universe is not rotating by any measurable amount, so this theory has lost popularity over the years. However the rotating universe theory does show us that reverse time travel is not in violation of Einstein’s General Theory of Relativity.
Another highly theoretical prospect to travel backward in time involves an infinitely long cylinder rotating near the speed of light, which would also drag space, time, and light along its surface, therefore propelling you back in time. These methods are merely mathematical examples illustrating the possibilities of backward time travel, and by no means offer a practical solution. The most intriguing method for building a time machine involves physics we are only beginning to understand: Wormholes.
The most plausible method at this time to travel back in time is to transverse a wormhole. By creating or finding a wormhole, stabilizing it using negative energy, and moving one end near a high gravity source such as a neutron star or black hole, you might be able to enter one side and emerge from the other before you left. This undertaking would require vast amounts of energy, on a scale we can only conceive mathematically, and would depend heavily on our ability to manipulate our region in space at very fundamental levels. While theoretically possible, our understanding of the universe needs to be greatly advanced before we can begin to work out the specifics of such a device.
If one day we were able to figure out a method to unhook ourselves from the timeline and move about it as we please, we may find that paradox’s emerge as we try to alter the past, potentially with disastrous results. We are all familiar with the Grandfather Paradox, or the idea of going back in time and killing ones parents, and thereby disabling the possibility of being born. A more interesting and practical paradox is the Information Paradox. If someone travels into the past with the plans to build a time machine, and gives those plans to someone in the past who then builds a time machine and travels into the future, there is no way to determine where the original information came from.
The Information Paradox is what led Stephen Hawking to formulate his famous “Chronology Protection Conjecture”, which basically states that all causal loops would be prevented by some unknown means, perhaps the proverbial “hand of God”. More specifically, casual loops (paradoxes) would be prevented due to explainable phenomenon occurring for (seemingly) unexplainable reasons, yet always preventing backward time travel. One example would be if you were using a wormhole, it would not remain open long enough to penetrate because the instant it was opened, particles (and therefore matter) would begin flowing into it, causing a self reinforcing buildup as they traveled back in time - and already existed in the future, which would destroy the wormhole almost as suddenly as it was opened. This clearly violates the laws of thermodynamics, because matter would be created from nothing.
While the prospects of time travel are indeed intriguing, we must realize that if we ever able to alter the arrows of time, it will probably not be nearly as exciting as science fiction makes it seem. More likely we will prove what we already speculate, we cannot change the past in relation to the present, hence anything that matters in any way. Even if we could go back in time and undo some tragic event, we would be doing it in a space time dimension disconnected with the one we are familiar with, so it would effectively be pointless. While we know a great deal about time and space, there is exponentially more to learn, and as we continue to gain knowledge, we may uncover truths about time which we have not even graced our wildest imagination yet.

Personal Review
In addition to the aforementioned article, I have also read Paul Davies book, How To Build A Time Machine (2001)4 in which he goes into much greater detail than the brief article covered in this paper. However, for those who are not inclined to read an entire book devoted to the subject, the paper does do a good job outlining the theories involved, if only in a very broad sense. The main thing we know after reading this paper is that we don’t know enough yet to prove or disprove the possibility of time travel. We do know that relativity plays a major role in the passage of time, and that every individual who experiences time experiences it at their own rate, relative to their surroundings.
My personal thoughts are that we are all already time traveling into the future, one nano-second at a time. Because we are only ‘aware’ of the current moment in time, we can only experience one moment per unit of time, which the smallest unit is limited by the speed at which the electrical impulses move through our neurons allowing us to form a single thought. Therefore, we are all traveling forward in time, and while we may be able to change the rate at which we move through time relative to someone else’s time, as in the Twin Paradox, we ourselves are not actually going through our own personal time at a different rate than before. If we climb into a super fast spaceship in hopes of taking advantage of time dilation to see the future of the universe and human civilization unfold, we must be careful because we may find ourselves very lonely, far ahead of the expansion of everyone else’s time arrow, and we may need to wait millions of years for the rest of the universe to catch up.
On the other hand, I do not believe that from within our own dimension we could move backward in time because our consciousness only ‘exists’ in the current moment. Even if some device were constructed which by some means unknown to our current understanding of the laws of physics, allowed us to move backward in time, this would mean that our ‘thinking’ process and our consciousness would also run backwards which would negate the benefit of moving backward in time in the first place. We would still be experiencing one event per unit of time, then another event, then another event, which means that we are still experiencing a forward arrow of time in our own mind.
On the other hand, if somehow we could separate ourselves from our current space-time dimension, and look upon our current universe from another dimension, I do believe it might be possible to see the entire timeline at once, and possibly re-inject ourselves into the timeline at a previously un-experienced point. This may effectively move us backwards in time with regards to our previous timeline, however to us seeing this past would be our future, not our past. Any events in which we interfered with such as preventing our parents from meeting would have no effect on our current timeline; therefore we would never really slowly disappear from reality as in the movie Back To The Future (1985)5, - so, at least we have that going for us.

References
1 Davies, P. (2002). How To Build A Time Machine. Scientific American, 287, 50-55
2 http://dictionary.com
3 Hawking, S. (1996). The Illustrated A Brief History Of Time. Bantam: New York
4 Davies, P. (2001). How To Build A Time Machine. Penguin Group: New York
5 Robert Zemeckis (Director). (1986). Back To The Future [motion picture]. USA

FTL

Will we one day be able to breach the light speed barrier and travel to the distant cosmos by exploiting the laws of physics?

This is an issue which has puzzled me for many years, and left me with many unanswered questions. I find this question puzzling due to the vast distances between stars in the universe, and my own desire for knowledge of the many planets outside of our own solar system. The closest star system to our own is Alpha Centauri, which is a mere 4.2 light years away. Using the fastest rockets available today, it would take us over 20,000 years to reach. More interesting star systems are thousands of times further. To travel these great distances within a human lifespan, we must find a way to either breach or bypass the light speed barrier.
To figure out how this can be done, I wanted to first look at the speed of light itself. Albert Einstein’s most sacred work was his theory of relativity, in which he describes the speed of light as the ultimate upper limit of how fast anything can travel in the universe. But why? People used to think the speed of sound could never be broken. The reason light speed is different is due to the fact that as an objects speed increases, so too does its mass. This strange phenomenon is calculated with the famous equation, E=mc2. This means that as an object gains speed, greater and greater amounts of energy are needed to continue the object accelerating, all the way up to infinity. This is a common problem in particle accelerators, where we find that an electron traveling at 99.999% of the speed of light has more than 200,000 times more mass than an electron at rest, exactly as relativity predicts. So for now we must accept that by using conventional means, we cannot travel faster than the speed of light. Therefore we must look to the unconventional, quantum mechanics, for a way around this tedious barrier.
To gain some insight into circumventing relativity, I read an interesting book called “Quantum: A guide for the perplexed” (Al-Khalili, (2004)). In this book I learned about the Casimir Effect and how negative energy may hold the secrets of interstellar travel. In 1948 Dutch theoretical physicist Hendrik Casimir predicted that an unseen force lay in the void of empty space. This force, aptly named the Casimir Effect, was proven and measured many years later at the Los Alamos National Lab. This force is the manifestation of virtual particles containing negative energy which pop in and out of existence in the quantum vacuum of empty space. Might it be possible to harness this energy in large enough quantities to propel a spaceship to superluminal velocities?
I now turned to a paper that I found written by Miguel Alcubierre in 1994 titled: “The Warp Drive: Hyper Fast Travel within General Relativity.” In this paper, Alcubierre explains that instead of using negative energy to fuel a spaceship, you need to use this energy to bend the fabric of space, something that gravity does for us already. This would allow two distant places to be very close together for a short time. In this way you could travel virtually anywhere in the universe in almost no time at all. By surrounding your spaceship in this region of bent space, you could stretch the space behind you and contract the space in front of you, surfing in this distortion until you have arrived at your destination. The idea of curving space may seem impossible to some; however as I mentioned above, gravity does this all over the universe, and is responsible for planets orbiting stars.

For a better understanding of how gravity can warp space, I looked to a book by Stephen Hawking titled: “The Universe in a Nutshell” (2001). While studying this book I realized why we need the negative energy of the quantum vacuum, and not just regular energy to create a region of warped space. This is because negative energy exhibits antigravity in the same way regular energy exhibits gravity. We need them both to create the pushing and pulling forces which are responsible for expanding the space behind us (antigravity) and shrinking the space in front of us (gravity). Now that it seems like we may have found an answer, we need to find out if we can gather the massive amounts of energy required. Some opponents of this idea state that there is not enough energy in 10 billion universes for such a ‘warp drive’ (“Current Science,” 1997). However, as we continue to explore quantum mechanics I believe we will overcome that boundary in the near future.
According to Brennan (1997), the Heisenberg Uncertainty Principle allows us to borrow vast amounts of energy from the quantum vacuum for very brief periods of time. The shorter the amount of time, the more energy we can borrow. Theoretically we can borrow more than enough for which would be required to warp space in a small region, as long as it’s only for a few picoseconds. We may also be able to tap into the vast amounts of dark energy shown to exist by the WMAP satellite in 2007, which found that a full 72.1% of the universe is composed of this energy which we cannot see (map.gsfc.nasa.gov (2010).
Now all that remains is to bring these technologies together into a useable format. While the science may be understood behind these properties, we do not have the technology available to bring them to life as of yet. As our particle accelerators grow more powerful and our understanding of the universe increases, the answers may be closer than one might think. While the laws of physics allow us to bend space at our leisure mathematically, much research must be done before we will actually know the intricacies and pitfalls of the actual procedure. We may find our atoms fly apart while traveling through warped space, but then again, we thought the same would happen beyond Mach 1.