How Does Time Travel Work? The Physics of Time, or the Weird World of Temporal Mechanics
Time means something different for everyone. It can be a reminder of our mortality to some and an opportunity to grow for others. But for most of us, we don’t realize that time is not only relative in a metaphysical way but also in a physical way. Yes, time has some interesting properties from the real world that you can use to back up your philosophical views. But would you really want to? Better read on and make sure that time is not turning its back on you.
Einstein and Time
Everything was just fine with time for the average person until the early 20th century. Albert Einstein published his Theories on Relativity and amongst its work was how it showed time to be relative to your reference frame. To clarify that, lets imagine you are on a train. When you look out the window, you see people going by while if you look to the inside of the train everyone seems to be moving nowhere. Of course, though you are moving forward to a person on the street while they are seemingly standing still. Depending on which frame you are in, the train or the street, your perspective is different. This differences can be applied to time as well, and Einstein expressed his idea in the equation t= to/γ where γ = [1-(v/c)2]0.5. The v is the velocity of the object in question, c is the speed of light, to is the time to someone standing still and t is the time the person who is moving is actually going through. The equation shows that if you are standing still, v = 0 and therefore γ = 1 so t = to. No surprise. But what if v approaches c? As you get faster and faster, γ gets closer and closer to 0 which means t gets closer and closer to infinity. So the faster you are moving then the slower you move in your frame, for someone outside your frame sees your time go by at a longer rate. You yourself would not notice a change in time. Weird, right? Welcome to relativity.
Time Doesn't Exist?
So time does have some counterintuitive properties already. But what if someone told you time does not exist? Sure, some people state that time is just a measurement that humans created to note the passage of events and that outside of our existence time is not real. It is ultimately a comforting construct. Well, sure you could supposedly argue for that, of course. But what if science had actually found out that time may not exist on some level?
Ferenc Krausz at the Max Planck Institute of Quantum Optics in Germany was measuring the leap electrons take when they jump from energy levels using UV laser pulses. He was attempting to measure beyond the Planck time, or the smallest length of time possible according to advanced physics. This happens to be 10-43 seconds. And how did Ferenc do? The jumps took 100 attoseconds, which to give perspective is 10-16 seconds. So while he did good, it was not close to the Planck time. And what is so special about that anyway? (Folger 78).
According to theory, nothing can happen below the Planck time because it doesn’t exist. Einstein’s equation doesn’t help us with this either and that is a part of the problem. Relativity and quantum mechanics are difficult to mediate with each other for one talks about the large scale while the other deals with the small. But in the 1960’s John Wheeler and Bryce DeWitt found a possible solution: the Wheeler-DeWitt equation. It works great to describe reality by successfully merging quantum and relativity but it removes time from it, something that is a hard pill to swallow. Still, many feel a universe without time is the best bet (79).
And they are not the only ones to propose a timeless Universe. Julian Barbour proposes that what we see as time is just the passage of moments called “nows.” All these “nows” exist all at once in “Platonia” (named after Plato, who was always wondering about the nature of reality). It is our passage from one "now” to another that creates the illusion of time. Anything that you remember is just a “record” of that particular “now” you experienced in “Platonia,” an arrangement of molecules and nothing more. Anything that we use to notate the passage of time like fossils or clocks are just objects is particular “nows.” Of course, it should come as no surprise that this idea is completely untestable as of now, so we should treat this with great skepticism (Frank 58, 60).
What Arrow of Time?
Now don’t go beating up scientists yet. They just want to develop theories that best explain our world, and it is through the quest to explain that we sometimes arrive at an idea we would least expect to. Like questioning the arrow of time. Why does time seem to only go in one direction and not backwards? Much math has shown that it is possible to yet we have not witnessed it happen. We only seem to see things go from point A to point B. But what if you thought of time as a transition from order to chaos? That is, what if it’s just a measurement of entropy. Then time would just be the passing of moments and would be a part of the universe which is governed by quantum physics and relativity. Those moments may be analogous to the tiny quanta that everything can be broken into. Those quanta have multiple wave functions and when witnessed fall into place. Similarly, time may also act that way. Once viewed it then falls into a state that we witness, hence why we see time as a forward progression (Folger 79, 83).
String Theory provides another viewpoint on this supposed arrow of time. It is another way to tie quantum mechanics with relativity, but it comes at an interesting cost: a reality governed by dimensions we may never be able to test for. While this would eliminate it from being a science, we simply do not know yet if we can or can’t find out. So why even consider it? If it can successfully relate those two seemingly irreconcilable sciences then it may help us understand the Big Bang, an incredible singularity. Before it, there was nothing according to our theories but Steinhardt and Turok, a pair of scientists, developed cyclic cosmology to perhaps change that. Our Universe is a Brane, a string theory term for a “3-D world in a higher dimension space.” It is not stationary but moves through the 4th dimension. This not only implies that there are other universe but that collisions between them can spark new Big Bangs as energy is released. Some observations from the cosmic microwave background seem to back this up for possible collisions can be seen imprinted on it (Frank 56-7).
Okay, so we may live in a multiverse. Where does the topic of time come back to this? Well, after Universes collide the energy released slowly becomes matter and the space between the colliding Universes increases post collision until it reaches a point where gravity pulls them closer and closer until another collision occurs. This is why we call this version of cosmology cyclic for it goes through familiar motions and events seem to repeat themselves on and on. We have an arrow of time that clearly goes forward now. And best of all, cyclic cosmology can be proven if the readings from gravity waves match predictions. Perhaps BICEP2 or some other study may prove or disprove this soon (57).
What about backward time? Can it exist? Yes, says Sean Carrol and Jennifer Chen. They started their work in 2004 and did not want the higher dimensions that come attached to string theory. Instead, they turned to inflation, which was a brief moment early in the Universe where space expanded rapidly, causing the Universe to be isotropic. It also happens to imply that we live in a multiverse, just like cyclic cosmology. But in this multiverse dark energy prevails and occasionally has “random fluctuations” according to quantum mechanics. It is those fluctuations that cause inflation. But nothing is to stop some universes from having forward or backward time because of the fluctuations causing each Universe to have its own set of rules. Some can start in low entropy and go to high (like our Universe) which implies forward time but the theory also says some can start in high entropy and go to low, which would be the reverse of what we experience. Hence, backward time may be possible (Frank 57-8).
Past, Present, Future?
While the above titles often are used by us to refer to a location in time, George Ellis felt they were not appropriate in terms of precision. After he started his doctorate at Cambridge in 1960, he began to look into Einstein's field equations, of which he had great talent for. He looked deeper into the equations and felt they implied a future that was like an unexplored land: already there and just needing pioneers. But if this is true, then we are predestined to act in certain ways, which defeats free will. After working a bit on this with Hawking, he left Cambridge in 1973 and went to his home in South Africa where he fought Apartheid until its end in 1994. Once that was done, her went back to the problem at hand: removing the philosophical implications from the future scope (Merali 42-3).
Ellis' main problem is relativity, so he found a way to modify it rather than toss it out (after all, it does have an outstanding track record) in 2006. In Ellis' revision, space is still 4-D but time is not infinite in all directions. What we call the present is just the outermost boundary of time and the past can influence the present but the future has no definition. Frames of reference are just the steps that are taken for information to be conveyed from one system to another according to Einstein but Ellis' spin on it is that the frame becomes a reality as the info is passed on. Ellis' work seems to remove a need for the future to ever exist anymore, but what he has done is made it an uncertainty aka a quantum event! A measurement of a situation is what causes the quantum possibilities to solidify into our reality of the present as a quantum collapse occurs. This would be huge, for it is no secret in the science community that quantum mechanics and relativity do not get along at all (44).
Something that all of this discussion of course circumnavigates goes back to the notion of time not existing. After all, we still do not know about what is beyond the Planck time. It would help if we could determine why time has to exist in the first place, which is a hard question to answer. We don’t know why it is a part of space-time. The entropy argument for time progressing forward works great – except for gravity, which brought us structures such as planets and galaxies. It brought high entropy to low, the reversal of what we can define time as doing. Some suggest using the moment of inertia of the Universe instead, or how the mass is rotating around. Scientists have been able to create equations that have the Universe go from a simple state to a more and more complex one (Lee). We got plenty of possibilities to investigate and more than enough time to work on them.
Folger, Tim. “In No Time” Discover: June 2007. Print. 78-9, 83.
Frank, Adam. “The Day Before Genesis.” Discover: April 2008. Print. 56-8, 60.
Lee, Chris. “One Arrow of Time To Rule Them All?” ars technica. Conte Nast., 31 Oct. 2014. Web. 19 Dec. 2014.
Merali, Zeeya. "Tomorrow Never Was." Discover: June 2015. Print. 42-4.
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© 2015 Leonard Kelley