The Real Science of Time Travel Is Absolutely Fascinating

The Real Science Behind Time Travel

Since Reset involves time travel, I thought some of you might be curious about the current state of the science behind time travel. Can scientists send human beings back in time or forward into the future today?  No. Can scientists send photons, electrons, and quarks back in time or forward into the future today.  No.  But there are numerous experiments that have successfully sent photons, electrons, and quarks back in time in simulated space-time conditions.  And since the human body is composed of electrons, quarks (a proton is  made of 2 valence up quarks and 1 valence down quark and a neutron is made of 2 valence down quarks and 1 valence up quark), and photons (which are produced during energy metabolism pathways when free radicals react with nearby molecules), it is only a matter of time until scientists figure out how to extend the knowledge and technology that they have learned about time travel simulations at the quantum (sub-atomic) level to real time travel for human beings at the macro level. In my last post, I discussed the Multiverse and Parallel Worlds themes in JittiRain’s wonderful Boys Love drama, Vice Versa, I praised JittiRain because she got the multiverse science right. Incidentally, I would like to praise the writers of Back to the Future.  99% of the time travel science in that movie was also spot on. So, I will examine the current science behind real time travel with the hope that it will help you appreciate the time travel scenes in Reset.

How Einstein’s Relativity Equations Started the Science of Time Travel:  No matter how unpleasant it might be, it is impossible to understand time travel without some discussion of Einstein’s Theory of Special Relativity (published in 1905) and Einstein’s Theory of General Relativity (published in 1915) because everything we know about time travel comes from these two theories.  For example, in 1908, Hermann Minkowsky was the first to propose a flat four-dimensional space-time continuum for our universe in the absence of gravity but he based this theory on Einstein’s Theory of Special Relativity.  Here, three of the four dimensions are spatial in nature (x, y, z; length, height, and width) and the fourth dimension is time, t, which is a temporal dimension and not an additional dimension of space. Everything that we know about mass, energy, and the speed of light; E = mc², also comes from Einstein’s Theory of Special Relativity.  More importantly, everything we know about gravity comes from Einstein’s Theory of General Relativity.  It was Einstein’s Field Equations that proved that gravity is not a force of attraction between two objects (as Sir Isaac Newton proposed) but is actually a curvature in our space-time continuum caused by interaction with nearby objects of mass (stars, galaxies, etc.).  As for time travel, the postulates, theories, and equations that are most respected derive from exact solutions to Einstein’s Field Equations that formed the basis of his Theory of General Relativity.

Traversable Wormholes and Closed Time-like Curves: The two theories of time travel that are most promising, in my opinion, are Traversable Wormholes and Closed Time-like Curves.  Both these theories involve the curvature of our space-time continuum.  Most important, both theories result from exact solutions to Einstein’s Field Equations.  I will try to describe Wormholes and Closed Time-like Curves using a simple trampoline to represent the flat, four-dimensional, space-time continuum of our universe.  This model is known technically as Minkowski Space but most of us refer to it as “outer space”.  Now, let’s drop two 300-pound (136.1kg) bowling balls from a height of 10 feet onto the flat four-dimensional surface of our trampoline and observe the various geometric shapes that the flat four-dimensional fabric of our trampoline can take. I am only interested in the shapes of the Traversable Wormhole and the Closed Time-like Curve.  If the impact of the trampoline with the bowling balls results in the complete warping of the flat surface fabric of the trampoline so that it sags to the ground and folds over onto itself and takes the shape of a dumbbell, where the two bowling balls at each end of the dumbbell are connected by a thin six-inch long tunnel, this would resemble a Traversable Wormhole.  The two bowling balls on each end of our dumbbell are called “mouths” where a  “mouth” may be a black hole, a parallel universe, a star, or even something as small as a quark.  As you can see, the wormhole allows for travel back and forth between the two “mouths”.  Another possible geometric shape that could form as the result of the warping of the fabric of the trampoline by impact with the two bowling balls is a horizontal figure 8 curve which very closely resembles the infinity sign in mathematics. The geometry is created when the warped fabric of the trampoline forms a cone-shaped curve around each of the two bowling balls such that the vertices of the two cone-shaped curves meet halfway between the two bowling balls to form a point center.  This geometric shape resembles the infinity sign in mathematics and represents our Closed Time-like Curve.  Movement along this figure 8 loop clearly allows for time travel both forward into the future and backward into the past.

Traveling Back in Time via the Traversable Wormhole and the Closed Time-like Curve:  A wormhole is a theoretical tunnel through our spacetime continuum that connects two distant points (those points could be black holes, universes, stars, etc.).  While most wormholes are not stable, the Traversable Wormhole could be stabilized enough to allow us to move through it.  For example, the HD1 galaxy is 13.5 billion light years away from earth but the journey would take only a few minutes via a wormhole, from the perspective of the traveler.  If we wish to go back in time via a Traversable Wormhole, one of the two “mouths”  would need to be sped up to near the speed of light (e.g., subluminal) to slow down time compared to the other “mouth”. If we then wish to reverse the process and go forward into the future, one of the mouths would need to be sped up to a speed faster than the speed of light (superluminal) compared to the other mouth.  But is it possible to move faster than the speed of light in a wormhole?  Absolutely! For example, let's visit the HD1 galaxy again. HD1 is located 36 billion light years away from earth.  Since a light-year is the distance light travels in one year, it would take 36 billion years for light to reach HD1 from earth  if traveling the long way round; e.g., outside the wormhole.  But it would only take a few minutes for a human to reach HD1 from earth via a Traversable Wormhole.   That’s the beauty of a Traversable Wormhole.  It is traversable and it is reversible. But wormholes are susceptible to collapse.  So we would need a way to hold open the wormhole as we travel through it.  This requires negative energy density.  While negative energy density can be created in the lab, e.g., the Casimir Effect, it cannot be scaled up enough to hold open even a tiny wormhole.  A Closed Time-like Curve is also created by the warping of our space-time continuum and takes the shape of a horizontal figure 8; e.g. similar to the infinity sign in mathematics, ∞.  If we navigate around the figure 8 loop of a Closed Time-like Curve  in what is known as the creation of a lifeline or worldline (basically, your past, present, and future), it is obvious that we would eventually reach the same point where we started from (the infinity sign is just two round loops that touch each other at a point).  Effectively, we have “looped” or traveled back in time via a Closed Time-like Curve.

The Grandfather Paradox and the Closed Time-like Curve:  The problem with the Closed Time-like Curve (CTC) is that it violates the Causality Principle; e.g., its cause and effect are not always in the correct order; CTC also violates Stephen Hawking’s Chronology Protection Conjecture, which states that laws of physics prohibit time travel.  But the major problem with the Closed Time-like Curve is the Grandfather Paradox, where a young boy goes back in time and kills his own grandfather (an unmarried and childless adult at the time).  The death of the boy’s grandfather ends the lifeline of the grandfather and prevents the creation of a lifeline for the boy, e.g., he does not exist so how could he kill his grandfather?  But the opposite scenario is just as scary.  What if the young boy goes back in time but decides not to kill his grandfather so that the grandfather’s lifeline remains intact, e.g., he eventually meets a woman, marries and has a son.  That son then has a son of his own, e.g., the same nasty murderous little git that wants to go back in time and kill his grandfather again. Remember we are in a loop. This is the problem with the Closed Time-like Curve and it’s a big one! It invites time paradoxes.

Solutions To the Grandfather Paradox: Is there a way to improve the Closed Time-like Curve system so that it avoids creation of a Grandfather Paradox? I can think of several. 1) The Theory of Many Worlds tells us that we create a new parallel world (reality) for every choice that we make, much like the two identical daughter cells produced by the parent amoeba.  So there are two possibilities for the young boy traveling back in time to kill his grandfather.  Either he will choose to kill his grandfather in parallel Universe A and live out his life a killer, or he will choose not to kill his grandfather and live out his life in parallel universe B as a filial grandson. No Grandfather Paradox is created because each choice requires him to branch off the main Closed-Time-like Curve.  So the Grandfather Paradox is avoided.  2) Quantum Superposition.  This theory tells us that an object can assume many quantum states (realities) until the point of observation. Think about a coin flip at the start of a football game.  While the coin is spinning in the air, two states are possible, heads and tails. We won’t know the final state of the coin until it hits the ground.  The coin is said to be in a state of Superposition. The same is true of a qubit in a quantum computer, e.g., it exists as both 0 and 1 at the same time.  That’s why it can handle such large and complex calculations, it works at a much faster speed than other computers.  So if we apply this principle to a space-time continuum, e.g., there will be states (universes or realities) in superposition.  So whether the young boy choses to kill his future grandfather (state 1) or not (state 2), there is a finite probability for the existence of both states.  So the Grandfather Paradox cannot happen here. 3) Quantum Entanglement.  Entanglement involves the correlation of particles  where the state of one particle is dependent on the state of the other.  It creates permanent pairs of particles or even worlds that will be paired forever wherever. Let’s use the opposite spin states of an electron as an example. If we separate an entangled pair of electrons and place one electron in New York City and the other in Los Angeles, and, we reverse the spin of the electron in New York City from clockwise to counterclockwise, its entangled partner in Los Angels will immediately on its own reverse its spin from counterclockwise to clockwise so that the two electrons can once again remain in opposite spin states. This partnership of opposites holds even if the two entangled electrons are infinitely far apart.  Quantum Entangled pairs require a shared history and since parallel universes are simply branches off a mother universe, e.g. similar to the parent and twin daughter amoeba analogy discussed earlier, it might be possible to entangle two parallel worlds.  If this happened, the two universes would most likely be opposites, e.g., very much like what we saw in JittiRain’s Boys Love drama, Vice Versa. And if these opposite worlds exist, then there is a negative state universe where the grandson goes back in time and kills his grandfather and a positive state universe where the grandson goes back in time but does not kill his grandfather.  So no Grandfather Paradox is created.  4) Space-Time Remembrance.  Some scientists now believe that space-time remembers (not time as we usually think of it, but space-time). Seth Lloyd, a physicist at MIT in Boston, utilized Quantum Teleportation (the passage of information from one point to another via a quantum computer) to program photons to annihilate each other inside a Closed Time-like loop.  Guess what?  They refused to do it!   Both the arriving photon and the target photon either disappeared or were scattered when nearing each other.  Seth Lloyd theorized that space-time remembers what happened at every moment of the past and will not allow it to be changed.  Photons have a history in the space-time environment. Their history says that they do not willingly annihilate each other.  So in this experiment, Lloyd believes that space-time itself preserves the past. If it is true that space-time has a memory and preserves the past, it will never allow a young man to go back in time, kill his grandfather, and prevent his own birth.  

How Quantum Decoherence Effects Time Travel:  Quantum Decoherence is a principle of physics that states that the laws and equations that govern quantum (sub-atomic) physics may not apply to a macroscopic (human) environment.  This means that the mathematical solutions to Einstein’s Field Equations that predict time travel via a Traversable Wormhole and/or a Closed Time-like Curve at the sub-atomic level are susceptible to failure when applied to a macroscopic environment (humans).  This happens because some quantum phenomena; e.g., Quantum Superposition and Quantum Entanglement, are naturally weak and when forced to interact with strong forces like electromagnetism and molecular vibrations that occur in a macroscopic environment, will likely lose wave coherence and as a result, their wave equations are subject to fail. The science of human time travel is complex and it will likely require another Einstein to make it happen.  If only we could get our hands on a quantum-modified Flying 1981 DMC-12 DeLorean!  Anyway, I hope this post helps you to understand the current state of time travel in the real world and why it is so difficult to wrap our heads around it. I also hope this discussion of the science behind time travel helps you to understand the time travel plotlines in this wonderful drama (Reset).