Time and Time Travel

I was going to wait a bit but this section on Time and Time Travel seems to fit very nicely right here. John Wheeler, Nobel Laureate in Physics, stated “Time is what prevents everything from happening at once.” In the previous post, we saw that the basic unit of the universe is the interaction. That would mean that Dr. Wheeler’s statement is actually backwards. The fact that things cannot happen all at once is why we have time! Let’s look at one example from the realm of nuclear physics. Assume we have two distinct protons. Since they are distinct, they are some distance from each other. (If they were in the same place, then there wouldn’t be two different particles so they would not be distinct.) . When these protons exchange a photon, that photon must pass from one particle to the other. Since photons travel at the speed of light, there is an order imparted to interactions. First these two protons exchange a photon and then after they change state they can exchange another photon with another proton. Things do not happen at the same time because an interaction requires the exchange of something and that something has a speed less than the speed of light.

So things cannot happen all at once because the only way they can change is by interaction and the unit of interaction cannot travel faster than the speed of light. There is no need for time to keep things from happening at the same time. All that is required is a speed limit on interactions. There is actually a lot more going on within these interactions but we’ll get to these later. For now, I’d like to stay with time and causality.

Einstein’s work developing the theories of relativity (special and general) showed that things that appear to happen at the same time in one frame of reference could happen at different times in another frame of reference. An example is in order here. Since he could not move at speeds near the speed of light, Einstein had to use his imagination to do “thought experiments.” In one of his most famous experiments, he imagined a train that could travel at close to the speed of light. He had one person sitting in the middle of the train and another sitting at a train station. He imagined that as the train went by the station and the person in the middle of the train car was lined up exactly with the person at the station, two lightning bolts hit the front and beck of the car at the same time (according to the person at the train station). He asked the question, “Did the person sitting in the train see the lightning bolts hit the front and back of the train at the same time?” The answer is no, since the train is traveling so fast the person in the train is a little closer to the front of the train than the back so they would see the front bolt hit first and the second bolt hit a little bit later. Einstein deduced from this that people saw time differently based on their relative speed. This was an amazing insight, since up until then everyone believed that time was the same for everyone, no matter if they were moving or standing still

Now I’m saying that the there is no time at all! But I am saying that time is a human invention, not something that is inherent in the fabric of the universe. Time is completely derived from the theory of interactions. Humans have memory and can remember the way things were before and after a number of interactions. Humans created time asa way to measure the duration of the change. This means time is related to space, which is just what Einstein thought when he created the concept of space-time. Are there any observations that support this interpretation? The answer is yes.

We discussed Feynman diagrams earlier. For simple system (like the particle diagram from last week's post) when the system goes from one state to another we see that that as going forward in time so going back to the original state would be going backward in time. But we're not seeing time going backward but just an example of a system switching between two simple states. There is no time at all, just a very simple system. We’re seeing a system switch between two or three states so over a number of interactions, each state is visited multiple times so depending on how the system transitions, we could call one way to be forward and the other backward.

Is there a direction of time? Since there is no time, there is no direction to time. What we perceive as a direction in time is an illusion. We talked about simple Feynman diagrams that can be reversed and still make sense. What about a series of events like an egg falling off of a table and breaking? The actual number of particles and interactions in just this simple series of events is staggering. It only looks simple because of the way the universe organizes itself. (We’ll talk about organization and hierarchy a little later.) If you saw a movie of an egg falling off a table shown in reverse, you would quickly discern it was nonsense. That’s because our experience tells us that systems don’t “magically” go from a disorganized state (broken egg) to a more organized state (whole egg). That is the concept of entropy, which we’ll get to a little later on.

Is there a way to explain time travel? I believe the answers come pretty clear based on last week's post. There is no way to travel into the future, because there is no future to travel to. It’s sort of like looking at a blank piece of canvas and “seeing” the finished picture. There is no picture there until the artist puts brush and paint to canvas. The future is merely the state of the universe after a number of interactions so until the interactions occur, there is really no “there” to travel to. Travel to the past is not much better. What would it mean to travel to the past? It means you would go to a state that existed previous to a number of interactions. There is no way to easily re-create the state of any system, let alone the entire universe, so although not zero, the chances of re-creating the universe in a previous state is slimmer than slim. Even worse, if you were able to re-create the state of the universe and insert yourself into that universe, you are now part of this new universe. All interactions in this universe are now different, since you were not in the original past, so the new universe would evolve in a different way. There would be no way for you to “return” to the universe you came from, since we’ve also decided there is no way to travel into the future. You would be “stuck” in this past and move into the “future” just like all the others in your “new” old universe.

Summary: There is no time travel, except in our minds.