First of all, time is weird.

Let’s start with a basic thought exercise. Think about time and what it is. Now, try to come up with an explanation of what it is with the purpose of explaining it to a two-year-old. Now, take everything you know about time and attempt to make the best definition with the purpose of trying to impress a physicist. Both of these explanations will be greatly different. You know, a moment to moment explanation versus the duration of 9192631770 cycles of radiation corresponding to the transition between two energy levels of the caesium-133 atom.

Time is something that is understood by a toddler yet physicists still have a hard time agreeing on certain aspects of it.

The main reason time doesn’t have a set measurement is because it obeys the laws of General Relativity. When time is affected by relativity it’s known as Time Dilation. “Time measured along different trajectories is affected by differences in either gravity or velocity – each of which affects time in different ways.” So one second measured by two different people at different places moving at different speeds will measure that second slightly different.

An astronaut living on the International Space Station will experience time slightly different than us here on Earth. For every six months on the station, an astronaut will be 0.005 seconds younger than everyone living on the surface of the planet.

The difference of time on the ISS is mainly because of the speed that the ISS is orbiting around the planet. Yes, gravity does play a part, but its part is statistically insignificant.

The effect that speed has on time becomes really interesting if we could move close to seventy-five percent of the speed of light. Up until that point, the effects on time are fairly negligible, but once we pass seventy-five percent, the effects grow exponentially.

If we board a spaceship here on Earth and then travel faster than the speed of light to another planet, we could get off the ship and look back and watch ourselves get onto the ship. This is the most basic form of time travel. In this case, we are watching the actual past as it unfolds.

Also, because of the laws of general relativity, imagine a second spaceship that was watching us board the spaceship and then travel to the planet. If the distance from Earth to that planet was ten light years, and the ship was able to travel that distance at ninety percent light speed, then to the observing ship the trip would take eleven years. However, on the original ship, not only time but also distance would dilate resulting in the ship reaching the planet in less than four and a half years having traveled roughly six and a half light years!

Time is a very complex subject, and the deeper we get into time travel, the weirder and more complex it becomes.

In the movie Interstellar, two astronauts travel to a planet that has higher gravity and is orbiting a black hole very fast. There are several variables at work, but in essence, once the astronauts get back to the ship they left only three hours before over twenty years have passed for the astronaut who stayed aboard. The two astronauts essentially traveled several years into the future. Even though this sounds very science fiction, the movie was surprisingly accurate on this account.

So using science, traveling into the future is not only possible, it will become normal as we begin to explore the universe more.

Is it possible to travel into our past?

Before we venture into traveling back into the past let’s talk about the Grandfather Paradox. Let’s say you traveled into your past looking for your grandfather. Once finding your grandfather, you accidentally kill him before he was ever able to help bring your father into the world. If you did this, then your father wouldn’t have existed, and therefore you wouldn’t have existed and been able to kill your grandfather, to begin with.

The grandfather paradox is something that physicists have given a lot of thought and energy in thinking about. This paradox complicates what could be possible when it comes to time travel. Many scientists don’t believe time travel is possible because of this Causality. So to help simplify things I will introduce Novikov’s Self-Consistency Principle.

The Novikov Self-Consistency Principle says that if there is an event that could cause a paradox, then “the probability of that event is zero.” To put it simply, there would be no chance to cause a paradox. This principle is a simple theory that isn’t widely accepted.

The reason I wanted to introduce this principle is to simplify time travel. This subject is complicated enough before we start introducing anything that could affect timelines.

Using physics that we understand, the easiest way to travel backward in time would be through a wormhole.

A wormhole could potentially become a bridge between two points in time. This bridge between two points in time is known as a Closed Timelike Curve. Basically, a CTC is a loop in time where a physical object links two points in time. That physical object could either continue to move forward in time or move back into the loop moving backward in time.

It would be easier to simply walk into Mordor than to create a wormhole. First, we would have to create a wormhole. Then we would have to speed the wormhole up to the speed of light (or past it) and return it to its point of origin. The time dilation would result in an accelerated wormhole entrance aging less than the stationary one.

If speeding a wormhole up to the speed of light isn’t possible, then maybe we could just move close to a black hole were gravity would become so great that it would slow down time. Then we could move that wormhole entrance to our destination for our desired time travel.

However, there is a major flaw with using a wormhole when it comes to traveling back in time. That flaw is that you can only use that wormhole to travel back to the time of the original creation of that wormhole. It might be a good tool for our descendants to travel back in time, but it isn’t any help to us where we haven’t created this wormhole yet.

Unfortunately, a closed time-like curve is the closest thing we have to an accepted theory when it comes to traveling backward in time. So as of right now, it is not only possible (in a sense) we have already traveled into the future… but it doesn’t look likely that we will be able to travel backward.

It is possible that some new understanding and discovery will be made that will completely change our current understanding of time and make backward time travel possible.

There is another form of time travel that I haven’t touched on because it gets even weirder than the previous ones. This form of time travel would require us being able to open a door to another universe. Time would pass differently in different universes, and potentially this could be an effective way to travel forwards in time.

But traveling to other universes could potentially open up the way for traveling back in time also. If we stepped into another universe close to a black hole (where time is going slower because of the high gravity) we would be in the past of that universe. If we left the black hole to a place were time was normal (comparatively) and then stepped back into our universe we would potentially be in our universe in our own past. Scientists argue whether this could actually work or not.

Time is often referred to as the fourth dimension right behind height depth and length. Our understanding of time is that it flows in one direction and cannot move backward. We do know, however, that physics isn’t always as set in stone as we would like. It is possible that another universe uses different physics altogether.

It’s possible that in another universe time moves in a different direction altogether. To beings in that universe and us as we were there visiting, it would appear to be moving forward, but compared to our own universe could be moving backward. If this were the case, then we could apply our known understanding of how to speed up time, to move quickly backward in time. Once we went back to the desired point, then we could return to our universe in the past.

Moving further into the obscure, the movie Source Code was a movie where Jake Gyllenhaal’s character’s consciousness was placed into the body of another person to live out his last eight minutes of life in an attempt to find out who bombed a train.

Would it be possible to send your consciousness back in time?

This is a tough one… First, what is our consciousness? Our brain is a three-pound mass of fatty tissue made up of about eighty-six billion brain cells called neurons. One of the most popular belief of how a memory is stored is a line of neurons that make up a network and fire all at the same time. Each time a memory is recalled that network of neurons fires together.

Scientists have already been able to activate specific desired memories by tracking individual parts of the brain and stimulating them. Potentially, in the future, we could create a map of an individual’s brain which would contain all of that person’s memory. Scientists already have a name for what this map would be called, a Connectome.

Once we are able to create a connectome of a person’s brain, we could copy and transfer that to any computer.

Downloading memories is within the realm of possibility. Now, what about uploading?

That’s a little trickier.

Brain plasticity allows for the brain to rewrite itself to remove some memories and rewriting others over them. We have seen evidence of this from patients who have recovered from traumatic brain injuries. Some patients need to learn how to walk and talk all over again after traumatic events. Sometimes old memories are salvaged but need to be rewritten to make the memory make sense. Often in these cases, the patient has slightly different feelings about the loved one because of the rewriting of the memory.

Using the brains plasticity along with Optogenetics (artificially stimulating a neuron by injection of algae and light) the physical neurons could be changed to accept a memory. The biggest problem would be getting the memory in place once the neurons were changed to accept them.

As of right now, there are a few theoretic ways that we could upload those memories, but none of them are highly likely to succeed.

Also, because of our brains plasticity, the introduction of a single memory would look and feel foreign to its host. And because of how different it is, it would probably be erased and written over with new authentic memories. Likely the only way to have a successful memory transfer would be a complete transfer were there were no leftover memories only the copied ones. But that was our plan all along, right?

This is all well and good, but does a lifetime of memories make up the consciousness? That is a philosophical question that I can’t even pretend to guess at.

For the sake of this article, let’s say that our connectome has everything in it needed to be a consciousness. Could we take this digital courteousness and send it through time with the purpose of uploading it into another person’s body?

If quantum physics have thought us anything, its that physics begin to break down and do strange things the smaller we get.

Quantum physicists have already observed the teleportation of matter on the quantum level. There have also been several scientific articles describing the phenomenon of time traveling particles. I haven’t read any of these articles so I can’t vouch for them, but it’s not too hard to imagine that digital information, because of its simplicity compared to a complex biological being, would be much easier to send through time. Not as easy as a quantum particle, but still easier.

Sometime in the future we potentially could send a connectome in the form of information back or forward in time. We could use any of the methods we covered in this article but it would take less energy.

But then we run into another problem. Once we get the information back in time, how do we upload it into the new host body? We don’t have to travel too far back before we don’t have any computers (the mid to late 1930’s (depending on your definition of a computer (wow, it’s almost like I broke the fourth wall within a fourth wall break (that’s a Dead Pool reference)))).

Here we run into pure science fiction. Currently, the only theories that we have involving the uploading of memories include the use of computers. Without the use of a computer. A science fiction author could make write a good novel where a conscious was sent back in time and the person woke up knowing what happened but not explain anything to the reader. Stuff like this happens all the time and allows us to enjoy things that aren’t plausible in books, movies, and tv shows. But things don’t work like that in reality. We can’t just leave out the hard parts hoping that things will work out.

So lets sum things up. Is time travel possible? Traveling forward through time is possible. Traveling backward in time, well things get very complicated there. Currently, we don’t have any solid evidence that traveling backward in time is possible. But there are strongly supported theories that support the idea that it would be possible.

Something else we should be thinking about is should we allow time travel if it ever became a possibility? Even small seemingly insignificant changes could easily lead to major changes in timelines.

Have you heard of the Butterfly Effect?

If I traveled back in time to be a “time tourist” my presence could cause someone to be slightly later in the timeline simply because they would have to step around me while I sought the sights. That slight delay could mean they wouldn’t get a specific taxi, or missing a bus, or getting water splashed on their shoes from a passing car or any number of other possibilities. Those changes could mean the difference in getting or keeping a job, meeting specific people or being in specific moods. Each of these would lead to larger things that would continue to separate the two timelines further and further apart.

After several generations of this, we would see changes as large as people not being born, as well as massive differences in political and social events. After only a couple of generations, it’s possible that the two timelines would no longer have anything that matched.

If a time traveler changed time enough that a war occurred and thousands or millions died, would that time traveler be responsible?

Let me know what you think in the comments below.