Every day we are constantly traveling through time. We’re constantly advancing into the future and everyone is having a different experience doing it. We have also looked back in time by analyzing the different celestial objects that are far off into our universe through cameras and telescopes. But what if we wanted to go further, go faster per se? How would we time travel into the future and past? It’s time to talk about what time travel really is and how it works, and some possible methods of accomplishing it.
So time travel is described as the action of moving between different points in time that is different from the present. It’s the movement through our fourth dimension, instead of our regular three spatial dimensions. It’s an idea that is mainly of fiction and has been utilized in many stories. The first instance of the idea ever recorded was in 9 BC in a Hindu text called “The Mahabharata”, which was an epic that revolved around two families battling for power during a war. The concept of the “time machine”, a device that would be utilized to time travel, came much later in 1881.
So, even though it may be a popular science fiction topic, is time travel actually possible? Well, the answer is both yes and no, and let me explain. So backward time travel, or traveling into the past, is currently deemed impossible, and many scientists are certain that this will never change unless a few conditions are met. Forward time travel, or traveling into the future, is something that is real and has been observed many times before, but probably not in the sense that you’re thinking about. All of this leads us to talk about Einstein and his good ol theories of relativity.
Einstein has two different theories of relativity that explain how our universe functions. General relativity is all about the geometry of our four-dimensional universe and is where the term “spacetime” originated. Special relativity, on the other hand, looks at the relationships of time, and has two postulates:
The speed of light doesn’t change for any observer
The laws of physics are the same in all reference frames
These two theories can give us more insight into how time travel could possibly work. Some solutions to general relativity can give us a method on how traveling backward in time could happen, and special relativity gives us more information about forward time travel actually happens. I’m going to go into more detail on how the latter works.
So because of special relativity and the concept of time dilation, objects that are in motion experience time more slowly than objects that are at rest. There have been many experiments that have confirmed this, including the Hafele-Keating experiment that tested this theory out through the use of atomic clocks and airplanes. So with this, time travel into the future is technically real, though it's really only a small one-way trip and isn’t necessarily as controllable as one may have imagined.
Now let’s get into some of the paradoxes that can occur with time travel. Many scientists believe that backward time travel will be impossible because of this issue of going back into a time period and affecting information in a way that would mess up the present.
Grandfather Paradox: This is something that investigates what happens when you mess with the past. Say you had some sort of method of time travel, and you decided to travel back far enough to when your grandfather was a teenager. If you killed your grandfather as a teenager, this now prevents one of your parents from being born, which also means that you shouldn’t technically exist. This leads to an extreme change to the present, because how exactly can you exist when you don’t technically exist? This paradox can technically apply to many actions taken in the past, and it leads to the potential for huge changes in the future that is impossible to account for.
Information Paradox: This one has to do with some issues that can arise when you travel into the future. Say you’re a scientist in your field that has access to some sort of way to time travel. You decide to go a few decades into the future and look at where science has progressed to. You happen to read this paper that talks about this amazing new discovery that changes the way we understand and think about our universe, and you take note of it. Now, let’s say you go back to the past, and you decide to publish a paper on this idea, which ends up being the paper that you read about in the future. This now becomes an issue because we never really know where the original information came from in the first place, essentially coming from nowhere.
Some physicists believe that regarding the grandfather paradox, we can avoid this issue by introducing the theory of a multiverse, aka many universes existing, or a parallel universe. But of course, this is all theory that hasn’t exactly been worked out. Also, there is this idea that with backward time travel, we can avoid any issue by letting people not have the ability to actually change anything that has happened but instead just observe it. I think an interesting idea would be to not allow people to change any aspects of the past or future and then wipe their memory of everything they saw so that it has no chance of affecting the future.
Now, let’s talk about some methods of time travel, concrete ways of traveling through the fourth dimension.
Rotating Black Holes
So like I mentioned in my last post, black holes could possibly act as a portal to another area of the universe. It is thought that a large and rotating black hole would allow for the much easier passage for a spacecraft traveling through, and there was a paper published in November 2018 that studied this. Basically scientists created a model that simulated the effects of a huge rotating black hole, similar to Sagittarius A* that is at the center of our galaxy, on a spacecraft trying to travel through it. It was discovered that the spacecraft wouldn’t necessarily experience any large, detrimental effects upon passing through the black hole’s horizon, and possibly have maybe no effects whatsoever.
As I mentioned in my last blog post, wormholes could possibly allow us to travel at speeds greater than the speed of light. Check it out to learn more!
This is something first pitched by Frank Tipler and is definitely a really interesting but wild idea. The idea is that you would take some sort of material that is 10 times the mass of the sun, squeeze it, roll it into a very long but dense cylinder, get it up to speed, maybe around a few billion revolutions per minute. Then, a spacecraft would be able to travel around the curve of this cylinder, aka a “closed timelike curve”, and this would act as some sort of passageway into different time periods of our universe. It is definitely something that would take such advanced technology that we can’t imagine right now but is super cool nonetheless.
As mentioned before, time machines are a transportation system that people would be able to utilize and get them to time travel. There has been this idea of creating a time machine through the use of exotic matter, which has what we call negative mass, a theoretical concept that exerts a negative pressure, basically pushing everything away from it. We could use its “negative energy density” aspect to help us move in the opposite time direction, though this is of course just an idea since we have yet to observe this type of matter.
Going into Stasis
This may seem like a copout answer, but it is somewhat true. If we were to put our life on pause and awaken it at some point in the future, that technically could count as time travel. This could happen through suspended animation and cryogenics, which is a way of freezing up your body and stopping it from functioning in a sort of way. You would still look the same and feel the same once you awaken in the future, and your body wouldn’t have aged, but you would have moved through time.
Despite all of this, you shouldn’t expect time travel to be coming to a store near you anytime soon. There is still so much information to look at and understand, and it may even turn out that all this information points to it just being completely impossible. But, it still is a superb concept to read and wonder about!