Time travel is one of the classic fantasy and science fiction elements to drive a plot or create a story.
“But, uh, Mr. Meharg, doesn’t everyone already know time travel is bogus?”
Well, yeah, but that still doesn’t mean we can’t look at some of the science behind the topic, so today’s lesson is on time travel. There are basically two types of time travel, one traveling into the past, and two, traveling into the future.
Inuyasha: A Feudal Fairy tail
Sailor Moon Crystal
FYI- I am only a high school science teacher and not Albert Einstein, Carl Sagan, Stephen Hawking, or Neil Degrasse Tyson. So do forgive me if I keep things a bit simpler than you might like.
Time travel is impossible
Leaving the various theories written by physicists aside, there is one major reason why time travel is impossible, and one minor one. The major reason is something called the grandfather paradox. In simple terms the grandfather paradox means that time travel is impossible because you could theoretically travel back in time and negate your own existence. If this were to happen it would cause a paradox and it is the creation of the paradox that prevents time travel in the first place.
The second lesser reason why time travel is impossible is that according to Steven Hawking we have not seen any time traveling tourists in the real world at this time. Not that it hasn’t stopped Hollywood from using this idea.
Time Travel Tourism
Most of the talk of time travel being impossible has focused on traveling into the past because as you will see it is a bit different from traveling forward into the future.
Time travel is possible
As previously stated there are a number of rather complex theories regarding whether or not time travel is possible but there are two potential ideas. Under Einstein’s theory of relativity, it is indeed possible to travel to the future in certain conditions.
Let’s assume there are two people, the first one is standing on Earth and the second one is on a space ship orbiting Earth. At this point time is essentially traveling at the same speed for both of them. Once the spaceship leaves Earth things begin to change. The faster the second person travels the slower his time will travel relative to the first one. As the ship approaches the speed of light this effect will increase to the point that one year on the ship could be hundreds to thousands of years to the person on Earth. Thus, in essence the person will have traveled through time. This plays an important role in one of Makoto Shinkai’s early works, The Voices of a Distant Star. The story is that of two lovers separated by great distances as one is traveling near the speed of light to fight off an alien threat to humanity, while her boyfriend remains behind on Earth. Another perhaps more well-known example is Gunbuster, where some of the characters appear ageless due to this phenomenon.
Voices of a Distant Star
The closer a person is to a very large mass (planet) and by default the gravity the slower time moves relative to a person further away from the object’s gravity. This has been observed on the International Space Station, with each Astronaut aging 0.007 seconds for every six months they spend on the station. Thus NASA’s Scott Kelly has traveled to the future having aged 0.014 seconds slower than the rest of the people on Earth after his yearlong mission in space.
So for any of us old guys who remember the original DBZ, the hyperbolic time chamber, that doesn’t exactly work correctly.
The gravity inside the chamber is several times higher than that of Earth’s and continues to increase the further away you move from the entrance. So yes the room will cause time to move at a different rate when compared to the outside world, but it would be slower not faster. The people training inside the chamber would find time moving slower compared to the outside, not faster. Imagine one year passing outside for every day inside the chamber. Not exactly the best training tool.
Exceptions to the rule
Assuming that a method of time travel to the past was created, how could you avoid the grandfather paradox. The answer is multiple universes. What this means is that if you traveled back in time and ended up changing something, you would return to your original universe while the universe you traveled to is now moving on a separate path. A classic example of this comes from Dragon Ball Z, where Trunks travels to the past to save the future, only to find that his future did not change. Another example is in the manga finale of Negima! Magister Negi Magi where multiple universes were created due to the time traveling of Asuna, Evangeline, and Chao.
The second exception to the rule would be a causal loop. This loop is a type of self-fulfilling prophecy, where your traveling back in time causes the situation that allows you to travel back in time in the first place. Some examples of this include Martian Successor Nadesico, Sailor Moon, Haruhi Suzumiya, and Silent Mobius.
Martian Successor Nadesico
Time travel is currently impossible and likely to remain so, but there are more accurate ways to portray it than others. Time travel creating multiple dimensions or stable time loops are the two methods that fit the current knowledge of time travel.