Astronomy Photos ByAcian



Author: Samantha
Ever since I was small I was heavily influenced by the cartoon—Doraemon, that it made me believe we can travel back and forth on timeline, simply with a time machine. My parents referred me as crazy after they heard my idea. Well, why not? Why must it be crazy?

To solve my questions and confusions, I got addicted to those thick physics reference books with born-to-be-boring covers. I flipped them over and over, and found my answer—several theories mentioning how to time travel.

1. Single trip—travel to the future
It is different from what people expected for a real time travel, as you can only travel to the future but not back to the past. This theory is well supported by Albert Einstein’s both Special Relativity and General Relativity. As he had mentioned, time can be extended or suppressed, depending on the relative velocity between the observer, or the gravity.

To explain the velocity one, I would get this with an brilliant example. Let’s say, if there is a pair of twins, Samantha and Pinky, Samantha travels to outer space with 99% speed of light; while Pinky stays on earth. After 20 years passed on earth, Pinky grows 20 years older; while Samantha grows nearly 3 years older only. If the spaceship never returns backward, both Samantha and Pinky would see each other’s clock runs slower while themselves’ ones run normally. If the spaceship turns backward and get back to the earth, from Samantha’s perspective, she sees her clock runs normally while Pinky’s clock runs faster; Pinky would also find her clock runs normally but slower for Samantha’s clock. Simply speaking, time depends on the speed of the observer. In that way, it can be said that Samantha travels to the “future” of the earth.

According to Einstein’s General Relativity, gravity can twist space-time to a certain extent. When the gravity of an object becomes larger, the observer on that object would see time runs faster in other places; you may say time tends to run slower on that object from an observer’s perspective from other places. For example, if the radius of earth is reduced to 0.9mm with mass unchanged, making a super high density, the gravity will be so large that even time would stop, just like a black hole, absorbing everything including light (some high-energy radiation can “escape”).

2. Round trip—travel back to the past and go to the future
Well, it it exists, just use a wormhole. It is a linkage between different spacetime curvatures, or you may say a pathway. To create a wormhole, there are two proposed ways.

First, within the spacetime that looks like smooth, there are uncountable numbers of quantum foams caused by spacetime turbulence. Wormholes may exist in these quantum foams. However, the size of each spacetime foam is extremely small; its radius is around 10^-35m, and they are very short-lasting, so it is somehow quite impossible to get through the wormholes. But some scientists suggested that we can throw exotic matter (if it exists) into the spacetime foam to extend its lifespan and enlarge its size, until it is large enough to allow a person’s entrance.  

Second, we can twist the spacetime and fold them together, then create a wormhole to link the two spacetime curvatures.

Okay now even assume that you are technically able to create a time machine, that wormholes do exist plus they can be manipulated by scientists, there are still problems ahead remained unsolved. For example, what would happen if a man goes back to the past and killed his mum? Would he still exist? Some scientists hypotheses “Parallel Universe” theory to explain it, that at the moment when the man killed his mum, a parallel universe would be created, in which both his mum and himself would not exist in there. Also, what would happen if one goes to the future and copied his future essay? Where does this essay originate from? These are the biggest questions in my mind.

Apart from the logic, some scientists proposed that for time travel, we have to have equal exchange of energy between the two spacetime curvatures, or else chaotic and destructive results might appear.

So, can we possibly travel freely on the timeline as we proposed? The answer remained a mystery. Personally, I believed we can as there are some fields in physics that are still untouched at the moment, that may explain all our confusions. Well if one day there is a guy on street telling me he comes from the future, I think I would be so thrilled to take a picture with him instead of getting scared away LOL.