Wormhole (simple version)

Wormholes are among the greatest mysteries of science. Such objects are hypothetical (they have never been proven), and were steamed from Albert Einstein's General Relativity equations. Essentially, wormholes are formed by two "mouths" and a "throat", which connect two points in spacetime, which would theoretically enable travel through space and time itself. However, when talking about wormholes (or any topic that involves more delicate matters), we must be especially careful not to fall into fiction and rather stick to scientific rigor.

Such objects are one of the science fiction favorites, being featured in several films, such as Interstellar, Star Trek, Donnie Darko, among others. In the case of Interstellar, there is a great deal of scientific rigor surrounding the film, which was achieved by the participation of the theoretical physicist Kip Thorne (who was also a close friend of Stephen Hawking).

Imagine an apple “inhabited” by a worm, which wants to leave point A on the surface of the apple and reach point B, opposite to point A, also on the surface of the fruit. If you walk through the shell, the shortest distance the annelid will have to travel will be the path described by the contour of the fruit. However, the worm has the possibility of a shorter path (a shortcut), which would be through the fruit. To cross the apple and reach the desired point, the invertebrate will have to dig, creating a tunnel/hole, and from that we have the analogy attached to the hypothetical cosmic objects.

Wormholes have different kinds of classification but more generally, we can divide them into intra-universe wormholes (whose connection leads from one place to another in the same universe) and inter-universe wormholes (which link one universe to another in a multiverse context, which also has no proof of its existence and remains hypothesized).

The Einstein-Rosen bridges, formulated by Albert Einstein and Nathan Rosen, have a very peculiar hypothetical component, the so-called white hole. In short, the white holes would be "inverted" black holes, since instead of attracting/sucking nearby objects they eject/launch objects from within them. Consequently, a property that illustrates very well the distinction between these two celestial bodies is that while in the black hole nothing can come out, once within its event horizon, in a white hole nothing can go in once out of it, regardless the energy applied trying to force the body into it. An Einstein-Rosen bridge is formed by a black hole (composing one end/mouth), the “bridge” (which replaces the singularity) and a white hole (composing the other end/mouth), which would give connection to a mirror universe with time "moving" backward from the previously "normal" universe. However, Schwarzschild's wormholes were later shown to be unstable by physicist John Wheeler, meaning that they would collapse very quickly, making the crossing impossible.

A wormhole is spherical in shape and can be simply viewed with the following intuitive thought: Imagine that you have a sheet of paper with two points marked P1 and P2. The sheet will represent the fabric of spacetime and the points are arbitrary positions in space. The shortest distance between P1 and P2 in the plane will be, by definition, a straight line. The wormhole has the effect of folding the fabric of spacetime, thus enabling the points to overlap so that the distance between them becomes much shorter (“shortcut”).

It is theorized the possibility of manipulation of a phenomena that occur in quantum mechanics, the so-called quantum vacuum fluctuations, which induce a negative energy density in certain regions over an interval of time, so that wormhole stability could somewhat be achieved.

As mentioned, our hypothetical object of study indicates the possibility of time travel, however, under certain restrictions. By causing a temporal dilation in one of the wormhole mouths, we cause one end to be “older” than the other. An observer crossing the “younger” opening will come out of the “older” mouth at a (past) time when the age of the oldest was equal to that of the youngest. As mentioned, there are conditions imposed, and it would not be possible to make a trip for any arbitrary time but only from when our wormhole had been “converted” into a time machine.

Despite being hypothetical objects that exist only in relativity equations, wormholes are nonetheless fascinating elements to study, with unique properties, providing inspiration to many science fiction writers.

Reference material: "A Brief History of Time" (Stephen Hawking) "Universe in a Nutshell" (Stepeh Hawking) / "The Science of Interstellar" (Kip Thorne)

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