Wormholes have long been a part of sci-fi tales and movies and thus, a centerpiece of pop-culture. Also, they have been one of the most fascinating time-traveling ideas.
In 1915 Karl Schwarzschild described space-time under the influence of a massive, uncharged, non-rotating, and spherically symmetric object –that we now understand as a Blackhole.
Later it was realized that in a certain coordinate system, the gravitational hole described by Schwarzschild’s solution was not the end and it continued even beyond just like a two-sided funnel.
Since all the energy and matter swallowed by the black hole eventually has to beam out, therefore, white holes may simply be the opposite end of black holes, connected by theoretical tunnels of space-time called wormholes. Such a multiple connected space-time could allow near-instantaneous travel across the universe.
Furthermore, they realized that it could too allow time- travel. It can be understood by imagining one side of the wormhole fixed at its position while the other one is being rotated in a circular motion at the speed of light then it’s clock would freeze compared to the other end. Therefore, when entering the non-moving end of the wormhole one would always be travelling back in time.
But the biggest question is how to make a traverse-able wormhole?
Kip throne and Michael Morris figured out some calculations that can keep the mouth of the wormhole open and allow travelling through it. But for all that we need is a type of exotic substance that works against the collapsing force of wormhole.
An exotic matter is one that has a negative energy density or we can say a substance that has a negative mass and thus negative gravity. But while passing through this region of wormhole one has to suffer the extremely high negative density which can be fatal. But in general, such exotic matter violates Einstein’s general relativity theory.
So, to overcome this limitation several different geometries have been suggested by Matt Visser such as a cubic wormhole, cylindrical wormholes, etc. which can keep the exotic matter out of the way of travellers.
Even those wormholes which do not need any kind of exotic stuff to keep them open are highly unstable and hopeless! Another idea is of using an already existing wormhole instead of creating one that might work according to John wheeler.
He explained how at microscopic scales the fabric of the space keeps varying. This might lead to tiny wormholes forming and dissipating in a fraction of seconds. All we need is the highly advanced technology that can pick off those tiny wormholes and magnify it into macroscopic scales. That’s maybe the reason why wormholes are still merely a part of only the sci-fi world.