A black hole is universally agreed upon to crush anything entering its opening, making travelling through one impossible. However, there is a special type of black hole theorized by mathematician Roy Kerr called the Kerr ring. The Kerr ring forms like any other black hole when a star collapses in on itself. What distinguishes it from other black holes is that it rotates, because the star that formed it was also rotating. Kerr believed that the rotation would prevent this form of black hole from having infinite gravitation at its core, allowing for objects to possibly pass through. If Kerr rings exist, passing through them could lead to another time in the past of future, or maybe even another universe.
Einstein-Rosen bridges, more commonly known as wormholes, are based on Albert Einstein’s general theory of relativity, which says that mass curves space-time. Imagine a sheet of paper held in a U-shape. There is a space between the two halves of the U. However, you can bring the two halves together by pinching them with your index finger on one side of the paper and your thumb on the other. The U-shaped paper represents space-time. The two fingers pinching the paper together each represent large masses. Even though the masses are in completely different parts of space-time, if they are large enough, they can curve space-time so much that the two sides of the U are brought together, creating a wormhole that allows the jump from one point in space-time to another.
However, there could be a number of factors that make the wormhole theory impossible. Astrophysicist Stephen Hawking believes that wormholes could exist, but only in quantum foam, the smallest environment in the universe. In quantum foam, tiny wormholes could appear in and out of existence, linking different times momentarily. In the future, these tiny wormholes could possibly be artificially enlarged according to Hawking, allowing for time travel to become reality.
The implications of being able to travel through time would be huge. Of course, it will be a long time before we can actually travel time, if we ever manage to at all. But if a means of traveling time were someday engineered, our world would change completely. Many moral issues of whether or not we should travel to the past to make the present better would occur. Maybe saving the lives of people by preventing a war hundreds of years in the past sounds good, but it could also lead to drastic implications for the people of that present time. It begs of the question of if pursuing time travel is even worth it if we would not use it because of moral standards. Personally, I believe that any venture for the sake of learning is worth it, and this one sounds especially exciting.