2 sci-fi concepts that are possible (in theory)

Wormholes

As a story-driver, the wormhole - a shortcut through space - seems to be a fictional concept. It existed long before sci-fi writers became familiar with it under its more formal name of an Einstein-Rosen bridge. It comes out of Albert Einstein's theory of general relativity, which views gravity as a distortion of space-time caused by massive objects. Theorizing that black holes have a direct connection to each other in 1935, Einstein worked with physicist Nathan Rosen. Wormholes grew out of this analysis.

In the 1980s, astrophysicist Carl Sagan decided to write a sci-fi novel, he began considering the idea of actually traveling through a wormhole. Physicist Kip Thorne developed a rapid method for traveling interstellar distances based on Sagan's advice, according to the BBC. Thorne duly devised a way — possible in theory, but highly improbable in practice — that humans might achieve interstellar travel by traversing a wormhole unscathed. After being adapted into a film with Jodie Foster in the main role, Sagan's book "Contact" (Simon and Schuster, 1985) was published. 

Scientists have come up with a better way to construct wormholes than Thorne's original proposal, despite wormholes never becoming the simple and convenient transport method portrayed in movies. The new generation of gravitational-wave detectors may also help locate wormholes if they already exist in the universe.

Warp drive

Getting from A to B much faster than today is a fundamental requirement for most space adventure stories. Wormholes aside, there are multiple stumbling blocks to achieving this with a conventional spaceship. Fuel usage is enormous, acceleration is crushing, and there is a strict speed limit enforced by the universe. This is the speed at which light travels — precisely one light-year per year, which in a cosmic context isn't very fast at all. 4.2 light-years from Earth lies Proxima Centauri, the second-closest star, while 27,000 light-years separate the galaxy's center.

It only dictates the maximum speed we can travel through space. Fortunately, there is a loophole in the cosmic speed limit. As Einstein explained, space itself can be distorted, so perhaps it's possible to manipulate the space around a ship in such a way as to subvert the speed limit. Space itself would be moving faster than light, but the spaceship would still travel slower than light through the space around it. 

As early as the 1960s, the "Star Trek" writers envisioned a warp drive that could quickly travel over vast distances. But to them it was just a plausible-sounding phrase, not real physics. In 1994, Live Science's sister site, Space.com, reported that Miguel Alcubierre found a solution to Einstein's equations that produced a real warp drive effect, which shrinks space in front of a spaceship and expands it to the rear. Alcubierre's and Thorne's solutions were no less contrived at first, but scientists are currently working to refine them in hopes that they might one day be practical.