One of the key plot devices in nearly every "Star Trek" episode and movie is the ability of starships to travel at lightspeed and beyond. This happens thanks to a propulsion system known as warp drive. It sounds "science-fictiony" and it is. Warp drive doesn't actually exist, yet. However, in theory, some version of this propulsion system could be created from the idea-given enough time, money, and materials.
Perhaps the main reason why it seems to be possible is that it hasn't been disproven yet. So, there is hope for a future with FTL (faster-than-light) travel, only it doesn't seem that it will happen any time soon.
What Is Warp Drive?
Warp drive is what allows the science fiction ships to get across space by moving faster than the speed of light. This is an important aspect since lightspeed is the cosmic speed limit-the universe's ultimate traffic law and barrier.
As far as we know, nothing can move faster than light. According to Einstein's theories on relativity, it takes an infinite amount of energy to accelerate an object with mass up to the speed of light. (The reason why light itself isn't affected by this fact is that photons, the particles of light, don't have any mass.) As a result, it would appear that having a spacecraft traveling at (or exceeding) the speed of light is simply impossible.
Yet, there are two loopholes. One is that there doesn't seem to be a prohibition on traveling as close as possible to lightspeed. And the second one is that when we talk about the impossibility of reaching the speed of light, we are talking about the propulsion of objects. However, the idea of warp drive is not necessarily based on the ships or objects themselves flying at the speed of light.
Warp Drive vs. Wormholes
Using a warp drive would be distinctively different from traveling across the universe using wormholes. These are theoretical structures that allow spaceships to travel from one point to another by tunneling through hyperspace. Effectively, they would let ships take a shortcut since they technically remain bound to normal space-time.
A positive byproduct of this is that the starship can get around undesirable effects such as time dilation and massive acceleration effects on the human body, which would really ruin the science fiction storylines.
The Idea of Warp
Our current understanding of physics and how light travels excludes objects from reaching such a velocity yet does not exclude the possibility of space itself traveling at or beyond the speed of light. In fact, some people who have examined the problem claim that in the early universe, space-time expanded at superluminal speed, if only for a very short interval.
If these hypotheses are proven true, a warp drive could take advantage of this loophole, subsequently leaving scientists with the question of how to generate the enormous energy needed to move space-time.
You can think of warp drive in this way: a warp drive is what creates the immense amount of energy that contracts the time-space in front of the starship while equally expanding space-time at the rear, ultimately creating a warp bubble. This would cause space-time to cascade by the bubble-the ship staying stationary to its local area as the warp proceeds to a new destination at superluminal progression.
Motivated by his fascination with Gene Roddenberry's revolutionary plot driver, Mexican scientist Miguel Alcubierre proved that warp drive was, in fact, consistent with the actual laws governing the universe. In his late-20th-century design, known as the Alcubierre drive, the starship rides a "wave" of space-time, much like a surfer rides a wave on the ocean.
Despite Alcubierre's proof and the fact that there is nothing in our current understanding of theoretical physics that prohibits a warp drive from being developed, the whole idea is still in the realm of speculation, and our current technology isn't quite there yet. People ARE working on ways to achieve such a feat, but there are many issues yet to be solved.
The creation and movement of a warp bubble necessitate the space in front of it to annihilate while the space at the back would rapidly grow. The annihilating space is what we refer to as negative mass or negative energy, a highly theoretical type of matter that hasn't been "found" yet.
Yet, three theories have moved us closer to the reality of negative mass. Casimir effect lays out a setup where two parallel mirrors are positioned in a vacuum. When we move them extremely close to one another, it appears that the energy between them is lower than the energy around them, thus creating what we call negative energy, even if only in minuscule amounts.
As of 2018, scientists from the University of Rochester demonstrated another possibility for the creation of negative mass using lasers. Even though these discoveries are inching humanity closer to a functioning warp drive, these minute amounts are a far reach from the magnitude of negative energy density that is needed to travel 200 times FTL (which is the velocity needed to get to the nearest star in a reasonable amount of time).
Perhaps most importantly, in 2016, scientists at LIGO (the Laser Interferometer Gravitational-Wave Observatory) proved that space-time can "warp" and bend in the presence of enormous gravitational fields.
Amount of Energy
With Alcubierre's design in 1994, and then Natario's in 2001, it seemed that the sheer amount of energy required to create the necessary expansion and contraction of space-time would exceed the output of the Sun, during its lifespan of 10 billion years. However, further research was able to lower the amount of negative energy down to that of a gas giant planet, which still seems to be rather difficult to come up with.
One theory is to use massive amounts of energy extracted from matter-antimatter annihilations-explosions of same particles with opposing charges-in the "warp core" of the ship.
Traveling With Warp Drive
Even if we succeeded in using, say, gravitational waves to bend the time-space around a given spaceship and/or creating negative energy that would do the same, and if, at the same time, we succeeded in harnessing immense amounts of energy, more questions would come up regarding warp drive travel.
Scientists are theorizing that along with our interstellar travel, our warp bubble would potentially collect a large number of particles, which could cause massive explosions upon arrival. Another possible issue connected to this is the matter of how to navigate the whole warp bubble and the question of how we would communicate with Earth.
Technically, we are still a long way away from warp drive capabilities and interstellar travel, but with the acceleration of technology and computers, maybe we are not that far off. With the recent advancements in science and the drive to push innovation, people like Elon Musk and Jeff Bezos who aspire to make us a space-faring civilization are the stimuli needed to crack the code of warp drive. For the first time in decades, there is a rock-and-roll-like excitement about space flight. This is another essential piece in the quest to become masters of the universe.