Without doubt, harnessing sufficient energy is  the largest obstacle to time travel. For example, time dilation (i.e., forward time travel) is only noticeable when mass approaches a significant fraction of the speed of light or sits in a strong gravitational field. To date, we have been able to accelerate subatomic particles to a point where time dilation becomes noticeable. We have also been able to observe time dilation of a highly accurate atomic clock on a jet plane as it flies over the airport, which contains another atomic clock. Using sensitive instruments, we can measure time dilation. We have also been able to measure time dilation due to differences in the Earth’s gravitational field. However, these differences are only evident using highly accurate atomic clocks. Our human senses are unable to detect a high mounted wall clock moving faster than our wristwatch, which gravitational time dilation predicts is occurring.

The fastest humankind has traveled is 25,000 miles per hour, using the Apollo 10 spacecraft. The speed of light in a vacuum is approximately 186,000 miles per second. This means that a spacecraft would have to go about 13,000 times faster than Apollo 10 for humans to experience noticeable time dilation, or a speed of about 90,000 miles per second, which is roughly half the speed of light. Today’s science has not learned to harness the amount of energy required to accelerate a spacecraft to a velocity of 90,000 miles per second.

Let us consider a simple example to illustrate the amount of energy required to achieve the above velocity. If we have a mass of 1000 kilograms (i.e., 2204 pounds), and we want to accelerate it to 10% the speed of light, the resulting kinetic energy would be about 1017 (i.e., a 1 with 17 zeros after it) joules, whether you calculate the kinetic energy using Newton’s classical formula or Einstein’s relativistic formula for kinetic energy. To put this in perspective, it is more than twice the amount of energy of the largest nuclear bomb ever detonated. It would take a modern nuclear power plant about ten years to output this amount of energy.

The above example gives us a conceptual framework to understand the amount of energy that would be required to accelerate a sizable mass, 1000 kilograms, or 2204 pounds, to just 10% the speed of light. If we wish to accelerate the mass, for example, a spacecraft, to a greater percentage, the energy increases exponentially. For example, to accelerate to 20% the speed of light would require four times the amount of energy.

Today’s engineering is unable to harness this level of energy. In the popular Star Trek television series and movies, the starship Enterprise is able to travel faster than the speed of light using a warp drive, by reacting matter with antimatter. Factually, there is almost no antimatter in the universe. This is one of the mysteries associated with the big bang science theory, which I discussed in my book, Unraveling the Universe’s Mysteries. In theory, during the big bang, matter and antimatter should exist in equal quantities. Our observation of the universe, using our best telescopes, detects almost no antimatter. However, Fermi National Accelerator Laboratory (Fermilab) in Illinois is able to produce about fifty billion antiprotons per hour. This, though, is a miniscule amount compared to the amount needed to power a starship. According to Dr. Lawrence Krauss, a physicist and author of The Physics of Star Trek, it would take one hundred thousand Fermilabs to power a single lightbulb. In essence, we are a long way from using matter-antimatter as a fuel. In addition, the Enterprise was able to warp space. This provided a means to skirt around Einstein’s well-established special theory of relativity, which asserts no mass can travel faster than the speed of light. There is no similar physical law that prohibits space from expanding faster than the speed of light. If we are able to manipulate space, similar to our discussion of the Alcubierre drive in the previous chapter, then scientifically the spacecraft could collapse space in front of it and expand space behind it. However, the Alcubierre drive requires negative energy. Today’s science is unable to create and harness negative energy in any significant way.

Therefore, topping our list of major scientific obstacles regarding time travel is generating huge amounts of energy, in either positive or negative form.

Source: How to Time Travel (2013), Louis A. Del Monte