This post is based on material from chapter 1 of my new book, How to Time Travel.

Einstein’s special and general theories of relativity underpin the science of time travel. They are briefly presented here as theoretical evidence that time travel is real. In addition, Del Monte’s existence equation conjecture is presented as theoretical evidence that time travel is real.

1. Einstein’s special theory of relativity—The scientific community considers the special theory of relativity the “gold standard” of scientific theories. It has withstood over one hundred years of experimental verification. In addition to yielding the most iconic scientific equation of all time, E = mc^{2}, it also gave us our first insight into the scientific nature of time and predicted time dilation, both conceptually and mathematically. Time dilation is the experimentally verifiable difference of elapsed time between two events as measured by observers, when either one or both observers are moving relative to each other at a velocity near the speed of light. It is an experimental fact that the second hand on a clock moving at a velocity close to the speed of light moves slower than a clock at rest. Time dilation is real and implies forward time travel. For example, if you board a spacecraft capable of traveling at 650 million miles per hour, a one-day journey measured by a clock onboard the spacecraft would be equivalent to the passage of one year on Earth. Time dilation experiments are routinely performed using particle accelerators, which we will discuss later in this chapter.

2. Einstein’s general theory of relativity—Numerous aspects of the general theory of relativity have been verified. For our purposes regarding time travel, it is important to focus on only two:

* Gravitational time dilation—Gravitational time dilation suggests that two observers differently situated from gravitational masses will observe time differently. For example, a clock closer to the Earth will run slower than a clock farther from the Earth. The stronger the gravitational field, the greater the time dilation. This has been experimentally verified using atomic clocks, and we will discuss the results later in this chapter.

* Closed timelike curves—There are numerous solutions to Einstein’s equations of general relativity that delineate the world line of a particle is closed, returning to its starting point. In the general theory of relativity, the world line is the path the particle traverses in four-dimensional spacetime. For example, when the particle starts out, it has four coordinates, three dimensional coordinates and one temporal coordinate. Here is a simple analogy. You are in a specific place, definable by three spatial coordinates, reading this book at a specific time, a temporal coordinate. If the world line of a particle returns to its starting point, the particle is said to have returned to its past, suggesting backward time travel is theoretically possible. However, to date, we have not been able to experimentally verify that this aspect of Einstein’s general theory of relativity is true. As previously discussed, there is evidence that the “arrow of time” can be twisted, and that events in the future can influence past events. However, this is not conclusive experimental proof that backward time travel is possible.

3. Del Monte’s existence equation conjecture—In summary, the existence equation conjecture is derived from Einstein’s special theory of relativity and predicts that a mass requires energy to move in time. If additional positive energy is added to the mass, for example, by accelerating it in a particle accelerator and increasing its kinetic energy, the mass will move more slowly in time. I interpret this as the fundamental explanation of time dilation. An interesting aspect of the existence equation conjecture is that it suggests adding negative energy to a mass will cause the mass to move backward in time. Since today’s science has been unable to produce and manipulate negative energy, this last point has not been experimentally verified. (Note: An entire chapter is devoted to explaining the existence equation conjecture in the referenced source, *How to Time Travel*)

Source: From chapter 1 of *How to Time Travel: Explore the Science, Paradoxes, and Evidence* (September 2013), Louis A. Del Monte (Amazon)

Image: Book Cover *How to Time Travel*

MikeFebruary 18, 2011 Time slows down for the object movnig, relative (and this is the important part) to an observer. Think of it like this (and this is an oversimplification): Lets say you are sitting in your car on the side of the road and a car goes past you at 60 mph. (Think of that car as light . ) The speed of the car relative to you is 60 mph (the speed of light).Now you start your car and accelerate to 30 mph (1/2 the speed of light). Another car then goes past you at 60 mph, but now since you are movnig at 1/2 the speed of the car that just passed you, it appears to you that the car in front of you has slowed down, as it is now pulling away from you at a relative speed of only 30 mph. With me so far .Now here’s where the relativity thing kicks in . If it’s a hundred miles to the state line from where you were sitting in the car when the first car passed you at 60 mph, when that car crosses the state line it is actually a hundred miles away from someone else who would have been standing there outside your parked car.But, to you, going 30 mph when that car passes, the faster car doing twice your speed at 60 mph, will be only 50 miles ahead of you when it crosses the state line. So, to you it’s like you slowed down the car in front of you by 1/2.Same thing would happen in space if a spaceship was traveling 1/2 the speed of light. Everything would look normal to an observer on earth, but time would slow by 1/2 to the astronauts in the spaceship.And, this is not just theory. It’s reality. Give you an example. GPS satellites that are in orbit above the earth rely on extremely precise internal clocks to calculate their position so that when you get a signal from them the location you get is accurate. Because they are traveling a a tiny fraction of the speed of light relative to us on earth, their clocks have to be readjusted every day by computer so they stay in synch with us.Regarding your bonus question, the question is moot. You cannot travel faster than the speed of light, or even achieve the speed of light. (Explanation reserved for your next question, perhaps.)

Hi Luyba,

Your example of the people in the spaceship is not correct. To the people inside the ship, time is moving normally (if for example they look at a clock in the ship). To the people on the Earth, it appears time has slowed down on the spaceship. This is called time dilation and is routinely proved using particle accelerators. If you doubt this is the case, I suggest you read read more about time dilation, especially the “twin paradox,” so that you gain a deeper understanding of it. Your GPS example is correct, but the reasoning is wrong.

I understand traditional text book science holds that light is the upper speed limit of the universe. However, this may not be entirely true. For example, quantum entanglement appears to occur instantaneously. Read more about it, if you have questions. How fast is instantaneous? It hasn’t been measured. I conjecture that quantum entanglement may be as fast as the speed of light or perhaps faster. No one really understands the mechanism (i.e., cause) that enables quantum entanglement, but it is widely accepted as a feature of quantum mechanics. I am illustrating that not everything is clear cut.