Theories behind Time travel

This lesson is on Albert Einstein and how his work applies to time travel theory. We'll investigate Einstein's theories of relativity, examples of distortion of time on Earth and in deep space, and the prospect of time travel for humans.
What Is Time Travel?
If you've ever watched a science fiction television show, or maybe read a book in that genre, you might have come across the image of a spaceship jumping into warp speed and zooming off into a twisted region of space to get to a faraway location. And all of this would have happened without any time passing. The spaceship's speed offers superhighways to far-off galaxies in an instant. Although right now these scenarios are fiction, the physics and math behind them are quite real. The formulas and theories we will learn about today suggest that time travel is possible. First, let's learn about the scientist that proposed these theories, Albert Einstein.

Albert Einstein
Albert Einstein was a German physicist and mathematician who in the early 20th century changed the way we look at the universe. Einstein contributed many groundbreaking ideas to physics, but one of the most important for time travel was his theory of relativity, which explains the relationship between space and time.

Einstein investigated the seemingly paradoxical movements of light at high speeds, leading him to his special theory of relativity in 1905. Later, he realized that gravity poses a similar paradox, and studied how time warps around extremely large bodies of mass, like black holes. This work was published in 1915 and is known as Einstein's general theory of relativity.

Problems With Speed and Light
Einstein found discrepancies between classic physics, such as Newton's work on motion and force, and modern theories of waves and light. Let's take a look at an example of how relative speed is supposed to look according to classic physics:

If a person is on a bus and throws a ball forward, the speed of the ball for an observer standing still outside the bus would be the speed of the bus, plus the speed of the ball. The speed of the ball is relative to the observer, meaning it changes depending on where you are. This is what normally happens.

Although the ball is only moving at 30m/s relative to the bus, the observer sees the speeds of the bus and ball added together
relativity of baseball
However, light doesn't act this way. The speed of light is always the same. If the person had a light on the bus, the speed of light would be the same for both the person on the bus and the observer on the ground. This is an example of how something in Newtonian physics doesn't match up with what we know about light.

Light always travels the same speed, so despite the difference in distance traveled, the light does not appear to be at a different speed like the ball does
relativity of light
The Theory of Relativity as a Solution
This problem perplexed Einstein and he set to work to try to understand how this could be possible. As it turns out, if you, the observer, and the person on the bus were to measure a ruler, distance would be shortened for the observer. The ruler would measure a tiny bit shorter if you measured it as compared to someone moving on bus.

Einstein used the mathematical equation for speed, or distance traveled divided by time, to get to work on this problem. Since the speed of light is constant, but distance measured for each person is different, time must change depending on where you are relative to the motion! So, Einstein figured out that for someone on the ground, time must be passing more quickly to account for the consistent speed of light.

Time passes on the bus just slightly slower than for that of the observer using the speed of light