“Today’s lesson”: About Gravity, Acceleration and their effect on T...

“Today’s lesson” is a new series of posts that will consist on a brief explanation about an interesting subject related to technology, science, science fiction or futurism. This is the first “Today’s lesson” chapter, welcome!

Have you ever heard about the “Twins paradox”?

It goes like this:

There are 2 identical twins, one of whom makes a journey into space in a high-speed rocket and returns home to find that the twin who remained on Earth has aged more. Source

In that simple example, what happens is the work of one of the laws of the Universe: Time is not really absolute in the whole universe, but relative to each observer. With simple words it means, time is not same but in varies from place to place.

A proper representation of the Twin Paradox

In the case of the twins and the ship, what happens is that the faster one travels in a ship (in particular, the closer one gets to the speed of light), the slower the time passes in relation to something that is stationery, as people on planet Earth, which causes according to the laws we know today the one in the ship to "travel to the future".

From Earth what we would perceive is how a clock inside the ship works extremely slow, and as everything that happens inside the ship appears to be in "slow motion", however, inside the ship the twin would not perceive anything different , and you would see your watch running at a perfectly normal rate.

The twin inside the ship would perceive that the clocks on Earth are way faster than normal, and everything that happens on Earth would appear incredibly fast, but once again, people on Earth would not notice anything strange or faster than normal. This phenomenon is called, Time Dilation.

What is Time Dilation?

When we move, at whatever speed, time slows down relative to a stationary observer, | Source

A slowing of time in accordance with the theory of relativity that occurs in a system in motion relative to an outside observer and that becomes apparent especially as the speed of the system approaches that of light. | Source

Did you knew "the clocks on the satellites appear to be ticking faster than identical clocks on the ground" Source Of course not by much, but this difference is still important enough to be taken into account in order to avoid GPS miscalculations

I believe many of us have already seen that example in one way or another, either on famous movies like Interstellar or science fictions books, however this effect of "time dilation" happens in 2 cases.

-1) When we are moving at incredibly high speeds.
-2) When we are near high gravitational fields, especially, black holes.

That is, objects very close to a star (or in particular, near a massive Black Hole) experience time (in relation to something stationary and distant observers of large gravitational fields) in the same way that the twin experiences it in the spacecraft .

The reason for this is very simple: Acceleration and Gravity are apparently equivalent.

What is Acceleration and what is Gravity?

Acceleration

The rate at which velocity changes with time, in terms of both speed and direction. | Source

The rate of change of velocity or speed. | Source

Gravity

Is the force by which a planet or other body draws objects toward its center. | Source

Is a force of attraction that exists between any two masses, any two bodies, any two particles. Gravity is not just the attraction between objects and the Earth. It is an attraction that exists between all objects, everywhere in the universe. | Source

How are gravity, acceleration and time related?

Black holes are one of the most mysterious objects in existence, and they can indeed allow us to travel to the future thanks to their immense gravitational field, although the risk to be trapped by it makes the thought less exciting... for now

We can understand it like is this: If you put a chair on its back on the ground, and sit on it, you notice how the Earth seems to "pull you back". That is, you feel Earth gravity.

However, if you are in space, floating, tied to a chair, and we put two rockets behind you and turn them on, you will also feel the exact same thing. The acceleration from the rockets will "pull you back" just like with gravity.

In other words, in both scenarios (with gravity, or with acceleration), the effect is the same in objects, and that is why time "expands" when we accelerate, as well as when we are near a large gravitational field.