The force of attraction, also called the gravitational force, between two objects depends on the mass of those objects. When the masses of two objects are doubled, the gravitational force between them is doubled.
Physicists define gravity not as a force but as a property of spacetime, where spacetime represents the three dimensions of space and the one dimension of time.
Spacetime is defined as a collection of points and intervals of time, all connected in a consistent way. These points and intervals of time are defined by coordinates that measure both distance and time.
The strength of the gravitational pull between two objects depends on how much mass they have and how close they are to each other. The more mass an object has, the stronger its pull on another object. If two objects are close to each other, then they will be pulled toward each other.
Double the distance between the two planets
Now let’s say you have two planets, Planet A and Planet B, in close proximity to each other. For the sake of this example, let’s say that Planet A has a mass of one unit and Planet B has a mass of two units.
Now, let’s say that the distance between Planet A and Planet B is one unit. Because of the close proximity of these two planets, there is a strong force of attraction between them. This force of attraction is known as gravity.
If we were to double the distance between both planets, then the force of attraction or gravity between them would be reduced by half. This is because we are multiplying the distance by one divided by two, which equals one.
Let’s try some examples to make this clearer.
Mass does not affect the force of attraction
Mass is a measurement of how much matter an object contains. More mass means more matter, and more matter means a bigger object.
We can see mass in action when an object is pushed or pulled by another object. The thing that pushes or pulls it is the force of attraction between the objects, and the more mass an object has, the more pull it has. This is why we say that weight does not matter- it does not affect the force of attraction between objects.
In our experiment, doubling the masses of both planets did not affect the force of attraction between them. This proved our hypothesis correct!
As we ran our experiment multiple times, we could tell whether or not we had done it correctly based on whether or not there was a shift in the orbit of either planet.
Distance affects the force of attraction
The farther away you are from something, the less gravitational force it exerts on you. That’s why you feel less pressure on your feet when you stand back from the mirror and why books weigh less on the moon.
The distance at which this effect disappears is called the gravitational softening length. On Earth, it’s about 10 times the diameter of a hydrogen atom. At that distance, gravity no longer distinguishes one object from another.
We can think of gravity as a phenomenon that occurs in both time and space. Because gravity affects time as well as space, it can be tricky to separate the two when studying it. However, studying gravity in a spaceless environment would prove impossible.
As such, scientists have created what are called relaxation times: periods of time in which nothing external affects gravity. These are measured in nanoseconds (ns), or thousand-thousandths of a second.
Planets become black holes
What happens when a planet becomes a black hole? We don’t know for sure, but we do have some ideas.
According to Einstein’s theory of general relativity, gravity is caused by distortions in the structure of space-time. A mass compresses the surrounding space-time, which pulls other masses toward it.
If a planet had enough mass, it could theoretically compress the fabric of space-time so much that it would turn into a black hole. A black hole has an event horizon—a point of no return where nothing can escape its gravitational pull—which would mark the boundary between the planet and empty space-time.
We can’t really observe what happens on the inside of a black hole, but we think that there might be this point called a singularity, where all of the mass is concentrated in one place.
Planets become white holes
It has been theorized that when two planets orbit each other, and then their masses are doubled, the force of attraction between them will be doubled as well.
This theory is based on the fact that the mass of a planet determines its gravitational force, and since this remains unchanged, the force of attraction should remain the same.
However, It has recently been discovered that planets can become white holes when they die. What exactly is a white hole? It’s the opposite of a black hole!
A white hole is a theoretical point in space-time from which matter and energy emerges instead of falling in. In other words, it’s the opposite of what a black hole does – it lets things go out instead of in.
The force of gravity weakens
In 2016, astronomers discovered a planet called Proxima b, which orbits the star Proxima Centauri, and it may be habitable. A 2018 study using data from the Hubble Space Telescope suggested there may be rocky planets orbiting nearby red dwarf stars.
Because red dwarfs are the most common type of star in our galaxy, this is an exciting prospect. It could mean that there are many potentially habitable worlds in our universe!
Because these planets orbit so close to their stars, they may undergo dramatic tides due to the gravitational pull of the star. This could possibly put life on such a planet into jeopardy.
By studying how tides affect Earth and other planets, scientists can figure out how to mitigate their effects. Tides cause water to flow in and out; similar phenomena occur with air and soil on Earth.
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