Gravity is a natural phenomenon, thanks to which all things with a mass or energy are brought toward one another.
On Earth, we see gravity as the force that makes everything fall back down to the ground, but that’s because the planet itself has a huge mass and energy, so everything is dragged towards it.
But gravity affects everything in the universe. It draws suns and planets and entire galaxies, and it shapes how they structure around each other.
Here on Earth, we feel the gravitational pull of other things, such as the moon. As that is how it is able to control the tides: gravity.
But let’s get to the main question for this article. Does the influence of gravity extend out forever? Well, the answer is a bit complicated.
Depending on who you’re talking to, the answer will be yes, or no. That is because there are two possible scientific theories that you can go by.
Let’s look at both theories in more detail.
Newton’s law of universal gravitation:
According to Newton’s law of universal gravitation, gravity should indeed extend out forever. It states that the force of gravity that is felt by one mass, coming from another, depends on the distance between them.
So for example, the gravity felt by object B, from object A, depends on the separation.
Let’s represent this separation as r. And the dependence of this separation, we represent as 1/r^2.
The law then goes on to state that the further away you get away from the sun, the bigger your r is, and so the gravitational force produced by the sun on you becomes weaker. However, it never fully disappears, so there is always a slight pull of gravity.
So for example, object A is a large astronomical body, and object B is a smaller mass. So object A has a gravitational hold on object B, which feels the gravitational force.
But the further away object B gets from object A, the weaker that gravitational force is, although it never fully goes away.
Newton’s law works really well for ‘closer’ distances, and it is very easy to use within our own galaxy, as the gravitational pull between masses doesn’t ever dissipate. And it’s more than true inside our planet, as we can very well experience.
So people that answer ‘yes’ to ‘does the influence of gravity extend out forever?’, are using Newton’s theory. But here’s the thing, this theory is wrong. And that’s where Einstein’s one comes in. Let’s take a look at that next.
Einstein’s general theory of relativity:
Einstein’s general theory of relativity explains many things, not just gravity. This is because it explains how spacetime behaves as a whole, as it depends on the amount of mass and energy present, its distribution, and its movement. (Everything is...relative!)
So in this theory, gravity isn’t really a direct force of one mass over another, but rather simply the way in which objects move through spacetime, which is curved.
In this way, a large astronomical body, such as the sun, isn’t shooting out gravitational force field lines to ‘trap’ other bodies.
Instead, the mass warps the space and time around it as it moves, and when another body travels through this warped spacetime, it is affected by its ‘force’.
On smaller scales, such as within planets, solar systems, galaxies, and even galaxy groups, there is enough localized mass to make it seem as though objects are gravitationally attracting other objects.
Basically, all the masses are able to directly affect one another, because they are close enough together that they are moving through each other’s warped spacetimes.
In this sense, on smaller scales, Einstein’s theory of relativity works almost in the same way as Newton’s law of gravity. And because Newton’s is easier, that’s what people will usually use.
But what happens on larger scales?
At larger distances, the mass of different astronomical objects are too sparse and far away from each other to keep acting like Newton’s gravity would.
At such large scales, spacetime is practically empty, with barely any warping. This means that objects don’t come into contact with each other’s force, and therefore aren’t affected by each other.
In fact, instead of moving towards each other, they move further away.
For example, two galaxies, that are too far away to come into each other’s spacetime, will move further and further away from each other.
Why? This is due to the cosmological constant present in Einstein’s theory. It states that the nature of spacetime, when it is empty, uniform, and flat, is to expand. You might have heard it said that the universe is currently expanding, and this is what it refers to.
Scientists call this the ‘cosmic expansion’, and the farther apart galaxies are, the faster they move and the faster the universe expands!
Basically, gravity has limits, after which it no longer takes effect, because the different masses are too far apart to influence each other. This is why, by Einstein’s theory of relativity, gravity does not extend out forever.
Does the influence of gravity extend out forever? The verdict:
Einstein’s general theory of relativity is a lot more complex than Newton’s, but it is currently the most correct theory in regards to gravity, as it takes a lot more factors into consideration.
So if we’re going by scientific accuracy, the answer to the question should always be no, the influence of gravity does not extend out forever.
Does that mean that everyone answering yes, is wrong? Well...kinda. They’re going by Newton’s law. And although Newton's law works on smaller scales, it is essentially outdated and wrong as a whole, as it does not apply to larger scales.
In conclusion, the influence of gravity does not extend out forever, as proven by Einstein’s general theory of relativity, which is currently the theory accepted as true.
Gravity extends out up to between galaxy groups, but beyond that, the universe becomes too empty for different masses to have an effect on each other.