Is Earth’s Gravity Infinite?
A rocket leaves Earth’s atmosphere. The astronauts inside begin to float. Things get weird.
Does this weirdness mean the rocket left Earth’s gravity? Does gravity vanish in space?
Not at all, but these are common misconceptions.
Earth’s gravity does not end at the border between the atmosphere and space…but why does it seem that way?
Currently, a space station is flying around our home planet about 16 times every single day. This blows my mind and makes me proud to be a part of humanity. If you don’t already know, it is called the International Space Station.
It may seem like there is no gravity in space because astronauts can float around like balloons. However, gravity is there and plays an important role.
There are two main factors that keep the station orbiting Earth:
1: At all times, the space station is accelerated towards Earth due to gravity
Imagine some godly creature decided to turn off Earth’s gravity…even though that is not how it works…just imagine! The International Space Station would stop arcing around the Earth, fly into the void of space, and probably be caught up in the gravity of some other massive object like the sun. It is almost like gravity is a rope holding the space station in place so that it goes around Earth.
2: The station was originally accelerated horizontally with respect to Earth in order to give the station speed
Since the atmosphere is basically nonexistent above the Kármán line (edge of space), the station is only accelerated once in order to get up to speed. Then, it coasts effortlessly, unless it needs to maneuver in some way. If the station somehow lost that horizontal velocity, Earth’s gravity would take full control and pull the station right back down to Earth. That velocity is key to keeping the station in orbit.
So…where does Earth’s gravity end?
Well, there is no clear boundary.
Newton’s law of universal gravitation tells us that the influence of gravity drops off relatively quick based on distance.
If you absolutely need to define a boundary, there are two factors that are important:
1: Multiple gravitational influences
There are certain points in space where a larger mass (like the sun) has more influence and an object will begin gravitating toward it instead of Earth. This somewhat creates a boundary.
2: The expansion of the universe
Imagine the universe consisted of only two objects: Earth and one less massive object. That less massive object would be completely controlled by Earth’s gravity. However, if it somehow managed to get very far away from Earth, there would eventually be a point that the expansion of space would cause the less massive object to move away from Earth. So, Earth’s gravity loses control, creating some sort of boundary.
Is Earth’s gravity infinite?
According to Newton’s law of universal gravitation…yes.
However, in reality, no. There are gravitational influences everywhere that create boundaries. As an object gets further from Earth, another gravitational influence eventually takes over.
Objects that are vast distances away from Earth are pushed away due to the expansion of the universe; I recommend doing some research on dark energy if you are interested in learning more.
