We all experience it every moment of our lives yet most of us misunderstand what it is. Gravity is not a force at all!
What we are taught
We are taught exactly what we experience. But what we experience has a larger truth that is often hidden and never taught. We are taught Gravity is a force. If we drop a ball from a height, it will fall to the ground due to the force of Gravity.
We are also taught intuitively that a heavier object will fall faster than a lighter object. As explained in part 1 of this series, this intuition is only due to air resistance. Remove all the air and then all objects irrespective of their mass, will fall at the same time with the same speed if dropped from the same height.
What then is Gravity ?
To understand Gravity, we first need to understand where we are. All planets, stars, galaxies, and everything we know out there in the universe are inside a medium - a fabric called Spacetime. ( Not just Space ). We touched upon Spacetime earlier and we understood that Space and Time affect each other. Motion through space affects the passage of time.
It turns out that this fabric in which everything is, can bend. Since we are hosted in this fabric, the bend or curvature of Spacetime occurs from all sides as shown in the image below.
Image source: https://www.forbes.com/sites/startswithabang/2019/02/16/ask-ethan-how-can-we-measure-the-curvature-of-gravity/?sh=37941e50134f
Gravity is nothing but the interaction of a passing object influenced by this Spacetime curvature. As you can see the curved lines cause the object traveling to get attracted or converge to the mass causing the curvature of the fabric. Thus, Gravity should not be thought of as a force, rather the source of the apparent attraction of gravity, is simply created by the fact that any object under the influence of gravity of another object, continues to follow its motion through the curved grid lines caused by the curvature of Spacetime.
Further, it turns out rather intuitively, that the more mass the object has, the more the Spacetime curvature or bend.
This is why a ball dropped from rest appears to fall on the surface of the earth. This is why a ball thrown with some speed travels for some time and distance but eventually appears to fall to the ground in a curved path as it loses velocity due to the air resistance of the earth's atmosphere. Give it enough push to attain sufficient velocity to escape the air resistance of our atmosphere, then it continues to orbit the earth without air resistance to reduce its speed. Without air resistance, its velocity is constant so it continues to follow the curved path along the Spacetime curvature created by the Earth. This is why satellites orbit the earth. This is why the moon orbits the earth. This is why the Earth orbits the Sun and this is why the solar system, orbits around the center of the Milky Way galaxy.
As John Archibald Wheeler, the theoretical physicist said beautifully
Spacetime tells matter how to move and matter tells spacetime how to curve
Pause for a moment now to wonder what you read. How does it feel to have this larger perspective and a deeper and clearer understanding of gravity? Does it alter how you think about Gravity now? Does it convince you that what we experience and our intuitive experience is not reality and that to understand reality, we need a much bigger perspective?
But what about Time?
We now have an intuitive sense of the bending of the fabric due to massive objects. We have an intuitive sense now that objects in motion will follow that curvature and be influenced by it. But what about Time ? Where does time come into the picture? How do we make any kind of intuitive sense of the bend of Time and what are its effects? What is the relationship between Gravity and Time?
These are the deepest questions and are a topic for the next part of this series.
If you want more of Gravity and love fiction, then you may enjoy my graphic novel from the series "Ventures in Space and Time" : Kohiti's Anomaly
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