Gravitational force or Curvature of Space-time.

Introduction and questions related to gravity.

We are familiar with Newtonian gravity which describes gravity as a force that pulls together objects with mass. But a very relevant question arises which was also a concern for Newton within his gravitational concept. The concern was, 1. How can a mass exert a force on another mass instantaneously, without getting in contact with it?. Gravity is a non-zero force even in a very deep space. So, the mass of Earth is exerting a force on the mass of some planet far, far away, in some distant galaxy instantaneously and with no contact (though gravitational force will be very, very weak as gravitational force decreases squared time the distance). Another radical thing that Newton did was he said that 2. The things falling on Earth and the moon revolving around the Earth. The cause for both these scenarios is one that is gravitational force But how? There is another fundamental question which is 3. Why does mass attract other masses? In this blog, we are tackling these three important questions and trying to understand gravity in much more detail.

Why does mass attract other masses?

The answer is pretty simple and straightforward, we don't know, neither Newton did.

How planets revolving around the sun is equivalent to an object falling back to Earth's surface when thrown in an upward direction?

To answer this question let us consider a moon with some mass and an earth with some other mass separated by some distance. According to gravitational force moon and the earth will attract each other or fall for each other as it happens in love. Here because the mass of Earth is much greater than the mass of the moon, the moon will fall down to Earth, rather than Earth falling back on the moon. In this scenario, one hidden assumption is that the moon and the earth are at rest, in their initial states. So, this is how gravity is the cause behind the objects falling back to our surface when thrown in an upper direction. But, according to the example moon should crash with the earth's surface, then why isn't the moon falling on Earth?

Here as mentioned above. The hidden assumption is that the moon and the earth are at rest. which is not the case in reality. In reality, the moon is moving with a velocity perpendicular to the direction of gravitational force. This is all that makes these above scenarios look very different from each.

Let us take the same example of the moon and Earth with different masses separated by some distance But this time let the moon not be at rest. Let it be moving with some velocity V in the direction perpendicular to the gravitational force exerted by the Earth. Because of this perpendicular velocity, the moon will take the resultant path of these forces and eventually fall on the earth's surface if v is smaller. If velocity in the perpendicular direction of the gravitational force of the moon is high enough such that it misses the earth's surface every revolution then the moon would start revolving around the earth and that is what happens. The moon misses the Earth's surface in every revolution because of its perpendicular velocity. Check out this video for more visual clarity.

How does mass exert force on other masses instantaneously without contacting with each other? Gravity as space-time curve.

Gravity, as famously described by Albert Einstein's theory of general relativity, is fundamentally different from the way it was understood in classical physics. In this groundbreaking theory, gravity is not a mysterious force acting at a distance, but rather a consequence of the curvature of space-time itself. This concept revolutionized our understanding of the universe and how it operates.

In essence, Einstein proposed that massive objects, like planets and stars, create curves or dimples in the fabric of space-time around them. Imagine a stretched-out rubber sheet, and place a heavy ball on it—the sheet warps around the ball. This is analogous to how mass warps the space-time continuum around it. Objects that are smaller or less massive will then move along the curved paths dictated by this warped space-time. In simpler terms, they follow the most natural paths available to them, which are known as geodesics. This bending of space-time around massive objects is what we perceive as gravity. It's as if the objects are simply following the curved roads created by the warping of space-time.

credit: quora

One of the remarkable predictions of general relativity is the phenomenon of gravitational time dilation. Clocks run at different rates depending on their proximity to massive objects. This means that time itself is not uniform throughout the universe but is influenced by the strength of the gravitational field at a given location. This concept has been experimentally confirmed and is crucial for the proper functioning of technologies such as GPS, which relies on highly accurate timekeeping. In summary, understanding gravity as a curvature of space-time not only provides a more profound insight into the nature of the universe but also has practical applications in our everyday lives.

In conclusion, the concept of gravity as a curvature of space-time is a cornerstone of modern physics. It replaced the classical Newtonian view of gravity as a mysterious force with a deeper understanding of how mass and energy interact with the very fabric of the cosmos. This theory has withstood rigorous testing and continues to shape our understanding of the universe, from the behavior of galaxies to the functioning of our global positioning systems. It serves as a testament to the power of human curiosity and our ability to unravel the mysteries of the natural world.