The gravity: Understanding gravity, black hole and space-time curvature Part 01

Table of contents:-

Understanding gravity

1. What is black hole? Is it just a hole?
2. How are black hole formed?
3. What is the cause of gravity?
4. Why do the masses create gravitational force?
5. What is warp fabric of spacetime?
6. What is Einstein mass energy relation?
7. Where does Einstein's mass energy applies?
8. What is space time curvature and why is it formed?
9. How can I imagine fabric of spacetime?
10. Space and time both are invisible, only effect can be seen. Then how can it form flexible fabric net?
11. Space curve and time curve intersect to form a fabric like structure?
12. Fabric of space time is present everywhere
13. Does it exert any upthrust on massive body?

1. What is black hole? Is it just a hole?

A black hole is not a literal hole; it's an extremely dense region in space where gravity is so strong that nothing, not even light, can escape its pull. It forms when a massive star collapses under its own gravity.

Photons, which are particles of light, cannot escape the gravitational pull of a black hole once they cross the event horizon. This is why black holes appear "black" or invisible, as no light or electromagnetic radiation can be reflected or emitted from them.

While photons are indeed massless, they still interact with gravity according to Einstein's theory of general relativity. Gravity in general relativity is not solely a force acting on mass; it also affects the curvature of spacetime. The intense gravitational field around a black hole causes spacetime to curve significantly, affecting the path of light, even though photons themselves have no mass. This gravitational bending of light is known as gravitational lensing.

In simple terms, even though photons have no mass, they are influenced by gravity. The strong gravitational field around a black hole curves the path of light, making it impossible for photons to escape once they cross a certain boundary called the event horizon. This is why we say nothing, including light, can escape from a black hole.

2. How are black hole formed?

Black holes are formed when massive stars undergo gravitational collapse. When a massive star exhausts its nuclear fuel, the outward pressure from nuclear fusion decreases, and gravity becomes the dominant force. The star's core collapses under its own gravity, and if the remaining mass is above a certain threshold (about 2.5 to 3 times the mass of our sun), the collapse continues, leading to the formation of a black hole.

There are also intermediate-mass black holes, which may form through the merging of smaller black holes or other processes. Additionally, supermassive black holes, found at the centers of galaxies, have masses ranging from hundreds of thousands to billions of times that of our sun. The exact formation mechanisms for these supermassive black holes are still under investigation.

3. What is the cause of gravity?

In the framework of Einstein's general theory of relativity, mass is indeed the cause of gravity. Massive objects, like planets, stars, and galaxies, curve the fabric of spacetime around them. This curvature of spacetime is what we perceive as gravity. Objects then move along the curves created by this curvature, influenced by the gravitational pull.

In simpler terms, mass tells spacetime how to curve, and curved spacetime tells objects with mass how to move. This is a fundamental concept in our current understanding of gravity.

According to our current understanding in physics, everything that has mass also has gravity. The strength of gravity depends on the mass of an object. The larger the mass, the stronger the gravitational pull. This principle applies to all objects with mass, from small particles to planets, stars, and galaxies.

4. Why do the masses create gravitational force?

The creation of gravitational force by masses is explained by Einstein's general theory of relativity. According to this theory, mass causes spacetime to curve. Imagine space as a flexible fabric, and mass as a heavy object placed on that fabric. The mass creates a curvature or depression in the fabric, and anything nearby will move towards the mass because of this curvature.

In simpler terms, mass warps the spacetime around it, and objects move along the curved paths created by this warping. This effect is what we perceive as gravity – the force that attracts objects with mass towards each other. So, it's the interaction of mass with spacetime that gives rise to the gravitational force.

Interestingly, in the context of general relativity, the paths that objects follow under the influence of gravity are not necessarily straight in the traditional sense. Instead, they are "curved" paths along the warped spacetime caused by the presence of mass.

In a more conventional sense, we might think of a straight path as a line with no curvature. However, in the presence of gravity and curved spacetime, what appears as a straight path for an object under the influence of gravity is actually a curve along the warped fabric of spacetime. This concept is a departure from our everyday intuition about straight paths, as it's influenced by the curvature of spacetime itself.

In everyday observations and small-scale scenarios, the effects of gravity often appear as if they are working in straight lines. This is because on Earth and in our everyday experiences, gravitational forces are relatively weak, and the curvature of spacetime is subtle. In these cases, the curved paths of objects influenced by gravity can approximate straight lines over short distances.

However, when dealing with massive objects or extremely strong gravitational fields, as is the case near black holes or in cosmological scales, the curvature of spacetime becomes more pronounced, and the paths that objects follow can deviate significantly from what we might consider a straight line in flat space.

So, while in certain situations gravity may seem to act along straight lines, it's more accurate to say that gravity influences the paths of objects by curving the spacetime through which they move.

Photons, being massless particles, do not experience gravitational attraction in the same way massive objects do. However, according to Einstein's general relativity, gravity affects not only mass but also energy and momentum. Light, which is made up of photons, has energy and momentum, and it can be influenced by gravity.

In the vicinity of a massive object like a star or a black hole, the gravitational field can bend the path of light. This phenomenon is known as gravitational lensing. While photons themselves are massless, they interact with the gravitational field by following the curved spacetime created by the massive object, resulting in a bending of their path.

It might seem counterintuitive, but according to Einstein's theory of general relativity, gravity does indeed influence not only mass but also energy and momentum. This is a departure from Newtonian gravity, where only mass was considered as the source of gravitational attraction.

In general relativity, mass and energy are interconnected through the famous equation E=mc^2. The presence of energy, even in the form of light (photons), contributes to the curvature of spacetime and thus influences the paths that objects, including light, follow under gravity. This aspect of gravitational theory has been experimentally verified and is a fundamental part of our current understanding of gravity.

5. What is warp fabric of spacetime?

The concept of the "warping" or curvature of spacetime is a way to describe how gravity works according to Einstein's general theory of relativity. Instead of thinking of space and time as separate entities, Einstein combined them into a four-dimensional fabric known as spacetime.

Massive objects, like stars or planets, cause this spacetime fabric to curve or warp. Imagine placing a heavy object on a stretched-out rubber sheet; the sheet bends around the object, creating a depression. In the same way, mass bends spacetime around it.

Objects then move within this curved spacetime, and what we perceive as gravity is the motion of objects following the curves created by the presence of mass. This conce

pt helps explain how gravity influences the paths of objects, even light, in a way that goes beyond the Newtonian idea of forces acting at a distance.

In the framework of general relativity, any form of energy, not just mass, contributes to the curvature of spacetime. This includes not only the rest mass of an object but also its energy due to motion, known as kinetic energy, and its potential energy. The famous equation (E=mc^2) illustrates the equivalence of mass and energy.

So, while massive objects contribute significantly to the curvature of spacetime, other forms of energy, such as the energy carried by photons (particles of light), also contribute. In practical terms, massive objects like stars and planets often dominate the gravitational effects we observe, but the general principle is that all forms of energy contribute to the curvature of spacetime according to general relativity.

Even photons, which are massless particles, contribute to the curvature of spacetime according to general relativity. Although they have no rest mass, they do carry energy and momentum. As per Einstein's equation (E=mc^2), energy is equivalent to mass, and this energy-momentum content contributes to the gravitational field.

In regions of strong gravitational fields, such as those near massive objects like stars or black holes, the path of light can be bent due to the curvature of spacetime. This phenomenon is known as gravitational lensing and has been observed, providing experimental support for the role of photons in the gravitational interaction.

6. What is Einstein's mass energy relation?

Einstein's mass-energy equivalence is expressed by the famous equation 

          

 E=mc^2

In this equation:

- E represents energy,

-m represents rest mass,

- c is the speed of light in a vacuum.

The equation states that the energy of an object is equal to its rest mass multiplied by the speed of light squared. This concept, a cornerstone of Einstein's theory of special relativity, implies that mass and energy are interchangeable. It also reveals the immense amount of energy that can be released from a small amount of mass, which is a key principle in nuclear reactions and the functioning of stars.

The equation E=mc^2 represents the total energy of an object, which includes both its rest mass energy mc^2 and its kinetic energy. The rest mass energy mc^2 is the energy an object possesses due to its mass even when it's at rest. The kinetic energy, on the other hand, is the energy an object possesses due to its motion.

So, E=mc^2 accounts for both the rest mass energy and the kinetic energy when an object is in motion. It's a general expression of the total energy of an object, encompassing both its mass and its motion.

7. Where does Einstein's mass energy applies?

Einstein's mass-energy equivalence, expressed by the equation E=mc^2, applies to various physical phenomena, and its implications are observed in different contexts. Some notable applications include:

1. Nuclear Reactions: The equation is fundamental in understanding the energy released in nuclear reactions, such as those occurring in the sun or in nuclear power plants. In these reactions, a small amount of mass is converted into a large amount of energy.

2. Particle Physics: In particle physics experiments, the conversion of energy into mass and vice versa is a common occurrence. Particle accelerators, like the Large Hadron Collider (LHC), demonstrate the principles of mass-energy equivalence.

3. Cosmology: In the early universe, during the Big Bang, tremendous amounts of energy were converted into mass as the universe cooled and particles formed.

4. Relativistic Astrophysics: When dealing with extremely massive objects like black holes, the mass-energy equivalence principle is crucial for understanding the immense energies involved in their formation and processes.

5. Medical Imaging: In positron emission tomography (PET) scans, the annihilation of positrons and electrons results in the conversion of mass into energy, and this process is described by E=mc^2

The equation is a fundamental principle of modern physics and has broad applications across various scientific disciplines.

8. What is space time curvature and why is it formed?

Space-time curvature is a concept in Einstein's general theory of relativity that describes how the presence of mass and energy warps the fabric of space and time. Instead of thinking of space and time as separate entities, Einstein combined them into a four-dimensional continuum called space-time.

The curvature of space-time is caused by the mass and energy distribution in the universe. Massive objects, like stars and planets, create a gravitational field around them, and this field causes the space-time fabric to curve. The more massive an object, the more it warps the surrounding space-time.

The curvature of space-time affects the motion of objects within it, including the paths that objects follow under the influence of gravity. Massive objects, in essence, tell space-time how to curve, and the curvature of space-time tells objects how to move.

In summary, space-time curvature is formed due to the presence of mass and energy, and it influences the motion of objects by determining the paths they follow under the influence of gravity.

9. How can I imagine fabric of spacetime?

Imagining the fabric of spacetime can be a challenging but fascinating concept. While our everyday intuition may not directly align with the nature of space-time, you can visualize it using a common analogy:

1. Rubber Sheet Analogy: Imagine space-time as a two-dimensional rubber sheet. Place a heavy object, like a bowling ball, in the center. The weight of the ball causes the sheet to curve around it, creating a depression. Now, imagine smaller objects, like marbles, rolling on the sheet. They will naturally move towards the depression, representing how objects move in the gravitational field created by mass.

2. Warped Grid: Picture a three-dimensional grid representing space and time. In regions with no mass or energy, the grid is flat. However, when a massive object is present, it warps the grid, causing it to curve. Objects then follow the curves in this grid, influenced by the curvature induced by mass.

Remember that these are just visual aids, and the actual nature of space-time is more abstract and mathematical. The curvature of spacetime is a way to describe how gravity works according to Einstein's general relativity, and while these analogies help provide a mental image, they have their limitations.

10. Space and time both are invisible, only effect can be seen. Then how can it form flexible fabric net?

The concept of space-time as a flexible fabric is an analogy used to help us understand how gravity works according to Einstein's general relativity. In reality, space and time are not physical substances like a fabric, but rather a mathematical framework that describes the structure of the universe.

The analogy of a flexible fabric is a way to visualize how mass and energy influence the geometry of space-time. Just as a massive object causes a depression in a rubber sheet, mass causes the curvature of space-time. The "fabric" metaphor is a tool to help us conceptualize the effects of gravity, not a literal description of the nature of space and time.

In essence, while we cannot directly see or touch space and time, we can observe their effects, such as the way objects move under the influence of gravity. The fabric analogy is a visualization aid to make the abstract concepts of general relativity more accessible.

11. Space curve and time curve intersect to form a fabric like structure?

The concept of space-time curvature in general relativity doesn't involve physical intersections of space and time like weaving a fabric. Instead, the idea is that space and time are combined into a four-dimensional continuum—space-time. In this framework, massive objects cause the fabric of space-time to curve.

The curvature of space-time is a mathematical description of how gravity works, showing how the presence of mass and energy influences the geometry of the universe. It's not that space and time are physically intersecting to form a fabric-like structure; rather, the fabric analogy is a visualization tool to help us understand how gravity affects the paths of objects in the universe.

In summary, the fabric-like structure is a metaphorical representation of the curvature of space-time caused by mass and energy, aiding our understanding of gravity's effects in a geometric sense.

12. Fabric of space time is present everywhere?

Yes, according to the principles of Einstein's general theory of relativity, the fabric of space-time exists everywhere in the universe. The curvature of space-time is influenced by the distribution of mass and energy. Even in regions where there may be no visible matter, space-time is still present and subject to curvature.

This concept is crucial in understanding how gravity operates on a cosmic scale. The presence of mass, even if it's diffuse or in the form of dark matter that doesn't emit light, contributes to the curvature of space-time. It's a fundamental aspect of our understanding of the large-scale structure and dynamics of the universe.

13. Does it exert any upthrust on massive body?

The concept of upthrust, commonly associated with buoyancy in fluids, doesn't directly apply to the fabric of space-time or gravity. Upthrust is a force exerted by a fluid (like air or water) that opposes the weight of an immersed object.

In the context of gravity and space-time curvature, massive objects are influenced by the curvature of space-time created by other masses. Gravity causes massive objects to follow curved paths in space-time, and these paths are determined by the distribution of mass and energy.

So, while there is no upthrust in the traditional sense, gravity acts as an attractive force, pulling objects toward each other through the curvature of space-time. The strength of this gravitational interaction depends on the mass and energy distribution in the surrounding space-time.