A Brief History of Time by Stephen Hawking

A Brief History of Time by Stephen Hawking

From the Big Bang to Black Holes

A Brief History of Time by Stephen Hawking

Buy book - A Brief History of Time by Stephen Hawking

What is the subject of the book A Brief History of Time?

Taking a look at both the history of scientific theory and the concepts that shape our current knowledge of the world, A Brief History of Time (1988) is a must-see for anybody interested in the history of science. In this book, Hawking provides a concise summary of both the history of the universe and the complicated physics that underpins it, all presented in a manner that even readers who are being exposed to these concepts for the first time can comprehend.

Who is it that reads the book A Brief History of Time?

  • Anyone who is curious in the origins of the cosmos, anyone who is curious about what quantum physics is, and anyone who is interested in how black holes function

What is Stephen Hawking's background?

PhD in theoretical physics and cosmology, Stephen Hawking (1942-2018) was a theoretical physicist, cosmologist, and author who is best known for his work on Hawking radiation and the Penrose-Hawking theorems. Between 1979 and 2009, Hawking held the Lucasian Professorship of Mathematics at the University of Cambridge, where he was also awarded the Presidential Medal of Freedom. He was also an Honorary Fellow of the Royal Society of Arts and a lifelong member of the Pontifical Academy of Sciences.

What exactly is in it for me? Discover the mysteries of the universe.

 Seeing the sky filled with stars at night is one of the most visually stunning and thought-provoking sights on the planet. There is something about the twinkling of the universe that begs us to take a moment and consider some of the most profound mysteries of the universe. A Brief History of Time will contribute to the illumination of these mysteries by revealing the principles that govern the cosmos. Because it is written in understandable terms, it will assist even those who are not scientifically inclined in understanding why the cosmos exists, how it came to be, and what the future will look like. You will also learn about odd phenomena like as black holes, which are a kind of vacuum that draws everything (or nearly everything) toward them. Even more importantly, you will learn the mysteries of time itself, since these notes offer the answers to queries such as "how quickly is time passing?" as well as "how do we know it's moving forward?"

With certainty, you will never look at the night sky the same way again after listening to these pieces of literature.

Developing theories based on what you've seen in the past may assist you in predicting the future.

 Probability is that you have heard of the theory of gravity or the theory of relativity. But, have you ever taken a moment to consider what we actually mean when we speak about ideas and concepts? To put it simply, a theory is a model that correctly explains huge groupings of data in the most fundamental sense. Scientific observations, such as those made in experiments, are collected and analyzed by scientists, who then utilize the information to create hypotheses for how and why events occur. Examples include the idea of gravity, which was established by Isaac Newton after studying a variety of events ranging from apples falling from trees to the movement of planets. A theory of gravity was developed using the evidence that was gathered by the researcher. Theories offer two significant advantages: First and foremost, they let scientists to make precise predictions about the course of events in the future.

For instance, Newton's theory of gravity enabled scientists to anticipate the future motions of objects such as planets. If you want to know, for example, where Mars will be in six months, you may use the theory of gravity to forecast the location with pinpoint accuracy. Second, theories are always disprovable, which means that they may be revised if new evidence is discovered that contradicts the theory in question. For example, people used to think that the Earth was the center of the universe and that everything else circled around it. As a result of his discovery that Jupiter's moons orbited the planet, Galileo was able to demonstrate that not everything really revolved around the Earth. As a result, no matter how solid a theory seems to be at the time of its formulation, a single future observation may always render it incorrect. As a result, ideas can never be proved to be true, and science is a process that is continuously changing.

A change in the way we think about how things move occurred in the 1600s, thanks to Isaac Newton.

 Prior to Isaac Newton, it was believed that an object's natural condition was one of complete stillness. This implies that if there were no external force acting on the item, it would stay totally still. Newton, in the 1600s, demonstrated conclusively that this long-held notion was incorrect. A new hypothesis was presented in its place, according to which everything in the cosmos, rather than being static, was really always in motion. Newton came to this conclusion as a result of his finding that the planets and stars in the cosmos were continuously moving in their relationship to one another. Examples include the fact that the Earth is continuously revolving around the Sun and that the whole solar system is rotating around the galaxy. As a result, nothing is ever really motionless. Newton devised three laws of motion to explain the movement of all things in the universe:

All objects will continue traveling in a straight path if they are not acted on by another force, according to the first of Newton's laws of motion. This was shown by Galileo in an experiment in which he rolled balls down a hill to illustrate his point. They rolled in a straight path since there was no other force acting on them other than gravity. Specifically, Newton's second law says that an object will accelerate at a rate that is proportionate to the force exerted on it. Consider the following example: a vehicle with a more powerful engine will accelerate more quickly than a vehicle with a less powerful engine. This rule also says that the larger the mass of a body, the less effect a force has on its motion, and vice versa. A larger vehicle will take longer to accelerate than a lighter vehicle if two vehicles have the same engine.

Gravity is described by Newton's third law. It asserts that all bodies in the universe are attracted to one another by a force that is proportional to the mass of the objects being attracted to. This implies that if you double the mass of one item, the force acting on it will be twice as powerful. If you double the mass of one item and treble the mass of another, the force will be six times as strong.

The fact that the speed of light is constant demonstrates that it is not always possible to measure something's speed in relation to another's speed.

 After seeing how Newton's theory did away with absolute rest and replaced it with the notion that an object's movement is relative to the movement of something else, we can see how it is still in use today. However, the theory also indicated that the relative speed of an item is important. Consider the following scenario: you are seated on a train that is traveling at 100 miles per hour and reading a book. I'm curious how quickly you're traveling. According to a witness who is watching the train go past, you are traveling at 100 miles per hour. However, in relation to the book you are now reading, your speed is 0 miles per hour. As a result, your speed is measured in relation to another item. However, one significant flaw in Newton's theory was discovered: the speed of light.

The speed of light is constant, not relative, and cannot be measured. It moves at a constant speed of 186,000 miles per second. Whatever else is moving at a faster rate than light, the speed of light will stay constant regardless. For example, if a train traveling at 100 miles per hour approached a beam of light, the speed of light would be 186,000 miles per second, according to the formula. However, even if that train came to a complete stop at a red signal, the beam of light would still be traveling at 186,000 miles per second. It makes no difference who is looking at the light or how fast they are moving; the light's speed will always remain constant. Newton's hypothesis is jeopardized as a result of this finding. When something moves, how can the speed of the object remain constant independent of the state of the observer? Fortunately, the solution was found in the early twentieth century, when Albert Einstein proposed his general theory of relativity.

According to the theory of relativity, time itself is not a fixed quantity.

 The fact that the speed of light remains constant was an issue for Newton's theory since it demonstrated that speed is not necessarily relative. As a result, scientists need an updated model that took into account the speed of light. The theory of relativity, created by Albert Einstein, is an example of such a theory. According to the theory of relativity, the rules of science apply equally to all observers who are free to move about. This implies that no matter what pace someone is traveling at, they will always experience the same speed of light. Although this seems to be fairly simple at first sight, one of its fundamental propositions is really extremely difficult for many people to grasp: the idea that time is relative is one of the most hardest to grasp.

Due to the fact that light does not vary in speed when seen by observers traveling at various speeds, witnesses traveling at different speeds relative to one another would actually estimate different times for the same occurrence. Consider the following scenario: a flash of light is sent out to two witnesses, one of whom is moving toward the light and the other who is traveling at a faster speed in the opposite direction of the light. Both viewers would experience the same speed of light, despite the fact that they are moving at very different speeds and in opposite directions. This would imply that they both see the flash event as though it occurred at a different moment than the other, which is incredible. This is due to the fact that time is defined by the distance something has gone divided by the speed at which it has moved. Although the speed of light is the same for both viewers, due to the difference in distance, time is relative to each observer in this case.

If both witnesses were equipped with clocks to record the moment the pulse of light was produced, they would be able to certify two distinct timings for the same occurrence. So, who is correct? In none of the observers' views; time is relative and unique to each of their perspectives!

Because it is impossible to obtain precise measurements of particles, scientists rely on a concept known as quantum state to make predictions.

 Everything in the universe is made up of particles such as electrons and photons. Scientists seek to measure them and analyze their speed in order to understand more about the cosmos and its inhabitants. When you attempt to examine particles, though, you will see that they behave in an unusual manner. Oddly enough, the more precisely you attempt to measure the location of a particle, the more uncertain its speed becomes; conversely, the more precisely you attempt to measure its speed, the less definite its position becomes. The uncertainty principle is the name given to this phenomena, which was originally identified in the 1920s. A consequence of the uncertainty principle was that scientists were forced to find other methods of looking at particles, leading them to begin looking at a particle's quantum state instead. The quantum state of a particle is a combination of several probable potential locations and speeds of the particle.

Because scientists are unable to determine a particle's precise location or velocity, they must consider the numerous possible places and velocities that particles may occupy. Researchers monitor every possible location where a particle might be and then choose the most probable one from among them as the particle travels around. Scientists treat particles as if they were waves in order to aid them in determining this. Because a particle may be in a plethora of various locations at the same time, they seem as a sequence of continuous, oscillating waves in their appearance. Consider the image of a piece of vibrating thread. When the string vibrates, it will arc and dip through a range of peaks and troughs. A particle acts in a similar manner, but its potential route is comprised of a sequence of overlapping waves that all occur at the same time.

Observing particles in this manner assists scientists in determining where a particle is most likely to be found. Most probable particle locations are those in which the arcs and peaks on the numerous waves coincide with one another, while the least likely particle locations are those in which they do not. This is referred to as interference, and it reveals which locations and speeds are most likely for the particle wave to go along its route.

Gravity is the consequence of large things bending the fabric of space-time to their will.

 When you look around you, you are viewing the world in three dimensions, which means that you can characterize every item by its height, width, and depth measurements. The fact remains that there is a fourth dimension, although one that we cannot see: time, which when combined with the other three dimensions forms a phenomenon known as space-time. Scientists utilize this four-dimensional model of space-time to explain the events that take place across the cosmos. In the context of time and space, an event is anything that takes place at a certain point in time. As a result, when determining the location of an event in conjunction with the three-dimensional coordinates, scientists include a fourth coordinate to represent the time of the occurrence. In order to determine the location of an event, scientists must take time into account since the theory of relativity says that time is relative. Therefore, it is an essential element in defining the nature of a particular incident.

The combination of space and time has had a remarkable effect on our understanding of gravity, which has evolved dramatically as a result. Gravity is the consequence of large objects bending the space-time continuum, as described above. When a large mass, such as our sun, curves, it has the effect of altering space-time. Consider the following scenario: Consider the concept of space-time as a blanket that is spread out and held in the air. If you put an item in the center of the blanket, the blanket will curve and the object will sink a little bit in the middle of the blanket. This is the effect that enormous things have on the fabric of space-time.

Other things will then follow these curves in space-time as they move across space. This is due to the fact that an item always chooses the shortest path between two locations, which is a circular orbit around a bigger object in the universe. If you take another look at the blanket, you'll see something. Putting a big item like an orange on the blanket and then attempting to roll a smaller object past it will result in the marble following the depression left behind by the orange. Gravity operates in the same manner!

In the event of the death of a star with a large mass, the star collapses into a singularity known as a black hole.

 In order to generate heat and light, stars need tremendous quantities of energy during their whole lives. However, this energy does not endure indefinitely; ultimately, it exhausts itself, causing the star to die. What happens to a star after it dies is determined by the size of the star. When a massive star exhausts its energy reserves, something extraordinary occurs: the formation of a black hole. Because the gravitational field of the majority of big stars is so powerful, a black hole may form. It is possible for the star to utilize its energy to prevent itself from collapsing as long as it is still alive. After running out of energy, the star is no longer able to defy gravity and its disintegrating body eventually collapses in on itself. Everything is being drawn inwards into a singularity, which is an endlessly dense, spherical point that exists nowhere else in the universe. This singularity is referred to as a black hole.

Space-time becomes twisted so sharply as a result of the gravity of a black hole that even light is bent along its path. Not only does a black hole pull in everything in its vicinity, but it also prevents anything that crosses a certain boundary around it from escaping again: this point of no return is known as the event horizon, and nothing, not even light, which travels faster than anything else in the universe, can escape back over it. A black hole's event horizon is defined as the point beyond which nothing can escape again. This poses an interesting question: since a black hole absorbs light and everything else that crosses its event horizon, how can we tell whether they are really there in the universe? Astronomers hunt for black holes by observing the gravitational impact they have on the cosmos as well as the X-rays emitted by their interaction with orbiting stars.

For example, astronomers search for stars circling dark and huge objects that may or may not be black holes in order to learn more about them. They are also on the lookout for X-rays and other waves that are frequently generated by matter as it is dragged into and ripped apart by a black hole. An even more mysterious source of radio and infrared radiation has been discovered in our galaxy's core; this source is thought to be a supermassive black hole.

Black holes produce radiation, which may cause them to evaporate, ultimately resulting in their death.

 The gravitational attraction of a black hole is so powerful that not even light can escape it. It stands to reason that nothing else would be able to escape as well. You'd be mistaken, however. As a matter of fact, black holes must emit something in order to avoid violating the second rule of thermodynamics. It is stated in the universal second rule of thermodynamics that entropy, or the trend toward greater disorder, rises at all times. And when entropy rises, the temperature must increase as well. A good illustration of this is the way a fire-poker burns red-hot after being placed in a fire and emits radiation in the form of heat. According to the second rule of thermodynamics, since black holes absorb disordered energy from the cosmos, the entropy of the black hole should rise as a result of this. And, as a result of the rise in entropy, black holes should be forced to allow heat to escape.

Although nothing can escape from a black hole's event horizon, virtual pairs of particles and antiparticles near the event horizon are able to do so because the second law of thermodynamics is conserved in the vicinity of the event horizon. Particles that cannot be observed but whose impacts may be quantified are referred to as virtual particles. One of the members in the couple has positive energy, while the other possesses negatively charged energy. Because of the strength of gravitational attraction in a black hole, a negative particle may be sucked into the black hole and, in doing so, provide its particle partner with enough energy to potentially escape into the cosmos and be released as heat. It is possible for the black hole to emit radiation in this manner, allowing it to obey the second law of thermodynamics.

The quantity of positive radiation released is counterbalanced by the amount of negative radiation pulled into the black hole by the black hole. This inward influx of negative particles has the potential to decrease the mass of the black hole until it ultimately evaporates and dies. And, if the black hole's mass is reduced to a sufficiently minimal value, it will most likely terminate in a huge final explosion equivalent to millions of H-bombs.

Despite the fact that we cannot be certain, there are significant indications that time will only continue to march ahead.

 Consider the possibility that the universe began to shrink and time began to flow backward. What would it be like to be there? The possibility exists that the clocks will go backwards and the path of history will be reversed. However, while scientists have not entirely dismissed the possibility, three significant indications indicate that time is moving forward exclusively. The thermodynamic arrow of time is the initial indication that time is passing from one point in the past to another point in the future. According to the second law of thermodynamics, entropy — the disorder of a closed system – tends to grow as time progresses in every closed system. This implies that the propensity of disorder to grow may be used to gauge the passage of time.

In the case of a cup that accidentally falls off a table and breaks, the order has been disrupted, and the entropy has risen. Because a shattered cup will never spontaneously reunite and enhance its order, we may conclude that time is only moving forward. The shattered cup and the thermodynamic arrow of time are both elements of the second indicator of forward time, which is controlled by memory and is represented by the psychological arrow of time as well. When you may recall the cup being on the table after it has been broken, you will not be able to "recall" its future location on the floor while it was still on the table before it has been shattered. The third indication, the cosmological arrow of time, refers to the expansion of the cosmos, and it corresponds to our experience of the thermodynamic arrow of time as well as the growth of our knowledge of it. This is due to the fact that entropy rises as the cosmos expands.

After reaching a certain point in time, chaos in the cosmos may cause the universe to shrink, thus reversing the direction of time in the cosmic arrow of time. However, we would not be aware of it since intelligent creatures can only live in an environment where chaos is increasing. The reason for this is because humans depend on the process of entropy to convert our food into usable form of energy. Because of this, we will continue to perceive the cosmic arrow of time as moving forward as long as we are alive.

There are three basic forces in the cosmos, in addition to gravity. These are: attraction, attraction, and attraction.

 Are there any particular forces operating in the universe? The majority of people will only be familiar with one of these forces: gravity, which is the force that attracts things to one another and which is felt in the manner that the Earth's gravity pulls us to its surface. The majority of people, on the other hand, are not aware that there are really three more forces that operate on the tiniest particles. When a magnet clings to a refrigerator or when you recharge your mobile phone, you are experiencing electromagnetic force, which is the first of these forces. It has an effect on all charged particles, including as electrons and quarks, as well as on their electric charges.

Magnets have north and south poles that may attract or repel other magnets. Positively charged particles attract negative particles and push away other positive particles, and vice versa. Electromagnetic force is represented by the north and south poles of a magnet. This force is considerably stronger than gravity and has a far greater influence at the atomic level than gravity does. For example, the electromagnetic force causes an electron to circle around the nucleus of an atom in a circular motion. The second kind of nuclear force is the weak nuclear force, which operates on all of the particles that make up matter and is responsible for the production of radioactivity. This force is referred to as "weak" because the particles that transport it can only exert force over a short distance, hence earning the name. Because of the increasing intensity of the weak nuclear force at higher energy, it eventually surpasses that of the electromagnetic force.

It is the third kind of nuclear force that holds protons and neutrons together in the nucleus of an atom as well as the smaller quarks contained inside protons and neutrons together. Strong nuclear force, in contrast to electromagnetic force and weak nuclear force, becomes weaker as the energy of the particle increases. During a period of very high energy, referred to as grand unification energy, the electromagnetic force becomes stronger and the weak nuclear force becomes weaker, while the strong nuclear force becomes weaker. At that moment, all three forces achieve equal strength and merge together to form various facets of a single force: a force that may have had a part in the formation of the universe, according to certain theories.

Despite the fact that scientists think the universe began with the big bang, they are unclear of the precise circumstances of how this occurred.

 The vast majority of scientists think that time started with the big bang - the instant when the universe transitioned from an endlessly dense state to a rapidly expanding entity that is still expanding today.... Although a variety of hypotheses have been suggested to explain how such a massive expansion of the universe might have occurred, scientists are still uncertain about how the big bang occurred. The hot big bang model of the universe's origin is the most generally accepted hypothesis of the universe's origin. According to this hypothesis, the cosmos began with a size of zero and was endlessly hot and dense to begin with. During the great bang, it expanded, and as it grew, the temperature of the universe dropped as the heat was dispersed across the universe. The majority of the components that exist in the universe today were formed within the first few hours of cosmic expansion.

Because of gravity, as the universe continued to expand, denser areas of expanding matter began to rotate, resulting in the formation of galaxies. Clouds of hydrogen and helium gases compressed inside these newly formed galaxies, causing the universe to expand. Their clashing atoms triggered nuclear fusion events, which resulted in the formation of stars. In subsequent years, as these stars perished and imploded, they triggered massive stellar explosions that expelled even more elements into the cosmos. As a result, new stars and planets were formed from the raw materials supplied by the Big Bang. Despite the fact that this is the widely recognized model of the big bang and the beginning of time, it is not the only one.

The inflationary model is another another option to consider. It is proposed in this scenario that the energy of the early cosmos was so tremendously great that the strengths of the strong nuclear force, the weak nuclear force, and the electromagnetic force were all equal in intensity. As the cosmos grew in size, however, the three forces began to vary significantly in their relative intensities. An tremendous quantity of energy was released as a result of the separation of the forces. An anti-gravitational effect would have resulted, forcing the cosmos to expand quickly and at an ever-increasing pace.

General relativity and quantum physics have not been able to be reconciled by physicists.

 The development of two main ideas has resulted from scientists' quest to better comprehend and explain the cosmos. A fundamental concept in physics is general relativity, which is concerned with a very big phenomena in the universe: gravity. One of the most fascinating branches of science is quantum physics, which deals with some of the tiniest things in the universe known to man: subatomic particles smaller than atoms. While both theories offer valuable insights, there are significant discrepancies between what is predicted by the equations of quantum physics and what is predicted and seen by general relativity, despite the fact that both theories are correct. This implies that, at this time, there is no way to combine them all into a single comprehensive unified theory of everything.

There is a problem with combining the two theories since many of the equations used in quantum physics result in apparently impossible infinite values, which makes it difficult to combine the two theories. Consider the fact that the equations of space-time predict that the curve of space-time is endless, which has been shown to be incorrect by observations. Attempts are being made by scientists to add other infinities into the equation in order to cancel out these infinities. It is unfortunate that this limits the accuracy with which scientists can forecast the future. It follows as a consequence that, rather than utilizing quantum physics equations to forecast occurrences, it is necessary to include the events themselves and modify the equations to make them fit! In a second, related issue, quantum theory proposes that all of the empty space in the cosmos is made up of virtual pairs of particles and antiparticles, which is inconsistent with reality.

The presence of these virtual pairings, on the other hand, creates problems for general relativity theory. This is due to the fact that the cosmos has an unlimited quantity of empty space and thus the energy of these pairings would have to have an infinite amount of energy. This is troublesome since Einstein's famous equation E=mc2 implies that the mass of an item is equal to its energy, which is a false assumption. As a result, the unlimited energy of these virtual particles would imply that they would likewise possess an endless mass. If there were unlimited mass, the whole universe would collapse under the strong gravitational attraction of the sun, resulting in the formation of one single black hole.

Summary at the end

Many people are turned off by physics because they see it as an inaccessible realm of long equations and complicated ideas. This is the primary message conveyed by these notes: This is true to a certain degree, but not entirely. However, the intricacy of physics should not deter those of us who are not specialists from understanding how and why the universe functions. Many rules and regulations exist to aid us in our quest to comprehend the mysteries of our world and our place within it. Rules and rules that are understandable to the majority of us. And, once we grasp their significance, we may begin to view the world in a different way.

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Written by BrookPad Team based on A Brief History of Time by Stephen Hawking

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