A Brief History of Time - Stephen Hawking
A Brief History of Time - Stephen Hawking
1. Our Picture of the Universe
Aristotle was the first to say that earth was round rather than flat, based on two observations-
a. In an Eclipses the shadow of earth was round.
b. North Star appeared lower in the sky when viewed in the South, than in the north.
Nicholas Copernicus first prosed the idea that Sun was stationary and Earth is revolving around it.
Edwin Hubble made the observation that wherever you look, distant galaxies are moving away from each other. In other words universe is expanding.
Today scientists describe the universe in terms of two basis partial theories - the general theory of relativity and quantum mechanics. Unfortunately these theories are found to be inconsistent with each other, the major search is to find one theory that will combine both - quantum theory of Gravity
2. Space and Time
Both Aristotle and Newton believed in absolute time.
Michelson-Morley experiment:
The result was negative, in that Michelson and Morley found no significant difference between the speed of light in the direction of movement through the presumed aether, and the speed at right angles.
Special Theory of Relativity:
Postulate 1: There is no preferred frame of reference. Everything works the same in any given frame of reference.
Postulate 2: The speed of light is the same in all frames of reference. All observers should measure the same speed of light, no matter how fast they are moving.
E=MC2 - nothing may travel faster than speed of light. Equivalence of mass and energy. As an object reaches speed of light, its mass rises ever more quickly, so it takes more and more energy to speed it up further. It can in fact never reach the speed of light, because by then its mass would have become infinite, and it would have taken infinite amount of E to get there. Only light, or other waves that have no intrinsic mass, can move at the speed of light.
General Theory of Relativity:
Gravity is not a force like other force, but is a consequence of the fact that space-time is not flat. It is curved or warped by the distribution of mass and energy in it. Bodies like Earth are not made to move on curved orbits by a force called gravity; instead they follow the nearest thing to a straight path in a curved space, which is is called as geodesic. Bodies always follow straight line in 4D space-time, but they nevertheless appears to us to move along curved paths in our 3D space.
The mass of sun curves space-time in such a way that although the earth follows a straight path in 4D space-time, it appears to us to move along a circular orbit in 3D space.
Another prediction is that time should appear to run slower near a massive body like the earth. This is because there is a relation between the energy of light and its frequency. As light travels up in the earth's gravitational field, it loses energy, and so its frequency goes down. To someone high up, it would appear that everything down below was taking longer to happen.
Twins Paradox: If one twin lives at sea level and another on the top of a mountain, then first twin will age faster than the second.
Time dilation:
In Newton's theory, if a pulse of light is sent from one place to another, different observers would agree on the time that the journey took, since the time is absolute.
In relativity, all observers must agree on the speed of light as constant. Hence there is no absolute time.
In below examples two frame of references are there. A - Inside a moving object. B - Outside as a stationary (relative) frame of reference. Time taken by the speed of light to the origin is to be measured by the person inside frame A (moving) and B observing from outside.
A - Distance is 2L, and time = 2L / c
B - Distance is >2L, and time = >2L / c
Time observed by the person standing outside (B) is more than measured by (A).
The uncertainty principle is at the heart of many things that we observe but cannot explain using classical (non-quantum) physics. Take atoms, for example, where negatively-charged electrons orbit a positively-charged nucleus. By classical logic, we might expect the two opposite charges to attract each other, leading everything to collapse into a ball of particles. The uncertainty principle explains why this doesn't happen: if an electron got too close to the nucleus, then its position in space would be precisely known and, therefore, the error in measuring its position would be minuscule. This means that the error in measuring its momentum (and, by inference, its velocity) would be enormous. In that case, the electron could be moving fast enough to fly out of the atom altogether.
Big Bang
How are Stars formed - A star is formed when a large amount of gas (mostly Hydogen) starts to collapse on itself due to its gravitational attraction. As it contracts the atoms of the gas collide with each other more and more frequently and at a greater and greater speeds - the gas heats up. Eventually, the gas will be so hot that when the Hy atom collide they no longer bounce off each other, but instead coalesce to form Helium. The heat released in this reaction, which is like a controlled Hy bomb explosion is what makes the star shine. This additional heat also increases the pressure of the gas until it is sufficient to balance the gravitational attraction, and the gas stops contracting. Stars will remain stable like this for a long time, with heat from the nuclear reaction balancing the gravitational attraction. Eventually, however the star will run out of its Hy and other nuclear fuels. When a star runs out of fuel, it starts to cool off and so it contracts.
1. Our Picture of the Universe
Aristotle was the first to say that earth was round rather than flat, based on two observations-
a. In an Eclipses the shadow of earth was round.
b. North Star appeared lower in the sky when viewed in the South, than in the north.
Nicholas Copernicus first prosed the idea that Sun was stationary and Earth is revolving around it.
Edwin Hubble made the observation that wherever you look, distant galaxies are moving away from each other. In other words universe is expanding.
Today scientists describe the universe in terms of two basis partial theories - the general theory of relativity and quantum mechanics. Unfortunately these theories are found to be inconsistent with each other, the major search is to find one theory that will combine both - quantum theory of Gravity
2. Space and Time
Both Aristotle and Newton believed in absolute time.
Michelson-Morley experiment:
The result was negative, in that Michelson and Morley found no significant difference between the speed of light in the direction of movement through the presumed aether, and the speed at right angles.
Special Theory of Relativity:
Postulate 1: There is no preferred frame of reference. Everything works the same in any given frame of reference.
Postulate 2: The speed of light is the same in all frames of reference. All observers should measure the same speed of light, no matter how fast they are moving.
E=MC2 - nothing may travel faster than speed of light. Equivalence of mass and energy. As an object reaches speed of light, its mass rises ever more quickly, so it takes more and more energy to speed it up further. It can in fact never reach the speed of light, because by then its mass would have become infinite, and it would have taken infinite amount of E to get there. Only light, or other waves that have no intrinsic mass, can move at the speed of light.
General Theory of Relativity:
Gravity is not a force like other force, but is a consequence of the fact that space-time is not flat. It is curved or warped by the distribution of mass and energy in it. Bodies like Earth are not made to move on curved orbits by a force called gravity; instead they follow the nearest thing to a straight path in a curved space, which is is called as geodesic. Bodies always follow straight line in 4D space-time, but they nevertheless appears to us to move along curved paths in our 3D space.
The mass of sun curves space-time in such a way that although the earth follows a straight path in 4D space-time, it appears to us to move along a circular orbit in 3D space.
Another prediction is that time should appear to run slower near a massive body like the earth. This is because there is a relation between the energy of light and its frequency. As light travels up in the earth's gravitational field, it loses energy, and so its frequency goes down. To someone high up, it would appear that everything down below was taking longer to happen.
Twins Paradox: If one twin lives at sea level and another on the top of a mountain, then first twin will age faster than the second.
Time dilation:
In Newton's theory, if a pulse of light is sent from one place to another, different observers would agree on the time that the journey took, since the time is absolute.
In relativity, all observers must agree on the speed of light as constant. Hence there is no absolute time.
In below examples two frame of references are there. A - Inside a moving object. B - Outside as a stationary (relative) frame of reference. Time taken by the speed of light to the origin is to be measured by the person inside frame A (moving) and B observing from outside.
A - Distance is 2L, and time = 2L / c
B - Distance is >2L, and time = >2L / c
Time observed by the person standing outside (B) is more than measured by (A).
Heisenberg Uncertainty Principle
Seeing a subatomic particle, such as an electron, is not so simple. You might similarly bounce a photon off it and then hope to detect that photon with an instrument. But chances are that the photon will impart some momentum to the electron as it hits it and change the path of the particle you are trying to measure. Or else, given that quantum particles often move so fast, the electron may no longer be in the place it was when the photon originally bounced off it. Either way, your observation of either position or momentum will be inaccurate and, more important, the act of observation affects the particle being observed.The uncertainty principle is at the heart of many things that we observe but cannot explain using classical (non-quantum) physics. Take atoms, for example, where negatively-charged electrons orbit a positively-charged nucleus. By classical logic, we might expect the two opposite charges to attract each other, leading everything to collapse into a ball of particles. The uncertainty principle explains why this doesn't happen: if an electron got too close to the nucleus, then its position in space would be precisely known and, therefore, the error in measuring its position would be minuscule. This means that the error in measuring its momentum (and, by inference, its velocity) would be enormous. In that case, the electron could be moving fast enough to fly out of the atom altogether.
Big Bang
How are Stars formed - A star is formed when a large amount of gas (mostly Hydogen) starts to collapse on itself due to its gravitational attraction. As it contracts the atoms of the gas collide with each other more and more frequently and at a greater and greater speeds - the gas heats up. Eventually, the gas will be so hot that when the Hy atom collide they no longer bounce off each other, but instead coalesce to form Helium. The heat released in this reaction, which is like a controlled Hy bomb explosion is what makes the star shine. This additional heat also increases the pressure of the gas until it is sufficient to balance the gravitational attraction, and the gas stops contracting. Stars will remain stable like this for a long time, with heat from the nuclear reaction balancing the gravitational attraction. Eventually, however the star will run out of its Hy and other nuclear fuels. When a star runs out of fuel, it starts to cool off and so it contracts.
When the star becomes small, the matter particles get very near to each other, and so according to the Pauli's exclusion principle, they must have very different velocities. This make them move away from each other and so tend to make the star expand, A star can therefore maintain itself at a constant radius by a balance between the attraction of gravity and the repulsion that arises from the exclusion principle, just as earlier in its life gravity was balances by heat. Chandrashekhar, however realised that there was limit to the repulsion that the exclusion principle can provide. The theory of relativity limits the maximum difference of velocities to speed of light. This means that when the star got sufficiently dense, the repulsion caused by the exclusion principle would be less than the attraction of gravity. Chandrashekhar calculated that cold star of more than 1.5 times the mass of sun would not be able to support itself against its own gravity. If a stars mass is less than C limit, it can eventually stop contracting and settle down to a possible final state as a "white dwarf". Other possible states are also possible as Neutron stars.
[NASA
Stars are born within the clouds of dust and scattered throughout most galaxies. A star the size of our Sun requires about 50 million years to mature from the beginning of the collapse to adulthood. Our Sun will stay in this mature phase for approximately 10 billion years. Stars are fueled by the nuclear fusion of hydrogen to form helium deep in their interiors. The outflow of energy from the central regions of the star provides the pressure necessary to keep the star from collapsing under its own weight, and the energy by which it shines. In general, the larger a star, the shorter its life. When a star has fused all the hydrogen in its core, nuclear reactions cease. Deprived of the energy production needed to support it, the core begins to collapse into itself and becomes much hotter. Hydrogen is still available outside the core, so hydrogen fusion continues in a shell surrounding the core. The increasingly hot core also pushes the outer layers of the star outward, causing them to expand and cool, transforming the star into a red giant.
Our own Sun will be a white dwarf billions of years from now. White dwarfs are intrinsically very faint because they are so small and, lacking a source of energy production, they fade into oblivion as they gradually cool down. This fate awaits only those stars with a mass up to about 1.4 times the mass of our Sun. Above that mass, electron pressure cannot support the core against further collapse. Such stars suffer a different fate as described below.
White Dwarfs May Become Novae
If a white dwarf is close enough to a companion star, its gravity may drag matter - mostly hydrogen - from the outer layers of that star onto itself, building up its surface layer. When enough hydrogen has accumulated on the surface, a burst of nuclear fusion occurs, causing the white dwarf to brighten substantially and expel the remaining material. Within a few days, the glow subsides and the cycle starts again. Sometimes, particularly massive white dwarfs (those near the 1.4 solar mass limit mentioned above) may accrete so much mass in the manner that they collapse and explode completely, becoming what is known as a supernova.
Supernovae Leave Behind Neutron Stars or Black Holes
Main sequence stars over eight solar masses are destined to die in a titanic explosion called a supernova. A supernova is not merely a bigger nova. In a nova, only the star's surface explodes. In a supernova, the star's core collapses and then explodes. In massive stars, a complex series of nuclear reactions leads to the production of iron in the core. Having achieved iron, the star has wrung all the energy it can out of nuclear fusion - fusion reactions that form elements heavier than iron actually consume energy rather than produce it. The star no longer has any way to support its own mass, and the iron core collapses. In just a matter of seconds the core shrinks from roughly 5000 miles across to just a dozen, and the temperature spikes 100 billion degrees or more. The outer layers of the star initially begin to collapse along with the core, but rebound with the enormous release of energy and are thrown violently outward. Supernovae release an almost unimaginable amount of energy. For a period of days to weeks, a supernova may outshine an entire galaxy. Likewise, all the naturally occurring elements and a rich array of subatomic particles are produced in these explosions. On average, a supernova explosion occurs about once every hundred years in the typical galaxy. About 25 to 50 supernovae are discovered each year in other galaxies, but most are too far away to be seen without a telescope.
Main sequence stars over eight solar masses are destined to die in a titanic explosion called a supernova. A supernova is not merely a bigger nova. In a nova, only the star's surface explodes. In a supernova, the star's core collapses and then explodes. In massive stars, a complex series of nuclear reactions leads to the production of iron in the core. Having achieved iron, the star has wrung all the energy it can out of nuclear fusion - fusion reactions that form elements heavier than iron actually consume energy rather than produce it. The star no longer has any way to support its own mass, and the iron core collapses. In just a matter of seconds the core shrinks from roughly 5000 miles across to just a dozen, and the temperature spikes 100 billion degrees or more. The outer layers of the star initially begin to collapse along with the core, but rebound with the enormous release of energy and are thrown violently outward. Supernovae release an almost unimaginable amount of energy. For a period of days to weeks, a supernova may outshine an entire galaxy. Likewise, all the naturally occurring elements and a rich array of subatomic particles are produced in these explosions. On average, a supernova explosion occurs about once every hundred years in the typical galaxy. About 25 to 50 supernovae are discovered each year in other galaxies, but most are too far away to be seen without a telescope.
Neutron Stars
If the collapsing stellar core at the center of a supernova contains between about 1.4 and 3 solar masses, the collapse continues until electrons and protons combine to form neutrons, producing a neutron star. Neutron stars are incredibly dense - similar to the density of an atomic nucleus. Because it contains so much mass packed into such a small volume, the gravitation at the surface of a neutron star is immense. Like the White Dwarf stars above, if a neutron star forms in a multiple star system it can accrete gas by stripping it off any nearby companions. The Rossi X-Ray Timing Explorer has captured telltale X-Ray emissions of gas swirling just a few miles from the surface of a neutron star.
Neutron stars also have powerful magnetic fields which can accelerate atomic particles around its magnetic poles producing powerful beams of radiation. Those beams sweep around like massive searchlight beams as the star rotates. If such a beam is oriented so that it periodically points toward the Earth, we observe it as regular pulses of radiation that occur whenever the magnetic pole sweeps past the line of sight. In this case, the neutron star is known as a pulsar.
If the collapsing stellar core at the center of a supernova contains between about 1.4 and 3 solar masses, the collapse continues until electrons and protons combine to form neutrons, producing a neutron star. Neutron stars are incredibly dense - similar to the density of an atomic nucleus. Because it contains so much mass packed into such a small volume, the gravitation at the surface of a neutron star is immense. Like the White Dwarf stars above, if a neutron star forms in a multiple star system it can accrete gas by stripping it off any nearby companions. The Rossi X-Ray Timing Explorer has captured telltale X-Ray emissions of gas swirling just a few miles from the surface of a neutron star.
Neutron stars also have powerful magnetic fields which can accelerate atomic particles around its magnetic poles producing powerful beams of radiation. Those beams sweep around like massive searchlight beams as the star rotates. If such a beam is oriented so that it periodically points toward the Earth, we observe it as regular pulses of radiation that occur whenever the magnetic pole sweeps past the line of sight. In this case, the neutron star is known as a pulsar.
Black Holes
If the collapsed stellar core is larger than three solar masses, it collapses completely to form a black hole: an infinitely dense object whose gravity is so strong that nothing can escape its immediate proximity, not even light. Since photons are what our instruments are designed to see, black holes can only be detected indirectly. Indirect observations are possible because the gravitational field of a black hole is so powerful that any nearby material - often the outer layers of a companion star - is caught up and dragged in. As matter spirals into a black hole, it forms a disk that is heated to enormous temperatures, emitting copious quantities of X-rays and Gamma-rays that indicate the presence of the underlying hidden companion.
If the collapsed stellar core is larger than three solar masses, it collapses completely to form a black hole: an infinitely dense object whose gravity is so strong that nothing can escape its immediate proximity, not even light. Since photons are what our instruments are designed to see, black holes can only be detected indirectly. Indirect observations are possible because the gravitational field of a black hole is so powerful that any nearby material - often the outer layers of a companion star - is caught up and dragged in. As matter spirals into a black hole, it forms a disk that is heated to enormous temperatures, emitting copious quantities of X-rays and Gamma-rays that indicate the presence of the underlying hidden companion.
From the Remains, New Stars Arise
The dust and debris left behind by novae and supernovae eventually blend with the surrounding interstellar gas and dust, enriching it with the heavy elements and chemical compounds produced during stellar death. Eventually, those materials are recycled, providing the building blocks for a new generation of stars and accompanying planetary systems.]
The dust and debris left behind by novae and supernovae eventually blend with the surrounding interstellar gas and dust, enriching it with the heavy elements and chemical compounds produced during stellar death. Eventually, those materials are recycled, providing the building blocks for a new generation of stars and accompanying planetary systems.]
The picture that we have from Oppenheimers work is - the gravitational field of the star changes the path of light rays in space time. When the star has shrunk to a certain critical radius, the gravitational field at the surface becomes so strong that the light cones are bent inwards so much that light can no longer escape. This region is what we now call a black hole. The boundary is called the event horizon and it coincides with the paths of the light rays that just fail to escape from the black hole. Acc to general relativity, there must be a singularity of infinite density and space time curvature within a black hole. At this singularity the laws of science and our ability to predict the future would break down. Singularities exist inside the black hole only. Weak cosmic censorship hypothesis - it protects observers who remain outside the black hole from the consequences of the breakdown of predictability that occurs at the singularity. In some solutions of the equation the astronaut falling into the black hole may not hit singularity but instead fall through "wormhole" and come out in another region of the universe.
The rate of energy loss in case of Earth and Sun is very low- about enough to run a small electric heater. This means it will take 1k mn mn mn mn years for Earth to run into Sun.
Any non rotating star, however complicated its shape and internal structure, would end up after gravitational collapse as a perfectly spherical black hole.
"Kerr black hole" rotates at constant rate.
After gravitational collapse a black hole must settle down into a state in which it could be rotating, but not pulsating. Its size and shape would depend only on its mass and rate of rotation, and not on the nature of body that had collapsed to form it.
Pulsars
We also have some evidence that there is a much large black hole, with a mass of about a 100 1k times that of the sun, at the centre of our galaxy. The extra gravitational attraction of such a large number of black holes could explain why our galaxy rotates at the rate it does.
NASA
Black holes can be big or small. Scientists think the smallest black holes are as small as just one atom. These black holes are very tiny but have the mass of a large mountain. Another kind of black hole is called "stellar." Its mass can be up to 20 times more than the mass of the sun. There may be many, many stellar mass black holes in Earth's galaxy. Earth's galaxy is called the Milky Way. The largest black holes are called "supermassive." These black holes have masses that are more than 1 million suns together. Scientists have found proof that every large galaxy contains a supermassive black hole at its center. The supermassive black hole at the center of the Milky Way galaxy is called Sagittarius A. It has a mass equal to about 4 million suns and would fit inside a very large ball that could hold a few million Earths.
https://www.youtube.com/watch?v=e-P5IFTqB98
The rate of energy loss in case of Earth and Sun is very low- about enough to run a small electric heater. This means it will take 1k mn mn mn mn years for Earth to run into Sun.
Any non rotating star, however complicated its shape and internal structure, would end up after gravitational collapse as a perfectly spherical black hole.
"Kerr black hole" rotates at constant rate.
After gravitational collapse a black hole must settle down into a state in which it could be rotating, but not pulsating. Its size and shape would depend only on its mass and rate of rotation, and not on the nature of body that had collapsed to form it.
Pulsars
We also have some evidence that there is a much large black hole, with a mass of about a 100 1k times that of the sun, at the centre of our galaxy. The extra gravitational attraction of such a large number of black holes could explain why our galaxy rotates at the rate it does.
NASA
Black holes can be big or small. Scientists think the smallest black holes are as small as just one atom. These black holes are very tiny but have the mass of a large mountain. Another kind of black hole is called "stellar." Its mass can be up to 20 times more than the mass of the sun. There may be many, many stellar mass black holes in Earth's galaxy. Earth's galaxy is called the Milky Way. The largest black holes are called "supermassive." These black holes have masses that are more than 1 million suns together. Scientists have found proof that every large galaxy contains a supermassive black hole at its center. The supermassive black hole at the center of the Milky Way galaxy is called Sagittarius A. It has a mass equal to about 4 million suns and would fit inside a very large ball that could hold a few million Earths.
https://www.youtube.com/watch?v=e-P5IFTqB98
Hy gas clouds collapse under their own gravity. Core nuclear fusion crushes H2 atom into Helium releasing a tremendous amount of energy. This energy in the form of radiation maintains the balance with gravity. As long as there is fusion in the core the star remains stable enough. But for stars way more mass than our own /sun, heat and pressure allows them to fuse heavier elements - H2, He, Carbon, Neon, O2, Silicon, Iron. Fusion reaction to generate Iron does not generate any energy, Iron builds up at the centre of the star and once it reaches the critical mass and the balance is broken. The core collapses, within a fraction of the second the star implodes moving at about the quarter of the speed of light feeding more mass into the core. More heavier elements in the universe are created as the star dies in a supernova explosion. This produces either a neutron star or if star is massive enough then entire mass collapses into a black hole. Event horizon - any thing crosses the EH needs to be travelling with speed of light because the gravity is so high that light also can not escape it, and speed > c is impossible. Singularity - may be infinite dense, i.e. all matter concentrated into a single space with no volume, no surface.
Inside the black hole, the effect of gravity is so huge over small distance that if someone enters the black hole will be blown to pieces. Smaller BH will kill faster, depends on the distance of the singularity from the EH. BH will eventually destroy owing to Hawking radiation. if we contract any thing below some critical radius will become black hole. Time reduces as one approaches the event horizon. Light coming out will become red shifted and slowly it will fade away and never see to cross the EH.
Black holes also spin.
Pulsars are rapidly spinning neutron star, which is very dense. Neutron star spin with incredibly strong magnetic fields, sends strong electromagnetic radiation including gamma rays, and as the pulsar rotates it sweeps the sky like a lighthouse. Hence to a distant observer it appears like a lighthouse.
Quasars: a massive and extremely remote celestial object, emitting exceptionally large amounts of energy, and typically having a starlike image in a telescope. It has been suggested that quasars contain massive black holes and may represent a stage in the evolution of some galaxies. Shining so brightly that they eclipse the ancient galaxies that contain them, quasars are distant objects powered by black holes a billion times as massive as our sun.
https://www.youtube.com/watch?v=3pAnRKD4raY
How can gravity act as such small distance and and quantum level ? for creating black hole.
Gravitational lensing - Instead of light from a source traveling in a straight line (in three dimensions), it is bent by the presence of a massive body, which distorts spacetime.
Photon Sphere
Wormhole
Stellar-mass black holes are left behind when a massive star explodes. These explosions distribute elements such as carbon, nitrogen and oxygen that are necessary for life into space. The connection between the formation of these supermassive black holes and the formation of galaxies is still not understood. It is possible that a black hole could have played a role in the formation of our Milky Way galaxy. But this chicken-and-egg problem — that is, which came first, the galaxy or the black hole? — is one of the great puzzles of our universe.
The event horizon of a black hole is linked to the object's escape velocity — the speed that one would need to exceed to escape the black hole's gravitational pull. Within the event horizon, one would find the black hole's singularity, where previous research suggests all of the object's mass has collapsed to an infinitely dense extent. This means the fabric of space and time around the singularity has also curved to an infinite degree, so the laws of physics as we currently know them break down. If Earth were compressed until it became a black hole, it would have a diameter of about 0.69 inches (17.4 millimeters). NASA's telescopes that study black holes are looking at the surrounding environments of the black holes, where there is material very close to the event horizon. Matter is heated to millions of degrees as it is pulled toward the black hole, so it glows in X-rays
Black Holes aint so Black
The event horizon, is formed by the paths in space-time of rays of light that just fail to get away from the black hole, hovering just on the edge. Paths of light rays in the event horizon had always to be moving parallel to, or away from, each other.
2nd law of thermodynamics-the entropy of an isolated system always increases, and that when two systems are joined together, the entropy of the combined system is greater than the sum of the entropies of the individual systems. (however it does not hold always, just always in the vast majority of the cases)
The area of the event horizon increases whenever matter fell into a black hole.
Acc to quantum mechanical uncertainity principle, rotating BH should create and emit particles. The spectrum of emitted particles was exactly that which would be emitted by hot body.
How was it possible that a BH appears to emit particles? The answer, quantum theory tells us, us that the particles do not come from within the BH, but from the empty space just outside the BH's event horizon.
Antiparticles
The + energy of the outgoing radiation would be balanced by the flow of negative energy particles into the BH. A flow of - energy therefore reduces the mass of BH. What happens when the mass of BH eventually becomes extremely small it not quite clear. But the most reasonable guess is that it would disappear completely in a tremendous final burst of emission, equivalent to the explosions of mn of H-bombs.
A primordial BH with an initial mass of a thousand mn tons would have a lifetime roughly equal to the age of universe. Initial primordial bh with initial masses less than this figure would already have completely evaporated, but those with slightly greater masses would still be emitting radiation in the form of X rays and gamma rays. These rays are like waves of light, but with much shorter wavelength. Such holes hardly deserve the epithet black - they really are white hot and are emitting energy at a rate of about ten thousand megawatts.
BH must radiate like hot bodies if our other ideas about general relativity and quantum mechanics are correct. The existence of radiation from bh seems to imply that gravitational collapse is not as final and irreversible as we once thought. If mass falls into the bh, its mass will increase, but eventually the energy equivalent of that extra mass will be returned to the universe in the form of radiation.
Antimatter
According to theory, the big bang should have created matter and antimatter in equal amounts. When matter and antimatter meet, they annihilate, leaving nothing but energy behind. And as far as physicists can tell, it’s only because, in the end, there was one extra matter particle for every billion matter-antimatter pairs. Physicists are hard at work trying to explain this asymmetry.
Black Holes aint so Black
The event horizon, is formed by the paths in space-time of rays of light that just fail to get away from the black hole, hovering just on the edge. Paths of light rays in the event horizon had always to be moving parallel to, or away from, each other.
2nd law of thermodynamics-the entropy of an isolated system always increases, and that when two systems are joined together, the entropy of the combined system is greater than the sum of the entropies of the individual systems. (however it does not hold always, just always in the vast majority of the cases)
The area of the event horizon increases whenever matter fell into a black hole.
Acc to quantum mechanical uncertainity principle, rotating BH should create and emit particles. The spectrum of emitted particles was exactly that which would be emitted by hot body.
How was it possible that a BH appears to emit particles? The answer, quantum theory tells us, us that the particles do not come from within the BH, but from the empty space just outside the BH's event horizon.
Antiparticles
The + energy of the outgoing radiation would be balanced by the flow of negative energy particles into the BH. A flow of - energy therefore reduces the mass of BH. What happens when the mass of BH eventually becomes extremely small it not quite clear. But the most reasonable guess is that it would disappear completely in a tremendous final burst of emission, equivalent to the explosions of mn of H-bombs.
A primordial BH with an initial mass of a thousand mn tons would have a lifetime roughly equal to the age of universe. Initial primordial bh with initial masses less than this figure would already have completely evaporated, but those with slightly greater masses would still be emitting radiation in the form of X rays and gamma rays. These rays are like waves of light, but with much shorter wavelength. Such holes hardly deserve the epithet black - they really are white hot and are emitting energy at a rate of about ten thousand megawatts.
BH must radiate like hot bodies if our other ideas about general relativity and quantum mechanics are correct. The existence of radiation from bh seems to imply that gravitational collapse is not as final and irreversible as we once thought. If mass falls into the bh, its mass will increase, but eventually the energy equivalent of that extra mass will be returned to the universe in the form of radiation.
Antimatter
According to theory, the big bang should have created matter and antimatter in equal amounts. When matter and antimatter meet, they annihilate, leaving nothing but energy behind. And as far as physicists can tell, it’s only because, in the end, there was one extra matter particle for every billion matter-antimatter pairs. Physicists are hard at work trying to explain this asymmetry.
Small amounts of antimatter constantly rain down on the Earth in the form of cosmic rays, energetic particles from space. But other antimatter sources are even closer to home. For example, bananas produce antimatter, releasing one positron—the antimatter equivalent of an electron—about every 75 minutes. This occurs because bananas contain a small amount of potassium-40, a naturally occurring isotope of potassium. As potassium-40 decays, it occasionally spits out a positron in the process. Our bodies also contain potassium-40, which means positrons are being emitted from you, too. Antimatter annihilates immediately on contact with matter, so these antimatter particles are very short-lived. Antimatter-matter annihilations have the potential to release a huge amount of energy. A gram of antimatter could produce an explosion the size of a nuclear bomb. However, humans have produced only a minuscule amount of antimatte
CERN
CERN
The Big Bang should have created equal amounts of matter and antimatter in the early universe. But today, everything we see from the smallest life forms on Earth to the largest stellar objects is made almost entirely of matter. Comparatively, there is not much antimatter to be found. Something must have happened to tip the balance. One of the greatest challenges in physics is to figure out what happened to the antimatter, or why we see an asymmetry between matter and antimatter.
Antimatter particles share the same mass as their matter counterparts, but qualities such as electric charge are opposite. The positively charged positron, for example, is the antiparticle to the negatively charged electron. Matter and antimatter particles are always produced as a pair and, if they come in contact, annihilate one another, leaving behind pure energy. During the first fractions of a second of the Big Bang, the hot and dense universe was buzzing with particle-antiparticle pairs popping in and out of existence. If matter and antimatter are created and destroyed together, it seems the universe should contain nothing but leftover energy.
Nevertheless, a tiny portion of matter – about one particle per billion – managed to survive. This is what we see today. In the past few decades, particle-physics experiments have shown that the laws of nature do not apply equally to matter and antimatter. Physicists are keen to discover the reasons why. Researchers have observed spontaneous transformations between particles and their antiparticles, occurring millions of times per second before they decay. Some unknown entity intervening in this process in the early universe could have caused these "oscillating" particles to decay as matter more often than they decayed as antimatter.
Consider a coin spinning on a table. It can land on its heads or its tails, but it cannot be defined as "heads" or "tails" until it stops spinning and falls to one side. A coin has a 50-50 chance of landing on its head or its tail, so if enough coins are spun in exactly the same way, half should land on heads and the other half on tails. In the same way, half of the oscillating particles in the early universe should have decayed as matter and the other half as antimatter.
However, if a special kind of marble rolled across a table of spinning coins and caused every coin it hit to land on its head, it would disrupt the whole system. There would be more heads than tails. In the same way, some unknown mechanism could have interfered with the oscillating particles to cause a slight majority of them to decay as matter. Physicists may find hints as to what this process might be by studying the subtle differences in the behaviour of matter and antimatter particles created in high-energy proton collisions at the Large Hadron Collider. Studying this imbalance could help scientists paint a clearer picture of why our universe is matter-filled.
https://home.cern/science/physics/matter-antimatter-asymmetry-problem
Others
The production of matter/antimatter pairs (left) from pure energy is a completely reversible reaction (right), with matter/antimatter annihilating back to pure energy. This creation-and-annihilation process, which obeys E = mc², is the only known way to create and destroy matter or antimatter.
Whenever and wherever antimatter and matter meet in the Universe, there’s a fantastic outburst of energy due to particle-antiparticle annihilation. We actually observe this annihilation in some locations, but only around hyper-energetic sources that produce matter and antimatter in equal amounts, like around massive black holes. When the antimatter runs into matter in the Universe, it produces gamma rays of very specific frequencies, which we can then detect. The interstellar and intergalactic medium is full of material, and the complete lack of these gamma rays is a strong signal that there aren’t large amounts of antimatter particles flying around anywhere, since that matter/antimatter signature would show up
Pair production is the creation of a subatomic particle and its antiparticle from a neutral boson. Examples include creating an electron and a positron, a muon and an antimuon, or a proton and an antiproton. Pair production often refers specifically to a photon creating an electron–positron pair near a nucleus. For pair production to occur, the incoming energy of the photon must be above a threshold of at least the total rest mass energyof the two particles, and the situation must conserve both energy and momentum.[1] However, all other conserved quantum numbers (angular momentum, electric charge, lepton number) of the produced particles must sum to zero – thus the created particles shall have opposite values of each other. For instance, if one particle has electric charge of +1 the other must have electric charge of −1, or if one particle has strangeness of +1 then another one must have strangeness of −1.
All the time in universe + mass particles and - mass particles create out of no where/out of nothing, exists for tiny amount of time and annihilate them. If these particles bumped against black hole, + mass will have just enough energy to escape the bh, but the - mass particle will fall inside. - particle decreases the mass of the bh, but + particle is observed as part of radiation. Around the black hole + particles fly off it, behaving just like heat. So bh instead of being black is emitting radiation. It decreases and temp increases and finally burst off.
The Origin and Fate of the Universe
Einstein's general the of Rel., predicted that space time began at the big bang singularity and would come to an end either at the Big Crunch singularity (if whole universe collapses) or at a singularity inside a black hole (if a local region, such as star were to collapse). Any matter that fell into the bh would be destroyed at the singularity, and only the gravitational effect of its mass would continue to be felt outside. On the other hand if quantum effects are taken into account, it seemed that energy or mass of the matter would eventually be returned to the rest of the universe.
"Hot Big Bang Model" - (generally accepted history of the universe)
This assumes that the universe is defined by a Friedmann model. In such model one finds that as the universe expands, any matter or radiation in it gets cooler. Since T is measure of average energy / or speed of particles, this cooling would have a major effect on the matter in it. As the T goes down, one would expect particles that attract each other to start to clump together. At lower temperature, when colliding particles have less energy, particle/antiparticle pair would be produced less quickly - and annihilation would become faster than production.
0 Sec - At the bb itself, the universe is thought to have had 0 size, and so to have been infinitely hot. But as the universe expanded, the T of the radiation decreased.
1 Sec - T would have fallen to about 10k mn degrees, about 1k times the temp at the centre of sun, but such T are reached in H bomb explosions. At this time universe would have contained only photons, electrons and neutrinos ( ext light particles that are affected only by the weak force and gravity) and their antiparticles, together with some protons and neutrons. As the U continued to expand and T drop, the rate at which electron/antielectron pairs were being produced in collisions would have fallen below the rate at which they were being destroyed by annihilation. So most of the electron and anti-e would have annihilated to produces more photons, leaving only a few e leftover. The neutrinos and anti-n, however would not have annihilated each other, because these particles interact with themselves and with other particles only weakly. So they should be still around today. If we could observe them it would provide a good test of this picture. Unfortunately, their energies nowadays would be too low to observe them directly. However if neutrinos have some small mass of their own, we might be able to detect them indirectly: they could be a form of "dark matter", with sufficient gravitational attraction to stop the expansion of U and cause it to collapse again.
100 Sec - T would have fallen to 1k mn degrees, the T inside the hottest star. At this T protons and neutrons would no longer have sufficient energy to escape the attraction of the strong nuclear force, and would have started to combine together to produce the nuclei of atom of deuterium, which contains one P and one N. The D nuclei would then have combined with more protons and N to make Helium nuclei which contains 2 P and N and also couple of heavier elements, Li and Beryllium. One can calculate that in hot bb about 1/4 of the P and N would have been converted into Helium nuclei, along with small amount of other elements. The remaining N would have decayed into P, which are the nuclei of ordinary H2 atoms. The radiation (in the form of photons) would still be around today, but its T reduced to only a few degrees above abs zero.
Few hours - prod of He and other elements would have stopped. And after that for next mn years or so, the U would just have continued expanding, w/o anything much happening. Eventually once the T would have dropped to a few thousand degrees, and e and nuclei no longer had enough energy to overcome the electromagentic attraction between them, they would have started combining to form atoms. The U as a whole would have continued expanding and cooling, but in regions that would have been slightly denser than average, the expansion would have been slowed down by the gravitational attraction. This would eventually cause them to stop expanding and start to recollapse. As they were collapsing, the gravitational pull of matter outside these regions might start them rotating slightly. As the collapsing region got smaller, it would spin faster. Eventually when the region was small enough to balance the attraction of the gravity, and in this way disklike rotating galaxies were formed.
As the time went on the H2 and He gs in the galaxies would break up into smaller clouds that would collapse under their own gravity. As these contracted and the atoms within them collided with one another, the T of the gas would increase; until eventually it becomes hot enough to start nuclear fusion reactions. These would convert the H2 into more He, and the heat given off would increase the P, ans os stop the clouds from contracting any further. They would remain stable in this form for a long time as stars like our sun, burning H2 into He and radiating the resulting energy in the form of light and heat. They would then start to contract slightly, ans as they heated up further, would start to convert He into heavier elements like C and O2. This however would not release much energy, so a crisis would occur. What happened next is not completely clear, but it seems likely that the central region of the star would collapse to a very dense state, such a neutron star or bh. The outer region the star may sometime get blown off in a tremendous explosion called Supernova, which would outshine all the other stars in the galaxy. Some of the heavier elements produces near the the end of stars life would be flung back into the gas in the galaxy, and would provide some of the raw material for the next generation of stars. Our own sun contains about 2% of these heavier elements as it is 2nd or 3rd generation star, formed some 5k mn years ago out of a cloud of rotating gas containing the debris of earlier supernovas. Most of the gas in that cloud went to form the sun or got blown away, but a small amount of the heavier elements collected together to form the bodies that now orbit the sun as planets like the earth.
The E was initially very hot and without an atmosphere. In the course of time it cooled and acquired an atmosphere from the emission of gases from the rocks, This early atmosphere was not one in which we could have survived. It contained no oxygen but a lot of toxic gases, such as hydrogen sulphide. There are however other primitive forms of life that can flourish under such conditions. It is thought that they developed in the ocean, possibly as a result of chance combinations of atoms into large structure, called macromolecules, which were capable of assembling other atoms in the ocean into similar structures. They would thus have reproduced themselves and multiplied. In some cases there would have been errors in the reporoduction. Mostly these errors would have been such that the new macromolecules could not reproduce itself and eventually would have been destroyed. However few of the errors would have produced new macromolecules that were even better at reproducing themselves. They would have therefore had an advantage and would have tended to replace the original macromolecules. In this way a process of evolution was started that led to the development of more and more complicated, self-reproducing organisms. The first primitive forms of life consumed various materials, including hydrogen sulphide, and released o2. This gradually changed the atmosphere that it has today, and allowed the development of higher forms of life such as fish, reptiles and mammals, the human race. This picture of the U has some unanswered questions:
a. Why was the early U so hot?
b. Why is the U so uniform on a large scale? why does it look the same at all points of space and in all directions? In particular why the background microwave radiation so nearly the same in all directions?
c. Why did the U start out with so nearly the critical rate of expansion that separates models that recollapse from those that go on expanding forever. so that even now after, 10k mn years later it is still expanding at nearly the critical rate? If the rate of expansion one sec after the bb had been smaller by even one part in k k mn mn, the U would have recollapsed before it ever reached its present size.
d. Why the U contains local irregularities, such as stars and galaxies. These are though to have developed from small diff in densities of the early U from one region to another. What was the origin of these density fluctuations ?
The general thr of relativity does not explain these questions because all laws fails at singularity. Space time begins at the Big Bang. But there ought to have been a model that picks the initial state to represent our U. One such possibility is what are called chaotic boundary conditions. These implicitly assumes either that U is spatially infinite or there are infinitely many Us. the initial state of the U is chosen purely randomly.
The production of matter/antimatter pairs (left) from pure energy is a completely reversible reaction (right), with matter/antimatter annihilating back to pure energy. This creation-and-annihilation process, which obeys E = mc², is the only known way to create and destroy matter or antimatter.
Whenever and wherever antimatter and matter meet in the Universe, there’s a fantastic outburst of energy due to particle-antiparticle annihilation. We actually observe this annihilation in some locations, but only around hyper-energetic sources that produce matter and antimatter in equal amounts, like around massive black holes. When the antimatter runs into matter in the Universe, it produces gamma rays of very specific frequencies, which we can then detect. The interstellar and intergalactic medium is full of material, and the complete lack of these gamma rays is a strong signal that there aren’t large amounts of antimatter particles flying around anywhere, since that matter/antimatter signature would show up
Pair production is the creation of a subatomic particle and its antiparticle from a neutral boson. Examples include creating an electron and a positron, a muon and an antimuon, or a proton and an antiproton. Pair production often refers specifically to a photon creating an electron–positron pair near a nucleus. For pair production to occur, the incoming energy of the photon must be above a threshold of at least the total rest mass energyof the two particles, and the situation must conserve both energy and momentum.[1] However, all other conserved quantum numbers (angular momentum, electric charge, lepton number) of the produced particles must sum to zero – thus the created particles shall have opposite values of each other. For instance, if one particle has electric charge of +1 the other must have electric charge of −1, or if one particle has strangeness of +1 then another one must have strangeness of −1.
All the time in universe + mass particles and - mass particles create out of no where/out of nothing, exists for tiny amount of time and annihilate them. If these particles bumped against black hole, + mass will have just enough energy to escape the bh, but the - mass particle will fall inside. - particle decreases the mass of the bh, but + particle is observed as part of radiation. Around the black hole + particles fly off it, behaving just like heat. So bh instead of being black is emitting radiation. It decreases and temp increases and finally burst off.
The Origin and Fate of the Universe
Einstein's general the of Rel., predicted that space time began at the big bang singularity and would come to an end either at the Big Crunch singularity (if whole universe collapses) or at a singularity inside a black hole (if a local region, such as star were to collapse). Any matter that fell into the bh would be destroyed at the singularity, and only the gravitational effect of its mass would continue to be felt outside. On the other hand if quantum effects are taken into account, it seemed that energy or mass of the matter would eventually be returned to the rest of the universe.
"Hot Big Bang Model" - (generally accepted history of the universe)
This assumes that the universe is defined by a Friedmann model. In such model one finds that as the universe expands, any matter or radiation in it gets cooler. Since T is measure of average energy / or speed of particles, this cooling would have a major effect on the matter in it. As the T goes down, one would expect particles that attract each other to start to clump together. At lower temperature, when colliding particles have less energy, particle/antiparticle pair would be produced less quickly - and annihilation would become faster than production.
0 Sec - At the bb itself, the universe is thought to have had 0 size, and so to have been infinitely hot. But as the universe expanded, the T of the radiation decreased.
1 Sec - T would have fallen to about 10k mn degrees, about 1k times the temp at the centre of sun, but such T are reached in H bomb explosions. At this time universe would have contained only photons, electrons and neutrinos ( ext light particles that are affected only by the weak force and gravity) and their antiparticles, together with some protons and neutrons. As the U continued to expand and T drop, the rate at which electron/antielectron pairs were being produced in collisions would have fallen below the rate at which they were being destroyed by annihilation. So most of the electron and anti-e would have annihilated to produces more photons, leaving only a few e leftover. The neutrinos and anti-n, however would not have annihilated each other, because these particles interact with themselves and with other particles only weakly. So they should be still around today. If we could observe them it would provide a good test of this picture. Unfortunately, their energies nowadays would be too low to observe them directly. However if neutrinos have some small mass of their own, we might be able to detect them indirectly: they could be a form of "dark matter", with sufficient gravitational attraction to stop the expansion of U and cause it to collapse again.
100 Sec - T would have fallen to 1k mn degrees, the T inside the hottest star. At this T protons and neutrons would no longer have sufficient energy to escape the attraction of the strong nuclear force, and would have started to combine together to produce the nuclei of atom of deuterium, which contains one P and one N. The D nuclei would then have combined with more protons and N to make Helium nuclei which contains 2 P and N and also couple of heavier elements, Li and Beryllium. One can calculate that in hot bb about 1/4 of the P and N would have been converted into Helium nuclei, along with small amount of other elements. The remaining N would have decayed into P, which are the nuclei of ordinary H2 atoms. The radiation (in the form of photons) would still be around today, but its T reduced to only a few degrees above abs zero.
Few hours - prod of He and other elements would have stopped. And after that for next mn years or so, the U would just have continued expanding, w/o anything much happening. Eventually once the T would have dropped to a few thousand degrees, and e and nuclei no longer had enough energy to overcome the electromagentic attraction between them, they would have started combining to form atoms. The U as a whole would have continued expanding and cooling, but in regions that would have been slightly denser than average, the expansion would have been slowed down by the gravitational attraction. This would eventually cause them to stop expanding and start to recollapse. As they were collapsing, the gravitational pull of matter outside these regions might start them rotating slightly. As the collapsing region got smaller, it would spin faster. Eventually when the region was small enough to balance the attraction of the gravity, and in this way disklike rotating galaxies were formed.
As the time went on the H2 and He gs in the galaxies would break up into smaller clouds that would collapse under their own gravity. As these contracted and the atoms within them collided with one another, the T of the gas would increase; until eventually it becomes hot enough to start nuclear fusion reactions. These would convert the H2 into more He, and the heat given off would increase the P, ans os stop the clouds from contracting any further. They would remain stable in this form for a long time as stars like our sun, burning H2 into He and radiating the resulting energy in the form of light and heat. They would then start to contract slightly, ans as they heated up further, would start to convert He into heavier elements like C and O2. This however would not release much energy, so a crisis would occur. What happened next is not completely clear, but it seems likely that the central region of the star would collapse to a very dense state, such a neutron star or bh. The outer region the star may sometime get blown off in a tremendous explosion called Supernova, which would outshine all the other stars in the galaxy. Some of the heavier elements produces near the the end of stars life would be flung back into the gas in the galaxy, and would provide some of the raw material for the next generation of stars. Our own sun contains about 2% of these heavier elements as it is 2nd or 3rd generation star, formed some 5k mn years ago out of a cloud of rotating gas containing the debris of earlier supernovas. Most of the gas in that cloud went to form the sun or got blown away, but a small amount of the heavier elements collected together to form the bodies that now orbit the sun as planets like the earth.
The E was initially very hot and without an atmosphere. In the course of time it cooled and acquired an atmosphere from the emission of gases from the rocks, This early atmosphere was not one in which we could have survived. It contained no oxygen but a lot of toxic gases, such as hydrogen sulphide. There are however other primitive forms of life that can flourish under such conditions. It is thought that they developed in the ocean, possibly as a result of chance combinations of atoms into large structure, called macromolecules, which were capable of assembling other atoms in the ocean into similar structures. They would thus have reproduced themselves and multiplied. In some cases there would have been errors in the reporoduction. Mostly these errors would have been such that the new macromolecules could not reproduce itself and eventually would have been destroyed. However few of the errors would have produced new macromolecules that were even better at reproducing themselves. They would have therefore had an advantage and would have tended to replace the original macromolecules. In this way a process of evolution was started that led to the development of more and more complicated, self-reproducing organisms. The first primitive forms of life consumed various materials, including hydrogen sulphide, and released o2. This gradually changed the atmosphere that it has today, and allowed the development of higher forms of life such as fish, reptiles and mammals, the human race. This picture of the U has some unanswered questions:
a. Why was the early U so hot?
b. Why is the U so uniform on a large scale? why does it look the same at all points of space and in all directions? In particular why the background microwave radiation so nearly the same in all directions?
c. Why did the U start out with so nearly the critical rate of expansion that separates models that recollapse from those that go on expanding forever. so that even now after, 10k mn years later it is still expanding at nearly the critical rate? If the rate of expansion one sec after the bb had been smaller by even one part in k k mn mn, the U would have recollapsed before it ever reached its present size.
d. Why the U contains local irregularities, such as stars and galaxies. These are though to have developed from small diff in densities of the early U from one region to another. What was the origin of these density fluctuations ?
The general thr of relativity does not explain these questions because all laws fails at singularity. Space time begins at the Big Bang. But there ought to have been a model that picks the initial state to represent our U. One such possibility is what are called chaotic boundary conditions. These implicitly assumes either that U is spatially infinite or there are infinitely many Us. the initial state of the U is chosen purely randomly.
Anthropic Principles: Weak AP - in a U that is large or infinite in space and/or time, the conditions necessary for the development of intelligent life will be met only in certain regions that are limited in space and time. The intelligent beings in these regions should therefore not be surprised if they observe that their locality in the U satisfies the conditions that are necessary for their existence. Why the bb occured 10k mn years ago ? Coz it takes about that long for intelligent beings to evolve.
Strong AP - there are either many different U or many diff regions in a single U, each with its own initial configuration, and perhaps with its own set of laws of science. In most of these U the conditions would not be right for the dev of complicated org; only in few U that are like ours would intelligent beings develop as as the q: why the U is the way we see it? The ans is : if it has been diff, we would not be here.
The laws of Sc, as we know contains many fundamental numbers such as - size of electric charge of e, and ratio of the masses of the P and e. We cannot at the moment predict the value of these numbers from theory- we have to find them from observation. It may be that one day unified theory is found which predicts all. The remarkable fact is that the values of these no seem to have been very finely adjusted to make possible the dev of life. For Eg. if the electric charge of the e had been only slightly different, stars either would have been unable to burn H2 and He, or else they would not have exploded.
Objections on Strong AP -
1. If the U are different, then what happens in another U can have no observable consequences in our own U.
If, on the other hand, that are just diff regions of a single U, the laws of Sc would have to be same in each region, because otherwise one could not move continuously from one region to another. In this case only initial configuration would be different and so St AP would reduce to Weak AP.
2. E is a medium sized planet orbiting around an average star in the outer suburb of an ordinary spiral galaxy, which is itself only one of about a mn mn galaxies in the observable U. Yet the SAP would claim that this whole vast construction exists simply for our sake. This is very hard to believe
In an attempt to find a model of the U in which many diff initial configurations could have evolved to something like the present U, a scientist suggested that the early U might have gone through a period of very rapid expansion. This expansion is called to be "inflationary" meaning that the U at one time expanded at an increasing rate rather than decreasing rate that it does today. Acc to Guth, the radius of U increased by a 1*38 zeros times only in tiny fraction of a second. Guth suggested that U started off with a BB in a very hot and chaotic state. At such high T all the forces would have been unified into a single force. As the U expanded, it would cool and particles energies would go down. Eventually there would be what is called a phase transition and the symmetry between the forces that would be broken: the strong forces would become diff from weak and electromagnetic forces. The T drop below the critical value w.o breaking the symmetry bw the forces. If this happened the U would be in unstable state, with more E than if the symmetry has been broken. This special extra Energy can be shown to have an anti gravitational effect: it would have acted just like the cosmological constant that Einstein introduced into general relativity when he was trying construct a static model of universe. Since the U would already been expanding just as in the hot BB model, the repulsive effect of this CC would there fore have been made the U expand at the ever increasing rate. Even in th regions were there are more matter particles than average, the gravitational attraction of he matter would have been outweighed by the repulsion of the effective CC. Thus these regions would also expand in an accelerating inflationary manner. As they expanded and the matter particles got farther apart, one would be left with an expanding that contained hardly any particles and was still in the supercooled state. Any irregularities in the U would simply have been smoothed out by the expansion, as the wrinkles in a balloon are smoothed away when you blow it up. Thus the present smooth and uniform state of the U could have have evolved from many diff nonuniform initial states.
This could provide solution to the problem raised earlier. The rate of expansion of the U would automatically become very close to the critical rate determined by the E density of he U. This could then explain why the rate of expansion is still so close to the critical rate, w/o having to assume that the initial rate was carefully chosen.
Chaotic Inflationary Model: Showed that the present state of U could have arisen from quite a large no of different initial configurations.
One has to use a quantum theory of gravity to discuss the very early stages of the U.
We don't yet have a complete and consistent theory that combines quantum mechanics and gravity. However we are fairly certain of some features that such a unified theory should have, One is that it should incorporate Feymann's proposal to formulate quantum theory in terms of a sum over histories. And other is it must be part of Einstein's idea that the gravitational field is represented by curved space-time.
Significance of imaginary number I --> All that mysterious i means is “Make a 90 degree turn”. +1and -1 are 180 degree turn.
Quantum theory of gravity.
There should be a particle called graviton. It should be massless and spin =2 and neutral. Not decided yet.
Because the universe is constantly expanding, scientists have suggested that the origins of the universecan be traced by thinking about the process in reverse. While backtracking, Hawking and Hartle realized the universe becomes smaller until you reach the extremely dense and high-energy ball necessary for the Big Bang to violently set the beginnings of the universe in place. Yet as you get smaller and smaller, you start seeing the origins of the universe at the subatomic level. Here's where things get a bit complicated. The duo theorized that once you get to such a tiny, detailed level -- where particles spontaneously pop up and disappear, space becomes separated from time. In essence, time loses the meaning we traditionally assign to it. As a result, it's impossible to measure events before the Big Bang because time -- as we know it -- doesn't exist. Hawking and Hartle said the universe doesn't have a boundary, much like Earth's rounded surface lacks an edge. Hawking likened his no-boundary proposal (aka Stephen-hawking-Hartle state) for the universe to traveling southward until you reach the South Pole. When you reach the South Pole, the term "south" loses its meaning. The same idea is applied to time before the Big Bang -- once you trace back the universe to its beginning, the concept of time (as we define it, at least) becomes obsolete.
The Arrow of Time
When one tried to unify gravity with quantum mechanics, one had to introduce thr idea of "imaginary" time. Imaginary time is indistinguishable from direction in space. This means that there can be no important difference between the forward and backward directions of imaginary time.
There are atleast 3 different arrows of time -
1. The thermodynamic arrow of time - The direction if time in which disorder or entropy increases.
2. Psychological arrow of time - direction in which we feel time to pass
3. Cosmological arrow of time - direction in which the U is expansion rather than contracting.
1. Thermo - 2nd law of thermodynamics results from the fact that there are more disordered state than ordered states.
2. Take for example computers - heat expelled by the Comp's cooling fan means that when a comp records and item in memory, the total amount of disorder in the U still goes up. The direction of time in which a Comp remembers the past is the same as that in which disorder increases. The psychological arrow is therefore defined within our brain by the thermodynamic arrow of time. Just as comp we must remember things in the order in which entropy increases.
U will not start to contract for at least another 10k mn years.
The no boundary condition implied that disorder would in fact continue to increase during contraction. The T and P arrow of time would not reverse when the U begins to reconstruct or inside a bh.
To summarize, laws of science do not distinguish bw the forward and reverse direction of time. However there are at least 3 arrows of time that do distinguish the past from the future. P arrow is essentially the same as T arrow, so that the two would point always in the same direction. The no boundary proposal for the universe predicts the existence of a well defined thermodynamics arrow of time becomes the U must start off in a smooth and ordered state. And the reason we observe this T arrow to agree with the C arrow is that intelligent beings can exist only in the expanding phase. The contracting phase will be unsuitable because it has no strong T arrow of time.
The progress of the human race in understanding the U has established a small corner or order in an increasingly disorder U.
The Unification of Physics
The uncertainity principle is a fundamental feature in the U we live in. A successful unified theory must therefore necessarily incorporate this principle.
String Theory
The gravitational force of sun on the earth was pictured in particle theory as being caused by the emission of a graviton by the a particle in the sun and its absorption by a particle in the E. In string theory, this process corresponds to an /h shaped tube or pipe. String th have a bigger problem:they seem to be consistent only if space time has either 10 or 26 dimensions instead of usual 4.
Why don't we notice extra dimensions if they are really there ? the other dimensions are curved up into a space of very small size, something like a mn mn mn mn mn og an inch. With space time on a very small scale it is 10 dimensional and highly curved, but on bigger scale you don't see the curvature or the extra dimension. Why other dimensions curled up ? presumbaly in the very early U all the dimensions would have been very curved. Why did one time and 3 dimensions flatten out while other .remained curled ? One possible answer is the anthropic principle. 2 dimensions creatures won't exist and fall off in two separate halves. If we had more than 4 dimensions, sun would have been unstable, E would have spiralled in or out of the sun. e would either escape from atom altogether or would spiral in.
Zionism
Strong AP - there are either many different U or many diff regions in a single U, each with its own initial configuration, and perhaps with its own set of laws of science. In most of these U the conditions would not be right for the dev of complicated org; only in few U that are like ours would intelligent beings develop as as the q: why the U is the way we see it? The ans is : if it has been diff, we would not be here.
The laws of Sc, as we know contains many fundamental numbers such as - size of electric charge of e, and ratio of the masses of the P and e. We cannot at the moment predict the value of these numbers from theory- we have to find them from observation. It may be that one day unified theory is found which predicts all. The remarkable fact is that the values of these no seem to have been very finely adjusted to make possible the dev of life. For Eg. if the electric charge of the e had been only slightly different, stars either would have been unable to burn H2 and He, or else they would not have exploded.
Objections on Strong AP -
1. If the U are different, then what happens in another U can have no observable consequences in our own U.
If, on the other hand, that are just diff regions of a single U, the laws of Sc would have to be same in each region, because otherwise one could not move continuously from one region to another. In this case only initial configuration would be different and so St AP would reduce to Weak AP.
2. E is a medium sized planet orbiting around an average star in the outer suburb of an ordinary spiral galaxy, which is itself only one of about a mn mn galaxies in the observable U. Yet the SAP would claim that this whole vast construction exists simply for our sake. This is very hard to believe
In an attempt to find a model of the U in which many diff initial configurations could have evolved to something like the present U, a scientist suggested that the early U might have gone through a period of very rapid expansion. This expansion is called to be "inflationary" meaning that the U at one time expanded at an increasing rate rather than decreasing rate that it does today. Acc to Guth, the radius of U increased by a 1*38 zeros times only in tiny fraction of a second. Guth suggested that U started off with a BB in a very hot and chaotic state. At such high T all the forces would have been unified into a single force. As the U expanded, it would cool and particles energies would go down. Eventually there would be what is called a phase transition and the symmetry between the forces that would be broken: the strong forces would become diff from weak and electromagnetic forces. The T drop below the critical value w.o breaking the symmetry bw the forces. If this happened the U would be in unstable state, with more E than if the symmetry has been broken. This special extra Energy can be shown to have an anti gravitational effect: it would have acted just like the cosmological constant that Einstein introduced into general relativity when he was trying construct a static model of universe. Since the U would already been expanding just as in the hot BB model, the repulsive effect of this CC would there fore have been made the U expand at the ever increasing rate. Even in th regions were there are more matter particles than average, the gravitational attraction of he matter would have been outweighed by the repulsion of the effective CC. Thus these regions would also expand in an accelerating inflationary manner. As they expanded and the matter particles got farther apart, one would be left with an expanding that contained hardly any particles and was still in the supercooled state. Any irregularities in the U would simply have been smoothed out by the expansion, as the wrinkles in a balloon are smoothed away when you blow it up. Thus the present smooth and uniform state of the U could have have evolved from many diff nonuniform initial states.
This could provide solution to the problem raised earlier. The rate of expansion of the U would automatically become very close to the critical rate determined by the E density of he U. This could then explain why the rate of expansion is still so close to the critical rate, w/o having to assume that the initial rate was carefully chosen.
Chaotic Inflationary Model: Showed that the present state of U could have arisen from quite a large no of different initial configurations.
One has to use a quantum theory of gravity to discuss the very early stages of the U.
We don't yet have a complete and consistent theory that combines quantum mechanics and gravity. However we are fairly certain of some features that such a unified theory should have, One is that it should incorporate Feymann's proposal to formulate quantum theory in terms of a sum over histories. And other is it must be part of Einstein's idea that the gravitational field is represented by curved space-time.
Significance of imaginary number I --> All that mysterious i means is “Make a 90 degree turn”. +1and -1 are 180 degree turn.
Quantum theory of gravity.
There should be a particle called graviton. It should be massless and spin =2 and neutral. Not decided yet.
Because the universe is constantly expanding, scientists have suggested that the origins of the universecan be traced by thinking about the process in reverse. While backtracking, Hawking and Hartle realized the universe becomes smaller until you reach the extremely dense and high-energy ball necessary for the Big Bang to violently set the beginnings of the universe in place. Yet as you get smaller and smaller, you start seeing the origins of the universe at the subatomic level. Here's where things get a bit complicated. The duo theorized that once you get to such a tiny, detailed level -- where particles spontaneously pop up and disappear, space becomes separated from time. In essence, time loses the meaning we traditionally assign to it. As a result, it's impossible to measure events before the Big Bang because time -- as we know it -- doesn't exist. Hawking and Hartle said the universe doesn't have a boundary, much like Earth's rounded surface lacks an edge. Hawking likened his no-boundary proposal (aka Stephen-hawking-Hartle state) for the universe to traveling southward until you reach the South Pole. When you reach the South Pole, the term "south" loses its meaning. The same idea is applied to time before the Big Bang -- once you trace back the universe to its beginning, the concept of time (as we define it, at least) becomes obsolete.
The Arrow of Time
When one tried to unify gravity with quantum mechanics, one had to introduce thr idea of "imaginary" time. Imaginary time is indistinguishable from direction in space. This means that there can be no important difference between the forward and backward directions of imaginary time.
There are atleast 3 different arrows of time -
1. The thermodynamic arrow of time - The direction if time in which disorder or entropy increases.
2. Psychological arrow of time - direction in which we feel time to pass
3. Cosmological arrow of time - direction in which the U is expansion rather than contracting.
1. Thermo - 2nd law of thermodynamics results from the fact that there are more disordered state than ordered states.
2. Take for example computers - heat expelled by the Comp's cooling fan means that when a comp records and item in memory, the total amount of disorder in the U still goes up. The direction of time in which a Comp remembers the past is the same as that in which disorder increases. The psychological arrow is therefore defined within our brain by the thermodynamic arrow of time. Just as comp we must remember things in the order in which entropy increases.
U will not start to contract for at least another 10k mn years.
The no boundary condition implied that disorder would in fact continue to increase during contraction. The T and P arrow of time would not reverse when the U begins to reconstruct or inside a bh.
To summarize, laws of science do not distinguish bw the forward and reverse direction of time. However there are at least 3 arrows of time that do distinguish the past from the future. P arrow is essentially the same as T arrow, so that the two would point always in the same direction. The no boundary proposal for the universe predicts the existence of a well defined thermodynamics arrow of time becomes the U must start off in a smooth and ordered state. And the reason we observe this T arrow to agree with the C arrow is that intelligent beings can exist only in the expanding phase. The contracting phase will be unsuitable because it has no strong T arrow of time.
The progress of the human race in understanding the U has established a small corner or order in an increasingly disorder U.
The Unification of Physics
The uncertainity principle is a fundamental feature in the U we live in. A successful unified theory must therefore necessarily incorporate this principle.
String Theory
The gravitational force of sun on the earth was pictured in particle theory as being caused by the emission of a graviton by the a particle in the sun and its absorption by a particle in the E. In string theory, this process corresponds to an /h shaped tube or pipe. String th have a bigger problem:they seem to be consistent only if space time has either 10 or 26 dimensions instead of usual 4.
Why don't we notice extra dimensions if they are really there ? the other dimensions are curved up into a space of very small size, something like a mn mn mn mn mn og an inch. With space time on a very small scale it is 10 dimensional and highly curved, but on bigger scale you don't see the curvature or the extra dimension. Why other dimensions curled up ? presumbaly in the very early U all the dimensions would have been very curved. Why did one time and 3 dimensions flatten out while other .remained curled ? One possible answer is the anthropic principle. 2 dimensions creatures won't exist and fall off in two separate halves. If we had more than 4 dimensions, sun would have been unstable, E would have spiralled in or out of the sun. e would either escape from atom altogether or would spiral in.
Zionism
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