Black Hole
Define Black Hole. Mystery of Black Holes. How black holes are formed. Nature of Black holes.
Black holes are some
of the strangest and most fascinating objects found in outer space.They are
objects of extreme density, with such strong gravitational attraction that even
light cannot escape from their grasp if it comes near enough. Albert Einstein
first predicted black holes in 1916 with his general theory of
relativity.
The
Black Hole, in the 1970s. It was about a space ship that was sent
to investigate a black hole that had been discovered. It wasn't a very
good film, but it had an interesting ending. After orbiting the black
hole, one of the scientists decides, the only way to find out what is
going on, is to go inside .So he gets into a space probe, and
dives into the black hole. After a screen writer's depiction of Hell, he
emerges into a new universe. This is an early example of the science fiction
use of a black hole as a wormhole, a passage from one universe to another,
or back to another location in the same universe. Such wormholes, if they
existed, would provide short cuts for Interstellar space travel,
which otherwise would be pretty slow andtedious, if one had to keep to
the Einstein speed limit, and stay below the speed of light.
In
fact, science fiction writers should not have been taken so
much by surprise. The idea behind black holes, has been around in the
scientific community for more than 200 years. In 1783, A Cambridge don,
John Michell, wrote a paper in the Philosophical Transactions of the Royal
Society of London, about what he called dark stars. He pointed out that a
star that was sufficiently massive and compact, would have such a strong
gravitational field that light could not escape. Any light emitted from
the surface of the star, would be dragged back by the star's gravitational
attraction, before it could get very far. Michell suggested that there
might be a large number of stars like this. Although we would not be able to
see them, because the light from them would not reach us, we would still
feel their gravitational attraction. Such objects are what we now call black
holes, because that is what they are, black voids in space. A similar
suggestion was made a few years later, by the French scientist the Marquis de
La~plass, apparently independently of Michell.
Both
Michell and La~plass thought of light as consisting of particles,
rather likecannon balls, that could be slowed down by gravity, and
made to fall back on the star. But a famous experiment, carried out by two
Americans, Michelson and Morley in 1887, showed that light always traveled
at a speed of one hundred and eighty six thousand miles a second, no
matter where it came from. How then could gravity slow down light, and
make it fall back. This was impossible, according to the then accepted ideas of
space and time. But in 1915, Einstein put forward his revolutionary GeneralTheory of Relativity. In this, space and time were no longer separate
and independent entities. Instead, they were just different directions in
a single object called space-time. This space-time was not flat, but was warped
and curved by the matter and energy in it. In order to understand this,
considered a sheet of rubber, with a weight placed on it, to represent a
star. The weight will form a depression in the rubber, and will cause the
sheet near the star to be curved, rather than flat. If one now rolls
marbles on the rubber sheet, their paths will be curved, rather than being straight
lines. In 1919, a British expedition to West Africa, looked at
light from distant stars that passed near the Sun during an eclipse. They
found that the images of the stars, were shifted slightly from their
normal positions. This indicated that the paths of the light from the
stars, had been bent by the curved space-time near the Sun. General
Relativity was confirmed.
Consider now placing heavier and heavier, and more and more concentrated weights on the rubber sheet. They will depress the sheet more and more. Eventually, at a critical weight and size, they will make a bottomless hole in the sheet, that particles can fall into, but nothing can get out of.
What happens in space-time according to General Relativity, is rather similar. A star will curve and distort the space-time near it, more and more, the more massive and more compact the star is. If a massive star that has burnt up its nuclear fuel, cools and shrinks below a critical size, it will quite literally make a bottomless hole in space-time, that light can't get out of. Such objects were given the name, black holes, by the American physicist, John Wheeler, who was one of the first to recognize their importance, and the problems they pose. The name caught on quickly. It suggested something dark and mysterious, But the French, being French, saw a more risky meaning. For years, they resisted the name, troo noir, claiming it was obscene. But that was a bit like trying to stand against ~le week end, and other franglay. In the end, they had to give in.Who can resist a name that is such a winner.
From the outside, you can't tell what is inside a black hole. You can throw television sets, diamond rings, or even your worst enemies into a black hole, and all the black hole will remember, is the total mass, and the state of rotation. John Wheeler called this, A Black Hole Has No Hair. To
The French, this just confirmed their suspicions.
A black hole has a boundary, called the event horizon. It is where gravity is just strong enough to drag light back,and prevent it escaping. Because nothing can travel faster than light, everything else will get dragged back also. Falling through the event horizon, is a bit like going over Niagra Falls in a canoe. If you are above the falls, you can get away if you paddle fast enough, but once you are over the edge, you are lost. There’s no way back. As you get nearer the falls, the current gets faster. This means it pulls harder on the front of the canoe, than the back. There’s a danger that the canoe will be pulled apart. It is the same with black holes. If you fall towards a black hole feet first, gravity will pull harder on your feet than your head, because they are nearer the black hole. The result is, you will be stretched out longwise, and squashed in sideways. If the black hole has a mass of a few times our sun, you would be torn apart, and made into spaghetti, before you reached the horizon. However, if you fell into a much larger black hole, with a mass of a million times the sun, you would reach the horizon without difficulty. So, if you want to explore the inside of a black hole, choose a big one. There is a black hole of about a million solar masses, at the center of our Milky Way galaxy.
Although you wouldn't notice anything particular as you fell into a black hole, someone watching
E = mc2 So if there's too much information in a region of space, it will collapse into a black hole, and the size of the black hole will reflect the amount of information. It is like piling more and more books into a library. Eventually the shelves will give way, and the library will collapse into a black hole.
If the amount of hidden information inside a black hole, depends on the size of the hole, one would expect from general principles, that the black hole would have a temperature, and would glow like a piece of hot metal. But that was impossible, because as everyone knew, nothing could get out of a black hole. Or so it was thought, but I discovered that particles can leak out of a black hole. The reason is, that on a very small scale, things are a bit fuzzy. This is summed up in the uncertainty relation, discovered by Werner Heisenberg in 1923 which says that the more precisely you know the position of a particle, the less precisely you can know its speed, and vice versa. This means that if a particle is in a small black hole, you know its position fairly accurately. Its speed therefore will be rather uncertain, and can be more than the speed of light, which would allow the particle to escape from the black hole. The larger the black hole, the less accurately the position of a particle in it is defined, so the more precisely the speed is defined, and the less chance there is that it will be more than the speed of light. A black hole of the mass of the sun, would leak particles at such a slow rate, it would be impossible to detect. However, there could be much smaller mini black holes. These might have formed in the very early universe, if it had been chaotic and irregular. A black hole of the mass of a mountain, would give off x-rays and gamma rays, at a rate of about ten million Megawatts, enough to power the world's electricity supply It wouldn't be easy however, to harnass a mini black hole. You couldn't keep it in a power station, because it would drop through the floor, and end up at the center of the Earth. About the only way, would be to have the black hole in orbit around the Earth.
People have searched for mini black holes of this mass, but have so far, not found any. This is a pity, because if they had, I would have got a Nobel Prize. Another possibility however, is that we might be able to create micro black holes in the extra dimensions of space time. According to some theories, the universe we experience, is just a four dimensional surface, in a ten or eleven dimensional space. We wouldn't see these extra dimensions, because light wouldn't propagate through them, but only through the four dimensions of our universe. Gravity, however, would affect the extra dimensions, and would be much stronger than in our universe. This would make it much easier to form a little black hole in the extra dimensions. It might be possible to observe this at the LHC, the Large Hadron Collider, at Cern, in Switzerland. This consists of a circular tunnel, 27 kilometers long.Two beams of particles travel round this tunnel in opposite directions, and are made to collide. Some of the collisions might create micro black holes. These would radiate particles in a pattern that would be easy to recognize. So, I might get a Nobel Prize, after all.
As particles escape from a black hole the hole will lose mass, and shrink. This will increase the rate of emission of particles. Eventually, the black hole will lose all its mass, and disappear. What then happens to all the particles and unlucky astronauts that fell into the black hole? They can't just re-emerge when the black hole disappears. The particles that come out of a black hole, seem to be completely random, and to bear no relation to what fell in. It appears that the information about what fell in, is lost, apart from the total amount of mass, and the amount of rotation. But if information is lost, this raises a serious problem that strikes at the heart of our understanding of science. For more than 200 years, we have believed in scientific determinism, that is, that the laws of science, determine the evolution of the universe. This was formulated by La~plass as, If we know the state of the universe at one time, the laws of science will determine it at all future and past times. Napoleon is said to have asked La~plass how God fitted into this picture. La~plass replied, Sire, I have not needed that hypothesis. I don't think that La~plass was claiming that God didn't exist. It is just that He doesn't intervene, to break the laws of Science. That must be the position of every scientist. A scientific law, is not a scientific law, if it only holds when some supernatural being, decides to let things run, and not intervene.
In La~plass's determinism, one needed to know the positions and speeds of all particles at one time in order to predict the future. But according to the uncertainty relation, the more accurately you know the positions, the less accurately you can know the speeds, and vice versa. In other words, you can't know ~both the positions, ~and the speeds, accurately. How then can you predict the future accurately? The answer is, that although one can't predict the positions and speeds separately, one ~can predict what is called, the quantum state. This is something from which both positions and speeds can be calculated, to a certain degree of accuracy. We would still expect the universe to be deterministic, in the sense that if we knew the quantum state of the universe at one time, the laws of science should enable us predict it at any other time.
If information were lost in black holes, we wouldn't be able to predict the future, because a black hole could emit any collection of particles. It could emit a working television set, or a leather bound volume of the complete works of Shakespeare, though the chance of such exotic emissions is very low. It is much more likely to be thermal Radiation, like the glow from red hot metal. It might seem that it wouldn't matter very much if we couldn't predict what comes out of black holes. There aren't any black holes near us. But it is a matter of principle. If determinism breaks down with black holes, it could break down in other situations. There could be virtual black holes that appear as fluctuations out of the vacuum, absorb one set of particles, emit another, and disappear into the vacuum again. Even worse, if determinism breaks down, we can't be sure of our past history either. The history books and our memories could just be illusions. It is the past that tells us who we are. Without it, we lose our identity.
It was therefore very important to determine whether information really was lost in black holes, or whether in principle, it could be recovered. Many people felt that information should not be lost, but no one could suggest a mechanism by which it could be preserved. The arguments went on for years. Finally, I found what I think is the answer. It depends on the idea of Richard Fein man, that there isn't a single history, but many different possible histories, each with their own probability. In this case, there are two kinds of history. In one, there is a black hole, into which particles can fall, but in the other kind, there is no black hole. The point is, that from the outside, one can't be certain whether there is a black hole, or not. So there is always a chance that there isn't a black hole. This possibility is enough to preserve the information, but the information is not returned in a very useful form. It is like burning an encyclopedia.. Information is not lost if you keep all the smoke and ashes, but it is difficult to read. Kip Thorne and I had a bet with John Preskill, that information would be lost in black holes. When I discovered how information could be preserved, I conceded the bet. I gave John Preskill an encyclopedia. Maybe I should have just given him the ashes.
What does this tell us about whether it is possible to fall in a black hole, and come out in another universe? The existence of alternative histories with black holes, suggests this might be possible. The hole would need to be large, and if it was rotating, it might have a passage to another universe. But you couldn't come back to our universe. So, although I'm keen on space flight, I'm not going to try that.
The message of this lecture, is, that black holes ain't as black as they are painted. They are not the eternal prisons they were once thought. Things ~can get out of a black hole, both to the outside, and possibly, to another universe. So, if you feel you are in a black hole, don't give up. There's a way out.
Consider now placing heavier and heavier, and more and more concentrated weights on the rubber sheet. They will depress the sheet more and more. Eventually, at a critical weight and size, they will make a bottomless hole in the sheet, that particles can fall into, but nothing can get out of.
What happens in space-time according to General Relativity, is rather similar. A star will curve and distort the space-time near it, more and more, the more massive and more compact the star is. If a massive star that has burnt up its nuclear fuel, cools and shrinks below a critical size, it will quite literally make a bottomless hole in space-time, that light can't get out of. Such objects were given the name, black holes, by the American physicist, John Wheeler, who was one of the first to recognize their importance, and the problems they pose. The name caught on quickly. It suggested something dark and mysterious, But the French, being French, saw a more risky meaning. For years, they resisted the name, troo noir, claiming it was obscene. But that was a bit like trying to stand against ~le week end, and other franglay. In the end, they had to give in.Who can resist a name that is such a winner.
From the outside, you can't tell what is inside a black hole. You can throw television sets, diamond rings, or even your worst enemies into a black hole, and all the black hole will remember, is the total mass, and the state of rotation. John Wheeler called this, A Black Hole Has No Hair. To
The French, this just confirmed their suspicions.
A black hole has a boundary, called the event horizon. It is where gravity is just strong enough to drag light back,and prevent it escaping. Because nothing can travel faster than light, everything else will get dragged back also. Falling through the event horizon, is a bit like going over Niagra Falls in a canoe. If you are above the falls, you can get away if you paddle fast enough, but once you are over the edge, you are lost. There’s no way back. As you get nearer the falls, the current gets faster. This means it pulls harder on the front of the canoe, than the back. There’s a danger that the canoe will be pulled apart. It is the same with black holes. If you fall towards a black hole feet first, gravity will pull harder on your feet than your head, because they are nearer the black hole. The result is, you will be stretched out longwise, and squashed in sideways. If the black hole has a mass of a few times our sun, you would be torn apart, and made into spaghetti, before you reached the horizon. However, if you fell into a much larger black hole, with a mass of a million times the sun, you would reach the horizon without difficulty. So, if you want to explore the inside of a black hole, choose a big one. There is a black hole of about a million solar masses, at the center of our Milky Way galaxy.
Although you wouldn't notice anything particular as you fell into a black hole, someone watching
E = mc2 So if there's too much information in a region of space, it will collapse into a black hole, and the size of the black hole will reflect the amount of information. It is like piling more and more books into a library. Eventually the shelves will give way, and the library will collapse into a black hole.
If the amount of hidden information inside a black hole, depends on the size of the hole, one would expect from general principles, that the black hole would have a temperature, and would glow like a piece of hot metal. But that was impossible, because as everyone knew, nothing could get out of a black hole. Or so it was thought, but I discovered that particles can leak out of a black hole. The reason is, that on a very small scale, things are a bit fuzzy. This is summed up in the uncertainty relation, discovered by Werner Heisenberg in 1923 which says that the more precisely you know the position of a particle, the less precisely you can know its speed, and vice versa. This means that if a particle is in a small black hole, you know its position fairly accurately. Its speed therefore will be rather uncertain, and can be more than the speed of light, which would allow the particle to escape from the black hole. The larger the black hole, the less accurately the position of a particle in it is defined, so the more precisely the speed is defined, and the less chance there is that it will be more than the speed of light. A black hole of the mass of the sun, would leak particles at such a slow rate, it would be impossible to detect. However, there could be much smaller mini black holes. These might have formed in the very early universe, if it had been chaotic and irregular. A black hole of the mass of a mountain, would give off x-rays and gamma rays, at a rate of about ten million Megawatts, enough to power the world's electricity supply It wouldn't be easy however, to harnass a mini black hole. You couldn't keep it in a power station, because it would drop through the floor, and end up at the center of the Earth. About the only way, would be to have the black hole in orbit around the Earth.
People have searched for mini black holes of this mass, but have so far, not found any. This is a pity, because if they had, I would have got a Nobel Prize. Another possibility however, is that we might be able to create micro black holes in the extra dimensions of space time. According to some theories, the universe we experience, is just a four dimensional surface, in a ten or eleven dimensional space. We wouldn't see these extra dimensions, because light wouldn't propagate through them, but only through the four dimensions of our universe. Gravity, however, would affect the extra dimensions, and would be much stronger than in our universe. This would make it much easier to form a little black hole in the extra dimensions. It might be possible to observe this at the LHC, the Large Hadron Collider, at Cern, in Switzerland. This consists of a circular tunnel, 27 kilometers long.Two beams of particles travel round this tunnel in opposite directions, and are made to collide. Some of the collisions might create micro black holes. These would radiate particles in a pattern that would be easy to recognize. So, I might get a Nobel Prize, after all.
As particles escape from a black hole the hole will lose mass, and shrink. This will increase the rate of emission of particles. Eventually, the black hole will lose all its mass, and disappear. What then happens to all the particles and unlucky astronauts that fell into the black hole? They can't just re-emerge when the black hole disappears. The particles that come out of a black hole, seem to be completely random, and to bear no relation to what fell in. It appears that the information about what fell in, is lost, apart from the total amount of mass, and the amount of rotation. But if information is lost, this raises a serious problem that strikes at the heart of our understanding of science. For more than 200 years, we have believed in scientific determinism, that is, that the laws of science, determine the evolution of the universe. This was formulated by La~plass as, If we know the state of the universe at one time, the laws of science will determine it at all future and past times. Napoleon is said to have asked La~plass how God fitted into this picture. La~plass replied, Sire, I have not needed that hypothesis. I don't think that La~plass was claiming that God didn't exist. It is just that He doesn't intervene, to break the laws of Science. That must be the position of every scientist. A scientific law, is not a scientific law, if it only holds when some supernatural being, decides to let things run, and not intervene.
In La~plass's determinism, one needed to know the positions and speeds of all particles at one time in order to predict the future. But according to the uncertainty relation, the more accurately you know the positions, the less accurately you can know the speeds, and vice versa. In other words, you can't know ~both the positions, ~and the speeds, accurately. How then can you predict the future accurately? The answer is, that although one can't predict the positions and speeds separately, one ~can predict what is called, the quantum state. This is something from which both positions and speeds can be calculated, to a certain degree of accuracy. We would still expect the universe to be deterministic, in the sense that if we knew the quantum state of the universe at one time, the laws of science should enable us predict it at any other time.
If information were lost in black holes, we wouldn't be able to predict the future, because a black hole could emit any collection of particles. It could emit a working television set, or a leather bound volume of the complete works of Shakespeare, though the chance of such exotic emissions is very low. It is much more likely to be thermal Radiation, like the glow from red hot metal. It might seem that it wouldn't matter very much if we couldn't predict what comes out of black holes. There aren't any black holes near us. But it is a matter of principle. If determinism breaks down with black holes, it could break down in other situations. There could be virtual black holes that appear as fluctuations out of the vacuum, absorb one set of particles, emit another, and disappear into the vacuum again. Even worse, if determinism breaks down, we can't be sure of our past history either. The history books and our memories could just be illusions. It is the past that tells us who we are. Without it, we lose our identity.
It was therefore very important to determine whether information really was lost in black holes, or whether in principle, it could be recovered. Many people felt that information should not be lost, but no one could suggest a mechanism by which it could be preserved. The arguments went on for years. Finally, I found what I think is the answer. It depends on the idea of Richard Fein man, that there isn't a single history, but many different possible histories, each with their own probability. In this case, there are two kinds of history. In one, there is a black hole, into which particles can fall, but in the other kind, there is no black hole. The point is, that from the outside, one can't be certain whether there is a black hole, or not. So there is always a chance that there isn't a black hole. This possibility is enough to preserve the information, but the information is not returned in a very useful form. It is like burning an encyclopedia.. Information is not lost if you keep all the smoke and ashes, but it is difficult to read. Kip Thorne and I had a bet with John Preskill, that information would be lost in black holes. When I discovered how information could be preserved, I conceded the bet. I gave John Preskill an encyclopedia. Maybe I should have just given him the ashes.
What does this tell us about whether it is possible to fall in a black hole, and come out in another universe? The existence of alternative histories with black holes, suggests this might be possible. The hole would need to be large, and if it was rotating, it might have a passage to another universe. But you couldn't come back to our universe. So, although I'm keen on space flight, I'm not going to try that.
The message of this lecture, is, that black holes ain't as black as they are painted. They are not the eternal prisons they were once thought. Things ~can get out of a black hole, both to the outside, and possibly, to another universe. So, if you feel you are in a black hole, don't give up. There's a way out.
You from
a distance, would never see you cross the event horizon. Instead, you would
appear to slow down, and hover just outside. You would get dimmer and
As far as the outside world is concerned, you would be lost forever.
Because black holes have no hair, in Wheeler's phrase, one can't tell from
the outside what is inside a black hole, apart from its mass and rotation.
This means that a black hole contains a lot of information that is hidden
from the outside world. But there's a limit to the amount of information, one
can pack into a region of space. Information requires energy, and energy
has mass, by Einstein's famous equation,
Most
famously, black holes were predicted by Einstein's theory of general
relativity, which showed that when a massive star dies, it leaves behind a
small, dense remnant core. If the core's mass is more than about three times
the mass of the Sun, the equations showed, the force of gravity overwhelms all
other forces and produces a black hole.
Nearest
black hole to Earth is astoundingly close, just 1,600 light-years
away. Not close enough to be considered dangerous, but way closer than thought.
Further research, however, shows that the black hole is likely further away
than that. Looking at the rotation of its companion star, among other factors,
yielded a 2014 result of more than 20,000 light years.
Cygnus
X-1 was
first found during balloon flights in the 1960s, but wasn’t identified as a
black hole for about another decade. According to NASA, the black hole is 10 times
more massive to the Sun. Nearby is a blue supergiant star that is about 20
times more massive than the Sun, which is bleeding due to the black hole and
creating X-ray emissions.
There
are at least three types of black holes, NASA says, ranging from
relative squeakers to those that dominate a galaxy’s center. Primordial black
holes are the smallest kinds, and range in size from one atom’s size to a
mountain’s mass. Stellar black holes, the most common type, are up
to 20 times more massive than our own Sun and are likely sprinkled in the
dozens within the Milky Way. And then there are the gargantuan ones in the
centers of galaxies, called “supermassive black holes.” They’re each
more than one million times more massive than the Sun. How these beasts formed
is still being examined.
The term "black
hole" was coined in 1967 by American astronomer John Wheeler, and the
first one was discovered in 1971.Black holes have three "layers" —
the outer and inner event horizon and the singularity. The event
horizon of a black hole
is the boundary around the mouth of the black hole where light loses its
ability to escape. Once a particle crosses the event horizon, it cannot leave.
Gravity is constant across the event horizon. The inner region of a black hole, where its mass lies, is
known as its singularity, the single point in space-time where the
mass of the black hole is concentrated. Under the classical mechanics of
physics, nothing can escape from a black hole. However, things shift slightly
when quantum mechanics are added to the equation. Under quantum mechanics, for
every particle, there is an antiparticle, a particle with the same mass and
opposite electric charge. When they meet, particle-antiparticle pairs can
annihilate one another. If a particle-antiparticle pair is created just beyond
the reach of the event horizon of a black hole, it is possible to have one
drawn into the black hole itself while the other is ejected. The result is that
the event horizon of the black hole has been reduced and black holes can decay,
a process that is rejected under classical mechanics. Scientists are still
working to understand the equations by which black holes function. In many ways a black
hole acts like an ideal black body.
General
Theory of Relativity:
It is
based on two principles
1) if
you have two objects nothing else,then it is not possible to tell which object
is moving and which object is standing still.this is even true if one object is
an entire planet.
A man
in space ship,the spaceship is standing still and it is the planet that is
moving.
After
all from the prospective of third obsever.in general any observer can believe
that they are standing still and the rest of universe is moving around and
every observer is equally correct.
2
)Speed of light is samefor all absservers
Spaceship
approaches the speed of light the slower the time will flow inside the space
ship.if the speed of spaceship approaches to the speed of light then time
inside the spaceship would stop together.As an object moves with more energy
its mass increases,this why nothing can travel with speed of light.gravity is
not a force but a curvature in space-time.
Whermhole
is a theoracticall tunnel providing shortcuts through space and time to travel
between different parts of universe.
In
1930 neithe rozen and Einstein mathematical caluculations for black hole.
In
late 199’s carl sagan purpose that whormhole can be used for space
travell apple example
LISA:Laser
Inferometer Space antenna join nasa and Europe space egency mission.
Switzerland
sarn experiment done on black hole creation.
In
1971,atomic clock slight difference.
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