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Latest News from TREZ:
New Rules / New Tags / BB Tags upgrade / TEX Tag / LaTeX partial tutorial / New contest / 2 new forums / topic preview feature / new affiliations / EXE 1 PA / few other TREZ changes I don't want to mention them one by one, 70th anniversary of WWII beginning / New Rules / Contest Winners Updated / TREZ Werewolf game / History of TREZ / Nemo's Random Event #8, New Banner / ZetaBoards Upgrade / New Dice Tag, Hacked Battle V contest / Navi Contest Results / Nemo's Random Event #7 / Custom Programs forum / Official RP at TREZ / Site updates, NO PORN HERE
Nov 11
Advanced Physics Made Simple
The Schwarzschild Solution
Shortly after Einstein developed the general theory of relativity, Karl Schwarzschild found a solution for the equations of general relativity in empty space. He started by assuming only that the solution was SPHERICALLY SYMMETRIC. This means that no matter how the system is rotated about its center, it remains the same. He then applied the required mathematical conditions to general relativity, and came up with a solution that approximates the behaviour of planets around the sun. In fact, one of the first tests of general relativity was the prediction of the motion of Mercury using the Schwarzschild solution. Another benefit of the solution is that it is static. This means that a star can pulse and evolve in any spherically symmetric way, and there is no way of measuring the effect on gravity.
Unfortunately, there is a problem with the Schwarzschild solution. When the distance from the center of the system is equal to a constant multiplied by the total mass of the body, the Schwarzschild metric (recall that this is the function used to measure distance in general relativity) becomes infinite, and has no time dependence. Although it cannot be proved here, this corresponds to light being trapped at this distance. Even worse, when the distance is smaller, time and space swap properties, so that ordinary distance acts like time and time acts like distance.
Black Holes
The Schwarzschild solution has a problem at a certain distance, called the Schwarzschild radius or the Event Horizon, at which light cannot escape. Because no light escapes from the event horizon, the object would appear black, and thus was dubbed a black hole. However it is very rare to have a high enough mass density, and usually the Schwarzschild radius lies within the body where the Schwarzschild solution doesn't apply. It is still debated if such high density objects could exist.
According to a person who falls into a Black Hole, the event horizon does not exist (this is shown by transforming to other solutions for spherically symmetric bodies) but when they cross it, they can no longer send messages to the outside world. The person then continues to fall towards the center.
According to a person who stays at a constant distance from the black hole, the person who falls in never reaches the event horizon. They appear to slow down forever, and messages sent from the person seem to slow down.
White Holes
The black hole is not the only interpretation of the Schwarzschild solution. There is another possibility which instead of trapping everything in the event horizon, continuosly emits stuff. They would emit so much light, that the would be very bright white objects. In theory, anything could come out of a white hole, from dust particles to a stream of toasters. More than likely, only fundamental particles would be emitted, but there is no reason to assume this.
The problem with white holes is that they violate the SECOND LAW OF THERMODYNAMICS. Basically it states that any ordered system becomes more disorganized (like if you drop an egg, it will become a disordered mess, but a disordered mess will never spontaneously form a perfect egg), and so a system which produces adds order to a system is not possible. This is why many believe that a white hole can not exist.
Worm Holes
If a white hole and a black hole could be linked somehow, then stuff which falls into the black hole could suddenly appear coming out of a white hole elsewhere in the universe. In science fiction, such a phenomena allows people to travel across large amounts of space, faster than normal travel through space will ever allow.
However in the real world, there are many problems with traveling through a worm hole. The first problem is that the black hole and white hole would have to be very similar, and so even a small particle could break the symmetry and destroy the worm hole. This may be possible to resolve by using exotic matter which is not currently known about and which could stabilize a worm hole. The second problem is surviving such a trip. The gravity around black and white holes is so large and varies so much in space that anything in the region of a black hole would be ripped apart. ( For example if the space shuttle approached a black hole, the front would be pulled in faster than the back of the ship and probably break it)
Naked Singularities and the Cosmic Censorship Hypothesis
It has been hypothesized that a black hole would collapse to a single point, and at this point, called a SINGULARITY, the laws of physics do not apply. For a true black hole, this does not cause any problems, since the event horizon hides the singularity and so nothing outside the black holes is affected.
However there is a lot of research which indicates the possibility of NAKED SINGULARITIES. These are similar to black holes in that the center of the system is a singularity where the laws of physics fail, but differ dramatically because light can escape from them. Therefore the singularity can be observed and studies, and some research indicates time travel may occur at the singularity.
The problems which accompany a naked singularity made some physicists decide there must be a COSMIC CENSORSHIP HYPOTHESIS. This rule, which as yet has no proof, states that nature abhors a naked singularity (thus its title) and so, if it can ever be proved, everything works without problems from a singularity.
Nov 08
Black Holes
Black hole
This image is a simulation of what a black hole might look like. No black hole has ever been photographed.A black hole is an object in the universe that has such a strong pull of gravity, even light can't escape it. Until recently, many astronomers did not even know if they existed, but by using telescopes and looking at the universe, they found objects with such a very strong force. They decided it was a black hole with a strong gravitational force. This does not mean that the origin of such a strong force can not be something different than gravitational one.
History
In 1783, an English geologist named John Michell wrote that it might be possible for something to be so big and heavy that the escape speed from its gravity is equal to speed of light. Gravity gets stronger as something gets bigger or more massive. For a small thing, like a rocket, to escape from a larger thing, like Earth, it has to go upward very fast or it will fall back down. The speed that it must travel upward to get away from Earth's gravity is called escape velocity. Bigger planets (like Jupiter) and stars have stronger gravity than Earth, so the escape velocity is much faster. John Mitchell thought it was possible for something to be so big that the escape velocity would be faster than the speed of light, so even light could not escape.
Some scientists thought Mitchell might be right, but others thought that light had no mass and would not be pulled by gravity. His theory was forgotten.
In 1916, Albert Einstein wrote an explanation of gravity called general relativity. It is a very complicated theory, but there are two important things about it:
Mass causes space (and spacetime) to bend, or curve. Moving things "fall along" or follow the curves in space. This is what we call gravity.
Light always travels at the same speed, and is affected by gravity. If it seems to change speed, it is really travelling along a curve in spacetime.
A few months later, a German physicist named Karl Schwarzschild calculated that a black hole could exist.
In 1930, Subrahmanyan Chandrasekhar predicted that stars heavier than the sun could collapse when they ran out of hydrogen to burn and died. In 1939, Robert Oppenheimer and H. Snyder calculated that a star would have to be at least three times as massive as the sun to form a black hole.
In 1967, John Wheeler gave black holes the name "black hole" for the first time. Before that, they were called "dark stars."
In 1970, Stephen Hawking and Roger Penrose proved that black holes must exist. Although the black holes are invisible (they cannot be seen), some of the matter that is falling into them is very bright.
Formation of black holes
Most black holes are made when a giant star, at least three times bigger than our own Sun, dies. Stars die when they run out of hydrogen or other fuel to burn and start to cool off.
A supegiant star's death is called a supernova. Stars are usually in equilibrium, meaning they are making enough energy to push their mass outward against the force of gravity. When the star runs out of energy, gravity takes over. Gravity pulls the center of the star inward very quickly (so quickly that it would have to be repeated several thousand times before it took up a single second), and it collapses into a little ball. The collapse is so fast and violent that it makes a shock wave, and that causes the rest of the star to explode outward. As the gravity pushes the star inward, the pressure in the center of star reaches to such an extreme level that it enables heavier molecules like iron and carbon interact to release nuclear energy. The release of the energy from the star during a very short period of time (about one hour) is with such a high rate that it outshines an entire galaxy.
The ball in the center is so dense (a lot of mass in a small space, or volume), that if you could somehow scoop only one teaspoon of material and bring it to Earth, it would sink to the core of the planet. This densely packed ball is called a singularity.
Even without a supernova, a black hole will form any time there is a lot of matter in a small space, without enough energy to act against gravity and stop it from collapsing.
If super novas are so shiny, why we do not see them often? Actually, there are usually hundreds of years between naked-eye super nova sightings. It is because the period of being a super nova in a star life cycle is only a few hours out of the billions of years in a star's life span. The probability of looking at a star in sky and that being in super nova state is equal to the ratio of an hour over several billion years.
It is worth mentioning that all of the heavier materials like carbon, oxygen, all the metals, etc, that make the life on the earth possible and are ingredients of all living creatures, can only form in the extreme pressure at the center of a super nova. So we are all a remnant ash from one exploding star several billion years ago.
Appearance of black holes
The singularity in the middle of a black hole cannot be seen, because light cannot escape its gravity. Around the tiny singularity, there is a large area from which no light can escape. The boundary of this area is called the event horizon. The gravity of the black hole gets weaker at a distance. The event horizon is farthest point where it is still strong enough to trap light. The singularity is like the pipe in a sink drain while the event horizon is like the place where the water falls into the singularity.
A black hole pulling off the outer layer of a nearby star. It is surrounded by an energy disk, which is making a jet of radiation Even farther away, light and matter will be pulled toward the black hole. If a black hole is surrounded by matter, the matter will form an "accretion disk" (accretion means "gathering"). An accretion disk looks something like the rings of Saturn. The disk is very hot and shoots x-ray radiation into space. Think of this as the water spinning around the hole before it falls in.
Most black holes are too far away and small to see the accretion disk and jet, though. The best way to know one is there is by seeing how stars, gas, and other things behave around it. With a black hole nearby, even objects as big as a star move in a different way, and a lot faster than they would if the black hole was not there.
Also, if a black hole passes between us and a source of light very far away, the light will become quite distorted, much like a fun-house mirror in a circus, until the black hole moves out of the way. The light can also be magnified, like a magnifying glass, allowing scientists to see things farther away.
We cannot actually see black holes; one way of detecting them is to look at the sky when a black hole passes between us and a source of light, the light bends around the black hole creating a mirror image, so when astronomers see patches of sky that are identical, they may have found a black hole.
Black holes have also been found in the middle of every major galaxy in the universe. These are called supermassive black holes, and are the biggest black holes of all. They formed when the Universe was very young, and also helped to form all the galaxies.
Some black holes are also responsible for making quasars. When astronomers first found quasars, they thought they had found objects close to us, but after using a measuring technique called red shift, they discovered these quasars were actually very far away in the universe. A quasar occurs when a black hole consumes all the gas surrounding it. As the gas gets close to the black hole itself, it heats up from a process called friction, and glows so brightly that this light can be seen on the other side of the Universe. It is often brighter than the whole galaxy the quasar is in.
A lot of science fiction writers use black holes in their stories, and many scientists wish to find one relatively close to Earth to study one better.
Scientists also think black holes might cause wormholes, theoretical "portals" through space.
From Wikipedia.
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