What is the fundamental thing that makes up matter? Do extra dimensions exist? If they do, where are they? Do parallel universes exist? How our visible universe was created?

Imagine you could find an explanation for everything in the universe, from the smallest events possible to the biggest. This is the dream which has captivated the most brilliant scientists since Einstein. But to make the dream true they needed “The theory of everything” which will unitie all the four fundamental forces into a single equation. The four forces (gravity, electromagnetism and the strong and weak nuclear forces) would be unified by an equation perhaps one inch long. During the last thirty years of his life Albert Eienstein sought, relentlessly for this theory and he came up empty handed and once said “Nature shows us only the tail of the lion”. But now scientists says that they have got that theory and that is the super string theory.

**In the heart of string theory:**

Think of a guitar that has been tuned by stretching the string under tension across the guitar. Depending on how the musical notes will be created by the string. These musical notes could be said to be excitation modes of that guitar string under tension.In similar manner, in string theory the elementary particles could be thought of as the musical note or excitation modes of elementary strings.So, roughly speaking everything in the universe in made of tiny strings, because the sub-atomic particles are really just resonance or vibrations of a tiny string.In string theory as in guitar playing, the string must be stretched under tension in order to become excited. The strings are floating at space time.If string theory is a quantum theory of gravity(it’s a theory which can unifie General Reletivity & Quantum mechanics, where general reletvity explains the largest events & quantum mechanics the smallest thing in the universe) then the average size of a string is about 10*-33 centimeters, or about a millionth of a billionth of a billionth of a billionth of a centimeter. Unfortunately, this means that the strings are too small to see by current or expected particle physics technology.There are both open & closed looped strings.

**Extra dimensions:**

We live in a universe of three dimensional space (3D), or can say four dimensional space-time. It means we can move back-front, up-down & left-right in these three ways. With these three dimensions adding time we get four dimensional (4D) space-time. But string theory says something different, strange and amazing.If a string has to oscillate properly if needs ten dimensions! Yes ten dimensions. But where are the extra six dimensions? Super string theory gives the answer. The extra six dimensions are compactified. The best way to draw this is to use complicated 6D geometry called Calabi-You manifold, in which all the intrinsic properties of elementary particles are hidden.There are infinite number of ways to wind a string around and extra dimension. Each way in topologically described by an integer called winding number, which can be positive or negative depending on the orientation of the string.

Five theories of everything!At first of early nineties there was total five distinct string theories in 10D space.The theories are So (32), Type I ,IIA,IIB & E8 X E8 heterotic.In that time string theory was said as “The theory of everything”. But it has five types. So it there are five theories of everything! and it is really impossible because we need only one. Besides Michel Duff (University of Michigan) and his team combined gravity and super symmetry which is called supergravity. Their equation said that totally there will be .11 dimensions where string theory said 10. So with everything string theory was in an embarrassing position. They were trying to add the eleventh dimension. It might rescue them.

Brane world:In 1995 Joe Polchinski of the University of California in Santa Barbara electrified the string-theory community with a major discovery that has subsequently impacted every field of physics. He discovered D-branes.D-branes are surfaces where the free ends of open strings are fixed. They come in various dimensions. 0.2-branes for example are two dimensional and can also be called D2-membranes, or super membranes. D0-branee are like particle like and D1-branes are string like. Higher dimensional objects can exist as well. D-branes are essential for making string-theory mathematically consistent, and have far-reaching implications for a theory of quantum gravity.

Five theories of everything!At first of early nineties there was total five distinct string theories in 10D space.The theories are So (32), Type I ,IIA,IIB & E8 X E8 heterotic.In that time string theory was said as “The theory of everything”. But it has five types. So it there are five theories of everything! and it is really impossible because we need only one. Besides Michel Duff (University of Michigan) and his team combined gravity and super symmetry which is called supergravity. Their equation said that totally there will be .11 dimensions where string theory said 10. So with everything string theory was in an embarrassing position. They were trying to add the eleventh dimension. It might rescue them.

Brane world:In 1995 Joe Polchinski of the University of California in Santa Barbara electrified the string-theory community with a major discovery that has subsequently impacted every field of physics. He discovered D-branes.D-branes are surfaces where the free ends of open strings are fixed. They come in various dimensions. 0.2-branes for example are two dimensional and can also be called D2-membranes, or super membranes. D0-branee are like particle like and D1-branes are string like. Higher dimensional objects can exist as well. D-branes are essential for making string-theory mathematically consistent, and have far-reaching implications for a theory of quantum gravity.

**M-theory:**

At last scientist’s were able to add the last one dimension, the eleventh dimension and something happened remarkable — the five theories turned out to be simply different manifestations of a more fundamental theory. It means in 11 dimensions looking from the mountain-top, looking down you could see string theory as being part of a much larger reality, reality of eleventh dimension.So with the addition of one extra dimension string theory made sense again, but it had become a very different kind of theory.Here the tiny invisible strings of string theory stretched and they combined. The astonishing conclusion was that all matter in the universe was connected to one vast structure: a membrane. In effect our entire universe is a membrane. The quest to explain everything in universe could begin again and at its heart would be this new theory. It was dubbed membrane theory or M-theory, but so enigmatic and profound did the idea seem that some thought ‘M’ should stand for other things as — magic, mystery, majesty, madness or mother theory. This is the mother of all superstring theories.

**The 11th dimension:**

With M theory it seemed at least there was a theory which might explain everything in the universe, but before they could decide if this was true the scientists needed to know more about this new eleventh dimension. It quickly became clear it was a place where all the normal rules of commonsense have been abandoned. For one thing it is both infinitely long but only a very small distance across.Scientists like Paul Steinhard (Princeton University) and Burt Or rut (University of Pennsylvania) tell that this 11th dimension exists only one trillionth of a millimetre away from every point in our three dimensional world. So it’s closer than your clothes to your body and yet we can not sense it. In this mysterious space our membrane universe is floating. At first no one could imagine how that worked. Then some suggested it might float like a thin rubber sheet. Others that it might be more like a bubble which vibrated as it was blown aimlessly across space. But is our universe alone or there are parallel universes? Let’s explore it. The journey began with Lisa Randall.

Parallel Universes:

Lisa Randall (Harvard University) had been fascinated by an apparently inexplicable phenomenon: the weakness of gravity.We know there are four fundamental force in our universes. If we assume the intensity of gravity ‘1′, then the intensity of weak Nuclear Force-10*30, strong Nuclear force- 10*40 and strong Nuclear force-10*42 (42 zero after 1). So gravity is extremely weaker than the other three forces. Now you might look around and say gravity does not seem weak, but if you think about if you have the entire earth pulling on you and yet can manage to pick things up.When M Theory emerged, Randall and Sundrum (John Hopkins University) wondered if it might be provide and explanation. Could gravity be leaking from our universe into empty space of the eleventh dimension?Randall tried to calculate how gravity could leak from our membrane universe into empty space, but she couldn’t make it work. Then she hard a theory that there might be another membrane in eleventh dimension. Now he had really strange thought. What if gravity was not leaking from our universe but to it? What if it came from that other universe? On that membrane or brain, gravity, would be as the other forces, but by the time it reached us it would only be a faint signal. Now when she reworked her calculations everything fitted exactly. So our gravity is just a weak signal leaking out of another universe into ours which spends most of the time near the other brane. We only feel the tail end of gravity.The weakness of gravity could at last be explained, but only by introducing the idea of parallel universe. Randall’s idea opened a pandora’s Box. Now suddenly physicists all over the world piled into the eleventh dimension trying to solve age-old problem and every time it seemed the perfect explanation was another parallel universe. Everywhere they looked it seemed they began to find more and more of them.within no time at all eleventh dimension seemed to be jam packed full of membranes. These membranes were possible other parallel universes. In those universes there may be people like us or not, may be different kinds of laws of physics.So M-theory was getting more and more stranger. But could it really be a theory which explained everything in our universe? Did it answered what caused the Bigbang, it mean the explosion from which our universe was created?

Before the Big bang:

Imagine there is an enormous ship standing at harbour which is 150 or 200ft high. This giant wave suddenly jumped from sea surface to air & crushed its windows. It means from 2d to 3d. Burt ovrut suggested our universe is moving through the eleventh dimension like giant, turbulent waves.Burt’s idea caught attention of the physicists and cosmologists. After a conference in Cambridge in which he explained this idea first time, Neil Turok (Cambridge University), Paul Steinhurdt and Burt decided to discuss about bigbang. Started to throw ideas. Suddenly they knocked at the right door and the mystery of bigbang opened.The idea was——-If two brains collide each other then it produces all the effects of early universe. It means Bigbang is the result of the collision of two brains or parallel universes. But the problem was things are not smooth out in our universe. In fact we have little clamps, we have galaxies & lumps of matter. Now they had to explain how the collision of two parallel universe could go on create these lumps of matter. Could they solve it?Yes, they solved it. They answer was — people tended to think of brains as being flat perfect sheets, geometrical plains, but the picture could not be correct. It cannot be perfectly flat. It has to ripple. When the rippling brains approach to each other and collide they don’t hit at exactly the same time, same place, but in fact they hit at different points and at different times. This rippling collision produces lumps of matter.So they finally had their complete explanation of the birth of our universe and the latest understanding of the universe is that there could be infinite number of universes each with a different laws of physics. Bigbangs probably take place all the time. Our universe co-exists with other universes which are also in process of expansion. Our universe could be just one bubble floating in an ocean of other bubbles. Perhaps out there in space there is another universe heading directly towards as — it may only be a matter of time before we collide.

Parallel Universes:

Lisa Randall (Harvard University) had been fascinated by an apparently inexplicable phenomenon: the weakness of gravity.We know there are four fundamental force in our universes. If we assume the intensity of gravity ‘1′, then the intensity of weak Nuclear Force-10*30, strong Nuclear force- 10*40 and strong Nuclear force-10*42 (42 zero after 1). So gravity is extremely weaker than the other three forces. Now you might look around and say gravity does not seem weak, but if you think about if you have the entire earth pulling on you and yet can manage to pick things up.When M Theory emerged, Randall and Sundrum (John Hopkins University) wondered if it might be provide and explanation. Could gravity be leaking from our universe into empty space of the eleventh dimension?Randall tried to calculate how gravity could leak from our membrane universe into empty space, but she couldn’t make it work. Then she hard a theory that there might be another membrane in eleventh dimension. Now he had really strange thought. What if gravity was not leaking from our universe but to it? What if it came from that other universe? On that membrane or brain, gravity, would be as the other forces, but by the time it reached us it would only be a faint signal. Now when she reworked her calculations everything fitted exactly. So our gravity is just a weak signal leaking out of another universe into ours which spends most of the time near the other brane. We only feel the tail end of gravity.The weakness of gravity could at last be explained, but only by introducing the idea of parallel universe. Randall’s idea opened a pandora’s Box. Now suddenly physicists all over the world piled into the eleventh dimension trying to solve age-old problem and every time it seemed the perfect explanation was another parallel universe. Everywhere they looked it seemed they began to find more and more of them.within no time at all eleventh dimension seemed to be jam packed full of membranes. These membranes were possible other parallel universes. In those universes there may be people like us or not, may be different kinds of laws of physics.So M-theory was getting more and more stranger. But could it really be a theory which explained everything in our universe? Did it answered what caused the Bigbang, it mean the explosion from which our universe was created?

Before the Big bang:

Imagine there is an enormous ship standing at harbour which is 150 or 200ft high. This giant wave suddenly jumped from sea surface to air & crushed its windows. It means from 2d to 3d. Burt ovrut suggested our universe is moving through the eleventh dimension like giant, turbulent waves.Burt’s idea caught attention of the physicists and cosmologists. After a conference in Cambridge in which he explained this idea first time, Neil Turok (Cambridge University), Paul Steinhurdt and Burt decided to discuss about bigbang. Started to throw ideas. Suddenly they knocked at the right door and the mystery of bigbang opened.The idea was——-If two brains collide each other then it produces all the effects of early universe. It means Bigbang is the result of the collision of two brains or parallel universes. But the problem was things are not smooth out in our universe. In fact we have little clamps, we have galaxies & lumps of matter. Now they had to explain how the collision of two parallel universe could go on create these lumps of matter. Could they solve it?Yes, they solved it. They answer was — people tended to think of brains as being flat perfect sheets, geometrical plains, but the picture could not be correct. It cannot be perfectly flat. It has to ripple. When the rippling brains approach to each other and collide they don’t hit at exactly the same time, same place, but in fact they hit at different points and at different times. This rippling collision produces lumps of matter.So they finally had their complete explanation of the birth of our universe and the latest understanding of the universe is that there could be infinite number of universes each with a different laws of physics. Bigbangs probably take place all the time. Our universe co-exists with other universes which are also in process of expansion. Our universe could be just one bubble floating in an ocean of other bubbles. Perhaps out there in space there is another universe heading directly towards as — it may only be a matter of time before we collide.

**Referance:**

Elegent Universe-Brayan Greene

Superstrings-Leonerd Susskind http://www.physicsweb.com/

BBC science & nature

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