Beyond the reality we know

But to make the dream true they needed 'The theory of everything', which will untie 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 Einstein 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 say that they have got that theory and that is the super string theory, which believes in eleven dimensions. So maybe the mystery unfolds at the eleventh dimension.

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 the vibration created by the string different musical notes are created.

In similar manner, in string theory the sub-atomic particles are really just resonance or vibrations of a tiny string. The strings are floating at space time. So roughly speaking everything in the universe is made of tiny strings. There are both open and closed looped strings.

Extra dimensions
We live in a universe of three dimensional (3D) space, or four dimensional space-time. It means we can move back-front, up-down and 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 it needs ten dimensions! But where are the extra six dimensions (6D)? The extra six dimensions are compacted. The best way to draw this is to use complicated 6D geometry called Calabi-Yau manifold.

Five theories of everything!
At first of early nineties there were 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 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 at that point 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 called D-branes.

D-branes are surfaces where the free ends of open strings are fixed. They come in various dimensions. D2-branes for example are two dimensional and can also be called D2-membranes, or super membranes. D0-branes are like particle like and D1-branes are string like etc. 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 scientists were able to add the last one dimension, the eleventh dimension and something remarkable happened -- the five theories turned out to be simply different manifestations of a more fundamental theory. So 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 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. This is the mother of all superstring theories.

The eleventh dimension
Quickly it became clear that 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 Ovrut (University of Pennsylvania) says that this eleventh dimension exists only one trillionth of a millimetre away from every point in our three dimensional world. In this mysterious space our membrane universe is floating. Some suggested it might float like a thin rubber sheet. Others say 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 Universe
Lisa Randall (Harvard University) had been fascinated by an apparently inexplicable phenomenon: the weakness of gravity.

We know there are four fundamental forces in our universe. The other three forces are at least 10^30(30 zeros after 1) times stronger than gravity. For example if you think about if you have the entire earth pulling on you and yet can manage to pick things up.

Randall and Sundrum (John Hopkins University) used M Theory and the theory that there might be another membrane universe at the other side of the eleventh dimension. Their calculation told something strange and enigmatic -- Gravity was leaking to our universe from the other parallel universe. On that membrane or parallel universe, gravity would be as the other forces, but by the time it reached us it would only be a faint signal. 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 should be 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 answer what caused the Big Bang?

Big Bang
Imagine there is an enormous ship standing at a harbour which is 150 or 200ft high. This giant wave suddenly jumped from sea surface to air and crushed its windows. It means that the giant wave jumped from 2D to 3D. Burt Ovrut suggested our universe is moving through the eleventh dimension like giant turbulent waves. Neil Turok (Cambridge University) and Paul Steinhurdt joined him to explore the cause of Big Bang and solved the mystery.

The idea was
If two branes collide then it produces all the effects of early universe. It means Bigbang is the result of the collision of two branes or parallel universes. But the problem was things are not smooth out in our universe. In fact we have little clamps, we have galaxies and lumps of matter. Now they had to explain how the collision of two parallel universes 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 different laws of physics. Big Bangs 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 us -- it may only be a matter of time before we collide.

References: Elegent Universe-Brayan Greene, Superstrings-Leonerd Susskind www.physics web.com, Bigbang Wikipedia and BBC-Science & Nature.

The author is a physics student at the University of Dhaka