PHYSICS

QUANTUM FIELD THEORY :PART 3

It from bit…Everything is information(John Archibald wheeler)

Look up at the stars and not your feet.Try to make sense of what you see,and wonder what makes the universe exist(Stephen hawking)

Brane theory

Quantum field theory is the crown jewel of physics. Each and every prediction of the theory has been experimentally found to be correct. However there are certain loose ends which are excluded from the theory.Firstly gravity is not included in the framework. Secondly the masses,charge of fundamental particles cannot be derived from the theory.

Brane theory is a quantum field theory that tries to explain the above problems that are unsolved in classical QFT. It is conceptually and mathematically elegant. However its predictions have not been tested experimentally. Part of the reason lies in the fact that one will require accelerators which are much more powerful to test its predictions than those available today.

Branes as solitons in a eleven dimensional universe

Branes are like travelling waves on a flowing river. When a dam gate over a river is suddenly opened a travelling wave travels along the river water surface. The travelling wave is a soliton and is an energy wave with a prolonged existence. The universe is supposed to be eleven dimensional and solitons of similar dimensions can exist in all of them. Thus one dimensional Branes are called zero Branes,two dimensional Branes as strings and so on. The prediction of extra dimensions is not surprising. The electromotive force was predicted by Kaluza as waves moving around a circular dimension.Six of the extra dimensions are supposed to very small,Planck level sizes and responsible for the various fundamental forces similar to Kaluza theory. Five of the dimensions are large and constitute our universe. We are supposed to live in a five dimensional Brane.

Particles as vibrations of strings

All particles are supposed to be waves with different frequencies on strings and these include bosons and fermions. Strings thus unite fermions and bosons which was not there in classical QFT. Gravity is supposed to be transmitted by a closed string called graviton. String theory thus unites gravity with the other three fundamental forces.

  Particle interactions occur in the form of strings uniting or dividing into other strings . It resembles the gauge interactions of classical QFT. However since the interactions do not occur as point particles the calculations do not produce infinities. This enables gravitational interaction to be included

Calabi Yau spaces and particle mass and interaction strengths

The problem with classical QFT was that the particle masses and interaction strengths are not predicted by the theory. In Brane theory the six small dimensions are responsible for the mass and strength of particles. The six small dimensions are supposed to form spaces with particular topological configurations. Vibration of strings within these confined spaces called calabi yau spaces gives the particles mass and interaction strength. Since millions of different shapes of calabi yau can occur we have a choice of mass and strength of fundamental particles. However why the particular calabi yau space is unique to our universe is not known

 However in Brane theory there is another explanation for particle strengths. Similar to strings higher dimensional Branes such as 3-Branes and 4-Branes can also merge and split.The Branes can be moreover connected by strings like ropes. The number of intervening strings and the angle of Branes in the merged state determine string tension. A particular Brane configuration may thus be responsible for the interaction strength of particles in our universe

Evolution of the universe

The universe may be infinite in time,the Big Bang being only a phase in its existence. According to the cyclic eckryptic universe there are two 4dimensional branes near each other and their relative movements transfer energy of collisions to an energy of particles on the Brane surface. However there may not be a requirement of two Branes, According to physicist Lisa Randall a single4dimensional brane will warp the fifth dimension in such a way that there is a gradient of gravity away from the Brane surface.  This can result in a sense of psssage of time.

 Whatever the mechanism it is true that the universe has evolved. The Branes constituting the present universe creates particles with particular masses and interaction strengths. If the strengths had been different the Brane may not have lasted long enough . This creates a selection mechanism which favours a Brane configuration with infinite longevity.

Black holes and information paradox

Black holes are formed when a massive star collapses as a result of having spent all its hydrogen fuel required to sustain the star  with thermonuclear reactions.As a result gravitational attraction of the star causes a collapse and mass is concentrated . The concentration is to such a level and the resulting gravity of the star is so intense that light waves incident to it cannot escape. Such a star is called a black hole.

  The information paradox arises because whatever object falls within a black hole has an information content. Thus a car is made of parts with a definite configuration and if a car falls within the black hole its information is lost forever from the universe.Information or entropy,is a fundamental law of our universe and it can never decrease  in the universe taken as a whole.Entropy may decrease locally compensated by an increase in entropy as a whole and this occurs in all self organization processes such as living organisms.

 To solve the information paradox we have to use duality of information. When a car falls in a black hole there are two views .For an outside observer the velocity of the car slows down as it approaches the black hole horizon as light from the car takes longer time to reach our eyes due to it being slowed down by gravity. Ultimately the car becomes motionless at the black hole horizon and stays there forever .The dual view is that of the car occupant.For the car  as it approaches the horizon it keeps on accelerating. At some time it crosses the horizon. Now inside the black hole time and space coordinates get interchanged. The car moves towards centre of black hole and this represents its time dimension as it is unidirectional. The other directions are its space dimensions. As the car approaches the centre the space dimensions contract like the sides of a funnel. The car  morever  takes infinite time to move to the centre as it is preceded by other objects falling inside the hole including the original star itself and the temporal order has to be maintained.

    The white hole is a reverse of the black hole and it too has a horizon from which nothing can escape. Here also time is represented  by a unidirectional movement of objects but in opposite direction from inside the hole to the horizon. According to physicist Carlo rovelli at the centre of black hole a quantum gravity effect may reverse the direction of time in a black hole and convert it to a white hole. The object configuration and information may thus be preserved  as the objects having fallen in the black hole make a return journey. The information falling inside the black hole is thus given back to the universe as a white hole. It has been speculated that our universe may be just such a white hole with unidirectional time and information being used to create the future. While the future is well defined for objects falling inside a black hole the same is uncertain for objects coming out of a white hole as is true in our universe.

Time  and Malcadena conjecture

If the universe is five large dimensions then according to Argentinian physicist Juan malcadena the classical QFT with the three fundamental forces are confined to the four dimension part. The fifth dimension can only be traversed by gravity. Moreover there is a correspondence between the gravity interactions played out in fifth dimension and quantum mechanical particles in four dimensions . So our four dimensional universe is a hologram.

   To understand this consider a 2 dimensional universe containing two objects a cow and a dog. Now time cannot occur in this universe. Time is movement and movement implies that the projection of an object becomes smaller to us as it goes farther away. In a 2dimensional universe no matter how far we place two objects their relative sizes remain same.However  suppose the 2dimensions is surrounded on all sides by another 3dimensions. Now movement of the two objects relative to each other can take place in third dimension. A projection of the relative sizes on two dimensions now leads to size difference with distance between them. But this movement is occurring in the third dimension. Thus for beings in 2dimensions though they are not aware of third dimension their time passage is only because of movement in third dimension. An analogous situation creates time in our 4dimensional universe. The movement of closed strings or gravitons in fifth dimensions creates a sense of time in our four dimensions.

   According to physicist Kip Thorne the walls of our four dimensional Brane has five dimensional projections. These projections are separate four dimensions attached to all the walls . These four dimensional spaces can be penetrated only by gravity. Each 4dimension has movement in unidirectional time. This is projected to the corresponding wall of the 4dimensional Brane in which we live. The combined projection of all 4dimensional parts is fused as a hologram in our universe. 

 The hologram is continuously playing out unidirectionally. The past is increasingly distant across  5dimensions. As distances increase it will take more time to communicate and speed of communication becomes infinite. With infinite speed time dilation occurs and time stops. Thus the past is frozen but preserved.

Ack: The science of interstellar,warped passages,White holes,D Branes -superstrings and new perspective of the world