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Posted 3 October 2007

A Journey Through Time

by Frikkie de Bruyn

"The reason that there is something instead of nothing is that nothing is unstable".
- Franck Wilckzyk


According to Einstein’s General Theory of Relativity the entire universe was created in a tremendous explosion about 13.7 billion years ago. Stephen Hawking proved that if you apply the general relativity equations to the very end, the very early universe was incredibly small, much smaller than an atom, infinitely hot, infinitely dense with an infinite force of gravity called a singularity. It is natural to ask: “What was it like then?” and even: “What happened before the Big Bang?” To try to answer some of these questions we have to take a journey back in time to the very, very early universe, known as the Planck era. When I use the word ‘time’ I do not refer to what we understand in everyday life as time, but rather the increase in entropy or disorder in a universe that started of in a very orderly way and since then, in accordance with the second law of thermodynamics, the entropy increase, never decrease. This can obviously be interpreted as a one way directional time. To avoid confusion it would be more appropriate to describe it as a journey backwards to view the evolution of the physical processes in the universe to its beginning. I use time in the context of a measurement of the interval between spatially separated events. This is a valuable tool used by cosmologists with great success to discover what conditions were like in the very early universe.

Our journey starts with the formation of our own star, the sun and the planets about 4.6 billion years ago. About 11 billion years ago our own galaxy, the Milky Way, formed. At about 5 billion years after the Big Bang the first galaxies were formed. By about 700 000 years after the Big Bang the universe was a seething mass of plasma consisting of electrons, protons, helium nuclei and very energetic photons in constant collisions at about 4 000 degrees. The constant collisions of energetic photons with particles prevent the formation of atoms. There was no darkness and the sky was ablaze with the brilliance of the sun. By about 3 minutes after the birth of the universe helium formed from the fusion of hydrogen nuclei and the temperature at nearly 1 billion degrees. The average density of matter was that of lead. At one second the lepton era (such as the electron) ended and the ratio between protons and neutrons became fixed at 1 neutron for every 5 protons and the temperature was 5 billion degrees. About .0001 second the quark era ended while the temperature rose to 1 trillion degrees. Quarks combined in groups of two or three to form neutrons, protons and other heavy particles which only existed for a very brief period. The density of matter was similar to the density of the nucleus of an atom.

The next part of our journey takes us to a universe of about 1 thousand trillion degrees at 1 billionth of a second after its birth. The well known electromagnetic force and the weak nuclear force merged into one force. Quarks and anti-quarks are no longer confined in particles like protons and neutrons, but form part of super hot and dense plasma of particles. Recent research, when approximately similar conditions were created, showed that the very early universe may have consisted of a fluid with a very low viscosity. At 10-35 second after the Big Bang a spectacular change in the size of the universe occurred. This is generally referred to as the GUT (Grand Unification Theory) era when the strong nuclear force became one super force with the electromagnetic and weak nuclear forces. The temperature was ten thousand trillion trillion degrees and the density of matter had soared to an incredible 1075 gm/cm3. The major constituents of the universe were electrons and quarks together with their anti-particles. Some scientists think that very massive particles called Leptoquark Bosons also existed causing the quarks to decay into electrons and vice versa. Moving further backward we witness the vacuum of space undergoing a phase transition from a higher to a lower energy state. The universe underwent a brief but incredible exponential expansion and swelled to billions of times its former size. At this stage the excess of matter over anti-matter would have appeared. It is uncertain why this happened but some believe that this was caused by the decay of very massive particles called X Higgs Bosons. This was the last stop in our journey. We have now entered a strange no-mans land, the Planck era.

The Planck era refers to the universe no larger than 10-33 cm at a time of about 10-43 second. It is impossible to observe say a length of 10-33 cm because it is far smaller than the wavelength of light. We must use mathematical theories to mentally explore what the universe was like then. We know that the force of gravity must have been predominant and that the general relativity equations cannot describe the interaction of gravity with matter at the Planck scale. Researchers are currently trying to extend General Relativity to include the microscopic properties of gravity, that is, we need a Theory of Quantum Gravity to describe the microscopic world at the Planck scale. Such a theory is still far from complete but we have some idea what it has to look like. First it will describe the interactions of gravity with matter at the quantum level. We know that the force of gravity can be seen as the exchange of gravitons (the force carrying particle of gravity) between two or more bodies. Our bodies are being pulled towards the centre of the earth through the exchange of gravitons between our bodies and the earth. The curvature of spacetime as described by Einstein’s General Relativity Theory can be seen as being caused by billions of gravitons at the quantum level causing spacetime to curve. We are used to calculate the geometry of 3-dimensional space but at the Planck scale we are not allowed to simultaneously determine its exact geometry and rate of change in time. We are faced with the possibility that we may never know what the geometry of the very early universe was and that we may not be able to calculate with certainty the history of the very early universe at the quantum level. This is due to the restrictions imposed on our ability to do measurements at the quantum level, called the uncertainty principle.

Our notions of space and time have to change radically if we are to study the quantum origin the universe. The well known physicist, John Wheeler, described space at the quantum level as similar to quantum foam with quantum fluctuations dominating the scene. Quantum fluctuations can also be seen as the creation of virtual particle pairs (particles and their anti-particles) which have to annihilate and return the borrowed energy within the time limit set by the uncertainty principle. Virtual particles cannot be detected with a particle detector, but we know they exist because of their influence on certain quantum interactions. What about time? The smearing effect of the uncertainty principle means that time is smeared out and becomes another spatial dimension. We cannot talk about the well known three dimensions when we study the quantum world. There are no up, down, forward or backward dimensions. In fact we are faced with the incredible situation that that gravity was the only force, the super-force. Imagine, if you can nothing. This is what we are faced with when we study the primordial vacuum from which, scientists think, the universe was born. The vacuum could have been there for an eternity, when a quantum fluctuation could have gained strength and caused a run-away reaction from which our universe was born. The universe may have been created from nothing.

Frikkie de Bruyn

 


Selected bibliography

Aczel, A (2000) God’s Equation: Einstein, Relativity and the Expanding Universe. Judy Piatkus Ltd., London.
Bodanis, D (2000) E = mc2; A Biography of the World’s Most Famous Equation. Macmillan, London.
Gribbin, J (1988) In Search of the Big Bang, Quantum Physics and Cosmolgy. Corgi, London.
Hawking, S & Penrose R (1996) The Nature of Space and Time. Princeton University Press, Princeton, New Jersey.
Weinberg, S (1997) The First Three Minutes: A Modern View of the Origin of the Universe. Second Edition. Andre Deutsch, London.

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