Notes on the Early Universe and giant tortoises.
A well-known scientist (some say it was Bertrand Russell) once gave a public lecture on astronomy. He described how the earth orbits around the sun and how the sun, in turn, orbits around the center of a vast collection of stars called our galaxy. At the end of the lecture, a little old lady at the back of the room got up and said: “What you have told us is rubbish. The world is really a flat plate supported on the back of a giant tortoise.” The scientist gave a superior smile before replying, “What is the tortoise standing on?” “You’re very clever, young man, very clever,” said the old lady. “But it’s turtles all the way down! — A Brief History of Time, Hawking, 1988
With the post Bits inside an Apple, we saw that the Universe can be thought as a quantum computer, and its language are the Laws of Physics. A quantum computer is able to simulate the Laws of Physics, even those that have not yet been discovered. These kind of computers, whose architecture mimics the structures of space and time, can effectively reproduce the movement of all the elementary particles and the interactions among them.
This new post is dedicated to a brief overview on the beginning of the Universe and the meaning of two fundamental quantities for a physical system: energy and entropy.
###Our whole universe was in a hot dense state… (theme song of The Big Bang Theory)
The Universe as we know is made up of atoms and elementary particles, such as electrons, photons, quarks and neutrons. Science gives already an excellent way to describe the Universe in terms of physics, chemistry, and biology. The computational Universe is not an alternative to the physical Universe. The Universe that evolves processing information and the Universe that evolves from the Laws of Physics are the same Universe. These two descriptions are just complementary ways for capturing the same phenomenon.
The Universe began about 14 billion of years ago, in a tremendous explosion called Big Bang. It is expanded and cooled, and various forms of condensed matter came out of the cosmic soup. About 3 minutes after the Big Bang: the building blocks for simple atoms such as hydrogen and helium were formed.
These building blocks, driven by the force of gravity, collapsed and formed planets and galaxies about 200 million years after the Bing Bang. From a quantum point of view, the Universe can be imagined as a kind of cosmic soap-opera where the actors perform all the possible permutations of the drama.
In Physics, energy is what is needed to make a work. The energy contained in the mass of elementary particles is called radiant energy. Energy is very interesting because has a very nice characteristic: it preserves itself. This feature is the so called First Law of Thermodynamics.
The energy enables physical systems to do things. But where does the energy comes from? Quantum mechanics describes the energy in terms of quantum fields, a sort of underlying texture throughout the Universe, whose waves produce elementary particles. All the energy around us has been literally sucked from these quantum fields during the expansion of the Universe. The gravity is an attractive force, and as the Universe expands, it sucks the energy from the quantum fields. The energy of the quantum field is positive, and is balanced by the negative energy of gravity.
In a computational Universe, the principal element is the information that tells the physical systems what to do. If we observe an atom in small scale, we can see that it jiggles around a point. This kind of dance is due the heat, and the dance step is called entropy, which represents the information required to specify the causal movement of atoms. In a physical system, the entropy is considered a measure of the degree of molecular disorder existing. An equivalent definition, is the information contained in a physical system that is invisible to us all.
The Second Law of Thermodynamics states that the entropy of the Universe never decreases. In other words, the amount of energy that is unusable because cannot be converted into mechanical work, is being reduced more and more. Free energy is nothing but a form of highly ordered energy (e.g. chemical links in molecules contained in the foods are examples of free energy).
The energy is conserved and the information never decreases. Doing something requires energy. Specifying what to do requires information. The interaction between energy and information makes the Universe a computing Universe.
After the Universe began to expand, it brought out more and more energy from the underlying quantum texture of the space-time. Current Physics theories suggest that the amount of energy at the beginning of the early Universe grow most rapidly (a process called inflation), than the amount of information which grow less rapidly.
The early Universe was very simple and orderly. It could be described with few bits of information. The energy created was free energy. This lack of information did not last long; in fact, as the Universe expanded, the free energy of quantum fields was subtracted and converted into heat, creating new particles and getting the other jiggling. As a consequence, more information was required to describe them. After a billionth of second, there were 10 to the 50 bits of information.
The Laws of Quantum Mechanics are responsible for the emergence of details and structure in the Universe. Contrary to our intuition, the quantum mechanics produces detail and structure because of it is inherently uncertain. Indeed, the density of the early Universe was almost the same everywhere, but not exactly the same. In quantum mechanics, quantities as velocity, position, or energy density does not have precise values, but are fluctuating values (indeed, quantum mechanics describes the probability of their values). The small asymmetries in the density of the Universe led to the creation of galaxies.These small variations have been amplified by gravity, which has the ability to amplify small fluctuations because of the physical phenomenon called chaos. In a chaotic system, small differences are highly amplified along the time.
Our Universe started about 14 billion years ago from the Big Bang, a huge explosion. What happened before the Big Bang? Nothing. Indeed there was neither time nor space. We are not affirming that there was an empty space, but that the space itself did not exist. There is nothing wrong to start from empty.
Programming the Universe, by Seth Lloyd
Ultimate physical limits to computation, by Seth Lloyd
The Universe as Quantum Computer, by Seth Lloyd
Quantum Computing, Wikipedia.org
The Road to Reality: A Complete Guide to the Laws of the Universe, by Roger Penrose
Laws of thermodynamics, Wikipedia.org