- Lee Smolin, Quantum Gravity; String theory and Loop Quantum Gravity: M theory?
Why is the universe as it is? Why is it so structured after 14,000 million years?
What are space and time? Are they continous or discrete?
The problem of quantum gravity is how to combine the understanding of space and time we have from relativity theory with the quantum theory, as both tells us something essential and deep about nature.
In the new framework, space is not smooth and continuous, but instead comprises indivisible chunks just 10-35 metres in diameter. Loop quantum gravity then defines space-time as a network of abstract links that connect these volumes of space, rather like nodes linked on an airline route map.
The picture that emerges from both relativity and quantum theory is of a world conceived as a network of relations.
Newton's hierarchical picture, in which atoms with fixed and absolute properties move against a fixed background of absolute space and time, is quite dead.
This doesn't mean that atomism or reductionism are wrong, but it means that they must be understood in a more subtle and beautiful way than before.
For loop quantum gravity to succeed as a fundamental theory of gravity, Newton's law of gravity should naturally arise from it.
What is the relation between the observer and the observed?
A quantum theory of gravity must be a theory of cosmology. As such, it must also tell us how to describe the whole universe from the point of view of observers who live in it, for by definition there are no observers outside the universe.
What causes the incompatibility between General Relativity and Quantum Mechanics?
As Bohr and Heisenberg taught us, quantum theory seems to make sense only when it's understood to be the description of something small and isolated from its observer — the observer is outside of it.
Is it time to throw away decades of work on string theory?
For Lee Smolin, the real blow to the idea that the choice of which laws govern nature is determined only by mechanisms acting at the smallest scales came from the dramatic failure of string theory.
As a theory of the elementary particles it has certainly so far failed, for while it initially seemed that there was only one possible consistent string theory, we now know there are a great many such theories, each apparently as consistent as the others, and all leading to different universes.
There are principles of self-organization acting on astronomical scales.
The idea that a galaxy is a self organized system — more an ecology than a nonliving clump of stars and gas — has become common among astronomers and physicists who study galaxies.
The universe will be seen as a network of self-organized systems.
There are mechanisms of self-organization extending from the largest scales to the smallest, and they explain both the properties of the elementary particles and the history and structure of the whole universe.
By a cosmological sort of natural selection, the properties of particles and forces, are chosen to maximize the number of black holes the universe produces.
Lee Smolin - "A Theory of the Whole Universe" (Edge.org - The Third Culture: Beyond the Scientific Revolution - Chapter 17, 1995)
"You are made of spacetime" (NewScientist, 12 August 2006)
Three Roads to Quantum Gravity, by Lee Smolin. Basic Books
ARVAL - Gallery:
- The Cosmic Microwave Background - A Relic from the Origin of the Universe
- Hubble Finds Evidence for Dark Energy in the Young Universe
- Blast from the Past: Farthest Supernova Ever Seen Sheds Light on Dark Universe
ARVAL - Space Telescope Science Institute (STScI) - Background Information:
- Building a Ladder to the Stars
- The Hubble Constant
- Cosmic Yardsticks
- Dark Matter
ARVAL - Royal Greenwich Observatory (RGO) Leaflets:
- Cosmology, Stars, Galaxies, Supernovae, Pulsars, Black Holes
This page was updated in: April 26 '07
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