Seven theories of everything, Knowing the mind of God - Really! (No, just joking!)
Seven theories of everything, Knowing the mind of God - Really! (No, just joking!)
Mar 06, 2010, 03:37 PM
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The "theory of everything" is one of the most cherished dreams of science. If it is ever discovered, it will describe the workings of the universe at the most fundamental level and thus encompass our entire understanding of nature. It would also answer such enduring puzzles as what dark matter is, the reason time flows in only one direction and how gravity works. Small wonder that Stephen Hawking famously said that such a theory would be "the ultimate triumph of human reason – for then we should know the mind of God".
But theologians needn't lose too much sleep just yet. Despite decades of effort, progress has been slow. Rather than one or two rival theories whose merits can be judged against the evidence, there is a profusion of candidates and precious few clues as to which (if any) might turn out to be correct.
Here's a brief guide to some of the front runners.
This is probably the best known theory of everything, and the most heavily studied. It suggests that the fundamental particles we observe are not actually particles at all, but tiny strings that only "look" like particles to scientific instruments because they are so small.
What's more, the mathematics of string theory also rely on extra spatial dimensions, which humans could not experience directly.
These are radical suggestions, but many theorists find the string approach elegant and have proposed numerous variations on the basic theme that seem to solve assorted cosmological conundrums. However, they have two major challenges to overcome if they are to persuade the rest of the scientific community that string theory is the best candidate for a ToE.
First, string theorists have so far struggled to make new predictions that can be tested. So string theory remains just that: a theory.
Secondly, there are just too many variants of the theory, any one of which could be correct – and little to choose between them. To resolve this, some physicists have proposed a more general framework called M-theory, which unifies many string theories.
But this has its own problems. Depending how you set it up, M-theory can describe any of 10500 universes. Some physicists argue that this is evidence that there are multiple universes, but others think it just means the theory is untestable.
Loop quantum gravity
Although it hasn't had the same media exposure, loop quantum gravity is so far the only real rival to string theory.
The basic idea is that space is not continuous, as we usually think, but is instead broken up into tiny chunks 10-35 metres across. These are then connected by links to make the space we experience. When these links are tangled up into braids and knots, they produce elementary particles.
Loop quantum gravity has produced some tentative predictions of real-world effects, and has also shed some light on the birth of the universe. But its proponents have so far struggled to incorporate gravity into their theories. And as with string theory, a true experimental test is still some way off.
Causal dynamical triangulations looks pretty similar to loop quantum gravity at first glance. Just as loop quantum gravity breaks up space into tiny "building blocks", CDT assumes that space-time is split into tiny building blocks – this time, four-dimensional chunks called pentachorons.
The pentachorons can then be glued together to produce a large-scale universe – which turns out to have three space dimensions and one time dimension, just as the real one does. So far, so good, but there's a major drawback: CDT as it currently stands cannot explain the existence of matter.
Quantum Einstein gravity
This idea, proposed by Martin Reuter of the University of Mainz, Germany, takes a rather different tack.
Part of the problem with unifying gravity and quantum mechanics is what happens to gravity at small scales. The closer two objects are to each other, the stronger the gravitational attraction between them; but gravity also acts on itself, and as a result, at very small distances a feedback loop starts. According to conventional theories the force should then become ridiculously strong – which means there's something wrong with the conventional theories.
However, Reuter has come up with a way to generate a "fixed point": a distance below which gravity stops getting stronger. This could help solve the problem, and lead to a quantum theory of gravity.
All the theories above assume that space and time exist, and then try to build up the rest of the universe. Quantum graphity – the brainchild of Fotini Markopoulou of the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada, and colleagues – tries to do away with them.
When the universe formed in the big bang, Markopoulou says, there was no such thing as space as we know it. Instead, there was an abstract network of "nodes" of space, in which each node was connected to every other. Very soon afterwards, this network collapsed and some of the nodes broke away from each other, forming the large universe we see today.
Developed by Olaf Dreyer of the Massachusetts Institute of Technology, internal relativity sets out to explain how general relativity could arise in a quantum world.
Every particle in the universe has a property called "spin", which can be loosely thought of as what happens to the particle when it is rotated. Dreyer's model imagines a system of spins existing independently of matter and arranged randomly. When the system reaches a critical temperature, the spins align, forming an ordered pattern.
Anyone actually living in the system of spins will not see them. All they see are their effects, which Dreyer has shown will include space-time and matter. He has also managed to derive Newtonian gravity from the model: however, general relativity has not yet emerged.
In 2007 the physicist (and sometime surfer) Garrett Lisi made headlines with a possible theory of everything.
The fuss was triggered by a paper discussing E8, a complex eight-dimensional mathematical pattern with 248 points. Lisi showed that the various fundamental particles and forces known to physics could be placed on the points of the E8 pattern, and that many of their interactions then emerged naturally.
Some physicists heavily criticised the paper, while others gave it a cautious welcome. In late 2008, Lisi was given a grant to continue his studies of E8.
Used with no permission. But they didn't pay me for reporting on my research, so I reckon they owe me! It's a different world since the interweb ....
Mar 07, 2010, 01:11 AM
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The fact is a Theory of Everything (ToE) does not necessarily answer any particular question, as listed in the opening paragraph. Such a theory would only provide a foundational framework from which the answers to these questions could, in principle, be derived. If we knew every property there was to know about a gas molecule, it does not entail that we know every possible dynamic construct achievable within that gas. It merely entails that we can derive the various possibilities from it, with more effort, given the underlying theory.
The newscientist noted this, more or less, by linking to this article:
But yet again they missed the mark. Just because reductionism does not 'automatically' provide us with a complete description of all possible emergent properties does not entail that they can't be derived from the properties of the fully reduced system, or that such is not amenable to mathematics. Eric Kvaalen made a very astute observation in the comments to the newscientist article "Why nature can't be reduced to mathematical laws ":
Why nature can't be reduced to mathematical laws]Objection
Thu Oct 02 16:05:02 BST 2008 by Eric Kvaalen
As of this time, the URL for the article is wrong--it should be http://arxiv.org/abs/0809.0151
If you read the article, you will find that what the authors have done is to simulate a Turing machine with an Ising lattice in a half plane. The input to the Turing machine is the (infinite) edge of the lattice, and the question is what properties of the lowest-energy state of the lattice can be computed. Their conclusion is that you cannot compute in a finite amount of time properties that involve the whole infinite lattice.
But you can compute the state of any node in the lattice.
If you think of the lattice as evolving to its ground state with time, then we can compute how this happens. The only things we cannot compute are properties that depend on the whole infinite lattice in its final state.
Even if properties of infinite systems cannot be calculated, the properties of arbitrarilly large finite systems can be calculated from the underlying interactions.
This artificial dichotomy between reductionism and constructivism is especially rampant in our efforts to understand consciousness. This same sort of false dichotomy also used in paranormal claims, such as http://www.authorsoftheimpossible.com/.
 True, the sum is greater than the parts.
 True, complete knowledge of the properties of the parts does not entail complete knowledge of the whole.
However,  and  does not entail that the whole has properties not derivable from those parts, or even sillier that the mathematical rules themselves become invalid. Even though the mathematics may indeed exceed our practical limits to solve, the mathematics still hold true. It's an issue of complexity exceeding the complexity of the parts, not some emergent property that is not subject to the laws of those parts. It gets even more complex when emergent properties result from a field of other emergent properties, rather than from actual parts. Emergent properties comes down to how you define sets to treat as though they are new parts, like where is the edge of a tornado even at a single moment in time. Emergent parts are not separate parts. What about a bunch of tornadoes interacting with each other? The distinction between tornado and air is still artificial. Such arguments assigning the emergent properties dichotomous and separate rules from the parts that define them is invalid, however important this emergence is to our sense of the qualia of 'meaning'.
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