Davide Castelvecchi
“You Are Made of Space-Time: Our Ultimate Origins Revealed.”
New Scientist, 12
August, 2006.
A radical version of a candidate theory of everything (TOE)--loop
quantum gravity--suggests that reality may, at bottom, be a quantum computer generating braids of information. As background information, it may be well to know that there have been two main approaches to this TOE. The first approach is the far larger effort and goes by the name of superstrings theory. Because superstrings theory is so excessively mathematical in its temper, some theoretical physicists have characterized it as less of a theory and more of a pure formalism--that is, pure mathematics. Certainly, the inability of superstrings theory to make testable predictions that can be confronted by the verdict of observed reality reinforces this characterization.
The second approach to a TOE has been a far smaller effort and has been led by Roger Penrose of Oxford University and Lee Smolin of the Perimeter Institute in Waterloo, Ontario, Canada. The Penrose program is called twistor theory (http://www.edge.org/documents/ThirdCultre/v-Ch.14.html). Twistor theory has been characterized by Smolin as follows:
In twistor theory, the fundamental things in the world are the processes. … In the twistor description of space and time, the fundamental entities are not events in space and time but processes, and the idea of twistor theory is to formulate the laws of physics in this space of processes and not in space and time. Space and time as we think about them emerge only at a secondary level.
Smolin''s own program is called loop quantum gravity. As we shall see, the radical version of it that is the subject of this article has also been influenced by the Penrose twistor theory''s insistence of the primacy of processes. In the standard version of loop quantum gravity, space is revealed to have an irreducible structure: atoms or loops of space 10-36 meters in diameter. Within this framework, what we know as space-time is generated as a network of abstract links connecting the atoms of space. Even at this stage, theoretical physicists already noted that these links could form braid-like structures. However, they didn''t know if these braids corresponded to anything physical.
That they might was first suggested by the work, in 2004, of Sundance Bilson-Thomson, of the University of Adelaide. Bilson-Thomson was working on an old particle physics model (dating from the 1970s) involving entities called preons that had been postulated as the constituents of the more familiar subatomic
particles, such as the electron, proton, neutrino, and quarks. Preon models had been shelved because the models indicated that the preons should have more energy than the particles they constituted.
To get round this problem, Bilson-Thomson decided to consider preons, not as point-like
particles, but rather as ribbon-like entities with length and width. Leaving in abeyance the question of what, exactly, these preons were, Bilson-Thomson decided, instead, to simply concentrate on how they interacted with one another. In so doing, Bilson-Thomson''s preons generated braid-like structures which appeared to map out the entire zoo of particles in the standard model of particle physics.
When Smolin stumbled upon Bilson-Thomson''s work, he decided to extend an invitation to Bilson-Thosmson to come work with him at the Perimeter Institute (which has become one of the premiere institutions in the world for doing theoretical physics). Joining Smolin and Bilson-Thompson at Smolin''s instigation was Fotini Markopoulou, already at the institute.
Markopoulou, in collaboration with David Kribs of the University of Guelph in Ontario, has been working on radical version tum gravity that treats the universe as a quantum computer. The necessity for such a version was urged by the fact that the network links or braids in loop quantum gravity only last, on average, 10-44 second before assuming a new configuration whereas a subatomic particle, such as a photon or electron, subsists for much longer than that. If loop quantum gravity is to be able to afford the processes responsible for generating subatomic particles, clearly something had to be done to surmount the problem.
This is where the quantum computer comes in. Markopoulou and Kribs found out that if they replaced the quantum of space of standard loop quantum gravity with a quantum bit (qubit) of information (which qubit actually corresponds to a superposition of potentialities); and if the qubits operated as interacting collectives (isolated qubits are far too delicate and ephemeral), then the qubit collectives could be invested with resilience sufficient to preserve the quantum braid of standard loop quantum gravity such that they could conceivably be held responsible for the generation of subatomic particles.
If this qubit version of loop quantum gravity is true, then this means that space itself, as the Penrose twistor theory asserts, is a secondary phenomenon emerging from a more primary phenomenon: in this case, the process corresponding to qubit interactions. Although, much, much more work has to be done to see if this radical version of loop quantum gravity is indeed the TOE theoretical physicists have been seeking, if it is, however, then it has a pretty telling commentary on the conflicted, fractured character of affairs on this planet largely wrought by the activities of our species--the commentary being that the substantive and the real are, at bottom, webs of relations sustained by cooperative collectives of superpositions of potentialities too frail to survive on their own.