Summary of Session 9 (Friday, November 3, 1995)
"Theories Of Everything"
Chaired by Dan Hussey
Nature appears to contain four forces that mediate the interaction between material bodies: the electromagnetic, the strong, the weak and the gravitational force. Physicists try to combine these forces into more universal ones, in order to show that the world is based on a limited number of principles.
The magnetic and electric forces were combined to the electromagnetic interaction by Maxwell in the 1890's. This force is mediated (represented) by "virtual photons". Weinberg and Salam were able to describe the electromagnetic and the weak force by an "electroweak interaction" in the 1960's. The mediating "W and Z bosons" were discovered in 1984, claiming a major triumph for unification and the Standard Model. Next is the strong force (and it's "gluon" mediators) that needs to be integrated with the electroweak interaction. Thiswould result in a Grand Unified Theory (GUT), that would only leave out gravitation. Gravitation is presently not understood in terms of Quantum Mechanics (QM). The so called gravitons that are supposed to mediate the force are never seen. Of course there is a beautiful theory in the form of Einstein's General Relativity that explains all processes we are presetly aware of in the universe. It is in situations with extreme gravitational interaction (beyond those found in black holes) that the exchange of gravitons could be of use in a theory of Quantum Gravity, or even better: a Theory of Everything (TOE) Would that TOE then be what we are looking for? That depends on what you mean by "Everything".
Almost every modern day physicists (the one that uses QM and doesn't worry about it's interpretation) will declare that that will be it. There are only four forces (there exists even a proof that no more can exist*). They determine the interactions between all known quarks and leptons. If no other particles exist and the quarks and leptons have no sub structure, then thissingle TOE will fully describe the behaviour of groups of these particles, and in principle the most complex systems that are made up by them.
But how about creation, how did it all come into being? How about the Heisenberg Uncertainty Principle? Doesn't that mean we cannot predict anything beyond some (very limited) complexity? And even without Heisenberg, how can it explain the Mind an concience? Were it particles that created the mind or the other way around? The modern day phyicist will probably raise his shoulders and wonder where you worry about. As long as he/she can predict his reactions or trajectories with the TOE he/she will claim to "understand the world".
Here is where Philosophy and Religion comes in to ask for more. What does the physicist mean with "understand the world"? We need to include answers to the above questions in a final TOE. Most physicists will (maybe after some considerable pressure) admit that physics cannot provide that. How can we imagine i.e. where the expanding universe is expanding into? A common view is "into another dimension". You will arrive at the place you started if you keep travelling in the same direction. Space is curved. Finite without boundaries. But curved in a fourth dimension that we cannot be aware of. We have no kowledge of any space dimension beyond the three we are familiar with. Like the two-dimensional inhabitants on the surface of a sphere, who never seem to reach a boundary in their two- dimensional universe. If the sphere gets bigger, the inhabitants see distances grow and wonder what's behind the farthest galaxies. Themselves of course! Distances are not just increasing in their two- dimensional space, space itself is expanding. Other universes might be expanding next to theirs, but they won't know. What if they hit each other while expanding? They would collide on the intersection of two spheres, which is a circle somewhere in their two-dimensional world. The radius of the circle can increase or decrease. If you're inside, and it decreases, could you see colliding galaxies all around you, coming closer and closer?
At the end of the last century, it was felt that mechanics, electromagnetics and thermodynamics were explaining almost every process imaginable, and that the end of physics was in sight. There were only some minor prolems left related to the speed of light and the behaviour of atoms, that needed to be resolved. With the advent of a TOE the same thing might happen and physics might be reduced to measuring and registering the predictions of the TOE.
Another question is how we verify the new TOE. Merging of the four forces to a single one is not expected to appear at present, and in the foreseeable future attainable accelerator energies. Energies that were present in the first second after the Big Bang when the forces were united were exceeding 10**19 GeV. 10**4 GeV could be reached at present if we would have built the Supeconducting Super Collider in Texas, or if the Large Hadron Collider in Europe gets funding. Even those machines are ten thousand trillion times too small to verify unification directly. On the other hand, more modest discoveries, like that of the proposed Higgs boson could be done at LHC energies and would i.e. give us insight in why particles have mass, and at the same time give stronger confidence in the present theories of the Standard Model. Also, one never knows what the future might bring. As recently as 30 years ago it was unthinkable that computers or accelerators would be possible at this time with the present capabilities.
The emergence of complexity in the universe can be simulated by computer as done in 'Conway's Game of Life'**, in which we have a flat, rectangular lattice of cells that contain either a 1 or a 0. The cell is alive if 1 and dead if 0. The cell goes through clockcycles and will change its state at each cycle dependent on its 8 neighbors. We can define that dependency with some logical equation and give the computer a pattern of cells to start with. The pattern may grow and the results may become rather complex.
Real cells, or take atoms with their defineable interactions with their neigbors, in nature can grow into unimaginable complexity. Products may eventually start thinking and figger out the basic building blocks and interactions that started it all (could it be that it is the mind that was first and successively finds out about its basic components?). A TOE based on physics and mathematics will never literally be a theory of everything even if an underlying order in the Quantum Mechanical indeterminacy is resolved.
*Frank H. Shu, The Physical Universe. 1982
** Gerard 't Hooft, Physics and our view of the world. 1995