They could be little spheres or lumps. They could be little doughnuts, or little strings or string loops, or little pieces of membrane. Of these simpler possibilities the strings and string loops are the simplest alternatives to point particles. It turned out to be a very powerful model.

Collisions between strings no longer have the zero distance problem of point particles and it was expected that there would be no more dreaded infinities in real calculations.

* There are thousands of different point particle theories in principle, with the right ones selected by finding all the conservation laws that nature obeys. However there seem to exist only five types of string theories.  These five theories, in order to properly incorporate quantum physic, must be for strings that move in nine space dimensions.

This theory is related to an earlier 11-dimensional theory for point particles that is mentioned in the earlier Tree of theories. These five theory cousins are tamper proof. There is nothing that can be fundamentally changed in these theories. They are unique. This fact holds the promise that one may actually have arrived at the "only uniquely possible theory of everything.

*However, it turns out that this does not mean that we have the HOLY GRAIL in hand. In order to have a theory that gives a world with three expanded dimensions out of a theory written in terms of nine space dimensions, seven of these space dimensions must be curled-up somehow to Planck size. And there it turns out, that there are thousands, perhaps millions of ways in which this reduction to only three extended dimension could be accomplished. The number of possible structure patterns of seven curled-up dimensions appears to be staggering. The important point here is that EACH OF THESE PERHAPS MILLIONS OF WAYS OF CURL-UP LEADS TO A DIFFERENT WORLD WITH DIFFERENT KINDS OF PARTICLES AND DIFFERENT KINDS OF FORCES.

These are all possible solutions of the one unique theory. Below is shown a feeble cartoon of a two dimensional universe space with different patterns of one curled-up dimension. In each of these possible solutions the structure of the underlying pure space, the STATE OF THE VACUUM, is different.

Before we report on one possible answer, let us see what string theory does to our notions of the nature of space.

We must talk about STRINGY SPACE. In Einstein's Theory the structure of space is described by certain MEASURES OF GEOMETRY. In our extended space these measures, the so called metric coefficients, appear to be very closely to the value 1. 0 . Quantum theory demands that we cannot make such quantitative statement with total certainty. This value 1. 0 is only an average of very many measurements. We must accept that these values undergo fluctuations continuously. The magnitude of these quantum fluctuations, it turns out, are determined by how large a patch of territory we are trying to measure. A patch the size of an atom is extremly large compared to the Planck Length.

Space on that level could be visualized as having a multiconnected foam like structure, like a sponge. One might visualize this by flying high above the ocean. From that distance the ocean surface looks ver flat. Sitting however in a small canoe on the surface of the ocean one might find oneself overwhelmed by the mountainous waves.

1. One would expect that ordinary extended space under some circumstances might crumble and curl up and dissappear, annihilate in a spray pieces of quantum foam, like an ocean wave is breaking up into millions of droplets, no longer forming a smooth surface. Black hole Singularity and Big Crunch Singularity of the universe are possible candidates for such events.

2. Conversely, one can imagine that out of foam like quantum chaos there might suddenly emerge like out of nowhere a smooth extended space, like a large soap film can emerge out of a soap bubble foam. We can imagine CONDENSATION OF SPACE OUT OF QUANTUM CHAOS

3. We can also imagine then, that it is possible that in such quantum foam there may be embedded a multitude of extended universes, perhaps even connected, by WORM HOLE LIKE CHANNELS.

NOTHINGNESS in this view, that means the absence of organized space and matter would be some chaotic pattern of such interacting strings, structureless ever changing in rapid pace. Emergent extended space and matter would be the manifestation of some pattern of order in this network of interacting gravitation like strings.

Rudiments of a String quantum theory of Gravitation that have been constructed so far are using loops and knots as the basic organization patterns that constitute space. There are possibly millions of such organization patterns each representing a different kind of universe, each with different kinds of particles and forces.

Now we are approaching finally that haunting question how out of millions of possible universes our special universe may have been selected. Before we present the latest ideas on this let us first stop and reflect about some features of our universe.