A great thread i found on string theory

It is against the philosophy of string theory to imagine that the

worldsheet is "made of" individual worldlines. This would mean that on the

two-dimensional worldsheet, there is a preferred direction of time at each

point - this direction would describe the direction of the worldline of

the point-like particle.

On the worldsheet of a string, all directions are treated democratically.

In fact, the two-dimensional theory that describes the internal dynamics

of the worldsheet has a much bigger group of symmetries: the general

diffeomorphism symmetry: this theory is a two-dimensional counterpart of

general relativity and implies that all "reference frames" are equally

good in formulating the physical laws. Any extra structure of lines (or

choice of coordinates) that you imagine on the worldsheet is unphysical.

If we look at a particular point P of the string at time t_2, it is not

possible to say where this point of the string was at time t_1. In fact,

this feature helps string theory to regulate short-distance divergences

because it is also impossible to say exactly at which point of the stringy

worldsheet (imagine the pants diagram) the interaction occured.

The string worldsheet has another symmetry - the Weyl symmetry that allows

one to multiply the worldsheet metric by an arbitrary scalar function of

the worldsheet coordinates. This symmetry, together with the

diffeomorphism symmetry, forms "conformal symmetry" - and therefore the

two-dimensional theory describing the worldsheet is a "conformal field

theory", a theory whose local dynamics only depends on the angles, not the

distances. The Weyl symmetry guarantees that the string carries no

information about its "density" of particles - it only matters which curve

(or worldsheet) it spans in spacetime, but it does not matter how you

parameterize the string or the worldsheet.

All these things mean that you should be very careful when you try to

imagine the string as a family of point-like particles. Despite all these

facts, we can often encounter situations in string theory that allow us to

describe the string as a composite of point-like particles called the

"string bits". String bits can be identified in Matrix string theory or

the PP-wave limit of AdS/CFT correspondence.

There are other extended objects in string theory - such as D-branes - and

the discussion would have to be changed a bit for them. For example, they

are not invariant under conformal symmetry, and on the other hand, a

D-brane of dimension "p" can be usefully imagined as a bound state of

D-branes of smaller dimensionalities p-2k.