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.
