502
E. Rabinovici
following the realization that string theory in particular allows what are called brane
configurations. Branes are solitons, extended objects embedded stably in a space
time of larger dimension. Vortices and magnetic monopoles were mentioned as
such lower dimensional objects. There is a consistent possibility that for example
a four dimensional universe can be embedded in higher dimensions. The known
gauge interactions living only on the brane while gravity extends to the full space.
If our universe has this structure many things can be explained and in particular
this has given rise to the possibility the extra dimensions could be much larger than
previously expected. Actually they could extend up to the submicron region. This
could lead to measurable deviations from Newton’s gravity at those distance scales.
Astrophysics gives upper bounds on how large such extra dimensions may be but in
any case this is a very significant relaxation of a bound, in fact I am not aware of
any bound on such a fundamental quantity in physics that has been altered to such
an extent by a theoretical idea. All this said one should stress the obvious, also the
bounds have been relaxed the true value of the extra dimensions may still be very
small, perhaps even Planckian. Some suggestions of larger extra dimensions could
well be tested at the LHC.
The fact that unification may occur not far from the planck scale brings quantum
gravity to the front row and with it a theory which attempts to be able to indeed tame
quantum gravity that is string theory.
8.4 String Theory [4]
8.4.1 No NOH Principle
String Theory is at this time far from being a complete theoretical framework, not
to mention a phenomenological theory. That said, the theory of extended objects
has evolved significantly and has shaped and was shaped by aspects of modern
mathematics. In my opinion is it appropriate to highlight the qualitative aspects of
string theory and the ideas behind it. This choice is not made for lack of formulas
or precision in string theory. An essential catalyst in the process of the formation of
string theory was urgency, the urgency created out of the near despair to understand
the amazing novel features of the hadronic interactions as they unfolded in the
1960’s. String theory was revitalized in the latter part of the twentieth century by
the urgency to understand together all of the four known basic interactions. Here
I shall briefly review some of the motivation to study a theory of extended objects
and discuss the challenges string theory faces, the successes it has had, and the
magic spell it casts. We start by reviewing a hardware issue, the hard wiring of some
scientific minds. Researchers using string theory are faithful followers of an ancient
practice, that of ignoring the NOH principle. The NOH principle is very generic, it
states that Nobody Owes Humanity neither a concise one page description of all the
basic forces that govern nature nor a concise description of all the constituents of
E. Rabinovici
following the realization that string theory in particular allows what are called brane
configurations. Branes are solitons, extended objects embedded stably in a space
time of larger dimension. Vortices and magnetic monopoles were mentioned as
such lower dimensional objects. There is a consistent possibility that for example
a four dimensional universe can be embedded in higher dimensions. The known
gauge interactions living only on the brane while gravity extends to the full space.
If our universe has this structure many things can be explained and in particular
this has given rise to the possibility the extra dimensions could be much larger than
previously expected. Actually they could extend up to the submicron region. This
could lead to measurable deviations from Newton’s gravity at those distance scales.
Astrophysics gives upper bounds on how large such extra dimensions may be but in
any case this is a very significant relaxation of a bound, in fact I am not aware of
any bound on such a fundamental quantity in physics that has been altered to such
an extent by a theoretical idea. All this said one should stress the obvious, also the
bounds have been relaxed the true value of the extra dimensions may still be very
small, perhaps even Planckian. Some suggestions of larger extra dimensions could
well be tested at the LHC.
The fact that unification may occur not far from the planck scale brings quantum
gravity to the front row and with it a theory which attempts to be able to indeed tame
quantum gravity that is string theory.
8.4 String Theory [4]
8.4.1 No NOH Principle
String Theory is at this time far from being a complete theoretical framework, not
to mention a phenomenological theory. That said, the theory of extended objects
has evolved significantly and has shaped and was shaped by aspects of modern
mathematics. In my opinion is it appropriate to highlight the qualitative aspects of
string theory and the ideas behind it. This choice is not made for lack of formulas
or precision in string theory. An essential catalyst in the process of the formation of
string theory was urgency, the urgency created out of the near despair to understand
the amazing novel features of the hadronic interactions as they unfolded in the
1960’s. String theory was revitalized in the latter part of the twentieth century by
the urgency to understand together all of the four known basic interactions. Here
I shall briefly review some of the motivation to study a theory of extended objects
and discuss the challenges string theory faces, the successes it has had, and the
magic spell it casts. We start by reviewing a hardware issue, the hard wiring of some
scientific minds. Researchers using string theory are faithful followers of an ancient
practice, that of ignoring the NOH principle. The NOH principle is very generic, it
states that Nobody Owes Humanity neither a concise one page description of all the
basic forces that govern nature nor a concise description of all the constituents of