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E. Rabinovici
understanding the value of the cosmological constant. If that scale is indeed not
elementary, one would be searching for the stuff the strings themselves are made
off. Such searches originating from other motivations are underway, some go by the
name of Matrix Model. Particle Physics as we know it is described by the standard
model evolving in an expanding universe. The methods used to study string theory
are best developed for supersymmetric strings, and for strings propagating on time
independent background, nature is explicitly neither. What then are the successes of
string theory?
8.4.5 Successes: Black Holes, Holography and All That . . .
A major success described above was to obtain a theory of gravity well defined
to several orders in perturbation theory, in addition, no obvious danger signals
were detected as far as the higher order in perturbation theory are concerned, non
perturbative effects are yet to be definitely understood. This issue involves the short
distance structure of string theory. String theory is supposed to be a consistent
completion of General Relativity (GR). General relativity suffers from several
problems at low energies. String theory, which according to a correspondence
principle, is supposed to reproduce GR in some long distance limit, will thus have
inherited in this merger, all the debts and problems of GR. If it does solve them it will
need to do it with a “twist” offering a different point of view. That perspective could
have been adopted in GR but was not. This has occurred in several circumstances,
one outstanding problem in GR is to deal with the singularities that classical gravity
is known to have. These include black holes, big bangs and big crunches as well as
other types of singularities. String theory can offer a new perspective on several of
these issues. Let us start with black holes. The first mystery of black holes is that
they seem to posses thermodynamical properties such as temperature and entropy.
This is true for charged black holes as well as for uncharged Schwarzschild ones.
In the presence and under the protection of a very large degree of supersymmetry,
string theory tools enabled to provide a detailed microscopical accounting of the
entropy of some black holes. More precisely it was shown in these special cases
that the number of states of a black hole is identical to the number of states of
essentially a gauge theory. It was possible to count the microscopic number in the
gauge theory case and the resulting number of states was exactly that predicted
for black holes! These are mostly higher dimensional very cold black holes. This
has not yet been fully accomplished for uncharged black holes. Black holes have
several more non-conventional properties. The above mentioned entropy of a mass
M black hole is much smaller, for many types of black holes, than that of a non
gravitating system of particles which have the same energy, M. In fact one may
suspect that such black holes dominate by far the high energy spectrum of any
gravitating system. The Schwarzschild radius of these black holes actually increases
with their mass. In general one associates large energies with short distances, in the
case of black holes large energies are related also to large distances. A meticulous
E. Rabinovici
understanding the value of the cosmological constant. If that scale is indeed not
elementary, one would be searching for the stuff the strings themselves are made
off. Such searches originating from other motivations are underway, some go by the
name of Matrix Model. Particle Physics as we know it is described by the standard
model evolving in an expanding universe. The methods used to study string theory
are best developed for supersymmetric strings, and for strings propagating on time
independent background, nature is explicitly neither. What then are the successes of
string theory?
8.4.5 Successes: Black Holes, Holography and All That . . .
A major success described above was to obtain a theory of gravity well defined
to several orders in perturbation theory, in addition, no obvious danger signals
were detected as far as the higher order in perturbation theory are concerned, non
perturbative effects are yet to be definitely understood. This issue involves the short
distance structure of string theory. String theory is supposed to be a consistent
completion of General Relativity (GR). General relativity suffers from several
problems at low energies. String theory, which according to a correspondence
principle, is supposed to reproduce GR in some long distance limit, will thus have
inherited in this merger, all the debts and problems of GR. If it does solve them it will
need to do it with a “twist” offering a different point of view. That perspective could
have been adopted in GR but was not. This has occurred in several circumstances,
one outstanding problem in GR is to deal with the singularities that classical gravity
is known to have. These include black holes, big bangs and big crunches as well as
other types of singularities. String theory can offer a new perspective on several of
these issues. Let us start with black holes. The first mystery of black holes is that
they seem to posses thermodynamical properties such as temperature and entropy.
This is true for charged black holes as well as for uncharged Schwarzschild ones.
In the presence and under the protection of a very large degree of supersymmetry,
string theory tools enabled to provide a detailed microscopical accounting of the
entropy of some black holes. More precisely it was shown in these special cases
that the number of states of a black hole is identical to the number of states of
essentially a gauge theory. It was possible to count the microscopic number in the
gauge theory case and the resulting number of states was exactly that predicted
for black holes! These are mostly higher dimensional very cold black holes. This
has not yet been fully accomplished for uncharged black holes. Black holes have
several more non-conventional properties. The above mentioned entropy of a mass
M black hole is much smaller, for many types of black holes, than that of a non
gravitating system of particles which have the same energy, M. In fact one may
suspect that such black holes dominate by far the high energy spectrum of any
gravitating system. The Schwarzschild radius of these black holes actually increases
with their mass. In general one associates large energies with short distances, in the
case of black holes large energies are related also to large distances. A meticulous