|Signatures of the extra dimensions required by string theory could be
seen by future gravitational-wave detectors. That is the conclusion of
researchers from the Max Planck Institute for Gravitational Physics in
Germany, who have identified two ways in which gravitational waves could
be affected by the consequences of string theory - a theoretical
framework that invokes speculative concepts such as extra dimensions to
try to fill important gaps in our understanding of physics, including
the nature of quantum gravity.
Gravitational waves are ripples in space-time that are created when
massive objects are accelerated under certain conditions. The
researchers calculate that adding N extra dimensions to 4D space-time
results in a 'breathing-mode' oscillation that would be present in a
gravitational wave. The second distinct feature of extra dimensions is a
discrete set of higher-frequency signals accompanying a gravitational
The first gravitational-wave detection was made in 2015, when the LIGO
observatory spotted a signal from a coalescing binary black hole. The
researchers say that LIGO's current configuration of two detectors will
not be able to detect the breathing mode. However, it is possible that a
breathing mode could be detected once a third detector in Italy, called
Virgo, reaches its full sensitivity in 2018.
As for the higher-frequency signals, the team point out that the trend
in future detectors is towards lower frequencies, and therefore a
special observatory would be needed to see that effect.