What is gravity
2018
We review the historical pursuits and recent developments on the
origin of gravity. We start with the Newtonian gravity and Einstein
gravity to introduce the two major leaps of the historical pursuits
on the origin of gravity. Then we introduce the recent developments
on the origin of gravity from the point of view of modified gravity,
quantum gravity and holographic gravity. For Newtonian gravity, we
start with Keplers law on planetary motion to introduce the Newtons
universal law of gravitation, and recent developments on the modified
Newtonian dynamics and dark matter; for Einstein gravity, we explain
the geometrization of gravity, and introduce the application of Einstein
gravity on cosmology and gravitational waves; for modified gravity,
we introduce it from the point of view of extra gravitational degrees
of freedom, higher derivative gravity and higher dimensional gravity;
for quantum gravity, we introduce it from the point of view of covariant
quantum gravity, canonical quantum gravity and other scenarios of
quantum gravity; for holographic gravity, we introduce its holographic
picture, emergent properties and its connection with quantum information.
However, the answer to the question of gravity origin still remains
unknown. We point out here that three possible roads to approach the
nature of gravity can be taken in future. The first one is the coming
observations of gravitational waves from both ground-borne and space-borne
gravitational-wave detectors. A system involving either black hole
or neutron star has certainly run into the regime of strong gravity,
which is quite different from previous tests for general relativity
that is in the regime of weak gravity. The gravitational-wave observation
will most likely provide us with clues on classical gravity with any
possible deviations if Einstein gravity does modify itself at classical
level. The second one is the understanding of the cosmic acceleration
at both early-time and late-time. The cosmic acceleration at early-time
is supposed to be driven by cosmic inflation, and the cosmic acceleration
at late-time is supposed to be driven by the cosmological constant
or alternatively dark energy. Future precise observations of radiation
fluctuations and matter fluctuations will show us the way approach
the nature of quantum gravity. The third one is the cognition of the
relation of quantum gravity and quantum information. The past fifty
years or so of pursuit on quantum gravity has leaded us to the path
on the conjecture that quantum gravity might be emerged from quantum
information. Although the perspective of this idea is not clear, it
might be our best shot for now.
Keywords:
- Correction
- Source
- Cite
- Save
- Machine Reading By IdeaReader
0
References
0
Citations
NaN
KQI