### f(R) gravity

(class of modifications to general relativity)

The term **f(R) gravity** refers to a particular type of theory of
gravity that is a modification of general relativity (GR), the current well-accepted
model. They encompass some of the modifications to GR being explored
as means of explaining current cosmology data (particularly
the data motivating dark energy) and as a step toward combining
GR with quantum mechanics for a Theory of Everything.
The gist of *f(R) gravity* and the motivation for its name is that
in some equations, it plugs in a function of **R** (*R* being the **Ricci scalar**)
in an equation term where "normal" GR has just R itself. Some
consequences can be worked out based on merely this fact, that the
term replacing the Ricci scalar is dependent on the Ricci scalar
but independent of other factors, which gives some opportunity for
exploration of such theories. By this definition of f(R) gravity,
some otherwise-explored alternatives can be classified as f(R)
gravity theories, but generally go by their already-established
names. Another class of recent gravity theories is termed
**scalar-tensor gravity** (and I don't know whether these two classes
of theory are mutually exclusive).

An additional motivation for the development of such modified GR
theories is that as our ability to observe black holes continues
to grow (such as the development of the Event Horizon Telescope, gravitational-wave detectors,
the refinement of techniques to detect black hole characteristics
through observation of galaxies and the constant development
of telescopes and instruments), opportunities grow to eliminate
or confirm these theories.

(*physics,gravity*)
**Further reading:**

https://arxiv.org/abs/1002.4928

https://arxiv.org/abs/1901.08690

Index