2-6
Alternative hypotheses
Further
information: Alternatives to general relativity
Because dark matter has not yet been conclusively identified,
many other
hypotheses have emerged aiming to explain the observational phenomena
that dark matter was conceived to explain. The most common method
is to
modify general relativity. General relativity is well-tested on
solar system
scales, but its validity on galactic or cosmological scales has
not been
well proven. A suitable modification to general relativity can
conceivably
eliminate the need for dark matter. The best-known theories of
this class
are MOND and its relativistic generalization tensor-vector-scalar
gravity
(TeVeS), f(R) gravity,negative mass, dark fluid, and entropic
gravity. Alternative
theories abound.
A problem
with alternative hypotheses is that observational evidence for
dark matter comes from so many independent approaches (see the
“observational
evidence” section above). Explaining any individual observation
is possible but explaining all of them in the absence of dark
matter is very
difficult. Nonetheless, there have been some scattered successes
for alter
native hypotheses, such as a 2016 test of gravitational lensing
in entropic
gravity and a 2020 measurement of a unique MOND effect.
The prevailing
opinion among most astrophysicists is that while modifications
to general relativity can conceivably explain part of the observational
evidence, there is probably enough data to conclude there must
be some
form of dark matter present in the Universe.
2-6
a
In popular culture
Mention
of dark matter is made in works of fiction. In such cases, it
is
usually attributed extraordinary physical or magical properties.
Such descriptions
are often inconsistent with the hypothesized properties of dark
matter in physics and cosmology.
