From Osher Doctorow

The solution to the problem of "Quantum Gravity" via unlimited light
speed and unlimited speed in general becomes surprisingly simple.
Although Muller and King and Adis (2006) point out that it is not the
acceleration but the difference in path lengths that explains the
differential aging of the twins in the Twin Paradox, for Quantum
Gravity it is the unlimited velocity and hence the possibility of
unlimited acceleration that is most relevant.

Gravitation is radially "inward" toward a (massive) object, and in the
Twin Paradox the travelling twin accelerates radially "outward. Any
force at all that results in outward accelerated motion from an object
is a "5th force" oppositely directed to gravitation. Explosions are
the most common forces of this type, but so would be fuel-driven
spacecraft launches, the Big Bang, whatever drove the Inflation and
late acceleration cosmology eras, etc. They have to be strong enough
to reach Escape Velocity in the context of Earth, or its analogies
from the Solar System, galaxy, etc. Even repulsion between same sign
electrical charges may qualify under this scenario.

Classifying the remaining 3 forces may be somewhat influenced by the
above. Electromagnetism involves internally different (even
orthogonal) directions between electricity and magnetism, which could
well be regarded as 2 of the 3 remaining forces, with the Strong and
Weak forces having to be represented by either one additional force or
one additional force plus one of the previous ones mentioned. Of
course, the forces may turn out to total 6, which seems a little less
geometrically simple. With gravitation and its "opposite", and the
electric and magnetic forces, we could have 2 radial (gravitation and
its "opposite") and two tangential (electric and magnetic) forces (the
latter 2 in a tangent plane).

Gravitational collapse of stars emerges as an analog of "escape
velocity" in the opposite direction, with the massiveness of the star
now entering into the force factors. But here a curious quandary
occurs. When you accelerate outward from Earth, you don't seem to
"squeeze" anything, while when you accelerate inward toward Earth or a
star at an "escape velocity" analog, you seem to squash spacetime or
its "contents", leading to the possibility of punching through
spacetime itself to create modified "Baby Universes", as a sort of
double Escape Velocity (inward and simultaneously outward at least at
some point or limit). There is even the possibility that outward
acceleration ultimately ends up squeezing something inward, resulting
in Neo-Cyclic cosmologies.

Osher Doctorow