Quantum Gravity and Cosmology

What it takes to produce a gravitational repulsion is a negative pressure. According to general relativity, it turns out... both pressures and energy densities can produce gravitational fields, unlike Newtonian physics, where it's only mass densities that produce gravitational fields.

So may the gravitating attraction of the earth be caused by the continual condensation of some other such like ethereal spirit, not of the main body of phlegmatic ether, but of something very thinly and subtilely diffused through it, perhaps of an unctuous or gummy, tenacious, and springy nature, and bearing much of the same relation to ether, which the vital aereal spirit, requisite for the conservation of flame and vital motions, does to air. For, if such an ethereal spirit may be condensed in fermenting or burning bodies, or otherwise coagulated in the pores of the earth and water, into some kind of humid active matter, for the continual uses of nature, adhering to the sides of those pores, after the manner that vapours condense on the sides of a vessel; the vast body of the earth, which may be every where to the very centre in perpetual working, may continually condense so much of this spirit, as to cause it from above to descend with great celerity for a supply; in which descent it may bear down with it the bodies it pervades, with force proportional to the superficies of all their parts it acts upon; nature making a circulation by the slow ascent of as much matter out of the bowels of the earth in an aereal form, which for a time constitutes the atmosphere; but being continually buoyed up by a new air, exhalations and vapours rising underneath, at length, (some part of the vapours which return in rain excepted,) vanishes again into the ethereal spaces, and there perhaps in time relents, and is attenuated into its first principle: for nature is a perpetual worker, generating fluids out of solids, and solids out of fluids, fixed things out of volatile, and volatile out of fixed, subtile out of gross, and gross out of subtile; some things to ascend, and make the upper terrestrial juices, rivers, and atmosphere; and by consequence others to descend for a requital to the former.

According to Newton's law of gravity, every object in the universe attracts every other object... with a gravitational force...



F
=



m
M
G


R

2






{displaystyle F={frac {mMG}{R^{2}}}}

... almost as famous as



E
=
m

c

2




{displaystyle E=mc^{2}}

... On the left side is the force,



F


{displaystyle F}

, between two masses... On the right side, the bigger mass is



M


{displaystyle M}

and the smaller mass is



m


{displaystyle m}

. ...The last symbol...



G


{displaystyle G}

, is a numerical constant called Newton's constant. ...Ironically, Newton never knew the value of his own constant. ...



G


{displaystyle G}

was too small to measure until the end of the eighteenth century. ...Cavindish found that the force between a pair of one-kilogram masses separated by one meter is approximately 6.6 x 10-11 newtons. (The Newton is... about one-fifth of a pound.) ...Newton had one lucky break... the special mathematical properties of the inverse square law. ...[B]y the miracle of mathematics, you can pretend that the entire mass is located at a single point. This... allowed Newton to calculate the escape velocity...



E
s
c
a
p
e

v
e
l
o
c
i
t
y
=


2
M
G

/

R




{displaystyle Escape;velocity={sqrt {2MG/R}}}

... the bigger the mass [



M


{displaystyle M}

] and the smaller the radius



R


{displaystyle R}

, the larger the escape velocity.