“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.”

— Alan Guth

Lecture 1: Inflationary Cosmology: Is Our Universe Part of a Multiverse? Part I.
The Early Universe (2012)

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Alan Guth 17

American theoretical physicist and cosmologist 1947

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“A positive pressure produces an attractive gravitational field… Positive pressures are just sort of normal pressures and attractive gravity is normal gravity, so normal pressures produce normal gravity, but it is possible to have negative pressures, and negative pressures produce repulsive gravity, and that's the secret of what makes inflation possible.”

Alan Guth (1947) American theoretical physicist and cosmologist

Lecture 1: Inflationary Cosmology: Is Our Universe Part of a Multiverse? Part I.
The Early Universe (2012)

“It turns out that the energy of a gravitational field—any gravitational field—is negative. During inflation, as the universe gets bigger and bigger and more and more matter is created, the total energy of matter goes upward by an enormous amount. Meanwhile, however, the energy of gravity becomes more and more negative. The negative gravitational energy cancels the energy in matter, so the total energy of the system remains whatever it was when inflation started—presumably something very small. …This capability for producing matter in the universe is one crucial difference between the inflationary model and the previous model.”

Alan Guth (1947) American theoretical physicist and cosmologist

"A Universe in Your Backyard," in Third Culture: Beyond the Scientific Revolution (1996) ed. John Brockman, p. 279.

“Although the Special Theory of Relativity does not account for electromagnetic phenomena, it explains many of their properties. General Relativity, however, tells us nothing about electromagnetism. In Einstein's space-time continuum gravitational forces are absorbed in the geometry, but the electromagnetic forces are quite unaffected. Various attempts have been made to generate the geometry of space-time so as to produce a unified field theory incorporating both gravitational and electromagnetic forces.”

Gerald James Whitrow (1912–2000) British mathematician

p, 125
The Structure of the Universe: An Introduction to Cosmology (1949)

“We have known since the middle of the nineteenth century that the world is not composed only of particles. …the world is also composed of fields. …General relativity is a theory of… the gravitational field. …Because there are three sets of field lines, the gravitational field defines a network of relationships having to do with how the… lines link with one another. …This is why we call relativity a relational theory.”

Lee Smolin book Three Roads to Quantum Gravity

Three Roads to Quantum Gravity (2000)

“In what respect… does the general theory of relativity differ…? The answer is: in its universality; the force of gravitation in the geometrical structure acts equally on all matter. There is here a close analogy between the gravitational mass M…(Sun) and the inertial mass m… (Earth) on the one hand, and the heat conduction k of the field (plate)… and the coefficient of expansion c… on the other. …The success of the general relativity theory… is attributable to the fact that the gravitational and inertial masses of any body are… rigorously proportional for all matter.”

Howard P. Robertson (1903–1961) American mathematician and physicist

Geometry as a Branch of Physics (1949)

“In Einstein's general theory of relativity the identity of these two coefficients, the gravitational and the inertial mass, is no longer a miracle, but a necessity, because gravitation and inertia are identical.”

Willem de Sitter (1872–1934) Dutch cosmologist

Kosmos (1932), Above is Beginning Quote of the Last Chapter: Relativity and Modern Theories of the Universe -->

“It is curious that the popular conceptions of evil and malignant beings are of the type that would be produced by increased gravitation”

William Crookes (1832–1919) British chemist and physicist

toads, reptiles, and noisome creeping things — while the arch fiend himself is represented as perhaps the ultimate form which could be assumed by a thinking brain and its necessary machinery were the power of gravitation to be increased to the highest point compatible with existence — a serpent crawling along the ground. On the other hand, our highest types of beauty are those which would be common under decreased gravitation.
The "daughter of the gods, divinely tall," and the leaping athlete, please us by the slight triumph over the earthward pull which their stature or spring implies.
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“We shall therefore assume the complete physical equivalence of a gravitational field and a corresponding acceleration of the reference system.”

Albert Einstein (1879–1955) German-born physicist and founder of the theory of relativity

Statement of the equivalence principle in Yearbook of Radioactivity and Electronics (1907)
1900s

“So it was better to think of formulations which could explain the creation of matter without violating the law of conservation of matter…For that we used what is called as negative energy, which at that time was considered unrealistic. There was a good example of negative energy, mainly Newtonian gravity. Newtonian gravity is a negative energy system because gravitational potential energy is negative and we i. e, Fred Hoyle and me, worked out a fairly consistent method of describing this whole thing. Today what people call phantom fields, an idea which is catching up with people trying to explain some problems of the big-bang, these phantom fields are what we had proposed way back in the 1960’s.”

Jayant Narlikar (1938) Indian physicist

An Exclusive Interview with Prof. Jayant Vishnu Narlikar

“I do not see any reason to assume that the heuristic significance of the principle of general relativity is restricted to gravitation and that the rest of physics can be dealt with separately on the basis of special relativity, with the hope that later on the whole may be fitted consistently into a general relativistic scheme. I do not think that such an attitude, although historically understandable, can be objectively justified. The comparative smallness of what we know today as gravitational effects is not a conclusive reason for ignoring the principle of general relativity in theoretical investigations of a fundamental character. In other words, I do not believe that it is justifiable to ask: What would physics look like without gravitation?”

Albert Einstein (1879–1955) German-born physicist and founder of the theory of relativity

1950s, On the Generalized Theory of Gravitation (1950)

“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.”

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Alan Guth 17

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