What's the difference between cosmology and quantum physics?

I suggest you get the book, "The Fabric of the Cosmos" by Brian Greene. To say that quantum mechanics is "only a theory" shows a misunderstanding of what a scientific theory is. A scientific theory is a hypothesis supported by empirical evidence.

It is NOT just a guess. As one example, calculations arising from the "theory" of quantum electrodynamics are among the most precise in describing how the world works. However, theories are not fact, and cannot be proven correct, because finding one example that doesn't fit means that the theory doesn't accurately reflect the way the world works.

One example of this process is our understanding of gravity. Newton saw gravity as two masses attracting each other, and developed his law of universal gravitation (F = G*M1*M2/R^2). However, Einstein had some questions (such as, what would happen if the Sun were to vanish, and observations of the precession of the orbit of the planet Mercury), which led him to develop a new theory of gravitation - general relativity - in which mass warps space, and the warping affects how mass moves.

Like QED, the equations of general relativity are extremely accurate. But, when general relativity is combined with quantum mechanics, at very short distances the equations produce results that are nonsensical. (Quantum foam is one of those.

Infinite gravitational attraction between point particles is another.) The current efforts are to combine quantum mechanics and gravity, typically by using a gravitational field and a graviton as a force-carrying particle. String theory is one approach, which has extended from single dimensional "strings" (to eliminate the problems of point particles) to multidimensional "branes". Brane cosmology is one approach to explain such things as the Big Bang, inflation, and other stuff.

But get Greene's book. It does a way better job than any Y! A post of providing an overview of all this material at the level of a technically-oriented layperson, with hardly an equation to be found.

There are other books out there aimed at the same audience. I also tried "Warped Passages" by Lisa Randall, and Greene's is easier to read. Haven't tried any others.

Nobody knows the answer to your question. What you're looking for is called a "Theory of Everything" or "Grand Unified Field Theory." Space itself can't flux or bend; the density of physical material that is filling space can only change over time.

Einstein called it "space-time," but we are finding out now what the "space" is actually made of. There have been many attempts to unify quantum mechanics with general relativity but, so far, they have all failed. To answer your question we would have to know all of the Fundamental(Dimensionless) physical constants, but we do not.

Many scholars claim that "Godel's incompleteness theorems" prove that any attempt to construct a ToE is bound to fail. It's ironic that the guy would correct you for not knowing what a scientific theory was, would then suggest a book about a non-testable 'theory.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.