# Is it possible to understand inflation through Einstein?

Hi guys,

I am writing a philosophical article about Leibniz's famous question "Why is there something rather than nothing?" and in this context I also discuss scientific theories about the origin of the universe, among these the inflationary theory proposed by Guth. Now since it is going to be a philosophical article, I can't discuss these theories in full technical details (which are over my head anyway, since I am not in the least bit mathematically gifted). This approach works fine for most of the theories I intend to discuss but I am having some special problems with the inflationary theory. I'm trying to understand how the inflation process involves an increase of negative gravitational energy and positive energy with the overall energy level remaining zero. I thought that maybe I could use Einstein's general theory of relativity to clarify this, namely as follows:

On Einstein's general theory of relativity, gravity just is the curvature of space. But gravity also represents negative energy as opposed to the positive energy represented by matter. The process of the inflationary expansion of space, therefore, can also be seen as a process in which the negative energy of gravity increases exponentially. But how is this possible, given the law of energy conservation? This is possible because of the mutual cancellation of positive and negative energy. One form of energy can increase arbitrarily only as long as the opposite form of energy increases with the same amount, so that the total amount of energy remains constant. This is precisely what happened during inflation: the exponential increase of the negative energy of gravity/space went hand in hand with an equal increase of positive energy. Out of this positive energy then emerged matter and antimatter through quantum fluctuations. Thus as Hawking writes about the inflation process: "when the universe doubles in size, the positive matter energy and the negative gravitational energy both double, so the total energy remains zero. During the inflationary phase, the universe increases its size by a large amount. Thus the total amount of energy available to make particles becomes very large." (Hawking, A Brief History of Time, p.147)

Now my question to you is: Does this interpretation of inflation by way of the idea that space=gravity=negative energy make sense or is it total bollocks?

## Answers and Replies

PeterDonis
Mentor
2020 Award
The interpretation of gravity as representing "negative energy" (more precisely, that the gravitational potential energy of the universe is negative and exactly balances the positive energy due to matter and radiation) does make sense, in the sense that there is a way to interpret GR's description of the universe so that the total energy of the universe is exactly zero. However, not all physicists agree with this interpretation. An article describing the "gravity is negative energy" interpretation is here. An article describing an opposing interpretation--that energy is simply not conserved in GR in a non-stationary spacetime, such as our expanding universe--is here.

• bapowell