I have couple questions regarding the following YouTube video:
https://www.youtube.com/watch?v=MTUsOWtxKKA&t=14s
1. When Universe was at size of one billionth of a proton, what was the energy of the universe at that point?
2. It says during the inflation expansion of universe, the space mass density of universe stayed constant. If this was the case, as the universe got bigger, then where this extra energy was coming from?
Thanks for your response.
Here is what the standard theory of inflation says according to Alan Guth
The increase in mass probably seems strange at first, because it sounds like a gross violation of the principle of energy conservation. Mass and energy are equivalent, so we are claiming that the energy of the matter within the patch increased by a colossal factor. The reason this is possible is that the conservation of energy has a sort of a loophole, which physicists have known at least since the 1930s,
but haven't talked about very much. Energy is always conserved; there are no loopholes to that basic statement. However, we normally think of energies as always being positive. If that were true, then the large amount of energy that we see in the universe could not possibly have gotten here unless the universe started with a lot of energy. However, this is the loophole: energies are not always positive. In particular, the energy of a gravitational field is negative. This statement, that the energy of a gravitational field is negative, is true both in the context of the
Newtonian theory of gravity and also in the more sophisticated context of
general relativity.
So, during inflation, total energy is conserved. As more and more
positive energy (or mass) appears as the patch expands at constant density, more and more
negative energy is simultaneously appearing in the gravitational field that fills the region. The total energy is constant, and it remains incredibly small because the negative contribution of gravity cancels the enormous positive energy of the matter. The total energy, in fact, could very plausibly be zero. It is quite possible that there is a perfect cancellation between the negative energy of gravity and the positive energy of everything else.
Cosmic Questions - Guth: How Does Inflation Work?