I posted these on Reddit but some questions weren't answered so I was wondering if people here could help:(adsbygoogle = window.adsbygoogle || []).push({});

First Part

I was informed that the universe did actually exponentially gain energy during inflation and perhaps other periods of its development. Is the energy of the universe now the same as it was at the Big Bang, more, or less?

At the Big Bang there was very low volume (infinitesimal?), very high temperature/pressure (fuzzy on which it would be), and very low entropy. (And a certain amount of energy)

The increase in volume of the universe (big bang, expansion, etc) resulted in the temperature decreasing, entropy increasing, and energy staying constant?

So how does this affect the entropy and energy relation above?

I assumed since the change in energy is equal to the temperature times the change in entropy that the universe started off as having very low volume, very high temperature/pressure, and low entropy. The high pressure drove the expansion in volume which caused temperatures to decrease and entropy to increase.

So that's wrong.

But if the inflationary period came with an exponential growth of energy, how did the universe getcolder? Was this compensated by a massively exponential increase in entropy?

Why do we need something with negative pressure to be responsible for inflation. Wouldn't the extremely high positive pressure with low volume of the initial Big Bang conditions be enough to drive inflation?

Second Part

I'm a little confused by this:

http://en.wikipedia.org/wiki/Flatness_problem

Which seems to imply the universe is more curved now than it was soon after the Big Bang. Look at the graph on the right side. It's not drawn to scale but clearly implies that with continued expansion the mass-energy density to critical density ratio (Omega) will change which should mean a difference in curvature... no?

So while it's still close to flat, it was closer to flat in the early period of the universe than it is now? And this is due to the mass-energy density decreasing quicker (due to expansion) than the curvature? Wikipedia said:In other words the term |Ω − 1| is currently less than 0.01, and therefore must have been less than 10−62 at the Planck era.

- And this is a problem because this implies the curvature had to be closer to flat (Omega had to be closer to 1) very early on, and this low level of curvature could not have contributed enough to the expansion of the universe to match the contribution of the mass-energy density? When they should have matched? Implying curvature was being governed by some other factor? (Assuming one didn't go the philosophical route of invoking the anthropic principle)

- OR am I reading the Wiki's language incorrectly and it merely says that curvature and mass-energy density should match but they don't as mass-energy density decreases faster than curvature which implies curvature in the past approaches the necessary value for the critical density? Which then implies that curvature is being affected by more than just mass-energy density?

So the inflationary model says there's an inflaton field which drove the sharp exponential inflation during the early period of the universe which quickly flattened out the universe (overriding the effect of mass-energy density?) and then the curvature began to deviate away again slowly as the universe continued to expand?

So now the curvature will increase slightly to match our current Omega which is slightly off the critical density? Should this not then mean that the universe is actually not flat but spherical (due to omega slightly greater than one) and soon to be hyperbolic because of the decreasing energy density? (due to expansion driven by dark energy)?

And this explains how the universe lasted long enough to reach its current (relatively) highly differentiated stage at local levels (due, I suppose, to its advanced age and gravitation) while simultaneously holding global equilibrium (i.e, homogeneity and thermal equilibrium) rather than collapse almost as soon as it had began? Or additionally is it that this explains how the universe grew as much as it did in as short a time period as it did? Were we expecting a smaller size for the universe's age or something which also influenced the development of inflationary theory? (You can ignore this last paragraph if it doesn't make sense, I'm not too sure what I'm going on about either)I thank you all in advance for any help you can provide in clearing up my confusion! Does this mean that it's slowly gaining curvature? Will it eventually become spherical or perhaps hyperbolic? But even then, if it's not perfectly flat, it gets progressively less flat with time.

Does the expansion from dark energy affect flatness?

Third Part

Regarding this thread:

https://www.physicsforums.com/showthread.php?t=506985

Why is the idea that the total energy in the universe "zero" so popular (re: Laurence Krauss) and why is the flatness of the universe used to back this up when, according to that post, an open universe would not conserve energy so the total energy of the universe cannot be "zero", can it? What's the energy being defined as zero and why is that energy used to predict things about the universe when "the" energy (as the term is used in that post) is not zero?

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# I have some somewhat detailed questions about inflation, curvature, and entropy

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