Talk:Cosmic inflation

Has anyone come across a resolution concerning temporal consequences of cosmic inflation making the universe expand faster than the speed of light? i.e., if the universe's outer boundary is moving that fast, then it can travel backward in time, causing an implosion, a duplication of all matter, and massive temperature/density increase until the inflationary period ended.

Which might not be a bad thing, as it would increase information transfer between the universe's parts, but has this been addressed at all?

Apparently there is no temporal consequence from SR, since relativistic time reversal only applies to things moving through space but not the expansion of space itself.

The speed of light can be defined only in terms of the metric tensor; inflation theory uses a metric with nonzero curvature; making that argument invalid.

63.205.40.227 02:05, 4 Feb 2004 (UTC)

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I think this overstates the case. WMAP supports cosmic inflation but it is one of several supporting bits of evidence.

This theory was revealed to be correct with NASA's historic February 11, 2003 release of data collected from the Wilkinson Microwave Anisotropy Probe (WMAP).

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I have a question. If it's true that the Universe is expanding in a accelerated rate, then would cosmic inflation explain universe's current accelerated expansion rate?

negative pressure vacuum energy density

What is vacuum energy density? Do you mean false vacuum? How could vacuum itself (with no mass-energy) contain pressure? Do you mean that spacetime has an energy which is always positive (or non-zero)? Is it because according to Einstein's theory of general relativity, bodies create the space around them? -- Orionix 22:30, 9 Mar 2005 (UTC)

Vacuum energy is not really related to the false vacuum -- a true vacuum can have an energy density as well. One thing that quantum field theory has taught us is that there is energy in a vacuum -- see Casimir effect. With energy comes pressure, since pressure is just the work done to change the volume of a box. In the case of vacuum energy, the pressure is negative since increasing the volume of the box increases the energy, and so you must do work on the box (with an ordinary gas of particles, it is the opposite). Gravity, however, is strange, and making spacetime have positive energy actually makes the expansion accelerate. See the explanation under cosmological constant in dark energy. --Joke137 17:02, 10 Mar 2005 (UTC)

Hi, thanks for the explanation.

I'm really not an expert in the mathematics of QFT but i know the basic idea which is that at high energies matter is better described by fields rather than by classical means.

This great work may also teach us one day that discrete particles do not exist and that all matter is a wave structure, continuous in the space it occupies (or is part of).

I was wondering whether cosmic inflation could explain how the universe came into being and also why it's accelerating. According to what i understood, cosmic inflation occurred during the time of superunification (Planck era, <math>10^{43}<math> second) or grand unification (GUT era, <math>10^{35}<math> second) while the universe existed in a state of nonzero energy density (also called false vacuum). A false vacuum is a combination of mass density and negative pressure that results gravitationally in a large repulsive force (antigravity).

A problem with this theory is the "graceful exit" (the fine-tuning). As of 2005, do you have any idea of how this problem could be solved in inflation? -- Orionix 18:30, 14 Mar 2005 (UTC)

In answer to some of your questions... Inflation does not provide any explanation of what happened before inflation. In fact, some theorists think that generating the necessary initial conditions for inflation to start is a major problem for inflation. There was indeed a much larger energy density during the early universe inflation than the energy density which we observe in the universe today, but this is not necessarily a false vacuum. The original idea by Guth did use a false vacuum and this lead to the so called graceful exit problem. However, that was abandoned in favor of other models which do not suffer from this problem. There is still a fine tuning problem with any known inflation models, where fine tuning has a technical meaning, but this is not the graceful exit problem of the old inflation based on a false vacuum. -- matt 19 Mar 2005