Newbie question about inflation

[briandunning]

Is it known which of the four fundamental forces drives inflation?

If this is too stupid a question, feel free to flame me into the stone age. :)

 

[selfAdjoint]

None of them; that is why it has sometimes been conjectured to be a "quintessence". The current standard explanation is that the Einstein equations at the beginning of time had a certain modification, an extra constant called the cosmological constant, and this made them describe a dynamically expanding universe, not a static one. The other name for it is "dark energy". It is just an inner property of spactime to expand, under this interpretations.

There are some technical problems with this explanation; the cosmological constant itself is not zero, if it were, the universe would be static, at least under the Einstein equations. But the c.c that is inferred from the microwave background is very very small. Why is it so small? This is puzzling to physicists and cosmologists, and there is a flood of speculative theories about it.

 

[mathman]

the cosmological constant itself is not zero, if it were, the universe would be static, at least under the Einstein equations.

The non-zero cosmo costant is presumed to be responsible for the acceleration of the expansion. It it were 0, the expansion would be slowing down. The universe would not be static. Einstein's original thought when introducing the c c was to allow for a static universe. Without it, a static universe would be an unstable equilibrium.

 

[selfAdjoint]

The non-zero cosmo costant is presumed to be responsible for the acceleration of the expansion. It it were 0, the expansion would be slowing down. The universe would not be static. Einstein's original thought when introducing the c c was to allow for a static universe. Without it, a static universe would be an unstable equilibrium.

Thank you mathman. I had an uneasy feeling when I typed that, and I am glad you found what it was. I actually knew it but it was temporarily hidden from my conscious mind when I posted.

 

[Chronos]

The dark energy scenario is often represented as a phase transition - the same force is responsible for the initial inflationary epoch, which subsequently relaxed and allowed a period of gradual deacceleration, then transited into the more recent epoch of accelerated expansion.

 

[turbo]

The dark energy scenario is often represented as a phase transition - the same force is responsible for the initial inflationary epoch, which subsequently relaxed and allowed a period of gradual deacceleration, then transited into the more recent epoch of accelerated expansion.

We certainly are in a "golden age" of rational thought. Einstein was embarrased by his earlier inclusion of a cosmological constant into GR to keep the Static Infinite Universe static, thinking it a blot on his cosmology. Why was he so picky? Today, we can happily contemplate inflation, which expands the U so quickly that causally-connected volumes of spacetime are driven out of each other's horizons. Then, these non-connected parts of the U decide to stop inflating simultaneously, after which these non-connected areas undergoing an almost linear expansion decided to accelerate their expansion very smoothly to give us the homogenous U we see today with its almost monotonous CMB. All this coordination and FTL communication is a bit tough to take, and especially so when you contemplate the energies that would be required to start and stop these processes. This Feynman lecture about conservation of energy, cited in another post, should cause a little reflection about conservation of energy, and where the energy to start and stop these processes could come from. Conservation of energy is an important concept, yet it seems to be ignored in standard cosmology.

http://home.hockaday.org/HockadayNet/academic/physics/SciTeach/FeynEng.html

 

[hellfire]

Inflation, as well as the current acceleration of space, arise both due to something whose behavior is equivalent to a homogeneous perfect fluid exerting a negative pressure. I think it is very speculative to relate both to one single cause. One usual scenario is e.g. to consider that an unstable situation of a scalar field (scalar fields, or spin-0 fields, in some unstable situations, behave like perfect fluids exerting a negative pressure) was the reason for inflation. It became stable after a short time and inflation ended. On the other hand, the reason for the acceleration of space is usually considered to be related to a geometrical modification of the action of gravity; the cosmological constant (which does also behave like a perfect fluid exerting a negative pressure).