Dark Energy: Supernovae Ia, Vacuum Energy & Quintessence

[pi.rootpi]

Hi, I have another doubt

In addition to the Supernovae Ia, which more brought us to think the expansion was accelerating? And is there any difference between dark energy and quintessence? Because I've heard that dark energy is like vacuum energy (cosmological constant) and quintessence... I don't really know

Thanks for all, since I'm in Physics Forums I've learned lots of healpful thigs!

 

[marcus]

There are 3 or 4 independent sets of data that support the dark energy interpretation. Here's a thread on a recent one
https://www.physicsforums.com/showthread.php?t=280456

It's a thread I set up in Cosmo forum in case anyone wanted to discuss the latest confirmation of dark energy----by counting clusters of galaxies of various masses, at near and medium distance (low and medium redshift).

A good way to answer your question is to go here,
http://blogs.discovermagazine.com/cosmicvariance/2008/12/16/dark-energy-no-longer-a-surprise/
and look at the figure of overlapping intersecting ovals. These show confidence bounds on two important Cosmology parameters----dark energy fraction (around 0.74) and dark energy equationofstate (around -1)

The four intersecting colored ovals are

Supernovae---yellow oval
WMAP cosmic microwave background data----blue oval
BAO baryon acoustic oscillation data-----green oval
cluster mass counts (the latest stuff)-----pink oval

combined---red blob where they intersect

You will see how each oval helps to narrow down the ranges on these two parameters. Those two numbers go into the cosmo models that give us estimates of other kinds of things that we can compare with observation.

In case anyone is unfamiliar. There is a welldefined energy density of 0.85 nanojoules per cubic meter, called critical density. The number 0.74 means that dark energy is estimated to be 74 percent of critical. That gives us a figure for it in nanojoules per cubic meter, if we want.
The equationofstate is just the ratio of the DE pressure to the DE energy density. As more data accumulates it seems increasingly likely that this ratio is -1.

 

[George Jones]

And is there any difference between dark energy and quintessence? Because I've heard that dark energy is like vacuum energy (cosmological constant) and quintessence... I don't really know

Unlike vacuum energy, quintessence is a new field that could vary in space and time. See

https://www.physicsforums.com/showthread.php?p=1327486.