# Dark Energy

## What's dark energy?

• ### Dark energy? That doesn't exist

• Total voters
8
meteor
What's dark energy?
It's important to know what is the most common type of energy of the universe

Staff Emeritus
Gold Member
All of your choices are the same thing.

The names "quintessence," "vacuum energy density," "lambda," "cosmological constant" and "dark energy" are all synonymous.

- Warren

Last edited:
meteor
No. Vacuum energy is due to the negative pressure of virtual particles that continually appears in space. Quintessence is aa propossal of Paul Steinhardt, and consists of a scalar field that permeates the space

Gold Member
Dearly Missed
Originally posted by meteor
No. Vacuum energy is due to the negative pressure of virtual particles that continually appears in space. Quintessence is a propossal of Paul Steinhardt, and consists of a scalar field that permeates the space

I have the impression (correct me if i am mistaken) that
if the dark energy is "vacuum energy" then it must be constant throughout space

but it seems to me that now so many different people have
proposed different kinds of "quintessence" that the idea has
some flexibility----some kinds of quintessence are imagined to have a variable energy density (?)----and especially the equation of state is less restricted

for vacuum energy one must have an exact equality:
p = - rho
where p is the pressure

for quintessence I believe there is a parameter w
which may be exactly -1, or may be some number near -1,
and the equation of state is then

p = w rho

people who want more freedom to play around theoretically may
prefer quintessence because the possibilities are not so
narrowly restricted as with vacuum energy

but I believe it is very much the same thing fundamentally----a constant or nearly constant energy density associated with the vacuum

I must agree with chroot. The vacuum energy can be modified and shown to be equivalent to a uniform scalar field that permeates all space.

All choices are equal, hence I chose the one that has both.

meteor
Brad_Ad23: Marcus is right. The vacuum energy is the same that the cosmological constant of Albert Einstein and is supposed to be constant through time. Quintessence is supposed to change in time and place. For example, nowadays it exerts negative pressure. But from Big Bang til 50000 years after it, it exerted positive pressure. It's not discarded that quintessence can return to exert positive pressure (thus provoking the universe to contract again)
There's something I can't comprehend: How can vacuum energy drive the acceleration of the universe?
I'm interested to hear the possible alternatives of the people that have voted Other thing
Comment: NASA researchers believe that dark energy is more likely vacuum energy than quintessence

Isn't dark matter just the matter that we can't see, I mean of the stuff in space much is not in the form of a sun as not giving off light or detectable energy at this time so that there might be a lot of space dust or small rocks and be attributed to dark energies that speed up galaxy rotations?

meteor
Dark energy don't speed up galaxy rotations

A new candidate to dark energy has appeared: the generalized Chaplygin gas