Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Dark Energy

  1. Vacuum energy

    1 vote(s)
  2. Quintessence

    2 vote(s)
  3. Vacuum energy and quintessence

    2 vote(s)
  4. Another thing

    2 vote(s)
  5. Dark energy? That doesn't exist

    1 vote(s)
  1. Jul 29, 2003 #1
    What's dark energy?
    It's important to know what is the most common type of energy of the universe
  2. jcsd
  3. Jul 29, 2003 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    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: Jul 29, 2003
  4. Jul 29, 2003 #3
    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
  5. Jul 29, 2003 #4


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    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
  6. Jul 29, 2003 #5
    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.
  7. Jul 31, 2003 #6
    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
  8. Aug 2, 2003 #7
    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?
  9. Aug 2, 2003 #8
    Dark energy don't speed up galaxy rotations

    A new candidate to dark energy has appeared: the generalized Chaplygin gas
  10. Aug 2, 2003 #9
    I know what marcus was saying. I was saying that the mechanism behind this is believed to be operating under the premise of the negative pressure that quantum fluctuations as a whole make. The more space expands, the more space there is for added flux, and hence you get an accelerative process. Up until the point where the universe was large enough to sustain this, the quantum vacuum or whatever you wanted to call this would have had a negligable impact.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook