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Dark Energy

  1. Apr 2, 2003 #1
    Dark Energy is now thought by some to contain 65% of the total mass of the universe. It will accelerate the expansion of the universe for some 20 million years. Then all normal matter/energy will have its constituents torn asunder resulting in a universe consisting entirely of Dark Energy.

    I conjecture that the universe will then fold upon itself, ever more tightly until reaching infinite density at which point …......Well a Big Bang.

  2. jcsd
  3. Apr 2, 2003 #2


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    In cosmological terms, 20 million years is a very short time. Maybe you meant 20 billion?
  4. Apr 2, 2003 #3


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    Dark energy has been measured very precisely to be 73% of the universe's mass-energy density. (WMAP, 2003)

    I have no clue where you came up with 20 million years either, nor why you feel the universe will have its constituents 'torn asunder' at that time. In fact, I'm not really even sure what it would mean for a universe to have its constituents 'torn asunder.'

    And really, very few people will care about your blue-sky conjecture......

    - Warren
  5. Apr 2, 2003 #4
    Yes, 20 billion is what I intended. The conjecture is mine. The expansion scenario that results in the disintegration of matter can be found via a simple google search.

  6. Apr 3, 2003 #5
    Probably the cosmic redshift is not properly considered in the current understanding of the universe.

    Too much mess suggests incorrect essentials.
  7. Apr 3, 2003 #6


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    I am familliar with the "Big Rip" idea (somewhat), but the concept of the universe folding in on itself after all matter has been torn apart is hard for me to follow. Have you in mind a mechanism by which this folding would be caused?
  8. Apr 4, 2003 #7
    I have to make several assumptions:
    Dark energy is homogeneous in the universe
    Passage of time is not everywhere constant

    Recently it’s been found that polarized light from a distant source rotates but less than light from an equally distant source at a right angle from the first source. As light is affected only by gravity, and the gravitational influence of Dark Energy is homogeneous, what might cause this difference in rotation? I can only surmise that the distance the light travels from their respective sources is different even though we perceive it to be the same. To account for this, the fabric of space must be convoluted and the passage of time must vary. As dark energy progresses towards becoming the dominant force, the convolutions will occur more frequently halting and reversing the expansion until infinite density is reached.

  9. Apr 4, 2003 #8
    ok some real basics
    1 what is "DARK ENERGY" ?
    what does it do, where is it?

    2 is there a light energy?

    3 why the % of total mass 65 or 73 or whatever, is the # from string "T", or Q or some other way??

    as far as I know nobody has ever seen, tested, created, or captured any 'DARK ENERGY' so, it is just a guess, as to what the missing mass maybe????

    btw I donot like dark BS be it mass energy or any other unproven dark math fixing stuff reminds me of eathor or crystial sphears!!!
    and maybr the math is just WRONG,
    and what we see is what we have got!!!
  10. Apr 7, 2003 #9
    Well Dark Matter accelerate the rate of expansion of space-time
    It is everywhere in the universe
    What do you mean by "is there a light energy?"

    Well dark matter is not affected by photons I don't think

    Doesn't dark matter take up about 99% of our universe?

  11. Apr 7, 2003 #10


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    Ouchie! We have a mix up here!

    Dark matter = wierd matter that have a mass (and hence gravity) but does not really detectably interact in other ways.(and this includes EM, so no photon interactions, at least directly). Accounts for descrepacies in Galactic formation, and stuff.

    Dark energy = wierder stuff that accelerates the expansion of space time. (and Geniere, it may not do so by gravity) Also known as the cosmological constant. Accounts for compelling evidence the expansion of the universe is expanding despite the gravity of dark/non-dark matter.

    Where is dark energy? What is it? We really don't know yet.

    The energy is a hint. We don't think it is matter, but the % comes from calculations giving estimates to the effect of dark energy on universal expansion. So it's an educated guess.

    Quite possibly. But there is evidence that there is at least some stuff in the universe we can't yet detect. Indeed, it's pretty unreasonable to assume all of it can be detected in ways we have so far perfected. Whether we will find the alternative to what is indeed pretty much a fudge is another matter.

    As Sherlock Holmes said: "Once you eliminate the impossible, whatever remains, however improbable, must be correct!"
  12. Apr 7, 2003 #11
    I always thought Dark Energy was distributed among dark matter -perhaps this is the reason for the fault I find with your assumption- and dark matter is clumped in various places, not evenly spread among the universe? If I have the right idea, then it would appear that dark energy couldn't be homogeneous or maybe I am thinking of the wrong meaning of homoegenous.

    FZ+, thank you for the description you provided, you clarified a lot for me.
  13. Apr 7, 2003 #12
    Dark Matter is thought to be extremely massive particles and would likely clump. Their very large mass is said to cause them to be "sluggish" and so take a longer time to clump then normal matter. Apparently millions of these super massive particles pass through each of us every second.

    Dark Energy would propagate at C and be equally distributed just as is the cosmic background radiation.

    You'd be better off to browse the web then put much credence in my interpretations.

  14. Apr 8, 2003 #13
    Like FZ says, there is a fundamental difference between DM and DE. DM is much older, rising mainly from discrepencies in orbital velocities of stars in galaxies - they rotate much faster than can be accounted for by keplerian motion, unless there is a large amount of unseen matter (more than light emmitting matter) in them. Candidates have been WIMPS and MACHOS, weakly interacting massive particles, and massive compact halo objects, respectively. Both have the feature of not emmitting EM waves that we could detect.
    DE is relatively new, but possibly an overlooked conclusion of general relativity, indicating that there is an inherent acceleration effect in space. DE is a way to explain the anomalous acceleration effect found in 1998 by observations of distant supernovae that were dimmer than was expected.
  15. Apr 8, 2003 #14
    I would agree with what FZ+ and schwarzchildradius have stated concerning both DE and DM.

    The exception arises in DE, as it is a recent construct proposed as to respond to the observations that couldn't be accounted for by the previous explanations.

    But, it is based upon the notion of Doppler shifting of light from distant stellar objects, and I have, in the previous PF, tried to demonstrate why this notion is wrong.

    Doppler shifting of sound occurs because of the resistance of the medium of propagation, the atmosphere, doppler shifting of radar occurs as a result of interaction with matter moving relative to the source of the radar.

    Doppler shifting of interstellar light would be another thing as, to the best of anyones present knowledge, there is NO resistance to the passage of light in interstellar space.

    The exception arises in Gravitational redshifting, a phenomenon that is observed from our own Sun, hence we know that light is being shifted by the gravitational energy that all stellar bodies produce, hence it could be simply that the observed redshifting of the light is not as a result of regressional (or progressional) motions, but simply as a result of the gravitational redshift that the stellar bodies induce.

    Even better is the distinct possiblity that it is a combination of the two, that would 'cloud things up' quite well.

    DE is still an unproven phenomenon, postulated as to account for recent observations.
  16. Apr 8, 2003 #15
    Hat into ring...

    Aren't matter and energy the SAME THING?

    If there's an energy pushing things "outward"...might there not be a corresponding energy pulling things "inward" ... you know, to keep the thing (Universe) stable (tho dynamic) over "time"?

    Could someone please give me an example of something (other than the Universe) that continues to accellerate and/or expand without EVER being STOPPED by something else??
  17. Apr 8, 2003 #16
    Re: Hat into ring...

    Matter and energy the same thing, sorta, E = Mc2 proves that one, but the energy that is matter is seen as 'constrained', or 'bound up' in matter, hence unavailable except in nuclear processes like fission or fusion, breaking or combining atoms, respectively.

    Energy pushing outwards is the light (radiation, or EMR) emitted by the Sun, energy pushing back is gravity, balanced, they are the cause of the spherical shape of the sun, and it's literal size is a function of the relativities of those two opposing forces.

    Something going on forever in a straight line is simple enough, Voyageur the space probe is still going, but it is NOT accelerating, probably decelerating slightly due to gravitational interactions over distances that are becoming vast, quickly, as it is known to have left our solar system, which would have had a gravitational effect upon it, and probably still does, but very slight.

    Newton’s law (predicts) tells us that an object in motion stays in motion, unless an energy, or force, acts upon it.
  18. Apr 9, 2003 #17

    Did some referencing yesterday, the initiation of the 'Dark Energy' comes from observations of Super novas that are dimmer (less light emitted) then was originally expected.

    The simple reality is that it could very well be (un certain) that the present theory concerning Super Nova’s has a slight flaw in it, inasmuch as, it could very simply be a function of gravity, that is presently (sorta) known, and unknown, as it is unrecognized for what it is.

    Known is that gravity can stop the emission of light, A Black Hole is well recognized as being able to do such, unknown would be that gravity might just have the ability to diminish the light emitted by any star/stellar body, and that the mechanism of that is, as yet, unknown.

    Hence, the idea of Dark Energy, is still a variable that has opportunity for either, refinement, as it might just be a "Wrong Guess", as the method of production of the observed phenomenon might just be an unrecognized ability of gravity itself.

    The reasoning for the possibility of it being gravity is as a result of the simplistic knowledge that when a stellar body goes Super Nova, the gravity of the resultant stellar Body would increase, probably substantially, and as the end result of some of the Nova'ed bodies, is a Black Hole, which has the ability to occlude light completely, there exists the distinct possibility that the precursor body to a Black Hole might just be gravitationally strong enough to diminish, to the degree observed, the emission of light.

    Time will tell.

    (The addition of what I know, in it's completeness, might just be the thing that they need to ascertain the certainty that is sought)
  19. Apr 9, 2003 #18


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    I doubt the gravitational explanation. While that would clealy have an effect, I think the amount of redshifting we experience is way too much to be accounted for by gravitational effects.
    But yes, doppler shifting of light is different from doppler shifting of sound. The former comes as a sort of effect of GR. As the light wave has the same velocity (c) , its wave length changes according to the objects' relative velocity.
  20. Apr 9, 2003 #19
    If I understand this even remotely...

    ...the esteemed THEY conjecture that the Universe will keep expanding at an accellerated pace. THEY believe this because certain evidence suggests that there is a possible "Dark Energy" that comprises about 2/3rd of Everything That Is...while the proposed "Dark Matter" comprises only about 1/3 of Everything (leaving a little sliver somewhere for baryonic matter).

    This rough equation suggests (to THEM) that the force of the energy that is pushing things outward is "outrunning" the overall force of gravity that is pulling things inward.

    So now I have another question (only ONE?): does E-MC2 suggest that "matter" is CONCENTRATED ENERGY...or visa versa?

    Mr. Robin Parsons, I especially await your reply because I UNDERSTAND THEM!
  21. Apr 9, 2003 #20


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    The supernova redshift surveys aren't the only experiments supporting a dark-energy dominated universe.

    In truth, the term 'dark energy' is misleading, and tends to sound rather contrived -- almost as if all the cosmologists are off their rockers and are just grasping at straws.

    Dark energy (or lambda, as most cosmologists would rather you call it) is literally just one term added to Einstein's field equations. This term is essentially a negative pressure term; a higher energy density results in a more strongly negative pressure. The proportionality constant between the energy density and the pressure is not fixed; it can vary between -1 and some small positive value. It can shown that universes in which this constant is smaller than -1 are unstable. It appears experimentally (WMAP 2003) that the proportionality constant must be very close to -1, and in fact probably is exactly -1.

    This term may be interpreted physically as a) a tangible "dark energy" that permeates the entire universe or b) as a basic characteristic of the universe, like the gravitational force, or the fact that there are two kinds of electric charge. The presence of this term is no stranger than the presence of any of the others.

    - Warren
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