Astronomy Without A Telescope – Enough With The Dark Already

Article written: 4 Jun , 2011
Updated: 24 Dec , 2015
by

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The recent WiggleZ galaxy survey data further confirming that the universe is expanding with a uniform acceleration prompted a lot of ‘astronomers confirm dark energy’ headlines and a lot of heavy sighs from those preferring not to have the universe described in ten words or less.

I mean how the heck did ‘dark energy’ ever become shorthand for ‘the universe is expanding with a uniform acceleration’?

These ‘dark energy confirmed’ headlines risk developing a popular view that the universe is some kind of balloon that you have to pump energy into to make it expand. This is not an appropriate interpretation of the dark energy concept – which only came into common use after 1998 when Type 1a supernova data were announced, suggesting an accelerating expansion of the universe.

It was widely accepted well before then that the universe was expanding. A prevalent view before 1998 was that expansion might be driven by the outward momentum of the universe’s contents – a momentum possibly established from the initial cosmic inflation event that followed the Big Bang.

Current thinking on the expansion of the universe does not associate its expansion to the momentum of its contents. Instead the universe is thought of as raisin toast dough which expands in an oven – not because the raisins are pushing the dough outwards, but because the dough itself expands and as a consequence the distance between the raisins (i.e. galaxies etc) increases.

It’s not a perfect analogy since space-time is not a substance – and, at the level of a universe, the heat of the oven equates to the input of energy out of nowhere – and being thermal energy, it’s not dark.

Alternatively, you can model the universe as a perfect fluid where you think of dark energy as a negative pressure (since a positive pressure would compress the fluid). A negative pressure does not obviously require additional contents to be pumped into the fluid universe, although the physical nature of a ‘negative pressure’ in this context is yet to be explained.

Various possible shapes of the observable universe - where mass/energy density is too high, too low or just right (omega = 1), so that the geometry is Euclidean and the three angles of a triangle do add up to 180 degrees. Our universe does appear to have a flat Euclidean geometry, but it doesn't have enough visible mass/energy required to make it flat. Hence, we assume there must be a lot of dark stuff out there.

The requirement for dark energy in standard model cosmology is to sustain the observable flat geometry of space – which is presumed to be sustained by the mass-energy contents of the universe. Too much mass-energy should give a spherical shape to space, while too little mass-energy should give a hyperboloid shape.

So, since the universe is flat – and stays flat in the face of accelerating expansion, there must be a substantial ‘dark’ (i.e. undetectable) component. And it seems to be a component that grows as the universe increases in volume, in order to sustain that flat geometry – at least in current era of the universe’s evolution.

It is called ‘energy’ as it is evenly distributed (i.e. not prone to clumping, like dark matter), but otherwise it has no analogous properties with any form of energy that we know about.

More significantly, from this perspective, the primary requirement for dark energy is not as a driver of expansion, but as a hypothetical entity required to sustain the flatness of space in the face of expansion. This line of thinking then begs the question of just what does drive the accelerating expansion of the universe. And an appropriate answer to that question is – we haven’t a clue.

A plausible mechanism that accounts for the input of energy out of nowhere – and a plausible form of energy that is both invisible and that somehow generates the production of more space-time volume are all required to support the view that dark energy underlies the universe’s accelerating expansion.

Not saying it’s impossible, but no way has anyone confirmed that dark energy is real. Our flat universe is expanding with a uniform acceleration. For now, that is the news story.

Further reading:
Expansion of the universe
Shape of the universe

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57 Responses

  1. You could even go further and say that this confirmed that the Universe appears to be expanding at an increasing rate!

  2. Pensive it http://bit.ly/mqSuSr little serving as an example of my research results- see Interesting facts about the Universe, as I see its- New Discovery of the Universe

    • Anonymous says

      Heads up on comment policy:

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      • IVAN3MAN_AT_LARGE says

        Yo Uncle_Fred, that list should be a permanent feature via a “Comment Policy” link under the “Navigation Links” on the right hand column.

      • Anonymous says

        That’s a good idea. I’ll propose it to Frasier.

  3. Wezley Jackson says

    Great article Mr Nerlich!!!! Hallelujah! I thought I was going to go bonkers if I read another (Discovery confirms Dark…blah.blah..) announcement.

    People, and surprisingly also some clever scientists seem to be forgetting lately that DM/DE are PLACEHOLDER names – Remember the Aether that so many mainstream scientists defended a century ago? … These placeholders were invented as a sort of fill-in-the-blank for the “Missing Matter” which is required to explain orbital motions of galaxies and increasing accelerated expansion of spacetime – my understanding at least…

    Another discovery was made by another astronomy team recently (sorry can remember the precise details) that a team of astronomers recently discovered 14% of the missing matter in the form of hot gasses observed within our own Galaxy which was previously overlooked – even though scientists assumed we had accounted for all matter… Shows me that my skepticism was well-founded.

    Anyway I am not here to express any theories. Just wanted to say thanks Mr Nerlich and could we have more articles like this that present alternative views or at the very least highlighting where we are up to as a scientific community with these questions / theories and explaning clearly concepts and theories as per Scientific Method for general reading (ie, not blindly accepting and repeating ad hominem something unproven)? Its exciting to ponder these mysteries together and I enjoy your great articles on this site

    Thanks

    • Member
      Steve_Nerlich says

      Re missing matter, you are thinking of this I think (Fraser-McKelvie et al):
      http://arxiv.org/abs/1104.0711
      Also Australian research 🙂

    • WaxyMary says

      Wez,

      My appreciatory thanks also go out to Steve Nerlich for his exploration of current progress and his finger-on-the-pulse presence here. But I have a few thoughts for you.

      You say, “a team of astronomers recently discovered 14% of the missing matter in the form of hot gasses observed within our own Galaxy which was previously overlooked – even though scientists assumed we had accounted for all matter… Shows me that my skepticism was well-founded.”

      You really need to re-read the paper/article you misremember and/or conflated with your own personal belief structure, as what you are saying above is not what the article said, at all, in any way, shape or form. Your words indicate several ‘facts’ as the opposite of what is said about them in the paper you claim as the source (to remember in part and to be the source of your conviction in your skepticism). This does a disservice to the writers of said paper and to those of us who have read said paper.

      As to placeholder names and IDs, yes DM and DE are such beasts, but the aether was not such a placeholder during the time of its reign. The placeholder names do suggest some factor of the item for which they are holders though, and you seem to think that there is not any need for the terms. Indeed, you crow about adding to the percentage of known matter and subtracting from the amount of DM (the paragraph I address above this one). Again, re-read the paper/article (you do not reference).

      If you wish to rewrite the past feel free to say as much as you do your rewrite, but please, do not couch it as if you are just misremembering small, minor facts in your replies to me, or anyone, over this. If this is not personal conflation then you have an agenda which you are not claiming and that is disingenuous.

      Mary

      • Wezley Jackson says

        And I guess part two would be I am not being disingenuous or pushing any barrows. I stated I didn’t remember all the details of the paper but do remember reading explicitly a quote on a space / astronomy publication where the author quoted the paper as having possibly found up to 14% of the missing matter in our own galaxy.

      • Wezley Jackson says

        Part One was too long – I am reposting but it ended up long again..(not trying to preach or push a barrow on any pet theories).. I think you misunderstood what I was saying because perhaps I should have said: “Luminiferous aether”

        It certainly was a momentous placeholder of the last century and greats like Drs Hubble and Einstein were working on this as one of the unexplained phenomena – how light could refract so in a vacuum.

        Quoting wikipedia:

        Luminiferous aether – In the late 19th century, luminiferous aether or ether, meaning light-bearing aether, was the term used to describe a medium for the propagation of light.[1]

        Due to the negative outcome of aether-drift experiments like the Michelson-Morley experiment, the aether as a mechanical medium having a state of motion, is not used anymore in modern physics, and is replaced by the theory of relativity and quantum theory.

        A very relevant parallel I am using to point out that until positive proof of a phemena’s existence is widely accepted of by the scientific community it is simply a placeholder or term.

      • Anonymous says

        In his later years, Michelson redid the rectilinear ether drift experiment, which had failed to find ether drift because it employed a rectilnear interferometer that concealed it through cancellation. In the Michelson-Gale experiment, he used a curvilinear Sagnac interferometer the size of a f a few footall fields. Eveen thugh his experiment with Morley had failed, it nevertheless won him a Nobel prize. His successful experimennt with Gale did find the ether drift and was roundly ignored. Go figgah.

      • Anonymous says

        Sure. Any sources?
        And why do we place space-probes around Saturn? Why does your GPS work? Because General Relativity is right, and ether is wrong.

      • Anonymous says

        A quick Google search turns up:

        – Wikipedia says the later experiment was consistent with relativity and Lorentz ether theory. http://en.wikipedia.org/wiki/Michelson%E2%80%93Gale%E2%80%93Pearson_experiment . Furthermore, Lorentz ether theory was developed following null drift results. http://en.wikipedia.org/wiki/Lorentz_ether_theory
        – At least one pro-ether website interprets the result as a confirmation of Lorentz ether theory, yet grudgingly admits “one would have to use general relativity to attempt to explain it.” It calls mainstream physicists “relativists” and “relativistic researchers” along the way, fun. http://www.conspiracyoflight.com/Michelson-Gale/Michelson-Gale.html

        So, no drift there.

      • Wezley Jackson says

        I think a lot of people misinterpreted my cut and paste because maybe I should have delineated the Wikipadia quote better which was summarising why Lumeniferous Aether turned out to be an incorrect place-holder theory. Please see my other posts for further clarification that I was not pushing any pseudoscience here..

      • Torbjörn Larsson says

        Remember the Aether that so many mainstream scientists defended a century ago? …

        It certainly was a momentous placeholder of the last century and greats like Drs Hubble and Einstein were working on this as one of the unexplained phenomena – how light could refract so in a vacuum.

        Whut?

        If you drag in something completely irrelevant to the context, the least one expects is that you get your “cut & paste” correct.

        First, aether was an old, natural idea which analog applies for matter waves like sound and surface waves. It was used but hardly “defended” because it was taken for granted, no one questioned it.

        At the time of Einstein’s work observing and/or explaining aether was rather high brow background work, which interested few AFAIK. It became interesting after the fact.

        Second, Hubble had nothing to do with this. He started to work the very year Eddington tested special relativity (1919).

        Third, how light refracts in vacuum was long known, and later followed from Maxwells theory. It was Newton that had trouble with it, and so _suggested_ precisely the aether (again, it had a long history).

        What was missing was the expected observation of aether dragged around by massive objects.

      • Wezley Jackson says

        I knew you could put it more accurately than I…

        I have read many of your posts and know your level of knowledge in these areas would be well above mine. I find a certain please in understanding the evolution and particularly the history of the Scientific Model’s progress – Although in truth I just surf Wikipaedea and science sights for brainfood as a hobby – I don’t have any dogs in this race…

        Cheers,

        Wezley

    • Torbjörn Larsson says

      I think the term you want is “Eureka!” or possibly “laetor, scientias!” Religion has nothing to do with this.

      People, and surprisingly also some clever scientists seem to be forgetting lately that DM/DE are PLACEHOLDER names

      Not exactly, they originated as (very descriptive) placeholder terms, but they describe theory entities that are real if the theory a) describes reality b) is robust.

      a) is already verified, the theory has been tested; even its individual constituents (except inflation) has been amply tested on their lonesome. So DE & DM are real within the theory.

      b) is a good bet. Standard cosmology emerged out of a history of much confusion and “not seeing the wood for the trees”, but when it did it integrated observations neatly and naturally. It is a really good bet to claim that DE & DM are real irregardless.

      the Aether

      The epicycles, the phlogiston, et cetera. The point is that those theories were useful until they no longer held up to test of predictions.

      The same holds for all theories, whether they are wrong or, ultimately, correct. So that isn’t an argument.

      Unless you have decided that Aether was “wrong” instead of “once useful”. But then you are no longer concerned with scientific facts and theories and reality, but religious and philosophical “truth” – of which there is none. (Or more technically, as many versions of conflicting truth as you want – and more.)

      These placeholders were invented as a sort of fill-in-the-blank for the “Missing Matter”

      Now you are turning history on its head for the purpose of your headless ideology.

      It was realized that some dark matter (not dark energy) could be explained by the then not so constrained normal matter. The remainder was the “missing matter”; it had been missing whether or not cosmology demanded it or not.

      Further on it turned out that better constraints shows that not all dark matter was non-luminous normal matter. And things like the Bullet cluster showed these constraints were correct and that remaining dark matter is non-baryonic.

      at the very least highlighting where we are up to as a scientific community

      That is precisely why we should not condone pseudoscience “alternate views”! The scientific community is not “up to” that.

    • Torbjörn Larsson says

      I think the term you want is “Eureka!” or possibly “laetor, scientias!” Religion has nothing to do with this.

      People, and surprisingly also some clever scientists seem to be forgetting lately that DM/DE are PLACEHOLDER names

      Not exactly, they originated as (very descriptive) placeholder terms, but they describe theory entities that are real if the theory a) describes reality b) is robust.

      a) is already verified, the theory has been tested; even its individual constituents (except inflation) has been amply tested on their lonesome. So DE & DM are real within the theory.

      b) is a good bet. Standard cosmology emerged out of a history of much confusion and “not seeing the wood for the trees”, but when it did it integrated observations neatly and naturally. It is a really good bet to claim that DE & DM are real irregardless.

      the Aether

      The epicycles, the phlogiston, et cetera. The point is that those theories were useful until they no longer held up to test of predictions.

      The same holds for all theories, whether they are wrong or, ultimately, correct. So that isn’t an argument.

      Unless you have decided that Aether was “wrong” instead of “once useful”. But then you are no longer concerned with scientific facts and theories and reality, but religious and philosophical “truth” – of which there is none. (Or more technically, as many versions of conflicting truth as you want – and more.)

      These placeholders were invented as a sort of fill-in-the-blank for the “Missing Matter”

      Now you are turning history on its head for the purpose of your headless ideology.

      It was realized that some dark matter (not dark energy) could be explained by the then not so constrained normal matter. The remainder was the “missing matter”; it had been missing whether or not cosmology demanded it or not.

      Further on it turned out that better constraints shows that not all dark matter was non-luminous normal matter. And things like the Bullet cluster showed these constraints were correct and that remaining dark matter is non-baryonic.

      at the very least highlighting where we are up to as a scientific community

      That is precisely why we should not condone pseudoscience “alternate views”! The scientific community is not “up to” that.

      • Wezley Jackson says

        Apologies – the H word was not meant to offend. I meant it in the latin sense of the word (rejoice) although now I could have used a more sciencey word or if you want Bingo/Yatze!!!

        In terms of your last sentence, you say I am disrespecting the readership by elevating pseudoscience… Please point out the theory or science (of my own) in any of the sentences of my paragraphs???

        I think you seem to believe everyone in the scientific community must accept the existence of DM/DE. I admit the bullet cluster image (Hubble/STi team) is convincing evidence of a map of DM. Also the lensing of glalaxies with HUDF is very convincing and confirms GR at the very least.

        However, there are so many other pieces of evidence pointing in different directions (like the found missing matter I which Mr Nerlich was kind enough to link to above which I did mention in my post).

        I wasn’t trying to stir the pot here and gave accorded respect to current scientists working to confirm DE/DM – did you notice I accorded “Lumeniferous Ether” respect even though it turned out to be incorrect? Yes it has a pseudosciency ring to it because its older english.

        My whole point is lets not get ahead of ourselves and tell the general public “DE is confirmed” just yet. If it turns out we prove it with repeatable experiments I will be one of the first to post conceding its an amazing momentous discovery!

        I mostly don’t comment because I know how out of my depth I am and have enjoyed reading the articles and forums for many years. Just current mainstream media bias towards 100% acceptance/confirmation of both DM and DE as confirmed discovered phenomena by press-release has been getting to me lately and that’s why I posted. If you are so sure DM/DE exists then please link me to the peer-reviewed Theory paper explaining these two phenomena quantitatively with repeatable experiments and then I will be silent on the matter in future.

        I look forward to your enlightened comments in future and enjoy any info the good members of this forum wish to provide.

        Best,

        Weez / Wezley

  4. TerryG says

    Nice catch Steve Nerlich.

    There are heaps of unsolved problems in study of Logic, and therefore plenty of gaps in the Mathematical knowledge we use to model and describe the observable universe. There are vastly more uncomputable problems than computable problems. Currently, we might not even have enough knowledge to decide if the “known unknown” of Dark Energy will ever be knowable.

    The recent headlines “Dark Energy Confirmed” just aren’t particularly illuminating.

    • Torbjörn Larsson says

      gaps in the Mathematical knowledge we use

      I am usually among the first that claims that math is quasiempirical, however physics is entirely empirical so adds much testability on math. Physics &noteq; math.

      There are vastly more uncomputable problems than computable problems.

      Yes, but if they are uncomputable why would they be relevant to physics? How does nature compute uncomputable results given local, finite resources?

      we might not even have enough knowledge to decide if the “known unknown” of Dark Energy will ever be knowable.

      Simple, just verify if the theory incorporating it is testable. (I.e is an actual theory.) It is, so we can eventually decide (know).

  5. Anonymous says

    The FLRW equation for the scale parameter a = a(t) is

    (a’/a)^2 = 8?G?/3 – k/a^2

    where (a’/a)^2 = H, the Hubble parameter, and flatness means k = 0, spherical geometry is k = 1 and hyperbolic geometry is k = -1. There is an equation of state for the mass-energy and pressure in the spacetime

    d(?a^3)/dt}+ pda^3/dt = 0

    I will consider an approximate de Sitter spacetime, which has ? = constant, and is identified in ways not entirely understood with the quantum field vacuum. The FLRW equation for k = 0 is then

    da/dt = sqrt{8? G?/3}a

    which has the solution a = sqrt{3/8?G?}~ exp(sqrt{8?G?/3}t). Using the Einstein field equation we then have that the stress energy is T^{00} = 8?G? = ?, which is the cosmological constant. Returning the first equation, the FLRW equation, we then see that H^2 = ?/3. The dynamical equation for the dS spacetime with ? = const gives

    ?d(a^3)/dt + pda^3/dt = 0

    or p = -?. This is the equation of state for p = w?, and w = -1. This corresponds to a case where the total energy is zero and the first law of thermodynamics is dF = dE – pdV = 0 means the energy that is increased in a unit volume of the universe under expansion is compensated for by a negative pressure which removes work from the system. Further pdV = d(NkT), and for a constant thermal energy for the vacuum and Nk = S the entropy of the universe.

    We know that dark energy is due to a cosmological constant induced from a vacuum energy. What we do not know is the nature of that vacuum energy. Based on current quantum field theory it should be much larger. Polchinski worked out how it could be much smaller than previously thought. However, it is still too large. From that perspective this is still “dark.”

    LC

    • Wezley Jackson says

      You just blew my freakin mind. Ouch my brain is hurting… I am not well versed as you on the math but from an armchair distance certainly appreciated your last paragraph. I have often thought perhaps quite a logical explanation is dynamic equilibrium – forgive my mathless presentation but if one had a bulk/void or zero point energy vacuum and then dropped a singularity (white hole) in the middle of it, it would race outward in all directions to fill the 0 point vacuum, however that expansion would be dictated by the mass of the singularities initial mass/energy (as the 0 point vacuum is obviously 0). (sorry didn’t get much past Intermediate algebra in University and maybe well out of my depth on my half explanation of how it all works maybe 😉 seems logical to me. Am I making any sense? Weez / Wezley…

      • Anonymous says

        There is a “white hole-like” element to this. However, the category of spacetime according to the Petrov-Penrose-Pirani scheme is different for a cosmology and a black hole. This results in some departures that diverge from such analogies.

        LC

      • Wezley Jackson says

        I am not trying to start any theories here (I know you and some of the others have way too many of those posts here before) – just pointing out that if indeed the big bang originated from a infinitesimally small point of matter/energy (which seems to be the case based on countless papers on Big Bang cosmology linked to the Hubble and other astronomy data). So maybe – MAYBE (not a theory – just asking) that tiny ultra compressed mass/energy that started inflation and the universe was a white hole?
        I don’t mean an AGN white hole in our spacetime – I mean the end of the funnel of a black hole of a larger parent universe). Seem logical?

        Quantifiable/Observable – We see agn’s which some scientists believe could contain white holes (not yet proven). We see black holes. We see (mostly) empty space with accelerated matter streaming from a central point.

        Can anyone tell me whats all the way inside (past the quantum singularity) inside a black hole? We can theorize to get close and there are peer reviewed papers (sorry it is late and i have the flu but you can google them) about the possibility of white holes in our own universe (and suggestion that this could exist in a multiverse situation). Ie that point of light/matter that started the universe was a rupture into a void – 0 point vacuum. There are various theories (such as brane and ekpyrotic) which I find interesting reading (but don’t necessarily accept) that attempt to explain how the rate of expansion could have been driven by the initial parameters of the big bang observed by modern science.

        Go ahead and shoot me down if I have misrepresented anything. Honestly I am not trying to stir you – I am prodding for your knowledge and wisdom on these subjects- and as a disclaimer nothing of what I wrote above was trying to challenge DM/DE or any other theory (as a matter of fact in my mind the jury is out – I am undecided but open to information and enlightenment).

        Best,

        Wezley

      • Wezley Jackson says

        ps. what pops out the end of a funnel (as a compressed condensate plasma or liquid) can be characterised by either flat 3-dimensionally curved matter geometries (that is conical sections – which can be repeated in optics and mechanical physics experiments). Ie, flat convex/coverse 3-dimensional curved (co-planar hyperboloid/ paraboloid) shapes (my own experimental/applied/research physics understanding of how the behavior of our local space time geometry could be considered the logical result of a white-hole from a parent universe…. Please illuminate me if this all sounds too far-fetched or if you have any general comments or wish to provide any supplementary links (sorry I am up late with the flu and didn’t have time to properly link to peer review for the above paragraph- –disclaimer: I am an armchair cosmologist.

        Best,

        Weez/ Wezley

      • Anonymous says

        You are trying to say a lot of stuff here. I will say a couple of things. If k = 0 and the universe consists of a flat space that expands in curved spacetime then there is no point from which the universe emerged from. The picture of the big bang as having some point of origin is not entirely right — and for a couple of reasons. The flat space may have emerged ”as is,” or it emerged from the puncturing of a 3-sphere where the sphere with a point removed was stereographically projected onto a flat space. The emergence of this flat infinite R^3 space may have something to do with D3-brane interactions which recharge them. Type IIB strings which connect D3-branes in a manner similar to springs may cause these branes to collide and bound off of each other. This will excite the string vacuum and generate strings on the D3-branes. From there an inflationary spacetime is generated, and our observable universe is a nucleation bubble in this space.

        LC

      • Torbjörn Larsson says

        I realize the terminology gets a bit confused when one tries to grasp this at first. It is spacetime that is zero energy (in standard cosmology), not zero point energy of quantum fields.

        [Actually the whole point with the latter is that these fields can’t take zero energy as lowest energy level, due to uncertainty (if you will).]

    • Member
      Steve_Nerlich says

      In this context, I understand vacuum energy offers ‘the worst prediction in theoretical physics’ – i.e. out by 120 orders of magnitude.

      I like the concept of a negative pressure that removes work 🙂

    • Anonymous says

      The negative pressure does remove work to compensate for the continual “generation” of energy density. That only works for the special case that w = -1. General relativity is funny with energy conservation. Energy conservation only holds if there is a timelike Killing vector which projects onto the energy part of a four momentum vector to produce a constant scalar. This is an isometry of the spacetime which gives energy conservation. Many spacetimes do conserve energy, such as those for black holes. However, those for cosmologies in general do not, except for this case.

      Polchinski and Bousso demonstrated that this vacuum or cosmological term is due to the flux on a Dp-brane, the so called NS5-brane. Under a certain transversality condition the flux is parallel to the brane and this energy drops. However, it is still far too large. The problem is really there are far too many degrees of freedom in our theories. A degree of freedom contributes energy to the vacuum. The simple fact is that we still do not have it figured out yet.

      LC

    • Torbjörn Larsson says

      Not exactly. Vacuum energy and no constraint offers “the worst prediction” for cc. I.e. if you only have naturalness of the models to go from, the cc is much too low.

      However, as soon as you try to embed vacuum energy into modern physics such as standard cosmology this changes. In fact, you can run the whole field if you want:

      First, the expectation value of a cosmological vacuum would tend to minimize. Out goes naturalness as safe prediction, it is a tentative start value. [Note, that is my personal interpretation.]

      Second, if you then put in string theory, it happens to neatly explore all those orders of magnitude down to around where we are. So it is feasible and predicted as a bound.

      Third, multiverses, which comes naturally out of standard cosmology inflation and/or the zero energy of its spacetime (tunneling) and/or bubble nucleation, will indeed permit a minimization process.

      Fourth, there are theories like environmental selection where the value of cc is predicted naturally. Susskind and Bousso are the go to men to read on that, especially the later.

    • Wezley Jackson says

      Double-Yatze! 🙂

      Its refreshing that one person’s theory is as valid as the other until the peer rev. paper explaining DM/DE is globally accepted and this thread has been great because we can share information courteously even with opposing views in these forums (provided we aren’t espousing our own theories without peer-revved links).

      Personally I respect the scientists and work that has gone into DM/DE research but also ask that the science press attempt to explain better that DM/DE are ‘the leading suspects’ to explain some big unanswered questions in Big Bang cosmology. However, until then lets hope the average reader understands that scientists are reserving “confirmed” (sic. to exist as scientific phenomena) for a future date when a total body of evidence or theory is presented…

      Thanks again for great article and comments and for providing the link for one of my post’s reference.

      Best,

      Wezley

  6. WaxyMary says

    Steve,

    You said, “I mean how the heck did ‘dark energy’ ever become shorthand for ‘the universe is expanding with a uniform acceleration’?”

    I ask in turn what would you use as a placeholder term for ‘uniform acceleration’ re the universe’s expansion. What negative factor term would you wish to use. The current one is DE and if that term is not approbate then suggest another please as some term is needed for this observed condition of ‘uniform acceleration of expansion of the universe’ or UAEU if you wish to coin an acronym.

    The paper you mention does, indeed, confirm such acceleration for the nonce even if that confirmation may be slightly wrong over greater lengths of spacetime in our ‘better’ observations sometime in the future. Currently it does seem uniform in acceleration though to a high degree of sigma. If it turns out at some time in the future there is an additional component and the acceleration is being accelerated or slowed down in some minute fashion this still does not change the current state of affairs and the need for a placeholder as descriptive of the observation as dark energy.

    The wish for a flat universe vs the reality or ‘what may be correct’ is the reason given for use of such an expansive energy source to drive to flatness the hyperboloid state we would otherwise expect. The simplest explanation, all things being equal…

    Mary

    • Member
      Steve_Nerlich says

      Mary – thanks for the question. As a science journalist wannabe, I am just objecting to media reports stating DE is real – when the good science done here has only confirmed accelerating expansion. I do not seek to offer an alternative theory.

      Also, I think there is some confusion around just what place DE is supposed to be holding – expansion or geometry or both? Hence, I think there is a need for writers to be clearer on what exactly they are talking about when they do employ DE as a placeholder.

    • Anonymous says

      I’m only an armchair observer myself but I understood the name was originally based on the result of the expansion. In some key cosmological models, the energy in the form of matter and radiation was exactly equal but opposite in sign to the gravitational potential energy giving a total of zero. As galactic clusters move apart, the potential energy rises so the kinetic energy would have to reduce to conserve the total, rather like a bullet fired upwards on Earth. Accelerating expansion, like the bullet at first slowing the speeding up as it left the Earth would imply the total energy was increasing regardless of the cause, hence it requires an unknown (“dark”) source for this extra energy.

      I am aware that defining concepts like “total gravitational potential energy” in GR is not trivial, but historically isn’t that where the term came from?

      From the FAQ:

      http://www.desy.de/user/projects/Physics/Relativity/GR/energy_gr.html

      “We will not delve into definitions of energy in general relativity such as the hamiltonian (amusingly, the energy of a closed universe always works out to zero according to this definition), …”

      • Member
        Steve_Nerlich says

        Yes agree – but DE also used to explain the flatness of space – in the context of 73% of the universe is DE.

      • Anonymous says

        Does we observe flatness and then suggest DE to explain it, or is flatness inferred from observations that quantify DE as being at roughly the right level for flatness? Either way, is “energy” not an appropriate name for the phenomenon which contributes that 73% to the postulated flatness?

  7. Wezley Jackson says

    Hello Mary. I think you misunderstood the paragraph in which I mentioned the “Aether” – to which I was referring was: Luminiferous aether.

    Please wikipedia it. It was well and truly a momentous placeholder of the last couple centuries for explaining the how light could exhibit its refractory properties – the leading theories of the day couldn’t account for light being refracting in a vacuum. Greats like einstein, hubble, schrodinger worked on this picking up on the work of Huygens and earlier Newton ..

    In the late 19th century, luminiferous aether or ether, meaning light-bearing aether, was the term used to describe a medium for the propagation of light.[1] (quoting wikipaedia).

    Not to belabour the point but “term” and placeholder are not too dissimilar beasts.

    Best regards,

    Wezley

  8. Anonymous says

    Has the Fat Lady sung for dark energy?

    We had similar problems with Dark matter. There was a problem with explaining galactic rotations in the 1930’s. Back then, the proposed solution was that there was a lot of other stuff out there that we couldn’t see. Years passed and nobody ever saw it, and the idea began to have a whiff of the aether about it. Just lately we have been able to use gravitational lensing to produce maps of the distributions of dark matter. To my surprise, and I can’t have been the only one, there it all was, hanging about galaxies pretty much as Zwicky imagined it, and we still can’t see the bloody stuff.

    I like the idea of a flat universe. It is neat. If you have positive or negative curvature, then you have to explain why we have a particular radius and not another. The constant expansion of the universe is also neat: it may be that the expansion is not just constant with time, but it somehow _is_ time. However, if the variations we look for appear like energy, then it makes sense to look for this energy and see whether we can detect variations in its distribution. We looked for dark matter for 80 years, and we could map it in the end. We only have had dark energy for about 12 years, so I don’t think we are quite done looking yet.

    However, I do agree with Steve Nerlich’s argument. A universe that seems to have a completely uniform distribution of exactly the right amount of dark energy to make the universe flat and uniformly expanding isn’t exactly a proof of dark energy. Find dark energy in lumps or find it doing something else, and maybe the rest of us will agree it is really there.

    • Anonymous says

      The point of the previous article on DE which had this same image of the candle and ruler distance was there are no lumps detected.

      There are comments here which compare dark energy to luminiferous aether or to the Ptolemaic epicycles. This is a sort of historicity type of argument. I have to implore people not to make these comparisons with abandon. The Ptolemy system was canonized by the Church and it became a matter of theology. It was not upheld in an open scientific manner. The comparisons with the aether are only on track with the fact we have some sort of over accounting of states or degrees of freedom. DE is there, but our attempts to understand it do not work well. With the aether there was an implicit over counting of states, where the motion of a body involved complicated interactions with this “fluid,” which was ultimately composed of something analogous to “atoms.”

      The text by Ptolemy “Almagest” is something you might want to look at. It is a part of the great book series published by A .J. Ayers. Ptolemy employed Euclid’s elements of geometry in a very difficult way. The book is not at all easy reading. It was a first attempt to understand the universe with the mathematics of the time, and it clearly demonstrates a high intellectual effort.

      LC

      • Anonymous says

        The XKCD cartoon gets it just about right…

        http://xkcd.com/895/

        Physical analogies are sometimes helpful, but they can take on a life of their own and start shaping people’s understanding rather than just helping get the ideas across. For me, the basic equations are the thing, and I can leave the non-productive arguing about what is ‘actually there’ to philosophers. We postulate the existence of DE; and we try to find ways of detecting it. If DE seems to completely and uniformly fill all space, then we might try postulating that the properties of DE are the properties of space itself. Either way, we still have to prove what we say. I trust none of us are saying ‘the aether does not exist, so neither does DE, QED.’

        BTW: I was reading a .pdf reprint of a publication of J. J. Thompson on Maxwell’s equations on Project Gutenberg. I am familiar with the equations in their modern form, but the explanation was in terms of electrostatic field lines rather than magnetic field lines. This made the explanation utterly alien and impenetrable to me, but it appears electrostatic field lines were the model of choice for a whole generation after Maxwell. If it works, go with it.

        Cheers.
        Richard

      • Anonymous says

        In some sense the questions which we ponder today might be hobbled by such “pictures.” A lot of hypotheses today that are “hip” tend to rely upon such imagery.

        LC

  9. Han Vinke says

    Dark Energy has a problem, see

    http://www.universetoday.com/86000/black-holes-spin-outta-control/

    In an expanding universe you cannot explain the apparent increase of momentum in black holes.

    • Torbjörn Larsson says

      The above and below constitutes another two useless comments in the “DE war” against accepted science:

      In an expanding universe you cannot explain the apparent increase of momentum in black holes.

      The article you links to claim no such connection to expanding universes.

      You can as well point to the US deficit and claim that an expanding universe can’t explain the problem.

      Dark Energy will be forever very real as long as the speed of light is considered to be a constant.

      Well, duh. That is a feature, not a problem.

      The expansion or contraction rate of the universe is r = 3 (dimensions) H/ln2 .

      Except of course in our universe, where the expansion is accelerating (due to DE, btw).

      If the speed of light is coupled to loss of information

      And how do you do that? You argue about entropy, not light nor universal expansion.

      (in a state of low entropy).

      Actually the universe starts out hot and with low and increasing entropy. It is relatively high entropy though, but only due to the relatively small volume. As it expands, so does too the ability to increase entropy – it expands.

      In the state of entanglement you have reached maximum entropy …

      No, then the system couldn’t evolve further.

      In the state of entanglement … where speed of light is ? .

      No, you are mistaking correlation for causality, or perhaps erroneously alluding to instantaneous “Copenhagen collapse” of the wavefunction. Bell test experiments tests the former as wrong (relativity applies), observations of decoherence implies the latter is wrong.

      At the final state of a collapse you get a situation where mv^2/r= G m1m2/r^2 and you see that momentum and gravity cancel out each other.

      Well, duh. You assumed that, right there. LOLogic: “Circular argument iz circular”.

      • Han Vinke says

        -“The above and below constitutes another two useless comments in the “DE war” against accepted science”

        I leave that to the reading public. As a scientist you should consider other possibilities – I simply point at a possible alternative. I fully agree DE & DM are real within the current theory, no objection at all.

        -“Except of course in our universe, where the expansion is accelerating (due to DE, btw).”

        This universe IS known to expand with a factor 3H/ln2. Exponential inflation simply means that length grows proportional to exp(H?t). The rate r at which the universe doubles its volume is simply r = 3 H/ln2. The factor 3 comes from spatial volume being 3 dimensional.

        -“As it expands, so does too the ability to increase entropy – it expands”

        In this universe there is just one force creating entropy – gravity. As the universe expands the effects of gravity creating entropy will diminish. Producing in time less power to drive this expansion.
        At the same time there is accelerated expansion. How do you do that? By adding an unseen DE, with no further explanation.

        – “If the speed of light is coupled to loss of information And how do you do that?

        Simple – you can see that if space contracts there is a loss of spacial information. Volume is a third power where r is a second power. Length diminishes proportional to exp(H?t). There is a difference between 2 dimensional and 3 dimensional space. Volume shrinks to a factor r^3 where r in flat space shrinks to a factor 2. Volume change= 4/3pi(6r^2+12r+8). This will lead the universe in time to appear as flat space.

        This loss of 3D information maybe proportional to the speed of light. Because light is just an expression of entropy. And entropy just slowly starts rising in a contracting universe.

        – “Degree of entanglement shouldn’t affect availability of energy levels (entropy). It is the same number states regardless of entanglement.” I will not debate eigenstates here. But ACHIEVING entanglement is something that can only done by maximizing entropy (isolate parts from the rest of the universe).

        – Yes I assume that in the finale state of a collapse you will have a situation where mv^2/r= G m1m2/r^2. I see no circular reasoning at all. It would show that a collapse cannot go on forever. And it shows clearly the relation between momentum and gravity. And time will create entropy because in a shrinking universe the momentum will increase.

        In an expanding universe you cannot explain the apparent increase of momentum in black holes. In a contracting universe you would be able to explain the apparent increase in momentum.

  10. Dark energy is confirmed to be uniform and smooth, which means that its strength is the same no matter the distances between galaxies The only other fundamental force that does not diminish with distance, is the strong force, and the nuclear force is ONLY a residual force of the strong force. We see all EM, Gravity, and Weak forces at all scales in the universe. But NOBODY looks for the strong force in the large scale structures in the Universe ! Dark energy like the strong force both do not diminish with distance, but remain constant steady in strength ! After a limiting hadron size distance has been reached, the strong force remains a steady constant strength of about 10,000 newtons, no matter the distance between quarks. Normal matter everywhere in the Universe, is made principally of leptons and quarks, all of which carry charge. Baryons are made up of quarks. the positive nucleus is >99.9% mass of the atom. Gluons zip between quarks, and carry the strong force. Charge is analogous to mass in SR, where frame-dragging and the geodetic precession or thomas effect in EM are analogs. Quarks have a 3 color property analogous to charge in EM. Newtons G constant is analogous to Coulomb’s force constant k. QUESTION PLEASE SCIENTISTS TO ANSWER : Why can’t the smooth uniform Dark energy force, be the strong force, in QCD ? 99% of the mass of protons and neutrons is QCD binding energy. Pions contain the quark-gluon sea ! Please investigate this theory.
    http://Hologramuniverse.wordpress.com

  11. Anonymous says

    There are some mentions of aether theories here. The comparison between dark energy and aether theory might be made with the question of how many degrees of freedom do there exist with space. In the old aether theory the motion of a particle or an electromagnetic wave was tied to its interaction with this fluid of sorts which pervades all of space. This meant electromagnetic propagation was dependent on its interaction with this fluid. We might then think of this fluid as made of atomic-like particles, similar to water, which means the propagation of light ultimately involved a complex interaction with a vast number of these particles. The Maxwell theory required no such interactions at all, but many were convinced there was some underlying aether interaction. Each on of the “particles” which defined this aether had a degree of freedom, or energy, and for N of these particles in a volume of space there is then an energy E = nK, K = kinetic energy of each particle, and by an equipartition theorem K = 3kT/2. It has an entropy and effective temperature and so a volume of space has a huge entropy E = ST, S = entropy = (3n/2)k, k = Boltzmann constant.

    In an analogous way we do not know how the quantum field vacuum of the universe is as small as required for a cosmological constant ? ~ 10^{-54}cm^{-2}. The cosmological constant defined as due to a source will then by the Einstein field equation

    ? = (8?G?/c^4),

    where ? is the vacuum energy density due to quantum fields. The quantum vacuum energy is due to a nonzero commutator of momentum and position which results from quantization. I will not belabor this point much, but this is measurable in the Casimir effect. However, what that measures is a change in the vacuum energy due to the confinement of the vacuum in an apparatus. What we do not know is the energy density ? of the universe at large. Our current theories give a huge value. String theory does reduce this from 10^{123} times what is expected by standard quantum field theory to about 10^{40} times what we expect. That is progress, but it is not the final goal. This problem is similar to that of the old aether theories — we are overcounting the number of physical degrees of freedom.

    I think there is some deep issue with respect to symmetries on low and high dimensional spaces which reduce the numbers of degrees of freedom from these huge values. In other words, the symmetries in a large dimensional space (which would have a large number of degrees of freedom) have vacuum structure defined on low dimensional spacetimes associated with conditions near event horizons.

    LC

  12. Anonymous says

    There are some mentions of aether theories here. The comparison between dark energy and aether theory might be made with the question of how many degrees of freedom do there exist with space. In the old aether theory the motion of a particle or an electromagnetic wave was tied to its interaction with this fluid of sorts which pervades all of space. This meant electromagnetic propagation was dependent on its interaction with this fluid. We might then think of this fluid as made of atomic-like particles, similar to water, which means the propagation of light ultimately involved a complex interaction with a vast number of these particles. The Maxwell theory required no such interactions at all, but many were convinced there was some underlying aether interaction. Each on of the “particles” which defined this aether had a degree of freedom, or energy, and for N of these particles in a volume of space there is then an energy E = nK, K = kinetic energy of each particle, and by an equipartition theorem K = 3kT/2. It has an entropy and effective temperature and so a volume of space has a huge entropy E = ST, S = entropy = (3n/2)k, k = Boltzmann constant.

    In an analogous way we do not know how the quantum field vacuum of the universe is as small as required for a cosmological constant ? ~ 10^{-54}cm^{-2}. The cosmological constant defined as due to a source will then by the Einstein field equation

    ? = (8?G?/c^4),

    where ? is the vacuum energy density due to quantum fields. The quantum vacuum energy is due to a nonzero commutator of momentum and position which results from quantization. I will not belabor this point much, but this is measurable in the Casimir effect. However, what that measures is a change in the vacuum energy due to the confinement of the vacuum in an apparatus. What we do not know is the energy density ? of the universe at large. Our current theories give a huge value. String theory does reduce this from 10^{123} times what is expected by standard quantum field theory to about 10^{40} times what we expect. That is progress, but it is not the final goal. This problem is similar to that of the old aether theories — we are overcounting the number of physical degrees of freedom.

    I think there is some deep issue with respect to symmetries on low and high dimensional spaces which reduce the numbers of degrees of freedom from these huge values. In other words, the symmetries in a large dimensional space (which would have a large number of degrees of freedom) have vacuum structure defined on low dimensional spacetimes associated with conditions near event horizons.

    LC

  13. jblanque says

    The problem is with fundamentals.
    What if there were no big bangs? What if the redshift doesn’t happen by way of an acceleration of the rest of the Universe away from our own Galaxy?
    There is the CREIL effect. There are some other alternative explanations.
    Cosmologists are more and more like hammers; they see everything as a nail.
    The current level of the Cosmology remembers me the Ptolemy times, when everyone was explaining the epicycles, but only a few were near the truth, questioning the fundamentals.

  14. Torbjörn Larsson says

    First I thought Steve was playing the prosecutor card and tried to show why standard cosmology is preferable over naive “observation driven” ad hoc hypotheses. Because an interpretation of “no energy” and “just expansion” is so confused.

    But from a comment below, I assume it is serious: “As a science journalist wannabe, I am just objecting to media reports stating DE is real – when the good science done here has only confirmed accelerating expansion.”

    OK. So this seems confused to me, and trying to clarify why will constitute my comment:

    – “from this perspective, the primary requirement for dark energy is not as a driver of expansion, but as a hypothetical entity required to sustain the flatness of space”

    The very reason why dark energy was discovered is because of the accelerated expansion. This is what similar Wikipedia articles on DE itself tells you.

    It is true that it doesn’t mean expansion always, “a strong constant negative pressure in all the universe causes an acceleration in universe expansion if the universe is already expanding, or a deceleration in universe contraction if the universe is already contracting.”

    That it means space is flat is an _outcome_ of standard cosmology. Go read the papers on the WMAP site; you don’t even have to force it, it is a natural consequence.

    If you want flat space as a prediction, it is inflation within standard cosmology that predicts it. That has nothing to do with DE (except setting up the circumstances so it is causing accelerated expansion instead of decelerated contraction).

    – “It is called ‘energy’ as it is evenly distributed”

    It is called energy because it behaves like an energy term in GR models. And AFAIU _only_ energy can have the “negative pressure” (acting repulsively). [Disclaimer: Haven’t studied GR.]

    – “A plausible mechanism that accounts for the input of energy out of nowhere”

    As someone said, surely once you accept spacetime out of nowhere, energy out of nowhere is easier to swallow!?

    But in fact there is no energy created. Flat space, remember? I.e. zero energy. DE makes up for a deficit, unless you would want to explain the creation of negative energy.

    – “a plausible form of energy that is both invisible”

    The parsimonious hypotheses is that it is a cosmological constant. If so, the parsimonious hypotheses for _that_ is already known vacuum energy, the sum of zero point energy of particle fields. Which is indeed both invisible and know to exist.

    – “and that somehow generates the production of more space-time volume”.

    No, that is the expansion itself that does that, remember? What it does is accelerate the ongoing process (or decelerate, if we lived in a contracting universe). Different thing.

    – “no way has anyone confirmed that dark energy is real.”

    I don’t think science deals in confirmation. But for all practical purposes, yes. DE has passed another test, standard cosmology (and so the existence of DE) is more “confirmed” than before.

    • Anonymous says

      The worst thing one could do is have negative energy! That would really foul things up. Dark energy is dark because we do not understand its real nature. We know it is there, but the nature of the quantum fields which comprises it is unknown.

      DE manifests itself as an accelerated expansion. Ordinary gravity by mutual attraction of galaxies would cause the expansion to decelerate. The best reason for the word “dark” is that we do not know what the source of this spacetime curvature is. Think of Maxwell equations. The Maxwell-Faraday equation curl H = 4?J + ?D/?t can involve a current source J. The Einstein field equation is similar in one can have curvature without a source, but in the case of the expanding universe there is some source, the quantum vacuum, which causes flat space to constantly expand with time. Our situation would be analogous to having some form of electromagnetic radiation occurring from somewhere, but where we can’t detect the source.

      LC

      • Jon Hanford says

        Thank you. Thank you. Thank you, TLO and LC, for delving into the evidence for DE and pointing out some of the irrelevant arguments against it’s existence. There ARE multiple lines of evidence supporting the existence of DE (and not just the two _independent_ supernovae studies in ’98-’99): http://en.wikipedia.org/wiki/Dark_energy#Evidence_for_dark_energy

        The very existence of DE certainly came as a surprise to most if not all cosmologists. The facts are what they are. Scientists studying DE are not doing so out of faith or some belief in it’s existence!

        (…and if scientists are just “making it up” to procure grant money, a common sentiment among some, they surely could be MUCH more creative o_O)

      • Anonymous says

        To be honest when I first read a short release on this I did a major
        head slap. “Of course I thought, it is a de Sitter spacetime.” I
        thought that before any theory was pressed to the problem. It was one
        of the great epiphanies in my life, for instantly I knew how this
        worked, just as I have written in some of these blog posts.

        The unknown is why does the acceleration seem so slow? A vacuum should
        be large and the universe would accelerate away enormously. Of course
        this gets into the problem of how inflation ends, when the universe was
        expanding away at a huge rate. Supersymmetry does not help much in a
        funny way, for broken supersymmetry raises the zero point energy from
        zero to a finite value; almost the opposite of what we observe.

        LC

  15. Torbjörn Larsson says

    Besides violating policy, it is wrong. Of course scientists use hammers (developed methods) on everything that looks like a nail. It is called “to make progress”.

  16. John Stepp says

    I think the point made in the article, that we talk too much about dark energy* is a good one.
    Therefore I will not point out the feeding frenzy (oh hell, I just did) involved in trying to explain it here.
    Funny though**.

    *Should that be in caps?
    **There seems to be some circular logic going on around here, where can I get some?

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