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New Clues About the Nature of Dark Energy

Posted by michael on from the spaced-out dept.

Jim Mansfield writes "With the Hubble space telescope no longer being serviced by NASA, it's good to see one of their hardest working and most famous satellites in the news again. According to their press release on the nature of dark energy, Einstein may have been right after all - and even if he turns out to have been wrong, it seems that dark energy is not going 'to cause an end to the universe any time soon' ... whew, that's a relief." See also a space.com story.

22 of 166 comments (clear)

  1. ...End of time? by nharmon · · Score: 5, Interesting

    If the repulsion from dark energy is or becomes stronger than Einstein's prediction, the universe may be torn apart by a future "Big Rip," during which the universe expands so violenty that first the galaxies, then the stars, then planets, and finally atoms come unglued in a catastrophic end of time.

    This is quite a shift from the implosion theory that results in pre-'Big Bang' conditions causing a loop in time.

    1. Re:...End of time? by sbma44 · · Score: 4, Interesting

      Yeah, but that theory's been out of vogue for a while. It's theoretically tidy (and therefore attractive), but I believe the last few years' astronomical data has shown the universe's rate of expansion is accelerating. Something new woulkd have to turn up for the Big Crunch to come into vogue again.

    2. Re:...End of time? by SashaM · · Score: 3, Interesting

      I always wonder whether the "It's accelerating so it'll drift apart in the end" folks understand basic calculus. The rate of expansion accelerating doesn't mean it will continue accelerating - the third derivative of x(t) could be negative, or the fourth, and then the fifth could be positive again. You need to know all of the derivatives to know the function itself (and even that isn't true for some functions - e^(-1/x^2) IIRC).

    3. Re:...End of time? by Anonymous Coward · · Score: 2, Interesting

      In a Friedmann-Lemaitre cosmology, if the universe is dominated by mass, then the rate of expansion cannot accelerate.

      This is why the observation of an accelerating rate of expansion (first convincingly made in 1998) indicates that there is something other than mass... and that something, whatever it is, in fact dominates the evolution of the universe at the moment.

      As for whether the universe drifts apart in the end... you are right that this is a strong prediction. But it is at least a feature of a fairly general class of models for dark energy. I'm pretty sure that, at this point, most astrophysicists think it is quite likely that the universe will expand forever.

  2. The future of the Unvierse by Neuropol · · Score: 4, Interesting

    After we have all (I assume that doesn't include any creationsists) adhered to the scientific theory of The Big Bang and the beginning of the Universe as we know it, I can only think that we can begin to accept the fate of the Universe.

    As dark matter destabalizes, essentially matter is pulled apart at the atomic level. Some thing tells me The Big Rip, is what we are in for.

    The universal constant is a nice theory and would be the better, happily-ever-after option, but in reality it seems a little far fetched if the expansion of the Universe is accelerating. It means that eventually speed will over come matter and every thing disintegrate and get ripped apart.

  3. Relief? by philbert26 · · Score: 5, Interesting
    If a big crunch doesn't end the universe, then heat death will. Eventually the universe will reach a state of maximum entropy, and nothing interesting will happen.

    Before it gets to that stage, stars will become a rare occurance. The chain of star birth and death results in smaller stars, and once stars get small enough they become like our Sun -- too small to undergo the explosive death that would provide enough mass for future stars. Eventually there won't be enough clouds of hydrogen massive enough to start nuclear fusion.

    Given enough time, current theories suggest that the universe seems to be screwed either way.

    1. Re:Relief? by thelasttemptation · · Score: 2, Interesting

      Tho what's to say that we won't have the tech to scoop up the matter and make our own stars? Maybe the universe counts on intelligent life to keep it going?

    2. Re:Relief? by sploxx · · Score: 3, Interesting

      Being a physics student, I really don't understand the heat death argument. The heat death argument relies on the 2nd law of thermodynamics -i.e. there can't be an entropy loss. But this is not exactly true. It is unbelievable improbable that an entropy loss occurs. If one supposes that time goes one after a heat death, there can and will be a restructuring(*) of the universe. The probability that a restructuring happens is unbelievable small. But as time approaches infinity, the probability that this happens will approach one. Of course, for us, that doesn't really matter much because we'll all dead before. (*) - restructuring here: Formation of stars a solar-system and something like an earth.

    3. Re:Relief? by xigxag · · Score: 4, Interesting

      It's true that entropy can decrease when matter/energy enters a spontaneously ordered state, e.g. all the gas collects in the corner of the room. In itself that's infinitesimally unlikely, yet still possible. But in the case of the universe we live in, there's an additional wrinke. The edges of the "room" are expanding faster than the speed of light. Which means, eventually, every particle will disappear over every other particle's event horizon, and it will be impossible to put them back together again.

      Another person downthread alludes to the idea of surviving through increasing entropy by presumably using decreasing amounts of energy. In other words, as the universe gets older and colder, there will be, say, 1/100th the free energy available utilizable by a heat pump. So a form of alife could simply run itself 100 times more slowly and thereby experience time subjectively at a linear rate. Right? Wrong. Two problems pop up. One is proton decay, which means the building blocks of any sentient computer will eventually decay on their own. And second is the cosmic background radiation. Machines work on the principle of taking in energy and outputting it in the form of waste heat. But once the universe has cooled down to the same temperature as the CBR, it will be impossible for any machine to output waste heat. It will cease to function. There is some work being done on reversible computing which might, in the long run, be able to tackle the second problem, but not the first.

      --
      There are two kinds of people: 1) those who start arrays with one and 1) those who start them with zero.
    4. Re:Relief? by naasking · · Score: 2, Interesting

      Machines work on the principle of taking in energy and outputting it in the form of waste heat.

      Machines work on the principle of energy conversion; waste heat is just an unwanted side effect of imperfect energy conversion.

      But once the universe has cooled down to the same temperature as the CBR, it will be impossible for any machine to output waste heat.

      Once the universe cools to CBR levels, there will be no differences in energy levels, and thus no energy flow is possible (thus, no motion, no conversions, etc).

      --
      Higher Logics: where programming meets science.
    5. Re:Relief? by barawn · · Score: 2, Interesting

      One is proton decay, which means the building blocks of any sentient computer will eventually decay on their own.

      You do realize that no one has seen one proton decay. Not one, right? Proton decay assumes supersymmetry is valid, and as many physicists have noted, supersymmetry is an excellent theory, which predicts a whole host of particles - half of which have been discovered.

      Proton decay isn't real - not yet. And there is no a priori reason to assume that it is. Its current lower bound is 10^33 or so years. At this point you can't simply claim that proton decay happens - in fact, you'd rather claim that it doesn't.

    6. Re:Relief? by thelasttemptation · · Score: 2, Interesting

      So the Second Law of Thermo says we can't scoop up matter and shove it together?

      Hrm. That's intresting...

  4. non-physical physics by Space+cowboy · · Score: 4, Interesting
    Right now we're about twice as confident than before that Einstein's cosmological constant is real,


    Of course, 2x (near-as-dammit-zero-certainty) is pretty much the same as (near-as-dammit-zero-certainty)...

    A lot of new physics does seem to be increasingly theoretical and "out there" on the proverbial limb. It would be good for the practical lot to catch up with the theoretical lot... unfortunately, trying to verify these out-there hypotheses seems to involve larger and larger atom-smashing accelerators. Lets just hope they don't need to find the 'Higgs Boson' (hint: ohhh WAAAY ohhh, ummm barrray :-)

    Simon
    --
    Physicists get Hadrons!
    1. Re:non-physical physics by grogzilla · · Score: 2, Interesting
      Understanding dark energy and determining the universe's ultimate fate will require further observations.


      I'd say this is a bit flimsier limb to stand on. For a bit of perspective, let's consider the sheer mountains of daily empirical data that a meteorologist has to work with, and yet the "ultimate fate" of weather can rarely be predicted more than a few days in advance.

      Of course the size of the system does come into play, and the scope of the effects being observed. It may be far easier to understand the largest of systems (universa level) than the smallest (sub-quantum level), and the mid-point (human-size events) may be the most difficult. Just thinking out loud here, IANAAP (i am not an astro-physicist)

      But does anyone else find at least mildy amusing, the apparent ease with which such a whimsical statement is made?

    2. Re:non-physical physics by fermion · · Score: 2, Interesting
      There are two types of out there physics. The type that can be proven to not be true by observation, and those that can't be proven to not be true by observation. Which is a little different from being shown to be close enough to reality. The former go away and the later continue to provide us many hours of speculative enjoyment. The common feature of all of these is that they solve some theoretical problem. Fortunately solving some theoretical problem is not enough and the theories tend to languish until some pratical means of verification can be developed.

      It was only a hundred years ago that Planck looked the black body radiation problem and the ultraviolet catastrophe and sent of a postcard claiming that fatal flaw was the assumption that energy was continuous. He threw out that faulty assumption, did up the math, and heralded in a world of devine dice, half dead cats, and apparently solid objects moving through apparently solid walls. In essence, rubbish.

      The process of identifying assumption (the hard part) and challenging those assumption is what has brought the western world out of morass partially created by a boorish devotion to greek philosophy and political control by the Church.

      --
      "She's a scientist and a lesbian. She's not going to let it slide." Orphan Black
  5. Re:Dark Matter and Ether by Aardpig · · Score: 5, Interesting

    and in very complex systems Newton can't be used (chaos)

    Hang on a moment; I thought the Lorenz attractor (which is the canonical example of chaos) was based on a system obeying Newtonian mechanics.

    Why would it be so strange if systems with enormous scales and very small accelarations would not obey Newton's laws?

    This is the line of thinking which led Mordechai Milgrom to propose Modified Newtonian Dynamics (MOND) in the 1980s. MOND posits that Newtons second law (F=ma) is modified when the acceleration is very small. It is able to "explain" the unusual rotation curves of galaxies, without the need to invoke dark matter. It can also explain phenomena which the dark matter hypothesis can't, such as the Tully-Fisher relationship observed in the surface brightness of galaxies.

    However, its important to remember that MOND cannot be considered a physical theory; it is more of an empirical modification of known physical laws (like the Lorentz transformation was), which still awaits a physical explaination.

    --
    Tubal-Cain smokes the white owl.
  6. Re:Dark Matter and Ether by quinkin · · Score: 2, Interesting
    Oh man... where to begin.

    You say they 'believe', then call it a hypothesis - one is faith the other is science.

    "otherwise those huge systems of galaxies don't obey Newton's laws" - As the story notes, the proposed dark matter is related to Einstein's cosmological constant. Now as to why Einstein 'believed'(sic) in it? Because that is what observation showed. The question here is why and is it truly constant.

    "It does feel a bit like Ether to me to introduce a form of matter/energy which has never been measured at all." - Now that I can agree with.

    In my usual agnostic way, I am certain that dark matter might exist.

    Q.

    --
    Insert Signature Here
  7. Re:Dark Matter and Ether by mmusson · · Score: 2, Interesting

    I find it strange that scientists 'believe' in dark matter. ... I think dark matter doesn't exist.

    Dark matter does not necessarily mean exotic matter. There have already been detections of white dwarf stars at the edges of a galaxy. These are just very very dim stars. This discovery means that a significant part of the mass attributed to dark matter could be ordinary matter in dead stars that are no longer radiating at currently detectable levels.

    --
    SYS 49152
  8. Re:Einstein was wrong anyway by GMFTatsujin · · Score: 3, Interesting

    This whole "Eistein was right after all" angle is misinformed. He wanted a static universe because that was the historic conception of the universe. His own science didn't allow for it, but he wrangled an equation for one out of it anyway. Turns out he was wrong, is wrong, and will always have been wrong. Einstein's motivation for putting in the cosmological constant was ideological, not observational -- and that's a recipe for Dumb Science.

    Dumb Science isn't "right after all," no matter how much you respect the guy who came up with it.

  9. A "Circular" argument? by Cragen · · Score: 2, Interesting

    Whatever happened to the idea that something going away from us would eventually "re-appear" on the opposite side of the Universe and start heading towards us? (I have no clue what hypothesis was/is called.) Perhaps everything expanded to the edge, ALREADY, and is now "expanding" towards the center, again, and is therefore being more attracted to everything else cause it's getting CLOSER! (I have to stop now. My brain is going to take a little break.) Whew. Next?

  10. Re:Dark Matter and Ether by kisak · · Score: 2, Interesting

    First of all Newton was not proven wrong by quantum mechanics and the general relativity, in a way Newton's law has been put on a more secure footing by being supported by these two breakthroughs of modern physics. Sure, modern physics understands that Newton's laws don't apply for high velocities (close to the speed of light, c) and very small systems (when Planck's constant h becomes a siginificant number). But both quantum mechanics and general relativity gives you Newton's equations when c = infinity and h=0, which means that for most situations Newton's laws are "exact". Even to simulate molecules and galaxies Newton's equations are "exact enough".

    Second, chaos is a general property of any differential equation which is complex enough. So, chaos can appear in classical mechanical systems and are not related to quantum effects or relativity (even though chaos phenomen also appear in these).

    Ether was discharged as a hyphotesis by Einstein and others since something that could not be experimentally observed or was not needed theoretically to explain the observations, is per definition an empty concept. If dark matter can explain experimental observation or makes a nice theoretical framework for what is observed, then one should not discharge it even though it is still a bit an empty concept (which is why it is called "dark matter" I guess, can't be seen, don't know what it is). The judge is still out if dark matter will help us in understanding the universe, but it is better to start by building on the fundament of previous physics, instead of throughing out Newton's laws that have passed the test of three hundred years of observations.

    --

    --- guns don't kill people, people with guns kill people ---

  11. Re:http://www.ebtx.com/ntx/ntx16.htm by Anonymous Coward · · Score: 1, Interesting

    Is the universe expanding, or are we all shrinking? From a relative point of view there is no difference.

    That's an interesting idea, and it would be nice to know, but what difference does it make?

    I mean, I want to be careful to not say that usefulness defines truth, but wouldn't all of our theories work exactly the same way if that were true?