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Space Science

Huge Lenses To Observe Dark Energy 121

Posted by timothy
from the that's-what-my-huge-lenses-do-too dept.
Iddo Genuth writes "UK astronomers, as a part of the Dark Energy Survey collaboration, have reached a milestone in the construction of one of the largest ever cameras to detect dark energy by completing the shipment of the glass required for the five special lenses. Each step in the process of completing this sophisticated camera brings scientists closer to detecting the invisible matter that cosmologists estimate makes up around 75% of our universe."
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Huge Lenses To Observe Dark Energy

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  • Oymoron anyone? (Score:3, Insightful)

    by plasmacutter (901737) on Friday July 04, 2008 @12:57AM (#24055195)

    If it is detectable in any way, it's not "dark" anymore!

    Wouldn't it be better to call it an effort to "define" dark energy?

    • by SEWilco (27983) on Friday July 04, 2008 @01:10AM (#24055289) Journal
      "I see nothing... nothing!" Yup, must be dark energy out there.
    • Re:Oymoron anyone? (Score:5, Interesting)

      by pudro (983817) on Friday July 04, 2008 @02:46AM (#24055741)
      Basically, they will take more accurate measurements than before. Then they will look at how badly gravity-only models fail. They will adjust this as much as possible using the imaginary qualities of "dark matter". When they still come up well short of getting it right, then the rest will be explained away by assuming "dark energy" wherever needed to adjust for the failure.

      When "96% of the universe" is only detectable by how your model fails with the visible stuff alone, measurements of the visible stuff become useless. It isn't even science at that point.
      • Re:Oymoron anyone? (Score:5, Insightful)

        by Urkki (668283) on Friday July 04, 2008 @06:51AM (#24057047)

        When "96% of the universe" is only detectable by how your model fails with the visible stuff alone, measurements of the visible stuff become useless. It isn't even science at that point.

        I'd say it is. I'm under the impression, that dark matter & energy hypothesis (I think it's fair to call it a hypothesis at this point) is the simplest explanation for all the observations that we have. So I'd say it's very much science, as good science as we're capable of.

        Feel free to provide a nicer model that still explains the current observations, though. I'm sure the Nobel Foundation will reward you for your efforts if you get it right enough!

        • by Fyzzler (1058716)
          I'd say it is. I'm under the impression, that dark matter & energy hypothesis (I think it's fair to call it a hypothesis at this point) is the simplest explanation for all the observations that we have. So I'd say it's very much science, as good science as we're capable of. Feel free to provide a nicer model that still explains the current observations, though. I'm sure the Nobel Foundation will reward you for your efforts if you get it right enough!

          It's String and Fairy dust, I say!

          If you are l
          • by Urkki (668283)

            If you are looking for a nicer model, how about this one.,
            http://en.wikipedia.org/wiki/Modified_Newtonian_dynamics [wikipedia.org]

            Can you tell me, does this explain/produce the wobble observed in this [slashdot.org] experiment, for example? 'Cos if it doesn't, then there's some work to be done with it still, before it's worth considering as a valid alternative...

            • I think the wiki made pretty clear that it's not a new theory. It intends to be a kind of "relativity-lite" in the sense that relativity proved that the existence of an aether was not necessary to explain the wave-like effects, MOND demonstrates that the existence of "dark" matter might not be necessary to explain astronomical observations.

              Surely you can agree that postulating the existence of matter that doesn't behave anything like anything we can observe in the lab, except gravitational interaction, AND

              • by Urkki (668283)

                Surely you can agree that postulating the existence of matter that doesn't behave anything like anything we can observe in the lab, except gravitational interaction, AND that this matter composes 90% of the universe is somewhat less than ideal.

                Frankly, I don't see how discovering that current physical theories need to be seriously tweaked is any more ideal than discovering that there's more to existing stuff than meets the eye.

                Discoveries about nature of existing stuff have been far more frequent (atom structure, nucleus structure, quarks, neutrinos, Casimir effect, the fundamental forces...) than discoveries about basics of core physical theories (realtivity and quantum mechanics). So in this case, my money is on again discovering that new stuff

                • by Hojima (1228978)

                  Your view of modern physics is similar to the view that physicists of the past shared with classical physics (the physicists believed our tools were not accurate enough). IMHO, dark matter is a shortcut that scientists are currently taking to get past the fact that they can't predict things perfectly the way they are. It would make more sense that there is some small, nearly undetectable property of matter that can only be expressed enough to be detected over the span of the universe. Who knows, the vacuum

          • It's String and Fairy dust, I say!

            Turtles, all the way down.

        • by pudro (983817)
          I'd say a basic electro-dynamic model explains everything far more simply and produces far less surprises. It isn't perfect, but it matches what we see far better than the "96% dark stuff" theory.

          And before you even imagine that my suggested theory has ever been "proven" wrong, I will tell you the two biggest ways in which attempts to prove it wrong have failed:

          1. They almost always attack assumed properties of an electro-static model (i.e. not the model in question).

          2. The "flaws" they point out a
      • Re: (Score:3, Insightful)

        by gstoddart (321705)

        When "96% of the universe" is only detectable by how your model fails with the visible stuff alone, measurements of the visible stuff become useless. It isn't even science at that point.

        How can observing the only stuff we can possibly observe be useless and not even science?

        Are you proposing we start looking at all of the things we can't see with the technology we don't have because that would be better somehow? Is it more efficient to skip straight into the stiff you can't even conceive of yet?

        We can try

      • by Loraque (201014)

        Almost everybody doesn't know what the SUPER smart guys, that think about CRAZY stuff, and have no option to hypothesize things... up until someone builds new tools to answer questions that they asked.

        These guys are going to get it WRONG a fair amount of the time. Wrong is just as good as right, with questions as whacked out far out as these are.

        The Science you are thinking of is in how it is applicable. That is totally not really the job of these other guys.

        Dreamers, if it makes it easier. Thank GOD there

        • by pudro (983817)

          These guys are going to get it WRONG a fair amount of the time. Wrong is just as good as right, with questions as whacked out far out as these are.

          You miss the point. While they are getting it wrong, they learn nothing from their mistakes and lead us further down a dead end road. Meanwhile, there are people out there trying to lead us down other roads whose nature is not yet known. These other paths could be the correct path, or perhaps another dead end. Either way, to continue down the same dead end we've been on is a waste of time.

    • Re:Oymoron anyone? (Score:5, Informative)

      by dargaud (518470) <slashdot2@nOspAm.gdargaud.net> on Friday July 04, 2008 @03:14AM (#24055929) Homepage
      Well, it doesn't mean that the lens sees it, but that the lens can see the effect it has on the things you _can_ see. For instance you look at a galaxy field and you notice that some are distorted in certain ways, you can infer that there's a hidden mass between you and those galaxies. The LSST [lsst.org] project on which I work has a similar goal.
    • Re: (Score:3, Funny)

      by bobbozzo (622815)

      I don't think Nibbler's gonna be too happy with someone sticking a huge lens up there...
       

    • by 4D6963 (933028)

      If it is detectable in any way, it's not "dark" anymore!

      Hey I didn't know "dark" now meant "invisible", thanks for the update! And while you may argue that something dark is invisible on a black background you have to remember that there's hardly any sort of truly black background in the sky.

      • Re: (Score:3, Informative)

        by gstoddart (321705)

        If it is detectable in any way, it's not "dark" anymore!

        Hey I didn't know "dark" now meant "invisible", thanks for the update!

        No, really. He's right.

        From Wiki [wikipedia.org]:

        In physics and cosmology, dark matter is matter that does not interact with the electromagnetic force, but whose presence can be inferred from gravitational effects on visible matter.

        If we could detect it though any other mechanism than inferring it exists based on gravitational effects, it literally would cease to be dark matter -- because that's h

        • by 4D6963 (933028)

          If it is detectable in any way, it's not "dark" anymore!

          Hey I didn't know "dark" now meant "invisible", thanks for the update!

          No, really. He's right.

          Translation : dark means invisible. Quite what I said.

    • by jeepien (848819)

      If it is detectable in any way, it's not "dark" anymore!

      That's fine. Objective met.

      Then they'll just start referring to it as "plaid matter" or whatever.

    • by edittard (805475)

      In other news, after the world's biggest flashgun (with a guide number of 47 gazillion) reaches completion, scientists begin the search for 3.2 squillion AA cells.

  • dark energy? (Score:5, Insightful)

    by ILuvRamen (1026668) on Friday July 04, 2008 @12:59AM (#24055217)
    They're making it sound like dark energy is visible light. If it's "dark" that means it's undetectable by normal means like giant lenses for instance. How could you just see dark energy? Isn't it more like something you'd detect with sensors, not a giant lense? But no, straight out of the article, they're gonna use it to for "detecting the invisible matter" because it has "advanced optics." Btw they said MATTER, not energy so apparently that's what they're actually looking for. Well that would officially make it dim matter, wouldn't it? Like I always thought, dark matter is just matter without a whole lot of light shining on it cuz it's in between galaxies and stuff.
    • Re:dark energy? (Score:5, Informative)

      by FooAtWFU (699187) on Friday July 04, 2008 @01:06AM (#24055263) Homepage

      If you can get good enough optics, you can watch regular light and detect when it's being affected somehow by dark matter.

      Confusing enough summary though.

      • Not exactly (Score:5, Informative)

        by Moraelin (679338) on Friday July 04, 2008 @04:40AM (#24056371) Journal

        That's somewhat incorrect, and makes a hash of two unrelated things too:

        1. Dark matter. Unlike what its name might imply, it isn't dark as in "light absorbing". It's dark as in, it doesn't interact with light at all, except through gravity.

        It's only "dark" in the same way as a sheet of glass is dark against the night sky.

        But even that metaphor is misleading. "Dark matter" is just a name for a lot of mass that should be there according to calculations (or our understanding of gravity is completely broken at large scales), but hadn't been observed. It's just a funky name. It doesn't mean it's actually dark in any form or shape.

        The best example of a scale where this is visible is inside a galaxy. With just gravity determining the speed of rotation around the centre, the stars closer to the centre should rotate faster than those on the edges. (In the same way as Mercury rotates around the sun once every 0.24 years, Earth in a year, and Pluto in 248 years.) But galaxies don't seem to rotate that way. They rotate more like a solid texture, so to speak. So there must be some mass distributed through the disc, in addition to what we see.

        But again, the whole point is that we can't see it. If it were just a cloud of pitch-black baryonic matter, that would actually be easy and comfortable. We'd just do what you said: look at what happens to the light of stars behind it. Since it's plenty of it inside a galaxy, we have plenty of stars to look at and notice if something like that was between us and them. But all we can see is some extra gravity, with all that involves for both star movement and gravitational lensing.

        A much more accurate name would be "completely transparent matter."

        2. Dark energy.

        This is an even funnier concept. With all that mass in the universe, there's gravity all around. Duly noted, the gravity pull of a hideously distant galaxy is really tiny, but it's there. The universe expansion should slow down as gravity pulls everything towards the centre. The funny thing is: it doesn't. It's actually accelerating, and weirdly enough, the farther something is, the faster it seems to accelerate away.

        There is _something_ that pushes stuff away from the centre, and it's not like any force we already know.

        It's also something we'd be hard pressed to reproduce in a lab. Whatever it is, it's insignificantly weak at small ranges, and only starts to matter at very very very large distances. Even at galactic scales (hundreds of thousands at light years) it seems to do practically nothing at all, but move a few _billion_ light years away, and you start seeing whole galaxies accelerating away. It's not something you can reproduce in a lab.

        It's also weird in that a normal energy (e.g., the potential energy in a compressed spring) would get used up, or rather converted into work, as it pushes stuff away. So the force would logically diminish. This one only seems to grow stronger.

        So basically this big "WTF?" is what's called "dark energy". There's some energy that's pushing the universe apart, but we don't know what it is, and how to detect it.

        • The universe expansion should slow down as gravity pulls everything towards the centre. The funny thing is: it doesn't. It's actually accelerating, and weirdly enough, the farther something is, the faster it seems to accelerate away.

          IANAAP, but shouldn't the universe be working in a similar fasion regardless of where you choose to look? I don't know how many times there have been adjustments to the age of the universe - with conflicting ages reported by different teams. If they are all subscribing to the same set of theories, how can this be?

          IANANS but I suspect that before the nuclear forces where properly understood, there was a lot of "dark matter" located near the atoms.

          Although I confess to not knowing a whole lot about the

          • Re:Not exactly (Score:5, Informative)

            by Moraelin (679338) on Friday July 04, 2008 @07:54AM (#24057383) Journal

            Well, that's how science works. If someone comes up with a better theory that doesn't involve "ether", we'll go with that one.

            There are several hypotheses to that effect already. One is for example the Modified Newtonian dynamics [wikipedia.org], which pretty much just messes with the F=ma to explain galaxy rotation.

            Another possibility would be to mess with gravity itself. For small distances it would be as usual inversely proportional to the square of the distance, but then it would gradually turn into just 1/r instead.

            If you want to explain away dark energy too, it gets funnier, since past a point it must actually become negative.

            That said, it's not just hypothesized "ether", though.

            We _know_ for example that any star, including our sun, produces immense quantities of neutrinos. Which are just that: totally transparent matter. They have an almost zero (not exactly zero, but very very very very close) probability to interact with ordinary matter, and a bunch of them passed right through you as you read this message. The only real interaction between neutrinos and the rest of the universe (or each other) is that they both create gravity and are subject to gravity.

            That's one kind of "dark matter" that we already know exists, and have been detected. They're not just hypothesized.

            Now whether they're _all_ the missing matter or not, that's another question.

            We also have one famous photo in which two galaxies collide, and the bulk of the gravity lensing "fields", i.e., the gravity wells, actually moved ahead of the actual galaxy. It's as if the galaxies were braked by friction with each other's dust and interstelar atoms, but whatever creates the bulk of the gravity well moved ahead.

            • [...] The only real interaction between neutrinos and the rest of the universe (or each other) is that they both create gravity and are subject to gravity.

              Actually, neutrinos interact through the "weak" nuclear force, which is why they're usually described as "weakly interacting" - which is an unfortunately uninformative way to put it. This means that they have a specific, well defined, but rare interaction with ordinary matter that lets neutrino detectors find them.

              What are called "forces" are actually types of fields generated by the presence of certain properties, such as mass or electric charge. The "weak" force is a field which allows certain types of

            • Here [theworld.com]'s another. Look at the pdfs entitled "The Cosmological Consequences of the Product Rule" and "Einstein's Vision" for a compelling model without dark matter.
        • by Urkki (668283)

          There is _something_ that pushes stuff away from the centre, and it's not like any force we already know.

          Nitpick: there's no center, so stuff isn't pushed away from center. All stuff is pushed away from all other stuff at large scales, and that's what we call "dark energy".

          Nice post otherwise!

    • Re: (Score:2, Insightful)

      The stupid reporter doesn't know the difference between dark energy and dark matter.

      As for dark energy, which I guess is what they're going for since it's called the Dark Energy Survey, to paraphrase Einstein, "It's dark, like fudge."

    • Easy. All you need is an Amber Spyglass.

    • ... density of galaxies at a given red shift? You see the repulsive effect by what it does to the galaxy distribution looking back in time (and out in space). So really this is yet another galaxy survey, just more comprehensive. With bells on it if the stub article in wikipedia is to be believed. (Your mileage may vary).

      Dark matter = crap needed by the auditors to explain galaxy rotation etc. (Bookkeeping in other words).

      Dark energy = Einstein's big mistake aka the cosmological constant. The big proble

      • Not an astronomer and deeply unhappy with this stuff which strikes this ex chemist as being very phlogiston or caloric or aether.

        It should, but so what? Any physicist will tell you that dark matter and dark energy are just placeholders for things that they don't understand. Just because we know phlogiston, aether, and caloric don't exist now doesn't mean the people who came up with them were doing bad science.

    • Re: (Score:3, Interesting)

      "If it's "dark" that means it's undetectable by normal means like giant lenses for instance. How could you just see dark energy? "

      I would imagine it's like 'seeing' wind because trees sway.

  • by EEPROMS (889169) on Friday July 04, 2008 @12:59AM (#24055221)
    Hurry Quantum boy, get into the dark energy mobile...
    [Presses Big Red Button]
    (((((((((((((((BOOOOOOOOOOOOOOM))))))))))))
    Narrative: Somewhere on a distant planet
    Astronomer "Did you see that flash, hah proof dark energy doesn't exist"
  • What about planets (Score:4, Insightful)

    by collywally (1223456) on Friday July 04, 2008 @01:08AM (#24055277)
    I know that planets aren't considered dark matter but I always wonder if the scientists out there are taking into account all the planets and asteroids out there that we cant see. I mean every other day, it seems, I'm reading about new gas giant planets detected around distant suns and the articles always make out as if its a surprise to the guys who found it. Is it possible that we might have underestimated the amount of planetary debris that we just can't see with current telescopes?
    • Re: (Score:1, Funny)

      by Anonymous Coward
      Screw space debris, what's really been underestimated is the peeping potential that thing must have!
    • by tirerim (1108567) on Friday July 04, 2008 @02:12AM (#24055607)
      Not really. In our own solar system, all the planets combined are less than a thousandth the mass of the sun. It's pretty much impossible for planets to make up a significant fraction of the mass of a stellar system -- if they did, they would have wound up as a star.

      MACHOs [wikipedia.org] may still make up some fraction of dark matter, but the idea that they could make up most of it has been largely disproved, and they're not really planets, either. It's fairly certain at this point that most dark matter is non-baryonic.
  • +++ America Nonline Chatroom +++ SciPhyGuy1933: Hey, my calculations don't make any sense... it seems like there should be more mass at the center of this galaxy I'm observing. Iwonbensteinsmoney: Do you realize what this all means?!?! Everything we used to know about science and all of our formulas are flawed! Egad! Cutiebaby2x0x0: Oh you boys.. just do what I do when I don't know the answer to something. Just make something up.. SciPhyGuy1933: That's the most prepost.. er.. wait... she might b
  • by little1973 (467075) on Friday July 04, 2008 @01:44AM (#24055471)

    Dark energy may be an indicator that we live in a false vacuum [wikipedia.org]. If this is the case and the true vacuum is speeding towards us with the speed of light then we are doomed. So, add another doomsday scenario to your list.

    • by imsabbel (611519)

      Yeah. And when that happens, we are supposed to cheer for a bunch of post-human smut assholes that thing destroying the universe is a nice thing to observe without interference just because something will be there afterwards, too.

    • Is that what you get in a Dyson sphere? [wikipedia.org]

      P.S. re: your sig, I'd say Dick Cheney is living proof that government can make man richer, provided we're talking about the right man...

    • Look at the picture on the right. Some geeks will not know what it is, but it is in fact a picture of a bra falling off. This is not something that usually happens as a result of late night discussions about dark matter.

      Memo to self: must get out more. Also, must try harder not to trivialise serious subjects.

    • Even if we are living in a false vacuum, it is possible that we can have numerous even infinite numbers of instances of truer vacuum speeding towards us without consequence. That's because the part of the universe we're in would be expanding at a slow but consistent rate. So as long as all instances are far enough away that they're recessing from us at faster than the speed of light, we're ok.
  • huge lenses (Score:5, Funny)

    by ouachiski (835136) on Friday July 04, 2008 @02:12AM (#24055605)

    scientists needing huge optics 8-) whood a thought it

  • by FurtiveGlancer (1274746) <AdHocTechGuy@a o l .com> on Friday July 04, 2008 @02:16AM (#24055641) Journal
    I did not find TFA very illuminating. Of course the topic was optically sensing the effects of Dark Energy which doesn't radiate, so maybe I wasn't supposed to be illuminated.
  • by Jane Q. Public (1010737) on Friday July 04, 2008 @02:44AM (#24055735)
    There are explanations other than "dark matter" and "dark energy" that can explain the observations we see. MoND, for example (Modifien Newtonian Dynamics) is a quite popular theory among physicists, and it does not require that we believe that most of our universe is basically undetectable by humans.

    Occam's Razor works strongly in favor of MoND over such hypotheses as dark matter... only time will tell.
    • by imsabbel (611519)

      Non of them are as consistent.

      And there is nothing strange about a large part of the universe being quasi-undetectable. (which would be dark matter).

      Dark _energy_ otoh isnt that illogical in terms of occams razor. Its as simple as the thought "the universe being here cannot be energy neutral as a whole".

      • I am not sure I agree about the consistency. MoND is pretty consistent.

        As for the other, Occam's Razor has little to do with logic per se. Rather, it implies that the simplest solution (i.e., the one that introduces fewest complications) is the most likely to be correct.

        Logical or not, requiring that people ASSUME that most of the universe is made of barely- or non-detectable matter or energy is introducing outside complications of huge proportions. In contrast, MoND requires nothing of the sort. Ergo
        • by Have Brain Will Rent (1031664) on Friday July 04, 2008 @03:34AM (#24056027)
          As for the other, Occam's Razor has little to do with logic per se. Rather, it implies that the simplest solution (i.e., the one that introduces fewest complications) is the most likely to be correct.

          Actually it says that the solution requiring the fewest assumptions is the one most likely to be correct. The correct solution could still be more complex (which is my assumption on what you mean by complications) than other proposed solutions. When the number of assumptions is equal then the solution with the lower complexity is favoured.
          • I am aware of what it "says", and you merely paraphrased what I myself wrote. I am also aware that a more-complex answer (or even one with more assumptions) COULD still be the correct one, but you miss the point. I did not say that dark matter was not the right answer, I stated that Occam's Razor argues against it. And so it does... the number (and magnitude) of assumptions are NOT equal here, at all! MoND is actually a fairly simple principle, requiring only a few minor admustments to "known" values of cer
            • I'm sorry you think I missed your point.

              And I'm sorry you didn't get it but I didn't paraphrase what you wrote re Occam's Razor, I gave a more complete and correct definition of Occam's Razor.

              Have a nice weekend.
              • Occam's Razor is actually "Entia non sunt multiplicanda praeter necessitatem", and it means (roughly, in English): "Entities should not be unnecessarily multiplied." Whether that means "including fewest assumptions" or "introducing fewest complications" is rather a matter of interpretation, or even just wording. I think we both have the gist of the idea, and that arguing about points any finer is, well... pointless.
                • And yet, you do. lol!
                  • I wasn't. Do you see any argument there?
                    • Oh no, of course you wouldn't nit pick... or, oh wait... here you are doing it again... even your denial is implicitly nit picking a definition of nit picking just to defend yourself against the nit picking you had already done. lol!!!

                      Please, I beg you, point the gun away from your foot and save yourself by stopping now.
                    • A couple of posts ago, I went out of my way to point out that we were basically AGREEING, and you call it nitpicking. Well, go stuff it. I have no use for conversation with somebody who wants to make an argument out of nothing.
                    • I went out of my way to point out that we were basically AGREEING

                      uh huh... suuurrrre you did...

                      I have no use for conversation with somebody who wants to make an argument out of nothing.

                      Thank goodness, at least we can be sure you aren't sitting there talking to yourself. lol!

                    • If you don't understand that, then there is no point in conversing anyway. Goodbye.
        • I am not sure I agree about the consistency. MoND is pretty consistent.

          MOND itself is inconsistent with relativity, although people have made attempts to embed something like it within a relativistic theory (e.g., TeVeS). TeVeS is complicated enough, requiring three different kinds of gravitational fields which interact in a very specific and rather ad-hoc way.

          But the internal consistency aside, MOND isn't that consistent with observational evidence, which is the real test. See this post [slashdot.org].

          Logical or not, requiring that people ASSUME that most of the universe is made of barely- or non-detectable matter or energy is introducing outside complications of huge proportions.

          Why? There are no shortage of dark matter candidate particles which may very well exist

      • lets look at EU (electric universe theory aka plasma science) since it predicts galaxy formation, rotation, and fractalization.
        something like 99 percent of matter is plasma, if you want to condense it into a super galaxy cluster or a star (hmmm...fractal in nature) the best way would be to use a pinch effect [slashdot.org], stars would form along the threads of plasma (Birkland currents [wikipedia.org]) that are connected to the center of mass/energy (think galactic plasma lamp) Remember that the electromagnetic force is many orders
        • by jambox (1015589)
          Look, Jessica, I know you're hot but p[lease stop peddling EU pseudo science on here. It's quackery and is not accepted by any academics I've ever heard of.
    • by NeoSkink (737843) on Friday July 04, 2008 @03:13AM (#24055927)
      Occam's Razor actually works against MOND. MOND has to be changed to account for what we observe at pretty much every scale. The MOND that works for Galaxy rotation doesn't work for clusters, which doesn't work for lensing, which doesn't work for early structure formation, and so on.

      LCDM accounts for this. Heck, you don't think that we scientists got together one day and said "I know, lets make up some goofy theory and then fudge the data to fit it!" do you? You do realize multiple theories were purposed, predictions were created, new data was taken, and conclusions drawn about which theories were supported by the new evidence, right? And that LCDM is the one that survived all the vetting?

      Just checking... See, that's sort of how science is supposed (and did in this case) work.
    • by jo42 (227475)

      For evidence of 'dark matter', you just need to look in the space between Bush's ears...

    • Re: (Score:1, Insightful)

      by Anonymous Coward

      You know, you chose your username extremely well. You hold strong opinions (and voice them regularly) on a number of subjects which you demonstrate pretty thorough ignorance of. I realize it would decrease the humorous suitability of the username, but is there any chance you could maybe become informed at a basic level about things before commenting?

      (Now to ask the rest of Slashdot to adhere to the same standards...)

  • by Anonymous Coward

    If you smash your car into an invisible wall on a freeway, I'm sure you would be surprised since you didn't expect it. On the other hand those who are looking for invisible walls on freeways would be able to spot your lone smashed car on the freeway with their massive telescope and take a closer look.

    They are trying to find that lone smashed up car in space.

    • Now I get it! Thanks, I was just waiting for a car related analogy to clear everything up.
    • by F'Nok (226987) *

      I can't decide whether /. needs a [+1 Car Analogy] or a [-1 Car Analogy] moderation option.

      Either way, I couldn't have put cars in this!

  • by MichaelCrawford (610140) on Friday July 04, 2008 @03:10AM (#24055893) Homepage Journal
    The biggest lens in the world currently is the 40-inch Yerkes Observatory refactor, followed closely by the 36-inch Lick at Mt. Hamilton, overlooking Silicon Valley.

    But for many years the biggest mirror was the 200-inch Hale Telescope at Palomar Mountain near San Diego. Nowadays there are several monolithic 8-metre mirrors, and the two 10-meter Keck telescopes atop Mauna Kea, Hawaii; they are composed of carefully aligned hexagonal subsections.

    Why the big disparity?

    With a lens, you have to grind and polish both sides, and what's worse, a single lens won't do because all glass refracts different colors differently, giving rise to chromatic aberration. A minimum of two lenses is required, for four surfaces to fabricate.

    For both lenses and mirrors, the tolerance of the surface is a small fraction of a wavelength of light across the whole surface. But for lenses, all the surfaces must also be very accurately parallel.

    But really the worst problem is that with a lens, the light goes through the thickness of the glass. The glass must therefore be very uniform and free of internal stresses that could alter the index of refraction in different places.

    Such glass is very difficult to make; no doubt these lenses are only possible because of recent advances in optical glass manufacture.

    That's not a problem for mirrors; observatory telescopes use "first-surface" mirrors, which are aluminized on the front, so the light doesn't go through the glass. Mirror glass therefore doesn't need such careful tolerances.

    But my guess is that they are using lenses because they have a much wider field of view; it's quite easy to make a lens with a sixty degree field of view, but with a mirror the field of view is typically a fraction of a degree. With small amateur scopes, the maximum field is about a degree, twice that of the full moon.

    That seems clear from the photo, because of the steep curvature of the glass; wide-angle lenses usually have very strong curves.

    And yes, I know what I'm talking about - I'm an avid amateur telescope maker [geometricvisions.com], and at one time was a Caltech astronomy student. I've published in the Astrophysical Journal, and have done observing runs at the Palomar 60 and 200 inch telescopes.

    • yes, a wide field of view is important when mapping 300,000,000 galaxies.
    • How do you prevent the aluminum first-surface from oxidizing? I assume the mirror has to be really, really shiny. And as far as I know everything made of aluminum get oxidized (rust) immidiately to a matte finish.

      So how do they do it? You could spray some varnish (or whatever) on it, but then it wouldn't be first-surface anymore.

      • Three answers: (Score:5, Informative)

        by MichaelCrawford (610140) on Friday July 04, 2008 @04:55AM (#24056445) Homepage Journal
        An uncoated mirror actually does oxidize, but it does so in a very nice way, forming an optically-homogenious layer of very tough aluminum oxide.

        In that respect it's completely different from iron oxidation.

        The other way is to overcoat it with something tough and transparent; traditionally silicon monoxide was used.

        One can both protect the aluminum and enhance its reflectivity by giving it multiple layers of tough, transparent minerals. Interference effects cause it to reflect better than aluminum would alone.

        That's how laser mirrors work - they're not aluminized. It's the same principle as antireflective coatings on camera and eyeglass lenses, but a different choice of refractive indices and thicknesses causes it to enhance rather than cancel reflections.

    • The maksutov and the schmidt camera. The Maksutov uses a correcting lens with two steeply spherical, parallel faces. The schmidt uses a nearly flat lens whose surface is actually a fourth-order polynomial.

      You can't really make very big maksutovs. You can make big schmidts - there is a 48-inch one at Palomar that is used for all-sky surveys, but they have a very practical problem that the focal surface is a very strongly curved sphere!

      It's very easy to make a lens that has a wider field than a schmidt

    • Re: (Score:2, Informative)

      by Kentari (1265084)

      Actually, the lenses here are "just" a corrector of a 500 Megapixel camera (FTA). The light gathering is done by the Blanco 4-meter telescope. The camera will have a huge field of view (for a professional telescope) of 2.2 degrees.

      Why lenses and not mirrors as corrector? Because mirrors reflect light and you have to either work with tilted mirrors or tolerate obstruction. Tilted mirrors as corrector would require very complex surfaces (read assymmetrical, aspherical, ...) which would actually be more diffic

  • "Damn, I dropped my contacts again. Oh wait, here they are. Hmmmm, they seam bigger for some reason...."

  • Hrm (Score:3, Interesting)

    by Auckerman (223266) on Friday July 04, 2008 @04:13AM (#24056261)

    You can't observe dark energy or dark matter. They are fill in terms for unobserved matter and energy that must exist based off our limited observations, but we can't see.

    I'm of the mind that neither exist and are kludges to stop the leaky pipes of modern science from falling apart, because key parts of our understanding of Cosmology and Astronomy are just plain WRONG.

    • you can't observe charge because it is a fundamental force of nature, but i've never read a textbook that listed dark energy a fundamental force.
  • The title of this story sounds like a description of a nerd leaning into his monitor to stare at goatse...

  • Both Dark Matter and Dark Energy are funny, unreal concepts.
    Wouldn't it better to assume that current, so called "mainstream" Gravity Theory is flawed?

    We need new, better Physics to explain these things properly. Something like Heim Theory [wikipedia.org] in which gravitation is repulsive for great distances:
    http://www.engon.de/protosimplex/posdzech/px_g_gravi1e.htm [engon.de]
    Also cosmic red shift can be explained now as a gravitational effect, and not as Doppler effect.

    Because of equivalence of mass and energy Heim says there must also exist a field mass of the field energy of each field. However in case of gravitational field this results in a secondary (very weak) additional gravitative source because a field mass possesses its own gravitational field. Mass is producing a gravitation effect, as it can be described with Newton's approximation. Heim says that the energy of this gravitational field corresponds its own field mass. This field mass again produces a second additionally gravitational field which is very weak. Again this field possesses its own field mass which produces a field. So you receive an infinite series, which however converges very fast against a calculable limit value.
    The whole description results in a short mathematical description for a corrected gravitation law, which corresponds with Newton's gravitation law within the observable area of space. However for very large distances it will provide completely different results. For very long distances graviton will produce a weak repulsing force which will only exist if a mass is moving toward the centre of the gravitational field. Among other things the phenomenon of the cosmic red shift can be explained now as a gravitational effect.

    • Both Dark Matter and Dark Energy are funny, unreal concepts. We need new, better Physics to explain these things properly.

      That's funny, because the "new, better physics" you desire sounds just like the existing physics.

      Something like Heim Theory in which gravitation is repulsive for great distances:

      That's exactly what the most conventional theory of dark energy is: the cosmological constant is a modification to general relativity which makes gravity repulsive at large distances.

      Heim says that the energy of this gravitational field corresponds its own field mass. This field mass again produces a second additionally gravitational field which is very weak. Again this field possesses its own field mass which produces a field. So you receive an infinite series, which however converges very fast against a calculable limit value.

      This is a feature of any nonlinear theory of gravity, including general relativity: the mass-energy of a gravitational field itself gravitates. When you start with a linear graviton theory and incorporate the infinite series of s

  • ... different from "dark matter"?

    To my knowing, the concept of "dark matter" existing out there wasn't enough to explain a supposed minimum mass of the universe (to allow for it to turn around and re-contract again, some time in the future) and then, in addition, "dark energy" came into the arena?

    Just asking.

    But then, IANAA (I am not an astronomer, and sometimes very sorry about it) ;-)

    • Yes, dark energy is different from dark matter. Dark energy is needed to explain why the expansion of the universe is accelerating, something that no form of matter (which slows the expansion of the universe through its gravitational attraction) can explain.

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