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Space Science

The Search for Dark Matter and Dark Energy 212

Posted by ScuttleMonkey
from the someone-needs-to-turn-on-a-light dept.
mlimber writes "The New York Times Magazine has a lengthy article on dark matter and dark energy, discussing the past, present, and future. 'Astronomers now realize that dark matter probably involves matter that is nonbaryonic ["meaning that it doesn't consist of the protons and neutrons of 'normal' matter"]. And whatever it is that dark energy involves, we know it's not 'normal,' either. In that case, maybe this next round of evidence will have to be not only beyond anything we know but also beyond anything we know how to know.'"
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The Search for Dark Matter and Dark Energy

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  • by Reason58 (775044) on Monday March 12, 2007 @06:38PM (#18323957)

    In that case, maybe this next round of evidence will have to be not only beyond anything we know but also beyond anything we know how to know.
    I knew he was going to say that.
    • by Tackhead (54550) on Monday March 12, 2007 @06:51PM (#18324161)
      > > In that case, maybe this next round of evidence will have to be not only beyond anything we know but also beyond anything we know how to know.
      >
      > I knew he was going to say that.

      As long as we're quoting Rumsfeld, "You do high-energy physics with the particle accelerators you have. It's not the particle accelerator you might want or wish to be able to build at a later time."

  • by Wah (30840) on Monday March 12, 2007 @06:42PM (#18324001) Homepage Journal
    ...big black holes that have already eaten everything around them? (i.e the "edges" of the universe)

    ..."in-transit" energy from 100,000,000,000 stars?

    ...large amounts of completely non-reflective dust and asteroids?

    ...a side effect of over-estimating the size of the universe? (i.e. stars like our 5 billions light years away don't exist anymore)

    /real questions
    //just curious..

    • by Gil-galad55 (707960) on Monday March 12, 2007 @06:48PM (#18324099)
      Large black holes are located at the center of galaxies, and their mass can be determined by examining rotation curves, etc. They are not dark matter candidates. Primordial black holes are not massive enough. There is some possibility that dark matter could be non-luminous dust, but there are some limits placed on observations of the comsic microwave background, which would have had to travel over 13 billion light years through such dust without being significantly attenuated.


      The 'size' of the universe is an ill-defined question. We can only observe what's in our past light cone, and it is *that* universe which suffers from a budget shortfall of matter/energy.

      • by radtea (464814) on Monday March 12, 2007 @07:28PM (#18324639)
        There is some possibility that dark matter could be non-luminous dust, but there are some limits placed on observations of the comsic microwave background, which would have had to travel over 13 billion light years through such dust without being significantly attenuated.

        Galactic dark matter, which is required to explain the rotation curves of spiral galaxies, can be completely explained by baryonic dark matter, which would be at least partially dust.

        Extra-galactic dark matter cannot be primarily baryonic. The baryon density of the universe is known from big bang nucleo-synthesis and the primordial H/He ratio, and is too small to account for extra-galactic dark matter. Therefore extra-galactic dark matter has no relation at all to galactic dark matter, as it cannot be made of the same stuff as galactic dark matter.

        So there are at least two completely different, totally unrelated dark matter problems. One can and probably is solved by baryons. The other requires exotic particles or possibly exotic physics.
        • Re: (Score:3, Interesting)

          by rasputin465 (1032646)
          So there are at least two completely different, totally unrelated dark matter problems.

          You're right that the universal baryon density doesn't specifically constrain galactic dark matter. But Occam's Razor suggests there is only one dark matter problem. Besides, you would have to explain why galaxies would have one type of dark matter while galaxy clusters have a completely different kind (and we know intra-cluster dark matter is non baryonic). It's much easier to explain the dark matter evidence at all s
        • by jpflip (670957) on Monday March 12, 2007 @10:24PM (#18326631)
          It's true that there are multiple scales to the dark matter problem, and that our arguments for exotic dark matter apply on the extra-galactic scale. I don't think theorists seriously argue that baryons solve the galactic dark matter problem, however. The Bullet cluster result (Google for Sean Carroll's excellent piece on this) tells us that the dark matter in galaxy clusters can't be baryonic either (it interacts too weakly with ordinary matter). The numbers we have from various experiments add up best if even galaxies are dominated by dark matter halos.
      • by rucs_hack (784150)
        Hawking speculates that micro black holes are throughout the universe. That makes for a lot of places where dark matter could hide.

        I can't find a paper in which he says this, so no citation.
      • by Wah (30840)
        Large black holes are located at the center of galaxies, and their mass can be determined by examining rotation curves, etc. They are not dark matter candidates.

        My general understanding is that these large black holes act as something of a "drain" on the galaxy, i.e. sucking everything it can into it leading to that spiral shape.

        So what happens when the galaxy is empty and only the hole remains?

        That's what I'm asking.
        --
        We can only observe what's in our past light cone, and it is *that* universe which suffer
    • Dark Matter Exists (Score:5, Informative)

      by baboonlogic (989195) <anshul@babooGAUS ... m minus math_god> on Monday March 12, 2007 @07:46PM (#18324897) Homepage

      Here [cosmicvariance.com] is an excellent article by Sean Carroll [preposterousuniverse.com] of the California institute of Technology that explains why all the suggestions of the parent post may not be correct.

      Basically, what it says is that if two large clusters of galaxies went right through each other, and dark matter was really like the normal matter in the way the parent post suggests, we would get a different result from what would happen if dark matter was for real. Astronomers have discovered one such system and this provides conclusive evidence for the existence of dark matter.

      • The problem is that the Dark Matter seems to be moving at a much faster rate than expected. So now the Relativists are posing a new interaction that only works between Dark Matter ;-). They don't concede defeat easily, those Relativists.
    • by master_p (608214)
      The most plausible explanation is that the standard model is not complete and therefore we need to invent dark matter in order to make the formulas work.
  • How about ... (Score:5, Insightful)

    by Anonymous Coward on Monday March 12, 2007 @06:42PM (#18324005)
    Very large bodies don't behave according to Newton. Very small bodies behave according to the rules of quantum physics, so it's clear that one law doesn't regulate every case. Dark matter/energy are just a fudge factor because we can't explain what happens without them, but that doesn't prove that they exist. All that is proven is that we don't understand what is happening.
    • Not really... (Score:5, Insightful)

      by Gil-galad55 (707960) on Monday March 12, 2007 @06:51PM (#18324159)
      On the contrary, very large bodies are extremely well-approximated by Newton, as it is the slow-velocity, weak field limit of General Relativity. There is already good photographic evidence for dark matter in the form of colliding galaxies (do your Google work), and current observational evidence points pretty strongly towards dark energy in the form of a cosmological constant. While it's true we don't know what that means, it's not just a fudge factor.
      • Re:Not really... (Score:5, Insightful)

        by vmcto (833771) * on Monday March 12, 2007 @08:22PM (#18325409) Homepage Journal

        You better tell John Moffat that very large bodies are extremely well-approximated by Newton so he can stop wasting his time on Tensor-Vector-Scalar [wikipedia.org] gravity.

        Dark matter seems like far from settled science to me. But it always does amaze me how dark matter proponents tend to treat it's existence just like the followers of intelligent design treat God.
        • Re: (Score:2, Funny)

          by Poruchik (1004331)
          That's because dark matter is God!
          • by robson (60067)
            That's because dark matter is God!

            That makes me wonder... can God create dark matter so dark that even he can't resist the inexplicable accelerating expansion of observable matter?
          • by kalirion (728907)
            That's because dark matter is God!

            OMG, you're right! Dark Matter - just look at the initials! How much more proof could we possibly need?
        • Re: (Score:2, Interesting)

          by antonyb (913324)

          Dark matter seems like far from settled science to me. But it always does amaze me how dark matter proponents tend to treat it's existence just like the followers of intelligent design treat God.

          See also: String Theory proponents.

          ant.

        • by wish bot (265150)
          I'm really glad you said this for me.

          I get increasingly annoyed by people who claim to use Occam's Razor to dissmiss the existance of a god, but are only too willing to eat up the lastest babble about dark matter (or string theory, etc, etc).

          Thank goodness that there are people like Moffat that use reason and intellect to look at the world. I mean really - "there's all this stuff in the universe, but it's INVISIBLE man, so you know, you can't like see it or anything...." - dark matter doesn't come close

      • The colliding galaxies you are talking about is not really colliding galaxies, but colliding clusters of galaxies, this one is called the Bullet Cluster. A cluster of galaxies is a huge body of matter, which is not adequately explained by the only other competing postulate MOND. MOND requires some dark matter to exist for it to fit the cluster of galaxies, but it can do so currently by using hot and massive neutrinos, instead of unobserved weird dark matter particles.

        But the real problem with using dark mat
    • Re: (Score:3, Interesting)

      by Biogenesis (670772)
      I thought this too for a long time, but it seems that the only evidence for dark matter isn't just galactic rotation curves. I'm having trouble finding it through Google, but while I was studying astrophysics last year we were shown an image of a gravitationally lensed quasar, but without any visible foreground stars. The lensing may have been caused by a clump of baryonic matter that just happened to be cold and not emitting much light, but it may also be dark matter. So unfortunately it's not quite as sim
      • by cluckshot (658931)

        Well I cannot be sure it is worked out since I haven't gone through the equations step by step, but it looks pretty good to me. ---> Fran de Aquino [elo.com.br]

        may just have worked this question out. I can assure you that something is definitely quite different than the standard cosmology is saying. Have fun.
        • I've only done an undergraduate degree majoring in physics, that guy's work is beyond me :p. I'm really glad that people are thinking about this stuff in ways other than just accepting the existance of dark matter and basing all their maths on that assumption. The "greatest blunder of Einstein's life" was when he assumed the universe was static.
      • Actually MOND makes it more easy for Dark Galaxies made up of hot and massive neutrinos to exist, because it makes gravity stronger. So yes, entire galaxies of hot and massive neutrinos are possible, and probably are present in most Clusters of galaxies. MOND shows that there is some matter missing from these Clusters. So the presence of Dark Matter is not fatal to MOND. The presence of Cold Dark Matter may be problematic, but still not fatal. The only thing that will be fatal to MOND will be if we find a b
    • by suv4x4 (956391)
      Very large bodies don't behave according to Newton. Very small bodies behave according to the rules of quantum physics, so it's clear that one law doesn't regulate every case.

      Don't forget that this "law" is simply an equation based on observable evidence. If it doesn't govern very large bodies, it simply means the equation is incomplete and missing one or more variables that start to matter at large scale.
      • It is not just a equation. It is a theory, which means that it contains a lot more features than a single equation. The equation is actually derived from the theory. The theory ie GR is very simple conceptually, that the speed of light is constant and mass curves the space it exists in. Everything follows from there. To change it will be very difficult. Now GR has 10 parameters of symmetry, we could go to higher symmetry eg 15, which is Conformal Symmetry and is observed for the other 3 forces. This will ca
    • by hxnwix (652290)
      Yes, let's just leave it at that *rolleyes*

      Look, a useful theory explaining dark matter isn't going to just fall out of the sky and hit us in the head!
  • by L. VeGas (580015) on Monday March 12, 2007 @06:45PM (#18324047) Homepage Journal
    Please move along.
  • And I just got my head around Quantum Physics... Now they are throwing this at me.

    I think this might be one of those things I chose not to learn and just leave to someone else.
    • If you think you understand quantum physics you are wrong.

      Steven Weinberg the Nobel prizewinner and another physics faculty member used to travel in the same physics department lift, and they would exchange pleasantries. This faculty member had a very bright graduate student. Weinberg had not seen him around for some time, so he asked his colleague what had happened to the grad student. He told Weinberg "He tried to understand quantum mechanics". Both men sighed and then exited the lift at their respec

      • by anandsr (148302)
        I understand that Quantum Physics is a set of equations which don't make much sense outside the realm of its mathematics, but it does make testable predictions.

        Now Dark Matter is a different beast. It is added to fit any observation. It does not allow you to make any prediction. It is simply a device to fit GR into observations. Normally this would not be a bad idea, except for the really unfortunate case that MOND does fit all galactic observations without needing any Dark Matter. This is really unfortunat
  • "Dark energy" (Score:2, Interesting)

    by omnilynx (961400)
    At this point, dark energy is really nothing more than a fudge factor. It's certainly nothing like the normal concept of energy. We don't even know if it's a cosmological constant or if it varies over time and space, let alone whether it's a property of spacetime or some form of particle. So far, I'm still unconvinced that it actually exists: it seems more likely to me that the current theories are simply slightly off in their formulas, and can be resolved without recourse to another of Occam's entities.
    • There is NO question that that expansion of the universe is accelerating. According to General Relativity, the ONLY way this can be happening is if the universe is dominated by a species with a negative pressure. If you're not happy with the name dark energy, call it 'quintessence', although this term has come to be applied to non-cosmological-constant dark energy, i.e., that provided by scalar fields in false vacuums, etc.
      • Sorry, but I think you completely ignored what the GP said and basically spouted a nonsensical stream of verbal diarrhoea which vaguely sounds like you know what the hell you are talking about when you actually don't. The GP was questioning the use of dark energy and dark matter as a kludge to make General Relativity work.

        In my mind, we should not be looking for convenient stop gap solutions pulled out of thin air for this discrepancy between what is observed and General relativity but rather looking for

      • GR does not work at Galactic Levels, so there is no question of it working at the Cosmic levels.

        The real problem is MOND. If it did not exist then Dark Matter would be free to exist wherever it wanted. But with MOND the picture becomes more complex, now DM must fit MOND. It is quite easily provable that DM cannot fit MOND, just apply it to small cluster of stars at the outer edge of Milky Way which show Dark Matter. The problem is that for DM to fit Milky Way, it cannot be present in the Clusters. But some
    • So far, I'm still unconvinced that it actually exists: it seems more likely to me that the current theories are simply slightly off in their formulas, and can be resolved without recourse to another of Occam's entities.

      I'm with you there - we either modify our understanding of gravity or we have to fill the universe with stuff and energy we can't see, detect, or comprehend, and if it's there it's completely unlike everything we can see. That could be true, but Occam's Razor doubts it.

      As I understand it, a
  • Some questions that spring to mind:

    If the grand majority of the 'stuff' in existence around the universe is matter that would be somewhat alien to our range of experiences, could this have an effect on inter-galactic travel? Would what we think it is so far be matter we'd have to worry about hitting and being damaged by at very high speeds?

    Is it dangerous? Would it be inert enough that it would be safe for life to come in physical contact with it?

    Could it be chemically interesting? Would the interactions
    • Dark matter is not chemically interesting since, by definition, it doesn't interact with normal matter. Hence, it's unlikely to be 'useful' in any current fashion!

      As far as whether it's dangerous -- if dark energy is a cosmological constant, it's a property of spacetime, and you are in a sense exposed to it right now. As for dark matter, again, it's something that would pass right through you, much like neutrinos.

    • Re: (Score:2, Interesting)

      by monster811 (752356)
      If it doesn't interact by the electromagnetic force, it cannot affect anything chemically. If it doesn't interact by the strong force, it cannot cause nuclear reactions. Even if it interacts by the weak force, the effect would be equivalent to the neutrinos already coursing through us. To my understanding, it's an explanation for effects specifically by gravity, which we already are experiencing.
  • Dazzling (Score:4, Funny)

    by psaunders (1069392) on Monday March 12, 2007 @06:51PM (#18324163)
    That same year, Michael Turner, the prominent University of Chicago theorist, delivered a paper in which he called this antigravitational force "dark energy." ... "It really is very different from dark matter," Turner said. "It's more energylike."

    That's an educated opinion, if I've ever heard one.

    • Well, I shall hereby prove that we are surrounded by dark matter, using the mass-energy equivalence work of Einstein and Poincare. We know that E == +|- m * C*C

      Let's append (d) to signify the quality of 'dark'.
      So, E(d) == m(d) * C*C

      As we are all aware, m(d) is the abbreviation for medical doctor (+|- the parentheses), so let's go ahead and substitute for physicists (and since the last parenthetical phrase says +|- the parentheses, lets get rid of the +|- and the parentheses), which would give us :
      Ed ==
  • "Normal?" (Score:5, Insightful)

    by Flwyd (607088) on Monday March 12, 2007 @07:00PM (#18324267) Homepage
    If dark matter makes up most of the mass in the universe, wouldn't the kind of matter we're familiar with be the abnormal kind?
    • by suv4x4 (956391)
      If dark matter makes up most of the mass in the universe, wouldn't the kind of matter we're familiar with be the abnormal kind?

      No, because we, as sentient beings on planet Earth define what "normal matter" is. Universe doesn't care at all.

      My point being, don't you begin thinking we're some sorta odd artifact in the universe. It's the wrong way to think about it. Not to mention I believe all this "dark matter" and "dark energy" scientists are looking for is a result of improper equations which make us believ
    • by GroeFaZ (850443)
      Wow. If I shall ever see something more politically correct than this statement, I can die happy.
      • Well, I could complain that "abnormal" implies "bad." Therefore, he should not have used the term "abnormal" but, instead, the politically correct "Differently Normal."
      • by gobbo (567674)
        Are you trying to say that all the great artists weren't weirdos, that the most innovative music doesn't come from marginalized cultures? It's the "abnormal" stuff that makes life and the universe interesting, the foam on the beer, the pepper on the pasta, yadda yadda.

        I like thinking that the visible universe is just a kind of interesting foam clinging to the more mundane stuff.
    • by hxnwix (652290)
      You sound confused. What's the matter?
    • Well, that's exactly what our neighbors made of normal matter think about it. They have a mayority of the mass of the universe after all.

      However, they can't see us either. The universe is a little like the silent hill movie.
  • ...what color dark matter is? God, I hope its not beige.
    • It's black, shiny, small, round, smelly, warm, and each pound of it weighs over ten thousand pounds.

  • Good to see that Rumsfeld has found a new job that lets him exercise his poetic skills.
    • by MadAhab (40080)
      I'm surprised that it took so long for Rumsfeld's name to crop up.

      Still, both as a fear of scientists and an artful dodge of politicians, The Unknowable is unlikely to leave us stranded at some cosmic stalemate. It just doesn't seem to be a feature of our universe.

      And dark matter would be a strange place for it to happen. I'd be less surprised, in fact, if it turned out that ghosts were really some dark matter beings who could occasionally stumble into clouds of weirdness that permit them to interact with e
  • And whatever it is that dark energy involves, we know it's not 'normal,' either.

    Nibbler knows what it is and from where it comes...

  • by TopSpin (753) *

    "It's a ridiculously simple, intentionally cartoonish picture," Perlmutter said.
    Way to arm the Intelligent Design crackpots.

    He may mean our interpretation is cartoonish, but it doesn't parse that way.



  • Can someone please think of the poor helpless penguins on Pluto? And make sure those future dark matter tankers have 6001 hull layers.

    Life is hilariously cruel.
  • Hmmm, dark energy - a Mars Bar made from dark chocolate... Yummm...
  • This may or may not be on topic:

    One thing I presently do not get is where the energy leaked from red shifted photons go.

    Every photon is quantized. It is a particle, emitted when an atom change from an excited to a less excited state (basically, an electron change from an outer to an inner position). This photon get different levels of energy depending on how far they jump, and different frequencies of light correspond to the photons in that light having a higher energy level.

    Now, enter cosmology: Th

  • Dark matter is a mysterious attractive force operating on a scale of of hundreds of thousands of light years with about 24% of the universe's energy budget. Dark energy is a reulsive force operating a scale of billions of light years with 70% of universe's energy budget. Whether these are conventional particles, unknown particles, geometric effects, etc. it is not yet known.

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