Science question about Dark Matter and Dark Energy

Discussion in 'After Hours Lounge (Off Topic)' started by Shawn Shultzaberger, Aug 23, 2006.

  1. Shawn Shultzaberger

    Shawn Shultzaberger Supporting Actor

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    I was reading this ( http://news.bbc.co.uk/2/hi/science/nature/5272226.stm ) but find I don't quite understand exactly what dark energy and dark matter are.

    In layman's terms what is dark energy and dark matter? Is dark matter just rocks, dust, carbon and etc that doesn't reflect light? Is it left over junk from the big bang? As far as dark energy, I have no clue as to what it is.
     
  2. Joe Szott

    Joe Szott Screenwriter

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    I'm certainly not an expert, but I did take a good deal of physics (including relativity and quantum) in college.

    From what I understand, they don't know what the heck dark matter or dark energy is. They just know that in order for what they are observing to be correct (for the math to "add up") there must be something else in the universe that is exerting a gravitational force (dark matter) or a force (dark energy) for our equations to make sense.

    This isn't the first time it has happened. For example, a lot of observed phenomenon in the universe was puzzling 70 years ago and mystery constants kept having to be inserted to make what astrophysicists were observing to make sense. Along comes Einstein with relativity (and setting the speed of light as a constant) and whamo! suddenly it makes sense again. The mystery constants could either be removed, or understood how and why they came about (hence, they ceased to be a mystery.) New equations are generated on this new theory that work and we move on to the next set of problems.

    Dark matter and energy are the same. In order for our observations to make sense (such that 2+2=4 even though it seems like 2+2=5) we have to insert an "extra" quantity to balance out the mathimatics (so 2+2=[5-1]=4). But what the heck is this mystery quantity? In lieu of knowing, we're calling it dark matter and dark energy.

    What exactly is it and where does it come from? We have no idea (other than pure theory), but it seems like it does exist. Or at least something unseen is exerting forces on the universe (like that implosion observed in the article), dark matter right now is as good an explanation as any other.

    Did that make any sense?
     
  3. Jeff Gatie

    Jeff Gatie Lead Actor

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    Dark matter has nothing to do with just reflecting light. It is matter which emits or reflects no EM radiation at all (including light), and can only be observed by gravitational effects.

    Wikipedia: Dark Matter

    Dark energy is a little bit more out there:

    Wikipedia: Dark Energy

    Edit: Joe beat me to it and correctly identified it more as theory which fits observation than anything that has been directly observed. Which kind of makes sense because by definition, is it really "observable"?
     
  4. Holadem

    Holadem Lead Actor

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    Joe, your explanations describe the concept of Dark Matter up until a few days ago.

    My understading is that this breakthrough provides the first direct evidence of the existence of this stuff.

    --
    H
     
  5. ChristopherDAC

    ChristopherDAC Producer

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    Basically, for years it has been known that, for example, the observable mass of the galaxies (what we can see, including things like dust clouds as well as stars) is not sufficient to exert enough gravitational force to hold their outer parts together at the speed they're rotating, and yet they aren't flying apart. Thus, there's some kind of unobservable mass. Now, from observations of the Solar System, where we can measure the masses and speeds of the various bodies directly if we like, with probes, we know that the same effect doesn't act on a local scale — apparently it only occurs in very large collections of matter, which is strange since physics usually demands that the small (if you can call hundreds of millions of miles "small") and the large act in similar ways. There have been two major schools of thought. One supposes that there is just a lot of ordinary matter in the "galactic halo" (the space above and below the flat galactic disc) which isn't hot enough to radiate its own light, nor diffuse enough to be visible by reflected or transmitted light, and these have become known as MACHOs (MAssive Compact Halo Objects). The other thinks that there is some new form of mass which doesn't interact to any extent with electromagnetism, but only with gravity, a.k.a. WIMPs (Weakly Interacting Massive Particles). Astrophysicists think they're funny.
     
  6. Joe Szott

    Joe Szott Screenwriter

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    The funny thing is I read it as the first direct inferrence that it exists.



     
  7. BrianW

    BrianW Cinematographer

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    The bottom line is that Dark Matter and Dark Energy are fudge factors inserted into cosmological theories in order to make them agree with observation. Their true nature is TBD.

    However, this new observation is actually quite exciting. We have been able to observe alleged Dark Matter influences only by observing the behavior of “regular” matter. The two were never separate, at least in a way that we could observe.

    But these colliding clusters of galaxies (!!!!) have, in effect, produced a Giant Salad Spinner that stops the passage of regular matter, but allows Dark Matter to pass through. So now we have a HUGE clump of Dark Matter that is no longer anchored to a galaxy (or galaxy cluster), just sitting there, alone, unspoiled by the presence of stars, rocks, dust, or any of that troublesome regular matter that always gets in the way.

    So some clever scientists decided to try to detect the predicted giant clump of Dark Matter by calculating the gravitational lensing effect it would have on galaxies behind it, and then observing said gravitational lensing to see if observations agrees with the calculated prediction.

    They did agree. So something incredibly massive, invisible, and non-interactive with the other three forces of nature (which is why it was flung from the Giant Salad Spinner) is definitely there.

    What it is, we don't really know. But this new observation is exciting because, until now, no one could really say whether Dark Matter was real, or whether we just didn't understand gravity at stellar distances. (Is lettuce inherently wet, or is it covered with an exotic theoretical substance called “water”?)

    Now that we have seen Dark Matter's influence apart from regular matter, we know that there's much more to it than just saying that gravity between bits of regular matter is more complex than we thought. Gravity, it turns out, appears to be precisely what we thought. (Whew!)

    So being able to detect it in the absence of regular matter has shed quite a bit of light on Dark Matter. [​IMG]
     
  8. Joe Szott

    Joe Szott Screenwriter

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    Yeah, no matter what your thinking on the theory was, these are some very exciting observations.

    Now if we could just slingshot a starship around a clump of dark matter, we could go back in time and save the humpback whales. Oh wait, that hasn't happened yet...

    [​IMG]
     
  9. Jeff Gatie

    Jeff Gatie Lead Actor

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    Can anyone tell me how this helps me survive and compete against my fellow man? [​IMG]
     
  10. Shawn Shultzaberger

    Shawn Shultzaberger Supporting Actor

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    Sure. You need to get zapped by it (Dark Matter) during an experiment like Tony Shalhoub in his guest appearance in one episode of the X-Files. Then you will have total power with just your shadow. [​IMG]
     
  11. Jeff Gatie

    Jeff Gatie Lead Actor

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    Ohh, I see. *** Quickly runs to the "Purpose of Life" thread to surreptitiously edit a few posts*** [​IMG]
     
  12. BrianW

    BrianW Cinematographer

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    If Dark Matter exists -- and this new observation suggests that it may -- then it most assuredly is in our own galaxy. We're swimming in it. It may be passing through your body right now.

    However, it may well be the case that DM is not an amorphous soup, distributed throughout the galaxy like a gas. DM may be constrained to obey its own set of physical laws and its own set of nuclear and electromagnetic forces that we canot discern. If so, then there may be DM stars numbering ten times the number of visible stars in our galaxy. There may be DM planets, and even DM people and civilizations. The average distance between DM stars would be much less than the average distance between visible stars, so DM civilizations may have been able to contact each other across stellar distances. Our own Earth may this minute be passing through a busy DM interplanetary transportation hub, bustling with unseen, unknowable forms of alien life.

    Do DM scientists speculate that some form of exotic Light Matter may exist in order to explain the ten percent of the Unverse's mass that appears to be missing? Or is the missing ten percent simply shrugged off as an observational error? Are they looking for us as diligently as we're looking for them?

    One thing is certain. If we ever do find a way to interact with them, we need to be careful. They outnumber us ten to one.
     
  13. Holadem

    Holadem Lead Actor

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    Well, DM does interracts with LM in the one way which has allowed astronomers since the dawn of this discipline to be aware of then invisible objects long before they could be directly observed (planets), or be proven to exsit to an absolute certainty (black holes): Gravity.

    This to me precludes the existence of dense, planet and star-like clusters of DM (unless density is an exclusively LM concept [​IMG]), since, while directly unobserveable, they would have similarly impacted their environement, no?

    --
    H
     
  14. Brad Porter

    Brad Porter Screenwriter

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    Here's my explanation of the mass discrepancy that avoids a need for Dark Matter.

    You know how they say that the "camera adds ten pounds"? Well, Hubble is a really big camera... [​IMG]

    And everybody knows that Dark Matter is just ghosts... prove me wrong!

    Brad
     
  15. BrianW

    BrianW Cinematographer

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    Yeah, you got me. Since we've never seen a visible star behaving like half a binary system because it's gravitationally linked with a DM star, there probably aren't any DM stars. Still, DM's exoticitatiousness may be of such a level that Brad's ghosts could still exist. I bet you can't prove him wrong!

    Even so, DM must be subject to some indiscernible force that prevents it from gravitationally collapsing into a singularity. Otherwise, all the galaxy's DM would have collapsed into a black hole by now.

    Um... or would that be "white hole"?
     
  16. ChristopherDAC

    ChristopherDAC Producer

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    Well, all the physics we know says that gravitation and inertia are both equal properties of mass, and this observation seems to show that is true, the "dark matter" obeys Newton's Laws of motion [as it would have to, or it wouldn't be associated with galaxies]. Therefore, "centrifugal force" [not a force, but hey] will keep if from being smashed in on itself, even if light pressure which acts on normal matter won't. Anyway, it only seems to exist in the spaces between stars, since the "extra mass" which appears in observations of the motion of the galaxies is not present in the Solar System — if it were, we would simply have included it (all unwitting) in the calculation of the Gravitational Constant, and it would have required an observation like this to show that it was something separate from normal matter.
     
  17. BrianW

    BrianW Cinematographer

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    But if DM behaves similarly to LM with regard to gravitation and inertia (which, I agree, it must, in order for the Giant Salad Spinner to have worked the way it did), and galactic rotation is enough to keep it from collapsing, then, like LM, it would form localized accretion disks, out of which would form DM black holes or DM stars, the gravitational signatures of which we surely would have seen by now.

    Something else is going on here. If DM is an amorphous fluid, then perhaps it simply has a maximum density that it can attain.

    And, if that is the case, it would render false the notion that it would be detectable -- or that it would contribute to the measurement of gravity in such a way that it would be accounted for -- if it were present in our solar system. If DM is an amorphous fluid of reasonably consistent density, we could be floating through it, and it would have no measurable gravitational effects on the scale of the solar syatem, and beyond, much like being in a room in the center of the Earth (were that possible) would render the Earth's might gravitation insignficant. If you're in the middle of it, and it's of uniform density, it all pretty much integrates out and doesn't contribute to the calculation of the gravitational constant.
     
  18. Grant B

    Grant B Producer

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    Dark Matter and Dark Energy = Fudge factors.
    Theorys don't work and need a lot more matter that nobody can see.
    I think they will go away when they get the theory correct.

    I think in the 1800s they used 'ether' in the same way
     
  19. BrianW

    BrianW Cinematographer

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    The science apologist in me compels me to point out that not all of science involves making up a bunch of crap to explain what we observe. (And, let's face it: Dark Matter is just a bunch of made-up crap.) On the contrary, some science involves finding a bunch of crap in our theories we didn't know was there, and has never been observed in nature. Things like black holes, gravitational lensing, and wormholes are all crap we surprisingly discovered lurking in our theories long before we observed them in nature. (And, yes, wormholes haven't been observed in nature... YET! [​IMG])

    This kind of crap is really cool because it's predicted to exist before it's found in nature. Thus, finding this crap in nature is a validation of the theory that predicted the crap in the first place, which is always an occasion for a High-Five exchange between the guys in the lab coats.

    Crap like Dark Matter, on the other hand, is just a wild-ass guess. If it does indeed exist, as this latest observaton strongly suggests, then it's because we just got very, very lucky.

    Make no mistake: this observation is a very big milestone in astrophysics. But if you see anyone in lab coats High-Fiving one another and congratulating themselves on how smart they are because they were right about Dark Matter, do me a favor and give them a very stern look. Shake your head and wag your finger, if you have to. Take whatever measures are necessary to let them know that you won't put up with that crap.
     
  20. Grant B

    Grant B Producer

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    Brian
    You're right but todays my day off so I don't want to be logical engineer Grant

    ..just a wild-ass guess
    Excuss me Brian but these are experts and highly educated scientists. They don't make wild-ass guesses.

    They make SWAGs - Scientific Wild-Ass-Guesses.
    WAGS.... the nerve of some people!
     

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