So? That only means DE works at a much bigger scale. Like I said before, the universe is certainly not homogeneous unless you go to huge distances, maybe of the order of 108 light years. At smaller distances, the homogeneity of the universe, which is the starting assumption for our cosmological models, doesn't work. But our models describe the universe with a very good precision, because 108 light years is nothing compared to the whole universe. So it is enough for DE to be uniformly distributed at such scales (or even bigger scales) for our cosmological models to work.
Proof of Dark Matter
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So? That only means DE works at a much bigger scale. Like I said before, the universe is certainly not homogeneous unless you go to huge distances, maybe of the order of 108 light years. At smaller distances, the homogeneity of the universe, which is the starting assumption for our cosmological models, doesn't work. But our models describe the universe with a very good precision, because 108 light years is nothing compared to the whole universe. So it is enough for DE to be uniformly distributed at such scales (or even bigger scales) for our cosmological models to work.
We also know tons about hydrogen.
Dark-stuff, we don't know much about: composition unknown, non-observable in a laboratory, for example.
The article that was linked to says that some scientists think it bogus and that it just displays our inadequate knowledge. Debate them.
Dark-stuff, we don't know much about: composition unknown, non-observable in a laboratory, for example.
The article that was linked to says that some scientists think it bogus and that it just displays our inadequate knowledge. Debate them.
To put it in a different way: a bar of pure gold is uniform at our scale. You can do all sorts of calculations assuming it is uniform and continuous (for example, integrate with a constant density to find its centre of mass). I hardly think anyone would say that this is not a valid approximation for macroscopic calculations. But a bar of gold is certainly not homogeneous: if we look at atomic scales we see that almost all the mass is concentrated in a tiny sphere, surrounded by a lot of empty space. This is just like the universe. At small scales we see almost all the matter concentrated in stars surrounded by a lot of empty space. And we must consider this distribution to describe phenomena occuring at these scales. But if we are only concerned with cosmology, we can take the universe as uniform, in the same way that we take the bar of gold as uniform for macroscopic purposes.
This is a different argument that has nothing to do with its presence on Earth.
All the cosmologists I know consider DM and DE to be the best working explanation we have. It is not completely satisfying because we still don't know their composition. This doesn't mean they are inadequate. They explain all the observations in a very precise and simple way. The alternative explanations are either incomplete or more complex. So, it is perfectly legimate to study possible alternatives but, right now, DM and DE are the accepted model. The linked article presented an observation that could not be explained by any altered graviation theory, only by dark matter.[1]
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[1] Actually, some sophisticated holographic models are not ruled out. But these models are still too complex to be the main option.
This is a different argument that has nothing to do with its presence on Earth.
All the cosmologists I know consider DM and DE to be the best working explanation we have. It is not completely satisfying because we still don't know their composition. This doesn't mean they are inadequate. They explain all the observations in a very precise and simple way. The alternative explanations are either incomplete or more complex. So, it is perfectly legimate to study possible alternatives but, right now, DM and DE are the accepted model. The linked article presented an observation that could not be explained by any altered graviation theory, only by dark matter.[1]
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[1] Actually, some sophisticated holographic models are not ruled out. But these models are still too complex to be the main option.
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Some dark matter definately exists. Brown dwarfs, gas clouds, etc. can't be seen unless they are effected by something else. Unfortunately this sort of thing is only thought to make up a small fraction of dark matter. Of course, if guesses about the amount of gas floating around a long way from anything are wrong, then this could turn out to make up a large proportion of dark matter, or even all of it.
All "evidence" for dark matter is observations of masses behaving differently from predictions based on our theory of gravity. We know this theory is wrong (or at least incomplete), since it does not work at very small scales and does not, so far, fit in to a unified theory. Dark matter is a solution that is proposed to prevent the theory of gravity requiring modification, and is not required in most of the MOND (MOdifided Newtonian Dynamics) theories. Personally I think this is a case of scientists clinging to old beliefs. Adding more and more arbitrary variable is a classic sign of a theory that is about to fall (like epicycles or the ether).
Dark energy is proposed because distant galaxies seem to be going faster than they should. The distance to the galaxies is found using standard candles, mainly type 1A supernovae and more recently quasars. Unfortunately there is very little evidence that these are actually standard. Recently there was proposed another class of supernovae because some that seemed like type 1A were giving the wrong answers. The paper I read that used quasars said itself that this was speculation, and yet this was used in the media to support dark energy as a theory. Until we can be much more confident in measuring distances, dark energy will remain pure speculation, unless other anomalies such as the Pioneer probes turn out to have the same explanation. As an example of how unreliable distance measurements are, the closet stars to us recently had their distance revised. http://www.newscientist.com/article/mg16221820.700.html
All "evidence" for dark matter is observations of masses behaving differently from predictions based on our theory of gravity. We know this theory is wrong (or at least incomplete), since it does not work at very small scales and does not, so far, fit in to a unified theory. Dark matter is a solution that is proposed to prevent the theory of gravity requiring modification, and is not required in most of the MOND (MOdifided Newtonian Dynamics) theories. Personally I think this is a case of scientists clinging to old beliefs. Adding more and more arbitrary variable is a classic sign of a theory that is about to fall (like epicycles or the ether).
Dark energy is proposed because distant galaxies seem to be going faster than they should. The distance to the galaxies is found using standard candles, mainly type 1A supernovae and more recently quasars. Unfortunately there is very little evidence that these are actually standard. Recently there was proposed another class of supernovae because some that seemed like type 1A were giving the wrong answers. The paper I read that used quasars said itself that this was speculation, and yet this was used in the media to support dark energy as a theory. Until we can be much more confident in measuring distances, dark energy will remain pure speculation, unless other anomalies such as the Pioneer probes turn out to have the same explanation. As an example of how unreliable distance measurements are, the closet stars to us recently had their distance revised. http://www.newscientist.com/article/mg16221820.700.html
ImaginalDisc
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Gosh, that was an ignorant statement. The universe is reletively uniform, over very large scales. It most obviously is not completely uniform, or planets, stars, and YOU would not exist. Hmmm, perhaps that does have some merit.
What "trouble parts" does Dark Matter "sop up"?
Big bang nucleosynthesis indicates that only a very small fraction of dark matter can be baryonic.
There are several independent observations that point to dark matter. The one linked in this thread actually rules out most of the MOND theories. Also, saying that GR is wrong is misleading. While it cannot be completely right at a fundamental level, we lack any experimental data in the region were it fails. But even if we find such data, that would not disprove GR at the scales we are using it right now, in the same way as newtonian dynamics are still valid in many situations. Consider the success of Gravity probe B as a good example of how accurate GR can be.
The existence of DE does not depend only on the observations of those supernovae. Again, there are independent clues. For example, the cosmic microwave background indicates the universe is almost flat, but the density without dark energy is only 30% of that necessary for a flat universe. The existence of DE solves this problem. Observations of supernovae arrive at the same amount of dark energy.
DE is speculation... for a certain value of 'speculation'. It explains our observations and it is simple. It is the generally accepted model. MOND models are not very popular among proffesionals, although there has been quite a lot of literature about them. The main reason people distrust DE is that it is strange. However, MOND is weirder, more complicated and with less physical justification. So, if DE is speculation any other model is even more speculative.
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Is there anything that could block or absorb 100% of the neutrinos being tossed at it?
If so I would what would happen if you created a capsule out of the stuff put a living thing in it with a closed environment that included all the things that we know the living creature would need for a month or two.
I doubt it has any merit but I am curious!
If so I would what would happen if you created a capsule out of the stuff put a living thing in it with a closed environment that included all the things that we know the living creature would need for a month or two.
I doubt it has any merit but I am curious!
Not at all, but perhaps it is your level of understanding that causes you to make such a statement.
Wikipedia entry on it says
Hint: incomplete understanding (what the article said) = inadequate theory (what I said).
From http://www.cnn.com/2006/TECH/space/08/21/dark.matter/index.html
Ie: if current theory predicts a lot more matter than what we observed, we'll not adjust the theory to fit the facts, but fit the facts to suit the theory by saying that therefore unobservable matter must be out there.
From the article
Argue with them.
bob_kark
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I'm curious, if M Theory were true, could it be possible that the evidence they have for dark matter could simply be the result of gravity leaking through from another dimension?
Also, to brettDbass, don't be too impressed, its really just an article from http://www.space.com.
Also, to brettDbass, don't be too impressed, its really just an article from http://www.space.com.
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TobiasTheViking
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That is one thing i've wondered.. though with one big difference, i fail to see how gravity could leak from another dimension. My idea is that it could leak from another parallel universe.
bob_kark
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That's what I meant actually...
That's what happens when I multi-task.TobiasTheViking
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good good, because i fail to see how someone could come from another dimension 
though something could come through a dimension we can't see, but is still a part of our univserse(thus not another dimension) from a paralell universe
And, btw i didn't get it from space.com, i thought about it all on me own(ok ok, with a great deal of help from the PBS show Elegant Universe with Brian Green, though he didn't state this or make any suggestion of it).
Thus i am better than you
Nah, kidding.
though something could come through a dimension we can't see, but is still a part of our univserse(thus not another dimension) from a paralell universe And, btw i didn't get it from space.com, i thought about it all on me own(ok ok, with a great deal of help from the PBS show Elegant Universe with Brian Green, though he didn't state this or make any suggestion of it).
Thus i am better than you
Nah, kidding.
Ie: if current theory predicts a lot more matter than what we observed, we'll not adjust the theory to fit the facts, but fit the facts to suit the theory by saying that therefore unobservable matter must be out there.
[...]
Argue with them.
Simply saying that our theory is wrong doesn't solve anything. Proposing additions to it like DM & DE does solve many problems. Proposing subtle modifications, such as MOND models, can explain many things, but still not all of them. Currently the only simple theory that explains all the data is DM. In particular, this latest observation seems to be a very clear demonstration of the existence of DM.
You are implying that we use DE and DM in an attemp to keep our theory, because we are constrained by tradition, we like it for emotional reasons, we are conservative or some similar reason. But think about DE: it has negative pressure and repulsive gravitation. This is very strange, very different from anything we know. DE is a more radical proposition than Newton's law of gravitation having an exponent different from 2 at small or large scales. The reason we introduce DM and DE into our theory is not because we don't want any change, this is far from what a scientists actually would like to see. The reason is that they provide a simple, workable, quantitative model that explains the observations. Other models are less physical, more incomplete or more complicated.
bob_kark
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Actually, I based my initial question from watching the same show. I missed one of the episodes though. I may have to buy the DVD now...good good, because i fail to see how someone could come from another dimension
And, btw i didn't get it from space.com, i thought about it all on me own(ok ok, with a great deal of help from the PBS show Elegant Universe with Brian Green, though he didn't state this or make any suggestion of it).
Thus i am better than you
Nah, kidding.
TobiasTheViking
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well worth the investment.. but you can(or atleast could) dload and watch it on the pbs homepage.
Well that's what I say since I don't know the details. Physicists actually have the details.
Its not exactly a simple things to posit matter that is in the majority of the universe (just not here though), doesn't interact with regular matter, and is invisible.
Hmm, I don't think I said or implied that at all. I just note DM was first proposed to keep in line with the status quo theory. It had to have been since then we didn't even have any indirect evidence.