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Search for the Missing Universe
Chris Gondek writes "The Sydney Morning Herald has reported that one of the greatest discoveries of our time could be made under the Yorkshire moors. Deep in a Yorkshire mine, scientists are toiling to solve a cosmic puzzle that has baffled astronomers for 70 years: about 90 per cent of the universe is missing. Analyse the movements of stars and you can work out how much matter is making them swirl round in galactic islands and how much makes galaxies cluster together as they do - in other words, you can work out how much mass makes the universe look the way it does. But measurements suggest that the universe is not what it appears."
The Bush administration today announced that they believe Iraq's WMD are being stored inside the missing 90% of the universe. "They're definitely there, in the missing 90%, because we can't see them." said White House Chief of Staff Ari Fleischer. "We'll continue to look for them, but if we don't find them, feel confident no one else will be able to, either."
about 90 per cent of the universe is missing
I'd look in Windows.
The coolest voice ever.
Whenever I lose something, sometimes it turns up in my shoes.
</obligsimpsons>
"Wow, you're like some kind of superhero able to ward off happiness and success at every turn."
-- Ryan Stiles
There is allways the chance it is just compressed....with bz of course :)
Computer science is a grab bag of tenuously related areas thrown together by an accident of history, like Yugoslavia.
Back in the 19th century, astronomers had noticed that there was a minute procession in the perihelion of Mercury (in other words, the point in Mercury's orbit that is closest to the sun kept moving forward) that they couldn't account for using the Keplerian/Newtonian model of celestial dynamics. Astronomers thought that it must have reflected the influence of some massive, distant unknown planet; predictions were made about where this planet was and what its mass was, but astronomers couldn't find it. Then all of a sudden General Relativity came along, and our understanding of mechanics in gravitational fields was improved, and the procession was easily predicted (within an incredibly small margin, as I recall). So it seems just as likely that the "missing mass" is due to a theoretical deficit as it is due to an observational deficit.
When I saw that, I remember thinking that's naive and contrary to the entire history of scientific research. Anyway, it reminds me that even some of the best minds say some of the stupidest things. Especially in physics.
I'm not a physicist but I'm pretty damn sure that Stephen Wolfram and Roger Penrose have had some pretty wacky theories when they venture away from straight physics, like into cellular biology, free will, philosophy, ...
Its not that 90% of the Universe is missing, but because of all the Email spam problems we have, the Earth has been Black Listed. I contened that once we solve the spam problem, we will be able to reach the rest of the Universe. With that said, dont epect to be able to reach the rest of the Universe for quite some time.
Not true.
Gravity is only tested to solar system scales, and in an indirect way, galactic cluster lensing effects.
At very large scales, say of the Hubble radius, we have no tests of gravity. Cosmological models are almost always based on the belief that Gravity works at the very large scales, an extrapolation of many orders of magnitude. There is no proof that this is a valid extrapolation, and there are hints that they are not. (Like they lead to an extremely highly unlike situation. Check out This Talk )
Large scale modifications of gravity may affect the smaller scales, but these effects are naturally suppressed (you can cook up theories where they are not suppressed, but then it is not "large scale" modifications anymore). So to discover these effects are hard.
We have experimental constraints of course, but they are not very strong.
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Yes, modifications to Gravity is one of the way to explain away dark matter/dark energy problems. It is an active field of research, but it is a hard one.
The problem is that while there is no direct tests of gravity at very large scales, there are a lot of "consistency" checks of the various cosmological observations (say of the cosmic microwave background anisotropies) that you have to satisfy.
In other words, there is no proof that such theories of modified gravity do not exist. But to find one is really hard.
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i'm currently investigating a similar matter: dark data. It seems to occupy around 90% of my hard disk.
Bye, Martin
and there's an on-going discussion as to whether or not neutrinos have mass, because if they do, there's enough of them that they might well make up the missing mass of the universe.
The discussion has pretty much moved toward conclusion, and the conclusion is that neutrinos DO have mass, and that the limits placed upon their mass, while greater than zero, do not yield enough total mass to account for the remainder of missing mass. These results might shift slightly with corrections of experimental error, but a drastic change is unlikely.
Dark Matter isn't the only explanation for Fritz Zwicky's 1993 observation.
MOND or Modified Newtonian Dynamics proposed by Moti Milgrom is I think better. If I were to bet on someone winning a future Nobel, Milgrom would be the person.
I'm driving the VLT as I type this...sentence was interrupted for a preset...I'm back now.
Anyway, I know a number of scientists that seriously consider the Newton's may not work at large scales. Nature recently rejected a paper from some rather prominent that seemed to confirm that gravity behaves differently at large scales. But, science is very reluctant to change its equations and publication will have to await more data.
Just remember - Dark matter may not exist. Be skeptical of those who treat it as fact.
MOND FAQ
Dark-Matter Heretic [This is a wonderful article]
Furthermore, if Al Quaeda were to buy, steal, or receive plutonium as a gift from the missing 90% of the universe, then Al Quaeda would be dangerously close to having a nuclear weapon. This is unacceptable.
Clearly, 90% of the universe needs to be destroyed. Facing clear evidence of peril, we cannot wait for the final proof -- the smoking gun -- that could come in the form of a mushroom cloud.
This argument is actually flawed.
The answer is a bit involved.
But basically, the weighing of the matter (as quoted in the article) does not depend on just mass, but a quantity called "mass-energy". It is true that a particle moving at very high speeds seemed to gain "mass". But depending on observers travelling at different velocities relative to this particle, each will see a different mass. However this particle, irregardless of its velocity, will have a consistent "mass-energy" to all observers. In other words, everybody in the unvierse can agree on the amount of "mass-energy" each particle have. So there is a consistent picture of weighing the amount of mass of the universe.
That is the beauty of Einstein's Special Relativity, which is to unify mass and energy into a (jargon warning) relativistically consistent picture of mass-energy.
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..IANAP (i'm not a physicist), though.
There are two strage things happening in the universe on the large scale. The first one is the "dark matter". Basically, if we apply Newton's equations for gravity to various galaxies, we find out that they are spinning too fast. If the force holding them together is what we think it is, most of the stars in a galaxy should have been slingshoted away and left the galaxy. So there must be something making the attraction stronger than we think.
The second strangeness - the "dark energy" - concerns the expansion of the universe. Different pieces of matter in the universe attract to each other by gravity. This slows down the expansion of the universe. As far as we know, gravity is the only thing that can affect the universe on a large scale. So, the expansion of the universe should be slowing down. However, as WMAP showed, the rate of expansion of the universe is actually speeding up. So, there must be something that makes the universe speed up faster than we think.
In both cases, there are two possibilities. The first one is that the anomality is equally distributed through space. This would mean that our equations are a little bit off. For instance, we can account for the "dark energy" by adding an extra term to Einstein's equation for the expansion of the universe. If we change Newton's equation to make gravity stronger over large distances, we can eliminate dark matter.
Yet, there is a possibility that there can be more of the "strangeness" in one point in the universe than in another. For example, one galaxy may be held together tighter than another one of the same size. That would mean that there is another strange beast in the universe apart from the types of matter and energy we know. A whole new branch of physics will be needed to deal with the beast and ask questions like "Why is there more dark matter here than there is there?" and "Does dark matter interact with ordinary matter in any other way than gravity?". Dark matter will compress things on a smaller scale; dark energy will expand things on a larger scale. Obviosly, the statement that "Universe is 75% (or whatever) dark matter" will only be meaningful in this case. As far as I know, we need more precise observations to choose between the two possibilities.
I hope that someone who actually is a physicist, is not asleep, or can reach the "Reply" button will explain all the points I'm wrong on...
If they ever find the missing 90%... I want back all my missing socks, several sets of keys, two wallets and my mind...
Prospecting Stinks. Stop Wasting Time on Cold Calling.
There is a more detailed article about this at the BBC
Clearly, 90% of the universe needs to be destroyed.
I think you meant "liberated".
I recall an earlier article about the universe being topologically equivolent to a torus. Could this topology account for some of the inconsistancies in these "mass of the universe" calculations?
Consider any two stars of mass m and M. With distance r between them:
The Gravitational force of attraction is G*M*m/r^2.
But you'd also have a gravitional force wrapped once around the torus of G*M*m/(r+L)^2.
Then you could wrap around again and again and again....
Of course, generally the distance would be too huge to make difference, but when you consider how many stars there are and the infinite number of loops around the torus you could make, it would add up eventually.
Any thoughts on this?
Fight or flight its all the same
Live to die another day
--Ryan
I can't believe no one brought this up yet. Recently some astronomers have been using hubble to look at the middle of galaxies and have discovered Supermassive Black Holes there. In fact, they've found a bunch of 'em, and there's a relationship between the size of the galaxy and the size of the singularity, and every galaxy seems to have one, even our own! And IIRC they figured this would account for the missing stuff.
-Peverbian
how unbearably sexy it is to hear a girl discussing mind-bending physics. Or anything that's way over my head, for that matter.
--- 11 meters/second, or 24 miles per hour - the airspeed velocity of an unladen European swallow. Really.
Although these experiments are performed deep underground, like neutrino, experiments their physics is somewhat different. Dark matter experiments are aimed at finding new fundamental particles as yet unknown to physics. Neutrino experiments, on the otherhand, study the properities of neutrinos and it is these experiments (SNO, SuperKamiokande) which have produced the exciting discovery of neutrino oscillations.
The reason dark matter is such an interesting field at the moment is because of the WMAP result. This indicates that only ~5% of the universe is what we call "baryonic matter" i.e. the stuff that we are made of. A further ~20% is made up of non-baryonic matter. This includes things like neutrinos, but just neutrinos is nowhere near enough. So, if we believe the WMAP result, there is a sizeable amount of matter which we cannot account for given our current understanding of physics.
However, dark matter experiments are not the only ones out there looking for this missing mass. I'm working on a collider experiment called D0 on the Tevatron collider at Fermilab near Chicago. This is currently the highest energy collider in the world (until the LHC at CERN, Geneva starts in ~2006). As such it is an excellent place to look for new physics and one such example is something called SuperSymmetry. You can essentially think of this as a symmetery between force and matter (in technical terms its a symmetry between fermions and bosons) and it doubles the number of fundamental particles.
So how does this explain the dark matter? Well, a lot of supersymmetrical models have the lightest supersymmetric particle being stable i.e. it cannot decay. Now being neutral, stable and weakly interacting, this would be an ideal candidate for dark matter and might make up the missing mass of the universe. So instead of looking for these particles scattering off nuclei (as dark matter experiments do) we can actually look to see if we can make them in high energy interactions.
Some interesting web sites you might like to read for more information are
-
UK Dark Matter Collaboration
-
D0 Public Information Page
-
The Particle Adventure: Basic explanation of particle physics
I'd particularly recommend the last site if you want to know how much we still have to understand! (click on "Unsolved Mysteries")