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."

Comments

Wrong credit

[Anonymous Coward]

Thats just a copy of a story in teh telegraph in london.

Duh, which way to mars?

[fearless_froggie]

I find it slightly strange that we expect to know where to find the entire universe, when we haven't even made it to Mars yet.

froggie

Thought...

[Skyshadow]

Rather than 90% of the mass in the universe being AWOL, isn't it possible that we don't have an accurate understanding of how gravity functions on an extremely large scale? Could this, in turn, be related to how the expansion of the universe appears to be actually speeding up rather than, as we'd expect, slowing down?

I'd welcome any thoughts on this one... Anyhow, it's late and this is way out of my area of expertise, so forgive my spitballing.

Re:Thought...

[efuseekay]

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.

Re:Thought...

[efuseekay]

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.

Re:Thought...

[Zebede]

Perhaps instead of 90% of the universe missing, *we're* the ones made up of 'dark matter'.

Anybody ever stop to consider that the other 90% must have some sort of structure? There's probably dark matter stars, planets, gas clouds, etc. Perhaps some sort of dark matter inteligent life as well. Whereas we are trying to figure out where 90% of our universe is, the other side may be trying to figure out where their missing 10% is.

Most of us here belive in some sort of extraterrastrial life. I doubt many of us are naive enough to belive that life only exists on a small blue planet in the backwaters of a single galaxy. Considering dark matter occupies 90% of the mass in the universe, I think it would be naive to assume that life consisting of dark matter doesn't exist as well.

Oh well, it's just a random thought. We can't (yet) even prove the existance of dark matter, let alone manipulate and study it. Observing and contacting a civilization composed of dark matter would be all but impossible.

Wouldn't it be funny if *we* are actually the strange aliens composed of the 10% of mass missing from the 'real' universe?

The New Gravity

[mindpixel]

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]

Re:The New Gravity

[mph]

I'm actually the observer, not the operator. (This is fine example of our tendency to see the world through our own perspective; I assumed you were an observer.)

This is the last of my three nights and we haven't opened yet. Hasn't even been close. Tonight looked promising in the afternoon, but the fog has just completely stalled out here. Another two hours or so and it will officially be a completely useless run. Glad you're doing better... send some of that up here.

This much I know..

[ilyag]

..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...

Re:Not True

[leonbrooks]

Gravity is only tested to solar system scales, and in an indirect way, galactic cluster lensing effects.

Agree. And we make an awful lot of assumptions about the continuity of physics even at galactic scales.

The bottom line is that we start by assuming that because a theory fits some observed properties of the universe -and- we have not yet thought of a better (or at least more appealing to us) theory, the one we have is true. "If the only tool you have is a hammer, every problem looks like a nail."

This is especially true of the really grand assumptions like "the universe has no centre and no edge" and "the en-bloc redshifting of distant objects is evidence of recession caused only by the stretching of space"; the problems these assumptions cause conventional science run deep, yet so well embedded in orthodox scientific dogma are they that the vast majority of scientists would rather reject the growing collection of conflicting data than the dogma. (see here for discussion of something even weirder).

Re:Stephen Hawking's wishful thinking

[Galvatron]

I think he said something to the effect that he believes that we'll figure out most of the big questions about the nature of the universe within 10 years or so. That was about 15 years ago.

I have a video clip (from circa 2001) where he's being asked about this very issue. His reply is "in 1980, I said I thought there was a 50-50 chance we would find a complete unified theory in the next 20 years. Well, we didn't make it. However, my estimate is still that we will find a complete unified theory in the next 20 years, but the 20 years starts now."

So, he admits he was wrong, that the promising theories did not pan out, but he's still optimistic. *shrug* If you think that a complete unified theory will never be found, that's fine, you're welcome to ignore his predictions. He's obviously biased, because he believes that there is a complete unified theory out there somewhere, waiting to be discovered, and he wants to know what it is.

Still, I wouldn't totally dismiss his beliefs out of hand just because it seems contrary to the history of science. If you think of the universe as being like a murder mystery, just because you've found many clues, which first caused you to to suspect one person, then proved his innocence and led you to suspect another, doesn't mean it's impossible to find out who the culprit really is. The analogy may not be perfect, but it is dangerous sometimes to conclude that future progress is either inevitable or impossible because of the past.

Re:Yes, there are tests...

[efuseekay]

It is a test of Newtonian gravity. In fact it is not even a test of newtonian gravity, but just a test of the centripetal force = newtonian gravity law. You can imagine either to be wrong, or inaccurate.

They found that gravity "breakdown" at some small acceleration scale. The problem with "acceleration scales" breakdown is that 'acceleration', as defined in their paper, is not a (jargon!) covariant statement. In other words, they are saying acceleration with respect to the center of mass of the cluster. But of course a different observer, say somebody flying in a spaceship next to the cluster, will measure a different acceleration wrt to him. This means that the apparent breakdown is depends on coordinates you choose, but physics should not depend on coordinates. While there is no proof one cannot formulate some screwy theory which can fit this observations and be also coordinate invariant, nobody has done it yet. (It's called MOND, and somewhere along this /. article somebody has posted the links.)

But it is true that the so-called "small acceleration" breakdown at about 10^{-8} cm/s is an annoying thing that won't go away. The Pioneer 10 spacecraft has the same anomaly. The paper you cited is a increase in the "scale" to globular cluster scale, which is interesting, but you can imagine (as the paper itself noted) many things can explain it other than modification to gravity. (the paper suggested perhaps some objects are actually binaries, so their counting of mass may be wrong.)

The point of the paper is that while you can argue away the same "breakdown" in newtonian physics in galaxy scales by putting in dark matter, you cannot do the same with globular clusters, since DM is not known to cluster around such objects. This is interesting, but we'll wait and see :).

But anyway, these are consider tests at "small scales" :). The large scales I mean, bigger than Galaxy Cluster scales...

Topology of the Universe

[SaXisT4LiF]

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?

Re:Topology of the Universe

[QuantumFTL]

Hmm, interesting question. Let's look at it point by point...

I recall an earlier article [slashdot.org] about the universe being topologically equivolent to a torus.

Firstly, the experiment didn't prove anything by a long shot, it merely suggested that the universe may be topologically equivilent to a torus or cylander. But let's assume it is for a moment.

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.

Nice to see someone remembers their introductory physics :) Unfortunately that's a classical approximation to gravity's actual effect, and we don't have any proof that it works like that on the kinds of scales we are talking about (see another post in this thread about Modified Newtonian Dynamics). But even assuming this is true, there's still a few problems.

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.

Well, kinda. There's two flaws with this. Lets look at the first one, mainly the inverse r^2 dependence and wrapping. Basically the magnitude of the gravitational effect from any given object A with mas m on an object B with mas M will be:

Sum n=1->infinity of G*m*M*(-1^(n+1))/(r+n*W)^2
where W is the width of the universe. The oscillating negative 1 term reflects the fact that the object Ahas "mirror images" on BOTH sides of object B (think about pacman, if you go far enough to the left, you'll eventually reach something to your right). This series converges VERY quickly (it's 1/(n^2) not 1/n so it converges, plus it's oscillating so additional terms pretty much cancel out). Because the width of the universe W is very large, and the series oscilates, the first term (classical term for an open universe with no wraparound) completely dominates. This would be true if the only two things in the universe was a large black hole the mass of the universe, and your object B... essentially closed or open makes almost no difference on the amount of attraction you feel unless you are at a distance from the object on the order of magnitude of W. (yes I know general relativity affects things like black holes but the length scales here pretty much nullify any need to take that into account)

So already this doesn't really make much of a difference, but there's still another reason! The universe is roughly isotropic as far as we can tell from long distances away... That is, the amount of mass to one side of you in the universe is pretty much the same as the other side. This means that mass that's far away from you has little effect, because all the force vectors from all the other galaxies pretty much add up to zero (they cancel each other out). So even if this wraparound effect really did add up to a lot, it's coming from EVERYWHERE and would cancel itself out!

But wait I'm not done yet, there's yet another reason! Even assuming that the visible mass of the universe created a net force on stars in some direction because of this wraparound effect, it makes no difference to intragalactic dynamics! The length scale here is the width of the universe, so this force would not vary significantly along the width of a galaxy, and would pretty much be a uniform acceleration. This uniform acceleration does not affect the relative motions of the stars WITHIN the galaxy (intragalactic dynamics). So even if everything you speculated was completely true, it'd still never make a difference. We're looking for a source of gravity pulling things TOWARDS the center of the galaxy, not away from it or in some arbitrary direction. As far as we can tell, the only force that can do this is gravity from some hidden source within the galaxy (unless you make modifications to the fundamental theory of gravity on these

Re:Is the basis of the mass question valid?

[TMB]

So, if we lack an understanding of what forces act on large scale distances to such a degree that ...well, it isn't even orders of magnitude, its positive where we'd expect it to be negative...hell, we don't even *have* candidates for repulsive forces acting on something the size of a galaxy at that distance, then why do we think that our calculations of what a target galaxy's mass *should* be based solely on...yup, our imcomplete equations for gravity, would be correct? Seems to me like they're both wrong in the same direction...if there were a sustained repulsive force, say...the force or "geometry" behind einstien's cosmological constant, then we'd fill in both blanks: repulsions to make distant galaxies travel away from us faster, and a force which would explain the lack of mass in galaxies.

A few points:

1. They're wrong in opposite directions. Dark matter pulls things tighter, and dark energy repels.
2. We have a couple of candidates for repulsive sources of gravity, though they're unsatisfying. The vacuum ("cosmological constant") isn't all that ugly in and of itself - it's the size that's ugly. Quintessence is ugly, but it's a candidate.
3. There are theories that try to use the dark matter particles to power the cosmic acceleration, the so-called "Cardassian models" (no, I'm not kidding, that really is what they're called). Basically, you need something that has no pressure on "small scales" (small = tens of Mpc) so it predicts clustering and structure formation the same as the currently-favoured Cold Dark Matter models but negative pressure on very large scales so it can power acceleration. They usually try to do this by having the particles self-interact or decay on really long timescales.

So yes, people have thought about it, but no one's come up with a single theory to explain both that seems any less contrived than having two slightly-less-contrived independent explanations.

[TMB]

Supermassive Black Holes

[Peverbian]

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

Recursive Universe

[Mittermeyer]

Personally I think the universe is recursive, i.e. the higher dimensions curve back into what we consider to be 4-D mass and exerts effects far beyond the relatively simple Newtonian gravity.

It's a side effect of the zero dimension, i.e. no length, width, depth or time, everything is connected.

You heard it here first.

Crighton who?

[thepupil]

Okay, check this out. Thomas Young proved around 1801 that light was a wave using a double slit experiment in which light created an interference pattern. However he was flooding photons into it. In 1989 this experiment was done again with a twist. Only one photon at a time was sent into the detection area, but the same pattern emerges. So what is causing the interference? And couldn't this interference also explain why we "think" 90% of the universe is missing? Couldn't it simply be just a macro scale effect. I leave you with references other than Michael Crighton: http://www.fnal.gov/pub/inquiring/questions/light_ dual.html http://physicsweb.org/article/world/15/9/1 I might have only a passing interest in science, but I do try to discern between legitimate sources and science fiction. As Dirac is said to state that each photon is interfering with itself it has also been postulated by multiverse theorists (such as David Deutsch) that the interference is coming from photons in parallel universes. Since we really don't have a complete understanding of quantum mechanics couldn't it be possible that the so called "missing" 90% is just the effect that parallel universes are exerting on this universe?