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# Most Detailed View of Dark Matter Mapped By Hubble

#### CmdrTaco posted more than 3 years ago | from the final-frontier dept.

93

astroengine writes "Building on previous studies by the Hubble Space Telescope, new analysis of gravitational lensing data has revealed the most detailed map of the distribution of dark matter yet. The distribution appears as a beautiful ghost-like or ethereal haze and could have serious ramifications on our understanding as to how galaxy clusters form and evolve."

cancel ×

### Re:You want pictures of Dark Matter? (2, Informative)

#### Anonymous Coward | more than 3 years ago | (#34248346)

there's a 25sec advertisement on the front of this linked video and then something fairly average that i couldn't see through to the end. which kind of begs the question of whether there is any decent hubble-related comedy out there?

### Re:You want pictures of Dark Matter? (2, Funny)

#### NatasRevol (731260) | more than 3 years ago | (#34248824)

You're just not looking far enough...

### Re:You want pictures of Dark Matter? (3, Informative)

#### bmo (77928) | more than 3 years ago | (#34251172)

With regards to your sig, it's not Apple you should thank, but the fine folks at KDE.org which did all the heavy lifting. Webkit is a modified version of khtml.

Just sayin'

--
BMO

### Re:You want pictures of Dark Matter? (1)

#### NatasRevol (731260) | more than 3 years ago | (#34257390)

Really? ALL the heavy lifting? You might want to look at what Apple has contributed back to the project since 2002. Which is exactly what open source is all about.

And then let me know when you see a phone that ships with KHTML on it.

### Re:You want pictures of Dark Matter? (2, Informative)

#### I_Human (781026) | more than 3 years ago | (#34250678)

Raises the question! Begging the question is a logical fallacy that has to do with circular logic.

### Re:You want pictures of Dark Matter? (1)

#### VShael (62735) | more than 3 years ago | (#34252660)

which kind of begs the question of whether there is any decent hubble-related comedy out there?

Rule 34, coming right u--

Oh wait, you said hubble-related *comedy*. My bad.

### Re:You want pictures of Dark Matter? (0)

#### Anonymous Coward | more than 3 years ago | (#34254124)

Use it right. [begthequestion.info]

### Just a question (3, Interesting)

#### Burnhard (1031106) | more than 3 years ago | (#34248240)

I'm just asking the question, because I don't have a great deal of knowledge about this, but could an alternative explanation be that our theory of gravity is wrong?

### Re:Just a question (1)

#### immakiku (777365) | more than 3 years ago | (#34248344)

Yea. The discovery is that, IF our theory of gravity is correct, this is more evidence for the existence of dark matter.

### Re:Just a question (1)

#### geekoid (135745) | more than 3 years ago | (#34248414)

well, more correctly: If this isn't caused by some property of gravity we have previously not known about, then it's more evidence of dark matter.

the Theory of gravity is just our understanding of the properties of gravity, and how to measure it. IT sin't wrong. It's provable correct. That doesn't mean more data won't refine our understanding.

### Re:Just a question (0)

#### Anonymous Coward | more than 3 years ago | (#34248766)

It's provable correct. That doesn't mean more data won't refine our understanding.

Perhaps. On the other hand no-one has ever made a measurement without explaining something as an measurement error.
Proof is an elusive thing.

### Re:Just a question (2, Informative)

#### BlackPignouf (1017012) | more than 3 years ago | (#34249240)

You have it backwards : nothing in physics is "provable correct".

A theory is only useful till it is proven incomplete or incorrect. If it holds a very long time, it is only "probably correct" or "correct enough for today".

The phenomenon that led scientists to develop the concept of dark matter could very well be hints that our theory of gravity is wrong/incomplete.

### Nothing is provably correct (2, Informative)

#### sjbe (173966) | more than 3 years ago | (#34250512)

It's provable correct.

No model in physics is "provably correct". That's not how the scientific process works. Scientific hypothesis and their resulting models can never be proven conclusively correct, they can only dis-proven. You can support a model with vast amounts of evidence and be quite confident that it is a useful and accurate model but it only takes a single piece of evidence to establish that the model is wrong. When we say something is a physical law we are basically saying we have a mathematical model for how this works and we've studied the hell out of it and every piece of evidence we've gathered so far supports the correctness of the model. That is NOT the same thing as saying we have proven this model to be correct - it is saying we have been unable to prove this model is wrong.

Of course we can also still use models that we know are less accurate (provably INcorrect) if they provide good approximations under known circumstances. We know relativity is a more accurate model of the physical world than Newtonian models for a great many problems. But the differences are negligible under many conditions and the relativistic models are much more mathematically cumbersome.

### Re:Just a question (1)

#### symbolset (646467) | more than 3 years ago | (#34251716)

It's not actually proof of anything. It is rather a graphical representation of the where the invisible mass would have to be to explain the difference between observed phenomena and our gravity model. Let us consider it not a proof, but a map of our ignorance. A lovely, mysterious misty map - which just happens to be in the form of Cthulu or the Flying Spaghetti monster, by mere coincidence.

### Re:Just a question (5, Informative)

#### Fluffeh (1273756) | more than 3 years ago | (#34248958)

but could an alternative explanation be that our theory of gravity is wrong?

Yea. The discovery is that, IF our theory of gravity is correct, this is more evidence for the existence of dark matter.

It is something more along the lines of this:
We have a good number of formulas and calculations that work properly with the things we can measure - planets, the sun, cars, planes, kitchen scales.
One of these might be:
y + 3 = 5
Nice and simple for this example. Lets say that the "y" here represents gravity and the formula has been proven in every experiment we have done.
We therefore assume that this calculation is correct and true. BUT when we try to use this calculation when looking at things like galaxies, we seem to find the wrong answer:
y + 3 = 7.2
This is clearly not correct, but as we don't want to throw out all the formulas and understanding we have about how things work, we add another variable to the formula like so:
y + 3 + x = 5
The "y" still represents gravity, but now we add the "x" which represents something we don't understand and we don't know where it came from. We call it Dark Matter because we can't see it, don't seem to be able to interact with it and have no real idea of what it is - but with this new addition to the formula, the answer once again comes out at what we know (think) to be true. We just now need to find what this x variable is.

THAT is why finding/understanding Dark Matter (and on that note, Dark Energy) is so important. We know (think we know) the right answers, but our formulas just don't seem to fit so well when applied to certain really, really, really big things (like clusters, superclusters etc). When we find this "x" in the formula, it will once again work perfectly for all our calculations.

### Re:Just a question (1)

#### musicalmicah (1532521) | more than 3 years ago | (#34251894)

That is the most elegant explanation of dark matter that I have ever seen or heard.

### Re:Just a question (1)

#### hitmark (640295) | more than 3 years ago | (#34252610)

Indeed. And it reminds me of how when Einstein first presented his theory of relativity, he had a constant (somewhat like that X) in there to maintain a steady state universe. But soon after new observations favored a expanding universe. So the constant was removed and the theory have been found to be highly accurate since then. So sometimes a X is not added, but removed, because it was put there based on either unreliable data or assumptions by the scientist(s) working on it. Such assumptions show up in various places like psychology, egyptology, economics, and mostly thanks to how the field was bootstrapped.

### Re:Just a question (1)

#### Fluffeh (1273756) | more than 3 years ago | (#34264924)

That is the most elegant explanation of dark matter that I have ever seen or heard.

Indeed. And it reminds me of how when Einstein first presented his theory of relativity, he had a constant (somewhat like that X) in there to maintain a steady state universe.

I know this is off topic, but thank you. Those two comments on my post just made my day! :)

### Re:Just a question (3, Informative)

#### Anonymous Coward | more than 3 years ago | (#34248370)

Dynamical studies of our own galaxy show there's a lot of invisible matter in it. This means that something has to happen with gravitational theory within a region much smaller than the observable universe, at speeds of only a few hundred kilometers per hour. The modified theory also has to conform to the known motions of solar system objects, which are known to extremely high accuracy. These conditions are very hard to meet.

### Re:Just a question (0, Troll)

#### BlackPignouf (1017012) | more than 3 years ago | (#34248426)

Indeed.

As we all know, pi = 3.
While I'm sure my theory is correct, it doesn't quite fit for some calculations so I introduce a dark number.

Thanks to this dark number, I can approximate the perimeter of a circle!

Problem solved.

### Re:Just a question (1)

#### \$RANDOMLUSER (804576) | more than 3 years ago | (#34249052)

I see what you did there. Well done. Although cosmology and particle physics requires more like 19 "dark numbers".

### Re:Just a question (0)

#### Anonymous Coward | more than 3 years ago | (#34249760)

As we all know, pi = 3.

It says so in the Bible. 1 Kings 7:23 (NIV) [biblegateway.com] :

"He made the Sea of cast metal, circular in shape, measuring ten cubits from rim to rim and five cubits high. It took a line of thirty cubits to measure around it."

(Yeah, this is what I like to throw at folks who claim the entire Bible is literally correct. 1 Kings 7 describes Solomon's Palace in otherwise precise language not unlike most patents. There's no reason to believe that it's fudging the numbers. So why didn't God tell his Chosen People, or at least their king, about pi?)

### Re:Just a question (1)

#### Nazlfrag (1035012) | more than 3 years ago | (#34251652)

Seeing 30/pi=9.549 that is a perfectly accurate measurement if we round to the nearest integer. There are plenty of places you can see the bible isn't correct (who did Cain marry?) but this isn't one of them.

### Re:Just a question (4, Interesting)

#### Monkeedude1212 (1560403) | more than 3 years ago | (#34248450)

I'm just asking the question, because I don't have a great deal of knowledge about this, but could an alternative explanation be that our theory of gravity is wrong?

Kind of.

In all other experiments, our understanding of Gravity works just fine. In this one situation however, it does not. Someone proposes the idea of Dark Matter - which fits the bill almost perfectly, as it accounts for what we've seen.

Alternatively, our understanding is wrong. We don't know how its wrong, or why its wrong, it's just not working. When we look at hundreds of other examples, it works. When we look at this one, it doesn't.

Is it more plausible to discount our theory based on the 1 case where it doesn't hold up, or assume there is something special about that one case that seperates it from the others.

Thats why Dark Matter holds some water. But - by all means, it is entirely possible that we don't have it quite right, we could be missing some variables that simply are negligable at a non-cosmic scale.

### At the risk of making scientists cringe... (3, Insightful)

#### Junta (36770) | more than 3 years ago | (#34248708)

I consider the possibility of an incomplete model of gravity as sort of like newtonian physics. We do all sorts of local observations and the models work fine, but then under 'fantastic' scenarios beyond our ability to observe or reproduce things don't work out right, i.e. extremely fast speeds. Then Einstein provides us with relativity and it provides a factor that makes it all work and even fits cleanly into Newtonian models as a term that is immeasurably small to explain how things appear to act different without having to apply totally different rules at some arbitrary point.

Dark matter may be something real, but right now it only manifests as something to get the math to work out using our current understanding. At the huge scale or even along a dimensional relationship we can't understand, some factor emerges that knocks off our predictions but is ever present with immeasurably small impact in the 'well-understood' cases. I personally consider either case equally likely, there is either a thing (dark matter) or a mechanism out there that just exists as a big question mark until either collaborating data on where and what the dark matter is appears, or a more precise model comes out to explain the discrepencies away.

### Re:At the risk of making scientists cringe... (2, Interesting)

#### AstrumPreliator (708436) | more than 3 years ago | (#34252498)

As someone who has studied algebraic geometry quite a bit I find the jump from classical mechanics to relativity to be very beautiful mathematically. The former is still useful as the approximation is close enough for the majority of situations, but it did unwittingly make some assumptions which turned out to be wrong. To me dark matter and dark energy seem like a kludge and I do hope we just unwittingly made some assumptions about the system that turn out to be false. Of course that's just the mathematician in me, always searching for perfection. Dark matter and dark energy may very well be real, I'm not a physicist.

### Re:At the risk of making scientists cringe... (1)

#### hitmark (640295) | more than 3 years ago | (#34252618)

I guess we can say that when it comes to the universe, perfection is highly overrated.

### Re:Just a question (0)

#### mark-t (151149) | more than 3 years ago | (#34248764)

I consider it more probable that our theory of gravity is simply not complete, even though we can only find very limited cases where it doesn't seem to work without the introduction of dark matter. I consider even this admittedly implausible notion to be vastly more likely than the existence of dark matter because using dark matter to explain it is too similar to the conspiracy theory fallacy.

### Re:Just a question (1)

#### Monkeedude1212 (1560403) | more than 3 years ago | (#34249698)

Than you surely wouldn't like much of quantum physics either. It'll all seem like a bunch of straw man arguments because you simply have to take their word that what they're saying is happening is actually happening.

### Add Pioneer anomaly and make that 2 cases. (0)

#### Anonymous Coward | more than 3 years ago | (#34252250)

There's strange stuff happening much closer to home, too. Any bets these cases have something to do with each other?

### Re:Just a question (1)

#### k.a.f. (168896) | more than 3 years ago | (#34252608)

Kind of.

In all other experiments, our understanding of Gravity works just fine. In this one situation however, it does not. Someone proposes the idea of Dark Matter - which fits the bill almost perfectly, as it accounts for what we've seen.

Alternatively, our understanding is wrong. We don't know how its wrong, or why its wrong, it's just not working. When we look at hundreds of other examples, it works. When we look at this one, it doesn't.

Is it more plausible to discount our theory based on the 1 case where it doesn't hold up, or assume there is something special about that one case that seperates it from the others.

Isn't that exactly the same situation as with classical mechanics? It worked really, really well in each every case, except you observed utterly insane speed values. It turned out that it was wrong and you had to include a factor for speed, which happened to be neglegible in all other cases. Now, as fas as I understand it, we have another theory that works really, really, well except when observing astronomical masses and distances. Why shouldn't that require another modification to the formula itself? (I've always had the suspicion that physicists are so keen on detecting new elementary particles to explain gaps in our explanations because you can at least experiment with them, just by upping the energy involved... whereas you can't do experiments on distant galaxies at all, you can just observe them.)

### Re:Just a question (1)

#### boristdog (133725) | more than 3 years ago | (#34248624)

Well, that will make flying cars a lot easier to build.

### Re:Just a question (1)

#### Abcd1234 (188840) | more than 3 years ago | (#34248636)

The evidence doesn't support any kind of modified gravity theory at this point. Hit Wikipedia on the Bullet Cluster and related results.

### Re:Just a question (1)

#### Steve Blake (13873) | more than 3 years ago | (#34250350)

Is that true of Moffat's STV Gravity (http://en.wikipedia.org/wiki/Scalar-tensor-vector_gravity/ [wikipedia.org] )? Moffat claims that SVT Gravity is consistent with the Bullet Cluster data (http://arxiv.org/abs/astro-ph/0606216/ [arxiv.org] ).

### Re:Just a question (2, Interesting)

#### Steve Blake (13873) | more than 3 years ago | (#34250402)

Sorry, wrong URL for the Moffat paper on the Bullet Cluster; see http://arxiv.org/abs/astro-ph/0702146/ [arxiv.org] .

### Re:Just a question (1)

#### jovius (974690) | more than 3 years ago | (#34248682)

You mean the theory that compares apples and oranges?

### Re: Just a question (3, Informative)

#### Black Parrot (19622) | more than 3 years ago | (#34248712)

I'm just asking the question, because I don't have a great deal of knowledge about this, but could an alternative explanation be that our theory of gravity is wrong?

Yeah, that or a lot of other things. There was a popular explanation called MOND - Modification of Newtonian Dynamics - but AIUI the evidence shot it down. However, I think there's some MOND variants still out there. But most cosmologists apparently lean toward DM as the best explanation for the available observations.

### Re: Just a question (0)

#### Anonymous Coward | more than 3 years ago | (#34252260)

MOND and variants solve one problem while not solving a whole bunch of problems that GR does. Things like frame dragging and mercury's procession.

Some recent observations of dark matter (indirectly) have pushed most of us "why dark matter" over to the best explanation and more and more observational evidence. Basically a alternative should at least be able to explain these "gravitational" maps. They don't, they only explain galactic rotation.

While dark matter helps explain the big bang, large scale structure of the universe, these kinds of gravitational maps as well as galactic rotation.

### Re:Just a question (1)

#### ModernGeek (601932) | more than 3 years ago | (#34248808)

How do we know that general relativity isn't wrong and we're not just "seeing" objects moving faster than the speed of light?

Occam's razor?

### Re:Just a question (1, Informative)

#### Anonymous Coward | more than 3 years ago | (#34248972)

That's what the MOND [wikipedia.org] theory is all about

### Short answer: No (5, Informative)

#### Velodra (1443121) | more than 3 years ago | (#34249072)

Long answer: Dark matter wasn't invented just because someone saw some anomalous behavior that didn't agree with theory, and said to themselves: "Oh, there has to be something mysterious at work here, we'll call it dark matter.". There are several reasons for believing in dark matter, for example that when measuring gravity we notice gravity coming from directions where we can't see any matter. However, the source of this gravity behaves a lot like matter would. For example we can observe these "invisible gravity sources" being thrown around when two galaxies collide. Because these "invisible gravity sources" acts a lot like matter, except for the fact that we can't see it, it's called dark matter.

If you're not yet convinced, take a look at this recent blogpost by a professional astrophysicist: http://scienceblogs.com/startswithabang/2010/11/the_simplest_argument_for_dark.php [scienceblogs.com] In this post, he basically explains how we can derive the existence of dark matter from: A) Assuming that the theory of general relativity is valid, B) assuming that the big bang theory is valid, and C) our observations of the cosmic microwave background.

### Re:Short answer: No (-1, Troll)

#### UnknownSoldier (67820) | more than 3 years ago | (#34250460)

> "Oh, there has to be something mysterious at work here, we'll call it dark matter.".
Ah, I see, the aether by any other name.

You can't see, touch, taste, smell, or hear dark matter or dark energy, yet you have faith that it exists ??

> B) assuming that the big bang theory is valid
That assumption is full of holes. There are numerous problems with the Big Bang ...
http://www.metaresearch.org/cosmology/bb-top-30.asp [metaresearch.org]

--
Inner Space not Outer Space is the FINAL frontier.

### Heh. (1)

#### Black Parrot (19622) | more than 3 years ago | (#34251276)

Love the picture of Einstein at the bottom.

#### AC-x (735297) | more than 3 years ago | (#34254666)

Another good demonstration of Dark Matter is when large galaxy clusters collide - the matter interacts creating a shockwave, while the mass (as detected by gravitational lensing) flies straight through unaffected
http://blogs.discovermagazine.com/cosmicvariance/2006/08/21/dark-matter-exists/ [discovermagazine.com]

Video demonstration

### Re:Just a question (1)

#### DigiShaman (671371) | more than 3 years ago | (#34249132)

Alternate hypothetical:

Proportional displacement. Gravity is a push, not a pull on matter. Think Casimir Effect on a huge scale.

### Re:Just a question (0, Troll)

#### UnknownSoldier (67820) | more than 3 years ago | (#34250482)

Nice to see someone open-minded to other possibilities.

Have you heard of Dewey B. Larson? He has some interesting physics.

http://www.reciprocalsystem.com/ [reciprocalsystem.com]

### Re:Just a question (0)

#### Anonymous Coward | more than 3 years ago | (#34267420)

In General Relativity, you can say that matter is either pushed or pulled or simply travelling in a straight line that appears curved. Excluding electromagnetism and the weak and strong forces matter just travels inertially. However, observers, especially those not moving inertially (i.e., experiencing some acceleration) may not agree on the distance any given bit of matter covers in a unit time (measured with an observer's local clock) or on the direction of its travel. There is an equivalence between an accelerating observer studying something inertial and an inertial observer studying something experiencing acceleration, and GR provides a framework for transformations involving this sort of symmetry. Consequently, one can say that gravitation affects an object moving inertially by changing its path through space and the rate at which its clock appears to tick relative to other clocks. Alternatively, and entirely equivalently, one can say that gravitation affects an object moving inertially by applying an acceleration.

Likewise, objects roll down a gravitational potential gradient. One could see this as being pulled down, or as being pushed down, or as simply gathering energy from the field in which the gradient exists. These are all equivalent.

In Friedman-Walker-Robertson cosmologies, the entire contents of the universe is modelled as a perfect fluid subject to pressure (and negative pressure, which is equivalent to and sometimes called tension) and that the expansion of the universe does not cool the universe. Pressure causes structure (galaxies, etc) to condense, negative pressure causes structure to separate. Pressure therefore is equivalent to gravitation. The metric expansion of space is equivalent to negative pressure. So in FRW (which is fundamental to the most popular cosmology, Lambda_CDM) matter really is pushed together at all but the largest scales (i.e., galaxy clusters, galaxies, star clusters, ..., stars). At the largest scales, a negative pressure separates these "bubbles" of overpressure, and that negative pressure is pretty much exactly equivalent to Einstein's cosmological constant.

When modelling the energy of an FRW universe, one takes into account the energy required to push structure together and to pull superstructure apart. It turns out that the energy to press the structure that we see together is higher than what can be accounted for through a mapping with General Relativity's mass-energy for known particles from the Standard Model. That is, normal matter (electrons, quarks, neutrinos) cannot explain the following equivalencies: why things fall towards nonluminous or light-occluding areas of the sky outside of galaxies within galactic clusters, why a diagram of the centre of mass of clusters of galaxies do not point to the centre of mass calculated by examining the luminous and light-occluding matter, why galaxies have not been pressured into a much smaller volumes of space (e.g., why are there spiral arms, why are globular galaxies so sparse) or what is providing tension on galaxies (remember tension == negative pressure), and so forth. The simplest KNOWN explanation that explains this without conflicting with other observations and experiments is some form of matter that doesn't collapse as quickly under pressure as normal matter does (for instance, because normal matter collides and radiates away photons and neutrinos, all of which allows the matter to shed kinetic energy that otherwise would prevent it from rolling further down the gravitational potential gradient).

That's all dark matter is. There are different proposals for how dark matter behaves, and the most popular one now is Cold Dark Matter -- cold, because it moves thermally rather than relativstically (from the point of view of our telescopes). CDM could be a number of things from some form of dust to a gas of particles that do not stick together in any way until forced into some sort of degenerate state by high pressure (maybe annihilating into standard model particles, maybe combining in some sort of dark matter chemistry or nuclear physics). A fairly popular hypothesis is that it's very similar to slow moving neutrinos. Neutrinos themselves move relativistically because they are so light that the slightest acceleration zips them off to ultrarelativistic speeds. That is, neutrinos could be considered HOT dark matter, where dark also alludes to their non-interaction with electromagnetism.

### Re:Just a question (1)

#### shadowofwind (1209890) | more than 3 years ago | (#34250778)

In regards to dark energy....According to a physicist who posted on here a couple of years ago (I'm too lazy to find it and link to it), the expected expansion rate of the universe is based on a solution to Einstein's equations that makes a homogeneity assumption that is now known to be false. Nobody has redone the solution using what is now known to be a more realistic matter distribution, because its hard, and because there's a disconnect between the theoretical and observational physics disciplines. And of course there's always a disconnect between what subject matter experts understand and the more simplified, sensationalist versions that the rest of us read about. So if what this man says is true, it seems the whole 'dark energy' thing is largely BS. I see no reason to posit a mysterious energy to account for a discrepancy between observation and a model, if the model is already known to be incorrect.

Of course dark matter is a different subject.

In my opinion its reasonable to assume that our theory of gravity is limited in certain regards, and those limitations might have some unknown implications in regards to dark matter. But there's a lot of evidence for dark matter, and one would expect that there is a lot of matter out there that's not easy for us to see, for various reasons.

### Re:Just a question (0)

#### Anonymous Coward | more than 3 years ago | (#34251482)

It is interesting to me there always seems to be more dark matter surrounding brighter more dense galaxies yet at the same time it is claimed DM is only weakly interacting.

I guess one resolution is to tweak the parameters of what weakly interacting means until theory matches observation. :(

### Re:Just a question (0)

#### Anonymous Coward | more than 3 years ago | (#34251946)

There is a theory called Modified Newtonian Dynamics (MoND) that postulated a modification on the extremely small scales. However, studies of galactic collisions have shown that the dark matter effect follows the stars (which more or less just pass by each other) and not the more massive clouds of interstellar gas (which do interact and end up between the two groups of stars), which is what we would expect weakly interacting dark matter to do.

### Re:Just a question (2, Informative)

#### symbolset (646467) | more than 3 years ago | (#34252066)

In a word: yes.

In a bunch of other words: yes, but... The standard model for gravity is used for a number of reasons, first among them that it fits better than the others. It's only off by about a factor of five (working with a universe of 20% normal matter, 80% dark matter). It doesn't devolve into some easily disprovable logical contradictions like most of the others. It's easy to say "yes, but..." It's much harder to propose a theory of gravity that stands up to close inspection of the world's physicists, astronomers and tenure committees. Here on slashdot we aren't (all) physicists, mathemeticians or professors seeking tenure so let's have some fun and talk about some alternatives. I'm no expert either, but I like to play with these ideas and it turns out they can be interesting.

The force of gravity is presumed to fall off as the inverse of the distance squared. If rather than this smooth integral it's a more complex function that would explain a lot. It would however complicate many other things. It should be possible to find describe the observable phenomena with a complex function of gravity over distance rather than missing mass - but then you wind up with a complicated answer that requires considerably more proof than a simpler one and is more subject to disproof. It's still one of my personal favorites. It can pay off to not get too emotionally attached to one theory though, because theories evolve as we learn.

Then there's the fact that we're evolving our understanding from the bottom of a gravity well of our planet, sun, local cluster, galaxy, local galactic cluster, local galactic string. We're looking at the Universe from the middle of dust clouds on all those levels, across vast voids between we cannot measure the properties of, and the properties of the voids may be as important as the properties of the masses in the larger scheme. We're speculating about the evolution of nearly 14 billion years from a viewpoint of mathematics born less than 3000 years ago (Euclid). We may as well be children studying wave motion by splashing in a puddle. We may discover things, but the discovery of all things seems unlikely. We are building a ship in a bottle here. We're composing a powerpoint presentation on a cellphone. Beside our own biases, we're watching the game through a knothole in the fence. It's possible that mass alters time in some way that creates the appearance of gravitic lensing effects that are not there. It's possible that gravity has some time function we're not aware of - a number of experiments to find "gravity waves" have been proposed, but afaik none have borne fruit. It's possible (and close to proven) that at least some of the "constants" in the equations are variable according to some not-understood function, and that in the foreign lands beyond the star of our birth the local rules are different.

We know that gravity affects both space and time. We know we don't fully understand the effects of either. Our Voyager probes, for example, appear to be slowing down at the edge of System Sol for no reason we can explain. Gravity slingshots have somewhat different results than predicted. Even on this minute immediate local level we don't fully understand gravity and its relation to spacetime, though we get closer with every measure. It's possible we're looking at the Universe through some edge effects that alter our view in ways we don't understand yet. When we come to understand them better we may be able to apply corrective lenses. In the mean time some explain the difference between theory and observation with "missing mass" which, if it does nothing else, quantifies the difference between the prediction and the observation in a way that can be modeled, manipulated and explained to the press without sounding too much like you're making the whole thing up. Ultimately it adds to understanding by quantifying the depth of our ignorance with a specific map to the undiscovered country to test new theories against. Like any good lie it can be useful, informative or entertaining even if it isn't true.

The universe is biggish. There are quite a few things to learn about it yet and I think that's a good thing. If the answers came too easy this game would get boring pretty quickly.

In summary: yes. You're invited to propose a better one. Or just to speculate about what it might look like. The next epiphany that leads us closer to an answer is as likely to come from you as anybody else. Discovery is funny that way.

### Re:Just a question (1)

#### radtea (464814) | more than 3 years ago | (#34255638)

could an alternative explanation be that our theory of gravity is wrong?

Sure.

An alternative explanation could also be that elves are holding the galaxy together. Seriously. There are an infinite number of alternative explanations. It's just that some of them are far more plausible than others.

General relativity is a beautiful theory that has been tested over a ridiculous range of field strengths and range, from orbiting black holes to galaxy clusters to GPS corrections here on Earth.

The only anomaly we've found so far are at large distance scales, where everything from Newtonian gravity (galactic dyanamics) to GR (gravitational lensing) fails to account for what we observe based on the matter distribution we can see or reasonably infer by other means.

There are two obvious solutions to this: our description of gravity is wrong, or there is more matter than we expect.

If our description of gravity is wrong it is wrong in precisely the right way required to emulate the effect of having more matter than we expect. This would be a curious coincidence, although not utterly impossible.

Science is the discipline of publically testing ideas by systematic observation and controlled experiment. We have the idea that GR is a good theory. We have the idea that dark matter explains large-scale deviations from it. We are testing this idea by subjecting it to more and more precise observations. If GR is not a good theory then that process will eventually yeild a result that cannot be explained by any self-consistent distribution of matter.

So far, that hasn't happened.

On the other hand, science can and does prove positive statements all the time, contra the bizarre claims of non-scientists like Karl Popper.

For example, science proves the existence of entities by positive detection of them. We proved the existence of neutrinos this way. You prove the existence of your socks this way. And we would like to prove the existence of dark matter this way: by detecting it in the lab rather than observing it in the sky. Depending on the characteristics of dark matter particles this may or may not be possible, and so long as we have not done this there will always be a tiny bit of doubt regarding its reality, and the suggestion that maybe the astronomical observations are better described by some modification to gravity.

### Re:Just a question (1)

#### Coren22 (1625475) | more than 3 years ago | (#34256482)

Dark Matter isn't the big deal there. Dark Matter is just Matter that doesn't emit energy, it could be just dust out in space. Dark Energy however is the stuff I can't get my head around.

### Look for the unicorn (1)

#### mangu (126918) | more than 3 years ago | (#34248354)

Luckily this story is a dupe and we know from the previous one that there's a unicorn in there [slashdot.org] .

Those colors come from the unicorn farting.

### Re:Look for the unicorn (4, Informative)

#### mcgrew (92797) | more than 3 years ago | (#34248444)

TFA is firewalled off, but I found a better FA [nasa.gov] -- straight from NASA's JPL. here [nasa.gov] is a hi-res photo of the "dark matter" lensing.

### Re:Look for the unicorn (1)

#### WrongSizeGlass (838941) | more than 3 years ago | (#34248536)

here [nasa.gov] is a hi-res photo of the "dark matter" lensing.

Thanks, that picture is much better. I can see the dark matter up there in the corner now. ;-)

But seriously, since we can't see dark matter why would they post a picture of, well, non-dark matter?

### Re:Look for the unicorn (1)

#### Jesus_666 (702802) | more than 3 years ago | (#34250872)

Because the way NASA etc. see the more distant regular matter indicates gravitational lensing while they can't see enough near matter to account for the neccessary mass. IANAAstronomer but I think the distorted galaxies we see in the GP's second image is either an actual image of such lensing or an exaggerated depiction of the same to get the message across.

### physics has hit a dark brick wall (-1, Troll)

#### Anonymous Coward | more than 3 years ago | (#34248438)

Who would have though Einstein could be so wrong in two of his famous quotes:
"All things should be only as complicated as they need to be.”
"The most incomprehensible thing about the universe is that it is comprehensible."

All these hacks like dark energy, dark matter, string theory, hundreds of field/particles/magic numbers in the standard model to try to describe and model known cosmology and subatomic particles.

Seems like we have reached the limit of our intelligence to further understand the universe. The current state of affairs in physics is a mess and nothing of significance has occurred in the field for the last 20 years!

### Re:physics has hit a dark brick wall (3, Insightful)

#### WrongSizeGlass (838941) | more than 3 years ago | (#34248592)

Seems like we have reached the limit of our intelligence to further understand the universe.

It took us how long to get to Relativity? That was only around 100 years ago. Give us a little more time and we'll get it. This isn't a timed test (unless we destroy our planet via wars, pollution, diseases, oppression or a combination thereof).

### Re:physics has hit a dark brick wall (1)

#### Raenex (947668) | more than 3 years ago | (#34254798)

This isn't a timed test (unless we destroy our planet via wars, pollution, diseases, oppression or a combination thereof).

Don't forget alien invasion.

### Where's Bender . . . ? (1)

#### PolygamousRanchKid (1290638) | more than 3 years ago | (#34248480)

Paste an image of Bender into that dark matter image, and it would look like the episode of Futurama, where Bender meets the God Entity.

"You were doing well until everyone died."

So who copied who?

### Re:Where's Bender . . . ? (5, Funny)

#### Bozzio (183974) | more than 3 years ago | (#34248650)

God: Bender, being God isn't easy. If you do too much, people get dependent on you, and if you do nothing, they lose hope. You have to use a light touch. Like a safecracker, or a
Bender: Or a guy who burns down a bar for the insurance money!
God: Yes, if you make it look like an electrical thing. When you do things right, people won't be sure you've done anything at all.

### They're ruining it for all of us. (3, Interesting)

#### Anonymous Coward | more than 3 years ago | (#34248558)

Building this map may result in the shortening [arstechnica.com] of the life span of the universe.

### Re:They're ruining it for all of us. (2, Interesting)

#### MozeeToby (1163751) | more than 3 years ago | (#34249294)

I understand the science journalist not understanding, but does the qualified physicist really not understand the difference between an 'observer' in the traditional sense and an observer in the quantum sense? All of the things that we detect with our advanced technology effect things throughout the universe whether we are looking at them or not, the things that they effect are observers. A grain of dust around a star that is given an every so slightly different orbit because of quantum effects is just as much an 'observer' as a human being looking through a telescope is.

### Re:They're ruining it for all of us. (1)

#### AC-x (735297) | more than 3 years ago | (#34254734)

Understanding of quantum physics fail. That supernova is being "observed" by every single atom that the light from it hits, it doesn't make any difference whether it's a piece of inert rock or a telescope CCD.

### Allan Sandage (5, Informative)

#### bhodikhan (894485) | more than 3 years ago | (#34248672)

I just learned that Allan Sandage died this weekend. He was a giant among astronomers and did a lot of work with the Hubble. Take some time and learn about him if you care about astronomy http://en.wikipedia.org/wiki/Allan_Sandage [wikipedia.org]

### Dear god! (-1, Troll)

#### Badbone (1159483) | more than 3 years ago | (#34248814)

Dark matter- God of the gaps. Can't explain something? Dark matter! That magical substance that is everywhere it wants to be, any way you need it to be!

Gravity calculations wrong? Dark matter! What? That's makes other calculations wrong? Dark matter! The more the better!

I'm being sarcastic here, but actually it's because I'm just so jealous. Real scientists can't simply explain things away by using Substance X.

Anything that we can not or have not been able to explain used to be called an act of God. Now, it's an act of dark matter. Hubble proves it!

### Re:Dear god! (2, Insightful)

#### geekoid (135745) | more than 3 years ago | (#34249014)

Incorrect. And frankly, you bone heads who keeps saying this are getting really annoying.

The most annoying thing is that ignorant people aren't ridiculed when making wildly incorrect statements.

### Re:Dear god! (0)

#### Anonymous Coward | more than 3 years ago | (#34249062)

Could be due to dark matter.

### Re:Dear god! (1)

#### lennier (44736) | more than 3 years ago | (#34250144)

But it's probably quantum.

### Re:Dear god! (1)

#### bmo (77928) | more than 3 years ago | (#34251222)

ignorant people aren't ridiculed when making wildly incorrect statements.

I don't think it's a problem with the ignorant people per se, it's with the willfully ignorant people, of which there are many. These types are what you could call fractally wrong^1 and to try and counter their spewage with logic is maddening, since one doesn't even know where to stop, so one gives up easily.

--
BMO

Fractal wrongness: The state of being wrong at every conceivable scale of resolution. That is, from a distance, a fractally wrong person's worldview is incorrect; and furthermore, if you zoom in on any small part of that person's worldview, that part is just as wrong as the whole worldview.

### Re:Dear god! (-1, Flamebait)

#### Anonymous Coward | more than 3 years ago | (#34249128)

You sound like a cunt. Now go fuck off.

### Re:Dear god! (3, Insightful)

#### mug funky (910186) | more than 3 years ago | (#34249702)

oh, ffs.

i know i shouldn't feed a troll (who should be modded as such btw), but let's cut a deal:
we'll compare notes.

### Re:Dear god! (1)

#### Black Parrot (19622) | more than 3 years ago | (#34251424)

Dark matter- God of the gaps. Can't explain something? Dark matter! That magical substance that is everywhere it wants to be, any way you need it to be!

Gravity calculations wrong? Dark matter! What? That's makes other calculations wrong? Dark matter! The more the better!

I'm being sarcastic here, but actually it's because I'm just so jealous. Real scientists can't simply explain things away by using Substance X.

Anything that we can not or have not been able to explain used to be called an act of God. Now, it's an act of dark matter. Hubble proves it!

Why do so many people have a knee-jerk rejection of anything new we discover about the universe? Is there any reason we should have discovered dark matter before now if it exists? Is there any reason our brains should have generated reliable intuitions about the structure of the universe?

Sure it's a hypothesis, but there are reasons cosmologists accept it.

And I hate to break it to you, but invoking "dark matter" doesn't just explain any arbitrary observation, like "goddidit" does. The hypothesis that there exists a great deal of something that has mass but doesn't otherwise interact much (or at all) with more familiar stuff has very specific implications for what we should see when we point out telescopes to the sky.

### Re:Dear god! (2, Insightful)

#### Lord Crc (151920) | more than 3 years ago | (#34252258)

Dark matter- God of the gaps. Can't explain something? Dark matter! That magical substance that is everywhere it wants to be, any way you need it to be!

Can't explain the missing mass of Beta decay? Introduce new particle! [fnal.gov] Can't explain how electrons are confined to the nucleus? Introduce new particle! [gsu.edu] Can't explain the inertial mass of particles? Introduce new particle! [wikipedia.org]

So yeah, introducing new particles to explain discrepancies in observations is something totally unheard of and not something a real scientist would do...

### Did anyone notice (1)

#### moxsam (917470) | more than 3 years ago | (#34248998)

It looks like a giant cosmic brain! I think they are onto someone.

### Goatee universe (2, Funny)

#### Caerdwyn (829058) | more than 3 years ago | (#34249148)

It seems that "dark matter" is by far the most common type of matter in the universe; what we call "normal matter" is very much in the minority.

You realize what this means?

WE are the "Goatee Universe [wikipedia.org] ".

### Re:Goatee universe (1)

#### mug funky (910186) | more than 3 years ago | (#34250090)

am i the only one who read that as "Goatse Universe"?

### Re:Goatee universe (1)

#### bmk67 (971394) | more than 3 years ago | (#34250210)

am i the only one who read that as "Goatse Universe"?

No.

no

### Re:Goatee universe (0, Offtopic)

#### Caerdwyn (829058) | more than 3 years ago | (#34250908)

Spock was a naughty Vulcan.

And a top.

Yes.

### 1982 called... (0)

#### rossdee (243626) | more than 3 years ago | (#34249248)

Anyone remember 70 column text on an Apple ][ graphics screen? It worked best on a monochrome monitor. I forget the name of the program, but I think it was by the Beagle Bros.

### Re:1982 called... (1)

#### UnknownSoldier (67820) | more than 3 years ago | (#34250622)

Dude, there were a LOT of Beagle Bros software...
http://stevenf.com/beagle/products.html [stevenf.com]

Assuming a non-proportional font...

280 / 70 = 4 pixels / character ?? That's 3 pixels per glyph including a 1 pixel "whitespace" to seperate glyphs.

or

56 col = 5 pixels/character

### Dark matter (0)

#### Anonymous Coward | more than 3 years ago | (#34250542)

Here's most detailed picture of dark matter [signaturestop.com] I've found.

### Cthulhu anyone? (0)

#### Anonymous Coward | more than 3 years ago | (#34250964)

OK, I know it's just my pattern-seeking brain working overtime... ... but does anyone else see Cthulhu in that picture at the link?!?

Just in case... Yog-Soggoth! Hast'r! Ph-nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn!

### Reminds me (1)

#### qmaqdk (522323) | more than 3 years ago | (#34252420)

This reminds me of something that has puzzled me for a while:

* The energy of a photon is proportional to its frequency.
* Photons are redshifted due to the expansion of space.

So the energy of the photons, e.g. from CMB, is lower. Where did the energy go? It must be connected to expansion somehow, but how? And on a second note, Einsteins famous equation tells us that energy is proportional to mass, so does this influence mass somehow?

This is probably obvious for you physicists out there, so I thought I'd ask.

### Re:Reminds me (1)

#### CXI (46706) | more than 3 years ago | (#34253706)

I have similar questions that make we wonder about how these types of calculations are made. Like you indicate, are the theories considering all the energy of all wavelengths inside and emanating from a galaxy or a cluster when calculating its mass? We only "see" a tiny fraction of that energy. Are they calling the rest of it dark energy (which to me makes it sound unnecessarily mysterious) instead of just regular energy we can't observe? It should be possible to estimate this energy and how its mass compares to the estimate of matter for the same object. I also wonder when dealing with such huge scales if time issues are included in the calculations. If you are mapping matter in 3D across millions or billions of years the matter itself is moving, making the map less and less accurate and more distorted the father out is it from us.

### Re:Reminds me (0)

#### Anonymous Coward | more than 3 years ago | (#34268486)

In General Relativity there is a generalization of the Newtonian conservation laws into a sort of energy-momentum conservation law.

There are a variety of ways you can look at this. One is that energy is removed from the gravitational field to change the momentum of an object. Another is that space-time itself moves by exchanging energy with other fields, such as the electromagnetic field. So, space can expand by making photons travelling through it redder (less energetic), or alternatively and equivalently the metric expansion of space creates higher gravitational potentials that photons must climb (redshiting through gravitational time dilation), or alternatively and equivalent the expansion of space changes the momentum of matter embedded in it leading to a doppler shifting of photons seen by an detector embedded in a galactic supercluster whose momentum relative to all other galactic superclusters increases.

Dark energy looks at the problem from the perspective of field theory, since Lambda_CDM cosmologists studying the early universe pretty much have to be relativistic gauge theorists.

The energy density in a field is the expectation value for a point in space times all the points in space. I.e., average energy per unit volume times number of unit volumes. In a Friedman-Walker-Robertson cosmology -- the most popular cosmological model -- the evolution of the volume of the universe is assumed to be adiabatic. That is, the global energy density of all fields is constant, whether space is expanding or contracting, or some mix. Because the universe is expanding, the total volume is increasing, and therefore the total energy is the energy density times total volume, and tadah total energy is increasing. However, because of relativistic effects, the energy of a field is not uniquely defined at any given point. This is also true even more generally of the curvature of space-time in GR. This drives a generalization of conservation of energy and conservation of momentum laws into a formalization written down as \del_mu T^(\mu\nu) = 0, which basically says that there is a balance between the evolution of space-time and the total mass-energy of everything in it (that is all the fields, bar gravitation). In a completely static space-time, mass-energy is constant; introducing a change in either produces a complementary change in the other. Since most physical observers will see a dynamical space-time, they will also see a violation of the conservation of energy! (Most of them will agree that energy is constantly increasing. Most nonrelativistic observers will also agree that there are a constant number of electrons and photons and similar particles in the universe as it expands, so where does the increase in energy come from? The vacuum? Some other field we don't know about? Some offsetting dynamism in the curvature of space-time that we do not presently see? We don't know. That energy is dark, like the dark ages are dark.)

I hope that helps somewhat. It's not super-rigorous.

Einsteins famous equation tells us that energy is proportional to mass, so does this influence mass somehow?

It's really either a series of equations or a longer one in the form of E^2 = (mc^2)^2 + (pc)^2 where p is momentum and m is inertial mass in the sense of intrinsic resistance to acceleration. Particle physicists in particular like to use centre of momentum frames which makes p = 0, so you often see E = mc^2.

Photons have m = 0, so the energy of a photon is E = pc; for "real" observers, a photon's momentum is nonzero. They also have energy E = hv, where h is Planck's constant and v is the photon's frequency; they also have energy E = \lambda / h, where \lambda is the photon's wavelength. Thus we have a relationship between a photon's wavelength and its momentum. Since for a photon c and m are both constant, any "robbing" of energy or "donating" of energy must affect the wavelength.

Climbing up a gravitational potential gradient requires energy, so when a photon leaves the gravity well (like a star and its home galaxy) it redshifts. Rolling down a gravitational potential gradient increases energy, so when a photon falls into a gravity well (like our galaxy and planet) it blueshifts. This happens to any photon no matter what its energy happened to be. This gravitational time dilation affects the whole set of photons emitted by a shining object equally, so spectral absorption and emissions lines shift as well.

The metric expansion of space creates a huge negative curvature in space-time, with greater curvature when the expansion is faster (like in the early universe). Negative curvature is the equivalent of having a greater gravitational potential; a gravitational potential is greater when an object at that potential can fall further. The gravitational potential is very high in deepest inter-galactic-cluster space, and very low at a black hole. From our point of view, photons emitted by stars in the early universe must climb up a very steep gravitational potential gradient and then roll down a relatively much gentler one. So they redshift much more than they blueshift, and in any case we always see the final integrated result. (If we know what the spectrum was like at the time of emission of a bunch of photons, and what sort of matter might absorb or scatter some of that spectrum along the way, we can determine the comoving distance to the source of the photons.)

Since redshifting and blueshifting an individual photon affects its energy, where did the energy go for a redshifted photon? It went into space-time curvature, i.e., gravitation altered its momentum, and a photon's energy is determined by its momentum, and its wavelength by its energy.

(Think about a photon passing by a huge mass while in flight; it follows a path that curves towards that huge mass, or equivalently its momentum is altered in proximity to the huge mass. A longer path == a change in momentum. A change in momentum means a change in wavelength. So if we are creating more space, we are also creating a longer path. It's still a longer path == a change in momentum. Thus the redshift of that photon.)

### and it was good (1)

#### MrKaos (858439) | more than 3 years ago | (#34253486)

Isn't it wonderful how science uncovers the nature of god's universe for all to marvel at?

This really illustrates intelligent design's truly blasphemous form.

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