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Dark Matter — "Alternative Gravity" Team Responds

kdawson posted more than 7 years ago | from the not-so-fast dept.


An anonymous reader writes, "Following previous results, an international team of astronomers answers, defending the case for a modification of the theory of gravity. This article presents an alternative to dark matter and states constraints on the neutrino mass. In short, dark matter is still not a necessity, provided that neutrinos weigh 2eV. This is allowed by what we currently know and should be tested in the KATRIN experiment in 2009."

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why would matter be dark (0)

phirzcol (447454) | more than 7 years ago | (#16058765)

regardless of their energy potential why does dark matter have to be dark? what has been done to look at the mass of all of the photons in the universe. no matter what some people say they have to have some mass. think about it, all of the photons that have ever been created, unless they run into something will continue to travel accross the universe. since the beginning of the universe their has to be quite a few of them

Re:why would matter be dark (0)

Anonymous Coward | more than 7 years ago | (#16058776)

Because it cannot be directly observed with optical equipement.

Re:why would matter be dark (1)

DoubleEdd (178052) | more than 7 years ago | (#16058789)

Dark matter has to be 'cold' - slow moving. If it goes too fast, like photons (or neutrinos for that matter) then structure can't form as it all gets washed out. It needs to be slow moving enough to clump. So even if photons did have a small mass that wouldn't work.

Re:why would matter be dark (1)

SixByNineUK (949320) | more than 7 years ago | (#16058826)

Perhaps the clumpyness comes from standing waves, or if it is directly related to the baryonic matter.

Of course this assumes that the baryonic matter formed first. I also think that this kind of model would imply that a star would produce a constant stream of photons that 'weigh' 10 times its own mass. There is some conservation of energy problems there!

I don't think that photons could naturaly clump under their own mass as I imagine very strange physics would result.

Re:why would matter be dark (2, Insightful)

SixByNineUK (949320) | more than 7 years ago | (#16058792)

I am not sure that photons 'have' to have mass. I would indeed suspect that they are 'forbidden' from having mass, due to the fact that they are traveling at the speed of light. If they did have any intrinsic mass, traveling at that speed would cause the mass to move towards an infinite value, esencialy meaning that light would not be able to travel at the speed of light.

Of course relitivity could be wrong, or light could travel slower than the 'speed of light', if that makes any sense.

Re:why would matter be dark (0)

DrKyle (818035) | more than 7 years ago | (#16058815)

If they didn't have mass they wouldn't bend their paths around large gravity wells, but they do.

Re:why would matter be dark (4, Informative)

SixByNineUK (949320) | more than 7 years ago | (#16058853)

I do not beleve that this is true.

Newtonian mechanics implies that for gravity to affect an object it must have a mass, however General Relitivity does not impose this restriction.
I am pretty sure that the gravity effect is caused by the distortion of space time such that the 'shortest' path (That which the light must follow) is curved.

I am not an expert in GR, but perhaps someone here can verfy my claims.

Re:why would matter be dark (5, Informative)

Claws Of Doom (721684) | more than 7 years ago | (#16058903)

Their paths don't bend - it is the paths themselves that are distorted in space-time by the gravity well. This distortion appears to be bent in three dimensions - to the photon it is perfectly straight...

(ok, ok, simply *massive* oversimplification here - to the point of error, but I hope you understand my motives.)

Re:why would matter be dark (1)

trewornan (608722) | more than 7 years ago | (#16058941)

Photons have mass only because they have energy and e=mc2. What the GP is referring to, is rest mass i.e. if a photon were to be at rest and therefore had no kinetic energy (ignoring for the moment that a photon cannot exist at rest) it would then have no mass.

Re:why would matter be dark (1)

Fordiman (689627) | more than 7 years ago | (#16059041)

And photons that are 'clumped', would thus have no mass.

On the other hand, query: Do high-energy (ie: high mass) photons have a gravitational effect? Or do the formulae only work given a rest mass?

Re:why would matter be dark (3, Informative)

Jerf (17166) | more than 7 years ago | (#16059345)

On the other hand, query: Do high-energy (ie: high mass) photons have a gravitational effect? Or do the formulae only work given a rest mass?
The formulas work for all mass-energy, which photons possess. Photons thus do technically interact via gravitation. However, if you do the math, you'll find that the interaction is very, very small, to put it lightly, so while it is technically wrong to say "photons don't interact with each other", it isn't very wrong.

Somewhere in the great online book Reflections on Relativity [] , there is a discussion of "kugelblitz"s, which is a theoretical black hole that consists entirely of energy, which could be just a lot of photons. The term isn't in much use in science (though I did find at least one reference) because it's not very useful; in practice, a photonic kugelblitz is impossible, and once such a black hole forms, it would be indistinguishable from any other black hole. But it is theoretically possible, because all mass-energy contributes to the gravitational field.

Re:why would matter be dark (1)

Gilmoure (18428) | more than 7 years ago | (#16059294)

So...when people slow down light [] , does it gain mass?

Re:why would matter be dark (4, Interesting)

SigILL (6475) | more than 7 years ago | (#16058835)

I am not sure that photons 'have' to have mass. I would indeed suspect that they are 'forbidden' from having mass, due to the fact that they are traveling at the speed of light.

Photons lack mass but (since they move at 1,0 c) they do have momentum. This is wat makes solar sails work.

Hey, maybe that's the answer: substitute momentum for mass in all gravity calculations and see if that makes it all work.

No mass for photons (5, Informative)

jpflip (670957) | more than 7 years ago | (#16058884)

I'd like to clear this up because there are very common misconception that photons are massive or that something has to be massive to feel gravity, both of which are false.

THEORY: In our current understanding, photons are forbidden from having mass because of the way quantum electrodynamics (the most precisely tested theory in the history of science) works. It's an exercise in field theory to show it, but the gist is that electromagnetism (light, charge conservation, electric and magnetic forces...) are a consequence of a symmetry of nature, and that symmetry only works if the associated carrier particle (the photon) has exactly zero mass.

EXPERIMENT: If the photon had even a very tiny mass, it would also mean that the electromagnetic interactions would become short range (just like the weak interactions, which are mediated by a massive carrier). The usual inverse square law would become an exponential falloff. This has been tested for in laboratories (and in astronomy!) very precisely, so there are ridiculously strict upper limits on the photon mass.

This doesn't mean photons don't feel gravity!! Gravity interacts with all energy, not just mass, and so the energy of a photon is enough to cause it to bend around massive objects.

Re:No mass for photons (1)

jimstapleton (999106) | more than 7 years ago | (#16058906)

given relativity, if a photon had mass, it would have infinite energy. one could correlate through that, if a photon had mass, and a (as in one, just one) photon existed, it would probably destroy the universe.

Re:No mass for photons (1)

Austerity Empowers (669817) | more than 7 years ago | (#16059272)

Ah, let the transportation safety board try to stop be from boarding a plane and giving photons mass! JUST LET THEM TRY! MUAHAHAHAHA!

Re:No mass for photons (0)

Anonymous Coward | more than 7 years ago | (#16059028)

If objects lose mass when they emit photons, where does it go? Seems there are so many "special cases" to make theories work. Damned physicists, they just change things up to sell more textbooks. Next they'll change the number of planets, just to make a buck.

Re:No mass for photons (2, Interesting)

Fordiman (689627) | more than 7 years ago | (#16059150)

"If objects lose mass when they emit photons, where does it go?"

Well that's not always true.

In a star, it loses mass which is converted to the energy of the photon. In a lightbulb, the photon's energy comes from the covering of a potential difference in voltage.

The thing is, while E=mc^2 and E=hw (E is Energy; m is mass; c is speed of light; h is planck's constant; w is angular frequency [similar to frequency, but in radians per time unit]) state that more energetic photons have more apparent mass than non-energetic photons (m=hw/c^2), the fact is that they have no rest mass (at rest, w=0, so m=0).

The truth is, however, that a photon's apparent mass is only really useful for momentum calculations. Higher frequency light takes more energy to redirect than lower frequency light.

Though, it gives me a question about the idea behind solar sails:
picture two perfectly paralell low-mass perfect reflectors (ie: no loss in the reflected light). They are in vacuum, and there is no friction. According to the theory that predicts the way a light sail would work, you should be able to shine a light perpendicular to one of the sails from between them, and they would slowly accelerate apart. When you shut the light off, the light bouncing back and forth would keep pushing.

Would the light decrease in frequency until it is 'at rest', and thus nonexistant? If not, where does the energy come from? Would the light, instead, decrease in speed, becoming normal matter? Is this even possible?

Re:No mass for photons (3, Interesting)

roemcke (612429) | more than 7 years ago | (#16059225)

When you shut the light off, the light bouncing back and forth would keep pushing.

After each "push" the photons will not be reflectet with the same frequency (the sails are moving away from the light. hint: doppler effect)

Re:No mass for photons (1)

roystgnr (4015) | more than 7 years ago | (#16059312)

In our current understanding, photons are forbidden from having mass

Technically aren't they just forbidden from having a non-zero "rest mass"? They still have energy, and that energy is still convertible to mass and still generates a gravitational field like mass. There are still reasons why photons can't directly account for the effects of dark matter, but it's not an intrinsic impossibility.

(I'd say photons can't indirectly account for the effects of dark matter either, but that would be tempting fate; you just know that the Foe would pick that moment to come pouring out of the Kugelblitz and wipe out civilization.)

Re:why would matter be dark (2, Funny)

eln (21727) | more than 7 years ago | (#16058802)

"Dark matter," also known as "adolescent matter" is so known because of its inherent moodiness. It spends a lot of its time wearing dark makeup and brooding.

Re:why would matter be dark (1)

miceliux (654192) | more than 7 years ago | (#16058814)

So..... you have no idea of physics, haven't you?

Re:why would matter be dark (1)

phirzcol (447454) | more than 7 years ago | (#16058846)

the only time you can view photons is if they are traveling tward you. as far as the grouping of dark matter photons are probably more or less evenly distributed on a macro scale and uneven on a micro scale(remember scale is relative to the entire universe)

Re:why would matter be dark (1)

ZonkerWilliam (953437) | more than 7 years ago | (#16059236)

Photon's are counter intuitive, picture it as having mass only when it's at rest, but none when it's moving. On the same note energy, in large enough quantities can warp spacetime, this could only happen in concentrated regions. Dark Matter can easily be defined as the particle alot of scientists are looking to as an explanation, the Axion. The Axion is defined as a weakly interacting, low mass particle, almost invisible to normal matter. So something that fits the bill, such as a neutrino with a low mass, could also explain what dark matter is. Although IMHO a neutrino's tend to move to fast (~C) and do not concentrate around galaxies, as far as can be detected. It doesn't appear that these people are factoring Neutrino Oscillation either, but i could be wrong.

So We Must Wait. (4, Insightful)

Mikkeles (698461) | more than 7 years ago | (#16058771)

Basically, then, until the mass of the neutrino has been tested, dark matter or alternate gravity are just speculations with the arguments being:

is too!
is not!
is too!


Re:So We Must Wait. (1)

God'sDuck (837829) | more than 7 years ago | (#16058869)

no they're not!

Re:So We Must Wait. (0)

Anonymous Coward | more than 7 years ago | (#16059346)

Not entirely true. Neutrinos definately have mass, it's been proven. All stars generate a staggering quantity of Neutrinos every second and have done so since the early days of the Universe. Neutrinos are likely the engine driving the Universe it simply needs to be confirmed. There is a known quanity of Neutrinos produced, obvious approximation but it is known. All that remains is to confirm the mass of Neutrinos. Gravitational theory has always had some fudge factors. Einstein came up with then dropped the gravitational constant to explain one of them. Neutrinos can fill in many of the gaps. It's a likely explaination but like all theories needs to be confirmed.

Does it allow for... (-1)

cp.tar (871488) | more than 7 years ago | (#16058772)

... the Dark side of the Force?

Anti-dark-matter scientists are like ID scientists (0, Troll)

BadAnalogyGuy (945258) | more than 7 years ago | (#16058773)

Look at your night sky. It's a whole shitload of blackness with some stars thrown in. Now consider that there is a form of matter which is very dense and very dark. So dark, in fact, that it doesn't give off any radiation at all. All it does is exert a gravitational pull on surrounding masses, just like everything else in the universe.

It isn't difficult to look up and see all that darkness and think that maybe there's something in that blackness that just can't be seen.

But these guys would have you change the Theory of Gravitation because they can't grasp that maybe there are weird states of matter that exist just outside our physical grasp. They'd rather you believe that neutrinos have mass. These neutrinos that have for eons blasted through us at the speed of light with no interaction at all, they are the cause of the entire universe bending unpleasantly.

If you say that neutrinos have a physical manifestation greater than zero, you're going to also have to explain why these particles exhibit no interaction with anything except for being able to curve the shape of space on a galactic level.

Re:Anti-dark-matter scientists are like ID scienti (5, Informative)

denominateur (194939) | more than 7 years ago | (#16058795)

err, neutrinos do have mass, but not as much as stated in the paper. As far as current experiments go neutrinos come in three flavours and interchanging between them is only possible if they have mass. It has been shown in experiments that they change type and hence must have mass.

Re:Anti-dark-matter scientists are like ID scienti (1)

timster (32400) | more than 7 years ago | (#16058797)

Well, minor nitpick: I don't see why neutrinos would interact with other particles just because they had some small amount of mass. It's not as if they would produce more than a truly tiny amount of gravity, and they obviously don't interact electromagnetically with anything.

Re:Anti-dark-matter scientists are like ID scienti (1)

geoffspear (692508) | more than 7 years ago | (#16058847)

Hydrogen and helium molecules also produce a "truly tiny" amount of gravity. Therefore, it's impossible that the Sun could actually be exerting enough pull on the Earth to keep it in orbit.

Wait, there might be a flaw in the logic here somewhere.

Re:Anti-dark-matter scientists are like ID scienti (1)

cp.tar (871488) | more than 7 years ago | (#16058799)

I would have replied to all the inconsistencies... then I noticed the name. Not a bad troll.

Re:Anti-dark-matter scientists are like ID scienti (1)

Abrax (981838) | more than 7 years ago | (#16058807)

Well, some real testing is needed. Is their any practical use for this like FTL travel?

Re:Anti-dark-matter scientists are like ID scienti (1)

SteveAyre (209812) | more than 7 years ago | (#16058817)

They do interact with matter, but because they're very small they simply pass straight through matter because the distance between particles in atoms / atoms are so great and only actually collide very rarely.

Re:Anti-dark-matter scientists are like ID scienti (1)

SteveAyre (209812) | more than 7 years ago | (#16058844)

Moreover recent experiments have shown they do have mass (see Wikipedia).

They know their mass is >= 0 and 2.2 eV, hence why the proposed 2eV is possible.

Re:Anti-dark-matter scientists are like ID scienti (1)

SteveAyre (209812) | more than 7 years ago | (#16058862)

(of the electron variety anyway)

Re:Anti-dark-matter scientists are like ID scienti (2, Informative)

Fordiman (689627) | more than 7 years ago | (#16058820)


Google "electron volt in amu":
1 electron volt = 1.07354412 × 10-9 atomic mass units

That's five whole orders of magnitude lighter than an electron. That sounds like a good reason they don't interact; it'd be like saying a dust cloud should interact with a chain-link fence.

Re:Anti-dark-matter scientists are like ID scienti (5, Insightful)

FhnuZoag (875558) | more than 7 years ago | (#16058842)


Neutrinos *do* have mass, and this fact is accepted by pretty much all physicists. The argument for this comes from discovery that they change states over the course of their lives, which means that they experience time, which means that they cannot travel at the speed of light, which means they must have a small mass. (This explains the apparently deficiency of solar neutrinos which was a problem in the 70s) Pinning down the exact value of this mass is more troublesome, though - for now, we know only that it's small, but positive.

What more puzzles me about this statement is that neutrinos have generally been counted as *part* of dark matter - in particular, they are proposed to constitute some of those so-called Weakly Interacting Massive Particles (WIMPs) which is one of two possible models for dark matter. I don't see how changing the details of these particles would change how neccessary they are, unless these guys are trying a bait and switch by redefining dark matter to be unneccessary. (Which would be a very dirty trick.)

Re:Anti-dark-matter scientists are like ID scienti (1)

spun (1352) | more than 7 years ago | (#16058987)

It sounds like they are going for a MMOND theory, modified modified newtonian dynamics. They admit the presence of dark matter. In fact, they reference another experiment as well as the bullet cluster observations that seems to show that MOND can't account for everything. So to save MOND, they are saying it doesn't have to account for everything. Massive neutrinos migth account for the rest.

No, YOU'RE like an ID scientist (2, Interesting)

Alaren (682568) | more than 7 years ago | (#16058879)

So dark, in fact, that it doesn't give off any radiation at all

And more to the point, fails to reflect radiation, fails to block radiation, in general, um, fails to interact except in terms of gravity.

What was that you were saying about explaining something with mass failing to interact? Your critique seems to preclude both alternatives. Now, I'm skeptical of dark matter, but if someone can catch some for experimentation, I'll gladly accept it as final proof. And it sounds like we are in fact going to test whether neutrinos have mass, so at least we're making experimental progress on the other side of the fence. I think that's great.

You mention ID. As of right now, dark matter remains largely a matter of faith. There's a some evidence (see? gravity! DARK MATTER!) but it's theoretical, not experimental; the same can be said of ID scientists (see? a universe! GOD DID IT!) (yes I recognize that the leap in ID is a lot longer, but the point is, it's there). Dark matter is a theory not because we are sure it's there, but because some scientist can't imagine any other explanation, again much like ID. It doesn't mean they're wrong, but they still lack experimental proof which means it is not a foregone conclusion that they're right.

I applaud all attempts to better explain our universe through rational means, I know it's difficult (too difficult for me, certainly). But don't discount alternative theories--especially theories that can and will soon be proven or disproven experimentally.

Re:No, YOU'RE like an ID scientist (2, Informative)

timster (32400) | more than 7 years ago | (#16058994)

I don't think anyone has a huge amount of "faith" in dark matter. The problem is that there is a conflict between theory and observation; gravity as we understand it doesn't predict the shape of the universe that we see, so we try to figure out what it is that we don't understand. That is how science progresses.

Our theories of gravity have held up well under testing many times, though it's fair to say that we don't know as much about it as we would like. Alternate gravity is also a matter of uncertainty, though, as we don't have any solid data showing that our gravity theories are wrong. Quantum physics has shown that there are many types of particles and many different interactions, suggesting that not all matter is structured the same way, so it's not unreasonable to suggest that there might be a type of matter that we don't understand.

Naturally there are physicists exploring both possibilities and they can be fans of one idea or the other, but that doesn't mean that they are acting on "faith". It's just how science has always progressed. There was a time before relativity was tested when it was controversial, and to some degree it still is.

Re:No, YOU'RE like an ID scientist (1)

dc29A (636871) | more than 7 years ago | (#16059010)

There's a some evidence (see? gravity! DARK MATTER!) but it's theoretical,

IANAP (I am not a physicist), but isn't the The Great Attractor [] more than theoretical proof of something dark that is attracting all those galaxies? Also, why do stars on the outer rim of galaxies revolve so fast around the core? Spiral galaxies do not seem to spin around their core like expected [] .

Dismissing dark matter as purely theoretical is shortsighted IMO.

Important Note (1)

dmatos (232892) | more than 7 years ago | (#16059034)

As has been explained before, and will doubtless be explained again, ID is not a scientific theory, and does not hold the same value as the scientific theory of the existence of dark matter.

If dark matter exists (ie, the theory), it can explain certain observed phenomena. However, where it differs from ID is that the theory can be used to make falsifiable predictions about things we have not yet measured. Using the theory as a base point, we can predict what will happen in certain regions of space if there are WIMPs there. We can predict how the universe is going to expand or contract. If any of these predictions are wrong, then the theory that there is dark matter is also wrong.

On the other hand, intelligent design does not offer any falsifiable predictions. There is no way to test the "theory" (in this case, non-scientific) to determine if it is false. If you can devise a test that would prove ID to be false, then that would elevate it to the status of a scientific theory. It still wouldn't be a useful theory, however, as it does not offer any predictions as to how unobserved phenomena will react when we do get a chance to observe them.

Dark matter is there because the math behind it explains the current set of observations, and because there is a way to prove that the current set of observations is not due to dark matter. Intelligent design is there because Christians are upset about the removal of their god from the science classroom.

Re:No, YOU'RE like an ID scientist (2, Insightful)

ajs (35943) | more than 7 years ago | (#16059229)

Dark matter is a theory not because we are sure it's there, but because some scientist can't imagine any other explanation

This is incorrect. Theory exists regardless of the existance of any one theorist who believes that the theory must be true or is the only explanation available.

To re-state: dark matter is a theory becuase it was a hypothesis which has endured the gathering of some experimental data, but there is not yet enough experimental data to exclude other possibilities. This is, in no way, a matter of faith. It's certainly a matter of speculation and experimentation, and anyone who tells you "dark matter exists" is over-simplifying to the point of error.

Now, this hypothesis that we're discussing is a different beast. It's a mathematical model that may or may not preclude dark matter by chaning the rules slightly. Changing the rules of gravity isn't that much of a big deal (we assume that the unification of gravity with the other forces will probably come with some surprises), but one does not speculate about those changes lightly. To wit, this theory is being greated with skepticism, not because it offends some faith in dark matter, but because it requires some heavy thinking about existing mechanics.

This is what science is all about. You build a model, and then you tear it down. You repeat this process until you have a model for which the difference between "sturdy" and "unassailable" is indistiguishable. At that point, you refer to the model as a "law". That is, "a very sturdy model". Then you move on to the implications of that model, and start building new models.

Re:Anti-dark-matter scientists are like ID scienti (1)

kestasjk (933987) | more than 7 years ago | (#16058905)

Neutrinos do have mass, that has been experimentally proven within experimental error. It was the first example my lecturer gave in Physics 101 of experimental uncertainty. We're just not sure how much mass.

I'm skeptical, but it would tidy things up nicely if it turned out right.

Re:Anti-dark-matter scientists are like ID scienti (5, Insightful)

vondo (303621) | more than 7 years ago | (#16058933)

I think I'd regret responding to the complete misunderstanding of forces and neutrinos in the body of your post. That would take pages.

Let me just respond to your title. That is completely wrong as well. Now, I think the alternative gravity guys are probably wrong and at this point I think they are stretching their theories to their limits. Dark matter is the "easiest" explanation. But, what they are doing is science. They are coming up with an alternate theory that makes predictions and testing them. The are countering circumstantial evidence for DM with another theory. They are not picking just one small thing, saying "Well that can't be true because of [insert some non-science babble like you just posted] so clearly God created everything." in contradiction to vast bodies of scientific evidence. And the alternative gravity people are publishing in peer-reviewed journals.

ID can't say any of those things. While the motivations may be similar (not wanting to give up on old ways of thinking about things) the methodology is completely different.

Re:Anti-dark-matter scientists are like ID scienti (0)

Anonymous Coward | more than 7 years ago | (#16058981)

Could you explain - in that case, let's say I travelled on a spaceship to a place where this dark matter was located based on gravitational measurements. Now, I am assuming the general location that it would be in could eventually be located, rather than simply being 'everywhere else than where we currently are'.

In that case, what would happen if I attempted to land on this in my spaceship, and take a piece of this and put it in my space pants?

Would it actually be black as blackness, as in light-absorbing?

Or would it be invisible, as if it was pushing light to flow around it?

Would I just pass through it, with a feeling like walking uphill (towards a 'gravitational bulge') as I walked towards it, and downhill when going away?

Would it be possible to cut off this piece and place it in my pants, only that my equipment would be attracted to it in a gentle sucking effect?

I think until these fairly basic questions are answered, which noone seems to be able to, 'dark matter' will earn a lot of skeptics and agnostics.

Re:Anti-dark-matter scientists are like ID scienti (0)

BadAnalogyGuy (945258) | more than 7 years ago | (#16059020)

If you were to take a spaceship to the place where dark matter exists, your ship would be obliterated by the tidal forces generated by the dark matter. Spacetime would physcially change as you approached and like a black hole, you would be sucked in.

Though to answer your question, yes, though your equipment may in fact be microscopic, the fact that you have any equipment at all would mean that you would be attracted to the dark matter. It would be the siren's song for your dong, so to speak.

Re:Anti-dark-matter scientists are like ID scienti (3, Funny)

stiggle (649614) | more than 7 years ago | (#16059013)

The sweaty fat kid at college had loads of mass and no one interacted with him.
Perhaps neutinos are similar. :-)

Re:Anti-dark-matter scientists are like ID scienti (1)

tie_guy_matt (176397) | more than 7 years ago | (#16059208)

Look at the sun. Look at how bright it is.

It isn't difficult to look up at all the brightness from the sun and think that maybe there is something there that we cannot see.

That thing in the sun that we cannot see is the planet Vulcan (not to be confused with the planet from Star Trek.) It is clear that this planet is the reason why the orbit of Mercury is not what we would expect using Newtonian physics. All we need to do is find that planet and newton's laws will be validated

But now this Einstein guy would have us believe that we should change Newton's law of gravity just because he couldn't grasp that there is a strange planet out there that exists just outside our ability to measure it.

My point is that any theory may seem insane until it is validated using physical measurements.

Those who push a theory that is eventually proven wrong are doing an important job. They are helping the theory that will be proven right to become that much stronger. So no matter which side is eventually proven right we really need to thank both sides!

Is there dark matter or do we need to change our ideas about the laws of gravity? I for one am going to wait until all the measurements are in before I make up my mind!

Dark-matter scientists are like ID scientists (0)

Anonymous Coward | more than 7 years ago | (#16059219)

They want you to accept this unseen unobservable force that explains the things we don't understand, because it's more comfortable than acknowledging that we don't have all the answers. ...

Ok, but seriously: Major scientific theories are always subject to change. As experiments disagree with accepted theory, there's always a choice between "tweaking" the theory while holding onto its core assumptions, vs. introducing a new theory.

As a matter of scientific philosophy, we replace more complex theories with simpler ones if they predict reality with the same accuracy. As a matter of history, the simpler theory often ends up proving to be more accurate as experiments are refined. "Simple" doesn't mean "easy for a lay-person to understand", though; maybe elegant is a better term than simple.

One camp wants to add a new concept (dark matter) to existing theory; the other wants a new theory that dosen't require the same new concept. Both can use their method to explain what we see today. Most importantly (and distinguishing both groups form ID scientists), it is conceivable to test the theories. Real observation may (probably will) eventually favor one or the other.

Frankly, I have my opinion, but it's based more on history of science than on details of the two theories. The only fact in this debate is, until experimentation can tell the difference between a reality obeying one theory vs. the other, anyone saying 'this way is Right and the other is Wrong' has failed to understand science.

Occam's Razor != Science (3, Interesting)

pavon (30274) | more than 7 years ago | (#16059243)

I am fine with the possibility that there is a lot of normal matter which is not detectable from earth. I am also fine with the idea that more exotic forms of matter and energy might exist. The current dark energy models are the best matches for astronomical observations thus far. And when it is all said and done, if dark energy continues to be the best description, it will prevail, but that doesn't mean we shouldn't stop testing it.

At one time, all the scientists thought there was this stuff called ether, and it was the best explanation for the observations we had. Then people did more tests, and discovered incongruities. In the end it was proven an incorrect idea, and was supplanted with a better model.

Einstein spent many years trying to find a deterministic alternative to quantum mechanics. There were many respectable scientists that felt that QM was merely a useful approximation, but after years of testing, a the consensus finally turned, and the community accepted that the non-deterministic aspects of QM were real.

Should we have blindly accepted Ether or QM, just because preliminary results showed promise with the ideas? No - we continued to question them and test them until they were disproved or time had shown them to be solid ideas. Dark Matter is in the same place as these theories once were. I don't know whether it will turn out to be correct or not, but I do know we should continue to challenge it, to think of new ways to test it, and to think of alternative explanations, because that is what science is about and that is how we take good ideas and turn them into a rigorous and well-established understanding of the universe.

You would call these people pseudo-scientists, and yet your only argument an application of Occam's Razor (and as others pointed out, faulty understanding of principles). But that's the funny thing about Occam's Razor - it is dependant on one's personal opinion of what is the most likely, or most simple explanation. Some would consider making up new particles that we have never observed a real stretch, others consider tweaking the existing rules a hack. That someone has a different view of what is elegant than you, does not make their ideas pseudo-science. What matters is if they are predictive and falsifiable, which these are.

Honestly, if you can't tell the difference between people that present testable alternative hypothesis, and people whose best "theory" that they could present amounts to "does this not appear irreducible", then you are the one that needs a refresher on what is and is not science.

It's the Ether (4, Insightful)

Fysiks Wurks (949375) | more than 7 years ago | (#16058785)

Dark Matter is the 21st century's ether.

Re:It's the Ether (1)

RangerRick98 (817838) | more than 7 years ago | (#16058822)

Does that mean I can take dark matter to recover my MP?

Black magic woman (1)

tepples (727027) | more than 7 years ago | (#16059244)

Does that mean I can take dark matter to recover my MP?

Only if your black magic comes from the dark side of the Force.

(Got a female illusionist of African descent?)

Re:It's the Ether (1)

Fordiman (689627) | more than 7 years ago | (#16058841)


Very good analogy. Much better than BadAnalogyGuy's.

Re:It's the Ether (2, Informative)

SixByNineUK (949320) | more than 7 years ago | (#16058889)

No, Gravity waves are the 21st century ether, Dark matter is the 21st century phlogiston

Re:It's the Ether (1)

Fysiks Wurks (949375) | more than 7 years ago | (#16058944)

Very good point...but ether is easier to say and sounds so much better than phlogiston. I've always read "Dark Matter" as "We just don't know" but the public preception is that it must exist because the smart scientist said so...

Now that's really confusing (1)

H3lldr0p (40304) | more than 7 years ago | (#16058945)

Are you saying that Dark Matter is why we have fire?

Re:It's the Ether (1)

StonePiano (871363) | more than 7 years ago | (#16058909)

This is a clever thought. You may be right. Ether was in fact a good scientific model. It attempted to explain certain things that are now explained by gravity and the like. But each of these models give us a fuller understanding, not necessarily a complete or final understanding.

Re:It's the Ether (1)

ceoyoyo (59147) | more than 7 years ago | (#16059153)

We talk about the aether all the time today, just in relation to gravity, not electromagnetism. We usually call it "the fabric of space" or some such today.

Re:It's the Ether (1)

Lord_Slepnir (585350) | more than 7 years ago | (#16058928)

I like, know what you mean. Last night I was huffing Dark Matter, it was like I was on FIRE man. I went tango dancing with Stephen Hawking and then we watched Charles Darwin and Al Sharpton settle the whole Intelligent Design vs. Evolution thing once and for all by having a hot dog eating contest.

That dark matter stuff is better than ether, man.

Re:It's the Ether (1)

Stalyn (662) | more than 7 years ago | (#16058957)

You mean aether. The big difference between the luminiferous aether and dark matter is that there was never any evidence of the aether however there is lots of evidence for dark matter, albeit indirect.

Re:It's the Ether (4, Insightful)

dmatos (232892) | more than 7 years ago | (#16059076)

To the scientific understanding at the time, there was evidence of the aether. It had been observed that light exhibited wave-like characteristics, and could, in fact, be understood as a wave. At that time, all waves were known to travel through a medium. There were no waves that could travel without one. There was no other medium in the vacuum of space, so it was decided that there must be an aether.

A perfectly valid scientific theory, as it was also falsifiable - as demonstrated by Michelson and Morley. When it was falsified, it required a major change in how the scientific communtiy thought about light. It is entirely possible that we'll see something similar with dark matter. Sure, an unobserved WIMP could explain things like the rotation of galaxies at their current rates. But, what happens when we get out there and don't find any? What then? Well, maybe it will require a major change in how we think about gravity. Maybe there's an entirely new force out there, that's weak enough that we can't see it on terrestrial or even solar scales. Who knows?

religeon of dark matter (1, Interesting)

pizpot (622748) | more than 7 years ago | (#16058804)

For me, dark matter is like religion. Made up to explain what we can't understand, and wrong.

Re:religeon of dark matter (2, Insightful)

grasshoppa (657393) | more than 7 years ago | (#16058872)

For me, dark matter is like religion. Made up to explain what we can't understand, and wrong.

Interesting observation, if a bit off. The difference being, of course, that we will eventually have a factual basis for dark matter ( whether it exists or not ), where as we will never know if $deity exists.

This is true for all supernatural values of $deity.

Re:religeon of dark matter (0)

Anonymous Coward | more than 7 years ago | (#16059253)

where as we will never know if $deity exists.

You will in about 60 years...give or take

weighs 2eV? (1)

DogAlmity (664209) | more than 7 years ago | (#16058831)

Thats electron Volts right? I don't get it. How does one measure weight with volts? Or does it mean it weighs as much as two electrons, in which case why not just say that?

Re:weighs 2eV? (1)

dlenmn (145080) | more than 7 years ago | (#16058886)

E=mc^2. eV is a unit of energy, so it's also a unit of mass. For subatomic particles it can make more sense to talk about their energy, especially since small things go back and forth between the two in reations, but energy must be conserved.

Re:weighs 2eV? (2, Informative)

Daniel_Staal (609844) | more than 7 years ago | (#16058888)

The famous equation: E=MC^2 converts to M=E/C^2. For truely tiny masses, that's the easiest way to measure and specify them.

Re:weighs 2eV? (0)

Anonymous Coward | more than 7 years ago | (#16058900)

ElectroVolt is an amount of energy you need to accelerate one electron against the potential of one volt. Note: energy. Energy and mass are bound by E=mc^2. eV are convenient unit in nuclear physics, especially if you use c=1 convention.

Re:weighs 2eV? (3, Informative)

FhnuZoag (875558) | more than 7 years ago | (#16058902)

Mass, man, mass. It's not weight, but mass.

After relativity and E=Mc^2, physicists have preferred to measure mass in terms of energy rather than silly units like grams and ounces. In short, we give the energy equivalent for the particle if it was somehow completely annihilated. 1 electron volt refers to the energy of one electron under an electric field at a point of 1 volt of potential difference. It doesn't have anything to do with the actual mass of the electron, but rather the electrical potential energy such an electron would hold.

Re:weighs 2eV? (1)

nagashi (684628) | more than 7 years ago | (#16058908)

Remember, E=MC^2 Mass can be represented as energy, and energy as mass. There's little difference when it comes down to it :)

Re:weighs 2eV? (1)

Fordiman (689627) | more than 7 years ago | (#16059000)

Electron Volt []

tested in 2009? (0)

Anonymous Coward | more than 7 years ago | (#16058860)

Holy date confusion! We are receiving test results from the future. Power up the tachyon beam, Cap'n.

Re:tested in 2009? (1)

Bondolon (1000444) | more than 7 years ago | (#16058887)

I believe it's saying that when this experiment takes place in 2009, this data will be tested.

Technically, neutrinos are dark matter (3, Informative)

Anonymous Coward | more than 7 years ago | (#16058918)

They're just proposing that there is no "exotic", new kind of dark matter.

Incidentally, I'd watch the Cosmic Variance [] blog in the coming days for a discussion of this point; Sean Carroll's post there on dark matter was linked to in the last Slashdot story.

Responding to other posters: the amount of photons in the universe can be estimated based on how many of them reach us, as well as from theoretical predictions on the emission of light from stars, the Big Bang, etc., and is woefully inadequate to produce the needed gravitational effects — not to mention it is too "hot" to be the kind of dark matter needed to explain early universe structure formation.

An eV, or electron volt, is a measure of energy: the amount of energy acquired when an electron is accelerated through a 1-volt electric potential difference. It is about 1.6 * 10^-19 joules. By E=mc^2, it also corresponds to a mass, about 1.8*10^-36 kilograms. An electron, by comparison, masses about 511,000 electron volts.

Re:Technically, neutrinos are dark matter (2, Insightful)

phirzcol (447454) | more than 7 years ago | (#16058972)

but,,, when looking at electron even with their small mass i ask what is the mass of every electron ever traveling in space since the start of the universe also what about the expansion of the universe is their a crest of mass at the "edge" of the universe, perhapse the extra mass is only reflected to us as a result of the distortion that exists as a result of the expantion of the universe, ie light that we see is old so a possible explanation is that there is a fraction diffrence between the speed of light and the speed of gravitons just rambling

Mod Up (1)

spun (1352) | more than 7 years ago | (#16059007)

From reading the summary, this is my understanding of what these guys are saying, too. Call it modified MOND.

Dark Matter Lite! (4, Funny)

Rob T Firefly (844560) | more than 7 years ago | (#16058975)

This article presents an alternative to dark matter
Just as dark as your regular matter, but with only 1/3 the calories!

Re:Dark Matter Lite! (1)

Chacham (981) | more than 7 years ago | (#16059143)

>>This article presents an alternative to dark matter
>Just as dark as your regular matter, but with only 1/3 the calories!


Of course, there's alma [] matter, which is just plain wet, eh. But, being full of DiHydrogen Monoxide (DHMO) [] which some want to ban [] but other defend [] .

Use the chain rule Luke (4, Interesting)

sweetser (148397) | more than 7 years ago | (#16059004)

Here's Newton's law of gravity:

        d mV/dt = - G M m/R^2 R_hat

It doesn't work for galaxies, it doesn't work for the big bang, it is broken for almost anything BIG. It also has a tiny bit of error that GR corrects, but that is minor. The problems with this law are HUGE. So we have two schools of thought. One wants to stuff the big M box with dark matter:

        d mV/dt = - G (M + Dark_M) m/R^2 R_hat

These folks get to put Dark_M wherever it needs to go to get the answer right. Then there the MOND folks who want to mess with the R:

        d mV/dt = - G (M + Dark_M) m/R^2 or if dV/dt is small, d m V/dt = - a_0 sqrt(G M/R^2) m R_hat

where a_0 is a new constant in nature that changes the form of gravity's law if tiny. I got my own proposal. Remember the chain rule from calculus?

        d mV/dt = m dV/dt + V dm/dt

That V dm/dt is the stuff of rocket science. We know it is not relevant for stars cause those big star things and galaxies don't change. But we could, just for the fun of it, do a relativistic swap-out, and consider:

        d mV/dt = m dV/dt + V dm/dt + V c dm/dR

Force is a change in momentum, which can be seen either as the usual acceleration, the rocket-ship effect, or as where stuff is distributed in space. That sounds like what is going on. So my proposed modification is this one:

        d mV/dt = m dV/dt + V dm/dt + V c dm/dR = - G M m/R^2 (R_hat + V_hat)

Too bad I suck at numerical integration or I'd try and see if it could match real data sets. I like it because it uses stuff we know is true (the chain rule) with a fun twist to make an old law point in a new direction.


Re:Use the chain rule Luke (1)

ZombieSquirrel (978302) | more than 7 years ago | (#16059094)

That middle part is way wrong.

Clarification: dark matter is STILL real! (5, Informative)

jpflip (670957) | more than 7 years ago | (#16059012)

People should NOT take the impression from this article that there is doubt that dark matter exists. The only doubt being raised is over what form the dark matter takes. Let me clarify:

(Note: Baryons are protons and neutrons. "Non-baryonic" means not made up of the building blocks of ordinary atoms.)

The beauty of the Clowes work (the "proof that dark matter exists" from a couple of weeks ago) is that the colliding clusters they worked on give simple, clean evidence that galaxy clusters are really dominated by invisible, non-baryonic dark matter. At it's core, it's a very simple argument. Two clusters collided, and the baryonic clouds (hot gas, seen with X-rays) experienced drag and got a bit hung-up passing through one another. Most of the mass, however (seen with gravitational lensing), passed straight through with no drag. We see the X-rays and lensing in two different places on the sky - they really are two different kinds of stuff. This is VERY direct proof that most of the mass in galaxy clusters is not the ordinary matter we see on earth - it's something non-baryonic that does not interact with light and does not interact much with ordinary matter. In other words, dark matter is real, physical stuff!

This article argues only about what that dark matter might actually be. It's generally believed that it can't be neutrinos, because neutrinos are so light that they would mess up galaxy formation, and so must be some new, exotic kind of particle. The logic here is that very light particles move so fast that they don't clump together well under their own gravity, which would disrupt the formation of galaxies and smaller clusters of galaxies. All this paper argues is that the dark matter might not be a truly new particle - the combination of modified gravity and neutrinos can be made to work. They still conclude that the invisible neutrinos must outmass the baryons in the clusters by a factor of at least 2.5.

Many people (particularly those who do not understand the evidence) dislike the idea of dark matter, thinking it sounds too much like epicycles. That's understandable, and it's good to be very skeptical of such a weird idea (I know I was). The truth is that there is now enough evidence to say that it really does exist, no matter how strange it may seem to us. The future lies is figuring out what the dark matter is actually made of, not bland assertions that "that just can't be right...".

Re:Clarification: dark matter is STILL real! (0)

Anonymous Coward | more than 7 years ago | (#16059078)

The truth is that there is now enough evidence to say that the earth is flat. The future lies is figuring out what the edges are made of, not bland assertions that "that just can't be right...".

KATRIN experiment homepage URL (2, Informative)

tobyvoss (584427) | more than 7 years ago | (#16059057)

KATRIN experiment homepage URL []

No guarantee (1)

roguegramma (982660) | more than 7 years ago | (#16059064)

Even if dark matter exists, there is no reason why it all would add up to (nearly) zero.

For example, if dark matter exists, what if there is just a little more of it than expected? Then the theory of "pushing gravity" 0Gravity [] would stand a chance.

Weight: thin as air, as the post is. (1)

sigmoid_balance (777560) | more than 7 years ago | (#16059085)

weigh 2eV
Last time I checked not all forces were weights and not all measures mass. The eV is a measurement for charge, which if you are keen on making comparisons could be the equivalent in electric field to mass in the gravitational field. But anyway the neutrino will not "weigh 2eV" ever.

Re:Weight: thin as air, as the post is. (3, Informative)

kakapo (88299) | more than 7 years ago | (#16059152)

The electron volt is a measure of energy -- the amount of energy needed to move an electron through a potential difference of one volt in an electric field. (Think of it as moving a small ball up a hill). Thanks to "E=mc^2" this is also a measure of an equivalent mass -- and it is frequeuntly used to specify the masses of subatomic particles. (For comparison, an electron "weighs" about 500,000 eV -- even by particle standards, 2eV is very small)

Re:Weight: thin as air, as the post is. (1)

sigmoid_balance (777560) | more than 7 years ago | (#16059197)

I stand corrected. Made a fool ... *departs in shame*

Re:Weight: thin as air, as the post is. (1)

trongey (21550) | more than 7 years ago | (#16059305)

I stand corrected. Made a fool ... *departs in shame*

Don't feel bad, you were incorrectly corrected.
If eV is being used as a unit of mass then a neutrino still can't "weigh" 2eV. It would have a mass of 2eV. So you were right after all.

Re:Weight: thin as air, as the post is. (1)

ceoyoyo (59147) | more than 7 years ago | (#16059332)

The eV is not a measure of charge. The eV is a measure of energy, which is equivalent to mass. Charge is measured in units of proton charge: electron = -1, proton = 1. That used to be considered the fundamental unit until we discovered quarks, which have charges that are multiples of +-1/3.

Prudence (2, Funny)

Digitus1337 (671442) | more than 7 years ago | (#16059182)

I try to be conservative, but not closed minded, in my accepting of new ideas. Concerning a concept as heavy as gravity, I think that scientists are just throwing us around, and i'm not falling for it.

Moo (-1, Offtopic)

Chacham (981) | more than 7 years ago | (#16059216)

What i don't understand is the plutonic nature of the hot and cold dark matter as it coagulates upon confrontation. The twin-mitosis experiment clearly shows a subjugation of the wrench-affect, and with it the gastronomical constant, when within range of the bibliosonic effect submitted via bionic alpha waves.

This experiemt blatantly ignored the effect and relies on neutrinos instead. IMO, this is just more useless talk, and we really need to support the quantum phatasmajelca machine to project more definite proofs.

Re:Moo (1)

PakProtector (115173) | more than 7 years ago | (#16059266)

Can we get a -1, Laypersonspeakify mod?

simple definitions (4, Informative)

peter303 (12292) | more than 7 years ago | (#16059273)

"Dark matter": an invisible attractive force operating on galaxy-level distances (at million light years). Size: about 23% of the energy-mass of the observed universe. Evidence: Galaxies spinning faster than the number of visible stars justify. Gravitational lenses stronger than visible stars justify. Suspects: known low mass particles like neutrinos; unknown low or high mass particles like strings, wimps; a new phsyical force; non-r-squared term in Newton's equation of gravitation, observational error ...

"Dark energy": an invisible repulsive force operating on universe-size distances (at billion light years). Size: about 73% of the energy-mass of the observed universe. Evidence: Hubble expansion is accelerating over time when gravity would suggest eventual deceleration or collapse. Suspects: energy in fabric of space-time, unknown force, observational error ...

"Observed matter": stars, galaxies, gas clouds, neutrinos; Size: about 4% of the energy-mass of the universe.

Useful research (-1, Troll)

ThePhilips (752041) | more than 7 years ago | (#16059310)


Thanks God, that's not my taxes are spent on that very useful research.

I'd rather help my friends artists to make another concert/exhibit - than to watch that sick show of theoretical scientists fighting for next trunk of federal money.

From someone who just finished *reading* the paper (5, Interesting)

Anonymous Coward | more than 7 years ago | (#16059337)

The real result of Clowe et al's fascinating work was to show that the missing mass in the bullet cluster must be COLLISIONLESS, whatever gravity looks like (a purely baryonic bullet cluster has been *falsified*). However, a big misconception about it was to think it was a direct *confirmation* of the Lambda-CDM concordance model that everybody is supposed to believe (may I recall that real science is about *falsifying* things, not "proving" them right), or that it was falsifying MOND. Actually, it is known for years that MOND is UNABLE to fit the temperature profiles of X-ray emitting clusters from their pure baryonic content. The fix, for MOND to stay in the game, was to propose that neutrinos have a 2eV mass and can then make up for the missing mass, in clusters ONLY, because they are too light to cluster on the galaxy scales (incidentally they are also too light to form structure in GR, but this is not a problem for structure formation in MOND). However, if dark matter is indeed cold as the lambda-CDM guys tend to take for granted, and even more since Clowe's work, why does the 2eV neutrino combined with MOND seem to work in ALL clusters??? The bullet cluster being a totally new kind of constraint for MOND on the galaxy cluster scale (constraint coming from gravitational lensing instead of temperature profiles), it was mandatory to check if 2eV neutrinos were excluded even in MOND, which would have *falsified* MOND indeed! This is what those guys wanted to do, to *falsify* MOND once and for all, but the surprising result is that they didn't manage to do so, because the SAME neutrino mass as the one needed to fit temperature profiles of other clusters ACTUALLY WORKS in the bullet cluster too. Their conclusion is thus just that MOND is *not excluded* by Clowe's data. One will thus have to wait for particle physics experiments to rule out massive neutrinos to rule out MOND. Until then, place your bets...
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