Do we need dark matter?

November 12, 2009 by Pete Wilton
Do we need dark matter?

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Illustration showing the proposed Square Kilometre Array telescope, image: Xilo Studios

It's the biggest problem in physics: the matter we can see in the universe accounts for just five per cent of the observed gravity that holds galaxies together.

The conventional explanation is that enormous amounts of invisible make up the missing 95 per cent but some have argued that it’s Einstein’s theory that’s at fault.

In a review in this week’s Science Pedro Ferreira of Oxford’s Department of Physics and Glenn Starkman of Case Western University assess how alternatives to dark matter are shaping up.

‘For over 25 years there has been a proposal that there is no dark matter, that we are simply misinterpreting the data and that what in fact is happening is that we don't understand ,’ Pedro tells me.

‘A rudimentary alternative was proposed in the early 80s but only recently were a few complete theories constructed that modify Einstein's theory of general relativity and that could in principle solve the dark matter problem without dark matter.’

Israeli physicist Mordehai Milgrom got the ball rolling in 1983 with a proposal that became known as modified Newtonian dynamics (MOND). Other alternatives build upon this work, such as Jacob Bekenstein’s TeVeS.

Pedro comments: ‘In the review we emphasize two main things. First of all that all of these theories seem to bring in something akin to dark matter through the back door. It is not that they need dark matter as well as modifications to gravity but that any attempt to modify gravity necessarily generates something dark.’

‘The second point is that, even though waters seem to be muddied, there should be observational tests which can distinguish between the two paradigms. By looking at how are distributed and how they distort any background light, it should be possible to pick out clues for modified gravity, i.e. to test whether Einstein was indeed correct.’

The hope is that galactic surveys, such as those carried out by the Joint Mission or Square Kilometre Array, will be able to see if the telltale signs predicted by these alternative theories really are out there.

More information: Einstein’s Theory of Gravity and the Problem of Missing Mass, Science 6 November 2009: Vol. 326. no. 5954, pp. 812 - 815; DOI: 10.1126/science.1172245

Source: University of Oxford, Science Blog. By Pete Wilton

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Husky
Nov 12, 2009

Rank: 2.7 / 5 (6)
Dark matter, Cassimir force, gravity, expansion of space.Could they be the same manifestation of zpe harmonics acting on different scales? Consider the cassimir experiment, where plates of metal are seemingly "attracted", but really compressed by a difference in alllowed energy modes inside and outside the tiny gap, creating a difference in radiation pressure, a tiny force and a really tiny gap, objects with larger gaps (say the distance sun-earth) would have to be really big to experience significant difference in radiation pressure from the surrounding medium. Well, Earth and sun are indeed huge, what we call gravity, attractive force = cassimir compression acting on intermediate scale ?? Now consider the expansion of universe, large gaps, lots of room for harmonic waves, in seeking lowest energy states, space just like the waves in a wild sea calm down the surface expands, cassimir force acting on grand scale? Is the energy in this harmonics the equivalent of missing dark matter
CptWozza
Nov 12, 2009

Rank: 3.1 / 5 (7)
Maybe one day, "dark matter" will sound as naive and contrived as the aether was, a fudge conjured up to plaster over something we don't yet understand.
Husky
Nov 12, 2009

Rank: 1 / 5 (2)
Maybe dark matter is hard to measure as a substance if it is the energy locked in zpe harmonics vibrating in such high frequencies that makes it below Planck scale? All the other measurable manifestations of mass, photons, forces around us, could be superimposed interference patterns casting a measurable shadow on larger, measurable scale? I hope the LHC and exawatt lasers will be able to "boil the vacume" and see what comes out
CptWozza
Nov 12, 2009

Rank: 3 / 5 (2)
I see your point Husky, but physicists already discuss the vacuum energy, they call this "dark energy" in contrast to dark matter. In my view, dark energy seems less contrived than dark matter, since the concept of vacuum polarisation comes straight out of the equations of quantum field theory. The vacuum is already bubbling so we don't really need to boil it as you suggest - so when the LHC fires up, the energy we put in results in the creation of particles higher up the 'vibrational energy' ladder.
Alexa
Nov 12, 2009

Rank: 2.3 / 5 (3)
For example the size of anomalous deceleration of Pioneer 10 spaceprobe is equal in roughly 10% precision to simple product of Hubble constant and speed of light:

a = H . c =(8 +- 1) x 10^-10 meters/second^2

The resulting difference can be assigned to hot portion of dark matter and/or errors of measurements - all these effects are indeed quite minute at solar system scale.
Nik_2213
Nov 12, 2009

Rank: 3 / 5 (2)
My preference would be Occam's Razor, and a simple extension to Einstein's math equivalent to 'elliptical' vs 'circular' orbits...

Yup, DM/DE smell of pre-Copernican epicycles...
joefarah
Nov 12, 2009

Rank: 5 / 5 (5)
Dark Matter is the Ether of the 21st century. Let's understand the problem better before creating an ether and going off on a tangent to detect it. On the other hand, it was the supposition of an ether that led to the Lorentz experiments and ultimately to Einstein Relativity theories... So maybe we should try to detect dark matter and then recompute our theories based on the failed detection results.
Alexa
Nov 12, 2009

Rank: 1 / 5 (1)
..electric universe? that is a radical different approach and an alternative..
Many particles in dark matter are charged and they repel at distance. But I don't think, just the charged matter could explain all aspects of dark matter. IMO Dark matter is a mixture of many concepts, relevant from different observational perspectives.
Dark Matter is the Ether of the 21st century
But Higgs field can be considered as modern version of Aether as well. Sparse clouds of dark matter cannot spread waves of high energy density, like gamma ray photons - so they're useless with respect to luminiferous Aether concept. Dark matter exhibits drag effect simmilar to Lens - Thirring effect, but their mechanism and consequences are different.
frajo
Nov 12, 2009

Rank: 3.7 / 5 (3)
all other theories are just getting dark mater in via the back door, only EU give a whose new theory.

Only EU gives a whole new theory? Do you know all of the other alternative theories?
megaskins
Nov 12, 2009

Rank: 1 / 5 (1)
Dark matter is the 20th century analog to aether. Discretized variable space is far simpler - space is discrete and not a smooth continuous analog. Space "expands" as it gets further from mass - when objects move thru space they jump from point to point - as the points get further away from each other, objects appear to accelerate. Objects away from strong gravity would dilate - point the Hubble at the outer edges of galaxies and I bet stars and appear larger than objects towards the center of a galaxy.
quartop
Nov 12, 2009

Rank: 2 / 5 (1)
Pregunta capsiosa de uno que ni a novato llega:
Si la materia conocida solo es el 5%, y la mataria obscura (Dark matter) es el 95%, entonces, proporcionalmente, somos 95% materia obscura!!!??
Noumenon
Nov 12, 2009

Rank: 5 / 5 (27)
No Quartop, we aren't 95% dark matter, we are 100% of the 5% known matter. No one has ever detected Dark Matter.
QubitTamer
Nov 12, 2009

Rank: not rated yet
i personally refuse to waste my time trying to guess the nature of the universe as a fish swimming in a polluted pond looking up at the sky through the bottom of an up-ended glass bottle floating on the surface. the problem being lack of empirical method in data collection and too many hypothetical math models being candidates to shoehorn what little real datasets we have. glad i don't have to work for any cosmologists. wish someone would just task hubble to begin a systematic survey of gravitational lensing or discrete / quantized 'jumping' of stars as they moved farther away from other gravitational masses. Vernor vinge actually described exactly this theory in one of his sci-fi novels.
Alexa
Nov 12, 2009

Rank: not rated yet
Gradually increasing number of theories is undeniable consequence of formal approach in physics, because formal math is poorly conditioned for description of multiparticle systems. String theory is pregnant example of its limit, because it exists in many versions - but other formal theories are facing similar problem, too. But dark matter is nothing new in astrophysics, as it was revealed before 76 years already.
brant
Nov 13, 2009

Rank: 3 / 5 (2)
I think it precisely because we have strayed from the path of true experimental science that we have so many differing views and opinions on things like dark matter, dark energy, the LHC, and what its going to detect or make. I insist that true nature of the universe can be known if we accept that which we believe to be unreal. Its right before us.

We have already investigated Aether theories probably just not the right one. If we put as much money into the aether as we put into the big bang I dont think we would have a universe that is 99.99% unknown.

If you look back, what we did is just blow right past the Aether for Relativity, without the aether ever being fully explored. Then we had to come up with dark matter and energy to fill the gap.
hessimoto
Nov 13, 2009

Rank: not rated yet
We haven't really done our "due diligence" when it comes to "dark matter". The test of "If you eliminate the impossible, whatever remains, however improbable, must be the truth" has not been completed in my opinion. Have we really eliminated all "normal matter" candidates for "dark matter"? Do we even know how much matter there is in our own Solar System to any degree of accuracy? I of course mean everything inside the influence of our sun (at least up to the heliopause). For example, I doubt we would be able to "see" the equivalent of our Oort cloud of other stars.
I will entertain "dark matter" theories only after these so-called mundane candidates have been thoroughly discounted.
frajo
Nov 13, 2009

Rank: 3.8 / 5 (4)
I insist that true nature of the universe can be known if we accept that which we believe to be unreal.

Physics is the art to create well-mannered models. Not to probe for metaphysical entities like "truth" and "reality". A well-mannered model agrees with observational data and yields falsifiable predictions.
Alexa
Nov 13, 2009

Rank: 5 / 5 (1)
..we have already investigated Aether theories probably just not the right one..
Only very dense particle environment can spread light of high frequency (like gamma radiation) in waves. IMO this model was omitted intentionally on behalf of combination of relativity and quantum mechanics, because it was known in physics from 1904 (Oliver Lodge).
Alexa
Nov 13, 2009

Rank: 1 / 5 (1)
..is the art to create well-mannered models..
We aren't paying physicist for decreasing of number of parameters in their theories, but for increasing of them. At the moment, you'll pay group of people for publications, instead of for explanation of reality, the only thing you can expect is, they begin to pile different models on background of well confirmed models without tendency to reconcile them mutually by some more general, but vague theory. Such approach is easily predictable and it manifests itself even in another branches (like the research of cold fusion, antigravity or room temperature superconductivity). These people doesn't look for new ways, they trying to combine existing ones for the sake of their safe publishing carrier.
Alexa
Nov 13, 2009

Rank: not rated yet
The problem of reconcilliation of relativity and quantum mechanics is quite simple, in fact. Try to imagine, you're sitting inside of huge dense blob of particle environment. Everything, including you is compressed/collapsed - this is perspective of general relativity. The waves, which are spreading through such blob are deformed together with your clock and distance measure. Therefore you'll not perceive deformation of light path, but deformation of space-time.

Another observer is trying to describe the very same blob from outside. He is not deformed by its density gradient, so he can see lensing phenomena and curvature of light path, spreading through it. Such view basically corresponds the view of quantum mechanics.

What the physicists are doing during the last 70 years is, they're trying to reconcile these two mutually inconsistent perspectives by common formal model. They can never succeed in it, but it's not so great problem, because they've families and perspective of job.
kevinrtrs
Nov 13, 2009

Rank: 3 / 5 (4)
Just a 2pc comment on a new theory by Carmeli Moshe, an Israeli physicist. In case you don't know, he extends Einstein's theory of general relativity to apply to Cosmological proportions. It fits neatly with current calculations but also elegantly does away with a need for dark energy and dark matter.

This is done in the same way that Einstein's equations did away with the unseen mass behind the sun that was needed to explain peculiarities in Mercury's orbit.

Be warned: Be prepared for a paradigm shift.
frajo
Nov 13, 2009

Rank: 1 / 5 (3)
You forgot to mention that the aforementioned "Cosmological Relativity" "has profound results for cosmology in general and in particular Young Earth Creation cosmology".
PeterROwen
Nov 13, 2009

Rank: 1 / 5 (1)
The concept of the AEther was discarded because of an erroneous concept of vacuum. We know that there is an aether, because 'space' is full of stray particles and that large constellations have bow-shocks. A paradigm shift may well be on its way relative to 'dark matter/dark energy' and it well may be an effect that is due to the very co-existence of matter and dark matter causing a distortion of our view of the universe on a scale hitherto undreamt of.
kevinrtrs
Nov 14, 2009

Rank: 3 / 5 (2)
@frajo.
OK, I see where you got it from. Carmeli is a dedicated evolutionist. It seems the creationists have simply followed the evidence and picked up on his work.
Evidence at the moment is that the Microwave BG radiation is not uniform, implying non-uniform matter creation and hence dispersion. This non-uniform dispersion has just been "officially" confirmed and is being studied further. Coupled to this, quantization of redshift evidence also indicates the same[google all the work done on it]. On top of that the quantization displays a mathematical topology which can only occur if the Milky way is within 1 million light years of the centre of the observations. Hence: a new line of thought is required to explain the evidence. And hence Carmeli's theory.
You can religiously stick with the original Big Bang assertion of a homogeneous universe that looks the same in all directions and deal with dark matter and energy or you can accept the evidence and follow where it goes. Your choice
Alexa
Nov 15, 2009

Rank: 1 / 5 (1)
Dark matter is formed by gradient of space-time, in this way it doesn't differ from ordinary matter. Of course, we can speculate about violations of Newton law, but such assumption doesn't explain anything.

TeVeS theory proposes better approach: From GR follows, every curvature of space has it's own energy density - this is basically, what the Einstein's field equations are about. But as we know from E=mc^2 formula, every energy density can be assigned to its corresponding mass energy density, which should exhibit it's own additional gravitational field and resulting additional curvature of space. As we know, the highest gradient of gravity field exists at the surface of massive object, so that such gradient results into sparse "cloud" of matter, which partially balances the gravity of matter, which has caused this gradient originally. http://arxiv.org/abs/0708.2639
Alexa
Nov 15, 2009

Rank: not rated yet
Dark energy is dual effect to dark matter. In TeVeS theory dark matter gravity balances the gravity of matter, which caused dark matter phenomena - i.e. it behaves like weak antigravity force, which repels massive bodies at large distance.

In this way, dark matter phenomena is source of anomalous deceleration, if you're sitting inside of gravity field and it behaves like anomalous acceleration, when you're sitting outside of it - so it can accelerate expansion of massive bodies in Universe, which is interpreted like result of dark energy.

Compare this situation to spreading of ripples at water surface, where ripples are condensing with increasing speed, which may be experienced like acceleration of space-time expansion, when you're observing water surface via surface ripples only.

http://www.scienc...4056.htm
Alexa
Nov 15, 2009

Rank: not rated yet
The problem of dark matter concept is, it consists of both deformation of space-time (which is basically formed by extremellly lightweight particles like neutrinos or axions - so called the cold dark matter), both heavy particles of real matter (mostly positrons and ionized atom nuclei, I presume - so called the "hot dark matter"). In general, the more older / large some dark matter cloud is, the more massive particles are trapped inside of it - which complicates models of dark matter and slows down acceptation of general theory of it, because each scientist tends to consider his own theory as the best one. http://en.wikiped...k_matter
jsa09
Nov 15, 2009

Rank: not rated yet
Aether has been discarded and brought back in through the back door. Description of universe with digital effect implies existence of Aether. Expanding universe created by expanding space implies existence of Aether.

I used to like MOND but cannot see how strength of gravity can remain the same at vastly different distances. Of course I do wonder about pressure from external source appearing to be a gravitic pull from internal source.

One also wonders if it is possible that expansion of space may produce a side effect of external pressure on galaxies - as in some kind of wave force back lash.

In any case, yes, theories are easy to come up with, proof is a lot harder.
kevinrtrs
Nov 16, 2009

Rank: not rated yet
Dear Alexa,
You write about dark matter and energy as if it actually exists, yet no-one has ever seen or detected it! I'd be much more comfortable with your writing if your language included words like "It is thought.." or "the latest models speculate that...". Just a thought. UseItDon'tUseIt....
maxmc
Nov 16, 2009

Rank: 2 / 5 (2)
dear everyone, here comes an idiotic post. Dark matter and the missing mass of the universe is actually a shadow. not any normal shadow though, a shadow in 3 dimensions, spawning from the 4th spatial dimension i guess. A dimension would always have a shadow of one less dimension than itself, the reason OUR shadows dont weigh anything is because they are infinitely thin. If you have a shadow in three dimensions who knows what its properties could be. Anyway, yea that may be why we cant detect dark matter, because we need to detect the light first in order to notice the difference. Anyway, write what you think.
SincerelyTwo
Nov 16, 2009

Rank: not rated yet
I'm thinking that dark matter and dark energy will ultimately be proven to be observations of the effects of a distinct dynamic in space-time, a kind of dynamic that our current physics does not describe. I'm willing to bet that on the larger scales, that of groups of galaxies, there is far more exaggerated defects/artifacts in the form of space-time which produces local attractive and a universal 'pushing' force. Something like an infinite fractal set of 'gravity wells' formed by the matter structure, and the forces between the structure would be 'buldging' and push outward.
Yellowdart
Nov 16, 2009

Rank: not rated yet
Frajo and Kevin,

There was also an article here: http://www.physor...620.html

Alexa
Nov 17, 2009

Rank: 5 / 5 (1)
You write about dark matter and energy as if it actually exists
..these effects were observed phenomenologically a long time ago - this is why we are talking about it by now.
SincerelyTwo
Nov 20, 2009

Rank: 5 / 5 (1)
Most of you have the obvious issue of not understanding why DM or DE are included in our current models.

Whether any of you like it or not, there are natural phenomena being observed *right now that did not match the results of our previous models. So what we did was explore how our models could be extended to maintain reliable predictions. The reason why those extensions are *not necessarily 'band-aid' fixes is because we have DIRECT OBSERVATIONAL EVIDENCE of an EFFECT that we can't explain, but we CAN DESCRIBE.

Scientists are NOT saying that something we can't see exists, they ARE saying that something is CAUSING an EFFECT we DO OBSERVE, and we CAN DESCRIBE. What we don't know is the CAUSE of the EFFECT, but we can SEE it is there.

Lensing effects, universal structure distributions, and rates of change in distance between large bodies contain the information which exposes the evidence.

If our physics didn't work, we wouldn't be exploring space with robots.
Rank 4.2 /5 (22 votes)
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