
Dark Matter Is an Illusion, New Antigravity Theory Says - evo_9
http://news.nationalgeographic.com/news/2011/08/110831-dark-matter-proof-gravity-quantum-theory-cern-space-science/?source=link_fb20110831darkmatterillusion
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jbri
This theory is basically that gravity is similar to other forces in that it's
not solely attractive, but things of opposite "gravitational charge" (i.e.
particles and antiparticles) repel.

If that holds, then an ambient gravitational field in an area would presumably
be strengthened by virtual particle pairs aligning their gravitational dipole
with that of the ambient field, quite neatly explaining the anomalous
observations that brought about the dark matter theory in the first place.

There are more recent observations that this new theory doesn't yet explain,
but it doesn't seem an insurmountable challenge.

Additionally, this theory makes one very testable hypothesis - that antimatter
is oppositely-charged, gravitationally, to normal matter. If that's not the
case, we should be able to determine that fairly soon (a few years, perhaps).

~~~
colanderman
Why wouldn't we see this effect on earth, and have taken it into account when
determining the strength of earth's own gravity?

Would we see this effect with electric fields as well?

Could differently oriented electric and gravitational fields compete to orient
a given dipole?

~~~
foob
You've ask a couple of very deep questions there.

 _Why wouldn't we see this effect on earth, and have taken it into account
when determining the strength of earth's own gravity?_ We could be observing
the impact of this without exactly realizing it. I won't speculate too much on
this because I haven't read enough about it but it might make more sense in
light of my next answer.

 _Would we see this effect with electric fields as well?_ We absolutely see
this effect with electric fields. In the last century we've grown to
understand that in electromagnetism we don't simply deal with isolated
electrons and positrons. These particles are actually surrounded with clouds
of virtual electrons and photons which have an impact on the field (this is a
simplified view but it's enough along the right lines to give you the right
impression if you haven't studied physics). When we talk about the field
around an electron we take this into account by assuming that all these
contributions sum to give us the field that we actually observe. If you want
to read more about this then
[http://en.wikipedia.org/wiki/Quantum_field_theory#Renormaliz...](http://en.wikipedia.org/wiki/Quantum_field_theory#Renormalization)
is a good starting point.

 _Could differently oriented electric and gravitational fields compete to
orient a given dipole?_ Yes, all relevant fields will have an impact on what's
happening. I don't want to speculate too much beyond my knowledge though and
when it comes to quantum gravity we're already there.

I know that this wasn't the deepest contribution but hopefully it will help
shed some light to someone...

~~~
127
One thing I don't understand: wasn't there just discovered a ring of
antimatter circling around the Earth? Wouldn't it just disperse into space if
antimatter caused antigravity? Stupid question, I know, but just something
that's beyond my comprehension.

~~~
hollerith
Tiny amounts of antimatter were just discovered circling around Earth. The
anti-grav effect on the antimatter particles is swamped by the effects of the
Earth's gravity and magnetic field.

~~~
mparr4
According to this theory, it would be the magnetic field alone--not the
gravitational field--that is overwhelming the antigravity effect. After all,
if these particles had an opposite "gravitational charge", then their
experience of gravity wouldn't be attractive but would be equal in magnitude
but opposite in orientation. Hence "anti"gravity.

~~~
hollerith
I accept the correction. Good one.

------
Steuard
I find it ironic that this article features a picture of data on the Bullet
cluster, which is currently one of the strongest pieces of evidence favoring
dark matter as a form of matter. Hajdukovic is quoted as saying that he's
"currently expanding his theory to account for these observations." That
translates as "I haven't found a compelling way of explaining them yet."

It's great that he's considering alternatives to the usual approach, and it
would be fantastic to have a second viable model to test observations against:
competing theories encourage open-mindedness. I'm really happy to have his
work up on the arXiv. But I don't believe that a speculative idea like this
merits attention in the mainstream press until it can at least give plausible
explanations for the major successes of existing models.

------
chc
Previous discussion: <http://news.ycombinator.com/item?id=2882670>

------
philwelch
This seems plausible to me. I'm not a physicist, but I think the case of dark
matter can be compared to the case of the planet Vulcan.

In the early 20th century, in the heyday of discovering planets by observing
existing planets and realizing that classical mechanics didn't quite predict
their orbits correctly, it was observed that Mercury's orbit didn't fit the
classical model well enough. Reasonably enough, it was presumed that there was
another planet orbiting inside of Mercury's orbit. This planet was dubbed
"Vulcan", and the fact that no one had ever observed Vulcan was explained away
by the fact that it was clearly too close to the sun to be observed. This was
all well and good until the early heyday of Einstein's theories, which made
small but crucial changes to the mathematical models of classical mechanics.
The orbit of Mercury was found to be perfectly consistent with Einstein's
model.

The question of dark matter supposes a dichotomy: either our current
understanding of physics is essentially accurate and there's a ton of
fundamentally unobservable matter in the universe that explains any anomalous
observations, or our model of physics isn't quite right yet. Intuitively, I
think it's more likely our physics are off.

~~~
splat
Either way our model of physics is off. Currently, the most reasonable
explanation for dark matter is that it consists of some unknown, weakly-
interacting particle. However, the standard model of physics predicts the
existance of no such particle. Even this, the most mundane possibility,
requires radical changes to our most fundamental physical theories.

~~~
philwelch
That sounds even sillier. The _most_ reasonable explanation is that there's
some impossible matter around? At least the planet Vulcan was an ordinary
planet that was just too close to the sun.

Again, I'm emphatically not a physicist. Stranger things have happened. It
just smells funny to posit dark matter as a hypothesis.

The only thing that's not suspicious is the anomaly itself. Physics has always
refined itself by looking at different scales. We were wrong about the quantum
level the first time we looked at it, and we were wrong about even the planet
Mercury, so it's to be expected that we're wrong about galaxy clusters.

~~~
ppog
"Impossible matter"? What's "impossible" about it? That we don't know what it
is, and that it isn't predicted by our current models, doesn't make it
"impossible." It means we're going to need to extend our models, which we've
been doing on a regular basis for hundreds of years. Rob Knop sums this up
nicely:

"In the face of evidence otherwise, many still insist that most of the
Universe must be made up of baryonic stuff that interacts with other baryons
and our familiar photons. Is this not just as much hubris as insisting that
the Earth, where we live, must be the center about which all the other Solar
System bodies orbit?"
([http://scientopia.org/blogs/galacticinteractions/2011/08/14/...](http://scientopia.org/blogs/galacticinteractions/2011/08/14/in-
which-i-compare-the-slashdot-commentariat-to-the-17th-century-catholic-
church/))

The dark matter hypothesis seems to have a great deal of explanatory power.
The antigravity hypothesis, like other MOND theories, has a good fit for the
specific phenomenon it was designed to tackle, but doesn't explain a lot of
the other things that dark matter does. Ethan Siegel has a good post on "What
Dark Matter's Alternatives Must Do"
([http://scienceblogs.com/startswithabang/2011/08/what_dark_ma...](http://scienceblogs.com/startswithabang/2011/08/what_dark_matters_alternatives.php))
which points out some of the stuff that dark matter explains and rival
theories don't (e.g. temperature fluctuations, hydrogen/helium ratio). He does
presciently note that 'antimatter has negative mass' could explain more than
traditional MOND theories but claims that this impacts other well-tested
assumptions such as conservation of energy.

He also has a specific article on the antigravity theory:
[http://scienceblogs.com/startswithabang/2011/09/dark_matter_...](http://scienceblogs.com/startswithabang/2011/09/dark_matter_haters_to_the_left.php)
(and yes, he does acknowledge that "dark matter ... historically has problems
for individual galaxies").

Of course, none of this is to say that the dark matter hypothesis won't
eventually be disproved and go the way of Vulcan as you suggest. Ironically,
though, it sounds to me like the MOND and antigravity theories are the Vulcans
here: they solve only one specific problem, while dark matter fits with so
much more.

~~~
philwelch
_That we don't know what it is, and that it isn't predicted by our current
models, doesn't make it "impossible."_

I was indulging in a bit of poetic license with that one.

I'll agree that we don't currently have a good theoretical alternative to the
dark matter hypothesis. Much smarter and more qualified people than me have
tried and failed to come up with one. But it still seems unsatisfying to me.

------
mberning
I remember being completely blown away in undergraduate physics classes by how
much of the world can be exactly and precisely explained by various subject
areas of physics (kinematics, gas laws, thermodynamics, etc.) Then at some
point I ran in to a wall with quantum mechanics and particle physics where I
had to throw up my hands. I was contemplating going to graduate school for a
masters in physics but I decided against it. It's vexing that there are such
disparities within the subject (not that there aren't in others as well, but
Physics seems especially afflicted).

~~~
fractallyte
!?

Within these 'disparities' lie new understanding, and awesome discoveries that
will _change the world_. Just as quantum mechanics did at the beginning of the
20th Century...

The resolution of these disparities is part of the thrill of Science!

------
JasPanesar
Someone might as well say it: The universe itself is an illusion too.

