
Universe's expansion may be understood without dark energy - joeyespo
http://www.physorg.com/news/2011-10-supernovae-universe-expansion-understood-dark.html
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gjm11
Actual paper at author's web site:
<http://www.helsinki.fi/~aannila/arto/light.pdf>. I have to say that a brief
perusal sets off my crank alarms, although the author does appear to be a real
physicist. ... Oh. On googling a bit more, I find that the author has also
claimed a proof that P != NP [EDITED to add: available at
<http://arxiv.org/abs/0906.1084>]. The signs aren't looking good.

~~~
lutorm
_a brief perusal sets off my crank alarms_

That's what I was going to say, too. And I got more convinced the further down
I got. The weird, convoluted wording was a big tipoff. And then this sealed
it:

 _When a star explodes and its mass is combusted into radiation, conservation
requires that the number of quanta stays the same, whether in the form of
matter or radiation._

There is no conservation law limiting the number of photons. This is obviously
observed any time you turn on a light bulb.

~~~
splat
If I were being charitable I might think that he was referring to conservation
of baryon number or lepton number...but all other indicators point to him not
knowing what he's talking about. I'm actually pretty surprised that this paper
was accepted. MNRAS is a fairly prestigious journal.

~~~
lutorm
That would take a significant amount of charitability (?) since he says

 _...whether in the form of matter or radiation_

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bh42222
I viscerally distrust anything from physorg.com. Anyone have a better option?

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J3L2404
"Annila shows that, when gravitational lensing is analyzed with this concept,
it does not require dark matter to explain the results."

Both dark energy and dark matter seem contrived and virtually anything would
be less hand-wavy. Just for aesthetic reasons I hope these are found to be the
modern equivalents of "ether" as a medium for EM waves.

~~~
splat
I have to disagree with you about dark matter and dark energy seeming
contrived.

First it's hard to call dark energy "contrived" when it hasn't really been
contrived, conceived, or created at all. That is, no one has really made any
strong, convincing claims as to what it actually is. The term is really just a
placeholder for the fact that something is providing a long-scale repulsive
force (and so probably has negative energy density). Although it can be
"explained" by a cosmological constant, that just punts the question to what
the cosmological constant physically is.

As for dark matter, it is the simplest, most elegant way to explain the
variety of observations that point to its existence. These observations
include small-scale dynamics of dwarf spheroidal galaxies, the rotation curves
of galaxies, gravitational lensing due to galaxy clusters, and more. All of
them can be explained if there exists some unknown particle which interacts
only weakly with other particles. While it's true that the standard model
predicts no such particle, it's also true that it's known that the standard
model is an incomplete theory.

You might argue that it could just as well be that our theory of gravity is
wrong. (Certainly at the quantum level we know for sure that that is the
case.) But inaccuracies in our theory of gravity at large scales have
difficulty explaining the dark matter problem in an elegant matter. Consider
dwarf spheroidals. These are the smallest of galaxies; in terms of luminous
mass, they are only slightly more massive than globular clusters. Yet globular
clusters are 1000s of times smaller than dwarf spheroidals. How can they
possibly remain gravitationally bound on the scale of 1000s of light-years
when globular clusters are only bound on scales of a few light-years? Dark
matter can explain this by simply saying that dwarf spheroidals have
relatively massive dark matter halos, whereas globular clusters have almost no
dark matter. (Which one would expect in standard galaxy formation scenarios.)
But modified gravity theories have difficulty explaining why two systems with
similar masses interact so differently.

We can similarly see that galaxies of all sizes exhibit a range of dark matter
fractions. If the problem was merely with our theory of gravity one would
expect all galaxies of a given luminous mass to have the same dark matter
fraction. Any modified theory of gravity which explained these observations
would _not_ be aesthetic. The aesthetic explanation would be some hitherto
unknown weakly interacting massive particle.

~~~
J3L2404
>The term is really just a placeholder for the fact that something is
providing a long-scale repulsive force

How is that not contrived?

>You might argue that it could just as well be that our theory of gravity is
wrong.

As an armchair physicist, I was rather hoping the Pioneer anomaly would lead
us down that road, oh well.

>Any modified theory of gravity which explained these observations would not
be aesthetic.

Well aesthetics do invoke subjective qualities. Relativity, modifying
Newtonian physics, could have be seen as ugly by some. E = mc^2 is so elegant
as to seem improbable.

~~~
splat
>> The term is really just a placeholder for the fact that something is
providing a long-scale repulsive force

> How is that not contrived?

All the phrase "dark energy" means is that the expansion of the universe is
accelerating. There must be _something_ which provides this repulsive force
(maybe some new particle, maybe some unknown property of the vacuum, maybe
some new theory of gravity on cosmological distance scales). Dark energy is
simply the generic name to describe this something, whatever it is. It makes
no claim as to _what_ is causing the repulsion. It's just a name for an
unknown. Calling dark energy contrived is like seeing an equation 6x + 4 = 7
and calling "x" contrived.

> Well aesthetics do invoke subjective qualities. Relativity, modifying
> Newtonian physics, could have be seen as ugly by some. E = mc^2 is so
> elegant as to seem improbable.

The virtue of relativity is that despite overturning a very elegant theory, it
creates new, elegant equations of its own. Any theory of gravity that could
explain the varying dark matter fractions would necessarily have to do so in
some basically arbitrary way (since dark matter fractions vary in an
apparently random manner). So any such new theory of gravity would have to be
ugly; there could be no redeeming features.

