Dark Energy May Be Changing 346
SpaceAdmiral writes "Nature is reporting that Dark energy, the hypothetical energy driving the universe's expansion, may not be as constant as previously thought. According to new research the strength of dark energy may be very different now than it was when the universe was young."
He does not really believe in Dark Energy (Score:5, Informative)
He actually believes in Dr. Mannheims Conformal Gravity. An attempt to define
gravity in terms of Conformal Symmetry, which the other three forces observe.
In the theory Dark Energy is just a manifestation of the repulsive component of
gravity. And this force changes with the evolution of the universe. He has just
found proof of this. This would mean that they have discovered something that has
not yet been predicted by the standard model. They have been hard at work to come
up with something that they can predict something that can be proved based on the
observation. The only other significant difference from the standard model is that
in the theory universe is always expanding, and there was no contraction phase.
The observations are not yet conclusive enough on this point.
more information (Score:5, Informative)
http://www.phys.lsu.edu/GRBHD/pressrelease/ [lsu.edu]
It seems that the results are very damning to cosmological
constants.
Unfortunately there are no good web sites talking about
Mannheim's theory the only paper that explains a lot of
it is "Alternatives to Dark Matter and Dark Energy" which
can be accessed at http://arxiv.org/abs/astro-ph/0505266 [arxiv.org]
Re:That's a pretty bold statement... (Score:5, Informative)
Dark matter [wikipedia.org] is required by looking at galaxy rotation curves. Essentially, the rotation speed of galaxies is too fast given the mass that can be seen, so there must be some mass that doesn't emit light as conventional, baryonic matter does. Dark matter was first hypothesized by Zwicky in 1933 and has been well accepted throughout the astronomical community for decades.
Dark energy [wikipedia.org] is required by looking at Type 1a supernovae from the early universe. Astronomers and cosmologists use Type 1a supernovae [wikipedia.org], which have a well known intrinsic brightness (they are called a "standard candle"), to establish a cosmological distance scale and measure the expansion rate of the universe. If the universe is composed of ordinary matter and dark matter, the self-gravity of all the matter in the universe would cause the expansion rate to slow over time. A goal of these observations was to determine whether there is enough matter in the universe to stop it from expanding forever and ultimately cause it to collapse back on itself in a "big crunch."
In about 1998, the supernova observations were pinned down well enough to show that the expansion rate is actually increasing with time. Therefore, there must be some "antigravity" force that causes the expansion of the universe to accelerate. This is dubbed "dark energy."
The "cosmic energy budget" says that about 4% of the mass/energy in the universe is ordinary matter, 23% is dark matter, and 73% is dark energy. The matter and dark matter total mass is measured from observations of the cosmic microwave background [wikipedia.org].
All of this is pretty well supported by the best current observational evidence, although the physical nature of dark matter and dark energy are both poorly understood (and new observations can always change things, of course).
The new claim in the current article is that the effect of dark energy has changed over time. The fundamental problem is that the new evidence relies on gamma-ray bursts, which are not nearly as well established a standard candle as the Type 1a supernovae, so it's much harder to say with certainty what distance they are at. Note that the new claim was presented at the American Astronomical Society meeting in DC last week; it has not yet appeared in a refereed journal. (Nature news is merely reporting on the AAS presentation.) The author himself has an appropriate degree of skepticism of his claim.
(Yes, I am an astronomy grad student, although I don't do any work on cosmology.)
Re:IANAP but... (Score:5, Informative)
In the theory repulsive component decays with the evolution of Gravity, and hence the Dark Energy which is what the repulsive component amounts to.
Re:It is changing, but we don't know which way (Score:5, Informative)
An analysis: http://cosmicvariance.com/2006/01/11/evolving-dar
if you'd care to understand.... (Score:2, Informative)
it has been reasonably established from several independent observations (cosmic microwave background, supernovae 1a, large scale structure) that the expansion of the universe is accelerating; the universe today is expanding faster than it was in the past.
now, guess what? we *see* it, but dont understand how or why. we only know that all "matter" (baryonic and non-baryonic) attracts, therefore there must be some *repelling* force; out of ignorance, astronomers call this repellant "dark energy". *theorists go wild*
but this is not the point. the real criticism of this study is on the interpretation of the observations. in fact, understanding that requires little esoteric theory, it's quite simple. the essence is that Gamma Ray Bursts, observations of extremely powerful stellar explosions, are used to derive the geometry of the universe. this *can* be done, empirically, if one knows 1) how bright the explosions were intrinsically, and 2) if one knows their distances independently (i.e. through spectroscopy).
BUT... GRB physics is quite messy, so at this point nobody can claim *yet* to know what their intrinsic brightnesses are (such that they can be used as "standard candles"). second, measuring distances requires accurate spectroscopy which is *really* hard, and close to impossible for the most distant and faintest GRBs. third, the current sample of GRB observations with spectroscopy is small.
the main reason why the conclusions/interpretations as published in Nature are disputed is because of these difficulties.
astrosociology: claim what you can as early as you can. if you're right, you're the first and eternal glory is your part, if you're wrong, ppl will forget you anyway.
if you ask me, Nature's standards are slipping...
Re:That's a pretty bold statement... (Score:3, Informative)
Physics is a science. Physics is not really a hard science in the same way as Math is a hard science. Physics is way harder science than Biology and Chemistry but still a lot softer than Math, which is the Queen of Science.
Since Physics is a "soft" science, they have "theories". Some of these theories are either incomplete, not fully understood or maybe incorrect. These theories are still very useful for Physicists, too useful too just discard just because they are not completely correct, complete or provable.
This is different from real hard science such as Math where there are no real "theories" per se and where statements that are not formally provable are worthless.
Anyway, some of these theories in Physics are to physicists too useful to just ignore just because they today are provably incorrect, or not currently provable correct which means
There are certain theories that stipulate x + y = z.
The problem here is that there are legions of observations that can not be explained using that theory and that according to the theory leads to 1 + 1 = 3.
This is obviously not good since the observations show that the theory is provably incorrect (or lets say incomplete), sso instead of discarding this still useful theory one has "invented" an extra term that explains why the calculations come to the "wrong" number and which covers the errors in the theory : DARK ENERGY/MATTER so then the theory becomes :
1 + 1 + "unobservable dark xxx" = 3
and everyone is happy.
We hard scientists, i.e. mathematicians, find this very funny. You might not understand the joke unless you are a mathematician.
We mathematicians also find the "heat distribution equation in one dimension" hilarious as well since an obvious consequence of it is instant communications faster than light as long as you can construct a thermometer accurate enough.
(of course we have our share of "issues" as well as Mr Goedel was so very kind to show us)
Math != Science (Score:5, Informative)
Mathematics is not a science. It is a tool (an important tool, but a tool nonetheless) that is used in science. Science (from Latin scientia - knowledge) refers to a system of acquiring knowledge - based on empiricism, experimentation, and methodological naturalism [wikipedia.org]. Mathematics is not based on experimentation or empiricism, it is based on deduction and logic.
Also, I don't know how you could argue that physics is not a "hard" science. As the sciences go, one can argue that physics is the "hardest" science of them all, because at a fundamental level, all the other "hard" sciences (chemistry, biology, geology, etc) derrive from physics in one form or another.
Re:That's a pretty bold statement... (Score:4, Informative)
For starters mathematics isn't a science - it tells us nothing about the physical world, mathematics is a tool, nothing more, nothing less. I have the highest esteem for mathematics, but it's not science.
Secondly science has never proved anything. The requirement of the scientific method is that hypothesis be falsifiable. If its predicted results turn out to be reproducably observed you have the makings of a good theory.
I don't know what your gripe about "stub fields" is, but unfortunately kinematics and Newtonian ballistics have been pretty well explained, so physicists have been compelled to move into more arcane fields. Too bad they've never produced anything of value like the computer chip or GPS.
Anyhow this rant reminds me of a joke I heard once whose punchline was something like "When I went to college I learned that all sociologists are really psycologists, who are really biologists, who are really chemists, who are really physicist, who use mathematics - The mathematicians just think they're god."
Re:That's a pretty bold statement... (Score:5, Informative)
The problem is that using theories, that are just theories and not provably correct
No theory is provably correct. All you can do is fail to disprove them. All you can ever say is that a theory explains the observable results as we can measure them, and that we have been unable to make any observations that run contrary to the theory.
In time, it may be that we improve our measurement-making capacity and find that the theory is *not* correct - this is essentially what happened to Newtonian mechanics. At very small scales and/or very high velocities Newtonian mechanics is wrong, and we need quantum mechanics (for the small) and relativistic mechanics (for the fast).
At no point, however, do we get to sit back, relax, and say "that's that - this one is proven to be correct". Science just doesn't work like that. The closest we get is "this one has survived many attempts to disprove it, so we can be pretty confident in it, but who knows what the future may bring?"
Re:That's a pretty bold statement... (Score:2, Informative)
Re:That's a pretty bold statement... (Score:1, Informative)
Re:That's a pretty bold statement... (Score:3, Informative)
Re:That's a pretty bold statement... (Score:1, Informative)
To be equally derogatory, I can dismiss an alternative theory of gravity as "merely a fancy error correction term". In reality, both dark matter and alternative gravity are equally valid hypotheses on the face of it; they're both alterations of our existing theories to accommodate new observations. However, it turns out that alternative gravity theories have not succeeded in explaining everything that dark matter does (which is far more than just galactic rotation curves), and it's not for lack of trying.
People don't hear much about alternatives to dark matter these days, not because astronomers are too stupid or biased to consider alternatives, but simply because the numerous alternatives that have been put forward have largely failed, and even when partially successful, are not nearly as successful as dark matter.