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Einstein's Theory Improved?
skaet writes to tell us that A Chinese astronomer from the University of St Andrews claims to have fine-tuned Einstein's theory of gravity. Dr Hong Sheng Zhao has created a 'simple' theory which could "solve a dark mystery that has baffled astrophysicists for three-quarters of a century." This new law seeks to discover whether Einstein's theory was correct and if dark matter actually exists.
Yes, most is actually transparent. There are many particles that don't interact with photons. They don't emit or absorb light, so therefore are impossible to detect with light and they can't block light either. A small percentage of dark matter is thought to be 'normal' matter that does reflect light, but the universe is big and not so bright. It's rare to get a chunk of rock or ball of gas reflecting much light in our direction. Astronomers have a hard time detecting planets many times larger than Jupiter
For the reasons why dark matter must exist; some reasons are straight forward, some are more round-about-observations. The easiest one is from galaxies rotating too fast. The fact that they stay together means something is holding them together. Since we don't observe anything like a giant rope or hand of God holding our sun in place, the only logical explanation is gravity. Since we can't see enough matter to make this much gravity, it must be dark.
The dark matter that's hypothesized because of the large scale curvature of the universe is not as straight forward, especially since it was recently found that the universe seems to be accelerating in it's expansion.
I'd also like to point out that gravity, electrons and other particles or forces are no less valid than photons as observational tools. We really don't have to 'see' something to know it's there.
Unfortunately, like Cambridge, St. Andrews has suffered from negative publicity as a result of its taking occasional pupils from failing schools and admitting them with A level scores which would not normally allow a student to be admitted. But at least it meant that some of the Windsors got access to higher education, so perhaps the policy is defensible.
Anyway, I'm very pleased that the astrophysics tradition is continuing. But I'm still left with a question: Why are the nicest British Universities (Cambridge, Durham, St Andrews) in such bloody cold places?
Pining for the fjords
f you check the equations, you'll find that light from a star causes its gravitational field to fall off as 1/r, whereas its mass causes it to fall off as 1/r^2.
Where on Earth you found that light has so much gravitational field? And why would be constant: shouldn't it vary with the luminosity of the star (which goes like mass^4, so it's highly nonlinear)??
Galaxy spanning in fact.
Ah, I see. You are off by four orders of magnitude. Come back when your astronomy is a little better.
http://arxiv.org/abs/astro-ph/0512425 The phenomena customly called Dark Matter or Modified Newtonian Dynamics (MOND) have been argued by Bekenstein (2004) to be the consequences of a covariant scalar field, controlled by a free function (related to the MOND interpolating function) in its Lagrangian density. In the context of this relativistic MOND theory (TeVeS), we examine critically the interpolating function in the transition zone between weak and strong gravity. Bekenstein's toy model produces too gradually varying functions and fits rotation curves less well than the standard MOND interpolating function. However, the latter varies too sharply and implies an implausible external field effect (EFE). These constraints on opposite sides have not yet excluded TeVeS, but made the zone of acceptable interpolating functions narrower. An acceptable "toy" Lagrangian density function with simple analytical properties is singled out for future studies of TeVeS in galaxies. We also suggest how to extend the model to solar system dynamics and cosmology, and compare with strong lensing data (see also astro-ph/0509590).
As a side note, the "ancient language" remained very consistant for a very long time. There is very little difference between the hebrew spoken then versus now. Only when you get far enough in the past to aramaic (spelling??), you get an actual different language.
although ISTR that on one occasion he relented a little and allowed the Israeli troops to take some of the young women of the cities they were destroying for themselves. For the Lord is a merciful god
You have your story mixed up a little. God told the Israelites to go annihilate a city (as in men, women, animals, anything that moves, some things that don't move, etc). The Israelites then decided that it was a waste to kill everything, and thought they should take back some wives, slaves, cattle, and other assorted wealth. Then God condemned them for disobeying him.
Computers allow humans to make mistakes at the fastest speeds known, with the possible exception of tequila and handguns
Theories become law when they are basically irrefutable
No, that's not what happens. Laws say what happens, theories say why and/or how it happens. Laws don't try to explain behaviour, they just state it. Hence the laws of thermodynamics are laws, while the theory of relativity is a theory and always will be.
It's official. Most of you are morons.
This would be God's Law:
Thou shalt not kill...
That would be God's instruction to man as reported through the ages, by man, in the Bible and its ancestor documents.
This would be a human's moronic attempt to "spread the word":
Now go over that hill there and kill everyone you find
That would be God's instruction to man as reported through the ages, by man, in the Bible and its ancestor documents (try I Sam 15.2-3,
Exodus 32:27, or many others).
Yes, it could be a false claim (of instruction by god) by fanatical idiots, but that applies to the first statement as well.
First off, I want to say a few words about dark matter. I think it's kind of irritating when people rant on about how dark matter is ad hoc fudging, etc. etc. Well, "fiddling around with the laws of gravity" isn't any better on that account. The fact of the matter is that all of theoretical physics is creating new models that fit our observations, and both dark matter and MOND fall into that category. The very existence of MOND as a theory shows that it is not easy to distinguish "matter that primarily interacts gravitationally" from "modifications to the laws of gravity". Historically, both "unseen matter" and "modifications to gravity" have been valid solutions to anomalous gravitational behavior (in the cases of Neptune's orbit and the perihelion precession of Mercury, respectively).
As it stands, dark matter models can pass many experimental tests, and they're still the way to bet. That being said, MOND is not a bad idea either. It's not as well supported by dark matter, and it has serious problems with galaxy clusters, but it can still account for a surprising amount of data (for a nonrelativistic theory!). The flaw of non-relativistic has been "corrected" by Bekenstein's TeVeS theory (the one that Zhao and Famaey's work is based on).
Unfortunately, TeVeS appears to be rather ad hoc (even compared to dark matter). Z&F's work does not appear to be much better in this regard. In addition, solar system observations appear to place serious constraints on such MOND-like theories, leading to anomalous non-inverse square forces in the outer solar system (and no, it doesn't seem to be of a form that can be attributed to the Pioneer anomaly, though the jury is still out).
The TeVeS/dark matter debate should be definitively resolved by the Planck mission, which will be capable of resolving the third acoustic peak in the the cosmic microwave background radiation power spectrum. TeVeS and dark matter make very different predictions for the structure of this peak. Of course, if TeVeS fails this test, maybe some other MOND-like theory could be put forward (if the entire class of theories hasn't already been ruled out by other means, such as solar system dynamics, by then).