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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.
It's not dark matter. It's light.
If 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. This is an old equation, originally derived for the gravitational field of a candle.
Needless to say, this effect is only present within the "sphere" of radius (speed of light)x(age of star), but of course for most stars, this is enormous. Galaxy spanning in fact.
This is all relatively offtopic by the way, but given the controversy surrounding dark matter, and the dubious qualities of "landscape theories" lately, I thought I'd throw this one into the mix as well.
I wonder if this is what the guys have come up with actually.
May the Maths Be with you!
I second that sentiment, and presume that he means it - with the publication of not just his office number, but his personal mobile (cell) number as well!
"There is nothing nice about Steve Jobs and nothing evil about Bill Gates." - Chuck Peddle
I am not an astronomer. I just tend to apply logic to everything I collide with.
And when I can't collide or interact with it, it kinda ruffles me the wrong way. What kinda magical stuff is this supposed to be. Doesn't interact, doesn't shine, doesn't emit, doesn't absorb, all it does is offer some convenient gravity to explain a few things that don't make sense otherwise.
It kinda reminds me how about 500 years ago astronomers came up with double and triple rotations of planets around an imaginary point to explain why the planets move the way they move since they believed the Earth and not the sun is the center of our system. And if they rotated around earth, they had to jump through a few hoops to explain that odd orbits they showed. Instead of abandoning the system that didn't work and accept one that does, they religiously clinged to it and tried to explain what could not be explained.
Maybe we're at that point again?
Maybe, just maybe, it's not dark matter but some of our "laws" are simply wrong. Or, if not wrong, they maybe don't extrapolate well into the larger scale, what works and makes sense in the (comparably) small scale of our solar system doesn't make sense and doesn't work on a galactic scale.
I do hope this is a step into the right direction. Science is all about not setting stuff in stone. Everything has to be questioned, everything has to be tested, even the most holy scriptures from the most revered astronomers of all times should be ripped if they showed an error.
If not, science is no better than religion.
We used to have a Bill of Rights. Now, with the rights gone, all we have left is the bill.
I did go there --- it's a great place (and the bright red gowns are no longer compulsory, although you get free entry to the castle if you wear your gown). I did first year astronomy before realising that my maths weren't up to it and switching to comp sci; St. Andrews has some genuinely decent telescopes despite being at sea-level in a built up area. The Greg is deeply impressive to go and see. It's amazing just how big it is.
For those who don't know, St.Andrews is the third oldest university in the UK, after Oxford and Cambridge; it was founded in 1413, and totally dominates the town. (The university owns most of the town centre.) Going there is an experience totally unlike any other university in Britain... I had a room in a hall of residence five minutes walk from the town centre, perched high on a cliff top overlooking the North Sea. Great view.
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.
Actually, things have changed. Until very recently, British students got their tuition fees paid by the state. Not long ago, however, the British parliament voted to make them pay a proportion --- but the Scottish parliament didn't. So students who go to a Scottish university get their tuition fees paid for them. As a result, all the Scottish universities have been inundated with students, and as the highest-prestige university in the country, St.Andrews can now basically name their price.
That doesn't explain Prince William, however, who is by all accounts not very bright.
I've heared once that the original hebrew text reads "Thou shalt not murder." If that's true, the contradiction is easy to resolve: Just define that killing ordered by god is no murder.
My understanding was similar but different. I had heard that the original ancient language of the bible did not have a rich engouh vocabulary to distingiuish between kill (e.g. an enemy) and murder (e.g. one in your own society), but the next most recent translation of the bible used the word "murder", not "kill".
The point is, when Moses was taking his tribe around the desert with their new commandments, they were to preserve their own society (which is what the 10 commandments promote), but if they had to kill competing tribes to survive, they could do so because it would be *killing*, not *murder*. Any society that condones unbridled murder within itself will quickly commit suicide.
He used to explain to us when we were kids, about ether filling up the space between sun and earth. Am talking about 1983-84...
Methinks, dark matter is either subspace, OR, gravitational constant varies wildly between various regions in space, thus altering the fundamental constant.
We may live in a bubble which has 9.8 m/s as gravity on earth. Voyager, which is out of solar system may have entered another such region where it varies....
"Doing what i can, with what i have." ~ Burt Gummer
This is not an improvement to Einstein's theory of gravity. It is, however, an improvement to Milgrom's Modified Newtonian Dynamics (MOND): MOND is merely an empirical correction to Newtonian gravity, so this is an improved 'empirical' gravity (well, it's got to survive a few more tests before we know if it's an improvement to MOND).
One big difference between Newton's theory of gravity and Einstein's theory of gravity is that Newton's theory says what gravity does (ie. it gives us the magnitude and direction of the force of gravity between two objects) whereas Einstein's theory says that and how as well (i.e. mass curves space-time). Einstein's theory improves on Newton's in that it is more accurate and actually provides insight (testable) into how gravity actually works.
It is likely that Einstein's theory will be improved upon at some time, and be replaced by a more enlightening theory (quantum gravity? string theory?), but for now it is the best theory of gravity we've got....
#include "cunning_plan.h"
"If something doesn't work first time, invent something imaginary"
This is not the first time in which an existing theory has had a part added (a fudge factor if you will...) to explain an anomalous phenomenon.
Such example include,
1. God
2. The aether
3. The cosmological constant
Each of these ideas have been used at some point to ensure that an existing theory (or foundationless preconceptions) coincide nicely with observation. In each case, they have been refuted at some point in the future.
The idea of modifying the rate of gravitational fall off with distance is not a new idea - back in the 1800s, Airy (If I remember correctly) discovered that if instead of gravity obeying an inverse square relationship, it obeyed an inverse relationship to a different power, the predicted orbit of mercury would fit the observed data. If this was proposed however, there would have been a lesser incentive to look for the more accurate theory that General Relativity provides.
I can't help but think that very rarely does true progress come from simple modifications to existing theory. When theory does not match observation, it is often a new idea entirely that is needed to resolve the problem. A modification to an otherwise elegant idea usually obscures the truth.
If this new theory really does provide highly accurate results, we should ask why and look for the underlying cause of gravity falling off faster than expected, rather be complacent with the introduction of a new constant.
Nothing sucks like a Vax, nothing blows like a PowerMac G4
I'm confused as to what really bothers you. Why should the stars "fall" into the halos? Are you implying that there should be a gravitational interaction between the stars and halo? There is --- the anomalously fast rotation rates are precisely the action of the stars "falling" into the halo. And it's inaccurate to describe dark matter as "invisible", at least as much as describing planets orbiting other stars as "invisible". Dark matter is not luminous, so it's hard to detect from some distance away even if the matter itself is opaque to visible light. In fact, one of the more significant searches for candidates of dark matter involved looking for microlensing and microoccultation events --- dark objects passing in front of background stars.
And your sarcasm and supercilious attitude ought to be tempered by the fact that many objects have been theoretically postulated and later discovered based upon anomalous orbital motion. Neptune leaps immediately to mind.
The problem is that as a result physicists really, really like very elegant theories when there's no particular reason to believe that the Universe itself has the same bias. Similarly, we like to take theories that work on scales and locations that we know and can easily interact with, and assume that they smoothly apply in the places that we can't get to know quite so easily. It's reasonable even if it isn't logical - we have to go with what we already have. It's a decision born of practicality.
In Cosmology, there's even a phrase for this: we assume homogeneity and isotropy. That is, that there's nothing special about where and when we are, and that the universe is pretty much the same (in physical laws) everywhere. The first time I heard about "dark matter," it was in the context of closure of the Universe. Physicsts really really wanted the universe to have enough mass/energy in order to be "closed," but we simply weren't finding enough matter. There was no reason to believe that the universe is closed (curvature 1.0), but it just seemed more elegant. So, they started to look for the "missing mass."
These are not logical assumptions, they're just assumptions that we have to make in order to get anywhere. Again, there's no reason that the universe will cooperate on this matter.
My own bias is to reject dark matter in favor of a revised theory of gravity, but that's just my own love of elegance - a different gravity feels more elegant than dark matter and dark energy, and in fact would hint at much more interesting cosmologies. But that's just how I am seduced by elegance...
"It is our blasphemy which has made us great, and will sustain us, and which the gods secretly admire in us." - Zelazny
Why don't the theorists stick to explaining what can actually be observed and measured, instead of making up stuff in order to prop up theories that have more likely found their limits.
Um, yeah, that's what they're doing. We have [b]observed[/b] and [b]measured[/b] things that the existing theory of gravity doesn't explain, so the theorists are trying to develop new theories to explain it. The ultimate goal being to craft a new theory that can make predictions which further [b]observations[/b] and [b]measurements[/b] can either falsify or verify. If the data verifies the predictions, then we have a good theory -- until we make an observation that the theory does not predict.
If you think "making up" dark matter to explain observations within the constraints of Einstein's theory is silly, what would you have thought about "making up" the concept of masses warping space-time to fix problems with Newton's theory?
The enemies of Democracy are
When you so-called "rational" Christians speak up LOUDLY & denounce the idiots who are claiming to represent you, then I'll stop bundling you all in the same package. If you don't speak up against them, then I have to assume that silence is assent.
First, and glaringly....you said:
about scales, from TFA:
A non-Newtonian gravity theory is now fully specified on all scales by a smooth continuous function.
so, this yet to be reviewed theory claims to have overcome your first objection, and you cannot prove them wrong until April.
you said:
ok, so no theory that you have seen can explain gravity better than dark matter without being REALLY contradictory to observations. Yeah, you know what I'm going to say...it is possible this new theory can do what you say it can't...which brings me to:
overall, i think you're wrong when you say dark matter absolutely must exist. Supposedly, this theory can explain gravity in a way that somehow changes predictably on different scales.
IANAA, but judging from the new kuiper belt object xena, I think the Oort Cloud may be the beginning of a new understanding of what it is exactly that lies between us and our nearest neighbors...on all scales. I think it's possible we will eventually observe many more such objects. While it may sound as if I'm supporting a dark matter theory, no...I am merely stating that neither dark matter nor this new theory will be the last, simplest theory of gravity. Dr Fameay from TFA would agree:
It is possible that neither the modified gravity theory, nor the Dark Matter theory, as they are formulated today, will solve all the problems of galactic dynamics or cosmology. The truth could in principle lie in between, but it is very plausible that we are missing something fundamental about gravity, and that a radically new theoretical approach will be needed to solve all these problems. Nevertheless, our formula is so attractively simple that it is tempting to see it as part of a yet unknown fundamental theory. All galaxy data seem to be explained effortlessly
Thank you Dave Raggett