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Fraser
2006-Feb-14, 07:25 AM
SUMMARY: Researchers at the University of St. Andrews and the Free University of Brussels think they have a solution that "fine-tunes" Einstein's groundbreaking theory of gravity to help account for the effect of dark matter. Dr Hong Sheng Zhao and Dr Benoit Famaey have created a new formula that allows the strength of gravity to vary over galactic distances, perfectly matching observations made by astronomers.

View full article (http://www.universetoday.com/am/publish/improved_einstein_theory.html)
What do you think about this story? post your comments below.

Launch window
2006-Feb-14, 08:01 AM
Modified gravity, this is a bit strange, is there any other way to test this ?

seems a bit like sci-fi material

antoniseb
2006-Feb-14, 01:17 PM
The idea of modified gravity to explain the movement of stars in galaxies is not new. The whole MoND idea is exactly that. This is a little different because it takes MoND (Modified Newtonian Dynamics), and applies the idea to General Relativity.

This does not explain why clusters of galaxies can do so well as gravitational lenses. It also has a problem at the largest scale because of a gravitational problem related to Olber's Paradox. In this case, if there is a component of gravity which falls off more slowly that inverse square, the most distant galaxies should collectively exert very significant influence on our space.

Also, if you believe in gravitons, where would the extra ones come from? They can explain inverse-square, and potentially weaker if they decay, but not this, where there is a 1/x component.

five_distinct
2006-Feb-14, 06:41 PM
Perhaps the most worrying aspect of this article is that galaxies appear to be under attack from giant, inverted apples.

Blob
2006-Feb-14, 10:13 PM
Hum,
Indeed.
By refining Milgrom’s and Bekenstein's original theory Dr Hong Sheng Zhao and Dr Benoit Famaey have unleashed a powerful contender to Dark matter*.


*It should be noted that through the simple act of observation, a universe teaming with large apples has been discredited long ago.

suitti
2006-Feb-14, 11:59 PM
There is a problem. The solution will be an extraordinary claim. For a solution, we'll need extraorinary evidence. Is it time to hold your breath?

Perhaps the Universe was created Last Thursday, and God was too stupid to notice this problem, despite having designed and built the Hubble Space Telescope, and data archives.

Gerald Lukaniuk
2006-Feb-15, 02:32 AM
I’m generally cynical of the old world empiricist mind sets to describe the mathematical expressions that quantify the activities the elements of the universe as Laws. Not having seen this new expression I doubt if it will prove seamless.
An answer to the too fast spinning galaxies has always been implied in the arguments of the General Theory of Relativity without the need to postulate ridiculous amounts of invisible stuff or give both kinetic energy and the force of gravity a Jekyll and Hyde personality. “Relativistic Effects” can be calculated by a theory postulates along with other conditions, that the universe not only does not but can not have an absolute inertial frame of reference to definite the motion of objects or the duration of events. Hence the speed of light can be constant, not being changed by the momentum or acceleration of the emitter but rather the motion “warping space-time” between the objects allowing the mutual observation of both objects that the others dimensions are dilated or constricted This also necessarily spawns the “twin paradox” . The metaphysical implications of a universe with no true inertial ground zero implies it makes no difference in this universe to say the earth is stationary (with zero inertia) and that the universe is really going through crazy motions around it as well as does to describe the Copernican model that we are constantly having to “patch up”. Even weirder also implies that many if not every separate object composed of matter in this universe could have equal probability of being “ground zero” or the inertial centre of the universe. This creates another paradox similar Schrödinger’s cat in quantum physics in that if the inertial centre the universe exists in every separate object and they call can be defined to be at rest inertial simultaneously despite their conflicting observations that it’s the other objects in space not them that are in motion. This is common experience of all objects. (Despite what we are told about the movements of the Earth we still feel the same sense of standing still as we would on any other non accelerating object in the universe. Similarly within our galaxy when we set our galactic pole as ground zero (the “center” of the universe) and focus the movement of its components there every thing falls into place The behavior of gravity is consistent with observations on Earth and we don’t need to conjure up fictitious dark matter as the centrifugal forces implied by the speeds of their orbiting components are balance by the estimated gravitational attraction of visible. As counter intuitive as it seems our sister galaxies or better “Island Universes” could share the same dynamics as us as if their galactic poles were at the center of their own universes or more correctly their own branch of this universe. If we embrace this new paradox as real rather than wish it away with the “Principle of Least Action” like Einstein we can see that as with the twin paradox issue is not what happens to gravity over great distances but rather what happens to light and the warping of space-time... Looking into the structure of the continuum offers the best hope in overcoming the restrictions of vast distances and ponderous time spans.

Astrowannabe
2006-Feb-15, 03:36 PM
Sorry Gerald Lukaniuk, but I had a very hard time following what your argument was. It kinda seemed like you where arguing that there actually is no problem with dark matter, that it's just a misunderstanding on the part of astronomers? I'm probably seriously misreading your post (and if so, I apologize). But let me just say that the problem of dark matter is very real, and weather the solution turns out to be some exotic form of particle, a modification to our laws of gravity or something else altogether, something new is needed to resolve the current conundrum.

I'm wondering how this theory explains the existance of dark matter galaxies that where recently discovered:

http://www.universetoday.com/am/publish/dark_matter_galaxy.html?2322005

Apparently they discovered and area inbetween galaxies that has a little bit of hydrogen gas rotating around a central point, and based on the rotation the gravitational effect from dark matter is something like 1000 times more then the hydrogen gas alone can account for. It doesn't seem like any modification to gravity could account for this and yet also be consistant with the rotation rates around "normal" galaxies where dark matter only accounts for 5 times the mass of the visible galaxy.

Either the new theory can correct the rotation rates of visible galaxies (which is probably what it does), in which case the gravity in this dark matter galaxy would still be far too small and we'd still need to invoke dark matter once again to explain it. OR it could modify gravity to explain these new dark matter galaxies, however gravity would then become so strong that ordinary galaxies would simply collapse. I don't see how it can do both.

Also, I don't suppose anyone knows what this new modification is? I think it said in the article that they would present it in april, but does anyone know if they are keeping it secret until then? I'd really love to take a look at it!

Blob
2006-Feb-15, 04:28 PM
Hum,
Their research was published on February 10th in the US-based Astrophysical Journal Letters.

Abstract:
The phenomena customarily described with dark matter or modified Newtonian dynamics (MOND) have been argued by Bekenstein to be the consequences of a covariant scalar field, controlled by a free function [related to the MOND interpolating function μ˜(g/a0)] 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 a μ˜ that varies too gradually, and it fits rotation curves less well than the standard MOND interpolating function μ˜(x)=x/(1+x2)1/2. However, the latter varies too sharply and implies an implausible external field effect. These constraints on opposite sides have not yet excluded TeVeS, but they have 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.

PDF Article (http://arxiv.org/PS_cache/astro-ph/pdf/0512/0512425.pdf)

Gerald Lukaniuk
2006-Feb-15, 07:19 PM
Sorry Gerald Lukaniuk, but I had a very hard time following what your argument was. It kinda seemed like you where arguing that there actually is no problem with dark matter, that it's just a misunderstanding on the part of astronomers? I'm probably seriously misreading your post (and if so, I apologize). But let me just say that the problem of dark matter is very real, and weather the solution turns out to be some exotic form of particle, a modification to our laws of gravity or something else altogether, something new is needed to resolve the current conundrum.

I'm wondering how this theory explains the existance of dark matter galaxies that where recently discovered:

http://www.universetoday.com/am/publish/dark_matter_galaxy.html?2322005

Apparently they discovered and area inbetween galaxies that has a little bit of hydrogen gas rotating around a central point, and based on the rotation the gravitational effect from dark matter is something like 1000 times more then the hydrogen gas alone can account for. It doesn't seem like any modification to gravity could account for this and yet also be consistant with the rotation rates around "normal" galaxies where dark matter only accounts for 5 times the mass of the visible galaxy.

Either the new theory can correct the rotation rates of visible galaxies (which is probably what it does), in which case the gravity in this dark matter galaxy would still be far too small and we'd still need to invoke dark matter once again to explain it. OR it could modify gravity to explain these new dark matter galaxies, however gravity would then become so strong that ordinary galaxies would simply collapse. I don't see how it can do both.

Also, I don't suppose anyone knows what this new modification is? I think it said in the article that they would present it in april, but does anyone know if they are keeping it secret until then? I'd really love to take a look at it!

Sorry if I failed to get my point across. I tried to explain in a non jargonistic way that like some other phenomenon that the enigmatic conclusions astronomers come to studying might be explained by spacial geometry (the road conditions and winding nature of the paths taken by our photon visitors) rather than formulating some arbitrary relationship (the traffic laws and speed limits "something" forces them to obey". Contrary to the announcements no "dark matter" has been found and that claim can not be made until until some can literally be put in your hand. The claim that it is intangeable to all forces but gravity sounds like a cheap carnival con scam. The total lack of local evidence for many light years around us nas turned up non of this stuff even though normal matter should be vastly outnumbered by it continues to make it laughable. The observation that some hydrogen gas in distance seems to be spinning around nothing doesn't necessarily mean there is an invisible object but rather it may be spinning or appear to be spinning around the same thing as a smoke ring or whirlpool...nothing.

Astrowannabe
2006-Feb-15, 09:32 PM
Thx for clarifying, Gerald.

So your basically saying that the problem lies not with there being extra matter out there that we can't detect, but that there is something affecting the light in an odd way we aren't familar with that gives it the apperance of there being more gravity then there is?

I wholeheartedly agree with you on the fact that no dark matter has EVER been found or detected (other then through it's gravity effects on normal matter), and I really doubt that any astronomer has ever claimed to have found dark matter.


The claim that it is intangeable to all forces but gravity sounds like a cheap carnival con scam.

Hard to argue with that point either, though I probably wouldn't have used "cheap carnival con scam". The fact is, we really don't know what dark matter is. We honestly don't even know for sure that it IS something at all, which is why there are plenty of theories like this one saying that dark matter doesn't exist, but that instead it's just gravity behaving differently. Even your idea that maybe it's simply an illusion of the light due to some other effect can't be discounted. So here is a brief list (VERY brief list) of what we do know:

1) stars towards the edges of galaxies are orbiting much too fast for the visible stars to hold onto them. (Our own Milky Way galaxy included)

2) light that passes near galactic clusters and is bent due to gravitational lensing is also bent much more then we would otherwise expect (and since gravity is the only thing that can bend light in this way, it means theres a lot of excess gravity there).

..........Ok, I think that does it. As you can see, we really don't know a lot about it. The 2 main theories I'm aware of to explain this are:

Dark Matter: This involves the "carnival scam" your refering to. Since we can't see it, it doesn't emit light. That means that it can't interact either with itself or with normal matter through the electromagnetic force. (If it could, it would produce light). While strange, we do know of a few particles that do the same, such as the neutrino. Also, this particle presumably exists throughout the universe, even in our solar system so it probably doesn't interact with normal matter through the nuclear force either otherwise we would have seen something by now. So we are basically looking for some kind of particle that can't be seen, and can't interact with matter but still produces gravity. Any ideas? me neither.

Modified gravity: This is the type of theory that the article is talking about. Since we can't see dark matter, then maybe there isn't any dark matter and instead gravity simply behaves differently when acting at large differences and at very low forces. If tuned just right, you supposedly can make gravity behave in a way that predicts the observed motions without the need for any extra matter. But like I said, I don't know how this will account for the recent dark matter galaxies.

Illusion theory: I've actually never really heard of this idea you proposed. I'm not really sure what illusionary mechanism could produce the 2 effects I mentioned. Could you elaborate?



The observation that some hydrogen gas in distance seems to be spinning around nothing doesn't necessarily mean there is an invisible object but rather it may be spinning or appear to be spinning around the same thing as a smoke ring or whirlpool...nothing.

Actually, it does mean that. In order for hydrogen gas to rotate there has to be sufficient gravity (and therefore, sufficient matter) to keep it in orbit. Without that the gas would simply travel off in a strat line a la Newtons laws of motion. In fact, if you do take a smoke ring and somehow spin it, it will fall apart. So these findings can't be simply dismissed. Something there MUST be generating gravity.

five_distinct
2006-Feb-16, 03:38 PM
I'm gonna have to agree with Gerald's take on Dark Matter....I have a feeling it's gonna be one of those things that in a few generations people are gonna look back at and say "wtf were they thinking?"

Blob
2006-Feb-16, 11:39 PM
Hum,
MOND cannot explain the observed masses of clusters of galaxies nor the gravitational lensing.
The theory does not fit, it seems to me, the microwave background data or large-scale structure formation.
Nor has it ever been `observed` or tested in the laboratory.

The Dark matter model fits the microwave background data and it fits galaxies and clusters and large-scale structure and gravitational lensing.
Though, It too has not been observed in the laboratory.

Gerald Lukaniuk
2006-Feb-17, 02:46 AM
General relativity predicts with sound observational collaboration that the presence matter of distorts the space and alters the flow of time (or the rate at which things change) around it. This "probably" but not necessarily directly proportional to not its inertial mass but its perceived "weight" or gravitational attraction on other bodies. The problem with assuming inertial mass is directly proportional to apparent "weight" is that the observered angluar motion of well understood objects in distant systems is greater than their estimated weight needed to hold them there. The annswer may lie in the catch words "distortion of space-time". If space-time can be really be distorted by matter it follows that distortions in space-time can really exist. Furthermore they can possibly exist temporarily of permanently without the continued influence of real matter or for any particular reason at all. Or maybe by such things as virtual particles forming ephemeral objects or manipulations of electro magnetism by methods implied by an as yet unformulated unified field theory. Similary we don't know why matter causes this distorting nor does relativity really describe how a distortions alone can initiate gravitational attraction (or where the energy comes from). This is an exciting time for if we can analyse the clues presented to us in such things a gravitational lensing and this new enigma as demonstating the characteristics of different types of distorted space the above mentioned manipulations may seem like childs play.

Gerald Lukaniuk
2006-Feb-18, 03:22 AM
It looks like this thread is dead so I'm resubmitting my response to you question. You ideas are well formulated and valuable.
General relativity predicts with sound observational collaboration that the presence matter of distorts the space and alters the flow of time (or the rate at which things change) around it. This "probably" but not necessarily directly proportional to not its inertial mass but its perceived "weight" or gravitational attraction on other bodies. The problem with assuming inertial mass is directly proportional to apparent "weight" is that the observered angluar motion of well understood objects in distant systems is greater than their estimated weight needed to hold them there. The annswer may lie in the catch words "distortion of space-time". If space-time can be really be distorted by matter it follows that distortions in space-time can really exist. Furthermore they can possibly exist temporarily of permanently without the continued influence of real matter or for any particular reason at all. Or maybe by such things as virtual particles forming ephemeral objects or manipulations of electro magnetism by methods implied by an as yet unformulated unified field theory. Similary we don't know why matter causes this distorting nor does relativity really describe how a distortions alone can initiate gravitational attraction (or where the energy comes from). This is an exciting time for if we can analyse the clues presented to us in such things a gravitational lensing and this new enigma as demonstating the characteristics of different types of distorted space the above mentioned manipulations may seem like childs play.