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"General Relativity describes gravity perfectly everywhere we've ever looked. From the smallest-scale attractions we've ever measured in a laboratory to the exp

"General Relativity describes gravity perfectly everywhere we've ever looked. From the smallest-scale attractions we've ever measured in a laboratory to the expansion and curvature of space due to Earth, the Sun, black holes, galaxies, or the entire Universe, our observations and measurements have never deviated from what we've observed. " So correct me if I'm wrong, but the rotation of galaxies completely defies even Newtonian principles, right? So we invented concepts of Dark Matter / Dark Energy as a placeholder, crossing our fingers that we're right on that?

PuffinBlue 8y ago
Not exactly. Imagine a china mug full of water. You can see the mug and the water being held in by the mug. Now imagine a glass of water. The purest most transparent glass ever, with an identical refraction index as the water. You can't see the glass. You just see the water being held together by something. You don't know the glass exists. You 'invent' the glass to explain the behaviour of the water, seeing as you know the how the mug affects the water.
- oldandtired 8y ago
  The glass is testable though and would quickly be found. Dark matter and dark energy are assumed to exist with no experimental observations occurring. Every experiment has so far failed to show the existence of said entities. One possibility is that we do not have any way to find said entities with any means at our disposal. Another possibility is that they do not exist (just a figment of imagination) and that the theories requiring them are wrong. In that case, one should be looking for other theories that might be a more capable explanation. The question here is to determine when or whether we should stop looking for these entities and maybe move onto another model/theory. The basic assumption of all gravity based theories and models is that the universe is electrically neutral everywhere and that magnetic and electric fields have no possible influence at stellar, interstellar, galactic and intergalactic distances. Whether this assumption is true or not is difficult to gauge since we only have visual observations (at all sorts of frequencies) and cannot actually get out there to make the required measurements. So we have to fall back to what we think is reasonable and work from there.
  - SiempreViernes 8y ago
    > The basic assumption of all gravity based theories and models is that the universe is electrically neutral everywhere and that magnetic and electric fields have no possible influence at stellar, interstellar, galactic and intergalactic distances This is impressively inaccurate: plasmas (charged and magnetic fluids) are basically the entirety of stellar evolution and the main part of everything up to galaxy evolution, so we have pretty good limits on the magnetic fields out in the universe. There is also direct measurements of magnetic fields integrated along the line of sight out to cosmological distances, and of course every spectra ever taken has measured the ionization level of the luminous gas.
    - oldandtired 8y ago
      I agree. Yet the models assume that gravity is the only influence for the motion of the galaxies, etc. We can see evidence of other phenomena but.... I have had this discussion with trained working physicists and the general reaction has been that these phenomena are completely insignificant in relation to stellar, interstellar, galactic and intergalactic motion. So where do we stand? If the orders of magnitude difference in strength between electric and magnetic fields and the strength of gravity is over 35. What kinds of effects do we expect with these kinds of differences? Especially when we are looking at plasmas and all sorts of ionisation. I don't know, but it does lead to intriguing questions.
  - deleted 8y ago
    [deleted]
oldandtired 8y ago
The rotation of galaxies defies any solely gravity based model, irrespective of whether or not we use General Relativity, Newtonian principles or other gravity models. The addition of entities to some of these models to bring about compliance of those models with observation has not yet led to any experimental verification of such entities. There are models of gravitation that are based on classical electromagnetics, wherein, gravity is a residual by-product of the electromagnetic interaction between the components of atoms. The models appear to be of the correct order of magnitude for the size of the forces. However, like a lot of models that have been developed in the last 100 years, there does not appear to be any traction to investigate these models as they are not the commonly ascribed-to models. So we are unable to see if these models produce better predictions for the experiments that are being done around the world.
- SiempreViernes 8y ago
  Please give us the CMB power spectrum with your favourite MOND theory before continuing on your tirade about how those theories are neglected without basis.
  - oldandtired 8y ago
    You make the mistake of thinking that it has to be a MOND theory, I wasn't even thinking of MONDs. There are other models that do not assume that gravity is the only significant force at such levels. Whether these other models can match up to the observations is what we need to investigate. The point here is that none of the current crop of theories matches what we see at all the different levels at which we make observations. This is not a problem per se but an intriguing opportunity to do further investigations into what could be better explanations. All I am saying is that the assumption of gravity being the only significant force (whatever gravity may be) has only led in the standard models, so far, to a proposal of dark matter for which all experiments designed to find it have failed. We have got to a position where there is a big discrepancy between the evidence that is being collected and what theory is predicting. There are plenty of questions being raised across the board about what the data collected actually means. I am simply putting forward that there may be a possibility that General Relativity has reached a limit of usefulness and may need to be superseded. There may be a model that gives an explanation of what we see without resorting to adding entities for which we have not received any confirmation by experiment. What that is, I don't know. I don't get paid to do that kind of research. If we can't find the experimental evidence to support an idea that theory requires, maybe we need to look elsewhere, including into alternative models and theories. Unless we are willing to look at different ideas and test them appropriately and rigorously when we come to significant roadblocks, we are then stuck in patterns that aren't helpful. This is the study of the universe we are looking at, at both the very small and the very large and everything in between. We make many assumptions in developing our theories and models, but if some of those are not quite the reality then our models can and do give results that seem okay, but in the detail are not. Mathematical models are always idealised models. They do not take into consideration all that exists in reality. For many purposes, that is acceptable - it becomes a case of close enough is good enough. But, if you take that same model into a physical situation where the idealisations used are not matching reality, then that model will give your incorrect results. For example, in the main you may be able to assume that some feature of reality is of very minor significance, but if you change to a place where that feature is now significant, your mathematics breaks down. You have to change your model or even develop a complete new theory by which you do your investigations. This kind of thing should be standard practice. I'll leave you with a final thought. At about the time that Gell-Mann was working on his ideas about quarks, there was another man working on another model to explain what was being seen at the sub-atomic level. Now, this man was not a theoretical scientist but he also came up with an idea of a 1/3 charged particle. His purpose for working on the theory was purely for his own interest (he was dissatisfied with the theory and models around at the time). One he had finished his work, he put it aside and went on with his quite successful life. One of his innate abilities was that he had an eidetic memory and when quizzed could described anything on any page of his 6000+ pages of documents. I received some of his papers years ago from someone who knew him and had obtained all of those papers. What I found intriguing was that part of the model he developed gave a much better and more easily calculable way of determining the binding energy of any nucleus (from H to Fe at least). He made it quite clear that the model was just that - a model and that one should not expect reality to actually match the model. In another part of the theoretical work he did, he made a slight modification to the electric field equation to include a Lorenz transformation which did away with the need for the strong nuclear force. Since then, I have come across still another modification of the electric field equation (from a completely different location) which gives rise to a residual force (always attractive) and on the same order of magnitude as gravity. Now, one of these modifications works on the very small and one works on the very large. Do they have any practical significance? I don't know, but unless there is interest in looking at whether they are capable of explaining what we see, we will never actually know. They may be dead-ends, but they may also open up completely new avenues for investigation.
aroberge 8y ago
Dark matter is also required to make the predictions of primordial nucleosynthesis correct and modeling of the large scale structures of the universe.
- AnimalMuppet 8y ago
  > Dark matter is also required to make the predictions of primordial nucleosynthesis correct... Could you expand on this a bit? I've seen that twice in the last week, but never heard it before. Can you give me a pointer to what you're talking about here?
mabbo 8y ago
My understanding (limited, admittedly) is that there are a number of phenomenon that dark matter explains very well, galactic rotation among them. Alternative theories of gravity that explain galactic rotation often don't fit all the others very well.
- karmakaze 8y ago
  Dark matter doesn't 'explain' being itself a fudge factor. We give it a name to resolve observations that do not fit our models. We have a strong belief in gravitational laws and theory that we take it as fixed and make the rest fit as needed. Not having an alternate theory of gravitation that is as good makes this reasonable.
  - mabbo 8y ago
    It's far more than a simple fudge factor. It says that there is matter with mass, affecting other matter via gravity, but no other interactions seem possible with it. That is a sound, almost complete theory with some unknowns around why it doesn't otherwise interact, what it actually is. Dark matter also explains certain gravitational lensing phenomenon, aspects of the CMB, from mass location during galactic collisions (and more). Other theories can possibly explain one or some of those observations, but nothing does a good job (or a simple one) of explaining them all. Dark matter is real enough to make verifiable predictions in other places. Other theories don't.

PuffinBlue 8y ago

Not exactly. Imagine a china mug full of water. You can see the mug and the water being held in by the mug. Now imagine a glass of water. The purest most transparent glass ever, with an identical refraction index as the water. You can't see the glass. You just see the water being held together by something. You don't know the glass exists. You 'invent' the glass to explain the behaviour of the water, seeing as you know the how the mug affects the water.

oldandtired 8y ago
The glass is testable though and would quickly be found. Dark matter and dark energy are assumed to exist with no experimental observations occurring. Every experiment has so far failed to show the existence of said entities. One possibility is that we do not have any way to find said entities with any means at our disposal. Another possibility is that they do not exist (just a figment of imagination) and that the theories requiring them are wrong. In that case, one should be looking for other theories that might be a more capable explanation. The question here is to determine when or whether we should stop looking for these entities and maybe move onto another model/theory. The basic assumption of all gravity based theories and models is that the universe is electrically neutral everywhere and that magnetic and electric fields have no possible influence at stellar, interstellar, galactic and intergalactic distances. Whether this assumption is true or not is difficult to gauge since we only have visual observations (at all sorts of frequencies) and cannot actually get out there to make the required measurements. So we have to fall back to what we think is reasonable and work from there.
- SiempreViernes 8y ago
  > The basic assumption of all gravity based theories and models is that the universe is electrically neutral everywhere and that magnetic and electric fields have no possible influence at stellar, interstellar, galactic and intergalactic distances This is impressively inaccurate: plasmas (charged and magnetic fluids) are basically the entirety of stellar evolution and the main part of everything up to galaxy evolution, so we have pretty good limits on the magnetic fields out in the universe. There is also direct measurements of magnetic fields integrated along the line of sight out to cosmological distances, and of course every spectra ever taken has measured the ionization level of the luminous gas.
  - oldandtired 8y ago
    I agree. Yet the models assume that gravity is the only influence for the motion of the galaxies, etc. We can see evidence of other phenomena but.... I have had this discussion with trained working physicists and the general reaction has been that these phenomena are completely insignificant in relation to stellar, interstellar, galactic and intergalactic motion. So where do we stand? If the orders of magnitude difference in strength between electric and magnetic fields and the strength of gravity is over 35. What kinds of effects do we expect with these kinds of differences? Especially when we are looking at plasmas and all sorts of ionisation. I don't know, but it does lead to intriguing questions.
- deleted 8y ago
  [deleted]

oldandtired 8y ago

The rotation of galaxies defies any solely gravity based model, irrespective of whether or not we use General Relativity, Newtonian principles or other gravity models. The addition of entities to some of these models to bring about compliance of those models with observation has not yet led to any experimental verification of such entities. There are models of gravitation that are based on classical electromagnetics, wherein, gravity is a residual by-product of the electromagnetic interaction between the components of atoms. The models appear to be of the correct order of magnitude for the size of the forces. However, like a lot of models that have been developed in the last 100 years, there does not appear to be any traction to investigate these models as they are not the commonly ascribed-to models. So we are unable to see if these models produce better predictions for the experiments that are being done around the world.

SiempreViernes 8y ago
Please give us the CMB power spectrum with your favourite MOND theory before continuing on your tirade about how those theories are neglected without basis.
- oldandtired 8y ago
  You make the mistake of thinking that it has to be a MOND theory, I wasn't even thinking of MONDs. There are other models that do not assume that gravity is the only significant force at such levels. Whether these other models can match up to the observations is what we need to investigate. The point here is that none of the current crop of theories matches what we see at all the different levels at which we make observations. This is not a problem per se but an intriguing opportunity to do further investigations into what could be better explanations. All I am saying is that the assumption of gravity being the only significant force (whatever gravity may be) has only led in the standard models, so far, to a proposal of dark matter for which all experiments designed to find it have failed. We have got to a position where there is a big discrepancy between the evidence that is being collected and what theory is predicting. There are plenty of questions being raised across the board about what the data collected actually means. I am simply putting forward that there may be a possibility that General Relativity has reached a limit of usefulness and may need to be superseded. There may be a model that gives an explanation of what we see without resorting to adding entities for which we have not received any confirmation by experiment. What that is, I don't know. I don't get paid to do that kind of research. If we can't find the experimental evidence to support an idea that theory requires, maybe we need to look elsewhere, including into alternative models and theories. Unless we are willing to look at different ideas and test them appropriately and rigorously when we come to significant roadblocks, we are then stuck in patterns that aren't helpful. This is the study of the universe we are looking at, at both the very small and the very large and everything in between. We make many assumptions in developing our theories and models, but if some of those are not quite the reality then our models can and do give results that seem okay, but in the detail are not. Mathematical models are always idealised models. They do not take into consideration all that exists in reality. For many purposes, that is acceptable - it becomes a case of close enough is good enough. But, if you take that same model into a physical situation where the idealisations used are not matching reality, then that model will give your incorrect results. For example, in the main you may be able to assume that some feature of reality is of very minor significance, but if you change to a place where that feature is now significant, your mathematics breaks down. You have to change your model or even develop a complete new theory by which you do your investigations. This kind of thing should be standard practice. I'll leave you with a final thought. At about the time that Gell-Mann was working on his ideas about quarks, there was another man working on another model to explain what was being seen at the sub-atomic level. Now, this man was not a theoretical scientist but he also came up with an idea of a 1/3 charged particle. His purpose for working on the theory was purely for his own interest (he was dissatisfied with the theory and models around at the time). One he had finished his work, he put it aside and went on with his quite successful life. One of his innate abilities was that he had an eidetic memory and when quizzed could described anything on any page of his 6000+ pages of documents. I received some of his papers years ago from someone who knew him and had obtained all of those papers. What I found intriguing was that part of the model he developed gave a much better and more easily calculable way of determining the binding energy of any nucleus (from H to Fe at least). He made it quite clear that the model was just that - a model and that one should not expect reality to actually match the model. In another part of the theoretical work he did, he made a slight modification to the electric field equation to include a Lorenz transformation which did away with the need for the strong nuclear force. Since then, I have come across still another modification of the electric field equation (from a completely different location) which gives rise to a residual force (always attractive) and on the same order of magnitude as gravity. Now, one of these modifications works on the very small and one works on the very large. Do they have any practical significance? I don't know, but unless there is interest in looking at whether they are capable of explaining what we see, we will never actually know. They may be dead-ends, but they may also open up completely new avenues for investigation.

aroberge 8y ago

Dark matter is also required to make the predictions of primordial nucleosynthesis correct and modeling of the large scale structures of the universe.

AnimalMuppet 8y ago
> Dark matter is also required to make the predictions of primordial nucleosynthesis correct... Could you expand on this a bit? I've seen that twice in the last week, but never heard it before. Can you give me a pointer to what you're talking about here?

mabbo 8y ago

My understanding (limited, admittedly) is that there are a number of phenomenon that dark matter explains very well, galactic rotation among them. Alternative theories of gravity that explain galactic rotation often don't fit all the others very well.

karmakaze 8y ago
Dark matter doesn't 'explain' being itself a fudge factor. We give it a name to resolve observations that do not fit our models. We have a strong belief in gravitational laws and theory that we take it as fixed and make the rest fit as needed. Not having an alternate theory of gravitation that is as good makes this reasonable.
- mabbo 8y ago
  It's far more than a simple fudge factor. It says that there is matter with mass, affecting other matter via gravity, but no other interactions seem possible with it. That is a sound, almost complete theory with some unknowns around why it doesn't otherwise interact, what it actually is. Dark matter also explains certain gravitational lensing phenomenon, aspects of the CMB, from mass location during galactic collisions (and more). Other theories can possibly explain one or some of those observations, but nothing does a good job (or a simple one) of explaining them all. Dark matter is real enough to make verifiable predictions in other places. Other theories don't.