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Thread: Matter in space

  1. #1 Matter in space 
    Forum Ph.D. verzen's Avatar
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    I am trying to convince someone that space is NOT empty and space is filled up with dark matter and dark energy. I linked him two articles but he doesnt bother paying attention to either of them. Does anyone have a good article they could link me to show him that I am right and that there is no such thing as empty space.


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    Dark matter and dark energy supposedly do not exist at all points in space. Though, radiation does, whether it is electromagnetic radiation or the solar wind (which is based off of massive particles).


    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

    "Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

    "Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"

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    Forum Ph.D. verzen's Avatar
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    So if radiation exists, that means that it is energy that fills up space, correct? Thus, space is not empty.. am I understanding this correctly?
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    Quote Originally Posted by verzen
    So if radiation exists, that means that it is energy that fills up space, correct? Thus, space is not empty.. am I understanding this correctly?
    Besides that, it is currently accepted that even space with all matter, radiation and fields removed is still something. It is essential to the big bang theory AFAIK.
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    im a little confused here. what do you mean by space being filled. you mean that if I were to go a trillionbillionzillion lightyears outside of the known universe - from the initial center - i would still encounter radiation?
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    Verzen for starters you really outta stop looking to be right and look for the right answer

    space is empty, that is the definition of space, space is a lack of matter



    The Parts of the Universe commonly known as as Space are not quite so empty, firstly there is Dark Matter and it's derivitive Dark Energy, however this is a completely theoretical notion, the words exist simply because 'it should be there' there is very little backing up evidence
    'space' is theoretically full of theoretical particles from Dark Matter to Tachyons to Higgs Boson



    If you skip the theory space is full of Radiation and other waves, light, sound, microwaves, gamma rays, all are filling up space, however since waves technically have no mass they are unable to 'fill' anything


    so there you go, your both right space is both full and empty
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    correct me if I'm wrong, because I want to make sure I'm right... but when we zoom into the microcosmic world, we see that there is space between every microcosmic particle. Even that which holds our atoms together for example, the strong nuclear force is caused by the gluon, which acts upon quarks, antiquarks, and even the gluons themselves. No matter how small we get, there is space there in between the little particles interacting and moving at super high speeds. Even protons are little packages of energy. There is nothing that just blankets and fills space. Dark energy and Dark matter would be expected to follow that same rule...

    Though space is full of all of this itty bitty crap flying everywhere, when you zoom in is there not space in between all of the pieces of the pieces of the pieces of that crap?
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    Forum Bachelors Degree Shaderwolf's Avatar
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    wait...
    .

    I just reread kalster's post.

    first... ttcfraser according to the big bang theory etc. etc. there is no center. Everything is the center. It's just expanding.
    ...
    wait...

    ...Dang my not studying for so long! I used to know so much so well! I feel so stupid. Please help...
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  10. #9  
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    Quote Originally Posted by ttcfraser
    im a little confused here. what do you mean by space being filled. you mean that if I were to go a trillionbillionzillion lightyears outside of the known universe - from the initial center - i would still encounter radiation?
    With current cosmological models there is no such thing as the "initial center", unless you accept that EVERYWHERE is the initial center. That is the nature of the Big Bang. It was not an explosion of matter within space, but rather an explosion of space-time itself.

    It is also not know if the universe is spatially finite or not, so it may well not be possible to go a "tillionbillionzillion lightyers" from anywhere. But in any case it is generall thought that the cosmological principle applies, and the universe is homogeneous and isotropic, and if so space looks the same, on the largest scales, everywhere. So, yes, you would encounter radiation, see stars and galaxies just as you can now with good telescopes.
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  11. #10 Re: Matter in space 
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    Quote Originally Posted by verzen
    I am trying to convince someone that space is NOT empty and space is filled up with dark matter and dark energy. I linked him two articles but he doesnt bother paying attention to either of them. Does anyone have a good article they could link me to show him that I am right and that there is no such thing as empty space.
    You should be prepared to lose your bet.

    Setting aside questions of the quantum vacuum/zero point energy for a moment, deep space is a very very good, though not perfect vacuum (i.e. void). There are a few hydorogen atoms per CC, there are lots of photons, and there are occasionally various high energy particles flying around. The cosmic background radiation permeates everything.

    http://en.wikipedia.org/wiki/Vacuum

    Dark matter, if it filled up space would not have the necessary graitational effect. For, were it uniformly distributed throughout the universe the gravitational effect would be ZERO, for the same reason that the gravitational field at the center of the Earth is zero, the pull from the distributed elements cancel one another out.

    Dark energy is perhaps a bit different, but there is no evidence that it exists in any describable form other than a cosmological constant in the Einstein field equations that govern general relativity. It may possibley be an effect of the zero point energy, but current calculations differ from observed effects by 120 orders of magnitude.
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    @Booms: I think you have your description of dark matter and dark energy backwards. Dark matter is something that shouldn't be there, but there's a lot of evidence that says something really is there. It's called dark just because no one knows what it really is. Dark energy is in a similar boat, but the two aren't related. There's a separate pile of evidence that says something is there, but again, no one knows what that is either.
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    that is true, and that should be where THAT discussion ends. I've seen to many posts start this way, and than be dragged off into meaningless argument over what is dark matter and whether it exists or not. there is something there, and we don't know what.

    i hit a road bump where I thought I knew what I was talking about, and was wondering if you could elaborate. so there is a "cosmic background radiation that permeates everything" you say. so, at the extremely small scale you are saying that yo could not find one bit of empty space. I never heard that before. I believed that, as I said, matter, energy, and that even the 4 fundamental forces worked by small... (for lack of a better vocabulary) were all pretty much a bunch of crap and bundles of crap, interacting ect. with each other. isn't gravity theoretically controlled by the graviton, as the other interactions are controlled by their respective particles? (I know we haven't found a graviton yet.) light - the proton and etc! so, if the forces are governed by little particles, how do they work the way that they do? There's the thing about the graviton, and than the more familiar Einstein theory of gravity being a distortion of space-time. How do those coincide? I heard that relativity and quantum mechanics didn't mesh. is there space or not?! what the heck! why am I so confused! got any good reading selections I could use? how about some explanations. How about chocolate? I need to cool down. Relax... I thought I at least knew more than this?
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  14. #13  
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    Quote Originally Posted by Shaderwolf
    that is true, and that should be where THAT discussion ends. I've seen to many posts start this way, and than be dragged off into meaningless argument over what is dark matter and whether it exists or not. there is something there, and we don't know what.

    i hit a road bump where I thought I knew what I was talking about, and was wondering if you could elaborate. so there is a "cosmic background radiation that permeates everything" you say. so, at the extremely small scale you are saying that yo could not find one bit of empty space. I never heard that before. I believed that, as I said, matter, energy, and that even the 4 fundamental forces worked by small... (for lack of a better vocabulary) were all pretty much a bunch of crap and bundles of crap, interacting ect. with each other. isn't gravity theoretically controlled by the graviton, as the other interactions are controlled by their respective particles? (I know we haven't found a graviton yet.) light - the proton and etc! so, if the forces are governed by little particles, how do they work the way that they do? There's the thing about the graviton, and than the more familiar Einstein theory of gravity being a distortion of space-time. How do those coincide? I heard that relativity and quantum mechanics didn't mesh. is there space or not?! what the heck! why am I so confused! got any good reading selections I could use? how about some explanations. How about chocolate? I need to cool down. Relax... I thought I at least knew more than this?

    The cosmic background radiation is apparently balckbody radiation corresponding to a temperature of abut 2.73 K and it is pretty much everywhere. So there are photons just about everywhere also. On the other hand, we are talking about light here and generally the criteria for a vacuum doesn't talk about light. So you can consider space to be a pretty good vacuum, and how good depends on where. But the vacuum in low earth orbit is better than the vacuum achieveable in laboratories. And the farther you get from stars and galaxies the better the vacuum is thought to be.

    The graviton, if it exists, is a quantum particle that carries the gravitational force in a manner similar to the way the photon carries the electromagnetic force. NOBODY knows how the graviton meshes with general relativity. Attempts to formulate a quantum theory of gravity have been notably unsuccessful. Attempts continue to occupy some of the very best theoretical physicists. If you can formulate a consistent and accurate theory,I can guarantee you an all-expense paid trip to Stockholm.

    Quantum mechanics and special relativity mesh just fine, That is what quantum field theories are all about. But nobody knows how to mesh quantum theories with general relativity, and it is general relativity that explains gravity.

    Quantum theory and general relativity do not mesh. Quantum theory is a stochastic theory -- it predicts only probabilities. General relativity is a deterministic theory -- it predicts precise outcomes.

    That is the basic problem. We have quantum field theories that describe the electromagnetic, weak, and strong forces in terms of particle exhanges, the particles being called bosons of one type or another. But we do not have such a theory for gravity. All we have is a name for the particle that carries the gravitational force, the graviton, but no viable theory to describe it, if it exists.


    If you are looking for a book, I suggest Lee Smolin's Three Roads to Quantum Gravity.
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    and in order to carry the gravitational force, the graviton would have to travel in between every single one of the objects that are being effected. according to newton's equation (1/r^2) that would be every object within a sphere with an infinite radius. I just got to thinking. How is that possible? do the other forces also follow similar equations? what exactly are these particles made of? not mass.... at least not that theoretical

    also...
    The cosmic background radiation is apparently balckbody radiation corresponding to a temperature of abut 2.73 K and it is pretty much everywhere.
    You used "pretty much" twice. so... theoretically, a perfect vacuum is achievable? It had almost sounded earlier as if you were inferring that the universe would not allow a perfect vacuum.

    also isn't gravity said to defy the speed of light. There are other things, like when we start to talk about quantum entanglement that do that aren't there? I know I'm asking allot of questions, so I will ask again... can you provide a list of books that I could read? I have a small background in calculus, but suck the crap up like it was candy, so you can suggest something with some of that in it.

    the quantum entanglement was leading to the suggestion of string theory. People don't like to bring that up, because it's not proven, but... can't things like this only be possible with multiple dimensions? Than I think sometimes because of the infamous double slit experiment. Observation? Possibilities? Mind Blowing! Dang It! I'm so sorry. This is all so closely related with each other. you're making me think! It's all unorganized though.
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    also isn't gravity said to defy the speed of light
    Actually its effects also propegate at the speed of light. If you were to snap your fingers and made the Sun disappeer, we would not know about it for 8 minutes odd, whereafter the light would suddenly stop and we would be flung in a straight line like a rock on a string when the string snaps.
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    Forum Bachelors Degree Shaderwolf's Avatar
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    Thanks K. That was one of the facts I wasn't sure about. (that's why I asked) nothing isn't supposed to, but doesn't quantum entanglement work instantly?

    Any help on anything else? There was allot there...I think. Any Books?
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  18. #17  
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    Quote Originally Posted by Shaderwolf
    and in order to carry the gravitational force, the graviton would have to travel in between every single one of the objects that are being effected. according to newton's equation (1/r^2) that would be every object within a sphere with an infinite radius. I just got to thinking. How is that possible? do the other forces also follow similar equations? what exactly are these particles made of? not mass.... at least not that theoretical

    also...
    The cosmic background radiation is apparently balckbody radiation corresponding to a temperature of abut 2.73 K and it is pretty much everywhere.
    You used "pretty much" twice. so... theoretically, a perfect vacuum is achievable? It had almost sounded earlier as if you were inferring that the universe would not allow a perfect vacuum.

    also isn't gravity said to defy the speed of light. There are other things, like when we start to talk about quantum entanglement that do that aren't there? I know I'm asking allot of questions, so I will ask again... can you provide a list of books that I could read? I have a small background in calculus, but suck the crap up like it was candy, so you can suggest something with some of that in it.

    the quantum entanglement was leading to the suggestion of string theory. People don't like to bring that up, because it's not proven, but... can't things like this only be possible with multiple dimensions? Than I think sometimes because of the infamous double slit experiment. Observation? Possibilities? Mind Blowing! Dang It! I'm so sorry. This is all so closely related with each other. you're making me think! It's all unorganized though.
    My "pretty much" was to admit the possibility of sheilding. Microwave radiation is just one form of electromagnetic radiation, and you can shield from it just like you can cast a shadow for visible light. Inside a sealed metal box you would not find the cosmic background radiation.

    You are going to have photons even inside a sealed metal box, due to thermal radiation unless that box is at a temperature of absolute zero. So it is pretty clear that, barring some exotic situation that I might be missing, you will find photons everywhere. If you throw in the effects of quantum mechanics, you will also find virtual particles everywhere. This starts to raise the question as to what is really meant by "vacuum" and that discussion could become rather long and involved.
    http://en.wikipedia.org/wiki/Vacuum_state
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    The graviton, if it exists, is a quantum particle that carries the gravitational force in a manner similar to the way the photon carries the electromagnetic force. NOBODY knows how the graviton meshes with general relativity. Attempts to formulate a quantum theory of gravity have been notably unsuccessful. Attempts continue to occupy some of the very best theoretical physicists. If you can formulate a consistent and accurate theory,I can guarantee you an all-expense paid trip to Stockholm.
    I have to take issue with one of your statements. In fact, it is quite possible to show that curved space-time is in fact directly equivalent to the interactions gravitons. The problem, however, is describing how gravitons actually interact, given that they have yet to be observed. It leads to infinite quantites which are not easily renormalizable.

    If you are looking for a source for what I say, here's the Wikipedia article:

    http://en.wikipedia.org/wiki/Quantum_gravity

    Further evidence can be seen in Lee Smolin's The Trouble with Physics

    and in order to carry the gravitational force, the graviton would have to travel in between every single one of the objects that are being effected. according to newton's equation (1/r^2) that would be every object within a sphere with an infinite radius. I just got to thinking. How is that possible? do the other forces also follow similar equations? what exactly are these particles made of? not mass.... at least not that theoretical
    If you were to think of Newton's Laws, you would only be able to create a rough approximation of general relativity, as space-time is dynamic in Einsteinian notions, whereas Newton's space-time is completely flat and never-changing. Further, Newton's Laws cannot be used to create an effective quantum theory of gravity, mainly because quantum field theory must be relativistic i.e. it takes into account relativity, which Newtonian space-time cannot.

    You are going to have photons even inside a sealed metal box, due to thermal radiation unless that box is at a temperature of absolute zero. So it is pretty clear that, barring some exotic situation that I might be missing, you will find photons everywhere. If you throw in the effects of quantum mechanics, you will also find virtual particles everywhere. This starts to raise the question as to what is really meant by "vacuum" and that discussion could become rather long and involved.
    Particle-antiparticle pairs and photons together serve to destroy the concept of a vacuum. I quite agree with you, DrRocket. The problem here is indeed the definition of a vacuum.

    also isn't gravity said to defy the speed of light.
    Don't even go there, unless you believe in DSR. The fact is, relativity has just one simple thing to say about speed: Absolutely Nothing Whatsoever May go Faster Than Light. No, not even gravity. Not even light itself can transcend its own eternal speed. The speed of light is fixed, and nothing may go past it.

    the quantum entanglement was leading to the suggestion of string theory.
    Not so. Quantum entanglement is part of quantum mechanics, which string theory and all other theories of unification must naturally build upon. Quantum mechanics does not require extra dimensions.

    Further, entanglement is currently little understood. I know very little about it myself for certain. There are multiple different theories to account for it, none of which have yet been shown to be valid by experiment.

    Than I think sometimes because of the infamous double slit experiment. Observation? Possibilities? Mind Blowing! Dang It! I'm so sorry. This is all so closely related with each other. you're making me think! It's all unorganized though.
    Good on you. If more people thought, the world would be a better place.

    As to the double slit experiment, the Copenhagen interpretation of quantum mechanics does provide an answer. It has to do with the probability waves of the photon, which of course spread out so that one goes through one slit, and the other through another. These waves then interact, creating the diffraction pattern we see.

    Sorry to disagree with you, but I quite fail to see how they are closely related. From discussing the existence of a vacuum, you have somehow jumped to entanglement, and further to gravity, both of which have nothing to do with each other.

    As to dark matter and dark energy, I think I should mention both have yet to be proven. They are only introduced to explain why the orbital speed of some stars are not in accordance with theory. The effect itself can be just as easily explained if you think that our ideas of gravity are incomplete and must be extended to account for these observations. We only prefer dark matter because it is much easier. Curse human laziness, lol...
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  20. #19  
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    Quote Originally Posted by Liongold
    The graviton, if it exists, is a quantum particle that carries the gravitational force in a manner similar to the way the photon carries the electromagnetic force. NOBODY knows how the graviton meshes with general relativity. Attempts to formulate a quantum theory of gravity have been notably unsuccessful. Attempts continue to occupy some of the very best theoretical physicists. If you can formulate a consistent and accurate theory,I can guarantee you an all-expense paid trip to Stockholm.
    I have to take issue with one of your statements. In fact, it is quite possible to show that curved space-time is in fact directly equivalent to the interactions gravitons. The problem, however, is describing how gravitons actually interact, given that they have yet to be observed. It leads to infinite quantites which are not easily renormalizable.

    If you are looking for a source for what I say, here's the Wikipedia article:

    http://en.wikipedia.org/wiki/Quantum_gravity

    Further evidence can be seen in Lee Smolin's The Trouble with Physics
    [I stand by my statement. You might want to read those articles a little closer and add Lee Smolin's Three Roads to Quantum Gravity and perhaps Richard Feynman's The Feynman Lectures on Gravitation

    The graviton is and remains a purely theoretical particle. There is no viable theory of quantum gravity, but if and when one is formulated the name for the messenger particle, the graviton, is ready and waiting. We do not yet have a description of the physics whereby that particle acts, although there is ongoing research to produce such a description. Thus far those efforts have not succeeded.

    Not only are quantum field theories of gravity not EASILY renormalizable, thus far attempts have not been renormalizable at all, at that is the heart of the problem.

    It is quite impossible to show that the curved space-time of general relativity is equivalent to a quantum theory. That is precisely the problem in developing a theory of quantum gravity. If you could do that you would have a quantum theory of gravity. General relativity is a completely deterministic theory and quantum theories are stochastic. What is needed is a theory that incorporates both quantum field theories and gravitation and that is closely approximated by general relativity in the limit where quantum effects are negligible.

    An alternative would be a deterministic theory that provides an alternative explanation for the sub-atomic world that closely approximates quantum field theories. Most physicists feel that it is general relativity that will have to be modified, but there are some in the other camp, Roger Penrose being one.

    In any case there is no consistent mathematical theory of quantum gravity at the moment and therefore there is no viable description of the graviton or quantum gravity. That could change.
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    I stand by my statement. You might want to read those articles a little closer and add Lee Smolin's Three Roads to Quantum Gravity and perhaps Richard Feynman's The Feynman Lectures on Gravitation

    The graviton is and remains a purely theoretical particle. There is no viable theory of quantum gravity, but if and when one is formulated the name for the messenger particle, the graviton, is ready and waiting. We do not yet have a description of the physics whereby that particle acts, although there is ongoing research to produce such a description. Thus far those efforts have not succeeded.

    Not only are quantum field theories of gravity not EASILY renormalizable, thus far attempts have not been renormalizable at all, at that is the heart of the problem.

    It is quite impossible to show that the curved space-time of general relativity is equivalent to a quantum theory. That is precisely the problem in developing a theory of quantum gravity. If you could do that you would have a quantum theory of gravity. General relativity is a completely deterministic theory and quantum theories are stochastic. What is needed is a theory that incorporates both quantum field theories and gravitation and that is closely approximated by general relativity in the limit where quantum effects are negligible.

    An alternative would be a deterministic theory that provides an alternative explanation for the sub-atomic world that closely approximates quantum field theories. Most physicists feel that it is general relativity that will have to be modified, but there are some in the other camp, Roger Penrose being one.

    In any case there is no consistent mathematical theory of quantum gravity at the moment and therefore there is no viable description of the graviton or quantum gravity. That could change.
    I am not denying your statements, DrRocket. I know and understand that a renormalisable theory of quantum gravity is currently impossible. I will look at those books; I believe i already have one in my collection, although I am not quite sure about that.

    What I am saying, however, is that it is possible to render gravity a quantised force, with a spin-2 particle called the graviton; however, actually calculating the interactions between any of them proves to be near impossible, primarily because gravitons interact gravitationally with each other. This is because, unlike photons, which possess no charge and do not feel the electromagnetic force, gravitons interact with anything carrying energy, which they also possess. In order to then simulate gravity between them, the gravitons themselves must emit gravitons, which must in turn emit gravitons and so on; very similar to the infinity problems incurred in QED, where an electron emits a photon containing enough energy to create a particle-antiparticle pair which in turn emits light and so on.

    However, doing the above runs into infinities, which renders the quantum gravity model incosistent and non-calculable.

    Further, I am sure you are quite aware of the need for gravity waves predicted by general relativity, which must be described by quantum mechanics. There are currently some experiments ongoing designed to try and observe the graviton; they are highly sensitive and thus far have not succeeded.

    General relativity is a completely deterministic theory and quantum theories are stochastic. What is needed is a theory that incorporates both quantum field theories and gravitation and that is closely approximated by general relativity in the limit where quantum effects are negligible.
    I completely agree with you. I myself prefer these methods to the second approach, which seems to me illogical; why change a theory if there are practically no disagreements with experiment? Apart from the dark matter question, Einstein's general theory of relativity thus far has been perfectly well-confirmed, and perfectly in accordance with experiment. Quantum mechanics itself has yet to be disproved. in fact, I would say it is impossible to disprove it, because it calculates probabilities and not definite outcomes.

    In fact, the only place where general relativity and quantum mechanics run into problems is their numerous encounters with infinity. Infinity becomes commonplace within balck holes, and is found in quantum interactions between particles.

    General relativity is a completely deterministic theory and quantum theories are stochastic. What is needed is a theory that incorporates both quantum field theories and gravitation and that is closely approximated by general relativity in the limit where quantum effects are negligible.
    In which case it should indeed have some experimentally falsifiable predictions. However, gravity being weak at the particular level, I find it very unlikely. Likewise, quantum mechanics can best be used to describe gravitons, which have yet to be discovered. I find it hard to think of an unique prediction of such a theory, given as stupendously little is inconsistent experiment. I personally believe that the best possible prediction would be if it somehow managed to explain the dark matter question. Would you agree?

    In any case there is no consistent mathematical theory of quantum gravity at the moment and therefore there is no viable description of the graviton or quantum gravity. That could change.
    Let us see now: string theory has failed (experimentally, of course; it manages to get the graviton to work), loop quantum gravity is growing, and i have yet to hear of other notable progress in other quantum gravity theories.

    While I agree with you that it might be possible that it could change, do you think there are experimental possibilities to test any predictoins of such a theory?
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    Quote Originally Posted by Liongold

    What I am saying, however, is that it is possible to render gravity a quantised force, with a spin-2 particle called the graviton; however, actually calculating the interactions between any of them proves to be near impossible, primarily because gravitons interact gravitationally with each other. However, doing the above runs into infinities, which renders the quantum gravity model incosistent and non-calculable.

    I do not understand the meaning of this statement. I have no idea what it means to "render gravity a quantized force" and at the same time admit that no calculations regarding gravity are possible with such a theory. Either one has a mathematically consistent theory that produces testable predictions or one does not have a theory at all. In this case one does not.


    Further, I am sure you are quite aware of the need for gravity waves predicted by general relativity, which must be described by quantum mechanics. There are currently some experiments ongoing designed to try and observe the graviton; they are highly sensitive and thus far have not succeeded.
    I am aware of experiments to detect gravity waves that go as far back as work in the 1960s to Weber at the University of Maryland (there may be earlier experiments that I do no know about). But those experiments are driven by general relativity and have nothing to do with quantum gravity or gravitons.

    In fact, the only place where general relativity and quantum mechanics run into problems is their numerous encounters with infinity. Infinity becomes commonplace within balck holes, and is found in quantum interactions between particles.
    This is true, but one ought to be careful with "infinities". General relativity runs into an issue with predictions of infinities in the curvature tensor the result of which is a set of singular points as is the case with black holes and the big bang. Quantum field theories run into trouble via because the perturbative calculation starts with a divergent series and then makes ad hoc approximations to eliminate 'infinities". That procedure is acceptable to the physicists and results in astonishingly accurate predictions, but the mathematical basis has yet to be established.

    There is a theorem of 'tHooft, for which I do not have a ready reference and the basis of which I do not understand, that says that a unified theory of gravity and the quantum field theories of the Standard Model will eliminate the problem of the infinities. So perhaps there is a deep association between quantum mechanical infinities and gravity, but if so no one yet knows how to exploit that relationship. Perhaps string theory will succeed, but thus far the promise of string theories and their successors (e.g. M Theory) have far exceeded the realizations.

    General relativity is a completely deterministic theory and quantum theories are stochastic. What is needed is a theory that incorporates both quantum field theories and gravitation and that is closely approximated by general relativity in the limit where quantum effects are negligible.


    In which case it should indeed have some experimentally falsifiable predictions. However, gravity being weak at the particular level, I find it very unlikely. Likewise, quantum mechanics can best be used to describe gravitons, which have yet to be discovered. I find it hard to think of an unique prediction of such a theory, given as stupendously little is inconsistent experiment. I personally believe that the best possible prediction would be if it somehow managed to explain the dark matter question. Would you agree?
    The dark matter question has very little to do with general relativity, except insofar as it is clear that there are gravitational effects that are inconsistent with the observed amount of matter in regions of galaxies. The problem arises as well if one models gravity using Newtonian laws. Perhaps there is an explanation in terms of particle physics, hence quantum field theory, if, for instance, suspersymmetric particles provide an explanation for the unobserved matter -- but that is very speculative at best.

    I think it more likely that the solution to questions of quantum mechanics and general relativity will come as a result of research to find a mathematically consistent theory that incorporates both general relativity and quantum field theory in the appropriate limits (the correspondence principle) and that is consistent with what we know of black holes and cosmology. That is basically the approach being taken by those pursuing string theories and loop quantum gravity. But neither approach has succeeded. Truly new mathematics is needed and it appears to be very difficult to develop that mathematics.


    Let us see now: string theory has failed (experimentally, of course; it manages to get the graviton to work), loop quantum gravity is growing, and i have yet to hear of other notable progress in other quantum gravity theories.
    As far as I can tell string theory is not yet even well-defined. Prior to 1995 there were 5 competing string theories and no way to select among them or to test them. Then Witten gave a talk and published a paper suggesting that the 5 theories were really just different presentations of a single theory, and M Theory was born. But while Witten provided a plausiblity argument for M Theory, the "dictionary" proving the equivalence of the the 5 string theories has not yet, so far as I know, been produced, so Wittens suggestion remains an unproven conjecture. Maldecena's 1997 conjecture of the AdS/CFT correspondence likewise is widely believed to be true, but also remains a conjecture.

    There is a quantum field theory that can address supersymmetry at least well enough so that if supesymmetric particles are created in the LHC they can be recognized. Detection of supersymmetric particles would help the cause of string theory, since string theories require supersymmetry. Supersymmetry, however does not require string theory so while detection would help string theory it would not be conclusive.

    So far as I can tell there is a lot of hype in the popular press regarding quantum gravity, gravitons, string theory, the holographic principle, etc. but not yet any hard physics. That is not to say that there is not good research going on, but it is to say that what is being bandied about is not yet real physics. NOBODY knows whether there are gravitons or not and most certainly nobody has a viable theory of quantum gravity, not a mathematically consistent theory and not an experimentally testable theory.
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    This is slightly off-topic, but I've been wondering about something for a while. I've heard two things on TV that sounds interesting when put together, but since I know very little about them, I can't actually say that they make sense.

    First, I've heard that naively putting the equations from GR and QM together causes the time variable to cancel out.

    Second, I've heard just enough about the holographic principle to be dangerous. There's some kind of correspondence between something on an n dimensional surface and particles within the n+1 dimensional space within that surface?

    Knowing only that little bit, it sounds like you could apply the holographic principle to recover time in the equations, but like I said, I don't even know if that actually makes sense.
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    I do not understand the meaning of this statement. I have no idea what it means to "render gravity a quantized force" and at the same time admit that no calculations regarding gravity are possible with such a theory. Either one has a mathematically consistent theory that produces testable predictions or one does not have a theory at all. In this case one does not.
    By quantisation, I mean transforming gravity into a force carried by particles, in much the same way that electromagnetism was quantised to be carried by photons.

    The calculations, as I have explained, delved into enormous and complex infinitinies because of the graivtons' tendency to self-interact.

    I am aware of experiments to detect gravity waves that go as far back as work in the 1960s to Weber at the University of Maryland (there may be earlier experiments that I do no know about). But those experiments are driven by general relativity and have nothing to do with quantum gravity or gravitons.
    I do not believe I mentioned quantum mechanics in context with the graviton. They are, as you say, driven by general relativity, correct. However, Einstein himself stated that it would be necessary to use quantum mechanics to describe the gravity wave, because of the wave-particle duality. It is in that context that I mention quantum mechanics with relation to the graviton.

    There is a theorem of 'tHooft, for which I do not have a ready reference and the basis of which I do not understand, that says that a unified theory of gravity and the quantum field theories of the Standard Model will eliminate the problem of the infinities. So perhaps there is a deep association between quantum mechanical infinities and gravity, but if so no one yet knows how to exploit that relationship. Perhaps string theory will succeed, but thus far the promise of string theories and their successors (e.g. M Theory) have far exceeded the realizations.
    I think you're referring to another proof, which does not actually say that unifying gravity and quantum mechanics will eliminate the infinities, but instead says that doing so itself is impossible. I remember this because string theory had to be developed using Grassmann numbers, where addition itself is non-commutative, which managed to exploit a loophole in the proof. I believe I read this either in Michio Kaku's Parallel Worlds or in Stephen Hawking's more recent The Universe in a Nut Shell or possibly even in Lawrence Krauss' Fear of Physics. The exact location eludes me, but I will check and find out.

    What you are expressing is actually an opinion; there is no actual grounding for that basis. A quantum theory of gravity may still delve into infinities, and no proof exists that does get us to realise that solving quantum mechanical infinities will enable us to eliminate gravitational infinities.

    And string theory has quite spectacularly failed, thankfully. at least now we can develop something else other than a theory that lacks the power of quantum mechanics or relativity.

    The dark matter question has very little to do with general relativity, except insofar as it is clear that there are gravitational effects that are inconsistent with the observed amount of matter in regions of galaxies. The problem arises as well if one models gravity using Newtonian laws. Perhaps there is an explanation in terms of particle physics, hence quantum field theory, if, for instance, suspersymmetric particles provide an explanation for the unobserved matter -- but that is very speculative at best.
    I quite realise that; I was saying that the idea of dark matter was proposed as an alternative to trying to extend gravity. General relativity accounts for 98% of the observation, but predicts a smaller value for the graviaitonal force, which is not in accordance with experiments. Newtonian dynamics has a smaller percentage of agreement with experiment. Modified Newtonian Dynamics is alright, but it feels quite wrong to me.

    Perhaps there is an explanation in terms of particle physics, hence quantum field theory, if, for instance, suspersymmetric particles provide an explanation for the unobserved matter -- but that is very speculative at best.
    Superstring theory attempted to provide several candidates for the dark matter, the axion being one of them. However, even that could not completely explain the the graviational inconsistency. Besides, supersymmetry as a theory itself was unable to save itself; SU(5), for example, predicted proton decay, which is as yet unobserved, and no evidence of supersymmetric particles have yet been found. I would say supersymmetry is incorrect, because it cannot determine by itself the rate of proton decay or the energies required for supersymmetric particles to appear.

    I think it more likely that the solution to questions of quantum mechanics and general relativity will come as a result of research to find a mathematically consistent theory that incorporates both general relativity and quantum field theory in the appropriate limits (the correspondence principle) and that is consistent with what we know of black holes and cosmology. That is basically the approach being taken by those pursuing string theories and loop quantum gravity. But neither approach has succeeded. Truly new mathematics is needed and it appears to be very difficult to develop that mathematics.
    I have wondered about this myself, and I have come to the conclusion that infinity itself has yet been explored fully. What do we know about infinity? Nothing, only that some infinities are bigger than others and that it has yet to defined. If infinity itself can be understood as imaginary and irrational numbers have, I see no reason why we cannot proceed ahead with full steam.

    As far as I can tell string theory is not yet even well-defined. Prior to 1995 there were 5 competing string theories and no way to select among them or to test them. Then Witten gave a talk and published a paper suggesting that the 5 theories were really just different presentations of a single theory, and M Theory was born. But while Witten provided a plausiblity argument for M Theory, the "dictionary" proving the equivalence of the the 5 string theories has not yet, so far as I know, been produced, so Wittens suggestion remains an unproven conjecture. Maldecena's 1997 conjecture of the AdS/CFT correspondence likewise is widely believed to be true, but also remains a conjecture.
    Quite so. The basic principles themselves remain elusive, and the theory simply exchanges unknown constants for more unknown constants that deal with the geometry of the hidden dimensions. Further, string theory has yet to be proven finite at all levels of approximation; it has only been shown finite to the second level of approximation. Mandelstam's original paper was believed to show its finiteness; however, this was and is a common misconception.

    Even allowing for all that, the original theory predicted a negative or zero cosmological constant, and had to be drastically altered to allow for a positive cosmological constant.

    So far as I can tell there is a lot of hype in the popular press regarding quantum gravity, gravitons, string theory, the holographic principle, etc. but not yet any hard physics. That is not to say that there is not good research going on, but it is to say that what is being bandied about is not yet real physics. NOBODY knows whether there are gravitons or not and most certainly nobody has a viable theory of quantum gravity, not a mathematically consistent theory and not an experimentally testable theory.
    Good mathematics is being done, not physics. I must diagree with you there. I have always considered making a theory based on mathematics as suspect; it's like saying that the universe is governed by equations, when's its the other way around.
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