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Thread: Is gravity a force or is it an effect?

  1. #1 Is gravity a force or is it an effect? 
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    I cant seem to find any type of direct answer as to if gravity is a real, physical force or if it is just a effect. It kinda makes you realize that our species is very primitive despite all our current advancements in science, i mean, you would think that we would know what gravity is by now...
    The more I read about gravity, the more i see how little we know about it.

    what do you guys think gravity is? do you think gravity actually exist as a physical force that acts on matter?
    Or could gravity just be some sort of effect we experience due to huge bodies of masses bending the space around them?

    it may be bit hard to understand exactly what im asking.
    so if gravity is a real, physical force, what do you guys think generates this force in the first place? is it some sort of magnetic like force that physically pulls matter together? kinda like how magnets exert forces upon each other?
    Or maybe gravity only SEEMS to be a active, physical force. could the force of gravity that we experience simply only be a effect caused by the bent space around large masses?
    Or maybe we only experience this force of gravity due to our perspective being in 3 dimensions, maybe there is a bigger picture that we are failing to understand or comprehend, its possible that there are things in play right now, all around us, but we may not be capable of comprehending these concepts at work, so maybe gravity is just a effect from something we cant comprehend so we perceive gravity as a physical force instead of seeing gravity for what it truly is?

    what do you guys think gravity is and how does it work?


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    Quote Originally Posted by xxsolarplexusxx View Post
    what do you guys think gravity is? do you think gravity actually exist as a physical force that acts on matter?
    Or could gravity just be some sort of effect we experience due to huge bodies of masses bending the space around them?
    It is both.


    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by xxsolarplexusxx View Post
    what do you guys think gravity is? do you think gravity actually exist as a physical force that acts on matter?
    Or could gravity just be some sort of effect we experience due to huge bodies of masses bending the space around them?
    It is both.
    its both? could you explain exactly how gravity is both? is there any solid proof that this is true?
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    Quote Originally Posted by xxsolarplexusxx View Post
    its both? could you explain exactly how gravity is both? is there any solid proof that this is true?
    It depends what model you use. In Newtonian gravity it is a force. In GR it is a pseudo-force that we perceive because of the curved geometry of space time.

    Science doesn't really deal in "proof" or "truth"; it is solely concerned with developing models to describe what we observe and then testing those models to see if they are accurate and useful. It doesn't say anything about what things "really" are. Nothing can tell us that.
    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
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    my view is that gravity is actually a force caused due to the pulling force earth has on us.This pulling force clearly must depend on the mass of the planet ,thats what causes the variation in the gravitational pull on each planet earth gravitational pull is 9.81 and jupiter is 24.79 so clearly gravitational pull must depend on the mass and density of the planet.Since in space there is no mass or density this is why gravity does not act out of space.This is just my point of view but i am no expert please correct me if i am wrong.
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    Quote Originally Posted by Rakila View Post
    Since in space there is no mass or density this is why gravity does not act out of space.
    Actually, gravity does act in space. That is what keep us in orbit around the Sun, for example (or the Moon orbiting the Earth).
    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by xxsolarplexusxx View Post
    its both? could you explain exactly how gravity is both? is there any solid proof that this is true?
    It depends what model you use. In Newtonian gravity it is a force. In GR it is a pseudo-force that we perceive because of the curved geometry of space time.

    Science doesn't really deal in "proof" or "truth"; it is solely concerned with developing models to describe what we observe and then testing those models to see if they are accurate and useful. It doesn't say anything about what things "really" are. Nothing can tell us that.
    if we look at the forces in nature that are described only as forces (the weak ,the strong and the electro-magnetic ,if that is correct or complete) what is it about them that allows us to label them as forces? Is it simply that an acceleration is observed(and predicted) or is there more to the effect than that?

    Is it that there is a particle that mediates the force (photon for EM, I think and other particles for Strong and Weak) ?

    Suppose the graviton is finally discovered,will that change the assessment of whether gravity is a "force" like the other forces?

    Or can the graviton mediate a forceful reaction and gravity still remain a geometric description of the motion of objects with respect to each other?
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by xxsolarplexusxx View Post
    its both? could you explain exactly how gravity is both? is there any solid proof that this is true?
    It depends what model you use. In Newtonian gravity it is a force. In GR it is a pseudo-force that we perceive because of the curved geometry of space time.

    Science doesn't really deal in "proof" or "truth"; it is solely concerned with developing models to describe what we observe and then testing those models to see if they are accurate and useful. It doesn't say anything about what things "really" are. Nothing can tell us that.
    i see, so its not really both since none of us can really say for sure what it is, so what do you believe it is? what scientist do you agree with? or do you have your own personal theory for gravity as well?
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    Quote Originally Posted by xxsolarplexusxx View Post
    i see, so its not really both since none of us can really say for sure what it is, so what do you believe it is? what scientist do you agree with? or do you have your own personal theory for gravity as well?
    It is not really a matter of which you believe, but which is most useful. So if you want to calculate the trajectory of a tennis ball you can use Newtonian physics and treat it as a (constant) force. If you want to study what happens around black hole, then you would need to use GR to model the curvature of space-time.
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    Quote Originally Posted by Rakila View Post
    my view is that gravity is actually a force caused due to the pulling force earth has on us.This pulling force clearly must depend on the mass of the planet ,thats what causes the variation in the gravitational pull on each planet earth gravitational pull is 9.81 and jupiter is 24.79 so clearly gravitational pull must depend on the mass and density of the planet.Since in space there is no mass or density this is why gravity does not act out of space.This is just my point of view but i am no expert please correct me if i am wrong.

    your statements are correct, how ever, there could still be other reasons why gravity acts the way it does, indeed, gravity does seem to more/less intense depending on the objects mass, but that does not clearly say its because of a physical force, there is many other possibilities could be the cause of such effects, for example, maybe how much a objects mass bends space determines the force of the gravity we experience. im not saying that i believe this or that this is true, im just using that as a example to demonstrate what I mean when i say that there may other possibilities. Im not sure why, I feel that we all are misunderstanding gravity and that we are all missing the bigger picture required to truly understand what gravity is and how it works.
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by xxsolarplexusxx View Post
    i see, so its not really both since none of us can really say for sure what it is, so what do you believe it is? what scientist do you agree with? or do you have your own personal theory for gravity as well?
    It is not really a matter of which you believe, but which is most useful. So if you want to calculate the trajectory of a tennis ball you can use Newtonian physics and treat it as a (constant) force. If you want to study what happens around black hole, then you would need to use GR to model the curvature of space-time.
    it is about what you believe lol, i was asking about your beliefs and theories, I could care less about which theory to use for calculating anything....the only things i ever need to calculate can be achieved by a simple calculator on my phone lol. but I do completely get what your saying and you are correct. im just saying my questions were about your personal theories n such @.@
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    I don't have "personal theories". There are too many morons polluting science forums with "personal theories" already.
    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
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    Gravity, including artificial gravity, is the time-dilation that exists between locations that are at rest relative to each other and dependent on the separation between the locations. Gravity doesn't merely cause the time-dilation... it is the time-dilation. The time-dilation indicates that the frame of reference is accelerating, in which the observer is experiencing gravity which may be real or artificial.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Quote Originally Posted by KJW View Post
    Gravity, including artificial gravity, is the time-dilation that exists between locations that are at rest relative to each other and dependent on the separation between the locations. Gravity doesn't merely cause the time-dilation... it is the time-dilation. The time-dilation indicates that the frame of reference is accelerating, in which the observer is experiencing gravity which may be real or artificial.
    That is the first time I have come across that description of gravity. Why do "locations that are at rest relative to each other" experience time dilation?

    I thought motion was required for time-dilation to arise.
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    Quote Originally Posted by xxsolarplexusxx View Post
    how much a objects mass bends space determines the force of the gravity we experience.
    It is a common misconception that the gravity we normally experience is caused by the curvature of space. I blame the rubber sheet analogy for promoting this error, and even if nothing else, this is one reason why the rubber sheet analogy is wrong even as an analogy. As mentioned in my previous post, the gravity we normally experience is about what happens with time, and is not about space. Even if space were perfectly flat, variations in time dilation with respect to location would produce the gravity that we experience. I'm not saying that the space around the earth is flat, only that the curvature of the space around the earth is irrelevant to the gravity that we experience.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Quote Originally Posted by geordief View Post
    That is the first time I have come across that description of gravity. Why do "locations that are at rest relative to each other" experience time dilation?

    I thought motion was required for time-dilation to arise.
    You've not heard of "gravitational time dilation" (or "gravitational redshift")? I didn't want to use the term "gravitational time dilation" say what gravity is because that would've been circular.

    The Pound–Rebka experiment measured the time dilation that occurs between two floors of a building.

    However, it is important to note that acceleration produces the same distance-dependent time dilation as does true gravity, as required by the equivalence principle.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Quote Originally Posted by KJW View Post

    You've not heard of "gravitational time dilation" (or "gravitational redshift")? I didn't want to use the term "gravitational time dilation" say what gravity is because that would've been circular.

    The Pound–Rebka experiment measured the time dilation that occurs between two floors of a building.

    However, it is important to note that acceleration produces the same distance-dependent time dilation as does true gravity, as required by the equivalence principle.
    Yes,of course.That was extremely silly of me.(some kind of a hole in my brain)

    I will reread your post and perhaps have a more sensible question in due course.
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    It is where you wrote "Gravity doesn't merely cause the time-dilation... it is the time-dilation." that I was surprised,KJW.

    I am prepared to accept it to be true (it seems that it might make things simpler rather than more complicated) but since I have not seen it spelled out quite like that before, can anything more be said about it or is it just one of those understandings that come when you have more or less mastered the subject in the round?
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  20. #19  
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    Quote Originally Posted by geordief View Post
    It is where you wrote "Gravity doesn't merely cause the time-dilation... it is the time-dilation." that I was surprised,KJW.

    I am prepared to accept it to be true (it seems that it might make things simpler rather than more complicated) but since I have not seen it spelled out quite like that before, can anything more be said about it or is it just one of those understandings that come when you have more or less mastered the subject in the round?
    The answer to your question is in the sentence that follows the statement that you quoted:

    Quote Originally Posted by KJW View Post
    The time-dilation indicates that the frame of reference is accelerating, in which the observer is experiencing gravity which may be real or artificial.
    Descriptively speaking, gravity is the phenomenon whereby an object that is released falls with an apparent acceleration that is independent of the object. It is the result of the observer accelerating upward. And it's always upward because that's how "upward" is defined and perceived. When the object is released, it continues inertially while the observer accelerates away from the object, thus appearing to the observer as if the object is falling. This is true for both real and artificial gravity. However, for real gravity, the above doesn't make sense unless it is appreciated that the spacetime is curved. Thus, two observers at opposite locations on earth can accelerate in opposite directions without actually moving away from each other.

    The curvature of a line cannot be determined from only a description of the line itself. This is because a coordinate transformation changes the description of the line without changing the line itself. To determine the curvature of a line, one also needs the connection that describes the underlying space and coordinate system. Knowing the metric of the space and coordinate system also provides the connection, and thus the time dilation provides information that determines the acceleration of the observer. In other words, the question of whether it is the falling object that is accelerating downwards or the observer that is accelerating upward is unequivocally answered by the time dilation that provides the connection of the observer's frame of reference.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by xxsolarplexusxx View Post
    i see, so its not really both since none of us can really say for sure what it is, so what do you believe it is? what scientist do you agree with? or do you have your own personal theory for gravity as well?
    It is not really a matter of which you believe, but which is most useful. So if you want to calculate the trajectory of a tennis ball you can use Newtonian physics and treat it as a (constant) force. If you want to study what happens around black hole, then you would need to use GR to model the curvature of space-time.
    Gravity is relative according to the general theory of relativity. So is redshift, according to the position of the observer. Since so many facets appear to be relative, so is 'usefulness' relative.
    Whether the theory is relevant to the situation you wish to explore, is a matter of opinion.
    So it seems, in my opinion, probable that what people believe to be true becomes a foundation for what is discovered, and since scientists generally believe in the existence of the graviton, it is likely therefore that evidence for the graviton will be forthcoming.
    If scientists don't believe something to be true, the reverse generally occurs, and absence of evidence for the Something becomes an argument in defence of its non-existence.
    This is a state of affairs which hopefully in time will be redressed by open-minded scientists not being afraid of their brains falling out.
    Due to the absence of gravity as a force in the thinking equation.
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    Quote Originally Posted by Quantumologist View Post
    Gravity is relative according to the general theory of relativity. So is redshift, according to the position of the observer. Since so many facets appear to be relative, so is 'usefulness' relative.
    I agree, usefulness is relative. For many purposes Newtonian gravity is useful but for some cases, it is useless and GR must be used.

    Whether the theory is relevant to the situation you wish to explore, is a matter of opinion.
    Not just opinion. It depends more on whether it is accurate enough and simple enough (you could always use GR as the most accurate description, but it is unnecessarily complex in many cases).

    So it seems, in my opinion, probable that what people believe to be true becomes a foundation for what is discovered, and since scientists generally believe in the existence of the graviton, it is likely therefore that evidence for the graviton will be forthcoming.
    Er, no. There are many things that were previously believed to be true but found not to be (and, of course, many that were confirmed). Whether the graviton is discovered or not depends on whether it is an accurate model of how things work, not whether people believe in it. And the problem at the moment is that we don't have a model of the graviton to test.

    If scientists don't believe something to be true, the reverse generally occurs, and absence of evidence for the Something becomes an argument in defence of its non-existence.
    At one point, no one believed that the universe was expanding, or that space and time were relative, or that atoms had component parts, or that the contents moved, or that expansion was accelerating, or ...

    Finding the unexpected is one of the ways that science progresses.
    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
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    Quote Originally Posted by Quantumologist View Post
    Whether the theory is relevant to the situation you wish to explore, is a matter of opinion.
    What?

    So it seems, in my opinion, probable that what people believe to be true becomes a foundation for what is discovered, and since scientists generally believe in the existence of the graviton, it is likely therefore that evidence for the graviton will be forthcoming.
    If scientists don't believe something to be true, the reverse generally occurs, and absence of evidence for the Something becomes an argument in defence of its non-existence.
    I do hope you don't mean this the way it comes across: i.e. that belief itself itself somehow a "cause" for the things discovered. Perhaps you could phrase it better (i.e. less woo-oriented)?
    Oh - "scientists generally believe in the existence of the graviton": citation required.
    Gravitons are predicted in string theory (which is, itself, somewhat speculative) and [m]ost theories containing gravitons suffer from severe problems - not an indication that "belief" is involved nor does it suggest the word "generally".
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    How very beautiful, Strange, to see you embracing my case. Que sera, sera. "Finding the unexpected is one of the ways that science progresses."
    Where the unexpected is to be found, therefore, is also a matter of relativity, in where and when the observer finds itself in the right place at the right time.

    No, Chewie, I don't necessarily believe that belief is in itself a cause for a discovery, although I did once read someone suggesting that the particle zoo was populated by an obliging deity dishing out bits of the universe to match the equations.

    This is a nice take on the situation of Standard Models http://www.abc.net.au/news/science/2...lained/7670338 and I do like the sound of SuperModels, don't you?

    Don't ask me to provide citations on the current conversational position of the graviton, please. You know where that is as well as I do.
    Last edited by Quantumologist; October 22nd, 2017 at 05:34 PM. Reason: New post arrived
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    Quote Originally Posted by Quantumologist View Post

    [snip]
    If scientists don't believe something to be true, the reverse generally occurs, and absence of evidence for the Something becomes an argument in defence of its non-existence.
    This is a state of affairs which hopefully in time will be redressed by open-minded scientists not being afraid of their brains falling out.
    [snip]
    Absence of evidence can be, contrary to the cliché, evidence of absence, provided a very diligent search has been made. Where is the magnetic monopole, for example? However it is not conclusive proof of absence of course. And science never closes the door.

    As I mentioned before, in science all "truth" is merely provisional.
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    Quote Originally Posted by Quantumologist View Post
    How very beautiful to see you embracing my case. Que sera, sera. Finding the unexpected is one of the ways that science progresses.
    Quite. So your previous claim that people only find what they believe in (and can't find what hey don't believe in) was just wrong.

    Where the unexpected is to be found, therefore, is also a matter of relativity, in where and when the observer finds itself in the right place at the right time.
    Huh!? Want to try again in English?
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    Quote Originally Posted by exchemist View Post
    Absence of evidence can be, contrary to the cliché, evidence of absence, provided a very diligent search has been made.
    Indeed. I have been searching for the unicorns in my garden every day for 10 years. It is quite a small garden and I haven't seen one, haven't heard one, and have found no hoof prints or droppings. I think this absence of evidence can be taken as pretty strong evidence for their absence. (But I'm still not sure if they were stolen or ran away.)
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    Quote Originally Posted by Quantumologist View Post
    No, Chewie, I don't necessarily believe that belief is in itself a cause for a discovery
    Ah, so you actually meant... what, exactly?

    You know where that is as well as I do.
    Better than you, apparently, since you've made a statement that looks to be faulty on a number of levels.

    Don't ask me to provide citations on the current conversational position of the graviton, please.
    If you can't back it up then withdraw it.
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    Quote Originally Posted by Strange View Post
    Quite. So your previous claim that people only find what they believe in (and can't find what hey don't believe in) was just wrong.
    Rabi's "Who ordered that?" springs to mind...
    "[Dywyddyr] makes a grumpy bastard like me seem like a happy go lucky scamp" - PhDemon
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    Indeed. Particle physics until the mid 70s was a continual journey of discovering new and unexpected particles. Since the discovery of quarks, it has all got relatively boring. Where is the new physics!
    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
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    Quote Originally Posted by Strange View Post
    I don't have "personal theories". There are too many morons polluting science forums with "personal theories" already.

    maybe thats true, but i would not consider talking about personal theories as polluting science forums, I believe its actually healthy for people to use their own thought processes to formulate new ideas and theories based on their own personal experience and information rather then simply memorize and then regurgitate knowledge they studied up on, im not saying everyone regurgitates memorized knowledge without the slightest true understanding of the given subject, however, their is indeed a large number of people who do just that and then get rewarded with a degree.....if no one ever puts in effort to develope new ideas and theories then our species would not be where we are at today.
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    Quote Originally Posted by KJW View Post
    Gravity, including artificial gravity, is the time-dilation that exists between locations that are at rest relative to each other and dependent on the separation between the locations. Gravity doesn't merely cause the time-dilation... it is the time-dilation. The time-dilation indicates that the frame of reference is accelerating, in which the observer is experiencing gravity which may be real or artificial.

    Damn son, my mind been blown! I always assumed time dilation was the direct effect of mass warping and bending the fabric of space-time, its a trip to think of gravity actually being time dilation, I dont fully understand exactly how this would work but I indeed see how such a thing could be possible, has this theory ever been tested and verified?
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    Quote Originally Posted by KJW View Post
    Quote Originally Posted by xxsolarplexusxx View Post
    how much a objects mass bends space determines the force of the gravity we experience.
    It is a common misconception that the gravity we normally experience is caused by the curvature of space. I blame the rubber sheet analogy for promoting this error, and even if nothing else, this is one reason why the rubber sheet analogy is wrong even as an analogy. As mentioned in my previous post, the gravity we normally experience is about what happens with time, and is not about space. Even if space were perfectly flat, variations in time dilation with respect to location would produce the gravity that we experience. I'm not saying that the space around the earth is flat, only that the curvature of the space around the earth is irrelevant to the gravity that we experience.

    yes, I know that the statement you cropped out of my previous post is not correct, this is because it wasnt meant to be correct, you may have took what i said out of context a little bit, i said that i was using that as a example to better clarify my meaning of a earlier statement I made, no biggie though.
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    Quote Originally Posted by KJW View Post


    Descriptively speaking, gravity is the phenomenon whereby an object that is released falls with an apparent acceleration that is independent of the object. It is the result of the observer accelerating upward. And it's always upward because that's how "upward" is defined and perceived. When the object is released, it continues inertially while the observer accelerates away from the object, thus appearing to the observer as if the object is falling. This is true for both real and artificial gravity. However, for real gravity, the above doesn't make sense unless it is appreciated that the spacetime is curved. Thus, two observers at opposite locations on earth can accelerate in opposite directions without actually moving away from each other.

    The curvature of a line cannot be determined from only a description of the line itself. This is because a coordinate transformation changes the description of the line without changing the line itself. To determine the curvature of a line, one also needs the connection that describes the underlying space and coordinate system. Knowing the metric of the space and coordinate system also provides the connection, and thus the time dilation provides information that determines the acceleration of the observer. In other words, the question of whether it is the falling object that is accelerating downwards or the observer that is accelerating upward is unequivocally answered by the time dilation that provides the connection of the observer's frame of reference.
    I feel that much of the meat in your response lies in the two words that you bolded.

    Do you think that you could perhaps provide a short definition of the "connection" and the "metric" -at least insofar as they apply in the context you gave them?

    I have come across these terms before and seem to dimly appreciate how fundamental they probably are to GR but I have no real familiarity with how they are used or what they really mean.

    btw you are talking of intrinsic curvature of the line, I suppose?
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    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by xxsolarplexusxx View Post
    maybe thats true, but i would not consider talking about personal theories as polluting science forums, I believe its actually healthy for people to use their own thought processes to formulate new ideas and theories based on their own personal experience and information
    However, making up "theories" based on personal experience and some half understood pop-sci articles, is not productive. And that is what 99% of people who post their ideas on science forums do. If someone wants to make up new theories then they need to first spend the years necessary to study the subject. There are no shortcuts (especially in modern physics).

    if no one ever puts in effort to develope new ideas and theories then our species would not be where we are at today.
    So obviously the people who do successfully come up with new theories are those with the knowledge, understanding, training and expertise to do that. You won't find that on science forums.
    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
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    Quote Originally Posted by xxsolarplexusxx View Post
    Quote Originally Posted by Strange View Post
    I don't have "personal theories". There are too many morons polluting science forums with "personal theories" already.

    maybe thats true, but i would not consider talking about personal theories as polluting science forums, I believe its actually healthy for people to use their own thought processes to formulate new ideas and theories based on their own personal experience and information rather then simply memorize and then regurgitate knowledge they studied up on, im not saying everyone regurgitates memorized knowledge without the slightest true understanding of the given subject, however, their is indeed a large number of people who do just that and then get rewarded with a degree.....if no one ever puts in effort to develope new ideas and theories then our species would not be where we are at today.
    Just to add emphasis to Strange's remarks, I think the key distinction between personal theories with value and those (most of those we see in a place like this) without value is whether or not the proponent has bothered to understand the current theory before coming up with his own. This is crucial because any new theory has to be able to account for what the current theory already explains and then manage to improve on it in some way.

    If you look at the history of science, it is hard to find examples of people who made a contribution without understanding the state of the art first.
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    Quote Originally Posted by geordief View Post
    Do you think that you could perhaps provide a short definition of the "connection" and the "metric"
    I hope I am not being patronising if I say I suspect you want an intuitive definition, and would not welcome the full mathematics.

    So. Given a space (or spacetime), and a single point therein, relativistic theories insist that one is free to use any coordinates one chooses provided only that one can specify a coordinate transformation formula that leaves everything invariant.

    Suppose that we can do this for any single spacetime point. Problems arise, however, when you try to do a coordinate transformation from one spacetime point to another such point. In particular, for a non-scalar object (vector, tensor) defined at one point, there is no coordinate transformation that leaves it invariant at another.

    The resolution of this dilemma is to introduce a gadget called a connection - basically it allows you to do calculus by treating different points as the same.

    The metric is easier to describe - it is a means of measuring things. Basically the length of vectors and the angle between them.

    Relativistic theories state that vector length (spacetime interval) depend upon the choice of coordinates, and since different coordinates very likely apply at different spacetime points, one talks (or should talk) about the metric field.

    This field is the principal object in the General Theory.
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    Quote Originally Posted by Guitarist View Post
    Quote Originally Posted by geordief View Post
    Do you think that you could perhaps provide a short definition of the "connection" and the "metric"
    I hope I am not being patronising if I say I suspect you want an intuitive definition, and would not welcome the full mathematics.

    So. Given a space (or spacetime), and a single point therein, relativistic theories insist that one is free to use any coordinates one chooses provided only that one can specify a coordinate transformation formula that leaves everything invariant.

    Suppose that we can do this for any single spacetime point. Problems arise, however, when you try to do a coordinate transformation from one spacetime point to another such point. In particular, for a non-scalar object (vector, tensor) defined at one point, there is no coordinate transformation that leaves it invariant at another.

    The resolution of this dilemma is to introduce a gadget called a connection - basically it allows you to do calculus by treating different points as the same.

    The metric is easier to describe - it is a means of measuring things. Basically the length of vectors and the angle between them.

    Relativistic theories state that vector length (spacetime interval) depend upon the choice of coordinates, and since different coordinates very likely apply at different spacetime points, one talks (or should talk) about the metric field.

    This field is the principal object in the General Theory.
    Thanks,that's lovely. Perhaps it will mean something more substantial to me at some stage down the curved line
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    Quote Originally Posted by xxsolarplexusxx View Post
    Quote Originally Posted by KJW View Post
    Gravity, including artificial gravity, is the time-dilation that exists between locations that are at rest relative to each other and dependent on the separation between the locations. Gravity doesn't merely cause the time-dilation... it is the time-dilation. The time-dilation indicates that the frame of reference is accelerating, in which the observer is experiencing gravity which may be real or artificial.
    Damn son, my mind been blown! I always assumed time dilation was the direct effect of mass warping and bending the fabric of space-time, its a trip to think of gravity actually being time dilation, I dont fully understand exactly how this would work but I indeed see how such a thing could be possible, has this theory ever been tested and verified?
    General relativity has been tested in many ways.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Quote Originally Posted by xxsolarplexusxx View Post
    Quote Originally Posted by KJW View Post
    Quote Originally Posted by xxsolarplexusxx View Post
    how much a objects mass bends space determines the force of the gravity we experience.
    It is a common misconception that the gravity we normally experience is caused by the curvature of space. I blame the rubber sheet analogy for promoting this error, and even if nothing else, this is one reason why the rubber sheet analogy is wrong even as an analogy. As mentioned in my previous post, the gravity we normally experience is about what happens with time, and is not about space. Even if space were perfectly flat, variations in time dilation with respect to location would produce the gravity that we experience. I'm not saying that the space around the earth is flat, only that the curvature of the space around the earth is irrelevant to the gravity that we experience.
    yes, I know that the statement you cropped out of my previous post is not correct, this is because it wasnt meant to be correct, you may have took what i said out of context a little bit, i said that i was using that as a example to better clarify my meaning of a earlier statement I made, no biggie though.
    Actually, I took what you said out of context completely because I saw it as an opportunity to address what I see as a common misconception, regardless of your intentions for saying what you said.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Baryonic matter is formed from dark matter, set in motion. The increase in dynamic pressure results in a decrease of static pressure. As with a vacuum, gravity is when you are pushed to Baryonic matter by the greater pressure from behind. Another way to look at it. Gravity is caused by mass, mass is caused by motion. Gravity is therefore caused by motion...
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    However, making up "theories" based on personal experience and some half understood pop-sci articles, is not productive. And that is what 99% of people who post their ideas on science forums do. If someone wants to make up new theories then they need to first spend the years necessary to study the subject. There are no shortcuts (especially in modern physics).
    I’m not online much anymore, so sadly I’ve missed some very interesting discussions here. KJW has explained the science very nicely indeed.
    As for the other topic, just to add to what has already been said by Strange and others - another problem I very often see with people and their personal ideas is that they personally identify with those ideas, and attach themselves to them. What I mean by this is that, when someone disagrees with the idea, then this is being perceived as a personal attack ( often subconsciously ) by its proponent, resulting in defensiveness and “lashing out” at others. This is a huge problem, because through self-identification the ability to objectively and critically examine an idea is lost - essentially it becomes “it makes sense to me, so it must be right”.
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    Quote Originally Posted by Markus Hanke View Post
    However, making up "theories" based on personal experience and some half understood pop-sci articles, is not productive. And that is what 99% of people who post their ideas on science forums do. If someone wants to make up new theories then they need to first spend the years necessary to study the subject. There are no shortcuts (especially in modern physics).
    I’m not online much anymore, so sadly I’ve missed some very interesting discussions here. KJW has explained the science very nicely indeed.
    As for the other topic, just to add to what has already been said by Strange and others - another problem I very often see with people and their personal ideas is that they personally identify with those ideas, and attach themselves to them. What I mean by this is that, when someone disagrees with the idea, then this is being perceived as a personal attack ( often subconsciously ) by its proponent, resulting in defensiveness and “lashing out” at others. This is a huge problem, because through self-identification the ability to objectively and critically examine an idea is lost - essentially it becomes “it makes sense to me, so it must be right”.
    Hi
    yes ,identification with one's ideas does seem to be a problem.Does it result ,I wonder from a lack of other concerns that it would actually be beneficial to strongly identify with /ramble.

    As to this Geometry/Force question I have been wondering whether an analogy could be the way a leaf grows when it starts off life with a tiny blemish or damage.As it gets bigger these get magnified and show up as distortions in the original perfect form.

    Does/did expansion of the universe mean that the tiny original gravitational field grew in this way and so ,even though it may have "begun life" as some force (which we do not understand yet) it ,so to speak established itself everywhere in the universe and so can be treated in a geometric way?
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    https://en.wikipedia.org/wiki/Restoring_force

    Excerpt: When a pendulum is put in motion the place of equilibrium is at the bottom of the swing, the place where the pendulum rests. When the pendulum is at the top of its swing the force bringing the pendulum back down to this midpoint is gravity. As a result gravity can be seen as the restoring force in this case.

    Is calling gravity a force in this example an error? Does gravity behave like a Restoring Force?
    All that belongs to human understanding, in this deep ignorance and obscurity, is to be skeptical, or at least cautious; and not to admit of any hypothesis, whatsoever; much less, of any which is supported by no appearance of probability...Hume
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    Quote Originally Posted by zinjanthropos View Post
    https://en.wikipedia.org/wiki/Restoring_force

    Excerpt: When a pendulum is put in motion the place of equilibrium is at the bottom of the swing, the place where the pendulum rests. When the pendulum is at the top of its swing the force bringing the pendulum back down to this midpoint is gravity. As a result gravity can be seen as the restoring force in this case.

    Is calling gravity a force in this example an error? Does gravity behave like a Restoring Force?
    Outside of general relativity, everyone calls gravity a force. So one should not be surprised to find many instances of people, including physicists, calling gravity a force. But this is strictly speaking an error, though it may also be a "lie-to-children". But it should be understood that there are real forces involved, for example, when a weight is being supported, there is a real force the weight exerts on the support as well as the opposite real force the support exerts on the weight.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Have read that a graviton, if discovered, will be massless. I think the natural tendency for most people would be to think of it as having mass. If massless, is there a reason, something layperson might understand? Is it about transferring mass?
    All that belongs to human understanding, in this deep ignorance and obscurity, is to be skeptical, or at least cautious; and not to admit of any hypothesis, whatsoever; much less, of any which is supported by no appearance of probability...Hume
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    The fact that gravity "appears to travel at the speed of light" means the particle responsible must be massless. If it had mass gravity would be "slower".

    (Inverted commas for simplifications)
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    Quote Originally Posted by PhDemon View Post
    The fact that gravity "appears to travel at the speed of light" means the particle responsible must be massless. If it had mass gravity would be "slower".

    (Inverted commas for simplifications)
    Is there a sense in which the Gravity Field has immediate effect (being everywhere if that can be said meaningfully) although changes in it do propagate at the speed of light ?

    Otherwise can the Gravitational Field be understood as a monolithic entity or a some kind of shifting mosaic(all the pieces being very very small if only in the model)?

    So is the Gravity Field monolithic or completely"decentralized"?Both?
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    Seeing how the graviton is probably massless, could a photon emit a graviton or two?
    All that belongs to human understanding, in this deep ignorance and obscurity, is to be skeptical, or at least cautious; and not to admit of any hypothesis, whatsoever; much less, of any which is supported by no appearance of probability...Hume
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