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Thread: Understanding Gravity

  1. #1 Understanding Gravity 
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    (Pre-warning- I'm not a great communicator, and am not exactly smart. A lot of what I write might be wrong, and I do not claim anything here as right. Please correct me on anything i seem to be mis-interpreting or am expressing wrongly.)


    I've been doing a lot of thinking about gravity, it being the only of the 4 fundamental forces not fully understood. One theory says that space is curved. And theres the analogy of the spread out bedsheet, etc. I can understand this 2 dimentionally, but how would this work in 3 dimensions? Would space curve more easily if the universe was flat? This theory seems to imply that space has a texture.

    My illustration:

    (space) (space)
    ____________\................../__________________
    ..........................\ o(earth)/
    ............................\........../
    ..............................\....../
    ................................\O/
    ...............................(sun)

    (The .....'s are just to allow the illustration to take shape, they don't mean anything)

    Earth is resting on the edge of "space".

    Is this right?

    How do moons orbit planets then? Shouldnt the moons be orbiting the sun also? Am i missing something? Does three dimentional space allow space to warp in a different way from what im thinking?

    And the alternate theory, gravitons. If gravity is always attractive, how would gravitons work? (This kind of relates to the other force particles as well) I understand repulsion: a matter particle emits a force particle and recoils back, another matter particle aborbs the force particle and changes its velocity in the other direction. How would attraction work with force particles? I can't seem to wrap my mind around it.

    If the first theory is right, then would gravity still count as a fundemental force? Since it doesn't require force particles at all, shouldn't it be classified as something else?

    And lastly, is there any way that both theories are right?


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  3. #2  
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    it being the only of the 4 fundamental forces not fully understood.
    Actually, no. Gravity is fully understood, explained as it was in 1905 in general relativity. What we cannot do, however, is unify this theory with quantum mechanics, the other theory that has dominated science. That is where all our methods fail, as it leads to mathematical infinities that crop up.

    One theory says that space is curved.
    Just nitpicking here. It should be space and time, according to general relativity. Both these quantities curve together to form curved space-time, forcing objects travelling in a straight line to adopt a bent path.

    This theory seems to imply that space has a texture.
    Not necessarily. By space-time curvature, this does not mean literally curved; it is simply a good analogy for the mathematical version of what happens. Space and time, in the mathematics, are said to be curvbed; this does not apply physically.

    Space and time are said to curve because the mathematics treats them as such. In reality, however, you would be hard-pressed to say if space-time were actually curved just by looking.

    I can understand this 2 dimentionally, but how would this work in 3 dimensions?
    Think of a sphere. You have just imagined curved space-time in three dimensions.

    Earth is resting on the edge of "space".
    No. Think of Earth being inside a sphere. It will then have to follow the path of the sphere i.e. the curve of the sphere. Earth is in space and time; its motion is simply being affected because it measures space-time in such a way that it appears curved and follows a curved path.

    How do moons orbit planets then? Shouldnt the moons be orbiting the sun also? Am i missing something? Does three dimentional space allow space to warp in a different way from what im thinking?
    You forget that planets also curve space-time. In fact, anything with energy curves space-time. As a result, the moon is now following the curvature of space-time caused by the Earth, forcing it to orbit the Earth.

    And the alternate theory, gravitons.
    Quite correct. However, a collection of gravitons can be shown to be mathematically equivalent to curved space-time; see Wikipedia's article on it.

    If gravity is always attractive, how would gravitons work? (This kind of relates to the other force particles as well)
    That is why gravitons are troublesome creatures. They attract everything, even other gravitons. When it does so, however, we have an infinity of gravitons appearing, because the original gravitons exchange gracvitons, which in turn exchange gravitons, and so on.

    I understand repulsion: a matter particle emits a force particle and recoils back, another matter particle aborbs the force particle and changes its velocity in the other direction.
    Well, the answer to your qualms about attraction are hidden here. The second matter particle simply changes its velocity in the direction of the first matter particle. Simultaneously, it also emits a particler to the first matter particle, forcing it to the same thing it has done. As a result, both of them attract each other.

    If the first theory is right, then would gravity still count as a fundemental force? Since it doesn't require force particles at all, shouldn't it be classified as something else?
    Gravity is always a fundamental force. Don't worry.

    And lastly, is there any way that both theories are right?
    General relativity was long demonstrated to be correct. Unifying it qwith QM is tricky, thjough,.


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    I see, thank you.
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    Hello,

    I do find your thoughts interesting and would love to ask, how do you think earth is resting at the edge of space, or what this does mean?

    Do you think earth was closed to the boundaries of space and that gravity has something to do with it?

    It's a little off of any path - very broadly interpreted I mean - , but, who knows. I btw. came to the clue, gravity was the result of earth being in a three dimensional spin. Better said a four dimensional spin since earth can't spin three dimensionally without changing it's position in space as well. Not even two dimensionally, I would say. Perhaps that helps. Thank you.

    Steve

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    Moderator note:

    certain posts in this thread have been split off to a thread in pseudoscience.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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    What if space time isnt curved/distorted by mass.

    What if it is space time itself that is pushing against mass.

    What if mass is not attracted to other mass but is pushed towards itself by space time.
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    What if space time isnt curved/distorted by mass.

    What if it is space time itself that is pushing against mass.

    What if mass is not attracted to other mass but is pushed towards itself by space time.
    In which case you'd best hop over to the section known as New Hypotheses and Ideas. The Physics forum really isn't the place for such discussions.

    As for why what you propose is unlikely is because space-time is not actually distorted, to say the least. According to relativity, it is your perceptions of space-time that are distorted that produce a gravitational field. Space-time are not material things that can twist and curve like sheets of rubber; they appear to be different for an observer close to a gravitational field than for one far away.

    I'm quite willing to explain more, but I think the above suffices.
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    Forum Ph.D. Steve Miller's Avatar
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    Quote Originally Posted by starski1982
    What if space time isnt curved/distorted by mass.

    What if it is space time itself that is pushing against mass.

    What if mass is not attracted to other mass but is pushed towards itself by space time.
    Somehow space would have to give way as some object (just like earth ) passes through, I think.

    I do speak a little German as well, as A. Einstein himself did, therefore I know the term 'space-time' in German was 'Raumzeit' which was something rather that was hard to get.

    That's some neologism (a creation of a word I mean )of A.Einstein unknown to the world before.

    Some common term but was 'Zeitraum' which means 'space of time' which are about the same syllables in German. But second one 'Zeit' first succeeded by 'Raum' meaning space.

    Also, either the prior known 'Zeitraum' as well as Einstein's creation 'Raumzeit' are both single words consisting of either two syllables.

    This, as a matter of fact, made me come to a halt and perplexes me a little since I still don't relate 'Raumzeit' - 'space time' - to something physically conceivable.

    It's even like that I thought how does he (A. Einstein ) relate space to time at all? Men have not been discovering space back when the space-time term has been created by A. Einstein.

    So now I visualize there might be a very well a second, third, fourth... star number : ) conception of time in space, other than the one human mankind took to space with the beginning space exploration, but this 'times' could be very well differ from earth time.

    Differ because the species had to establish an other lets say time frame known to us as 24 ours (or one day ), that was their 'applied and short cut conception' of one time from dawn to the next days dawn.

    We have to tale such thinking into account I think , and therefore we can not utilize space time the same way than earth time. Space time could not never be the same physical entity because of the afore mentioned thoughts I think,

    A. Einstein saw time as the or a fourth dimension. Now that I'm typing these lines I think space time was like that he also connects the third and fourth dimension as that he would see a space bound rocket launch taking earth time to space to make it space time too, or something like that.

    Well that could be true, but other species will take their time to space that way, or similar, either.

    Steve
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    Somehow space would have to give way as some object (just like earth ) passes through, I think.
    Not really. Space here is simply a concept of measurement in general relativity; the distortion of space-time can be better thought of if you consider that your measurements of space and time change fundamentally in a gravitational field, such that it resembles a Riemannian surface e.g. a sphere.

    This, as a matter of fact, made me come to a halt and perplexes me a little since I still don't relate 'Raumzeit' - 'space time' - to something physically conceivable.

    It's even like that I thought how does he (A. Einstein ) relate space to time at all? Men have not been discovering space back when the space-time term has been created by A. Einstein.
    Correct. They are indeed not physically conceivable objects; in relativity, what matters is how you measure the passage of time and your own dimensions. In a graviational field, both your measurements of your own dimensions (or space) and the passage of time change; hence the distortion of space and time.

    I should probably mention that Einstein defined time as the amount of time it took light to strike you.
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    Liongold,

    one of my goals was to point to differences in how we conceive the surrounding nature now, and how folks seemingly did decades back when A. Einstein lived.

    But you are right of course. I have mistaken space for space time from the beginning and was trying to base my posting upon this error. But also I have tried to explain it afterwards.

    Interesting how you do interpret relativity. Everyone seems to have its own little crazy spot there. But, I oppose to talk about something that's not conceivable physically. That's like talking about one thing but meaning something else. And this was not science, as for my understanding. Btw. history F-.

    So now what? Space time for granted, anything real to the garbage, everyone nuts, happy holidays?

    Steve
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    Quote Originally Posted by Liongold
    it being the only of the 4 fundamental forces not fully understood.
    Actually, no. Gravity is fully understood, explained as it was in 1905 in general relativity. What we cannot do, however, is unify this theory with quantum mechanics, the other theory that has dominated science. That is where all our methods fail, as it leads to mathematical infinities that crop up.

    One theory says that space is curved.
    Just nitpicking here. It should be space and time, according to general relativity. Both these quantities curve together to form curved space-time, forcing objects travelling in a straight line to adopt a bent path.

    This theory seems to imply that space has a texture.
    Not necessarily. By space-time curvature, this does not mean literally curved; it is simply a good analogy for the mathematical version of what happens. Space and time, in the mathematics, are said to be curvbed; this does not apply physically.

    Space and time are said to curve because the mathematics treats them as such. In reality, however, you would be hard-pressed to say if space-time were actually curved just by looking.

    I can understand this 2 dimentionally, but how would this work in 3 dimensions?
    Think of a sphere. You have just imagined curved space-time in three dimensions.

    Earth is resting on the edge of "space".
    No. Think of Earth being inside a sphere. It will then have to follow the path of the sphere i.e. the curve of the sphere. Earth is in space and time; its motion is simply being affected because it measures space-time in such a way that it appears curved and follows a curved path.

    How do moons orbit planets then? Shouldnt the moons be orbiting the sun also? Am i missing something? Does three dimentional space allow space to warp in a different way from what im thinking?
    You forget that planets also curve space-time. In fact, anything with energy curves space-time. As a result, the moon is now following the curvature of space-time caused by the Earth, forcing it to orbit the Earth.

    And the alternate theory, gravitons.
    Quite correct. However, a collection of gravitons can be shown to be mathematically equivalent to curved space-time; see Wikipedia's article on it.

    If gravity is always attractive, how would gravitons work? (This kind of relates to the other force particles as well)
    That is why gravitons are troublesome creatures. They attract everything, even other gravitons. When it does so, however, we have an infinity of gravitons appearing, because the original gravitons exchange gracvitons, which in turn exchange gravitons, and so on.

    I understand repulsion: a matter particle emits a force particle and recoils back, another matter particle aborbs the force particle and changes its velocity in the other direction.
    Well, the answer to your qualms about attraction are hidden here. The second matter particle simply changes its velocity in the direction of the first matter particle. Simultaneously, it also emits a particler to the first matter particle, forcing it to the same thing it has done. As a result, both of them attract each other.

    If the first theory is right, then would gravity still count as a fundemental force? Since it doesn't require force particles at all, shouldn't it be classified as something else?
    Gravity is always a fundamental force. Don't worry.

    And lastly, is there any way that both theories are right?
    General relativity was long demonstrated to be correct. Unifying it qwith QM is tricky, thjough,.

    Wrong advice here. Curvature does posit physicality. I understand relativity quite well, but i've never heard your statement before;

    Instead, curvature i equivalant to mass which is equivalant to energy which is equivalant to acceleration which is equivalant to spatial and temporal distortions.
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  13. #12  
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    Also when you said

    Not necessarily. By space-time curvature, this does not mean literally curved;

    Is also wrong. It has been experimentally proven for about a hundred years now that space and time are curved by the experiments proven by astrophysicist Arthur Eddington, who took pictures of light bending round the distortions that are predicted by relativity, the distortions are of course, curvature. It's quite a real thing you know?
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