Commander Posted January 27, 2015 Posted January 27, 2015 I believe, as I am lying on my bed being pressed down by gravity , it has to be a true force and not just Space Time Curvature !
ACG52 Posted January 27, 2015 Posted January 27, 2015 The force is supplied by your bed preventing your body from moving along the geodesic.
Robittybob1 Posted January 27, 2015 Posted January 27, 2015 The force is supplied by your bed preventing your body from moving along the geodesic. What I find hard to understand about these geodesics is that there is not just one geodesic but an infinite number going through every point in space. If Commander was in motion his geodesic would be different. but since he is lying there still it happens to be straight down to the center of the Earth, but he could have been in motion. So there is not just "the (one and only) geodesic" is there ?
ajb Posted January 27, 2015 Posted January 27, 2015 So there is not just "the (one and only) geodesic" is there ? But mathematically we know that (locally for sure) that given an initial position and an initial velocity the geodesic equation has a unique solution.
Robittybob1 Posted January 27, 2015 Posted January 27, 2015 But mathematically we know that (locally for sure) that given an initial position and an initial velocity the geodesic equation has a unique solution. So relating that to what I said that initial position is no different to any other position in space, but OK it where a mass is at a certain time, but that mass could be going in any direction, but you are right the path it takes can be calculated. So what convinces you there are geodesics?
Strange Posted January 27, 2015 Posted January 27, 2015 So relating that to what I said that initial position is no different to any other position in space, but OK it where a mass is at a certain time, but that mass could be going in any direction, but you are right the path it takes can be calculated. So what convinces you there are geodesics? Because they can be used to calculate the right result? The path can be calculated, the path is a geodesic.
magnocrat Posted January 27, 2015 Posted January 27, 2015 A rose by any name still smells the same.. 1
Commander Posted January 27, 2015 Author Posted January 27, 2015 (edited) If the water falls and hits the turbine blades it transfers force and energy thereby ! If the water simply follows geodesic paths and does not actually have Energy how do you explain that ? The force is supplied by your bed preventing your body from moving along the geodesic. Two identical Springs have been Compressed into an identical shape. One by a great stone following geodesic gravitational Curvature of the Potential Energy of the Stone. The other by my Own Muscular Power - without drawing on my weight - say hand power. Perhaps I expended some energy drawn from the metabolism of some Food content. Explain the setup with Curvature of Space and Strings and what happens if the spring expands to : Drive a Clock hands Project a Bullet Just release into Air or Water What happens if it simply expands into Vacuum or Empty Space ? Edited January 27, 2015 by Commander 1
ajb Posted January 27, 2015 Posted January 27, 2015 So what convinces you there are geodesics? I am not sure I understand your question, but... we can calculate geodesics and these correspond to the motion of test bodies under the influence of gravity alone very well. In short, general relativity is well tested, but much like the Lorentz force, geodesic motion as the equation of motion for test particles is added to general relativity. If the water simply follows geodesic paths and does not actually have Energy how do you explain that ? Who said that bodies moving under the influence of gravity do not posses energy? 1
studiot Posted January 27, 2015 Posted January 27, 2015 (edited) Commander, perhaps this will help clear up your difficulty. It is imporant to understand what a geodesic is. There are many types of geodesic. From your (are you retired?) former profession you will have studied navigation and probably met geodesics as a geometrical line in cartography which minimises the distance between two points. The geodesics here are not of this type. They do not live in normal physical 3 dimensional space, they 'exist' in an abstract mathematical space with abstract mathematical axes. They are defined as the line referred to these axes which minimises a particular mathematical expression. Have you studied the calculus of variations? You would need this for this type of geodesic. You are a clever fellow and I'm sure you will be able to follow what I'm trying to say (sorry I didn't put it very well to start with) so ask again if you want me to expand on this. Edited January 27, 2015 by studiot 1
Commander Posted January 27, 2015 Author Posted January 27, 2015 Commander, perhaps this will help clear up your difficulty. It is imporant to understand what a geodesic is. There are many types of geodesic. From your (are you retired?) former profession you will have studied navigation and probably met geodesics as a geometrical line in cartography which minimises the distance between two points. The geodesics here are not of this type. They do not live in normal physical 3 dimensional space, they 'exist' in an abstract mathematical space with abstract mathematical axes. They are defined as the line referred to these axes which minimises a particular mathematical expression. Have you studied the calculus of variations? You would need this for this type of geodesic. You are a clever fellow and I'm sure you will be able to follow what I'm trying to say (sorry I didn't put it very well to start with) so ask again if you want me to expand on this. Thank you Studiot, What you said makes nice reading. Yes, I will put in more efforts if required. I also am thinking about the whole thing from different view point, angle and perspective. Regards
Robittybob1 Posted January 27, 2015 Posted January 27, 2015 Because they can be used to calculate the right result? The path can be calculated, the path is a geodesic. I think I need to go and see if I know what a geodesic really is. 2
Endy0816 Posted January 27, 2015 Posted January 27, 2015 I tend to think of mass as seeking to move towards the bottom of 'valleys' in space-time it creates around itself. Obviously though it is not just mass which is impacted as light can end up bending from our POV as well. 1
studiot Posted January 27, 2015 Posted January 27, 2015 (edited) Robbitybob I think I need to go and see if I know what a geodesic really is. Help is available at ScienceForums if you want it. The name comes from cartography, and the cartographic explanation is the easiest to digest. Edited January 27, 2015 by studiot
Mordred Posted January 27, 2015 Posted January 27, 2015 I think I need to go and see if I know what a geodesic really is. Take out your basket ball measure the shortest distance between two points. There is your geodesic on a curved manifold 1
Robittybob1 Posted January 27, 2015 Posted January 27, 2015 Help is available at ScienceForums if you want it. The name comes from cartography, and the cartographic explanation is the easiest to digest. There are two places I know of as Science Forums, which one? Scienceforums.net (this site) seems a well moderated place in my opinion. Does the cartographic explanation and the way the word geodesic is used when talking of gravity match? I might have been thinking it was more just the ballistic path an object would take. Maybe you'd agree there are an infinite number of ballistic paths through any point, but let's see if there are fewer geodesics and how they differ. Take out your basket ball measure the shortest distance between two points. There is your geodesic on a curved manifold Now I get it; you are talking about two points on the surface on the ball, not between any two points.
studiot Posted January 27, 2015 Posted January 27, 2015 Robbitybob Does the cartographic explanation and the way the word geodesic is used when talking of gravity match? All geodesics have the same common idea. It's just that Mathematicians & Physicists have extended the idea from the original cartographic one. Mordred Take out your basket ball measure the shortest distance between two points. There is your geodesic on a curved manifold This is indeed a cartographic geodesic (for want of a better term) It is not a geodesic in the externsion of the term to Hamilton/Lagrange mechanics and General Relativity. A ballistic trajectory is one thing any geodesic most definitely is not. See what you make of my post 10
Robittybob1 Posted January 27, 2015 Posted January 27, 2015 (edited) All geodesics have the same common idea. It's just that Mathematicians & Physicists have extended the idea from the original cartographic one. This is indeed a cartographic geodesic (for want of a better term) It is not a geodesic in the externsion of the term to Hamilton/Lagrange mechanics and General Relativity. A ballistic trajectory is one thing any geodesic most definitely is not. See what you make of my post 10 Looking at one site :http://www.astronomynotes.com/relativity/s3.htm Light travels along the shortest path between two points in spacetime (a geodesic). If the geodesic is curved, then the path of light is curved. Einstein proposed in his General Relativity theory that what is called gravity is really the result of curved spacetime. but if light follows the geodesic, will a mass orbiting a star at the same distance be following a different curvature? I would say between two points in space there is only 1 geodesic but I have yet to be convinced that light and a massive object will follow exactly the same path between those two points. Do you think there is only one gravitationally induced path? I.e between a distant star and the Earth, if light takes a path as it grazes past the Sun it is deflected by a very small angle. Do you think a rocket ship could follow the same geodesic? That doesn't sound right to me! Edited January 27, 2015 by Robittybob1
studiot Posted January 27, 2015 Posted January 27, 2015 The manifold in cartographic geodisics is a surface in normal xyz space. The manifold in other forms of geodesic is not in xyz space, but in some lagrangian dimensional space. Further the cartographer's geodesic path minimises the distance function through the manifold, whereas other geodiscs may minimise some other function.
Robittybob1 Posted January 28, 2015 Posted January 28, 2015 The manifold in cartographic geodisics is a surface in normal xyz space. The manifold in other forms of geodesic is not in xyz space, but in some lagrangian dimensional space. Further the cartographer's geodesic path minimises the distance function through the manifold, whereas other geodiscs may minimise some other function. I must admit the equations for the gravitational geodesics are not easy to understand. I want to understand it but someone will have to explain the maths in words before I'll ever get it. Previously you said "A ballistic trajectory is one thing any geodesic most definitely is not", but isn't a rocket orbiting the Earth an extreme case of a ballistic trajectory? 1
fiveworlds Posted January 28, 2015 Posted January 28, 2015 (edited) No gravity is controlled by the mass of the objects near it. For instance I am not heavier than the planet hence I am dragged to the ground. An apple falls from a tree etc. of course any centripetal force exerted by the planet on us also has to be taken into account so it is not gravity alone that acts upon us but a culmination of many forces. there is wind resistance to be taken into account for instance this would be why a feather falls faster than a cannonball. By gravity alone both fall at the same rate but with wind resistance a feather falls slower Edited January 28, 2015 by fiveworlds 1
Commander Posted January 28, 2015 Author Posted January 28, 2015 (edited) So was that a yes or a no? Of course that was an yes ! If the water falls and hits the turbine blades it transfers force and energy thereby ! If the water simply follows geodesic paths and does not actually have Energy how do you explain that ? Two identical Springs have been Compressed into an identical shape. One by a great stone following geodesic gravitational Curvature of the Potential Energy of the Stone. The other by my Own Muscular Power - without drawing on my weight - say hand power. Perhaps I expended some energy drawn from the metabolism of some Food content. Explain the setup with Curvature of Space and Strings and what happens if the spring expands to : Drive a Clock hands Project a Bullet Just release into Air or Water What happens if it simply expands into Vacuum or Empty Space ? Yes, as I had indicated I am thinking of a new explanation for this phenomenon under consideration with all Accepted Theories [supported by perceivable evidence] and proposed explanation about multi-dimensional imaginary projections with mathematical supporting Equations ! [which is quite hard for many questioning minds to simply accept and for many pragmatists and logical minds to follow all the steps involved] Of course my proposal was after years of thinking and imagination. However I have not still worked out the Mathematical Supporting Arguments fully. I can anticipate that any new, out-of-box ideas in this area will have to face, Opposition by Believers of existing Science, Questions for proof and clarity and total ironing out of allied philosophies, Counter-Theories and Opposite Views etc and therefore I did not put it up here and had a second thought. Therefore, after putting up my Main Point of Contentions I have edited/modified/deleted my proposal from the thread "Everything is unique !" However I have a hunch that everything that has been posted here are archived and therefore even after editing and modifying every time-stamped states of these posts are recorded. I request the Moderators to clarify on this as to who all can have access to all Posts and Archives of Modifications ! Also, deleted attachments !! Thank you Moderators, [especially imatfaal, Phi for All & Swansont] Regards PS : This will help me in my further interactions ! Edited January 28, 2015 by Commander
hypervalent_iodine Posted January 28, 2015 Posted January 28, 2015 ! Moderator Note MomentTheory, keep your posts on topic. Commander, as far as I know, once you edit your posts, that's it. They aren't saved. However, you might want to check with an admin. They are much more involved in that aspect of site maintenance than we lowly moderators. If you have any other questions about this, please PM someone. 1
Commander Posted January 28, 2015 Author Posted January 28, 2015 ! Moderator Note MomentTheory, keep your posts on topic. Commander, as far as I know, once you edit your posts, that's it. They aren't saved. However, you might want to check with an admin. They are much more involved in that aspect of site maintenance than we lowly moderators. If you have any other questions about this, please PM someone. Hi, hypervalent_iodine, TY so much. Regards Thomas
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