curved space

[neolistic]

Now, id like to clear something up about curved space if i may. Now the theory of curved space states that space is curved in proportion to the object displacing the space. Now if this is true, shouldn't curved space best be compared to water. Say if you place a ball that would be, say the sun into the water, it would displace the water around it, but not curve the water around it. The displacement of the water will be apparent but it wont effect things around it. Say if you place other round objects to represent planets. The pressure of the water could account for gravity, but it doesn't explain why the planets stay in orbit. Why is the theory of curved space best compared to a trampoline net, since a trampoline net is only half of the big picture. That doesn't account for the upper half of space above, and around the object 360 degrees around. Like i mean space is not flat, why compare it to a flat surface, and not a 360 degree substance that displaces itself relative to the object. If you did a experiment under water you would see that the gravity pushing down on the objects is much like einstein predicted (force of the water pushing down on ball). But the reason for the objects to orbit the object in the middle isn't apparent.<br /><br />This reason for objects to orbit around a trampoline net is apparent, because of the curve a trampoline net makes. but not for a 360 degree force all around. If anything this curvature only adjusts for itself in space.<br /><br />Discuss..

 

[R1]

a lot of people are good at explaining this, so maybe there will be better explanations.<br />The way I would explain it is:<br /><br /><br /><br />that first one must realize that space and spacetime have 2 totally different definitions, or they<br />are affected in different ways and/or they have 2 different effects.<br /><br /><br />the trampoline, or famous rubber sheet (usually with a grid that looks like a spreadsheet)<br />in my opinion represents only <font color="yellow">one</font>2 dimensional slice of 3D (or 4) space (actually spacetime),<br />and you have to ignore how it looks real close to the sphere, because it actually should bottom<br />out at the sphere's center of gravity instead of the sphere's bottom<br /><br /><br />the curvature is then meant to facilitate the human visualization of presence gravity and<br />also the curving of the rate at which time flows.<br /><br /> <div class="Discussion_UserSignature"> </div>

 

[vandivx]

curved space was never meant to be physical picture of reality, not even as <font color="yellow">"only one 2 dimensional slice of 3D (or 4) space (actually spacetime)"</font><br /><br />curved space in GR is abstract construct, a mere pictorial representation of the underlying mathematics of curved space<br /><br />Einstein did talk about his belief that there is something physical existing in space but that was just conviction that he didn't know how to develop further and it accordingly ended only as his conviction<br /><br />S. Weinberg in his Gravitation and Cosmology said this about curved space:<br /><blockquote><font class="small">In reply to:</font><hr /><p>[because of the existence of the curvature tensor] it is not surprising that Einstein and his successors have regarded the effect of the gravitational field as producing a change in the geometry of space and time. At one time it was even hoped that the rest of physics could be brought into a geometric formulation, but this hope has met with disappointment, and the geometric interpretation of the theory of gravitation has dwindled to a mere analogy, which lingers in our language in terms like "metric," "affine connection," and "curvature," but is not otherwise very useful. The important thing is to be able to make predictions about images on the astronomers' photographic plates, frequencies of spectral lines, and so on, and it simply doesn't matter whether we ascribe these predictions to the physical effect of gravitational fields on the motion of planets and photons or to a curvature of space and time. [Wiley, 1972, p. 147]<p><hr /></p></p></blockquote><br /><br />vanDivX <div class="Discussion_UserSignature"> </div>

 

[kyle_baron]

<font color="yellow"><br />curved space was never meant to be physical picture of reality, not even as "only one 2 dimensional slice of 3D (or 4) space (actually spacetime)" <br /><br />curved space in GR is abstract construct, a mere pictorial representation of the underlying mathematics of curved space </font><br /><br />Hey, I was gonna say that! (The 1st sentence) <img src="/images/icons/wink.gif" /> I might add, that when it comes to space (or spacetime) we should be careful when we hear the words curve, expand, contract, etc. These words make space appear physical (which it is not). These words only describe how space acts in the presence of mass, which is a description of gravity.<br /><br /><br /> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[derekmcd]

The 'rubber sheet grid' is simply a visual representation to show the linear path an object would travel as it passes by the center of mass. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

 

[vandivx]

"Hey, I was gonna say that! (The 1st sentence) "<br /><br />LOL<br /><br />to dampen your jumping spree I have to add that those views are more or less official views, that the curved space is mere analogy etc., my private view is that there is something there which is responsible for gravitation among other things, I see curved space as mistaken notion which should be replaced by a different physical model<br /><br />reason nobody seriously pushed the physical reality of the curved space too much (and that included Einstein himself) was that it would bring way too many troubles all over the place with other theories out there, most notably it would play havoc with the special relativity, namely with the constant speed of travel of light which couldn't be understood then - Michelson-Morley experiment was searching for some such physical background and found none... everything has to be reconsidered in order to make way for physical background<br /><br />vanDivX <div class="Discussion_UserSignature"> </div>

 

[kyle_baron]

Ahhhhh.... good luck in finding that physical background (model) for empty space. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[R1]

well it doesn't have to be something physical, space could be quantum space, lacking everything<br />that makes it anything physical,<br /><br /> but vanDivx, I'm still trying to understand how space could be absolutely nothing,<br />not even quantum wave space or multidimensional string space, and yet be thinking that something<br />really is supposed to be somewhere in nothingness and providing evidence of gravity.<br /><br />I'm trying though, and I think I understand it a little, but I believe it's easier that empty space<br />actually has higher dimensions and quantum wave space points and gravity has something to do <br />with either or both in fact I think the higher diomensions might even have something to do with the limit<br />of c. I started reading that somewhere and I forgot where.<br /><br /> <div class="Discussion_UserSignature"> </div>

 

[methanebubbles]

this is kind of off topic but i just wanted to know (and can't start a new thread as is made clear by my question): how does one start a new thread? <div class="Discussion_UserSignature"> and we are all undeniably selfish. </div>

 

[bobw]

Go to the main page of one of the forums, like the link below.<br /><br />http://uplink.space.com/postlist.php?Cat=&Board=sciastro&PHPSESSID=<br /><br />In the menu bar near the top of the page it says:<br />Main Index | Search | My Home | Who's Online | FAQ | Logout | User List<br /><br />Below that is another menu bar that says:<br />Post | Previous | Index | Next | Expand | Collapse <br /><br />Click on the one that says "Post" <br /><br />The "Post" button doesn't show up if your <i>inside</i> a thread.<br /><br /><img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

 

[vandivx]

<font color="yellow">Why is the theory of curved space best compared to a trampoline net, since a trampoline net is only half of the big picture. That doesn't account for the upper half of space above, and around the object 360 degrees around. Like i mean space is not flat, why compare it to a flat surface, and not a 360 degree substance that displaces itself relative to the object.</font><br /><br />that's because you can't have 'curvature' in 3D in any globally consistent fashion and Einstein needed curvature since that enabled him to develop pretty successfull mathematical theory on that basis<br /><br />some scientists are content with seeing only part of the picture at a time (like that horse with blinds around his eyes) to enable them to accept some foggy understanding of the curvature in 3D, others correctly see that you can't have curvature in 3D but it doesn't matter becuase they take the 2D model as just an abstraction that has no physical reality, they don't believe in any physical medium, a manifold space (of GR) or whatever being there anyway<br /><br />vanDivX <div class="Discussion_UserSignature"> </div>