Why are planets spherical?

[bonzelite]

<font color="yellow"><br />basically what he is saying is since every thing expands at the same rate you could not tell the earth is catching up to you because the space in between th earth and you would also increase.</font><br /><br />correct. <br /><br />orbits occur from the natural acceleration due to expansion geometry between objects, at differeing velocities and sizes, in a non-expanding, infinite, free-floating space. gravity does not really exist as it is thought to be, ie, an endemic "force" that "pulls in" matter. <i>in my opinion,</i> until enough people, en masse, drop the erroneous gravitational force idea proposed by Newton, there will not be an acceptance of this concept.

 

[spacechump]

<i>gravity does not really exist as it is thought to be, ie, an endemic "force" that "pulls in" matter. in my opinion, until enough people, en masse, drop the erroneous gravitational force idea proposed by Newton, there will not be an acceptance of this concept.</i><br /><br />Newton's ideas still work because the approximations pulled out of his equations still work today for most things. Up the velocity and mass of an object to extremes and those approximations break down. GR is how gravity is accepted today and has passed all sorts of tests like the predicted starlight during the 1919 eclipse. It is like highly refining the approximations made by Newton's equations, the GR equations generating numbers much more accurate.

 

[Saiph]

well...bonz, your idea of an expanding space-time geometry causing all this...gives the same answers newtons does, so I don't know why you're bashing it.<br /><br />All you're saying is that Newtons gravitational force is as "fictitous" as the percieved centrifugal force that arises in a rotating frame of reference. But, just because it's an "illusion" doesn't mean it isn't useful, or that it can't be correct.<br /><br />I also fail to see what conceptual merits the "everything is expanding" notion has over the concept of a gravitational field or "action at a distance" that is the standard newtonian interpretation of gravity (and all the other fundamental forces!). Especially since this notion is suplanted in another popular paradigm: relativity, where gravity isn't really a force, but a consequence of space-time curvature.<br /><br /><br /><br />Oh, and the earth isn't even a good oblate, it's a pear shape. The main bulge of the earth is below the equator...so the southern hemisphere is a bit more "bloated" than the northern. But you've gotta be really, really, picky to care about that. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>

 

[derekmcd]

If gravity has nothing to do with mass, then how do planets even form and maintain their shape? <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>

 

[bonzelite]

<font color="yellow"> the GR equations generating numbers much more accurate.</font><br /><br />in my opinion, GR is incorrect in that it must have an expanding universe to maintain it's relevancy. that the universe is infinite and non-expanding, with the matter within it expanding to create acceleration, automatically nullifies GR and renders it impotent.

 

[bonzelite]

<font color="yellow"><br />If gravity has nothing to do with mass, then how do planets even form and maintain their shape?</font><br /><i>in my opinion,</i> shape is maintained due to expansion relative to the center of mass between objects and mass-distribution within objects. the center of mass between earth/moon, the barycenter, is within the earth, creating an inner wobble of the earth, creating the tides. the moon is not pulling on anything whatsoever, <i>in my opinion;</i> the tides being a result of a geometric effect of this barycenter wobbling.

 

[Saiph]

well...you're mistaken on the tides.<br /><br />The "barrycenter" wobble you describe is present. However, it's detected as a variation in the overall tide strength, not as the primary contributor (by far). <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>

 

[spacechump]

Exactly, in your opinion. You've got <i>nothing</i> to back it up. I could say that invisible ponies actually push matter to other matter but there's nothing I can show for it.

 

[spacechump]

<i>in my opinion, GR is incorrect in that it must have an expanding universe to maintain it's relevancy. that the universe is infinite and non-expanding, with the matter within it expanding to create acceleration, automatically nullifies GR and renders it impotent.</i><br /><br />And yet without GR we wouldn't have a functional GPS system.

 

[aerogi]

I've a question related to this topic. If it would be possible to 'cut' the earth with some laser technology into a cube form (I know it is not possible, but let's assume), besides the obvious problems of the magma etc, so because of the gravity it will get back to a sperical shape? And how long would it take to do so? Any ideas?

 

[CalliArcale]

That's an interesting question. It should slump back into a roughly spherical shape (an oblate spheroid) given enough time, but I don't know how long that would take. The tidal influence of the Moon might speed things by heating the Earth up; if the Earth were cube-shaped, it would have a significant impact on the gravitational relationship between Earth and Moon. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[robnissen]

Just think. If the square peg and the round hole are big enough. . . . the square peg will ALWAYS fit into the round hole. Of course, you might have a problem with the round hole becoming a sphere, maybe that London moment thing being discussed on other threads could keep it open long enough for the square peg to fit before the round hole becomes a sphere! <img src="/images/icons/smile.gif" />

 

[nova_explored]

well someone has to mention it- centrifugal force.<br /><br />in newtonian and einsteinian physics, gravity and centrifugal force are identical forces, the difference is gravity relates more to the relation of different masses in a geometric plane and centrifugal force is a localized affect due to spin, both within particles and very massive bodies like planets and stars. the reason a relative sphere is maintained is spin. the massive material settles to the center and the spin acts on every single point directed towards that center.<br /><br />when you get into QM you have repulsion on the planck level that also acts in accordance to electrodynamics to maintain that sphere.<br /><br />but in your model of a cube, if there were no spin, there could be no centrifugal force to pull mass towards the geometric center that spin creates. but it is impossible to not have spin in anything in the universe. spin is an inseperable force in all matter.<br /><br />in the cube model gravity would pull on all the mass towards a center, but that center could shift.<br /> <div class="Discussion_UserSignature"> </div>

 

[nova_explored]

oh hey, lol, i didn't read the very last post. someone did mention it. nevermind. <div class="Discussion_UserSignature"> </div>

 

[tom_hobbes]

Hey, I won't tolerate anybody knocking the 'Invisible Pony' theory. It's dear to my heart! <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><font size="2" color="#339966"> I wish I could remember<br /> But my selective memory<br /> Won't let me</font><font size="2" color="#99cc00"> </font><font size="3" color="#339966"><font size="2">- </font></font><font size="1" color="#339966">Mark Oliver Everett</font></p><p> </p> </div>

 

[spacechump]

<i>Hey, I won't tolerate anybody knocking the 'Invisible Pony' theory. It's dear to my heart!</i><br /><br />All right...from now folks we're here to discuss the pros and cons of a pony-based, <i>inflationary</i> universe. Go ahead Tom...<br /><br /><img src="/images/icons/wink.gif" />