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[[File:Irrotational vortex.gif|thumb|The self-gravitational involution of a mass can be visualized as a series of concentric shells. The higher a shell, the lower its rotational frequency. If we sufficiently extend the series of concentric shells, then the outermost shell's rotational frequency will be zero, so that the shell will have the lowest (''i.e.'', zero) actual energy (nonzero‑frequency [[angular momentum]]) and the highest (''i.e.'', zero) potential energy (zero‑frequency angular momentum).]]
EPositive actual energy (''E'' = [[w:Planck constant|''h'']][[w:frequency|''f'']]) is centrifugal [[angular momentum]],.<ref>Biedenharn, L. C.; Louck, J. D. [https://books.google.co.uk/books?id=8HWQwdXqcXAC&q=%22The+Planck+quantum+of+action,+h,+has+precisely+the+dimensions+of+an+angular+momentum%22&dq=%22The+Planck+quantum+of+action,+h,+has+precisely+the+dimensions+of+an+angular+momentum%22&hl=en&ei=5gq1TZWtItL-4wa0r7DMDA&sa=X&oi=book_result&ct=result&resnum=1 Angular Momentum in Quantum Physics]. Addison-Wesley Pub. Co., Advanced Book Program, 1981. "The Planck quantum of action, ''h'', has precisely the dimensions of an angular momentum, and, moreover, the Bohr quantization hypothesis specified the unit of (orbital) angular momentum to be ''ħ&nbsp;=&nbsp;h/2π''. Angular momentum theory and quantum physics are thus clearly linked."</ref> which is centrifugal when positive, and centripetal when negative. Negative angular momentum is [[Momentum|linear momentum]], which is thus always centripetal.⏎
Conversely, negative [[potential energy]] is centripetal [[Momentum|linear momentum]]. All negative potential energy is gravitational; other types of potential energy are temporary masks of gravity.<ref>[[w:Frank Shu|Shu, Frank H.]] [https://books.google.co.uk/books?id=v_6PbAfapSAC&pg=PA157 The Physical Universe: An Introduction to Astronomy]. University Science Books, 1982, p. 157. "'''Concluding Philosophical Comment.'''<br>Zeldovich and Novikov have made the following intriguing philosophical point about the picture of the formation of a neutron star sketched here. They note that stars begin their lives as a mixture mostly of hydrogen nuclei and their stripped electrons. During a massive star's luminous phase, the protons are combined by a variety of complicated reactions into heavier and heavier elements. The nuclear binding energy released this way ultimately provides entertainment and employment for astronomers. In the end, however, the supernova process serves to undo most of this nuclear evolution. In the end, the core forms a mass of neutrons. Now, the final state, neutrons, contains less nuclear binding energy than the initial state, protons, and electrons. So where did all the energy come from when the star was shining all those millions of years? Where did the energy come from to produce the sound and the fury which is a supernova explosion? Energy is conserved; who paid the debts at the end? Answer: gravity! The gravitational potential energy of the final neutron star is much greater (negatively; that's the '''debt''') than the gravitational potential energy of the corresponding main-sequence star (Problem 8.7). So, despite all the intervening interesting nuclear physics, ultimately Kelvin and Helmholtz were right after all! The ultimate energy source in the stars which produce the greatest amount of energy is gravity power. This is an important moral worth remembering and savoring. If we regard the neutron star as one gigantic atomic nucleus, we may also say that nuclear processes plus gravity have succeeded in converting many atomic nuclei into one nucleus. Problem 8.7 then shows that '''the ultimate energy source for the entire output of the star is the relativistic binding energy of the final end state'''."</ref>

The '''minimum total potential energy principle''', formulated in 1854 by [[w:William Thomson, 1st Baron Kelvin|William Thomson]],<ref>Smith, Crosbie; [[w:M. Norton Wise|Wise, M. Norton]]. [https://books.google.co.uk/books?id=2JYWeyAXpHUC&pg=PA533 Energy and Empire: A Biographical Study of Lord Kelvin] CUP, 1989, p.&nbsp;533. "Thomson had adopted in 1854 the view that "the potential energy of gravitation may be in reality the ultimate created anteceden(contracted; show full)—<span class="plainlinks">[https://en.wikiquote.org/w/index.php?title=Terence_McKenna&oldid=2251202 Terence McKenna]]]

==References==
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[[Category:Basic physics ideas]]
[[Category:Cosmology]]
[[Category:Energy]]