Editing Quantum foam (section)

==Background==

With an incomplete theory of [[quantum gravity]], it is impossible to be certain what [[spacetime]] looks like at small scales. However, there is no definitive reason that spacetime needs to be fundamentally smooth. It is possible that instead, in a quantum theory of gravity, spacetime would consist of many small, ever-changing regions in which space and time are not definite, but fluctuate in a foam-like manner.<ref name="WilczekLecture">[https://www.youtube.com/watch?v=914jzZ4LXcU&t=2887 See Derek Leinweber's QCD animations of spacetime foam, as exhibited in Wilczek lecture].</ref>

Wheeler suggested that the [[uncertainty principle]] might imply that over sufficiently small distances and sufficiently brief intervals of time, the "very geometry of spacetime fluctuates".<ref>{{Cite book|title=Geons, black holes, and quantum foam : a life in physics|last1=Wheeler|first1=John Archibald|last2=Ford|first2=Kenneth Wilson|publisher=W. W. Norton & Company|year=2010|isbn=9780393079487|location=New York|pages=328|oclc=916428720|orig-year=1998}}</ref> These fluctuations could be large enough to cause significant departures from the smooth spacetime seen at macroscopic scales, giving spacetime a "foamy" character.