Editing Theory of everything (section)

===Early 20th century===
In the late 1920s, the then new quantum mechanics showed that the [[chemical bond]]s between [[atom]]s were examples of (quantum) electrical forces, justifying [[Paul Dirac|Dirac]]'s boast that "the underlying physical laws necessary for the mathematical theory of a large part of physics and the whole of chemistry are thus completely known".<ref>
{{cite journal
 |last=Dirac |first=P.A.M.
 |date=1929
 |title=Quantum mechanics of many-electron systems
 |journal=[[Proceedings of the Royal Society of London A]]
 |volume=123 |pages=714–733
 |doi=10.1098/rspa.1929.0094
 |bibcode=1929RSPSA.123..714D
 |issue=792|doi-access=free
 }}</ref>

After 1915, when [[Albert Einstein]] published the theory of gravity ([[general relativity]]), the search for a [[unified field theory]] combining gravity with electromagnetism began with a renewed interest. In Einstein's day, the strong and the weak forces had not yet been discovered, yet he found the potential existence of two other distinct forces, gravity and electromagnetism, far more alluring. This launched his 40-year voyage in search of the so-called ''"unified field theory"'' that he hoped would show that these two forces are really manifestations of one grand, underlying principle. During the last few decades of his life, this ambition alienated Einstein from the rest of mainstream of physics, as the mainstream was instead far more excited about the emerging framework of quantum mechanics. Einstein wrote to a friend in the early 1940s, "I have become a lonely old chap who is mainly known because he doesn't wear socks and who is exhibited as a curiosity on special occasions." Prominent contributors were [[Gunnar Nordström]], [[Hermann Weyl]], [[Arthur Eddington]], [[David Hilbert]],<ref>{{cite book |arxiv=physics/0405110 |doi=10.1007/0-8176-4454-7_14 |isbn=978-0-8176-4454-3 | title=Hilbert's "World Equations" and His Vision of a Unified Science |series=Einstein Studies |volume=11 |pages=259–276 |year=2005 |last1=Majer |first1=U. |last2=Sauer |first2=T. |bibcode=2005ugr..book..259M |journal=<!-- Citation bot--> |s2cid=985751 }}</ref> [[Theodor Kaluza]], [[Oskar Klein]] (see [[Kaluza–Klein theory]]), and most notably, Albert Einstein and his collaborators. Einstein searched in earnest for, but ultimately failed to find, a unifying theory<ref name="Pais1982">{{cite book |author=Abraham Pais |title=Subtle is the Lord: The Science and the Life of Albert Einstein: The Science and the Life of Albert Einstein |url=https://archive.org/details/subtleislordscie00pais |url-access=registration |date=23 September 1982 |publisher=Oxford University Press |isbn=978-0-19-152402-8|author-link=Abraham Pais }}</ref>{{rp|ch 17}} (see Einstein–Maxwell–Dirac equations).