Editing Pilot wave theory (section)

===Empty wave function===
[[Lucien Hardy]]<ref>{{cite journal |last=Hardy |first=L. |year=1992 |title=On the existence of empty waves in quantum theory |journal=[[Physics Letters A]] |volume=167 |issue=1 |pages=11–16 |bibcode=1992PhLA..167...11H |doi=10.1016/0375-9601(92)90618-V}}</ref> and [[John Stewart Bell]]<ref name="bell-1992"/> have emphasized that in the de Broglie–Bohm picture of quantum mechanics there can exist '''empty waves''', represented by wave functions propagating in space and time but not carrying energy or momentum,<ref name="Selleri">{{cite book |last1=Selleri |first1=F. |last2=Van der Merwe |first2=A. |year=1990 |title=Quantum paradoxes and physical reality |url=https://books.google.com/books?id=qUgX3B02ofAC&pg=PA85 |pages=85–86 |publisher=Kluwer Academic Publishers |isbn=978-0-7923-0253-7}}</ref> and not associated with a particle. The same concept was called ''ghost waves'' (or "Gespensterfelder", ''ghost fields'') by [[Albert Einstein]].<ref name="Selleri"/> The empty wave function notion has been discussed controversially.<ref>{{cite journal |last=Zukowski |first=M. |year=1993 |title="On the existence of empty waves in quantum theory": a comment |journal=[[Physics Letters A]] |volume=175 |issue=3–4 |pages=257–258 |bibcode=1993PhLA..175..257Z |doi=10.1016/0375-9601(93)90837-P
}}</ref><ref>{{cite journal |last=Zeh |first=H. D. |year=1999 |title=Why Bohm's Quantum Theory? |journal=[[Foundations of Physics Letters]] |volume=12 |issue=2 |pages=197–200 |arxiv=quant-ph/9812059 |bibcode= 1999FoPhL..12..197Z |doi=10.1023/A:1021669308832|s2cid=15405774 }}</ref><ref>{{cite journal |last=Vaidman |first=L. |year=2005 |title=The Reality in Bohmian Quantum Mechanics or Can You Kill with an Empty Wave Bullet? |journal=Foundations of Physics |volume=35 |issue=2 |pages=299–312 |arxiv=quant-ph/0312227 |bibcode=2005FoPh...35..299V |doi=10.1007/s10701-004-1945-2|s2cid=18990771 }}</ref> In contrast, the [[many-worlds interpretation]] of quantum mechanics does not call for empty wave functions.<ref name="bell-1992"/>