The enigma of optical momentum in a medium

Stephen M. Barnett, Rodney Loudon

Research output: Contribution to journalArticle

155 Citations (Scopus)
93 Downloads (Pure)


It is 100 years since Minkowski and Abraham first gave rival expressions for the momentum of light in a material medium. At the single-photon level, these correspond, respectively, either to multiplying or dividing the free-space value () by the refractive index (n). The debate that this work started has continued till the present day, punctuated by the occasional publication of 'decisive' experimental demonstrations supporting one or other of these values. We review the compelling arguments made in support of the Minkowski and Abraham forms and are led to the conclusion that both momenta are correct. We explain why two distinct momenta are needed to describe light in a medium and why each appears as the natural, and experimentally observed, momentum in appropriate situations.
Original languageEnglish
Pages (from-to)927-939
Number of pages13
JournalPhilosophical Transactions A: Mathematical, Physical and Engineering Sciences
Issue number1914
Publication statusPublished - 13 Mar 2010


  • optics
  • optical momentum

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