Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:1608.00176

Reply to Elsässer's Comment on "How many principles does it take to change a light bulb ... into a laser?"

Howard M. Wiseman

Published Jul 31, 2016• 0 citations
arXivHTMLPDF

Abstract

In his Comment, Elsässer claims that the answer to my titular question is one, not four as I have it. He goes on to give the singular principle that supposedly captures the difference between a light-bulb and a laser: $g^{(2)}(τ=0)=1$. His claim is unconsidered and wrong, his proposed principle is impossible to apply and, when corrected, redundant (it then becomes one of the four I list already), his arguments are manifestly misdirected. My paper stands as is.

DOI
10.48550/arxiv.1608.00176

Related papers

Comment on "How many principles does it take to change a light bulb ... into a laser?" by Howard M. Wiseman, Physica Scripta 91 (3), 033001 (2016)

Wolfgang Elsäßer

In this comment on "How many principles does it take to change a light bulb ... into a laser?" by Howard M. Wiseman, Physica Scripta 91 (3), 033001 (2016) I am analyzing this extremely nicely formulated question in the framework of the Hanbury-Brown & Twiss experiment thus celebrating also its 60th anniversary. I am giving a straightforward, concise and unique answer on this question, emphasizing that the intensity correlations or the photon statistics make the difference between a light bulb and a laser.

arXiv:1607.03647•Jul 13, 2016•2 citations

How many principles does it take to change a light bulb…into a laser?

Howard M. Wiseman

Abstract Quantum optics did not, and could not, flourish without the laser. The present paper is not about the principles of laser construction, still less a history of how the laser was invented. Rather, it addresses the question: what are the fundamental features that distinguish laser light from thermal light? The obvious answer, ‘laser light is coherent’, is, I argue, so vague that it must be put aside at the start, albeit to revisit later. A more specific, quantum theoretic, version, ‘laser light is in a coherent state’, is simply wrong in this context: both laser light and thermal light can equally well be described by coherent states, with amplitudes that vary stochastically in space. Instead, my answer to the titular question is that four principles are needed: high directionality, monochromaticity, high brightness, and stable intensity. Combining the first three of these principles suffices to show, in a quantitative way—involving, indeed, very large dimensionless quantities (up to )—that a laser must be constructed very differently from a light bulb. This quantitative analysis is quite simple, and is easily relatable to ‘coherence’, yet is not to be found in any textbooks on quantum optics to my knowledge. The fourth principle is the most subtle and, perhaps surprisingly, is the only one related to coherent states in the quantum optics sense: it implies that the description in terms of coherent states is the only simple description of a laser beam. Interestingly, this leads to the (not, as it turns out, entirely new) prediction that narrowly filtered laser beams are indistinguishable from similarly filtered thermal beams. I hope that other educators find this material useful; it may contain surprises even for researchers who have been in the field longer than I have.

arXiv:1510.04805•Physica Scripta•Feb 3, 2016•14 citations

Can Light Be Described by Classical Mechanics?

Salvatore Capozzıello, Wladimir-Georges Boskoff

UNITEXT for physics•Jan 1, 2021•0 citations

Response to Wiseman, Rieffel, and Cavalcanti on Bell's 1964 Paper

Edward J. Gillis

Wiseman has claimed that Bell was wrong in stating that determinism was inferred rather than assumed in the summary of the EPR argument in his 1964 paper. The reply of Wiseman and his co-authors to my comment misstates my reasons for disputing this point, and fails to address the central criticism that their claim is based on a seriously flawed formalization of Bell's argument deriving from an unreasonably strong interpretation of the the terms, 'influence', 'affect', and 'depend on'.

arXiv:1608.06312•Aug 22, 2016•0 citations

Light Is Fundamentally a Particle, Not a Wave

Oluwayanmife Olamide

•Aug 30, 2026•0 citations

Reply to “Comment on ‘Nonlocality counterfactuals, and quantum mechanics’ ”

William George Unruh

Stapp [preceding Comment, Phys. Rev. A 60, 2595 (1999)] has argued that my criticism of his nonlocality proof is wrong. I point out that counterfactual arguments are fraught with dangers, and that any such claim should use them in a conservative manner. A reanalysis of his claims continues to lead me to the conclusion that the nonlocality of quantum mechanics remains unproven.

Physical Review A•Sep 1, 1999•2 citations
In his Comment, Elsässer claims that the answer to my titular question is one, not four as I have it. He goes on to give the singular principle that supposedly captures the difference between a light-bulb and a laser: g(2)(τ=0)=1g^{(2)}(τ=0)=1g(2)(τ=0)=1. His claim is unconsidered and wrong, his proposed principle is impossible to apply and, when corrected, redundant (it then becomes one of the four I list already), his arguments are manifestly misdirected. My paper stands as is.
In this comment on "How many principles does it take to change a light bulb ... into a laser?" by Howard M. Wiseman, Physica Scripta 91 (3), 033001 (2016) I am analyzing this extremely nicely formulated question in the framework of the Hanbury-Brown & Twiss experiment thus celebrating also its 60th anniversary. I am giving a straightforward, concise and unique answer on this question, emphasizing that the intensity correlations or the photon statistics make the difference between a light bulb and a laser.
Abstract Quantum optics did not, and could not, flourish without the laser. The present paper is not about the principles of laser construction, still less a history of how the laser was invented. Rather, it addresses the question: what are the fundamental features that distinguish laser light from thermal light? The obvious answer, ‘laser light is coherent’, is, I argue, so vague that it must be put aside at the start, albeit to revisit later. A more specific, quantum theoretic, version, ‘laser light is in a coherent state’, is simply wrong in this context: both laser light and thermal light can equally well be described by coherent states, with amplitudes that vary stochastically in space. Instead, my answer to the titular question is that four principles are needed: high directionality, monochromaticity, high brightness, and stable intensity. Combining the first three of these principles suffices to show, in a quantitative way—involving, indeed, very large dimensionless quantities (up to )—that a laser must be constructed very differently from a light bulb. This quantitative analysis is quite simple, and is easily relatable to ‘coherence’, yet is not to be found in any textbooks on quantum optics to my knowledge. The fourth principle is the most subtle and, perhaps surprisingly, is the only one related to coherent states in the quantum optics sense: it implies that the description in terms of coherent states is the only simple description of a laser beam. Interestingly, this leads to the (not, as it turns out, entirely new) prediction that narrowly filtered laser beams are indistinguishable from similarly filtered thermal beams. I hope that other educators find this material useful; it may contain surprises even for researchers who have been in the field longer than I have.
Wiseman has claimed that Bell was wrong in stating that determinism was inferred rather than assumed in the summary of the EPR argument in his 1964 paper. The reply of Wiseman and his co-authors to my comment misstates my reasons for disputing this point, and fails to address the central criticism that their claim is based on a seriously flawed formalization of Bell's argument deriving from an unreasonably strong interpretation of the the terms, 'influence', 'affect', and 'depend on'.