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PreprintarXiv licencearXiv

The finiteness conjecture for equilibria of electric fields generated by point charges of one sign

Abstract

We prove that the electric field generated in three-dimensional space by finitely many point charges of one sign has only finitely many equilibrium points, thereby answering a 1969 question of Morse and Cairns (restated by Eremenko in 2008 and, as a conjecture, by Shapiro in 2015). More generally, for nonzero charges qi of possibly mixed signs at distinct sites ai∈R3, we show that the Coulomb field has at most 2N−4(N−1)(9N2+9N+10) equilibria in the region where S(x):=∑iqi|x−ai|−3 does not vanish. Of course, for charges of one sign, S is nonzero everywhere. The proof rules out curves of equilibria using algebraic geometry and complex analysis on an associated complex curve, and then applies a Bézout count to obtain a quantitative bound. Well-known examples show that, in the mixed-sign case, the Coulomb field can vanish on curves contained in the zero set of S.

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BibTeX
@misc{enciso2026finiteness,
  title = {{The finiteness conjecture for equilibria of electric fields generated by point charges of one sign}},
  author = {Alberto Enciso and Daniel Peralta-Salas},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.03965},
  eprint = {2609.03965},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.03965},
}
RIS
TY  - UNPB
TI  - The finiteness conjecture for equilibria of electric fields generated by point charges of one sign
AU  - Alberto Enciso
AU  - Daniel Peralta-Salas
PY  - 2026
DA  - 2026/09/03
PB  - arXiv
DO  - 10.48550/arxiv.2609.03965
UR  - https://arxiv.org/abs/2609.03965
AB  - We prove that the electric field generated in three-dimensional space by finitely many point charges of one sign has only finitely many equilibrium points, thereby answering a 1969 question of Morse and Cairns (restated by Eremenko in 2008 and, as a conjecture, by Shapiro in 2015). More generally, for nonzero charges q_i of possibly mixed signs at distinct sites a_i∈R^3, we show that the Coulomb field has at most 2^N−4(N−1)(9N^2+9N+10) equilibria in the region where S(x):=∑_iq_i|x−a_i|^−3 does not vanish. Of course, for charges of one sign, S is nonzero everywhere. The proof rules out curves of equilibria using algebraic geometry and complex analysis on an associated complex curve, and then applies a Bézout count to obtain a quantitative bound. Well-known examples show that, in the mixed-sign case, the Coulomb field can vanish on curves contained in the zero set of S.
ER  -