Cited by 226Relativity and Gravitational TheoryCosmology and Gravitation TheoriesAdvanced Differential Geometry Research

The DOI matches its Crossref record; 237 of the 246 references it cites were found in a registry or an index; none of the 158 sources its claims cite is checked for support yet.

A Primer on Energy Conditions

Open access
Curiel, Erik·2017·Einstein Studies

Abstract

An energy condition, in the context of a wide class of spacetime theories (including general relativity), is, crudely speaking, a relation one demands the stress-energy tensor of matter satisfy in order to try to capture the idea that "energy should be positive". The remarkable fact I will discuss in this paper is that such simple, general, almost trivial seeming propositions have profound and far-reaching import for our understanding of the structure of relativistic spacetimes. It is therefore especially surprising when one also learns that we have no clear understanding of the nature of these conditions, what theoretical status they have with respect to fundamental physics, what epistemic status they may have, when we should and should not expect them to be satisfied, and even in many cases how they and their consequences should be interpreted physically. Or so I shall argue, by a detailed analysis of the technical and conceptual character of all the standard conditions used in physics today, including examination of their consequences and the circumstances in which they are believed to be violated.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

This paper surveys the standard energy conditions in general relativity—their formulations, consequences, violations, and interpretive status—arguing that these simple conditions have profound import for spacetime structure but lack a clear theoretical, epistemic, and physical understanding. It concludes that we face a dilemma: either accept the exotic physics implied by widespread violations or reconstruct fundamental theory to rule them out.

Key findings

  • Energy conditions such as NEC, WEC, SEC, DEC, SDEC, and averaged versions (ANEC, AWEC, ASEC) are generic constraints on stress-energy or Ricci curvature that support deep results, yet the paper argues they cannot be derived from other fundamental postulates and are imposed by fiat or checked for particular matter fields.
  • The consequences list is dominated by singularity and black-hole theorems, “at 10 each”; the NEC supports results including Penrose’s singularity theorem and Hawking’s Area Theorem, while the SEC mainly supports singularity theorems and the DEC is used in black-hole topology/Killing-structure results and positive-mass theorems.
  • Violations are widespread: cosmological evidence indicates the SEC must have been violated in the relatively recent past (redshift \(z < 7\)), and if accelerated expansion/dark energy is correct, the SEC is currently violated; inflation necessarily violates the SEC, while a negative cosmological constant does not violate the NEC.
  • Interpretive problems are pervasive: geometric, physical, and effective formulations are logically equivalent under the Einstein equation but have uneven clarity; impressionist conditions lack compelling interpretations or motivations; no standard energy conditions based on the Weyl or Bel-Robinson tensors exist; and the historical Trace Energy Condition was once universally assumed but is now believed violated at densities above 10 times atomic nuclei, where \(p = \rho\).

Methods

  • Conceptual, technical, and philosophical review of energy conditions in classical general relativity, with no new empirical data or experiments.
  • Surveys formulations (geometric, physical, effective; pointilliste vs. impressionist), catalogues consequences and known violations from the literature, and includes appendices on a failed Raychaudhuri derivation, recent conditions (FEC, DETEC, TOSEC), average radial acceleration, temporal reversibility, and constraints on spacetime theories.
  • Main analysis compares interpretations and logical relations among conditions, classifies consequences and violations, and discusses implications for the foundations of spacetime theories.

Limitations

  • The paper states it does not provide a decisive answer; it aims only to survey issues, clarify questions, propose conjectures, and open the field, so those hoping for a decisive answer “will leave disappointed.”
  • It states there are no compelling geometrical, physical, or effective interpretations or motivations for the impressionist energy conditions, and that many arguments about necessity, measure-zero claims, and foundational status are conjectural or hand-waving.
  • Evident from the text: there has been no direct experimental observation of a violation of any standard energy condition; evidence is indirect, many violation entries are marked “possibly” or “necessarily” and some are “my calculation,” and no general proof establishes when energy conditions must hold.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1007/978-1-4939-3210-8_3

Cites

237 of 237 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Verification

Claims the paper makes

138 Own interpretation · 108 Not checked yet · 52 No basis given · 10 Own result

Verify all 158 references — free account
  • Probably not a substantial claim. 94
  • It may state two separate claims as one. 55
  • The quote only partly states this claim. 2
136 of 136
  • The authors state this as an assumption.

    The Einstein field equation holds when relating geometric, physical, and effective formulations of energy conditions.

    “if the Einstein field equation is assumed to hold”
    “under the assumption that the Einstein field equation holds”
  • The authors state this as an assumption.

    Matter is not too exotic, for the effective formulation to be physically equivalent to the geometric and physical formulations.

    “and matter is not too exotic”
  • The paper relies on this without support.

    The conditions analyzed are all the standard energy conditions used in physics today.

    “all the standard conditions used in physics today”
  • The authors state this as an assumption.

    The discussion is restricted to the context of general relativity until § 5, unless explicitly stated otherwise.

    “From hereon until § 5, unless explicitly stated otherwise, the discussion should be understood to be restricted to the context of general relativity.”
  • The authors state this as an assumption.

    The Einstein field equation is assumed when comparing the geometric, physical, and effective forms of the energy conditions.

    “modulo the assumption of the Einstein field equation, logically equivalent.”
  • The authors state this as an assumption.

    The effective fluid described by the stress-energy tensor has a well behaved barotropic equation of state, i.e., a fixed invertible relation ρ(p) expressing ρ as a function of the single isotropic pressure p.

    “Assuming a well behaved barotropic equation of state for the effective fluid described by the stress-energy tensor, i . e ., a fixed relation ρ ( p ) expressing ρ as an invertible function of the single isotropic pressure p”
  • The authors state this as an assumption.

    For the effective form, the stress-energy tensor is of Hawking-Ellis type i and is diagonal in the fixed 1+3 orthonormal frame.

    “the stress-energy tensor (assumed, recall, for the effective form, to be of Hawking-Ellis type i ) is diagonal.”
  • The authors state this as an assumption.

    Gravity is everywhere attractive, interpreted as meaning that congruences of timelike geodesics with vanishing twist should always converge.

    “if we assume that 'gravity is everywhere attractive', and we interpret this to mean that congruences of timelike geodesics which have vanishing twist should always converge”
  • The paper relies on this without support.

    The stationary Killing field is spacelike in the ergosphere, so no observer can have its orbits as worldline.

    “Because the stationary Killing field is spacelike in the ergosphere, no observer can have its orbits as worldine.”
  • The paper relies on this without support.

    The energy defined by a stationary Killing field is observer-independent and obeys both a local and an integral conservation law.

    “The energy defined by a stationary Killing field, however, is observer-independent and so has prima facie physical significance, even more so given that it obeys both a local and an integral conservation law.”
  • The paper relies on this without support.

    Stress-energy tensors not of Hawking-Ellis type i are generally considered unphysical.

    “Since stress-energy tensors not of type i are generally considered 'unphysical'”
  • The authors state this as an assumption.

    Any physically reasonable spacetime theory should 'look enough like' general relativity so as to make all the elements of the list make sense in its context.

    “In constructing the list, I have been guided by the tenet that any physically reasonable spacetime theory should 'look enough like' general relativity so as to make all the elements of the list make sense in its context.”
  • The authors state this as an assumption.

    The list of structures and its ordering by fundamentality is of interest for the sake of argument.

    “Now, granting the interest of the list for the sake of argument, where, if at all, should one place energy conditions on it?”
  • The authors state this as an assumption.

    No global feature of the geometry, as constrained by a theory's field equations, should depend on anything but purely qualitative properties of stress-energy; a fortiori, no global feature of the geometry should depend on the species of matter present, so long as that species manifests a relevant qualitative property.

    “In particular, no global feature of the geometry, as constrained by a theory's field equations, should depend on anything but purely qualitative properties of stress-energy; a fortiori , no global feature of the geometry should depend on the species of matter present, so long as that species manifests a relevant qualitative property.”
  • The paper relies on this without support.

    Conformal transformations preserve causal structure.

    “since conformal transformations preserve causal structure, the transformed spacetime is still globally hyperbolic.”
15 of 15

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

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Citations

Cites

Show all 246 references

Research works printed but not linked: 3

  1. Harrison, B., M. Wakano, and J. Wheeler (1957). Report. In La Structure et l’Evolution de l’Univers, Onzieme Conseil de Physique Solvay. Brussels: Editions Stoops.
  2. Penrose, R. (1979). Singularities and time-asymmetry. See [108], pp. 581–638.
  3. ’t Hooft, G. (1988). On the quantization of space and time. In M. Markov, V. Berezin, and V. Frolov (Eds.), Quantum Gravity, pp. 551–567. Singapore: World Scientific Press.

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Metadata

Authors
Curiel, E.
Affiliations
Harvard University (US)
Corresponding author
Curiel, Erik
Venue
Einstein Studies
Published
2017
Pages
43-104
ISSN
  • 2381-5833 (ISSN-L)
  • 2381-5841
OpenAlex
W2133796620
Cited by
226
References
246
Citations by year
2026: 25 · 2025: 26 · 2024: 25 · 2023: 32 · 2022: 26 · 2021: 23 · 2020: 14 · 2019: 13 · 2018: 20 · 2017: 8
FWCI
62.39
Type
book chapter
Language
de
Open access
Locations
  • Einstein studies (publishedVersion)
  • PhilSci-Archive (University of Pittsburgh) (acceptedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • Open access LMU (Ludwid Maxmilian's Universitat Munchen) (submittedVersion)
  • arXiv (Cornell University)
Topics
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Relativity and Gravitational Theory
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Cosmology and Gravitation Theories
  • Physical Sciences › Mathematics › Geometry and Topology › Advanced Differential Geometry Research
Keywords
energy conditions, energy-momentum tensor, positive energy, general relativity, spacetime structure, epistemology of physics

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