### Abstract

We study two inverse problems on a globally hyperbolic Lorentzian manifold (M, g). The problems are:

Passive observations in spacetime: consider observations in an open set . The light observation set corresponding to a point source at is the intersection of V and the light-cone emanating from the point q.

Let be an unknown open, relatively compact set. We show that under natural causality conditions, the family of light observation sets corresponding to point sources at points determine uniquely the conformal type of W.

Active measurements in spacetime: we develop a new method for inverse problems for non-linear hyperbolic equations that utilizes the non-linearity as a tool. This enables us to solve inverse problems for non-linear equations for which the corresponding problems for linear equations are still unsolved. To illustrate this method, we solve an inverse problem for semilinear wave equations with quadratic non-linearities. We assume that we are given the neighborhood V of the time-like path and the source-to-solution operator that maps the source supported on V to the restriction of the solution of the wave equation to V. When M is 4-dimensional, we show that these data determine the topological, differentiable, and conformal structures of the spacetime in the maximal set where waves can propagate from and return back to mu.

Original language | English |
---|---|

Journal | Inventiones Mathematicae |

Volume | 212 |

Issue number | 3 |

Pages (from-to) | 781-857 |

Number of pages | 77 |

ISSN | 0020-9910 |

DOIs | |

Publication status | Published - Jun 2018 |

MoE publication type | A1 Journal article-refereed |

### Fields of Science

- CUSP
- ELASTOGRAPHY
- OPERATORS
- PROGRESSING WAVES
- SCATTERING
- SEMILINEAR WAVE-EQUATIONS
- SINGULAR SYMBOLS
- SPACETIMES
- TIME
- UNIQUE CONTINUATION
- 111 Mathematics
- 112 Statistics and probability

### Cite this

}

*Inventiones Mathematicae*, vol. 212, no. 3, pp. 781-857. https://doi.org/10.1007/s00222-017-0780-y

**Inverse problems for Lorentzian manifolds and non-linear hyperbolic equations.** / Kurylev, Yaroslav; Lassas, Matti; Uhlmann, Gunther.

Research output: Contribution to journal › Article › Scientific › peer-review

TY - JOUR

T1 - Inverse problems for Lorentzian manifolds and non-linear hyperbolic equations

AU - Kurylev, Yaroslav

AU - Lassas, Matti

AU - Uhlmann, Gunther

PY - 2018/6

Y1 - 2018/6

N2 - We study two inverse problems on a globally hyperbolic Lorentzian manifold (M, g). The problems are:Passive observations in spacetime: consider observations in an open set . The light observation set corresponding to a point source at is the intersection of V and the light-cone emanating from the point q.Let be an unknown open, relatively compact set. We show that under natural causality conditions, the family of light observation sets corresponding to point sources at points determine uniquely the conformal type of W.Active measurements in spacetime: we develop a new method for inverse problems for non-linear hyperbolic equations that utilizes the non-linearity as a tool. This enables us to solve inverse problems for non-linear equations for which the corresponding problems for linear equations are still unsolved. To illustrate this method, we solve an inverse problem for semilinear wave equations with quadratic non-linearities. We assume that we are given the neighborhood V of the time-like path and the source-to-solution operator that maps the source supported on V to the restriction of the solution of the wave equation to V. When M is 4-dimensional, we show that these data determine the topological, differentiable, and conformal structures of the spacetime in the maximal set where waves can propagate from and return back to mu.

AB - We study two inverse problems on a globally hyperbolic Lorentzian manifold (M, g). The problems are:Passive observations in spacetime: consider observations in an open set . The light observation set corresponding to a point source at is the intersection of V and the light-cone emanating from the point q.Let be an unknown open, relatively compact set. We show that under natural causality conditions, the family of light observation sets corresponding to point sources at points determine uniquely the conformal type of W.Active measurements in spacetime: we develop a new method for inverse problems for non-linear hyperbolic equations that utilizes the non-linearity as a tool. This enables us to solve inverse problems for non-linear equations for which the corresponding problems for linear equations are still unsolved. To illustrate this method, we solve an inverse problem for semilinear wave equations with quadratic non-linearities. We assume that we are given the neighborhood V of the time-like path and the source-to-solution operator that maps the source supported on V to the restriction of the solution of the wave equation to V. When M is 4-dimensional, we show that these data determine the topological, differentiable, and conformal structures of the spacetime in the maximal set where waves can propagate from and return back to mu.

KW - CUSP

KW - ELASTOGRAPHY

KW - OPERATORS

KW - PROGRESSING WAVES

KW - SCATTERING

KW - SEMILINEAR WAVE-EQUATIONS

KW - SINGULAR SYMBOLS

KW - SPACETIMES

KW - TIME

KW - UNIQUE CONTINUATION

KW - 111 Mathematics

KW - 112 Statistics and probability

U2 - 10.1007/s00222-017-0780-y

DO - 10.1007/s00222-017-0780-y

M3 - Article

VL - 212

SP - 781

EP - 857

JO - Inventiones Mathematicae

JF - Inventiones Mathematicae

SN - 0020-9910

IS - 3

ER -