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Electrostatic Boundary Conditions01:16

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Consider an external electric field propagating through a homogeneous medium. When the electric field crosses the surface boundary of the medium, it undergoes a discontinuity. The electric field can be resolved into normal and tangential components. The amount by which the field changes at any boundary is given by the difference between the field components above and below the surface boundary.
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Calculating areas within irregular boundaries, such as along rivers or curved roads, is crucial in various fields, including surveying, engineering, and environmental management. Surveyors often begin by creating a traverse, a connected series of straight lines approximating the area's boundary. The coordinates of each traverse point are essential for calculating the enclosed area. The double meridian distance formula is a widely used technique for this purpose. This method utilizes the...
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Related Experiment Video

Updated: Jan 23, 2026

Exploring the Effects of Atmospheric Forcings on Evaporation: Experimental Integration of the Atmospheric Boundary Layer and Shallow Subsurface
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No-Boundary Proposal as a Path Integral with Robin Boundary Conditions.

Alice Di Tucci1, Jean-Luc Lehners1

  • 1Max-Planck-Institute for Gravitational Physics (Albert-Einstein-Institute), 14476 Potsdam, Germany.

Physical Review Letters
|June 8, 2019
PubMed
Summary
This summary is machine-generated.

This study resolves the puzzle of the Hartle-Hawking no-boundary proposal using specific Robin boundary conditions in quantum gravity. This approach ensures convergent path integrals and stable universe geometries, overcoming previous instabilities.

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Area of Science:

  • Cosmology and Theoretical Physics
  • Quantum Gravity
  • Mathematical Physics

Background:

  • The Hartle-Hawking no-boundary proposal offers a quantum mechanical description of the universe's origin.
  • Previous attempts to formulate this proposal as a gravitational path integral faced challenges, particularly an unstable saddle point geometry.
  • This instability was linked to summing over universes starting from zero size.

Purpose of the Study:

  • To resolve the long-standing puzzle of realizing the Hartle-Hawking no-boundary proposal as a consistent gravitational path integral.
  • To identify a method that overcomes the instability issue associated with zero-size initial universes.
  • To explore the implications of alternative boundary conditions for quantum cosmology.

Main Methods:

  • Investigated gravitational path integrals within the context of gravity featuring a positive cosmological constant.
  • Introduced and analyzed a specific family of Robin boundary conditions.
  • Examined the convergence properties and saddle point geometries of these path integrals.

Main Results:

  • Demonstrated that specific Robin boundary conditions lead to manifestly convergent path integrals.
  • Showed that these convergent path integrals are approximated by stable Hartle-Hawking saddle point geometries.
  • Identified that the off-shell geometries under these conditions do not initiate from a zero size.

Conclusions:

  • The use of Robin boundary conditions provides a consistent framework for the Hartle-Hawking no-boundary proposal in quantum gravity with a positive cosmological constant.
  • This approach circumvents the previously identified instability by modifying the initial conditions of the universe.
  • Robin boundary conditions can be interpreted as representing an initial state with Euclidean momentum, distributing quantum uncertainty between initial size and momentum.