English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

In standard quantum field theories, the vacuum state is the building block on which the full space of states of the system is based. It is the ground state of the Hamiltonian, and corresponds to "empty space" in the conventional un­ derstanding of space and matter. How­ ever, in quantum theories, vacuum is not completely free from structure. This structure can be understood in terms of "quantum fluctuations" of the fields — fluctuations which are present even when there are no excitations (particles) present in the system. This vacuum ac­ tivity is somewhat analogous to the zero point fluctuations existing in a ma­ terial system at zero temperature, fluc­ tuations which are, for example, respon­ sible for helium remaining fluid even at the lowest possible temperatures. Vacuum fluctuations can give rise to physical effects when the boundary conditions defining the vacuum are changed. Thus, if conducting plates are introduced into the electromagnetic vacuum, the fluctuations of the fields around the plates will be influenced by the plates, and this gives rise to forces between the plates (the well-known Casimir effect). However, even without referring to changing boundary condi­ tions, there is a certain ambiguity in the definition of the vacuum state which comes from the fact that the Hamilto­ nian in relativistic theories is linked to the choice of space-time coordinates. Consequently, even when ordinary Minkowski-space quantum field theories are referred to non-inertial coordinates, the ordinary vacuum is no longer the ground state [1]. If a special choice of uniformly accelerated coordinates is made (Rindler coordinates) a new ground state can be found (Fig. 1). How­ ever, relative to this "accelerated va­ cuum", the ordinary Minkowski vacuum is not empty, but contains excitations (radiation). Fig. 1 — Accelerated Rindler coordinates (τη). Ordinary Minkowski space is hot with respect to the corresponding Hamiltonian, defined in either the " right Rindler wedge" (RRW) or in the "left Rindler wedge" (LRW). A uniformly accelerated point detector, fol­ lowing a path with η fixed is heated due to interactions with vacuum fluctuations.

Hawking Radiation, the Unruh Effect and the Polarization of Electrons