= Hannes Alfvén
{c}
{tag=Physicist}
{wiki}
= Hannes Olof Gösta Alfvén
{c}
{synonym}
= H. Alfvén
{c}
{synonym}
<Hannes Alfvén> predicted a wave coupling the <motion> of an electrically conducting <fluid> to a background <magnetic field>. In an <Alfvén wave>, bent magnetic-field lines provide a restoring effect while the material's inertia resists the displacement.
Linearizing ideal <magnetohydrodynamics> for a transverse disturbance along a uniform field gives the propagation <speed> $v_A=B_0/\sqrt{\mu_0\rho}$, with background field strength $B_0$, <vacuum permeability> $\mu_0$ and <mass density> $\rho$. A stronger field increases the restoring effect; greater material inertia slows propagation. The idea connects <plasma> dynamics in the laboratory with the behavior of astrophysical magnetic structures.<Existence of Electromagnetic-Hydrodynamic Waves by Hannes Olof Gösta Alfvén>[1942 paper, combined fluid–magnetic disturbance and propagation-speed relation]{ref}
\Image[https://commons.wikimedia.org/wiki/Special:Redirect/file/YoungAlfven.jpg?width=260]
{title=Portrait of <Hannes Alfvén>}
{description=Unknown author. Public domain in Sweden (PD-Sweden, as stated on Commons). https://commons.wikimedia.org/wiki/File:YoungAlfven.jpg[Source usage terms], via Wikimedia Commons.}
{source=https://commons.wikimedia.org/wiki/File:YoungAlfven.jpg}
{width=260}
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