These quotes are from Albert Einstein’s lecture at the University of Leyden on May 5, 1920. Titled “Ether and the Theory of Relativity,” he argued that General Relativity actually requires an “ether” or medium for spacetime, redefining it not as empty space but as a physical entity with properties (spacetime curvature), contrasting with his earlier Special Relativity work that discarded the old, undetectable luminiferous ether. He suggested that denying the ether meant assuming empty space had no physical qualities, which conflicted with the mechanics described by relativity, implying space itself carries physical properties, like gravitational potentials affecting light speed.
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Key takeaways
- Unified Forces: The drive to unify all forces (gravity, electromagnetism) led to needing a physical substrate for these interactions, which Einstein called the ether.
- Redefinition of Ether: This wasn’t the old, static “luminiferous ether” for light waves, but proposed a new, dynamic “aether” that is interwoven with spacetime and influenced by matter. It is the physical reality of spacetime itself, which can be curved and influenced by mass/energy.
- Space Has Properties: Denying the ether meant denying physical properties to space, but relativity showed space does have structure (spacetime) that dictates how things move and how fast light travels.
- “Space without ether is unthinkable”: Einstein’s famous concluding statement from that address emphasized that the geometry of spacetime, described by General Relativity, necessitates a physical medium or framework.
Quotes
- Space-Time as the New Aether: The “ether of the general theory of relativity” is essentially the curved spacetime fabric, where its state at every point is determined by matter and neighboring points.
- “Space without ether is unthinkable”: This famous quote highlights that space itself has structure and physical reality, not just empty void.
Context
- Inaugural Lecture: Einstein delivered this as his inaugural lecture at Leiden, marking his special professorship there.
- Friendship with Ehrenfest: His close ties with physicist Paul Ehrenfest facilitated his regular visits and lectures in Leiden.
This lecture was crucial in shifting the understanding of the ether from a physical medium for light to a fundamental aspect of the curved fabric of spacetime itself, a continuum described by relativity, as noted in Physics Today, Volume 59, Number 4.
