Ideas resembling dark energy appeared long before 1998, in both scientific speculation and science fiction, though the term dark energy itself didn’t exist yet.

Here’s a concise timeline of dark energy–like ideas before 1998, including both scientific and sci-fi sources:

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⚛️ Scientific & Philosophical Precursors

Year	Thinker / Source	Idea Similar to Dark Energy
1917	Albert Einstein	Introduced the cosmological constant (Λ) — a repulsive energy in space that counteracts gravity to keep the universe static.
1920s–1930s	Arthur Eddington	Suggested space itself might possess an intrinsic energy pressure — a “cosmic repulsion.”
1965–1970s	Various cosmologists (e.g. Zel’dovich)	Discussed “vacuum energy” and quantum fluctuations of empty space, later interpreted as a cosmological constant.
1980–1981	Alan Guth’s Inflation Theory	Proposed that a huge burst of expansion was driven by “false vacuum energy,” a temporary, high-density state of space — conceptually very close to dark energy.
Early 1990s	Cosmologists such as Turner, Peebles, Ratra	Began proposing “quintessence,” a dynamic field that could cause acceleration, decades before it was confirmed observationally.

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🚀 Science Fiction & Cultural Precursors

Year	Author / Work	Description
1918 – Olaf Stapledon, Last and First Men	Imagines cosmic forces that drive expansion and contraction of the universe — a metaphysical energy underlying space.
1937 – Olaf Stapledon, Star Maker	Describes “space as alive with creative energy” expanding the cosmos — remarkably similar in tone to later dark-energy ideas.
1950 – Isaac Asimov, Pebble in the Sky	Mentions cosmological radiation pressures and universal expansion beyond human comprehension — hints of an unknown energy.
1963 – Arthur C. Clarke, The Nine Billion Names of God	The universe accelerates toward an end triggered by a divine or cosmic force — analogous to a repulsive universal energy.
1970s – Various Star Trek episodes & novels	Refer to “negative energy” or “subspace fields” permeating the universe; although fictional, they echo the idea of invisible energy shaping spacetime.
1980s – Larry Niven & Jerry Pournelle	Works like The Mote in God’s Eye and Footfall invoke vacuum fluctuations and zero-point energy — early sci-fi treatments of “energy in the void.”
Early 1990s – Comics & speculative fiction	“Dark energy” occasionally used as a fictional term for limitless cosmic power, before it became scientific vocabulary.

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🧩 Summary Thought

Before 1998, scientists talked about vacuum energy or a cosmological constant, while sci-fi writers imagined mysterious, omnipresent cosmic forces.
When astronomers found the accelerating expansion in 1998, they merged those strands — the vacuum energy of theory and the cosmic repulsion of imagination — under the name dark energy.