The multiverse hypothesis arises naturally from established cosmological theories like string theory and eternal inflation. Once viewed as speculative, it has evolved into a core prediction embraced by leading scientists. Yet if our universe shares space with countless others in an expanding multiverse, why do they never collide?
The concept of a multiverse dates back to ancient Greek philosopher Anaximander and has persisted through centuries of scientific thought. It gained clarity with quantum mechanics and efforts to resolve the measurement problem.
In 1950, physicist Hugh Everett offered a groundbreaking solution: unobserved quantum states don't vanish but branch into parallel universes. These 'sub-universes' emerge during measurement and then become inaccessible. Known as Everett's Many-Worlds Interpretation, this idea laid foundational groundwork for modern multiverse theories.
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Scientists say the multiverse could be teeming with life, but also problematic
In 1982, Russian-American physicist Andrei Linde introduced eternal inflation amid research on cosmic inflation. This posits inflation halting in some regions while continuing indefinitely elsewhere, forming 'bubble universes' where space curves into spheres.
In 1983, Paul Steinhardt refined Linde's idea, demonstrating how halted inflation converts energy into matter and radiation. Alexander Vilenkin bolstered these findings, and by 1986, Linde formalized eternal inflation—a model now integral to standard cosmology.
Inflation resolves key puzzles: the universe's homogeneity and isotropy (horizon problem) and its spatial flatness (flatness problem).
The model predicts a specific power spectrum for primordial density fluctuations, a post-Big Bang critical temperature, super-horizon fluctuations, and gravitational wave signatures—all but the last confirmed by observations.
Inflation marked an early epoch where spacetime's inherent energy drove exponential expansion, rapidly stretching space in all directions.
On tiny scales, non-flat regions with matter became indistinguishable from flat ones as particles were driven apart, never to reconvene.
After fractions of a second, inflation ceases, converting spacetime energy into matter and radiation. Picture it as a ball atop a hill: it rolls as long as quantum fields sustain the peak.
For inflation to end, regardless of the driving quantum field, it must… (continued on next page)
