Cyclic model (cosmology)
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| Cyclic model (cosmology) | |
|---|---|
| Name | Cyclic model (cosmology) |
| Field | Cosmology |
| Introduced | 20th century |
| Proponents | Paul Steinhardt; Neil Turok; Richard Tolman; Roger Penrose |
| Related | Big Bounce; Ekpyrotic universe; Inflation |
Cyclic model (cosmology) The cyclic model proposes a cosmological scenario in which the Universe undergoes repeated epochs of expansion and contraction, offering an alternative to the Big Bang singularity and standard inflation paradigms. It connects ideas and contributors spanning Albert Einstein, Alexander Friedmann, Georges Lemaître, and modern teams led by Paul Steinhardt and Neil Turok, situating itself amid debates involving Roger Penrose and proponents of the Lambda-CDM model.
Introduction
The cyclic model frames cosmic history as a sequence of cycles that replace a unique origin event, contrasting with the singular beginning implied by classical General relativity solutions such as those by Stephen Hawking and George F. R. Ellis. It draws on concepts from Thermodynamics debates associated with Richard Tolman and mathematical structures from Friedmann equations used in Alexander Friedmann’s work, while engaging modern quantum proposals from Paul Dirac and Richard Feynman. As an approach, it interacts with frameworks developed in String theory, M-theory, and proposals by Edward Witten and Juan Maldacena.
Historical development
Early antecedents appear in the cyclic speculations of Richard Tolman and the oscillatory cosmologies of Friedrich Hoyle and associates during the mid-20th century, responding to observational programs led by Edwin Hubble and theoretical critiques by Arthur Eddington. Renewed attention followed advances in String theory in the 1990s when researchers including Paul Steinhardt, Neil Turok, and contributors from Princeton University and Cambridge University formulated the Ekpyrotic scenario alongside debates involving Roger Penrose’s conformal proposals. Later developments engaged mathematical tools from Quantum field theory debates involving Gerard 't Hooft and Alexander Polyakov, and numeric studies influenced by work at institutions such as CERN and Perimeter Institute.
Theoretical framework
The model typically employs effective field descriptions adapted from General relativity and modifications inspired by String theory and Brane cosmology proposed in contexts by Lisa Randall and Raman Sundrum. Central equations generalize the Friedmann equations and incorporate scalar fields analogous to those in inflation models championed by Alan Guth, Andrei Linde, and Alexei Starobinsky, but arranged to produce a slow contraction (ekpyrosis) followed by a bounce, invoking quantum gravity proposals associated with Loop quantum gravity advocates like Carlo Rovelli or holographic principles advanced by Juan Maldacena. Thermodynamic consistency references Richard Tolman’s entropy analyses and engages quantum vacuum energy discussions traceable to Wolfgang Pauli and Steven Weinberg.
Variants and related models
Prominent variants include the ekpyrotic and cyclic scenarios by Paul Steinhardt and Neil Turok, the conformal cyclic cosmology advocated by Roger Penrose, and bounce cosmologies emerging from Loop quantum cosmology research led by Martin Bojowald. Related alternatives encompass the Big Bounce proposals influenced by Abhay Ashtekar, chaotic inflation variants from Andrei Linde, and multiverse frameworks discussed by Max Tegmark and Alexander Vilenkin. Each variant links to different treatments of brane collisions in M-theory contexts advocated by Edward Witten and to holographic entropy bounds developed following ideas by Gerard 't Hooft and Leonard Susskind.
Observational predictions and tests
Cyclic proposals make observational claims about primordial perturbation spectra testable against data from Wilkinson Microwave Anisotropy Probe teams and the Planck collaboration, competing with predictions from Alan Guth–style inflation. Signatures include specific non-Gaussianities, spectral tilt variations, and suppressed primordial gravitational wave amplitudes compared to expectations from models by Andrei Linde and Alexei Starobinsky; these are probed by experiments at BICEP and future probes like the LiteBIRD mission. Cosmic microwave background anomalies discussed by Roger Penrose and large-scale structure surveys conducted by teams at Sloan Digital Sky Survey and Dark Energy Survey provide additional constraints, while high-energy tests at CERN and precision studies in Observatoire de Paris–affiliated collaborations inform related particle-physics assumptions.
Challenges and criticisms
Critics including proponents of the Lambda-CDM model and defenders of standard inflation led by Alan Guth and Andrei Linde emphasize unresolved issues: entropy buildup noted by Richard Tolman, the mechanism of a non-singular bounce in quantum gravity frameworks debated by Carlo Rovelli and Abhay Ashtekar, and the generation of nearly scale-invariant perturbations without excessive fine-tuning contested by Paul Steinhardt’s opponents. Philosophical and mathematical critiques arise in exchanges with Roger Penrose’s conformal arguments and in technical disputes involving renormalization techniques associated with Gerard 't Hooft and the consistency of embedding in M-theory contexts discussed by Edward Witten.
Implications for cosmology and physics
If realized, cyclic scenarios would reshape understanding across topics linked to Big Bang cosmology, constrain models for dark energy explored by teams at Supernova Cosmology Project and High-Z Supernova Search Team, and influence quantum gravity research at Perimeter Institute and Institute for Advanced Study. They offer alternative narratives for initial conditions debated by Stephen Hawking and James Hartle and feed into broader theoretical programs involving String theory and holography promoted by Juan Maldacena and Leonard Susskind. The debate continues to stimulate observational efforts by Planck (spacecraft), BICEP, and survey consortia such as Sloan Digital Sky Survey and theoretical work at institutions like Princeton University and Cambridge University.