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Boyle-Turok CPT-Symmetric Universe vs Janus Universe

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Time-Symmetric Cosmologies· within family

	Boyle-Turok CPT-Symmetric Universe Speculative	Janus Universe Speculative
Proposed	2021 / 2024	2018
Key figures	Latham Boyle, Neil Turok	Julian Barbour, Tim Koslowski, Flavio Mercati
In one sentence	The universe is CPT-symmetric: for every particle after the Big Bang there is an antiparticle mirror before it, making the cosmos a single self-contained quantum object.	Barbour and collaborators proposed in 2018 that the Big Bang is the central point of two universes, with time flowing forward into ours and backward into a mirror universe that we can never directly observe.
Predictions	Neutrinos are Majorana particles (testable via neutrinoless double beta decay) Exactly three right-handed neutrino species A small negative spatial curvature (Ω_K, the measure of how far space departs from perfectly flat), taking specific quantized values that next-generation CMB experiments could tell apart from a flat universe	A mirror universe exists with reversed time arrow relative to ours [[Entropy]] increases from the Janus point in both directions, never inversely No direct observational signatures from the mirror universe (it's causally disconnected from us) The arrow of time arises naturally from cosmic geometry rather than from special initial conditions
Where it breaks	The mirror sheet is unobservable by construction, raising the question of whether the CPT partner is a physical entity or a mathematical convenience. The mechanism by which the two sheets exchange information or enforce global CPT symmetry at the bang is not yet fully specified in the original formulation.	No direct observational test possible Other approaches to the arrow of time (statistical thermodynamics, decoherence) don't require a mirror universe The mirror universe is undetectable by definition Some critics argue the mathematics is more complicated than necessary
Key unresolved problem	The missing rulebook: the original model never fully spells out what forces the two mirror sheets of spacetime to obey CPT symmetry, a mirror-flip of matter, charge, and time, at the Big Bang when they cannot communicate.	The untestable twin: the mirror universe in the Janus model can never be detected, so there is no experiment that could tell it apart from simpler explanations for why time flows one way.
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Boyle-Turok CPT-Symmetric Universe

2021 / 2024 · Speculative

Janus Universe

2018 · Speculative

Proposed

2021 / 2024

2018

Key figures

Latham Boyle, Neil Turok

Julian Barbour, Tim Koslowski, Flavio Mercati

In one sentence

The universe is CPT-symmetric: for every particle after the Big Bang there is an antiparticle mirror before it, making the cosmos a single self-contained quantum object.

Barbour and collaborators proposed in 2018 that the Big Bang is the central point of two universes, with time flowing forward into ours and backward into a mirror universe that we can never directly observe.

Predictions

Neutrinos are Majorana particles (testable via neutrinoless double beta decay)
Exactly three right-handed neutrino species
A small negative spatial curvature (Ω_K, the measure of how far space departs from perfectly flat), taking specific quantized values that next-generation CMB experiments could tell apart from a flat universe

A mirror universe exists with reversed time arrow relative to ours
[[Entropy]] increases from the Janus point in both directions, never inversely
No direct observational signatures from the mirror universe (it's causally disconnected from us)
The arrow of time arises naturally from cosmic geometry rather than from special initial conditions

Where it breaks

The mirror sheet is unobservable by construction, raising the question of whether the CPT partner is a physical entity or a mathematical convenience.
The mechanism by which the two sheets exchange information or enforce global CPT symmetry at the bang is not yet fully specified in the original formulation.

No direct observational test possible
Other approaches to the arrow of time (statistical thermodynamics, decoherence) don't require a mirror universe
The mirror universe is undetectable by definition
Some critics argue the mathematics is more complicated than necessary

Key unresolved problem

The missing rulebook: the original model never fully spells out what forces the two mirror sheets of spacetime to obey CPT symmetry, a mirror-flip of matter, charge, and time, at the Big Bang when they cannot communicate.

The untestable twin: the mirror universe in the Janus model can never be detected, so there is no experiment that could tell it apart from simpler explanations for why time flows one way.

Reader vote

No votes yet