Editing Cyclic model (section)

== The Baum–Frampton model ==
This more recent cyclic model of 2007 assumes an exotic form of dark energy called [[phantom energy]],<ref name="Baum, Frampton 2007" /><ref name="Baum, Frampton 2006">
{{cite journal |author=Baum |first1=L. |last2=Frampton |first2=P. H. |date=2007 |title=Turnaround in Cyclic Cosmology |journal=Physical Review Letters |volume=98 |issue=7 |page=071301 |arxiv=hep-th/0610213 |bibcode=2007PhRvL..98g1301B |doi=10.1103/PhysRevLett.98.071301 |pmid=17359014 |s2cid=17698158}}</ref> which possesses negative kinetic energy and would usually cause the universe to end in a [[Big Rip]]. This condition is achieved if the universe is dominated by dark energy with a cosmological [[Equation of state (cosmology)|equation of state]] parameter <math>w</math> satisfying the condition <math>w\equiv \frac{p}{\rho} <-1</math>, for [[energy density]] <math>{\rho}</math> and [[pressure]] p. By contrast, Steinhardt–Turok assume <math>w {\geq}-1</math>. In the Baum–Frampton model, a septillionth (or less) <!-- Use 10<sup>−X</sup> notation please-->of a second (i.e. 10<sup>−24</sup> seconds or less) before the would-be Big Rip, a turnaround occurs and only one causal patch is retained as our universe. The generic patch contains no [[quark]], [[lepton]] or [[force carrier]]; only [[dark energy]] – and its entropy thereby vanishes. The [[adiabatic process]] of contraction of this much smaller universe takes place with constant vanishing entropy and with no matter including no [[black holes]] which disintegrated before turnaround.

The idea that the universe "comes back empty" is a central new idea of this cyclic model, and avoids many difficulties confronting matter in a contracting phase such as excessive [[structure formation]], proliferation and expansion of [[black holes]], as well as going through [[phase transition]]s such as those of QCD and electroweak symmetry restoration. Any of these would tend strongly to produce an unwanted premature bounce, simply to avoid violation of the [[second law of thermodynamics]]. The condition of <math>w <-1</math> may be logically inevitable in a truly infinitely cyclic cosmology because of the entropy problem. Nevertheless, many technical back up calculations are necessary to confirm consistency of the approach. Although the model borrows ideas from [[string theory]], it is not necessarily committed to strings, or to [[higher dimensions]], yet such speculative devices may provide the most expeditious methods to investigate the [[internal consistency]]. The value of <math>w</math> in the Baum–Frampton model can be made arbitrarily close to, but must be less than, −1.