Observational data from the CMB indicates that the observable universe began in a condition of extreme thermodynamic order: despite being hot and dense, it was gravitationally smooth and remarkably homogeneous. This initial low entropy is crucial: it underpins the second law of thermodynamics as applied to cosmology, which is in turn connected to the emergence of complexity and (at least so the story goes) to the arrow of time. Without such a low-entropy start, the universe would have been dominated by gravitational collapse, or would have lacked the thermodynamic gradients necessary for the evolution of stars, planets, and life. However, from the standpoint of statistical mechanics, such a configuration is overwhelmingly improbable. Given the phase space of all possible microstates compatible with the macroscopic constraints of the early universe, high-entropy (disordered) states vastly outnumber low-entropy ones. Yet our universe appears to have emerged from the tiniest corner of that phase space.
Why did the universe begin in such an exceptionally improbable state? It is not required by the laws of physics. Time-symmetric dynamical laws, like those governing GR or the Schrödinger equation, are compatible with universes beginning in high-entropy configurations, so the low-entropy start must be regarded as a contingent feature of our universe, not an inevitable consequence of known laws.
Several responses to this problem have been proposed:
Inflationary cosmology claims that rapid early expansion can smooth out initial irregularities, but as Penrose and others have argued, inflation may presuppose rather than explain low entropy, since the initial conditions required for inflation to begin are themselves highly special – as we shall see shortly.
Anthropic selection within a multiverse framework offers another perspective: perhaps most regions of the multiverse are high-entropy, but observers necessarily find themselves in the rare low-entropy pockets.
Some quantum gravity and causal boundary models attempt to derive the arrow of time and initial entropy from deeper pre-geometric or topological principles. These remain highly conjectural and mathematically undeveloped.
Penrose has emphasised the scale of the problem by estimating the phase-space volume of the observable universe's initial state: the probability of such a state arising by chance is roughly 1 in 10^(10^123), a number so minuscule that it effectively defies explanation.
The universe’s spatial geometry is observed to be extraordinarily close to flat: neither positively curved (closed) nor negatively curved (open), but spatially Euclidean. According to the Friedmann equations, the degree of spatial curvature evolves dynamically over time: any deviation from flatness in the early universe would have rapidly amplified, leading to a universe that is either extremely curved or has already recollapsed. Yet observations from the CMB reveal a universe that remains flat, implying that the total energy density of the universe at early times had to be equal to the critical density to within one part in 1060 or better. This uncanny balance is known as the Flatness Problem. Why did the early universe begin so precariously close to a state of critical density, with no obvious mechanism to enforce such a condition? Inflation provides a solution by stretching the universe toward flatness regardless of initial curvature, but it does so at the cost of introducing its own unexplained dynamics and parameters.
Observations show that widely separated regions of the sky, now tens of billions of light-years apart, exhibit nearly identical temperatures and physical properties in the CMB. This is puzzling because, under standard Big Bang expansion, these regions should have been causally disconnected: no light or energy could have passed between them before recombination, and certainly not before inflation. This uniformity implies that some kind of equilibration must have occurred between these regions very early in cosmic history, but according to the standard model without inflation, there was simply not enough time for such causal contact. This contradiction is known as the Horizon Problem. Inflation solves it by expanding a small, initially causally connected region to encompass the entire observable universe, making it uniform in the process. Unfortunately, this explanatory move leads to yet more problems.
In 2PC, fine tuning is an empirical prediction, so there is nothing in need of explanation. The entire history leading from the Big Bang to the evolution of the first conscious organism (LUCAS), was retroactively selected from the Pythagorean ensemble. See Psychegenesis and the Psychetelic Principle. It follows that the initial flatness and uniformity of the early cosmos can be explained as a selection effect. Only a timeline which started in a state of exceptionally low entropy can lead to the evolution of consciousness. This means we can get rid of inflation [link TBD].