Once Before Time - Martin Bojowald [136]
There are still more scenarios in loop quantum cosmology, but they do not crucially differ from what is sketched here. Common to all of them is the cyclic nature of the universe; linear forms such as appear in older versions of quantum cosmology do not come into play. Loop quantum cosmology always provides time before the big bang, but not a starting point of the universe a finite time ago.6 It seems clearly partial to the latter view in the question of whether physical principles favor a linear or a cyclic worldview. But it also brings in an entirely new feature, something to be taken into account for further detailed formulations of worldviews: cosmic forgetfulness.
37. Illustration of a universe starting with continuously growing cycles and eventually exploding in an inflationary phase. The vertical position corresponds to the expansion rate (upper half) or contraction rate (lower half), the horizontal position to the size of the universe. Contour lines encode the probability of finding a state of a given change rate and spatial size in the history of the universe. The starting point lies within the enclosed oval region, whence the cycles describe a spiral growing outward. The final inflationary phase is realized by the ribbon protruding to the right.
For many quantities, such as the total size of the universe or its expansion and contraction rate, the universe follows a deterministic process, a unique history free of singularities. But if we ask whether, in principle, all properties of the preceding cycle can be determined from observations, we will be disappointed: There are properties, such as the size of quantum fluctuations, that cannot practically be reconstructed from observations conducted in the next cycle. Herein lies the new element that surprisingly arises in loop quantum cosmology. Thus the picture is not purely cyclic, but contains a linear component; for the nonreconstructible properties acquire, as it were, a fresh start after every bang, even if other properties can traverse it in full remembrance. Mathematically derived details of quantum cosmology provide new principles, in this case a mixture of cyclic and linear worldviews, that in spite of all fantasy have not surfaced before. The further buildup of these pictures, especially with regard to possible observations, is currently in a phase of rapid progress.
She now called herself Quman7—with no small touch of unaccustomed irony, but maybe also in a whim of spontaneous gratitude. She rooted her new name in history, relying on deciphered messages from the human age of her predecessor universe. But a name was actually not needed, for she is a collective quantum form of life, based on sensitive superpositions in the wave function of the universe.
With growing density in a contracting universe, quantum mechanical properties gained more and more importance, and relieved the streaklike Quman from her former isolation in the all too classic phase. Now she blossomed, in the spring of a new universe:
Once more unfolding, fully correlated: world-comprising
And strongly heated, feasting, to excited high states rising;
In quantum acts of measurement herself entangled feeling,
And so with wildest quantum jumps into the future heeling.
Her existence is threatened only by decoherence, continuously gnawing away at her entanglement. But as a contemplative quantum form of life, she can decrease its implications by, so to speak, propagating by self-observation, thus producing copies of herself that follow her in time but, because