The Universe could be expanding today because it was contracting in the past, and will contract again in the future, presenting an oscillating solution.

Nima Arkani-Hamed, Alan Guth, Alexei Kitaev, Maxim Kontsevich, Andrei Linde, Juan Maldacena, Nathan Seiberg, Ashoke Sen, Edward Witten (2012) In a hypertorus model of the Universe, motion in a straight line will return you to your original ... [+] location. If time is like a torus, it may be cyclical in nature, rather than having always existed or coming into existence a finite amount of time ago. We do not, even today, know the origin of time. ESO and deviantART user InTheStarlightGarden

For a time, there were multiple competing ideas which were all consistent with the observations we had. This section may be too long and excessively detailed. Please consider summarizing the material. ( January 2022) Alim Louis Benabid, Charles David Allis, Victor Ambros, Gary Ruvkun, Jennifer Doudna and Emmanuelle Charpentier (2015) An expanding Universe could have originated from a singular point— an event in spacetime— where all of space and time emerged from a singularity.

In this chapter, Hawking describes the development of scientific thought regarding the nature of space and time. He first describes the Aristotelian idea that the naturally preferred state of a body is to be at rest, and which can only be moved by force, implying that heavier objects will fall faster. However, Italian scientist Galileo Galilei experimentally proved Aristotle's theory wrong with by observing the motion of objects of different weights and concluding that all objects would fall at the same rate. This eventually led to English scientist Isaac Newton's laws of motion and gravity. However, Newton's laws implied that there is no such thing as absolute state of rest or absolute space as believed by Aristotle: whether an object is 'at rest' or 'in motion' depends on the inertial frame of reference of the observer. This radiation wasn't just the same magnitude everywhere, but also the same in all directions. At just a few degrees above absolute zero, it was consistent with the Universe emerging from an earlier, hot dense state, and cooling as it expanded. According to the Big Bang, the Universe was hotter, denser, more uniform and smaller in the past. It only has the properties we see today because it’s been expanding, cooling, and experiencing the influence of gravitation for so long. Because the wavelength of radiation stretches as the Universe expands, a smaller Universe should have had radiation with shorter wavelengths, meaning it had higher energies and greater temperatures. Despite some baffling explanations in the penultimate chapter, Hertog saves the novel with a brilliant conclusion. Hertog explains in his final chapter that the implications of this final theory are broader than science, guiding humanity into a new era of progress. He holds a lofty, humanistic view of the future that lies before us — by marrying the universe’s origins to observation, we not only lay a comprehensive foundation for emerging science, but also adopt a deeply meaningful perspective that once again centers our place in the universe. But this severely alters our conceptions of how the Universe began. Earlier, I presented you a graph of how the size (or scale) of the Universe evolved with time. The graph displayed the differences between how the Universe would expand if it were dominated by matter (in red), radiation (in blue), or space itself (such as during inflation, in yellow) at early times. However, I wasn't completely honest with you in displaying that graph.Singularities are where the law of gravitation governing the Universe — Einstein’s General Relativity —yields nonsense for predictions. Relativity, remember, is the theory that describes space and time. But at singularities, both spatial and temporal dimensions cease to exist. Asking questions like “what came before this event where time began” is as nonsensical as asking “where am I” if space no longer exists. According to Hertog, Hawking did not wish to make philosophy, but made philosophy when making quantum cosmology. Hawking wished to unravel the mysteries of physics and Universe and despite his physical condition was able to communicate his optimistic enthusiasm to his research group in Cambridge. The current quantum theory of the Big Bang presently dismisses the theory of multiverse, at least until it is disproved by new telescope observations or other mathematical theories. Whenever we think about anything, we apply our very human logic to it. If we want to know where the Big Bang came from, we describe it in the best terms we can, and then theorize about what could have caused it and set it up. We look for evidence to help us understand the Big Bang's beginnings. After all, that's where everything comes from: from the process that gave it its start. Observationally, we don't know the answer to any of these questions. The Universe, as far as we can observe it, only contains information from the final 10 -33 seconds or so of inflation. Anything that occurred prior to that— which includes anything that would tell us how-or-if inflation began and what its duration was— gets wiped out, as far as what's observable to us, by the nature of inflation itself.