Chen Tian's body was still drifting through the universe, but his consciousness seemed to have returned to the place he had once yearned for day and night.
His mind began recalling everything from the past. Fragments of those memories began to appear, one after another.
At last, the scattered fragments of memory vanished, and a scene began to emerge.
It was a familiar scene, from a lecture he had attended. Back then, he had been obsessed with the sci-fi universe, buying every related book he could find and studying them in detail.
The people in that scene were the two famous foreign speakers whose lecture on the sci-fi universe he had attended.
The two of them were speaking at length about a story, while Chen Tian sat below, listening in rapt fascination. Vaguely, he seemed to hear one of them talking about the Steady-State Universe Theory. At that moment, he remembered!
Chen Tian's soul-consciousness awakened. He remembered the two men and the theory they had been discussing. They were Hermann Bondi and Fred Hoyle. Steady-State Cosmology had been proposed in 1948 by the young British astrophysicists Hermann Bondi, Fred Hoyle, and Gold.
Their view was this: In relativity, space and time were unified. Since the cosmological principle held that all positions in space were equivalent, then all moments in time should also be equivalent.
In other words, the large-scale distribution of celestial bodies—of matter—was not only homogeneous and isotropic in space, but should also remain unchanged over time.
That meant that in any era and at any location, the image of the universe seen by an observer would be the same on a large scale. This principle was called the Perfect Cosmological Principle.
Steady-State Cosmology held that the universe was infinite in both time and space.
It asserted that the universe had never had a beginning, or, more precisely, that the universe was in a process of continuous creation.
As the universe expanded, its overall density decreased, but more matter would be created to increase the density again.
Thus, as the universe continued expanding, new matter would continuously be created within celestial bodies to fill the gaps.
The greatest characteristic of Steady-State Cosmology was that it required matter and energy not to be conserved, and required the law of conservation of matter to be invalid.
For this reason, Hoyle proposed modifying the Einstein Field Equations. He believed that newly generated matter was produced by a vacuum phase transition, caused by newly generated vacuum making a transition from a high energy level to a low one.
Steady-State Cosmology caused a sensation when it was introduced, but such a fundamental change could not be adopted lightly. It would require the new theory to achieve great success and agree very well with observational facts. In reality, however, Steady-State Cosmology did not agree well with observations.
There was also Brane Cosmology. Why had the brane universe erupted from a point of infinite density—in other words, a singularity?
But even fewer people knew what had triggered that eruption. The known laws of physics could not tell us what had actually happened at that moment.
Niayesh Afshordi, an astrophysicist at the Perimeter Institute for Theoretical Physics in Waterloo, Canada, said, "Every physicist knows that a dragon might have flown out of the singularity."
At the same time, scientists found it difficult to explain how the universe left behind by such a violent Big Bang could possess an almost perfectly uniform temperature. This was because, since the universe's birth, there seemed not to have been enough time for thermal equilibrium to be reached.
For most cosmologists, the most reasonable explanation for this uniformity was that, shortly after the universe formed, some unknown form of energy caused the young universe to expand faster than light.
That resulted in the roughly uniform-temperature universe we see.
But Niayesh Afshordi stressed, "The Big Bang was far too chaotic, so it's difficult to determine whether this expansion truly existed."
In one paper, Niayesh Afshordi and his colleagues instead turned their attention to a hypothesis proposed in 2000 by a research team that included Gia Dvali, a physicist at Ludwig Maximilian University of Munich in Country D.
In this model, our three-dimensional universe was a brane floating above a "Bulk Universe" with four spatial dimensions.
Niayesh Afshordi's research team realized that if the Bulk Universe contained its own four-dimensional stars, some of those stars would collapse and eventually form four-dimensional black holes—similar to the way massive stars behaved in our universe.
These four-dimensional stars would explode like supernovae, violently ejecting their outer layers of matter, while their inner layers collapsed into black holes.
In our universe, a black hole was enclosed by a spherical surface called the event horizon.
Given that ordinary three-dimensional space required a two-dimensional object to create the boundary inside a black hole, the event horizon of a four-dimensional black hole in the Bulk Universe should be a three-dimensional object—a shape known as a hypersphere.
When Niayesh Afshordi's research team simulated the death of a four-dimensional star, they found that the ejected matter could form a three-dimensional brane around the three-dimensional event horizon and slowly expand.
The researchers hypothesized that the three-dimensional universe we lived in might be such a brane, and that the growth of the brane we detected was what we understood as the expansion of the universe.
Niayesh Afshordi said, "Astronomers observed this expansion and reasoned backward that the universe must have begun with a Big Bang—but that is only a mirage."
This model also naturally explained the uniformity of our universe.
Since the four-dimensional Bulk Universe might have existed for an infinitely long time in the past, it had sufficient opportunity for different regions of the four-dimensional Bulk Universe to reach equilibrium, and our three-dimensional universe had most likely inherited this state.
Brane Cosmology was a branch of physics stemming from Superstring Theory and M-Theory. It specialized in studying cosmic branes, holding that the universe was actually embedded in branes of higher dimensions. The field also studied how those higher-dimensional branes affected our universe. When his memories reached this point, they broke apart again. Chen Tian was bewildered. At that moment, it had seemed as though he had truly returned to Earth, the illusion as real as reality itself. Had it come from the depths of his memories, or had some cause produced an illusion within his soul? He had no way of knowing. He did not even know where he was. His memories kept resurfacing again and again, and those scattered fragments seemed to contain some vital information.
Chen Tian wondered why his memories had stopped at the moment when he was listening to a foreigner lecture on Earth, rather than at some other time.
What connection did this contain?
Could it be that something within his memories was constantly trying to give him a hint?
Before you continue