Chapter 145: Dark Matter and the Void

Hua Feng was well aware that pulsars compensate for the energy they radiate by consuming their own rotational energy, causing their rotation to gradually slow down.

However, this deceleration is so exceedingly gradual that the precision of their signal periods can surpass that of atomic clocks. The age of a pulsar can be inferred from its period; pulsars with shorter periods are younger. In addition to rapid rotation, pulsars possess extremely strong magnetic fields. Electrons are emitted from the magnetic poles, giving the radiation intense directivity.

Because a pulsar's rotation axis does not coincide with its magnetic axis, an observer receives a pulse during rotation whenever the beam points toward them. A pulsar is, therefore, a rapidly rotating neutron star.

A neutron star is the residual core left behind when a super-massive star explodes to form a supernova. It is an astronomical body of immense density, equivalent to packing the mass of the Sun into a sphere merely twenty kilometers in diameter.

Neutron stars can spin hundreds of times per second. Due to their ultra-strong gravitational forces and rapid rotation, neutron stars can generate substantial "ripples" in spacetime. However, if their surfaces contain bulges or other imperfections, these ripples will exhibit irregularities. The surface of a neutron star is believed to consist of a crystalline layer rich in neutron particles, forming a solid, hard outer shell. The atoms on the surface of a neutron star are packed far more tightly than iron, possessing a strength ten billion times that of the breaking point of steel.

This hard surface means a neutron star can support substantial surface elevations—effectively "mountains." It is possible that some terrain bulges ten centimeters high, extending across several kilometers, can be supported on a neutron star's surface. Research suggests that gold and other heavy metal elements may originate from the cataclysmic collisions of neutron stars.

A quark star is a hypothetical celestial body. Stellar explosions leave behind remnants: either a neutron star or a black hole. However, if the remnant is too small in mass to become a black hole, yet too massive to form a neutron star, a quark star is formed. Although none have yet been observed, astronomers believe they must exist. Quark stars are actually composed of strange quark matter, which is why they are also referred to as strange stars.

A black hole is a particularly dense, dark celestial body. Massive stars collapse toward the end of their evolutionary lifecycle, resulting in extremely dense matter. It possesses a closed boundary known as an "event horizon," concealing an immense gravitational field within. This gravitational field is so extraordinarily strong that nothing—not even photons, the particles comprising light, which travel at a speed of $c = 3 imes 10^8 ext{ m/s}$—can escape once it enters.

The genesis of a black hole is similar to that of a neutron star: the core of a star rapidly contracts under the weight of its own mass, triggering a powerful explosion. When all the matter in the core transforms into neutrons, the contraction process halts abruptly, compressing the material into a dense sphere. In the case of a black hole, however, the mass of the stellar core is so immense that the contraction proceeds without end; the neutrons themselves are crushed to powder under the sheer force of their own gravitational attraction, leaving behind matter of unimaginable density.

The most extraordinary feature of a black hole is its "cloak of invisibility," which is caused by warped space. Light travels in straight lines. According to general relativity, space becomes curved under the influence of a gravitational field. To visualize this intuitively, it is as though light originally intended to travel in a straight line, only for the powerful gravity to pull it away from its original trajectory.

On Earth, due to the weak gravitational field, this curvature is virtually imperceptible. Around a black hole, however, this deformation of space is immense. Consequently, even though some of the light emitted by stars blocked by a black hole falls into it and disappears, another portion of the light bypasses the black hole by traveling through the warped space and ultimately reaches Earth.

Thus, we can observe the starry sky behind a black hole effortlessly, exactly as if the black hole did not exist at all—this is the invisibility cloak of a black hole. Black holes can emit dazzling light, shrink in volume, and even explode. When British physicist Stephen William Hawking made this prediction in 1974, the entire scientific community was shaken. He discovered that the gravitational field surrounding a black hole releases energy while simultaneously depleting the black hole's energy and mass.

If a pair of particle and antiparticle is created near a black hole, and one of them is sucked into the black hole, the newly created antiparticle will be drawn in while the positive particle escapes. Since energy cannot be created out of nothing, we may consider the antiparticle as carrying negative energy; thus, the absorption of an antiparticle into the black hole can be viewed as the escape of a positive particle carrying positive energy from the black hole. Furthermore, Einstein's equation $E = mc^2$ demonstrates that a loss of energy results in a loss of mass.

As a black hole's mass becomes smaller and smaller, its temperature rises higher and higher. Consequently, as the black hole loses mass, its temperature and emissivity increase, causing it to shed mass even more rapidly. Therefore, Hawking predicted that black holes radiate energy at an extreme rate until they ultimately explode.

In 1917, Albert Einstein utilized general relativity to construct a "static, infinite, and unbounded" universe model, laying the foundation for modern cosmology.

In 1922, Alexander Friedmann discovered that, according to Einstein's field equations, the universe could also be expanding and oscillating.

In 1927, Georges Lemaître proposed a genuinely expanding universe model. In 1929, Edwin Hubble discovered that galactic redshift is directly proportional to distance, establishing the famous Hubble's law. This discovery provided robust support for the expanding universe model.

In the mid-twentieth century, George Gamow and his colleagues proposed the hot Big Bang cosmology model. The discovery of the cosmic microwave background radiation in 1965 confirmed the predictions made by Gamow and his team, establishing the Big Bang model as the standard cosmological framework.

In 1980, Alan Guth of the United States further advanced the inflationary universe model of the early Big Bang based on the hot Big Bang framework, which was subsequently refined by Andrei Linde.

This model includes a brief, exponential phase of rapid expansion—a process that smooths out spacetime, renders the universe flat, and resolves the horizon problem. He proposed that at the very inception of the universe, spacetime underwent a rapid expansion phase; within a fraction of a second after the Big Bang, in less than $10^{-34}$ seconds, spacetime expanded exponentially by a factor of $10^{78}$.

Historical Evolution of Computer Models:
In May 2014, scientists produced the most successful computer model of cosmic evolution, simulating the birth and evolutionary process of the universe starting from dark matter as its foundation.

The newly constructed computer model bore a striking resemblance to the real universe. This computer model can be utilized to test theories concerning the structure and operational principles of the cosmos. The related research findings have been published in the journal *Nature*.

Initially, the computer model displayed mysterious "dark matter" scattered throughout a void. Over millions of years, the dark matter clustered together, planting the seeds for the emergence of early galaxies. Anti-dark matter subsequently emerged, paving the way for future stars and life. Black holes also secured a place within the model, inhaling and expelling matter to generate a series of explosions that influenced star formation.

Researcher Mark Vogelsberger stated that the model corroborates numerous cosmological theories, including dark matter. He noted, "In the simulation, many galaxies closely mirror those found in the real universe. This implies that our understanding of the fundamental operational principles of the cosmos is correct and comprehensive. If you exclude dark matter, it scarcely resembles a genuine universe at all."

A pioneer of modern cosmology is Stephen Hawking, who famously stated: "There is no place for 'God' in the creation of the universe. There is no need to invoke 'God' to press the start button on the cosmos."

Hawking advocated leveraging mathematical and physical tools to pursue a grand unified theory, proving that "the universe was not born by chance and has no need for God," and that "the mathematical model of the universe is finite yet unbounded."

In a lecture, Hawking remarked:
"However, people have discovered in recent years that the laws of science hold true even at the inception of the universe. In that scenario, the universe can be self-contained and completely determined by the laws of science. The hypothesis formulated by Hartle and myself can be restated as follows: the boundary condition of the universe is that it has no boundaries."

The Genesis of the Universe:
At the dawn of the explosion, matter could exist only in the form of fundamental particles such as neutrons, protons, electrons, photons, and neutrinos. The continuous expansion following the cosmic explosion caused the temperature and density to plummet rapidly. As temperatures cooled, atoms, atomic nuclei, and molecules gradually formed, eventually combining into ordinary gases. These gases progressively condensed into nebulae, which further gave rise to diverse stars and galaxies, ultimately culminating in the universe we observe today.

The inflationary model permits the matter and energy of the universe to emerge from nothingness. Grand unified theories suggest that baryon number non-conservation is permissible, while the gravitational energy in the universe is roughly negative and precisely cancels out the non-gravitational energy, resulting in a total energy of zero. Consequently, it is entirely possible for the universe to evolve out of nothing.

"Nothingness" is not absolute nothingness; vacuum energy is precisely a special form of matter and energy. If we go a step further and state that vacuum energy originates from "nothing," then this "nothing" can only be an unknown form of matter and energy. From the perspective of modern physics, the vacuum can also be regarded as a form of matter.

No matter how colossal the universe may be, as a finite material system, it too has a history of birth, development, and demise. The inflationary model posits that the forms of matter and energy within the universe are not eternal, and treating "nothingness" as an unknown form of matter and energy holds certain significance epistemologically and methodologically.

Modern cosmology is not an obscure and useless philosophical speculation; rather, it is a modern science built upon astronomical observations, mathematical models, and physical experiments, possessing the full capability to comprehend the mysteries of the cosmos. Astronomers point out that the Big Bang was bound to occur because the "void" is inherently unstable—a conclusion that can be deduced from quantum mechanics and general relativity. At the scale of quantum mechanics, space becomes unstable, ceasing to appear smooth and continuous; space and time lose stability, intermingling to form spacetime foam, allowing microscopic spacetime bubbles to form spontaneously. Quantized spacetime produces fluctuations, and thus the universe emerges from the "void."

Regarding these theoretical concepts, Hua Feng held his own understanding within his heart. What he had to consider right now was not such macro-level notions, but the imminent "doomsday catastrophe."