The Origin and Evolution of the Universe

The Standard Big Bang Model
The Big Bang model posits that the universe originated from an explosion approximately 15 billion years ago. At the moment of this explosion, the size of the universe was considered to be zero, resulting in extremely high energy density and temperature. Following the explosion, the universe expanded and cooled, allowing for the formation of structures as we observe today.

There are at least three theoretical and practical foundations leading to this model. Interestingly, a writer was the first to suggest that the universe must have a starting point. The Olbers’ Paradox (1823) argues that if the universe is infinite in space and time, there should be so many stars that our line of sight would always encounter a star, making the night sky brightly lit like the sun, even at night. However, the actual dark night sky indicates that the universe does not exist eternally. In his long prose poem “Eureka” in 1848, Edgar Allan Poe suggested that this darkness was due to the stars not having enough time to illuminate the entire universe. The dark night sky serves as evidence that the universe is not eternal. This hypothesis not only withstands the test of time but also plays a crucial role in the formation of the Big Bang theory.

The second theoretical foundation is the General Theory of Relativity, which states that space-time is a dynamic quantity, dependent on matter, and simultaneously influencing matter (noting Engels’ view that space-time is a form of existence of matter). This leads to the conclusion that space-time can have a beginning and an end, an initial idea that Einstein himself tried to refute.

The practical basis for the model is Hubble’s discovery of the expanding universe in the 1920s. The fact that the universe is currently expanding and galaxies are moving farther apart indicates that they were once closer together when the universe was smaller. If we extrapolate back in time, we arrive at the moment of creation when the entire universe was concentrated at a single point, where energy density, temperature, and the curvature of space-time were infinite. A subsequent explosion would lead to the formation of the universe.

However, a high density of matter or gravitational force might cause the universe to collapse even as it expands. Along with other reasons, Alan Guth hypothesized inflationary expansion, allowing the universe to increase in size by a factor of (10^{30}) in an instant (from (10^{-35}) to (10^{-32}) seconds after the explosion). Surpassing this microscopic threshold of success and failure, the universe triumphantly expands and creates everything, including ourselves.

This is the standard hot expanding inflationary universe model. In 1991, when the Hubble Space Telescope on the COBE satellite measured the residual radiation from the past explosion as predicted, the Big Bang model gained widespread acceptance.

Unresolved Issues

The Big Bang is currently the best model available, but it certainly still faces many issues, including singularities and ultimate beginnings. Physics avoids singularities, where a quantity reaches infinite values—something that only exists in the abstract world of mathematics. The Big Bang itself is such a singularity, and it is something to be avoided. If the Big Bang gave birth to the universe, then what gave rise to the Big Bang? This question is welcomed by the church, as it views the Big Bang as an embodiment of a creator.

One way to circumvent the singularity problem is through string theory in particle physics. String theory posits that the most fundamental constituents of the universe are not particles (like electrons or quarks) but strings or superstrings in ten dimensions. There are five string theories, and by 1995, it was found that they were merely versions of a more fundamental theory known as M-theory, which involves eleven dimensions. Different oscillations of membranes manifest as the fundamental particles we observe. The old view, which considered fundamental particles as dimensionless points, led to singularities, whereas membranes do not because they have a defined size, albeit very small.

The problem of the ultimate beginning is more complex. One way to address this issue is to investigate the end. Will the universe expand forever or eventually collapse in a Big Crunch? If the universe has enough matter, gravitational forces will eventually overcome expansion, leading to a collapse back to a singularity. The explosion that created us could be the result of a previous collapse. This is Wheeler’s cyclical universe model, with cycles of expansion and contraction connecting in a circle, akin to Buddhist philosophy, serving as a method to avoid the ultimate beginning.

Unfortunately, the Big Crunch is not a perfect mirror symmetry of the Big Bang. As the universe contracts, photons will gain energy due to strong gravitational fields. Therefore, the universe at its end will be hotter than at its beginning. This means that the later explosions will be more powerful. This indicates that the universe still requires an ultimate starting point, similar to a model with only one Big Bang. The poet’s excitement has not diminished.

The Turn of the Millennium Revolution

The cyclical concept implies that the universe has enough matter to potentially contract. However, this notion was refuted in 1998. Observations of supernovae led to a revolutionary conclusion: the universe is expanding at an accelerating rate. This was disappointing news, as the cyclical model was preferred, where the universe and life could continuously be born and perish.

Why is the universe expanding faster and faster? The answer is fairly straightforward: due to a lack of the necessary amount of matter. More importantly, it seems the universe contains a form of special energy that has a repulsive gravitational effect.

Decades ago, astronomers thought the universe only contained ordinary visible matter. When they observed the rotation speeds of galaxies to be exceedingly high, they hypothesized the existence of dark matter, which is estimated to be ten times greater than visible matter (to provide enough gravitational force to counteract the centrifugal force due to the galaxies’ rotation; otherwise, galaxies would disintegrate). Dark matter is divided into two types: ordinary dark matter (such as brown dwarfs, black holes, etc.) and exotic dark matter (such as massive neutrinos, hypothetical axions, or WIMPs). Now, we need to add a new form of matter or energy, called dark energy, which constitutes up to two-thirds of the universe’s mass:

The nature of dark energy, which exerts negative pressure (to create repulsive gravity), may pose a long-term challenge to physics and cosmology.

The first candidate is vacuum energy. Physical vacuum is not a void but is filled with virtual particles and antiparticles, which are created and annihilated continuously due to the Heisenberg uncertainty principle. According to this principle, one cannot precisely determine the values of certain pairs of conjugate physical quantities (such as position and velocity) simultaneously. Therefore, vacuum energy cannot be zero, as that would imply zero fluctuation; meaning two quantities could be precisely defined at the same time, which is forbidden by the uncertainty principle. This is due to the creation of virtual particles and antiparticles. For instance, in every cubic centimeter before our eyes, there are always (10^{30}) virtual electrons! These produce measurable effects, such as the Casimir effect. Calculations show they create an energy density that is (10^{120}) times larger than other forms of matter, a staggering figure that astonishes the physics community!

The second candidate is the fifth component (a play on words referring to Aristotle, who viewed the four elements—water, fire, air, and earth—as constituting the universe). The simplest explanation is a quantum field that changes very slowly over time, which may account for the inflationary expansion phase. Another possibility arises from the physics of exotic extra dimensions, namely the ten-dimensional strings or eleven-dimensional membranes mentioned earlier. In this theory, ordinary matter resides on three-dimensional membranes. These membranes lie close together in the eleventh dimension. Light takes billions of years to travel along the three-dimensional membranes to reach our eyes, while gravitational (or repulsive gravitational) effects reach us immediately through the extra dimension, creating a tremendously large estimated value as previously mentioned. However, mathematical difficulties make it impossible to present a complete model, not only currently but possibly in the future.

Brane and Collision Models

To resolve the issues of singularities and ultimate beginnings, in late 2001, scientists Steinhardt, Turok, Khoury, Ovrut, and Seiberg proposed the brane and collision model, viewing the Big Bang not as the beginning of space-time, but as a transitional point between an expanding phase and a previous contracting phase. This is indeed a cyclical model but has advantages over other cyclical models.

The model hypothesizing our universe is a three-dimensional membrane drifting in four-dimensional space. Another membrane—a parallel universe—lies right next to it at a microscopic distance in the fourth dimension. This universe is closer than our skin, yet we cannot see or touch it. These membranes act like they are connected by springs: pulling back when they are far apart and pushing out when they come close, causing the membranes to oscillate away and then towards each other. Their sequential collisions are what we know as the Big Bang. The primordial energy of the Big Bang is the energy of these collisions; the density fluctuations (evident in the cosmic microwave background radiation measured by the COBE satellite in 1991 and are seeds for the later development of galaxies) are wrinkles of the membrane. During the oscillation and collision process, the membranes can still stretch and contract.

Compared to the standard inflation model, this model has the advantage of not requiring dark energy to explain the universe’s accelerating expansion. Simply put, it is the energy of the “spring.” According to Turok, another advantage is that singularities appear only in the fourth dimension (when two membranes collide, the distance becomes zero), which is the lightest form of singularity. And since they continue to expand before and after the collision, photons will not gain additional energy, meaning that the Big Crunch is not hotter than the Big Bang, allowing for the elimination of the ultimate beginning—a favored theological topic.

Of course, the model also leaves many questions unanswered. First, the lightest singularity is still a singularity. Next, it is unclear how the small fluctuations or wrinkles of the membrane reappear after a collision. According to Linde, a developer of the inflation model, it is like throwing a chair into a black hole and hoping it will be reborn. The nature of the spring force also presents a conundrum. However, many astronomers welcome the model, as noted by the famous string theorist Veneziano at CERN, who stated that we are more willing to accept the idea that the Big Bang is the result of something rather than the cause of everything.

“Monday’s Heresy”

All the models mentioned above encounter the dark energy problem. Therefore, since 1983, Mordehai Milgrom (Israel) proposed MOND, or Modified Newtonian Dynamics. He argued that Newton’s second law F=ma would transform into F=ma² at low accelerations, around 10^-10 m/s². This means that less force or less material is needed to accelerate galaxies. Consequently, the dark matter or dark energy problem would automatically be excluded.

Initially, the astronomical community rejected MOND. However, its successes in explaining the formation and evolution of galaxies (recent measurements aligning with Milgrom’s predictions from years ago) have convinced some scientists. However, they do not believe that Newton’s dynamics are incorrect; rather, they see it as a meaningful practical adjustment, referring to it as MIFF, or Milgrom Fitting Formula.

Finite or Infinite Universe?

Let us consider Mach’s principle, which states that an object’s inertia is due to its interaction with the entire universe. This can be better understood by examining the centrifugal force on a bucket of water. When water is spun in the bucket, the surface of the water becomes concave: we say it experiences the effect of centrifugal force. Is that because the water spins relative to the stationary bucket? Absolutely not, because if both the bucket and the water are spun at the same speed, the water surface still remains concave. Mach argued that the surface of the water is concave because it “knows” it is spinning relative to the entire universe. In other words, inertia is due to the interaction of the entire universe on the object. Therefore, the universe must be finite. If the universe were infinite, inertia would be infinitely large: no object could change its state of motion, which contradicts reality.

But that is just our universe. Many people hypothesize the existence of wave-like parallel universes or a multiverse, each with its own set of laws. Recall the colliding membranes; there may be more than just two. Or imagine the act of blowing soap bubbles, where each bubble represents a single universe. The bubbles may connect through wormholes. According to general relativity, these are shortcuts connecting spacetime regions within a bubble, and even linking different bubbles together. They allow energy to surge between bubbles. One can envision such a surge as the Big Bang that birthed the universe we inhabit.

Thus, we may be living in a finite single universe. This universe is one of countless membranes or bubbles of an infinite multiverse. Everyone can be satisfied, whether they prefer a finite or infinite universe.

This hypothesis helps eliminate the notion of a supreme creator. In the famous work “The Mysterious Melody” (translated into Vietnamese), Trinh Xuan Thuan places his faith in a divine light and suggests that he wants to believe in hope rather than despair. According to him, finding a suitable bubble for life among the infinite bubbles is impossible, just as viewing life as mere random occurrence does not satisfy human pride. I think the issue may be the other way around. If humans were created by a supreme being, we would merely be puppets. In such a case, there would be no free will, a favorite theme of Bergson; nor would there be the ability to choose among different possibilities, as a way to self-determine fate—an essential characteristic of being human. However, if we emerge as a marvelous combination of randomness and necessity, we must live worthy of all the challenges of existence. And that could carry a humanitarian significance.

How Does the Multiverse Arise?

As mentioned above, while each single universe is finite, the multiverse can be infinite. This suggests it contains infinite energy—something that seems meaningless physically. Fortunately, that is not the case.

Quantum fluctuations allow virtual particle-antiparticle pairs or energy “bubbles” to appear from the vacuum, as long as they vanish after a brief existence. The less energy a bubble has, the longer it can exist. Since gravitational field energy is negative and the energy contained in matter is positive, if the multiverse is flat (even if a single universe may be curved), then these two forms of energy can cancel each other out, resulting in a multiverse energy that is precisely zero. In this case, quantum rules allow it to exist indefinitely. In other words, the very state of uncertainty is what enables the universe to emerge from nothingness, a unique idea so striking that when Gamow recounted it at Princeton in the 1940s, Einstein stood frozen in the street, nearly causing both of them to be hit by a car.

One may ask, where does nothingness come from? Perhaps that is an unreasonable question. It is more reasonable to ask why there is uncertainty for the universe to come into being. And are there even more fundamental questions?

Finally, I would like to emphasize the unity between the micro and the macro. It is precisely by delving into the nature of the micro that science can understand the universe’s behavior. Opinions suggesting that reductionism—a method based on analysis to increasingly delve into the microstructure of the world—has lost its cognitive capacity are unfounded. In his 1992 book “Dreams of a Final Theory,” Nobel laureate Steven Weinberg, known for his work unifying weak and electromagnetic interactions, dedicated two chapters to criticizing philosophers and defending reductionism and analysis.