The beginning of the universe in the eyes of science

A special article in honor of Hebrew new year summarizing the creation of the world through the lens of science

The biblical story of creation begins with an act. The reason for the divine act is hidden from his interest, but the process of creation is correctly detailed. The process is not momentary, it is continuous and in a certain sense has no end. Surprisingly, I find in these diagnoses interesting parallels with the scientific story of creation. It also begins with an act, the reason for its occurrence is hidden from its interest and it also took time, and some would even argue, continues to occur. Beyond that, I am thrilled by the fact that in order to know the story of creation in its entirety, we are required to know the "Torah of Everything", the one that claims in one equation to contain nature at the height of its glory. Einstein used to say "I want to know what God thinks. Leave small details.' In my interpretation it says that in a certain sense, to know creation, is equivalent to knowing God, or all of nature. In honor of Rosh Hashanah, I thought it appropriate to describe here what the scientific community knows about the formation of the universe, what is visible and what is hidden, to sift out misconceptions and humble the decisive statements that are sometimes heard in the public.

Let's start with a common error - the "big bang" that happened about 13.8 billion years ago is not the moment of creation. At the same time there is no absolute scientific certainty about what happened before and if something necessarily happened before the bang. We have several hypotheses as to why it is not the primordial moment and a number of evidences that support this thought. It may surprise some of you, but the classical Big Bang model is unable to explain all observations in the universe. Therefore, many cosmologists refer to the bang as a historical event in the development of the universe, and not necessarily the moment from which it all began. Needless to say, the explosion was not really an event reminiscent of conventional explosions, but something more complex. According to the classical Big Bang model, the universe uniformly contained a boiling, dense and highly energetic plasma that expanded and cooled over time. With the cooling process, gravity became dominant and with its help complex bodies such as stars and galaxies were formed. If the cartoon image of the bang were correct, i.e. the one that depicts a world that was the size of an egg, which exploded in all directions, we would expect that in certain regions the universe would look different from other distant regions, but in fact, at large enough distances the universe appears homogeneous and isotropic, that is, the same everywhere in space and in every direction ( We will return to this point later).

Although the big bang theory explains the formation of galaxies and heavy elements, it is unable to explain why the universe is expanding. In fact, this theory does not contain an "explosion", if at all it explains what happened after the explosion. The classical model describes a universe that "began" after the expansion of space-time, without explaining how it happened. Beyond that, this theory is unable to explain where the matter in the universe came from. We can summarize this part by saying that the bang theory is a theory that does not explain what exploded, why it exploded or what happened before the explosion. In fact, it does not contain an explosion at all. Yes, the name is completely misleading and confusing.

On the theory of inflation

Is there a Torah that will solve these mysteries and that can be verified by observation? The answer to that is yes. We call this theory cosmic inflation. Broadly speaking, this is a theory that explains how the initial conditions for the Big Bang were created with the help of an exponential expansion of the universe that occurred before. The inflation mechanism is based on the fact that gravity is not just an attractive force. The first to use repulsive gravity was Einstein, who added the cosmological constant to his equations, in order to keep the universe static. If it weren't for the cosmological constant, the matter in the universe would collapse in on itself. Of course, today we know that the universe is not static, but is expanding rapidly. Thanks to general relativity, we know today that under the right conditions gravity can also repel bodies and not only attract them to each other.

When did inflation occur? There is no exact answer to this. It is very possible that the universe existed a long time before it began. This question can be replaced by another question - what is the energy density at which the inflation occurred? Physicists assume that the exponential expansion of the universe began when the energy density was high enough to unite the strong and electroweak forces. This is an energy scale that stands at 10 to the 16 giga electron volts. For comparison, one proton is energetically equal to 1 gigaelectron volt. Under these conditions, a tiny piece measuring 10 minus 28 centimeters is required to create the visible universe. In this process, the universe doubled its size every 10th power minus 37 seconds (tenth of a billionth billionth billionth billionth second). After the universe increased its volume about a hundred times, its size was the same as the size of a pea. This process took about 10 to the minus 35 seconds from the start of inflation, and from that the conditions for the Big Bang were created. The negative energy decayed, and in return the particles of matter and radiation were created. The universe continued to grow, but not at an exponential rate, this is because positive gravity slowed the expansion of the universe.   

Here comes an important note regarding exponential expansion. The negative energy is not small with the expansion of the universe. This may sound like a claim that breaks the conservation of energy, but it is not. The amount of negative energy in the universe balances with the amount of positive energy arising from the particles of matter and radiation known to us. In fact during inflation, the amount of negative energy increases and in turn the amount of positive energy increases as well.

Evidence for the theory of inflation

The main evidence for the existence of inflation in the early universe is observed in the cosmic background radiation. This is very low energy radiation that began to move freely hundreds of thousands of years after inflation. This radiation is uniform from all directions, up to one hundred percent. The energy differences are very negligible and confirm the fact that the universe is more or less homogeneous and isotropic at large enough distances. In the era of the big bang, when the universe contained boiling plasma, light rays bounced between the particles of matter at a high frequency. The strong interaction between light and matter prevented light particles from moving large distances freely. Only about 400 thousand years after the bang, when the plasma cooled enough, light began to travel freely over great distances.

The obvious question is can we explain the homogeneity that existed in the early universe? If we take into account only the classical model for the Big Bang, the answer to this would be no. The reason is that in order to obtain a homogeneous image like the one observed from the cosmic background radiation, it is required to move masses of matter at a speed close to 100 times the speed of light, in contradiction to the theory of relativity. The dynamics in the bang model simply do not allow such a high degree of homogeneity. On the other hand, inflation provides a natural explanation for this. Before the big bang, the universe was very small, so small that it was inevitably homogeneous in a relatively short time. The exponential expansion stretched the universe at zero time and preserved the relativistic conditions that existed when the universe was tiny.

Another evidence comes from the degree of curvature of the universe. One of the open mysteries in cosmology is why the universe appears flat. The simplest definition of a flat universe is that the sum of the angles in a triangle in this universe is 180 degrees. In a curved universe, the sum of the angles can be greater than 180 or less, see figure below.

The curvature of the universe depends on the density of the mass inside it. It is customary to measure the curvature using the ratio between the mass density in the universe and the critical density at which the universe goes from positive to negative curvature or vice versa. The ratio between the expectations is usually marked with an omega symbol. If omega is equal to one, the universe is flat. If omega is less than one, the universe has negative curvature, and if omega is greater than one, the universe has positive curvature. Calculations show that the state in which the universe is flat is not a stable state, so cosmologists are racking their brains trying to understand why our universe looks like this. If omega is less than one, even slightly, the universe will very quickly expand without stopping, and if omega was slightly greater than one, the universe would contract back. In order for the universe to be flat and stay that way, omega has to be very close to or exactly equal to one, and indeed so is their value.

In principle, it can be assumed that the universe began with omega equal to or very close to one. If it is a random selection of a number, it is a very, very accurate value, a bit like putting a pencil on its tip without it falling. Physicists tend to call this case "unnatural", because it is natural to expect that if we try to put a pencil on its tip, it will fall in almost every attempt. If it didn't fall, we would assume that it was luck or that there is a mechanism that stabilizes it. Reasonably, physicists looked for a mechanism that would stabilize omega to be very close to one. It turns out that the classical big bang model cannot explain why omega is approximately equal to one, but the inflation model does. In fact, the dynamics in the inflation model change omega to one at an exponential rate, no matter what its initial value was. Until 1998, cosmologists thought that omega should be 0.2 or 0.3, contrary to the prediction of the inflation model, but since then, measurements have shown that omega is very close to one. The reason physicists thought omega should be relatively low was because they didn't know that the universe was expanding at an accelerated rate, but when they took that into account, omega did add up to a number close to one.

A third evidence of inflation is precisely in the inhomogeneity of the universe (at short distances). Obviously, at short enough distances the universe doesn't really look uniform. The universe is littered with stars and planets at different distances and sizes, while the sky is almost completely empty between the bodies. As I mentioned earlier, in order for massive bodies to be formed, inhomogeneity and isotropy is required. In areas with a higher than average material density, a more powerful gravitational force will be felt which will attract more material to it and in a chain process will become more and more massive. But what is the mechanism that causes this inhomogeneity? It is amazing to discover that it was quantum mechanics, dominant at short distances, that caused these cosmic changes. Under the guise of the inflation model, it is possible to calculate exactly how the quantum fluctuations left a mark on the early universe until today. When the map of cosmic radiation is mapped by frequency, the quantum echo can be seen exactly to what the inflation model predicts. There were actually quite a few predictions of what the frequency mapping would look like, but the inflation model was the one that fitted the observations remarkably accurately.

The evolution of the universe

After inflation, from the big bang and after, the universe went through a series of processes, some of which I will briefly summarize.

Until about the second thousandth of a billionth from the moment of the bang, there was an asymmetry between the amount of matter and antimatter particles in the universe. The reason for this is unknown. The standard model assumes that the forces acting on matter and antimatter particles are completely equal. Therefore, it is likely that an equal amount of matter and antimatter was created at the beginning of the universe. Besides, when matter and antimatter particles collide, they are converted into light particles. If this is the case, when the universe was very dense, it is likely that in a powerful collision all the particles of matter and antimatter will be converted into light and the universe will be empty of matter. This assumption is at odds with observations and we do not have a convincing explanation for why there is material left in the universe.

Immediately after, the matter particles received their valve from the Higgs mechanism. This is an interesting phase transition in the universe where the weak force changes its strength. Between the millisecond and 20 microseconds, the quarks that filled the universe begin to crystallize into protons and neutrons that we all know make up the nuclei of atoms in the periodic table. Of course, many more particles of matter were created, but these eventually became the particles we all know. The next stage in the evolution of the universe is somewhat hidden from our interest because it involves the process of "stasis" of the dark matter, that is, the moment when the dark matter stops coming into contact with other particles, and mediates its influence only through the force of gravity. About a second after the bang, the neutrino particles started moving freely from the boiling plasma. Note that the neutrino particles moved freely before the light particles. Because of this, the study of neutrinos can provide a glimpse into an even earlier universe. Unfortunately, the neutrino is a particle that reacts to matter particles only through the weak force, so it is very difficult to measure its existence and effect. When the universe was 6 seconds old, the annihilation took place between the electrons and positrons (anti-electrons) and when the universe was 3 minutes old, the light elements began to form. It took hundreds of thousands of years until neutral hydrogen was energetically superior (over charged hydrogen), and from this critical point the light particles began to move freely.

Beyond the theory of inflation

So far the picture I described was based on observations of the universe and particle accelerators. From this point on we will discuss the more speculative parts of the inflation model. When inflation occurs in a certain region of space, the negative energy driving it fades over time locally. On the other hand, the amount of negative energy increases as the volume of the universe increases. This process creates regions in the universe that stop growing alongside an envelope that fills with negative energy. In fact, the negative energy accumulates faster than its rate of decay and therefore the expansion of the universe continues forever. In this process, islands are formed that stop spreading, which cosmologists call "sacks". Each such bag can represent a universe in itself with its own laws of nature. It is important to note that these restorations are in the fabric of one time space and can sometimes collide. Scientists have previously tried to look for gravitational signatures of collisions with other universes, but have yet to find any. A natural explanation for the existence of universes with different laws of nature also comes, interestingly, from string theory. This theory unites under a single formalism the theory of relativity and quantum mechanics. Yes, we've already quantized gravity, but no one claimed there was only one way to do it. String theory is a complicated theory, and sometimes it is difficult to solve problems with it, but sometimes the situation can be completely opposite. To the question of what is the basic state of the Torah, i.e. what is the physical state with the lowest energy, there are 10 to the power of 500 different answers. On the one hand, this is an obstacle. How can we choose the ground state that describes our universe? And what mechanism will choose this basic state? On the other hand, if there is no such mechanism, maybe this is a sign that they all exist? String researchers believe that each fundamental state describes a new universe and alongside it a set of different constants of nature. The idea goes hand in hand with the inflation model and multiple universes that this theory predicts.

In conclusion, I say that many of the riddles are from the total facts known to us. Not sure we will ever be able to answer them all. The most difficult question probably concerns the moment of the singularity, when the universe had zero size. At the same time, it is impossible not to be surprised by the fact that we, humans, are able to think about these questions and find answers, even if partial.

Do you have a scientific question? You are welcome to chat with me at the email address: noamphysics@gmail.com

This article is based on the series of lectures by Alan Guth from MIT. You can watch them HERE

More of the topic in Hayadan:

• Cosmic controversy
• The theory of cosmic inflation is in trouble
• Genesis was empty - how was our universe created? - Part IV
• Brainwashing - Omega not only in sports / Yitzhak Ferns
• Genesis was empty - how was our universe created? - The fifth and last part