COSMOS

3 The Cosmos, a
universe of
possibilities

What is the Universe? Where did it come from and where is it going? These ancient questions that accompany mankind already have an arsenal of answers given by theology and philosophy and have been tested in many other fields of knowledge.

There is , however, a path that seeks to understand this field and that is of particular interest to us: physics. Originally conceived in Ancient Greece as "the science of nature”, physics by definition dedicates itself to the not insignificant task of "investigating the laws of the Universe with respect to matter and energy, which are its constituents, and their interactions" [1]

Ernest Rutherford, the man who discovered the atomic nucleus, once said: "There are only two kinds of science:. physics and philately" [2] He called attention to the predominantly explanatory nature of physics, trying (albeit in and arrogant and somewhat unfortunate way) to show that all strands of science at some point use physics to make progress with their findings.

Astronomy, for example, by separating stars in colors, is philately. But it is only from the understanding of how they work, how they generate energy and how this energy is distributed on its surface that we can understand the 'why' of colors - and that is physics. The same goes for geology and rocks, oceanography and currents, meteorology and weather patterns, engineering, medicine and biology. Hand in hand with astronomy, and not forgetting philosophy, physics studies the Universe and attempts to answer three fundamental questions: Where have we come from? (our origin in the past); Who are we? (Our permanence in the present); and Where are we going? (our existence in the future). For this, it has created a new branch within it: Cosmology, or the study of the Cosmos.

And what is this term coined by Pythagoras, the Cosmos? In its original context the Greek mathematician recognized the existence of a celestial order intrinsic to the sky around him. For him order is the source of beauty, and this "total organization" which he named "Cosmos" (or κόσμος, in the original Greek - a word that is also the root of "cosmetic") was "the most beautiful of the bodies ". [3] This name, however, would only enter into our current vocabulary with the work of noted German geographer Alexander von Humboldt, who used the borrowed term to baptize his greatest work in the 19th century. [4]

The term "Universe", which we use daily as a synonym of Cosmos, was in fact born out of a conceptual error. Originally from the Latin unus verterem, "that which rotates as one", today the word does not represent the movement that defines the Universe - because it definitely does not rotate as one. It was a clear allusion to the pre-copernican conception in which the Earth was seen as a stationary star in the center of the cosmos, with everything else turning in unison around it.

With the old definitions out of date we return to the question: what can ultimately be understood as the Universe? The answer is simple: it is all that exists, it is the most comprehensive expression of natural existence. In its simplicity this definition has a mixture of clarity and obscurity, it is attractive and mysterious and does not require well-defined borders. If we accept that the Universe is all there is - and that we include all things in it such as objects, dimensions, realities, and everything that we may not even be able to suspect that exists - , then there is nothing more ambitious than to study it.

Our definition can be even bolder if we say that the Universe is not just all there is, but also what existed and will exist. Hereby we incorporate temporal divisions within it, yesterday, today and tomorrow, returning to the questions that have plagued mankind since the beggining of time "Where have we come from?"; "Who are we?"; and "Where are we going?".

We can say that there are different types of infinite as, even though the Universe of the distant past can also be defined as infinite, it has been increasing in size. In other words, the infinite of today is obviously greater than the infinite of the past.

Where have we come from? How was the Universe in the past? Is there an infinite past? Or did everything arise from a particular point in time?

The last two questions can be frightening and it is up to each one of us to choose the most comforting response: has the Universe existed for ever or did it emerge from a particular point in time?

Behind the first response we find infinity: the Universe has always existed. In this case our finite brains, transitory and ephemeral, may not be able to deal with the concept. How can we conceive of something that does not have a beginning?

Behind the second response is spontaneity: the Universe began at a certain point in time. In this case the question is how to deal with the fact that everything that exists, has existed or will exist was created out of "nothing."

Modern science does not have the answer. At least not yet. And it may never have it. But that does not stop us from contemplating the past, a very young and primordial Universe. Since the beginning of the twentieth century we know that the Universe is expanding and something that expands, although infinite in principle, necessarily increases in size. So we can say that there are different types of infinite as, even though the Universe of the distant past can also be defined as infinite, it has been increasing in size. In other words, the infinite of today is obviously greater than the infinite of the past.

The Universe of the distant past was smaller than it is today yet already contained everything that exists, has existed and will exist. Its energy density was much higher than it is today. Everything that exists now existed before but was more concentrated, tighter, occupied a smaller volume.

In this context of a very young Universe things that seem strange to us and that can normally no longer happen in the present time could occur: the transformation of matter into energy, and vice versa, was one of them. Today matter only becomes energy under very special conditions: inside stars or in nuclear bombs (to name a few better-known situations). However previously matter and energy were interchangeable, namely, when we are talking about the distant past it does not make sense to talk about one or the other of them seperately.

Matter and energy are like two sides of the same coin. This also applies to the present day, but in the present all, (or almost all), of the "coins" have only one of their sides exposed, revealing only heads or only tails. In the past, it was as if all of them (or almost all) were in the air, heads or tails, undefined. This is how the very young Universe was.

But we could also speak of an earlier period of which we know very little. It is possible that our Universe has always existed and that the expansion discovered in the twentieth century only represents the current dynamic phase of the Cosmos, in which the Universe expands so that one day it will contract. It is a cyclical movement: when it is very small it will expand again, with the cycle continuing successively and eternally. In this case humanity would only witness one moment of expansion, one which will be repeated numerous times. The other hypothesis to be considered is one in which the Universe is not eternal but had a well-defined beginning. According to this view, in which everything that is born must die, the Universe would also have a known or unknown "shelf life". However, the laws of physics are not prepared to deal with their own emergence and these unknowns about the origin of the Universe are waiting for an answer that we might never reach.

What we can confirm today as true is that in a certain moment - around 14 billion years ago - the Universe started to expand. And we call this moment the Big Bang. In its original formulation the expression Big Bang represented the instant that the Universe was born, a hypothesis conceived by George Gamow and his collaborators in the early 1940s, and it explained the current Universe very well. However, it established cosmology as a powerful parallel with the myths of theological creation (the most common in our culture is Genesis in the Bible, "Let there be Light!").

Thus, although some scientists rejected this theory - and it is important to note that in a literal sense the name Big Bang is an obviously undignified name for a hypothesis about the Universe - the alternatives proposed also did not have complete solutions. Two things survive from this divergence: the term Big Bang, created by detractors to make light of Gamow's idea; and the dichotomy that haunts us to this day, that of the infinite and the finite.

Matter and energy, which we know well, which only fifty years ago we thought was everything that existed in the Universe, makes up only 4% of everything that exists. In rounded and not very accurate numbers, the mysterious "dark matter" makes up 27% of the Universe and the remaining 69% (ie most of the Universe) is made up of the even more mysterious "dark energy".

In any case, it was at the beginning of the expansion where the "Higgs field", conceived in 1960 by Peter Higgs, stood out. [5] This field of information, later addressed in the scope of quantum mechanics (which gave birth to the famous Higgs boson, the particle that represents this field of study), permeated the early Universe and provided valuable information: some "coins that were in the air" were heads (matter), others tails (energy). And still within this analogy, the Higgs field designated values for each coin: Is it matter? What kind of matter? A Quark? An Electron? A Neutrino? Or is it energy? A Photon? A Gluon? This is how the Universe started, or at least this current phase of the Universe, referred to in the original question "Where have we come from?".

To address the next question, "Who are we?" Or "How is the Universe today?", We can divide the Universe into three major "conceptual blocks". Matter and energy, which we know well, would be block 1; the "dark matter", block 2; and "dark energy", block 3. Incredibly, block 1, which only fifty years ago we thought was everything that existed in the Universe, makes up only 4% of everything that exists.

In rounded and not very accurate numbers, the mysterious "dark matter" makes up 27% of the Universe and the remaining 69% (ie most of the Universe) is made up of the even more mysterious "dark energy". One of the central questions of cosmology with regard to this debate is the possibility that the Universe will expand forever: we know that the force of gravity has a generalized action over distance, and as weak as it may be in comparison to other forces of the Universe, it is the only one with a cumulative nature. From this it follows that if there is enough time two bodies (despite the total mass and the distance that separates them) will always end up connecting gravitationally.

This conclusion is powerful and begs the question: will the bodies throughout the Universe be able to attract each other gravitationally? Or: will they be able to stop the expansion? Is there enough gravity in the Universe that one day it will stop expanding?

Despite the focus on the future the answer to the last question clearly lies in the present and to answer it we must ask ourselves what there is in the Universe today.

Instead of studying the things in the Universe today to understand what would happen to it in the future we should see how it evolves over time and then find out what is in it today. Studies which measured the variation of the Universe's expansion rate arose from this thinking.

In the twentieth century the question was whether there was enough matter in the Universe to stop its expansion. Here we can note a fundamental distinction: the question refers to whether expansion can be stopped, not slowed. The subtle difference is in the fact that the slowing, or "braking", can be so weak that the expansion never stops, but expands at an ever slower rate. According to the twentieth century view there was no doubt about the existence of a gravitational brake on the expansion of the Universe and what we needed to know was simply whether this braking was strong or weak. In the absence of a conclusive answer both scenarios were contemplated. The original expansion, which began with the Big Bang, would become ever slower until at last it would stop and reverse. The Universe would become smaller with time until sometime in the distant future everything would shrink to a minimal volume, similar to the situation of the Big Bang.

What would happen after that? A new phase of expansion, in a model with an eternal Universe, or the end of all things? This scenario in which a densely populated Universe would possess a strong brake, is known as the Big Crunch, and enchanted cosmologists for a long time. In this theory the Universe does different things in different moments of its life, showing itself as interesting and challenging. The "death" of the Universe would be hot and convoluted.

The weak gravitational brake hypothesis conceives that the Universe is not dense in which case, in a Universe with little matter and energy, the expansion increasingly slows but never stops and continues forever. This scenario is known as the Big Chill and especially enchanted astrophysicists. A Universe that grows forever, that never collapses, would allow all of its constituents to completely live through their evolutionary cycles. In this case even if the Universe could be considered boring, as it would continue repeating itself, the same thing can’t be said for what would happen inside it.

So we can think that nebulae give rise to stars and planets; that stars have time to live their life completely, dying as white dwarves or supernovas, creating planetary nebulae, pulsars or black holes, contaminating new gas clouds cyclically until there is no more primordial hydrogen and nothing more can be created. In this silent and lonely future the "death" of the Universe would be cold and slow.

Given these assumptions scientific research recognized the great need to estimate how much matter (and energy) exists in the Universe. The question would no longer be simple after the discovery of dark matter, a concept that emerged in the 1930s with the Swiss astronomer Fritz Zwicky and his studies of the dynamics of the Coma cluster of galaxies. [6] Impressed by the difference between predicted and observed movements Zwicky suggested the existence of a matter that could not be detected but nevertheless exerted gravitational force. He named it "dark matter".

This idea resurfaced with force in the late 1970s with the work of American astronomer Vera Rubin on the rotation of galaxies, in particular our own, bringing the problem to a dimension that was closer to us. [7] The existence of a type of matter that we could not detect seemed like a good solution to explain the unusual dynamics found in the observations.

So the initial question about the components of the Universe (the one that would also give us the answer about its future) is complicated. Suddenly peering into deep space and surveying what was out there was not enough. By definition there was something that would not be observed there. And that unobservable thing, the dark matter, would have a strong effect on the results sought.

Faced with this evidence the safest method appeared to be the direct study of the rate of expansion of the Universe. That is, understanding how the expansion of the Universe changes over time has become crucial not only to understand tomorrow but also today. So, instead of studying the things in the Universe today to understand what would happen to it in the future we should see how it evolves over time and then find out what is in it today. Studies which measured the variation of the Universe's expansion rate arose from this thinking. They were created for a single purpose: to find out if the brake was strong (if there was a lot of matter, including dark matter) or if it was weak.

To everyone's surprise, especially for the teams of scientists involved in the discovery, observations showed something unthinkable: the expansion of the Universe was accelerating! Not only was the brake weak but there was an accelerator, something that contradicted all existing models.

The discovery, The discovery, made in the late twentieth century, revolucionized cosmology and introduced a new component into our model of the Universe: "dark energy". Unlike dark matter which carries this adjective because it cannot be seen, dark energy was so named because it is "strange, mysterious, unexpected." Its original nickname was "funny energy", or "strange energy". [8]

Today, nearly two decades after the original discovery, we have managed to divide the Universe into three well defined blocks and we know that the largest of them is dark energy, followed by dark matter and, in a distant third, everything that we are made of (ordinary matter and energy). With this discovery we can know what will happen to the Universe in the future: an accelerated expansion that will ultimately cause the fraying of space-time itself - a scenario known as the Big Rip.

The Universe does unusual and interesting things. And as we stated when talking about the definition of the Cosmos the future of cosmological research is brilliant, mysterious and full of promise.

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