The universe encompasses everything that exists, including all of the space around us, the energy within that space, and even time itself. It includes us, the Earth, the Moon, and other planets along with their dozens of moons, asteroids, and comets. Our Sun, which the planets of our solar system orbit, is just one of hundreds of billions of stars in the Milky Way galaxy. Most of these stars have their own planets, known as exoplanets. Our galaxy, the Milky Way, is just one of billions of galaxies in the observable universe, each of which is believed to harbor a supermassive black hole at its center. Beyond all of this, the universe contains other significant components known as dark matter and dark energy, which, as of now, remain undetectable by astronomers.
Despite the universe appearing to be a vast and strange place, it is not far removed from us. Wherever you are, the edge of space is only about 100 kilometers above your head, whether it’s day or night, indoors or outdoors. Additionally, space exists beneath us as well, 12,800 kilometers below the Earth’s surface, on the opposite side of our planet, which is surrounded by the unforgiving void of space and cosmic radiation. Technically, we are already in space, as the common human phrase “outer space” suggests a separation from Earth, when in reality, Earth is just a small part of the vast universe. The environment around our planet is hospitable to life, unlike other planets. So far, Earth is the only known exception for sustaining life, as the rest of the universe is largely hostile and unforgiving.
How Old is the Universe?
Scientists estimate that the universe is approximately 13.8 billion years old. This estimate was derived by measuring the ages of the oldest stars and the rate at which the universe is expanding. By observing the Doppler shift in light from galaxies, which shows that nearly all galaxies are moving away from each other at great speeds, scientists have been able to infer the universe’s expansion. Over time, gravity will slow down the movement of galaxies, and in the distant future, galaxies will be so far apart that their light will no longer be visible from Earth. By measuring the speed and distance of galaxies, scientists have deduced that if we could go back far enough in time, before galaxies formed and stars began fusing hydrogen into helium, the components of the universe would have been so close and hot that atoms could not form, and photons had nowhere to go, as everything was concentrated in a singular point.
It is impossible to pinpoint the exact location where the Big Bang occurred because, before that explosion, the universe, space, and even time as we know it did not exist. The universe and time began with the Big Bang, expanding from a single point into the vast universe we observe today.
What is the Universe Made Of?
The universe contains all energy and elements, primarily in the form of individual hydrogen atoms, the simplest atomic element consisting of just a proton and an electron. If a hydrogen atom also contains a neutron, it is known as deuterium. When two or more atoms combine, they form a molecule. When trillions of atoms come together, particles are formed. A few tons of additional elements like carbon, silica, oxygen, ice, and some metals would create an asteroid. If 333,000 Earth masses of hydrogen and helium were combined, you would have a star similar to the Sun.
For convenience, humans categorize the various masses of matter in the universe based on their characteristics, such as galaxies, star clusters, planets, dwarf planets, rogue planets, moons, rings, comets, and meteors. These are all material collections that display different properties but are governed by the same natural laws.
When scientists began calculating these masses of matter in the universe, they noticed that our Milky Way galaxy contains at least 100 billion stars, and the universe has at least 100 billion galaxies. If all galaxies were of the same size, this would give us an estimate of around 10,000 billion billion stars. However, the universe also appears to contain a form of matter and energy that we cannot see or directly observe. All the stars, planets, comets, black holes, and other observable objects make up less than 5% of the universe. About 27% is composed of dark matter, and 68% is dark energy, both of which remain poorly understood. Scientists refer to them as “dark” because they cannot observe them directly, at least not yet.
Human Understanding of the Universe Over Time
As centuries passed, human understanding of the universe and how it works has evolved. In ancient times, humans had little to no means of comprehending the universe and thus relied on myths and folklore to explain the origins of everything, which likely reflected their questions or fears, even if those answers were incorrect.
A few centuries ago, as humans began to develop mathematics, writing, and new principles of inquiry in the search for knowledge, these myths and folklore were gradually set aside, especially with the reliance on scientific tools that revealed the true nature of the universe. Just a few hundred years ago, when people began systematically investigating the nature of things, the term “scientists” did not even exist; researchers were then known as “natural philosophers.” Since then, our knowledge of the universe has leapt forward. A century ago, astronomers first observed galaxies beyond our own, and it was only half a century ago that humans began sending spacecraft to other worlds for the first time.
In our contemporary era, space probes have traveled to the outer solar system, sending back the first close-up images of giant outer planets and their countless moons. Rovers have moved across the surface of Mars for the first time, humans have built a space station orbiting Earth with a permanent crew, and the first large space telescopes have provided breathtaking views of farther parts of the universe than ever before. In the early 21st century alone, astronomers discovered thousands of planets orbiting other stars, detected gravitational waves for the first time, and produced the first image of a black hole. With continuous advancements in technology and knowledge, humans keep uncovering new secrets of the universe, but there remains much unknown. Most of the universe that can be known is still a mystery to us. Although exploring it is not an easy task, given the universe’s age of about 14 billion years, our solar system’s age of 4.6 billion years, life on Earth existing for about 3.8 billion years, and humans only being around for a few hundred thousand years. In other words, the universe has been around roughly 56,000 times longer than our human race. Accordingly, nearly everything that has happened has occurred long before humans ever existed. Clearly, we still have many questions awaiting answers, and our current knowledge is just the beginning. More discoveries are yet to come.
Is There Other Life in the Universe?
As humanity gains a broader understanding of the universe and gathers evidence of thousands of worlds, an age-old question haunts us: is there other life out there? This is a valid question with two parts. On the positive side, we now know far more than any previous generations that our galaxy is teeming with exoplanets, some of which are rocky and similar in size to Earth and have the necessary ingredients for life, such as water and energy sources. On the negative side, observing potential microbial life signs in the atmospheres of these planets is currently out of reach, as we lack advanced technology to verify this. The technology we have consists of telescopes that are limited to remote imaging and sending results via radio, and space probes have yet to reach those places for further verification.
While the chances of finding life elsewhere remain unknown, it is fair to say that the odds are improving as there is a known list of data needed to identify planets capable of hosting life, although this list is highly speculative. This list is known as the “Drake Equation,” proposed by astronomer Frank Drake in 1961. However, as of now, this list remains empty. NASA scientists suggest that if we develop and launch a powerful enough space telescope, we could determine if there is advanced life or biological life on other planets.
Currently, scientists use the habitable zone scale, which helps identify planets that might support life, similar to Earth. Each star, like our Sun, has a specific region around it that is warm enough to support liquid water and have a suitable atmosphere. In our solar system, Earth comfortably resides within the Sun’s habitable zone, Venus lies within the inner edge, while Mars is near the outer boundary. By determining the distance between a planet and its star, the size of the star, and the amount of energy it emits, we can estimate whether a planet falls within the habitable zone. If the star is large and hot, the habitable zone would be farther away, and if it’s smaller and cooler, the zone would be closer.
Over the past quarter-century, thousands of exoplanets have been confirmed in the Milky Way galaxy, potentially hosting trillions of planets, and thousands more are expected to be discovered in the coming years. Tools like the habitable zone scale will aid planet hunters in sorting through these increasing ranks to identify the most likely candidates for supporting life. However, there are some who oppose the use of this scale as it is an estimate based solely on calculations without confirmation of its components, such as the atmosphere and its gases, which may not be suitable. They prefer using advanced telescopes, though others argue that even these are insufficient as there may be life beneath the frozen oceans of other planets, which even the most advanced telescopes cannot detect. Some also suggest the possibility of receiving a radio wave from any intelligent life in the universe or detecting a signal indicating the presence of industrial compounds like chlorofluorocarbons in an atmosphere, which can only form with human intervention.
