From ancient philosophers to modern astronomers, humanity has long been contemplating the stars, wondering what exists beyond them. But many questions still remain unanswered – including how vast the cosmos really is.
In the last century, advances in observation and technology radically transformed our understanding of the universe. Thanks to instruments such as the James Webb (JWST) space telescope and decades of research, today we know more than ever about the size, shape and rate of expansion of the universe. But many questions still remain unanswered – including how vast the cosmos really is.
A century of discovery
In the early twentieth century, the astronomer Edwin Hubble changed our understanding of the night sky. Based on the fundamental work of Henrietta Swan Leavitt and others, Hubble revealed that what was once thought to be clouds of hazy gas, such as the Andromeda nebula, were actually whole galaxies far beyond our Milky Way. Used long exposure photography to capture variable stars images Cefeid – Pull stars whose predictable brightness patterns allowed astronomers to estimate cosmic distances.
Hubble’s innovative work in 1929 confirmed that the universe was expanding, a concept that had previously been theorized by astronomers such as Knut Lundmark. These findings launched the foundations of modern cosmology and redefined our place in the cosmos.
An endless limit?
Despite the huge advances, there are limits to what we can know. And now, we have bad news: “There is physically no way to know the size of the universe“Explains the astrophysics Sara Webb of Swinburne University of Technology, Ao.
What we can observe covers approximately 93 billion light years in diameter-the sphere of the “Observable universe”. This distance is not only 13.8 billion years since Big Bang, but also the continuous expansion of the space itself. Since space has been expanding since the beginning of the universe, the light of some of the oldest galaxies traveled impressive 46.5 billion light years to reach us.
This rapid expansion of space – faster than the speed of light – challenges intuitive physics, but is a fundamental feature of cosmological models.
“The emptiness of space and time does not really obey the laws of matter and physical things,” explains Webb. Although we cannot determine if the universe has a limit, many scientists believe it can be infinite.
What is the form of the universe?
Current evidence supports the theory that the universe It is “plan”. Not in the two-dimensional sense, but in the geometric context of spacetime, which is quadidimensional.
If the universe were curved as a sphere or a Donute, traveling straight through the space could eventually take it back to the starting point. Instead, a flat universe implies that this trip would continue indefinitely without returning to the starting point.
This form helps scientists refine cosmic expansion models and understand the effects of gravity on light and matter in vast distances.
Deviation to red and standard candles
The original observations of hubble were based on the “Red Deviation”a phenomenon similar to the doppler effect. Just as the tone of a siren changes depending on whether it is approaching or moving away from itself, the wavelength of light also changes. The light of the moving galaxies seems to be redder, and the farther a galaxy is, the redder its light becomes.
In addition to the deviation to red, astronomers use “Standard candles” to measure distances in the universe. They are objects with known intrinsic shine, such as cefected variables and certain types of supernovae. By comparing the brightness of these objects from the earth, astronomers can calculate the distance they are in – very similar to estimating the distance from a lamp based on their intensity.
Doctoral student Abigail Lee of the University of Chicago explains: “We know that these stars have exactly the same intrinsic brightness and therefore we can use this property to measure the distance.”
The role of dark energy
In 2011, three scientists received the Nobel Prize in Physics for the discovery that The universe is not just expanding – expansion is accelerating. This is believed to be driven by dark energy, a mysterious force that drives away the galaxies.
Unlike gravity, which attracts matter, dark energy seems to exert a repulsive force in space. However, this expansion is not noticeable at small scales. Gravity still dominates within galaxies, solar systems and even planetary orbits. Expansion becomes evident only when extremely distant objects are observed.
Hubble’s constant and tension
One of the most debated issues in cosmology is the speed with which the universe is expanding-a rate known as Hubble constant (H₀). Edwin Hubble initially estimated this speed at about 500 km/s per megaparsec, but modern measurements put it closer to 65–75 km/s/m.
However, scientists using two different methods continue to obtain inconsistent results. An approach is based on nearby standard candles, producing a value of about 73 km/s/m/MPC. Another uses observations of the microwave cosmic background-the oldest detectable light in the universe-and estimates H₀ at about 67 km/s/m/MPC.
This discrepancy, known as “Hubble tension”, remains without solution. Lee states, “Both measurements have so accurate uncertainties that there is no room for errors.” Even with better technology and JWST data, the discrepancy persists.
Some researchers believe that these differences may result from uneven measurement errors. Others suggest that they may indicate the need for new physics – perhaps a better understanding of dark energy or even a totally new theoretical picture.
And then?
Scientists are investigating both possibilities: to improve observation methods and explore new theoretical models. “Complementary approaches are good,” says Lee: “Perhaps we can stop looking for mistakes if people find a physical theory that connects everything, and perhaps they can stop if we find a big measurement error.”
However, the future of this investigation is uncertain. Large projects face significant budgetary threats. One of these missions, the Nancy Grace Roman space telescope, was specifically conceived to investigate the dark energy and the expansion of the universe. It is almost ready to be launched – below the budget and before the deadline – but the financing cuts proposed for NASA can prevent it from reaching the space.
In the end, even with our best bright instruments and minds, the universe still holds numerous mysteries. But what scientists have discovered over the last century is nothing less than remarkable. From the identification of galaxies beyond ours to the detection of cosmic acceleration, these discoveries continue to reshape our understanding of their own existence.
As webb says, “dark energy is in crisis at the moment, because nothing really agrees, although all the science that has been done is incredibly strict.” Whether the answer is in new technologies, new observations, or revolutionary theories, the pursuit of understanding the cosmos continues – and depends on both curiosity and commitment.
