The podcast NASA's "Curious Universe" opens a window to the cosmos In Spanish, blending human stories, cutting-edge science, and plenty of imagination. Through conversations with leading scientists, we delve into the great mysteries of the universe: what dark energy is, how the cosmos expands, and what role new space telescopes play in this research.
In one of its most powerful episodes, the program delves into the called the "invisible universe"...that part of the cosmos we cannot see directly but which governs everything that happens on a large scale. With presenter Noelia González and experts like Lucas Paganini and Guadalupe Cañas Herrera, we learn about missions such as the Nancy Grace Roman Space Telescope, Euclid, James Webb or the Vera C. Rubin Observatory, and we discover how, together, they are trying to reconstruct the complete history of the universe.
A universe we barely understand: we only see 5%
One of the messages that most shocks the listener is that everything we see—people, planets, and stars— It represents barely 5% of the universeAstrophysicist Lucas Paganini explains that normal matter, the kind that forms atoms, molecules, bodies, and galaxies, is only a small fraction of the total content of the cosmos.
The remainder is divided between two enigmatic components: approximately one 25% would correspond to dark matterA substance that neither emits nor reflects light, but whose gravity acts as a "cosmic glue" that holds galaxies and large-scale structures together. Without this invisible matter, galaxies could not maintain their shape or remain cohesive as we observe them today.
The main ingredient, around one 70% of the content of the universe is called dark energyIt is not "dark" because it absorbs light, but because it represents a huge gap in our knowledge: we know it's there because of its effects, but we don't know its physical nature. This component would be responsible for the fact that the expansion of the universe is accelerating over time.
Cosmologist Guadalupe Cañas Herrera resorts to a A very clear metaphor to understand the magnitude of the problemImagine you want to bake cookies, and the main ingredient in the recipe—flour—is precisely the one you don't know. You know how much you need to make the numbers work, but you have no idea where it comes from or how it behaves.
From a scientific point of view, it is devastating to have a cosmological model that fits with incredible accuracy And yet, to depend 70% on something we don't understand. It's like being able to predict the outcome of a recipe in detail… but without knowing if you're actually making cookies, bread, or something else entirely.
How did we know that the universe is expanding faster and faster?
The podcast reviews the history of how we arrived at the idea of a universe in accelerated expansionFor much of the 20th century, the scientific community knew that the cosmos was expanding from the Big Bang, some 13.8 billion years ago, but doubts remained: would it continue to grow forever? Would it slow down due to the gravity of all matter? Or could it even stop and collapse again?
The key piece of this puzzle was provided by the astronomer Edwin Hubble in the 1920sBuilding on the earlier work of Henrietta Swan Leavitt and observations of Cepheid variable stars in the Andromeda Galaxy, Hubble was able to measure distances to other galaxies. By combining this information with spectroscopic data collected by Vesto Slipher, Hubble discovered that the farther away a galaxy was, the faster it was moving away from us.
That analysis gave birth to the famous Hubble's law, which is interpreted as the expansion of space itselfObservations with the hubble telescope And other tools helped solidify this vision. To illustrate this, the program uses a very graphic image: a raisin loaf in the oven. The raisins don't actively move through the dough, but as it rises, they all move further apart.
Decades later, in the late 1990s, a group of researchers led by Saul Perlmutter, Brian Schmidt and Adam Riess He used Type Ia supernovae—very bright and relatively uniform stellar explosions—as "standard candles" to measure cosmic expansion. His goal was to confirm that the growth of the universe was slowing down over time, as seemed reasonable if gravity acted as a brake.
The surprise was enormous: the data indicated just the opposite. The universe is not only continuing to expand, but it is doing so at an ever-increasing rate.This discovery, which revolutionized modern cosmology, earned them the Nobel Prize in Physics in 2011. Since then, the most widely accepted explanation is that an unknown form of energy "pushes" space and accelerates its expansion: dark energy.
The problem is that The physics theories we use today are not enough to explain this phenomenonNeither Newton's gravity nor Einstein's general relativity, as we understand them, fully fit the larger cosmological scales. This forces the scientific community to reconsider whether our theoretical tools are sufficient or whether we need new physical laws.
Two major paths to explain dark energy
Within the current cosmological model, Guadalupe Cañas Herrera explains two main families of theories to interpret dark energyThe first assumes that there really is a new form of energy or substance that permeates the universe and causes this accelerated expansion.
According to this approach, in the known inventory of the cosmos—primarily normal matter and dark matter— There is no other type of matter with such a marked and opposite effect to gravityGravity tends to group galaxies and clusters together, while this new component would do the opposite: separate them more and more, push them further away and accelerate their distancing.
Theoretical physicists, in this case, postulate that there must exist some kind of field or energy with exotic properties which acts as the engine of expansion. We don't know what it's made of, nor how it interacts beyond its gravitational effect, but its presence fits with observations of supernovae, the cosmic microwave background, and the distribution of large-scale structures.
The second approach does not introduce a new ingredient, but rather It questions our own equations of gravity.The standard cosmological model is based on Einstein's general relativity, a theory that has passed all experiments in the solar system and on relatively small scales with flying colors. But when we extrapolate these equations to immense cosmological distances, we may be stretching their validity too far.
Within this framework, the field of "modified gravity"This research explores potential large-scale changes to Einstein's laws. Instead of introducing a mysterious energy that accelerates the expansion, it suggests that perhaps we don't fully understand how gravity behaves in the deep universe. Depending on how the problem is approached, the priority may be to discover a new type of energy or, instead, to reformulate our fundamental equations.
Roman: The telescope that wants to reveal the invisible universe
To make progress on these issues, more than good ideas are needed: we need observatories capable of scrutinizing the cosmos with unprecedented precisionThat's where NASA's Nancy Grace Roman Space Telescope comes in, the central protagonist of the podcast episode.
Lucas Paganini, scientist and program executive for this mission, explains that the Roman is designed specifically to investigate dark energy and map dark matter in three dimensions. In addition, it will also study exoplanets and other astrophysical phenomena, but its raison d'être is to unravel the invisible universe.
With a main mirror almost two and a half meters in diameter, Roman will have a resolution similar to that of the historic Hubble Space TelescopeBut with a field of view approximately one hundred times larger. This means it will be able to cover much wider regions of the sky in each observation, accumulating a colossal volume of data.
At NASA's Goddard Space Flight Center in Maryland, the telescope is assembled and tested in a gigantic clean room similar to a colossal operating roomAny dust particle or skin cell could pose a risk to the mission, because once launched into space, Roman will be irreparable. That's why all personnel work in the classic "bunny suit," a sterile white suit that covers them completely.
When it takes off, the observatory will travel to the Lagrange point 2 (L2), located about 1,5 million kilometers from Earthapproximately four times the distance between our planet and the Moon. From that stable and cool orbit, ideal for infrared observations, Roman will be able to calmly gaze into the deep universe.
The scientific heart of the mission is its wide field instrumentIt is a large cylinder attached to a panel that houses its sophisticated electronics. It is optimized for infrared observation, precisely the region of the spectrum where many distant galaxies become visible after their light is redshifted.
How to study dark energy without seeing it directly
One of the great difficulties of current cosmology is that We cannot directly "photograph" dark energyIt doesn't shine, it doesn't reflect, and it can't be detected directly. Therefore, Roman will act indirectly: he will observe the visible universe—in particular, billions of galaxies—to infer from their distribution, shape, and movement what is happening to spacetime.
Roman's wide-field instrument will take images with a resolution comparable to Hubble's but covering much larger areas of the skyIn this way, scientists will be able to map how matter (including dark matter, from gravitational lensing effects) is distributed throughout cosmic history.
During his extensive mapping project, Roman will study galaxies spanning from the current universe to times when the cosmos was only about 500 million years oldapproximately 4% of its age. By analyzing how the distances between galaxies have changed and how cosmic structures have formed, cosmologists can test different models of dark energy and gravity.
The key is in the redshift of lightAs the universe expands, electromagnetic waves stretch like a spring: the wavelength increases, and the light shifts toward the red and infrared regions of the spectrum. The farther away a galaxy is, the more its light has been stretched during its journey to us.
By precisely measuring how much the light from each galaxy has been redshifted, scientists can to estimate its distance and, at the same time, the moment in cosmic time in which we are seeing itWith millions of these measurements, three-dimensional maps are built that show how the expansion and distribution of matter change over billions of years.
Roman will also perform a large study of type Ia supernovaeThese same events spurred the discovery of accelerated expansion. These stellar explosions serve as reference points of known brightness: by comparing their intrinsic luminosity with the observed luminosity, extremely precise distances are obtained. With a huge sample spread across the sky and from different eras, it will be possible to determine whether dark energy has always behaved in the same way or whether it has varied over time.
A network of telescopes working as a team
Roman will not operate alone. The story told in the podcast emphasizes that Modern cosmology is a collaborative effort where different observatories complement each other.Each telescope provides a different type of data or approach, but they all fit together in the same cosmic puzzle.
The European Space Agency (ESA) is leading the mission Euclid, launched in 2023With a key contribution from NASA in the form of near-infrared detectors very similar to those carried by the James Webb Space Telescope, Euclid is also creating a three-dimensional map of the universe, observing billions of galaxies at distances of up to 10.000 billion light-years.
Its main objective is to trace the "footprints" of dark energy through the shape, position, and distances of galaxies. By combining matter distribution maps and gravitational lensing measurements—the apparent distortion of background galaxies by the gravity of foreground dark matter—Euclid and Roman will provide complementary perspectives on the same problem.
Guadalupe Cañas Herrera has played important roles in Euclid, both from the ESA, as well as institutions such as the Royal Observatory of Edinburgh or Leiden UniversityAmong other responsibilities, he led the development of CLOE (Cosmological Likelihood for Observables in Euclid), a software that allows comparing observed data with the theoretical predictions of different cosmological models.
In parallel, the james webb space telescope It focuses on observing small fields of the sky with incredible detail, studying extremely distant galaxies, star formation, and exoplanet atmospheres. Roman, on the other hand, will cover much larger areas with less fine detail—something like going from an extreme zoom to a cosmic wide-angle lens.
To all this is added the Vera C. Rubin Observatory, in ChileA powerful ground-based telescope supported by a large international collaboration that includes the U.S. National Science Foundation. The observatory is named after the astronomer who provided the first compelling evidence for the existence of dark matter by studying the rotation curves of galaxies.
Rubin will perform a systematic survey of the sky over timeThis will allow the detection of variable and transient phenomena, as well as contribute to a better understanding of dark energy. Missions like SPHEREx, which will map the entire sky in the near-infrared and observe hundreds of millions of galaxies, also come into play, adding another piece to the puzzle.
Lucas Paganini compares this ecosystem of instruments to the way in which We study the Earth using satellites and street-level photographsWe need images from different scales and angles to build a complete map: the same is true for the cosmos. No single telescope is enough to capture its full complexity.
Exoplanets, coronagraphs and citizen science
Although the central focus of the episode is dark energy, the podcast also shows that Roman will be a revolutionary tool for the search and characterization of exoplanetsThe mission has a technological demonstration coronagraph instrument that will block the blinding light of stars to reveal the planets orbiting around them.
A coronagraph works like a small opaque disc that It blocks the star's brightness in the telescope's field of view.This creates a shadow zone where much fainter objects, such as distant worlds, can become visible. This technology tests optical and light control techniques that will be essential for future observatories dedicated to searching for signs of habitability on exoplanets.
Roman's coronagraph will serve as the basis for the Habitable Worlds ObservatoryA future NASA mission designed to study Earth-like planets in unprecedented detail. The goal is to detect features such as the possible presence of oceans, atmospheres, or chemical compounds that suggest habitability.
Furthermore, Roman's wide-field instrument will perform a unprecedented planetary census within our galaxyThanks to techniques such as gravitational microlensing and precise transit observation, thousands of new exoplanets with a wide range of sizes and orbits are expected to be discovered.
With that catalog, researchers will be able to estimate How common are planetary systems similar to ours?With rocky planets in habitable zones, distant gas giants, icy worlds… and all the diversity we are already beginning to glimpse. Just a few decades ago, not a single exoplanet was known; now, we have cataloged more than 6.000, and the number will continue to grow.
NASA also promotes projects in citizen science as Dark Energy ExplorersThrough these initiatives, anyone with an internet connection can collaborate in data classification or analysis, helping to accelerate discoveries. It's a way of opening the door to the cosmic laboratory to society as a whole.
Knowledge that grows with time… and with curiosity
One of the most inspiring messages of the episode is that Our knowledge of the universe is still in its infancy.Lucas Paganini uses the image of a baby who only knows the room he lives in: he believes that room is his whole world, until one day he discovers that there is a house, then a neighborhood, a city, a country and, finally, an entire planet.
Something similar happens to us with the cosmos. We know that there is a "cosmic neighborhood" of galaxies, clusters, and filamentsBut we still don't have all the data needed to understand how it is organized, how it evolves over time, and what role dark energy plays in that process.
Each new set of observations—whether from Roman, Euclid, Rubin, Webb, or any other observatory—adds a small grain of sand to the great edifice of knowledgePerhaps an isolated result may seem insignificant, but added to many others it helps us to refine models, discard theories and pose new questions.
Guadalupe Cañas Herrera points out that, if the data ends up demonstrating that We need a different kind of physics to describe the universeThis doesn't mean that everything that came before was "wrong," but rather that there are still parts to complete. It could be a tough moment scientifically, because it would require rebuilding part of the theoretical framework, but it would also be incredibly exciting.
In parallel, the podcast emphasizes the The importance of nurturing scientific curiosity from childhoodGuadalupe is grateful to her father for never extinguishing her thirst for knowledge, for taking the time to seek answers, and for accompanying her on small experiments or observing the sky with binoculars. She encourages families to do the same: if there is a curious child at home, the best thing you can do is encourage them to ask questions, and more questions.
The history of scientific progress reminds us that In just a few decades we have gone from knowing of no exoplanets to discovering thousandsand from considering cosmic expansion a mere theoretical prediction to precisely measuring its acceleration. Now, the great task ahead is to figure out exactly what dark energy is and how it fits into a complete description of the universe.
"NASA's Curious Universe" conveys the idea that Our understanding of the cosmos expands at the same time as the universe itself.Driven by international collaboration, cutting-edge technology, and the insatiable curiosity of those who dedicate their lives to these questions, this project leaves the door open for anyone—including you—to one day contribute their own grain of sand to this search for answers about the invisible universe and distant worlds that may harbor other forms of life.
