While there are a great number of exoplanets out there that may house life, including exoplanets that are very different from Earth, we must be careful to distinguish possible biosignature molecules from abiotically produced ones, and be aware that many different atmospheric scenarios will have similar spectral features with vastly different molecules. K2–18b, hailed as a Hycean world with dimethyl sulfide in its atmosphere, may not be any of those things. (Credit: ESA/Hubble, M. Kornmesser)
A Cambridge-based team claims to find molecules on an exoplanet that are only produced by life on Earth. Don’t fall for the unfounded hype.
Out there in the Universe, every stellar system is like a lottery ticket. Every time a new star forms, there’s a chance that it’s going to form planets, including possibly rocky, Earth-sized planets. There’s a chance that the right conditions will emerge on that world — a mix of the raw chemical elements, a source of energy, and stable, life-friendly conditions — that allow for the creation of molecules that metabolize resources and can self-replicate. And there’s a chance that those molecules will survive and thrive over time, creating life that can evolve and alter the conditions on the planet itself. While we can be certain that Earth is one of the winning tickets in this cosmic lottery, it’s plausible that there are many other winners, including on worlds that are very different from Earth itself.
Although no one has yet found our second example (after Earth) of a definitively inhabited planet, a recent exciting claim asserts that we’ve now come tantalizingly close: by finding signatures of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) in the atmosphere of exoplanet K2–18b…
This illustration shows a human colony within a dome on an otherwise uninhabited planet. Humans have often dreamed of colonizing other worlds: both within our Solar System and beyond.(Credit: Corepics VOF/Shutterstock)
In all the known Universe, Earth is the only planet known to have native life. What should guide us in expanding humanity beyond our world?
Back in ancient times, we knew that there were five wanderers — or planets — that moved through the night sky: Mercury, Venus, Mars, Jupiter, or Saturn, in addition to the Moon and the stars. For generations, humans invented stories about the types of aliens that might be living on those worlds, and speculated wildly about what kinds of life forms might exist on worlds that orbited around other stars far beyond our own Solar System. Today, we know of more planets and many more moons within our Solar System, and are closing in on 6000 confirmed exoplanets around stars elsewhere in the Milky Way. All told, there are expected to be hundreds of billions or even trillions of planets within our galaxy, but none are yet known to harbor any form of life at all.
As humans, our dreams of space exploration are often accompanied by another dream: that of space colonization. Could we extend humanity’s presence to worlds other than our own? And if we can, should we? And if so, how should we do it in an ethical fashion? That’s the question of Anniece Isler, who was talking with her daughter and the…
In July of 1969, humanity took our first steps on the surface of another world: the Moon. This was the crowning achievement of NASA and the space program in the 1960s, representing a global victory for science and human achievement. Now, in 2025, it’s time to step back onto the path of science once again, and bring about a 21st century civilization that surpasses even the 20th century’s greatest achievements. (Credit: NASA/Apollo 11/Neil Armstrong)
After drastic cuts to the NIH, the FDA, the NSF, and the DOE, NASA science faces down its smallest budget ever. All of society will suffer.
It should be every scientist’s greatest fear: that 2025, in the United States, will mirror very closely what happened in Nazi Germany in 1933. In the 1920s and 1930s, physics and mathematics in Germany was second-to-none. Einstein achieved his great successes in Germany, and was lauded as a national hero for his work on relativity, quantum physics, the equivalence of mass and energy, and more. Lise Meitner, the first woman to become full professor (außerordentlicher) of physics in Germany, at the Kaiser Wilhelm Institute, and a codiscoverer of nuclear fission, was called “the German Marie Curie” by Einstein himself. Hans Krebs, Fritz Haber, Otto Stern, Leo Szilard, Edward Teller, Eugene Wigner, Otto Frisch, Max Born, Felix Bloch, Hans Bethe, and Viktor Weisskopf, among others, were incredibly prominent and successful German scientists during this time.
And then, on April 7, 1933, Germany passed a law making it illegal for those considered to be Jewish to hold any civil service jobs, including as physics or mathematics professors. By time the year ended, 18 mathematicians at the…
The SARS virus (orange) has a crown-like structure, meaning that it’s part of the coronavirus family of diseases. The novel coronavirus SARS-CoV-2, also known as the virus which causes COVID-19 in humans, is the largest, most lethal and long-term detrimental new pandemic to hit planet Earth since the dawn of the 21st century. Despite having a genetic sequence of only ~30,000 base pairs in it, this virus has killed over 7 million people since 2020, with many estimates for the true number of deaths rising into the tens of millions. (Credit: NIH)
In theory, scientists could’ve produced a deadly virus that accidentally infected lab workers. In practice, we know that didn’t happen.
For a very long time, after speaking with an enormous number of virologists and experts in related, adjacent fields — from the pandemic’s early days up through to the present — I’ve been someone who’s asserted that we can be certain that SARS-CoV-2, the virus that causes COVID-19, definitively spilled over from a wet market in China into the human population. The other mainstream narrative, that the virus was created in a Chinese laboratory through gain-of-function research which then infected lab workers at the Wuhan Institute of Virology, is undermined and refuted by an overwhelming suite of scientific evidence, all of which points towards the zoonotic spillover scenario.
You would think that going to the relevant experts and asking them what the scientific evidence supports, including why and how, would be the way to truly uncover the origins of the 21st century’s greatest global pandemic so far. But instead, the majority of Americans believe that the lab leak scenario — itself a conspiracy theory — has more merits, and that the “real” conspiracy is taking place among scientists who seek…
From the main mine that humans made in the Oklo region, one of the natural reactors is accessible via an offshoot, as illustrated here. The large uranium deposit present underwent nuclear fission on and off for hundreds of thousands of years some ~1.7 billion years ago. The yellow rock is uranium oxide. Oklo data shows that the fine-structure constant, which depends on the electron charge, the speed of light, and Planck’s constant, changes by less than ~0.3 parts in 10 quadrillion (10¹⁶) per year, eliminating the tired-light plus varying fundamental constant scenario. (Credit: Robert D. Loss (Curtin U.); US Dept. of Energy)
Planets can create nuclear power on their own, naturally, without any intelligence or technology. Earth already did: 1.7 billion years ago.
If you were hunting for alien intelligence, looking for a surefire signature from across the Universe of their activity, you’d have a few options.
You could look for an intelligent radio broadcast, like the type humans began emitting in the 20th century.
You could look for examples of planet-wide modifications, like human civilization displays when you view Earth at a high-enough resolution.
You could look for artificial illumination at night, like our cities, towns, and fisheries display, visible from space.
And there are many other options: you can look for a unique chemical “fingerprint” of biological processes in an exoplanet’s atmosphere by performing spectroscopy on the planet’s atmosphere, or rapid long-term evolution of certain chemical species. After all, there’s a tremendous amount you can learn even from a single pixel if you can directly image an Earth-sized exoplanet.
But there are technological achievements that we’ve realized here on Earth as human civilization has…
From their earliest beginnings to their final extent before fading away, Sun-like stars will grow from their present size to the size of a red giant (~the Earth’s orbit) to up to ~5 light-years in diameter, typically. The largest known planetary nebulae can reach approximately double that size, up to ~10 light-years across, but none of this necessarily means that the Sun is a typical, average star. (Credit: Ivan Bojičić, Quentin Parker, and David Frew, Laboratory for Space Research, HKU)
In around 7 billion years, we expect the Sun to run out of fuel, dying in a planetary nebula/white dwarf combination. Is that for certain?
Whenever a star is born, it expectantly follows a specific life cycle.
This Hubble Space Telescope image of open star cluster NGC 290, showcases a region where thousands of newborn stars were created 30–60 million years ago. They come in a wide variety of masses, where a combination of their initial mass and future interactions will determine their ultimate fates. (Credit: ESA and NASA; Acknowledgment: E. Olszewski (University of Arizona))
Stars are hot, dense balls of gas and plasma.
This cutaway showcases the various regions of the surface and interior of the Sun, including the core, which is the only location where nuclear fusion occurs. As time goes on and hydrogen is consumed, the helium-containing region in the core expands and the maximum temperature increases, causing the Sun to “cross the main sequence” as its energy output increases. The balance between the inward-pulling gravity and the outward-pushing gas pressure, only slightly augmented by radiation pressure, determines the size and stability of a star, while the core’s temperature and element abundance determines the rate and species of fusion inside. (Credit: Wikimedia Commons/KelvinSong)
Inside their cores, nuclear fusion occurs: fusing light elements into heavier ones, liberating energy.
The most straightforward and lowest-energy version of the proton-proton chain, which produces helium-4 from initial hydrogen fuel. Note that only the fusion of deuterium and a proton produces helium from hydrogen; all other reactions either produce hydrogen or make helium from other isotopes of helium. This reaction set occurs in the interiors of all young, hydrogen-rich stars, regardless of mass. (Credit: Sarang/Wikimedia Commons)
After its formation some 4.6 billion years ago, the Sun has grown in radius by approximately 14%. It will continue to grow, doubling in size when it becomes a subgiant, but it will increase in size by more than ~100-fold when it becomes a true red giant in another ~7–8 billion years, total, all while growing in brightness by a factor of at least a few hundred. (Credit: ESO/M. Kornmesser)
For stars like the Sun (or more massive), the star evolves: swelling into a red giant.
As the Sun becomes a true red giant, expanding to over 100 times its current size as its interior contracts and heats up to fuse helium, the Earth itself may be swallowed or engulfed, but will definitely be roasted as never before. The Sun’s outer layers will swell, but the exact details of its evolution, and how those changes will affect the orbits of the planets, still have large uncertainties in them. Mercury and Venus will definitely be swallowed by the Sun, but Earth will be very close to the border of survival/engulfment. (Credit: Fsgregs/Wikimedia Commons)
When a main sequence star, like the Sun, runs out of hydrogen in its core, its core becomes inert and the star expands into a subgiant, while hydrogen fusion continues in a shell surrounding the core. Eventually, the core contracts and heats up, where it can initiate helium fusion if the star’s core gets hot enough, which will only happen for sufficiently massive stars. (Credit: Thomas Kallinger/University of British Columbia/University of Vienna)
The prediction of the Hoyle State, an excited state of a carbon-12 nucleus, and the discovery of the triple-alpha process is perhaps the most stunningly successful use of anthropic reasoning in scientific history. This process is what explains the creation of the majority of carbon that’s found in our modern-day Universe: created in the hearts of evolved stars that fuse helium into carbon. The work of Hoyle, Fowler, and the Burbidges demonstrated that carbon was created via the process of stellar nucleosynthesis, rather than during the hot Big Bang. (Credit: E. Siegel/Beyond the Galaxy)
These two projections show the primordial sky in microwave light as seen by ESA’s Planck mission. At left, a hemispherical projection (encapsulating half of the sky) is shown; at right, a Mollweide projection (encapsulating the full sky) is shown. (Credit: ESA/Planck Collaboration (both); Damien George/thecmb.org (L))
It’s difficult to project a sphere onto a flat, two-dimensional surface. All maps of the Earth have flaws; the same is true for the cosmos.
The Universe is a vast and expansive place. From any location, you have total freedom to look in any direction you like: up or down, left or right, and near or far, to any distance in any direction that you choose. (Well, so long as there isn’t anything nearby in the way of a more distant object that you want to observe.) It’s like you have a buffet, an omnidirectional buffet, of targets to choose from. You can even imagine observing it all: not just the half of the sky you can see by lying down in a field on a clear night, but in all directions all at once, like if you had an array of lenses that looked around in all 360° at once (plus the ability to view 90° up and down from the horizontal), that gathered light from all possible angles simultaneously.
And yet, when we show images of the cosmic microwave background — whether from COBE, WMAP, Planck, or a different mission — they’re almost always shown as oval-shaped. What does that oval shape actually show us, and why do astronomers make that specific visualization choice? That’s what Ed Matzenik wants to know, writing in to ask:
“I don’t understand the projections we see of the CMB. They are usually a circle or an oval. Is that the whole sky or just a section? If I was looking at a sphere from inside I don’t know how I’d represent it on a flat sheet… hope you can clear up this mystery for me.”
Honestly, the first time I encountered them — and remember, I’m a professional cosmologist who first encountered them in graduate school — I suffered from almost exactly the same puzzlement. Let’s begin with something we’re much more familiar with in order to get started: planet Earth.
This view of the Earth comes to us courtesy of NASA’s MESSENGER spacecraft, which had to perform flybys of Earth and Venus in order to lose enough energy to reach its ultimate destination: Mercury. Several hundred images, taken with the wide-angle camera in MESSENGER’s Mercury Dual Imaging System (MDIS), were sequenced into a movie documenting the view from MESSENGER as it departed Earth. Earth, an oblate spheroid, rotates roughly once every 24 hours on its axis and moves through space in an elliptical orbit around our Sun. (Credit: NASA/MESSENGER)
This is going to sound obvious, but the first thing you have to realize about planet Earth is that, to a first approximation, its shape is spherical. The most accurate tool we use to model and represent…
If each time a quantum decision were made, our timeline split to allow for two (and only two) possible outcomes, then the number of overall possibilities would increase incredibly rapidly, depending on which combinations of outcomes and what order-of-interactions are allowed. These possibilities cannot all fit within our physical, observable Universe, but the mathematical structure known as a Hilbert space can contain them all. (Credit: E. Siegel/public domain)
The Multiverse isn’t just a staple of science fiction; there’s real-life science behind it, too. Here are 10 facts to expand your mind.
Bring up the concept of the Multiverse, and you’re likely to get a variety of responses. Some will look to it as an idea full of hope: the hope that there’s a version of you out there that made a bolder choice, had a better outcome, or avoided a critical blunder at some point along your life path. Maybe, out there in the Multiverse, is a version of you with a better life, a fatter wallet, a superior job and career, or a version who didn’t suffer the great losses, illnesses, or setbacks you’ve had to reckon with. On the other hand, maybe there are versions of you out there that have suffered far worse than you, including versions where you haven’t made it alive and well to the present day. The Multiverse, at least as most people think of it, is full of our hopes and fears as much as it is of any flavor of physics.
one that arises from the many-worlds interpretation of quantum mechanics,
and one that arises from the fact that out there, beyond the limits of our observable Universe, is “more universe” that’s forever beyond our reach, perhaps even an infinite amount of it, and perhaps where parts of it are very, very different from the Universe we inhabit and recognize.
I had the pleasure to film a video with Big Think about The secret of the multiverse, and to go along with this video, I’ve compiled a story highlighting 10 facts that challenge the way you think about the reality that arises from the Multiverse. Enjoy the video, and the 10 facts, below.
By creating two entangled photons from a pre-existing system and separating them by great distances, we can ‘teleport’ information about the state of one by measuring the state of the other, even from extraordinarily different locations. Interpretations of quantum physics that demand both locality and realism cannot account for a myriad of observations, but multiple interpretations all appear to be equally good. (Credit: Melissa Meister/ThorLabs)
Over a century after we first unlocked the secrets of the quantum universe, people find it more puzzling than ever. Can we make sense of it?
In all the Universe, with all we’ve learned about the underlying properties of reality, perhaps nothing mystifies our intuition more than the notion that reality is fundamentally quantum in nature. It isn’t puzzling so much for the fact that matter and energy can be broken down into fundamental, indivisible units known as quanta; that intuitive idea goes all the way back to ancient times, traceable to Democritus of Abdera. Instead, the troublesome aspect comes from the fact that, when we examine it closely, reality appears to be fundamentally indeterminate in nature. Moreover, the better we try and determine some aspect of it, the greater the fundamental uncertainty that arises in other places.
Is there a way to make intuitive sense of this? And how does the quantum nature of our very existence show up in our macroscopic, everyday lives? That’s what several people have recently written in to inquire, with the most succinct version of that question coming from Pat Connolly, who asks:
“Can you explain what it means to live in a quantum universe? Specifically, how does it impact and effect our “normal” day to day human activities?”
It sounds trite to say it, but our Universe as we know it, as well as life on Earth, could not possibly exist without the quantum nature of reality. Here’s how to make sense of that.
In a traditional Schrodinger’s cat experiment, you do not know whether the outcome of a quantum decay has occurred, leading to the cat’s demise or not. Inside the box, the cat will be either alive or dead, depending on whether a radioactive particle decayed or not. Although it’s rarely discussed, the validity of a Schrodinger’s cat experiment depends on the system being isolated from its environment; if the isolation isn’t perfect, the quantum nature of the superposition-of-states will be disrupted. (Credit: Dhatfield/Wikimedia Commons)
At the heart of quantum physics are a few simple realizations. The first one is obvious: that if you break the “stuff” that the Universe is made of down into its smallest, indivisible components, you will arrive at what know as fundamental particles. These particles come in two main classes:
Fermions, which are half-integer spin particles, including quarks (like the up and down quarks that make up protons and neutrons), charged leptons (like the electron), and neutrinos, as well as their…
This fun graphic illustrates the tension on Λ, Einstein’s cosmological constant, exerted by combining supernova data (right), baryon acoustic oscillations (left), and the cosmic microwave background (top). When all three data sets are combined, the idea of a cosmological constant struggles to hold together; it’s possible that something, but perhaps not necessarily Λ, is going to give. (Credit: Claire Lamman)
DESI, by mapping galaxies, has claimed they see evidence for dark energy evolving by getting weaker. But that’s only one interpretation.
There’s an extremely powerful idea in science that we take for granted, but apply all the time. The idea is simply this: that if we know the laws and rules governing a physical system, and we also know what the initial conditions of that system are, then we can apply the known rules to those initial conditions and evolve our system forward in time, making exquisite predictions for that system’s properties at all times. We can even do this for the entire Universe, with initial conditions given by the inflationary hot Big Bang and the types of energy present within our Universe, and then evolve it forward to form atomic nuclei, neutral atoms, stars, galaxies, and the grand cosmic web, all as the Universe expands and cools.
Our standard picture for this scenario, which fell into place in the late 1990s and early 2000s, is simply known as ΛCDM today. The Λ is for dark energy, which is assumed to be Einstein’s cosmological constant (from General Relativity) in its simplest form and makes up 68% of the Universe’s total energy today. The CDM is for cold dark matter, which makes up the majority of the rest of the cosmic energy budget (27%), with the remaining 5% made up of normal atom-based matter, plus a little bit more in the forms of photons and neutrinos.
Although this picture is excellent, it isn’t perfect. The Hubble tension shows us how measuring the Universe in different ways leads to different values for the expansion rate. There’s a tension in how rapidly structure forms on specific scales: the Sigma-8 tension. And now, with the latest data release from the DESI collaboration, we have strong, but not overwhelming, evidence in favor of evolving dark energy. But despite some very intriguing claims, things aren’t necessarily pointing to a cosmic revolution. Here’s the science that everyone should understand.
Measuring back in time and distance (to the left of “today”) can inform how the Universe will evolve and accelerate/decelerate far into the future. By linking the expansion rate to the matter-and-energy contents of the Universe and measuring the expansion rate, we can come up with an estimate for the amount of time that’s passed since the start of the hot Big Bang. The supernova data in the late 1990s was the first set of data to indicate that we lived in a dark energy-rich Universe, rather than a matter-and-radiation dominated one; the data points, to the left of “today,” clearly drift from the standard “decelerating” scenario that had held sway through most of the 20th century. (Credit: Saul Perlmutter/UC Berkeley)
