Time is normally something we measure with clocks: devices that record its passage from one moment to the next. While there is an interesting philosophical case to be made that time is an illusion, the fact that we can measure, quantify, and cannot stop its passage all strongly suggests that it truly exists. (Credit: LeArchitecto / Adobe Stock) The passage of time is something we all experience, as it takes us from one moment to the next. But could it all just be an illusion? One of the most important aspects of physics, or of any science in general, is to always muster up the greatest ch ..read more

This region of space, viewed first iconically by Hubble and later by JWST, shows an animation that switches between the two. Both images still have fundamental limitations, as they were acquired from within our inner Solar System, where the presence of zodiacal light influences the noise floor of our instruments, and cannot easily be removed. (Credit: NASA, ESA, CSA, STScI, Christina Williams (NSF’s NOIRLab), Sandro Tacchella (Cambridge), Michael Maseda (UW-Madison); Processing: Joseph DePasquale (STScI); Animation: E. Siegel)From inside our Solar System, zodiacal light prevents us from s ..read more

This portrait of astronomer John Couch Adams, drawn by J.S. Stodart after a photograph by J.E. Mayall. Adams, although initially blamed for his failure to find Neptune, found tremendous success later on by linking recurring meteor showers to periodic comets. (Credit: Wellcome Images/J.S. Stodart/J.E. Mayall)Adams was infamously scooped when Neptune was discovered in 1846. His failure wasn’t the end, but a prelude to a world-changing discovery. Perhaps its human nature to want to only think positive thoughts about our heroes. With the 2024 Olympics about to begin, we hope for a clean victory fo ..read more

One of the remarkable technological developments in recent years has been that of a “learning machine,” or artificial intelligence. Although its capabilities are profound and impressive, it’s powered largely by college-level math and a large set of high-quality data. Its capabilities are not limitless. (Credit: AkimD / Adobe Stock)It’s knowledgeable, confident, and behaves human-like in many ways. But it’s not magic that powers AI though; it’s just math and data. Why do machines learn? Even in the recent past, this would have been a ridiculous question, as machines — i.e., computers ..read more

This composite view of “the Penguin and the Egg,” known as Arp 142, shows two interacting galaxies, one gas-poor elliptical and one (former) gas-rich spiral, in wavelength ranging from 0.9 to 15 microns. In infrared light, perhaps the “Penguin” looks more like a seahorse. (Credit: NASA, ESA, CSA, STScI)For its 2-year science anniversary, JWST has revealed unprecedented details in “the Penguin and the Egg.” Here are the surprises inside. It was only two years ago that JWST’s first science images were released. This view showcases the difference between the JWST’s NIRCam and MIRI views, wit ..read more

Over time, the Sun loses mass through the emission of solar wind particles and the process of internal nuclear fusion. This mass loss gradually causes the planets to outspiral, and migrate farther from the Sun. However, this is not the dominant factor affecting Earth’s climate. (Credit: NASA/GSFC)As the Sun ages, it loses mass, causing Earth to spiral outwards in its orbit. Will that cool the Earth down, or will other effects win out? One of the most important rules in all of physics is the equivalence between mass and energy, first put forth by Einstein over 100 years ago: E = mc². Perha ..read more

For the first several billion years of our Universe’s history, the Universe’s expansion rate was decreasing and distant galaxies slow in their recession from ours, as the matter and radiation densities drop. However, for the past ~6 billion years, distant galaxies have been speeding up in their recession, and the expansion rate, though still dropping, is not headed toward zero. It’s because of cosmic expansion that we can see up to 46.1 billion light-years away when only 13.8 billion years have elapsed since the Big Bang. (Credit: NASA/STSci/Ann Feild)Just 13.8 billion years after the hot Big ..read more

The Bullet Cluster, the aftermath of a galaxy cluster collision that occurred 3.8 billion years ago in a region of space located ~3.7 billion light-years away, represents very strong evidence for the existence of dark matter. The separation of the gravitational effects (blue, reconstructed through gravitational lensing) from the location of the majority of the normal matter (pink, revealed by Chandra’s X-ray capabilities) is very difficult to explain without dark matter’s presence. (Credit: NASA/CXC/M. Weiss)The Bullet Cluster has, for nearly 20 years, been hailed as an empirical “proof” of da ..read more

In 1977, NASA’s Voyager 1 and 2 spacecraft began their pioneering journey across the Solar System to visit the giant outer planets. Now, the Voyagers are hurtling through unexplored territory on their road trip beyond our Solar System. Along the way, they are measuring the interstellar medium, the mysterious environment between stars that is filled with the debris from long-dead stars. Voyager 1 became the most distant spacecraft from Earth in 1998, and no other spacecraft launched, to date, has a chance of catching it. (Credit: NASA, ESA, and G. Bacon)On a cosmic scale, our existence see ..read more

At the start of the hot Big Bang, the Universe was rapidly expanding and filled with high-energy, very densely packed, ultra-relativistic quanta. An early stage of radiation domination gave way to several later stages where radiation was sub-dominant, but still remained, while matter then clumped and collapsed into gas clouds, stars, star clusters, galaxies, and even richer structures over time, all while the space between those bound structures continues expanding. (Credit: Big Think / CfA / M. Weiss)On the largest of cosmic scales, the Universe is expanding. But it isn’t all-or-nothing ..read more