All posts tagged: general relativity

Physicists rewrite Einstein’s equations to define spacetime evolution

Physicists rewrite Einstein’s equations to define spacetime evolution

Spacetime is often described as the stage on which the universe unfolds, a four-dimensional blend of space and time that bends, stretches and shifts as matter and energy move through it. However, despite more than a century of work since Einstein introduced general relativity, physicists still struggle to describe how that stage evolves when gravity becomes violent, nonlinear and hard to predict. A new theoretical study points to a different way of looking at the problem. Instead of treating spacetime only as geometry, researchers found that some of its structures may behave more like features in an electrically conducting fluid. In this view, these structures stay connected as spacetime changes. That idea comes from researchers at Adolfo Ibáñez University in Chile and Columbia University, whose work was published in Physical Review Letters. Using tools borrowed from electrodynamics and plasma physics, they argue that spacetime can contain what they call gravitational field connections. Additionally, they describe conserved quantities that place topological limits on how curved spacetime can evolve. In plain terms, topology deals with what stays …

The physics of no return: What actually happens if you get pulled into a black hole

The physics of no return: What actually happens if you get pulled into a black hole

In 1916, only a year after Albert Einstein had published his general theory of relativity, Karl Schwarzschild used mathematical calculations to show this: If sufficient mass could be placed into an extremely small volume, then this sufficiently dense mass would create a zone where gravity is so strong that nothing, including light, could escape from it. One hundred years later, scientists have actually imaged the shadow of such an object. They have also recorded the gravitational waves produced when two of these celestial bodies collide. However, the ultimate question (the ultimate unresolved question) in science about the fate of matter that crosses an event horizon of a black hole is still unanswered. The answer includes a long list of things: how atomic structure changes or gets stretched during the collapse of the star, spatial distortion due to relativistic time dilation, luminous rings of matter and debris surrounding the black hole, and the nature of the event horizon itself (which has no physical wall). It is simply becoming an irreversible relationship with the universe beyond the …

Distance in space is an illusion

Distance in space is an illusion

Andromeda sounds far away because 2.5 million light-years sounds far away. It lands with authority. It feels exact. It gives you the comfort of a labeled universe, one where galaxies, stars and planets sit at fixed intervals inside a giant cosmic grid. Might be time to ease up on that confidence. Einstein, Juan Maldacena, Mark Van Raamsdonk, Brian Swingle and other physicists have pushed modern physics into a place where distance stops looking like a simple fact and starts looking more like a useful habit of thought. The old picture still works for everyday life, and for plenty of astronomy. But at deeper levels, distance gets slippery. It depends on motion. It depends on gravity. It depends on how you define the measurement. And in some of the boldest theoretical work, it may emerge from quantum entanglement rather than existing as a basic ingredient of reality. That is a startling claim, but it does not come out of nowhere. It grows out of a series of cracks in common sense, and once you follow those …

Expanding catalog of black hole collisions is rewriting the history of the universe

Expanding catalog of black hole collisions is rewriting the history of the universe

Between May 2023 and January 2024, a global network of gravitational-wave detectors picked up 128 new cosmic signals, more than doubling the entire catalog built across the previous decade. The universe, it turns out, is not quiet. It is constantly shaking. The LIGO-Virgo-KAGRA Collaboration, an international partnership spanning observatories in the United States, Italy, and Japan, has published its fourth gravitational-wave catalog, GWTC-4.0, in a forthcoming special issue of Astrophysical Journal Letters. The collection represents the most comprehensive census yet of colliding black holes and neutron stars, and it is already pushing physics into territory no one has mapped before. “The beautiful science that we are able to do with this catalog is enabled by significant improvements in the sensitivity of the gravitational-wave detectors as well as more powerful analysis techniques,” said Nergis Mavalvala, dean of the MIT School of Science and a member of the collaboration. The timeline of observing runs covering a time span starting from 2015 and lasting up to the beginning of O4b on 2024 April 10. The periods in which …

Newborn magnetar offers rare evidence of Einstein’s relativity in a stellar explosion

Newborn magnetar offers rare evidence of Einstein’s relativity in a stellar explosion

The light did not fade the way it was supposed to. After blazing into view about a billion light-years from Earth, the supernova known as SN 2024afav settled into something stranger. Its brightness rose, peaked, and then began to dip in a series of rhythmic bumps. Each pulse came a little faster than the one before it, like a chirp tightening in pitch. That unusual pattern has now given astronomers what they say is their clearest evidence yet that some of the universe’s brightest stellar explosions are powered by newborn magnetars, dense neutron stars with extreme magnetic fields and rapid spin rates. The results, published in Nature, also point to a role for Einstein’s general theory of relativity in shaping the light from a supernova for the first time. “The idea that magnetars are involved has seemed to have a magical aspect for theoretical astronomers,” stated Dan Kasen, a UC Berkeley physicist. “However, with this evidence, we can now conclude with certainty that there is, indeed, a relevant and substantial magnetar component. The supernova’s light …