All articles tagged with #relativity
Astronomers have identified S301, a faint main‑sequence star on an 8.7‑year, highly eccentric orbit around the Milky Way’s supermassive black hole Sagittarius A*, reaching speeds up to 25,000 km/s (about 0.08c) at pericenter. This motion probes relativistic effects and could reveal the spin of Sgr A*, with S301 likely a captured binary via the Hills mechanism.
Researchers say a wave’s energy peak can reach a detector before the pulse that carries it through interference between a direct path and a reflected path. This can make the energy seem to travel faster than light, but information remains limited to the direct path’s speed, preserving relativity. The analysis is theoretical, based on acoustic and optical models, with no lab confirmation yet.
A PRE-study shows that interference between direct and reflected waves can reshape a pulse so its energy peak arrives sooner than the direct pulse, creating an apparent super-fast energy propagation in water. Crucially, this does not allow information to travel faster than light in a vacuum, and the authors suggest the same mechanism could, in principle, apply to light; experiments with sound or light are planned to test the idea.
A new accelerating wave equation describes waves whose speed changes over time, yielding a wave-frame “proper time” and a potential microscopic arrow of time. It frames momentum as conserved in the wave’s own reference frame and suggests time-varying photonic materials could test the idea, though practical experiments face energy losses, material damage, and other challenges.
Researchers propose an accelerating wave equation that describes waves whose speed changes with time, introducing a wave’s intrinsic time and revealing relativistic-like effects; the framework suggests a microscopic arrow of time within wave mechanics and offers a new lens on momentum in dielectrics, potentially testable in time-varying photonic systems, though practical challenges like energy losses and material damage remain.
An interview with Guido Tonelli ties humanity’s long obsession with time to a journey from myth (Chronos) to modern science, explaining how relativity rewrites time for fast-moving particles and gravity, how time’s arrow emerges for macroscopic systems but can blur or reverse in microscopic realms, and how the Heisenberg principle lets physicists measure particle lifetimes (including the Higgs boson). Tonelli argues time remains fundamental but not necessarily ultimate, with future theories potentially reimagining or even abandoning it as a basic concept, a vision explored in his book Time: The Dream of Killing Chronos.
Traveling at the speed of light is impossible for any object with mass because it would require infinite energy; you can get arbitrarily close, which would produce extreme time dilation so travelers age less than those left behind. In theory, concepts like Alcubierre warp drives and wormholes exist, but they require exotic negative energy and remain beyond practical reach. Near-light-speed travel is the active frontier, with Breakthrough Starshot outlining a feasible (though engineering-heavy) path to about 0.2c for gram-scale probes rather than humans, while real interstellar journeys for larger objects remain firmly beyond our current physics and technology.
Time is relative: moving through space changes how much time passes and how distances are measured, so fast travelers experience less elapsed time than those at rest, while light’s speed stays constant for all observers; massive objects can’t reach light speed, but time dilation and length contraction arise from different paths through spacetime, with practical implications from GPS accuracy to understanding simultaneity across moving frames.
Einstein’s special and general relativity show time is not fixed: moving clocks run slower and strong gravity slows time, enabling travel into the future. Some solutions to Einstein’s equations—such as Kerr spacetime around rotating masses—mathematically permit backward time travel via closed timelike curves, but these regions are inherently unstable and no practical method of time travel exists.
Astronomers have found star S301, a Sun-like star in the highly elliptical 8.7-year orbit around the Milky Way’s central supermassive black hole Sag A*, approaching within about 24 AU at closest approach and reaching speeds near 0.08c. The orbit shows relativistic precession of about 2° per pass, along with gravitational redshift and transverse Doppler effects, enabling tests of general relativity and potential constraints on alternative gravity theories. While dust and faintness hinder spectral data today, future observatories like the Giant Magellan Telescope could measure higher-order relativistic effects, further probing gravity near a black hole.
The 1971 Hafele–Keating experiment flew four cesium atomic clocks around the world and compared them with stationary clocks, finding results that matched Einstein’s relativity: eastbound clocks lagged about 60 nanoseconds and westbound clocks gained about 270 nanoseconds (with tight error bars), due to a combination of high speed and reduced gravity. This tiny, measurable effect scales with speed and altitude and is too small to enable real-world time travel, but it underpins how GPS timing is corrected and confirms the same relativistic effects observed in satellites, spaceflight, and even astronauts’ aging. Overall, time dilation is real and measurable, yet it remains a nanosecond-scale forward-only drift in everyday contexts.
Albert Einstein, celebrated for relativity and groundbreaking insights, also had notable missteps—most famously a mistaken belief that gravitational waves might not exist due to a mathematical hiccup later corrected with peer input, and early skepticism about black holes and quantum entanglement. The process of identifying and fixing these errors, rather than undermining his genius, helped push physics forward and underscored how even the brightest minds progress through errors and rigorous critique.
A dense, thruster-free satellite named LARES-2, paired with the older LAGEOS, was laser-tracked from Earth to isolate the frame-dragging effect predicted by general relativity. By canceling Earth’s oblateness and tidal perturbations over a 1,050-day cycle, the team measured the Lense-Thirring precession to about 0.2% accuracy, confirming Einstein and narrowing alternatives like Chern-Simons theory, while also delivering a more precise Earth-tide benchmark.
Astronauts in low-Earth orbit experience a tiny amount of time travel into the future due to special and general relativity: their clocks run slower because they move fast, while being higher up slightly speeds up time; the net effect is about 20–25 microseconds per day, amounting to a few milliseconds over six months and about nine milliseconds after a year; the phenomenon is real and measurable (as shown by Hafele–Keating experiments and GPS timing), but it is far too small to impact health—spaceflight’s health effects dominate.
Sergei Krikalev’s combined 803 days in six ISS missions yield roughly 0.02 seconds of relativistic time dilation compared with Earth time, via the dominant special-relativity effect of orbital velocity (with a smaller counteracting general-relativity pull from gravity). The net result is a tiny aging difference, not true time travel, but it serves as a standard teaching example of how motion affects time. The figure remains a well-cited physics fact, though later cosmonauts have accumulated more time in space and each have their own, slightly larger cumulative dilations.