Since our ancient human relatives began using stone tools to perform tasks, humans have harnessed scientific knowledge and new technologies to expand the boundaries of our understanding of the natural world. From quantum computing and microplastics to artificial intelligence and memory, explore these topics and more with our concise yet informative overviews and expert-curated resources.
Hours of research by our editors, distilled into minutes of clarity.
The Jungfrau Railway utilizes electric trains powered by hydroelectric energy to ascend the Swiss Alps, while Poland's Elbląg Canal hauls ships along cable-powered tracks driven by waterwheels. Germany's Wuppertal monorail navigates bends as it glides over a river valley, and New Mexico's Holloman High-Speed Test Track can achieve speeds of Mach 8.6 for rocket sleds.
More massive stars burn through their fuel at ever-increasing rates, causing them to have shorter lifetimes than less massive stars, despite starting with more hydrogen to fuse. In clusters of stars that likely formed together, observing what mass stars are no longer fusing hydrogen estimates the age of the cluster.
Mercury deviates within 7 degrees of the ecliptic that marks the path of the sun, with the other planets varying from 3 degrees to approximately flat. Even an alignment within 1 degree between all eight planets is estimated to occur only once every 13.4 trillion years.
The competition pits teams against each other in eight races targeting different innovations, such as arm prostheses, leg prostheses, and vision assistance. Participants in the Cybathlon use it to push the boundaries of technology, including brain implants and assistive software that incorporates AI.
According to quantum physics, traveling back in time to kill one's grandfather would not cause a paradox because time travel would bring one to a new timeline, where the person killed is not one's grandfather. Alternatively, causality would not be violated because the universe would prevent the murder from occurring.
Under this scenario, all matter and energy will be scattered as far out as possible, with no stars left to produce measurable light between objects. With no way of observing changes or increasing the disorder of the universe further, events could not be distinguished from one another, and time would lose meaning.
Within quantum mechanics, matter simultaneously exists as both fixed particles and extended waves, allowing it to emerge across barriers—just as sound travels through walls—before it fully enters the obstacle. The resulting measurements can show that particles spent negative time within a barrier, with the future occurring before the past.
Within physics, the second law of thermodynamics states that entropy always increases, as seen by a concentrated drop of dye slowly diffusing throughout a cup of water, increasing disorder. Because such processes do not unfold in reverse, entropy may be what provides time with a single direction, unlike space.
The frequency of visible light is significantly greater than that of microwaves used in cesium atomic clocks. This makes optical clocks about 100 times more accurate, losing at most one second across the entire age of the universe.
These absorptions happen in cycles, where one second is defined as 9,192,631,770 cycles of cesium atom radiation. Strontium atoms can be used to make clocks that do not gain or lose a second in 15 billion years.
