Energy source is an eternal topic of human development, as any activity in nature requires a supply of energy. In ancient times, nearly all production work relied on human or animal power, resulting in very low productivity for thousands of years. The Industrial Revolution in the 18th century changed this situation completely, replacing human labour […]
Black Holes, the most Powerful Engines in Nature Read More »
May 2021 marks a significant milestone in planetary exploration, when China’s spacecraft Tianwen-1 softly landed on the surface of Mars, and deployed the rover Zhurong. The complete success of China’s first interplanetary mission makes China the third country landing on Mars (after the Soviet Union and the United States), the second country releasing a Martian
Questioning the Heavens Read More »
In China, there is a popular nursery rhyme: Once upon a time there was a mountain, in which there was a temple, in which there was an old monk telling a story to a little monk. The story he was telling is: Once upon a time there was a mountain, in which there was a
Self-similarity: Properties and Applications Read More »
In part II we saw that in a non-rotating black hole, the spatial and temporal coordinates are exchanged. Now we can take a step further, to consider the case of a rotating black hole. The line element in such spacetime has very complicated coefficients, but we don’t need the specific expressions here. So let’s just
Can you Discriminate between Space and Time? (Part III) Read More »
In part I we showed that space and time coordinates lead to different types of interval, spacelike and timelike respectively. Hence if we are given a line element expression in terms of any coordinates, we can figure out which of the coordinates are spatial and temporal, by looking at the sign of their coefficients. The
Can you Discriminate between Space and Time? (Part II) Read More »
What is the universe? All of space and time along with their contents. The unity of space and time is well-embodied in its Chinese term: Yu Zhou, where “Yu” means all of space and “Zhou” means all of time. However, what is space and what is time, and what is their difference? This is an
Can you Discriminate between Space and Time? (Part I) Read More »
