Lecture by Dr. Stanisław Bajtlik, Kawiarnia Naukowa 1a, December 10, 2015 [58 min] https://wszechnica.org.pl/wyklad/co-t... We all use time, but no one knows what time is - said Dr. Stanisław Bajtlik during a lecture in Kawiarnia Naukowa 1a. The astrophysicist undertook to introduce the audience to the properties of time and explain how knowledge of these properties translates into practical application. The concept of time has long puzzled humanity. And it caused concern. Heraclitus of Ephesus wrote that one cannot step into the same river twice. Sextus Empiricus stated that one cannot step into the same river twice, but not at all. Between the beginning and the end of this process, the river changes. Physical processes begin in the past and find their end in the future. That is, in spheres that do not exist here and now. If physical processes occur in something that is not there and end in something that is not there, do they occur at all? – Stanisław Bajtlik expressed these concerns. The astrophysicist also recalled the ancient paradoxes of motion. An arrow released in a bow at a given moment of its motion is in a specific place. So it remains at rest. Theoretically, it cannot be in motion, although the observer sees that it is flying. Achilles and the tortoise are racing along the same section. Achilles, as the faster runner, allows the tortoise to move away. Although Achilles runs faster than the tortoise, according to the author of this paradox he should lose the race. Because each time he reaches the place where the tortoise was, the latter will move closer towards the finish line. This paradox was solved only in the 16th century, when mathematicians discovered the concept of finite series. According to him, the sum of infinitely many elements can be finite, so in this case distances and time intervals are getting shorter and shorter. People have been measuring time since time immemorial. As Stanisław Bajtlik said, megalithic structures and the Nerba disk from 4.5 thousand years ago were probably used for this purpose. The ancient Egyptians invented sundials and the hourglass. At the turn of the 13th and 14th centuries, the first mechanical clocks were constructed, but the minute hand was only a 16th-century invention. The first pocket watches were also created at that time, but they did not become popular until the 19th century. At the turn of the 19th and 20th centuries, the first quartz clocks appeared. They use the piezoelectric phenomenon to measure time. An electric voltage applied to the side walls of a quartz crystal causes its vibrations, which are counted by the watch system. Such measurement is much more accurate than in the case of mechanical timepieces. Atomic clocks appeared in the second half of the 20th century. They measure time using the vibrations of the atom and achieve an accuracy of 10-7 seconds per year. For centuries, only local time was used. Noon was determined based on observations of the sun. Clocks in different locations showed different times. The unification of time by introducing time zones - as the astrophysicist said - was forced only by the appearance of railways. This was first done in England. Currently, almost all of Europe from the Bug River to the Basque Country is in one time zone, although the actual differences in time are up to 2.5 hours. Russia has 7 time zones, the United States excluding Hawaii and Alaska - 4. China has only one time zone, and India and Nepal - in order to emphasize their independence - operate local time differing from the zone time by 45 minutes and 0.5 hours, respectively. In the 19th century, global time measurement systems began to be used. In 1884, GMT (Greenwich Mean Time) was introduced. It was an astronomical time based on the observation of the Earth's movement. However, the measurement of time was influenced by the vibrations of our planet and its gravitational attraction with other celestial bodies. GMT was in force until 1972. Currently, UTC (Universal Time Coordinated) is used. Its measurement is based on the average reading of about 230 different clocks, which are located in about 50 laboratories around the world. In Poland, these are the Orange laboratory and the Central Office of Measures in Warsaw. Find us: / Wszechnicafww / Wszechnicafww1 https://anchor.fm/wszechnicaorgpl---h... https://anchor.fm/wszechnica-fww-nauka https://wszechnica.org.pl/ #kawiarnianaukowa #czas #fizyka #astrofizyka #nauka