What is the longest time measurement

Big Bang HTL 1, textbook

sd23bp 14 Measurement 2.4 Tamed Time Time Measurement What is time? Why can we remember the past but not the future? Was there time before the Big Bang? Unfortunately we know little about the nature of time, and the questions posed above cannot be answered satisfactorily either. It's ironic: even though we don't know the time, we can still measure it very accurately. Discuss with your neighbor what is time for you! How could you describe it? Since 1983 the speed of light can no longer be measured. Sounds strange, but that's how it is! But why? It has to do with the definition of the meter! L Imagine that you live 10,000 years ago and you want to build a clock. What would be best for measuring time? How many degrees does the sun move in the sky in one hour? Try to estimate in your head! L How many seconds is there in a day exactly? And does this number stay the same, or do the days have a different number of seconds? Is there a longest and a shortest time? L F19 C2 F20 A1 F21 C2 F22 A1 F23 A1 F24 C1 Later attempts were made to become independent from the sun and developed water clocks, candle clocks and hourglasses. However, they all had one major disadvantage: you had to take care of them, i.e. refill them with water, turn them over or light them up again. Around 1300 an invention of enormous cultural and historical scope was made: the wheel clock. When the weight drops, a rope slowly unwinds, thereby moving the hands. The wheel clock spread rapidly across Europe because it was a symbol of wealth and energy. Many cities bought a watch because others already had one. The wheel clock was still quite imprecise, at first about 1 to 2 hours, later about 15 minutes a day. Around 1660, the Dutchman CHRISTIAN HUYGENS succeeded in significantly improving timekeeping. He used Galileo's idea to use a pendulum as a clock generator for clocks (see Fig. 11.5) and was able to increase the accuracy to around 1 second per day. Pendulum clocks have become an indispensable aid for astronomical observations (see also Chapter 11.1). Experiment: Pendulum Huygens found a very precise clock for his clocks in the pendulum. A half oscillation lasts exactly one second. Today's pocket watches are much more accurate because they perform up to eight semi-oscillations per second. But there are two other milestones in the accuracy of timekeeping. The quartz watch was invented in 1927. With it, an electromagnetic oscillating circuit is the clock generator, which has a frequency of almost 33,000 oscillations per second! A quartz helps that this frequency is adhered to exactly. Quartz watches are only about 1 second wrong in a month. That is very remarkable! But there is a clock that is even more precise: the atomic clock! The first atomic clock was built in 1948. Today (as of 2014) the best of these clocks are so accurate that they will only go wrong by 1 second in 20 billion years! Impressive, isn't it? Put simply, these clocks make use of the property of atoms to be able to emit or absorb electromagnetic waves with a very specific frequency during the transition between two energy states. The clock is generated by microwaves or light waves that oscillate at least a few billion times, sometimes even a few hundreds of trillion times per second. Atoms such as cesium-133 or strontium-87 are used to ensure that this specified frequency is adhered to as precisely as possible. And that leads us to the definition of the second. In principle, a day has 86,400 seconds (F23). This is how the second was defined earlier. But the problem is: this is an average value, because the period between Let's first take a look at the history of timekeeping. The sun was the very first means of telling time. The first sundials were probably built a few thousand years ago. In the simplest case, you put a stick in the ground and its shadow ran around it in the course of a day. Noon was when the shadow was the shortest, i.e. the sun was at its highest. Later the sundials became trickier and more precise (Fig. 2.10)! But the principle always remained the same: time measurement with the help of the rotation of the earth! Experiment: Sundial Fig. 2.10: The large sundial in Jaipur. The ramp on the left (over 30 m high) casts the shadow, which runs along the round scale (excerpt from the right) and can be read with an accuracy of 2 seconds. For testing purposes only - property of the publisher öbv

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