Keating flew synchronised, super-accurate caesium atomic clocks on various trips around the world on commercial airliners. In another crucial test, physicists Joseph Hafele and Richard E. The maximum speed he could get the electrons to travel before they became too heavy to accelerate further? The speed of light. He then measured their kinetic energy and found that as their speeds approached the speed of light, the electrons became heavier and heavier – until the point they became so heavy it was impossible to make them go any faster. In 1964, Bill Bertozzi at MIT accelerated electrons to a range of speeds. Many experiments have carefully tested Einstein’s predictions. Time was no longer constant and so relativity was born. If light has a finite speed, what if you strapped a torch to the front of a moving rocket? Wouldn’t the light coming from this torch be travelling faster than the speed of light? Einstein puzzled over this issue with several “Gedankens” (thought experiments) and came up with a crazy solution: the motion of an object must somehow make time slow down. This question gave Albert Einstein pause for thought. We know that light travels at a finite speed. The faster something travels, the more massive it gets, and the more time slows – until you finally reach the speed of light, at which point time stops altogether. His remarkable result of 315,000 km/s was within about 5% of our most recent measurements using lasers. Knowing the rotational speed, Fizaeau thus could calculate how long it took for light to travel 16 kilometres – and so how fast the light must be travelling. But as Fizeau turned the wheel faster, at a certain speed the pulse was blocked by the following tooth. What happened? At slow speeds, the light pulse always got back to Fizeau through the same gap in the cog’s teeth. On the return trip, the reflected light pulse could only reach Fizeau by passing back through one of the gaps in the cog-wheel. These pulses travelled about 8 kilometres to where Fizeau had positioned a carefully aligned mirror. The teeth of the rotating cog chop the light up into very short pulses. In his experiment, a beam of light was projected onto a rapidly rotating cog-wheel. He came up with an ingenious advance on Galileo’s method. The first experimental measurement of the speed of light came 150 years later with Hippolye Fizeau. It also allowed Römer to estimate the speed of light as 214,000 km/s. The different times for Io’s orbit reflected the different distances light had to travel. Römer realised his observations could be explained by the varying distance between Jupiter and Io, and Earth. The cumulative effect meant the predicted times could be in error by more than 10 minutes. At times when the Earth was moving away from Jupiter, the time between Io’s eclipses gradually increased as it moved closer the time decreased. Römer observed that the time between eclipses varied slightly depending on the time of year. The time for Io to make one complete circuit around Jupiter had been measured at 1.769 days. One of the ways sailors at sea checked their clocks was to observe the eclipse of Jupiter by its moon Io. Undaunted, Galileo concluded that light’s movement, “if not instantaneous, is extraordinarily rapid”.īut not long after, in 1676, we got a fair estimate of light’s speed from a young Danish astronomer by the name of Ole Römer. He had no such time keeping device and his reaction time would be way slower than that. The experiment failed dismally! To succeed, Galileo would have had to register a time difference of microseconds. Galileo would then time how long it took to see the return flash. The idea was that as soon as Galileo’s assistant saw the flash, he uncovered his lantern. He and an assistant perched themselves on distant mountaintops with covered lanterns. Galileo was among the first to think that light travelled at a finite speed. But why is it so?īefore the 1600s most people assumed light moved instantaneously. And that happens to be 299,792.458 kilometres per second. We all know the number one traffic rule of the universe – nothing can travel faster than the speed of light.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |