[ti:Scientists Measure Smallest Unit of Time Ever in ‘Zeptoseconds’] [by:www.51voa.com] [00:00.00]更多听力请访问51VOA.COM [00:00.04]German scientists say they have measured [00:04.44]the smallest unit of time ever recorded. [00:10.12]Researchers say the unit was measured in zeptoseconds. [00:16.60]A zeptosecond is a trillionth of a billionth of a second. [00:24.04]The researchers made the discovery [00:27.20]while studying how long it took a photon [00:31.24]– a particle of light – to cross a hydrogen molecule. [00:37.44]The German scientists say the photon crossed the molecule [00:43.32]in about 247 zeptoseconds. [00:47.96]"This is the shortest timespan that has been successfully measured [00:53.64]to date," the team said in a statement. [00:58.28]The results were reported in Science magazine. [01:03.52]The research was a project of physicists [01:07.28]from Goethe University in Frankfurt, Germany. [01:12.28]The team said the experiment represents major progress [01:18.00]in "the global race" to measure shorter and shorter units of time. [01:25.24]The method used to measure in zeptoseconds [01:29.72]involves what is known as the photoelectric effect. [01:36.20]This scientific law explains how and why some metals [01:42.44]give off electrons after light falls on their surfaces. [01:48.92]Albert Einstein is credited with discovering the photoelectric effect. [01:55.76]He was awarded the 1921 Nobel Prize in Physics for doing so. [02:04.16]The discovery helped lead to the development of modern electronics, [02:09.52]including radio and television. [02:14.16]The German scientists say they used equipment [02:18.92]at the DESY national research center, [02:22.36]which operates particle accelerators. [02:26.32]The machines are used to investigate the structure of matter. [02:32.36]The research includes experiments in photon science. [02:38.72]The researchers said they made the measurement [02:42.36]by releasing X-ray waves onto a molecule of hydrogen, [02:47.96]which is made up of two protons and two electrons. [02:53.72]They set the energy of the X-rays so that one photon would be enough [03:00.44]to expel both electrons out of the hydrogen molecule. [03:06.76]The scientists explained that electrons behave like particles [03:13.04]and waves at the same time. [03:16.72]So, after the first electron was ejected, [03:20.76]the second followed a short time later. [03:24.80]This process resulted in what the researchers called [03:29.20]"an interference pattern." [03:32.80]The researchers used this pattern [03:35.92]to measure the electrons as they were escaping. [03:41.20]Sven Grundmann is a doctoral student [03:45.20]at Goethe University who helped lead the research. [03:51.04]He said the team "used the interference of the two electron waves [03:57.40]to precisely calculate when the photon reached the first [04:02.60]and when it reached the second hydrogen atom." [04:07.56]The calculation added up to 247 zeptoseconds, " [04:13.56]depending on how far apart in the molecule [04:17.72]the two atoms were from the perspective of light," he said. [04:23.52]The research also involved a complex spectrometer, [04:28.16]an instrument used to measure atomic and molecular reactions. [04:34.56]Goethe University's Reinhard Dorner said the spectrometer [04:40.12]made it possible to observe "for the first time [04:44.68]that the electron shell in a molecule [04:47.88]does not react to light everywhere at the same time." [04:53.48]The time delay happens because information within the molecule [04:58.76]only spreads at the speed of light," Dorner added. [05:03.28]"With this finding we have extended our technology [05:07.88]to another application." [05:10.92]There has been earlier research on the speed [05:14.56]at which molecules change shape. [05:17.92]In 1999, Ahmed Zewail [05:21.96]– a professor at the California Institute of Technology [05:26.28]– won the Nobel Prize in Chemistry for his work in the field. [05:33.04]Zewail, an Egyptian, was recognized for experiments [05:38.20]that used laser light to study how atoms [05:42.60]in a molecule move during a chemical reaction. [05:47.44]His research involved femtoseconds, [05:51.72]a unit of measurement meaning one quadrillionth of a second. [05:57.84]The German scientists say their research [06:02.36]represents major progress from the earlier experiments. [06:07.48]They also say they plan to build on their findings [06:12.08]to measure even smaller units of time. [06:16.40]I'm Bryan Lynn. 更多听力请访问51VOA.COM