What is the shortest period of time that can be measured?

Did you know that there are even smaller units of time than seconds? Although for practical reasons we do not use them in our daily lives, in the field of scientific research they are frequently used. For example, a centisecond It would be equivalent to one hundredth of a second, that is, it would be 0.01 seconds. And the nanosegundo equals one billionth of a second, 0.000 000 001 seconds. But things go even further.

Los attoseconds they are units much smaller than what our head and experience can lead us to even understand or imagine. An attosecond is equivalent to a time interval of 0.000000000000000001 seconds, or what is the same, to one millionth of a billionth of a second. In fact, the ratio between an attosecond and a second is similar to the ratio between a second and the age of the universe (about fifteen billion years).

Thanks to these units of measurement, in 2010 he managed to measure the shortest controllable period of time until now, making use of light and its double nature of particle and electromagnetic wave to achieve it. And it is that, being a wave, light has a wavelength (the distance that the disturbance of a wave travels) and a wave frequency (the number of times that wave is repeated per unit of time), measured in Hertz (Hz). Is the frequencyis the key to achieve the aforementioned temporal measurements.

In it non-visible light spectrum (the one that the human eye is not capable of perceiving) cosmic rays, gamma rays, X-rays and ultraviolet rays have a high wave frequency (that is, a wave is repeated many times per unit of time), reaching over 10 exahertz. Progressively, this frequency decreases as the spectrum is traversed, passing through infrared, microwaves or radio waves.

For this reason, by observing the behavior of light, it has been possible to carry out this type of measurement of very, very small units of time, inaccessible through any other method. Specifically, through lasers, which can generate light pulses of up to 100 attoseconds. But the scientists of Max Born Institute for Nonlinear Optics and Short Time Spectroscopy (MBI) of Berlin (Germany) came to demonstrate in a study published in the journal Nature in 2010 a time control with a residual uncertainty of only 12 attosecondswhich is the world record for the shortest controllable time scale ever measured.

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In general, light is a very high frequency electromagnetic wave, but this time an ultra-short laser pulse was used, and specific stabilization methods were used for the position of the maximum of the phase of the light pulse. A correction that is based on the so-called acousto-optic frequency shifter and that brings real advances for this kind of research in nature.

Is there a lower limit of measurement?

Yes! Time cannot be measured as small as we want. We are talking about Planck time, also called chronon. Planck time is defined from fundamental constants of nature, such as Planck’s constant (h), the speed of light (c), and the gravitational constant (G). Its approximate value is around 5.39 × 10^-44 seconds. Below the Planck time, physics as we know it loses its meaning and a more complete theory, such as the still unexplored theory of quantum gravity, is required to understand what happens on these scales.

Koke, S., Grebing, C., Frei, H. et al. Direct frequency comb synthesis with arbitrary offset and shot-noise-limited phase noise.Nature Photon 4, 462–465 (2010). Do: 10.1038/nphoton.2010.91

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