Many physical phenomena are associated with unbelievably small time scales. Let me give a few examples.

  • The time scale associated with visible light is $\sim$ a femtosecond ($10^{-15}$ sec),

  • The half-life of a neutral pion $\sim$ an attosecond ($10^{-18}$ sec) etc.

Many more examples can be found here.

Do we have enough technology to measure such small times or they are just theoretically calculated values? What is the smallest time that we can measure?

  • $\begingroup$ Do you mean measure directly? Many decay times in particle physics are "measured" by looking at the distance a particle travels before splitting and its speed. Does this count as measurement for you? $\endgroup$ Commented Jul 29, 2020 at 7:49
  • $\begingroup$ Yeah, it does. Thanks $\endgroup$ Commented Jul 29, 2020 at 13:49
  • $\begingroup$ @FoundABetterName thank you for the comment, but I don't know the answer to this question: my comment was only to point others in the right direction. I assume that the smallest time measured would be the lifetime of some pretty heavy particle, like the top/Z/W, but other issues complicate the estimate: for example, the bottom quark while being quite heavy is also pretty stable because it can't decay in other quarks of the same family. $\endgroup$ Commented Nov 3, 2020 at 14:30

1 Answer 1


I am no expert in this field but as far as I know we can't measure the first 2 entries of the wikipedia list as it's currently far beyond our technological capabilities.

A google search yielded the following discovery from 2016 and I couldn't find anything smaller measured after that-

Don’t even try to capture a zeptosecond using a run-of-the-mill stopwatch. This tiny slice of time is a fraction of a second—so small it is equal to a single number one sitting 21 places behind the decimal point, a trillionth of a billionth of a second​, reports Rebecca Boyle at New Scientist. And researchers at the Max Plank Institute in Germany finally measured minute changes within an atom on the zeptosecond scale.

Basically they measured the electron emissions from a Helium Atom. When the helium atom ejected an electron, the infrared laser detected the emission, allowing the researchers to calculate the duration of the event down to 850 zeptoseconds. The experiment showed that it takes between 7 and 20 attoseconds for the helium atom to eject one of its electrons.

A zeptosecond is a trillionth of a billionth of a second (10^-21 seconds). This is the greatest accuracy of time determination ever achieved, as well as the first absolute determination of the timescale of photoionization.

You can read the full article here


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