Why the act of observing the world might physically change what you are measuring
In short: We define our fundamental units of time and length by the unchanging properties of atoms, ensuring they survive any cosmic catastrophe. Yet, as we push to measure the incredibly small, we hit a wall: the very act of observation can physically displace the object we are trying to study.
In 1981, Reginald Victor Jones delivered the Royal Institution Christmas Lectures, a series founded by Michael Faraday in 1826. While measurement is central to modern life—enabling everything from the microchip to the navigation of space probes near Saturn—Jones argued that we often take the precision of our tools for granted. By 1981, the definition of the metre had shifted from the rotation of the Earth to the specific wavelength of light emitted by a krypton 86 atom, mirroring how the second is defined by atomic properties. These standards are designed to be universal and indestructible.
However, our quest for precision faces inherent physical limits. We are increasingly constrained by Brownian motion, the constant, jittery agitation of the atoms and molecules that compose both our instruments and the objects we observe. Furthermore, measurement is not a passive act. When we shine light on an object to observe it, the pressure exerted by that light can physically shift the object from its original position. This creates a fundamental tension: as we refine our ability to measure smaller distances using techniques like optical levers or capacitance micrometres, we must contend with the fact that our presence as observers alters the reality we seek to quantify.
Jones cautioned against the hubris of measurement. While Plato famously claimed that 'man is the measure of all things,' Jones noted that many essential human qualities, such as love or courage, remain beyond the reach of any scale. He urged a balanced perspective, acknowledging that while measurement is a cornerstone of technological advancement and scientific discovery, it must be applied within its proper domain. Understanding these principles is vital for grasping how our modern world has evolved, including both its spectacular successes and its inherent dangers.
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