A nanometer is one billionth of a meter. To grasp this scale, consider a human hair, typically 80,000 to 100,000 nanometers wide. A single strand of human DNA is even finer, with a diameter of about 2.5 nanometers. Even a sheet of paper is approximately 100,000 nanometers thick. While the nanometer scale is tiny, the universe contains realms far smaller, revealing the fundamental building blocks of everything around us.
The Atomic World
Atoms are the primary constituents of all ordinary matter, existing at a significantly smaller scale than a nanometer. Their typical diameter ranges from 0.1 to 0.5 nanometers, or between 10-10 and 5 x 10-10 meters. For instance, a single gold atom measures about a third of a nanometer across.
Each atom possesses a central, dense nucleus, surrounded by a cloud of lighter particles called electrons. The nucleus contains two primary types of particles: protons, which carry a positive electrical charge, and neutrons, which are electrically neutral. The number of protons in an atom’s nucleus defines its atomic number, determining the element it represents and influencing its chemical properties.
Electrons, with their negative charge, orbit the nucleus and largely dictate how atoms interact to form molecules and compounds. The vast majority of an atom’s volume is empty space, with the electrons occupying a diffuse region far from the compact nucleus. If an atom were expanded to the size of a football stadium, its nucleus would be no larger than a tiny pebble at the center.
Beyond the Atom: Subatomic Particles
Deeper than the atomic scale are subatomic particles, many of which are fundamental, meaning they are not known to be made of anything smaller. Protons and neutrons, once thought to be indivisible, are actually composite particles. They are each composed of tinier constituents called quarks.
Quarks combine to form protons and neutrons, which belong to a class of particles known as hadrons. The electron, unlike protons and neutrons, is not made of smaller parts; it is a member of another family of fundamental particles called leptons. Six types of leptons exist, including the electron, muon, tau particle, and their corresponding neutrinos.
Neutrinos are particularly elusive, nearly massless and electrically neutral, interacting rarely with other matter. While protons and neutrons have a measurable size, roughly 0.8 to 1.75 femtometers (10-15 meters), fundamental particles like quarks and leptons, including the electron, are considered point-like, with no measurable size or internal structure. Beyond matter particles, fundamental particles called bosons mediate forces, such as photons for the electromagnetic force or gluons for the strong force.
Unveiling the Smallest Scales
Understanding these minuscule components of matter relies on sophisticated technologies and experimental methods. Scientists utilize tools to probe the subatomic realm and visualize structures at the atomic level. These instruments provide indirect evidence, allowing for the deduction of properties and behaviors of particles too small to be seen directly.
Particle accelerators, such as the Large Hadron Collider (LHC) at CERN, are instrumental in this research. The LHC, a 27-kilometer ring located 100 meters underground near Geneva, Switzerland, propels charged particles, like protons, to nearly the speed of light using electromagnetic fields. When these highly energetic particles collide, the immense energy involved can transform into new particles, allowing physicists to study the fundamental constituents of matter and the forces governing their interactions.
To image the atomic world, scientists employ advanced microscopy techniques like the scanning tunneling microscope (STM). This instrument uses an extremely sharp conducting tip that scans a surface, distinguishing features smaller than 0.1 nanometers. The STM operates by exploiting a quantum mechanical phenomenon called tunneling, where electrons can “tunnel” across a tiny gap between the tip and the sample, allowing for atomic-level imaging and even the manipulation of individual atoms.