From the universe itself down to the tiniest subatomic particle, objects in our world exist in a mind-boggling array of sizes. With microscopes, we can look directly at some of the objects and processes that are too small to be seen with the naked eye, and this has allowed us to make great leaps in our scientific understanding. However, there are many objects that are far too small to be seen even with microscopes.

Defining the microscopic scale

Within the scale of all things sits the microscopic scale, which can be thought of as the sizes of things that can be detected using microscopes.

Light microscopes let us look at objects as long as a millimetre (10-3 m) and as small as 0.2 micrometres (0.2 thousands of a millimetre or 2 x 10-7 m), whereas the most powerful electron microscopes allow us to see objects as small as an atom (about one ten-millionth of a millimetre or 1 angstrom or 10-10 m). So, we can think of the microscopic scale as being from a millimetre (10-3 m) to a ten-millionth of a millimetre (10-10 m).

Even within the microscopic scale, there are immense variations in the size of objects. After all, 10-3 m is 10 million times larger than 10-10 m – that’s a difference in scale equivalent to the size of Earth versus the size of a beach ball! It’s important to remember this when using a microscope – you need to know the magnification you’re using so that you can work out the actual size of the things you’re looking at.

Below the microscopic scale

Currently, the smallest thing that can be seen using a microscope is about the size of an atom. Anything smaller is below the current limit of resolution of the electron microscope, although the microscopic scale is likely to encompass even smaller objects as the technology of electron microscopes becomes more advanced. We know there are objects smaller than atoms, but they cannot be seen by microscopes. Scientists must turn to other tools to study these objects, including particle accelerators such as the Large Hadron Collider

Cells are on the microscopic scale

Cells – the building blocks of life – exist on the microscopic scale. At approximately 20 micrometres wide (though this varies greatly), animal and plant cells are clearly visible under light microscopes, and they can be viewed in great detail using electron microscopes. Looking at cells under the microscope has made it possible to understand how they grow and divide, how they communicate with their environment and why they are the shapes they are. We now know a great deal about how cells work, and most of this would not have been possible without microscopes.

These two scientists study cells under the microscope. Dr Rebecca Campbell (University of Otago) studies brain cells (neurons) and how they fit together with one another. Because she is interested in whole neurons, she uses light microscopes (particularly the confocal laser scanning fluorescence microscope) to study them. Associate Professor Tony Poole (University of Otago) studies the primary cilium – a small antenna-like structure on the surface of each of our cells. Primary cilia are far smaller than cells (just 0.2 micrometres), so Tony uses an electron microscope to learn more about them.

Rocks at the microscopic scale

We often think of rocks as large objects, but they have many features that are on the microscopic scale. By looking at rocks under the microscope, scientists can learn a lot about how and when the rock was formed and what has happened to it since.

Professor Dave Prior at the University of Otago is especially interested in earthquakes and what causes them. He studies microscopic features of rocks from New Zealand’s Alpine Fault to help him understand how they have been ‘squished’ underground in the distant past. David uses both light microscopes and electron microscopes to explore rock microstructure.

Nature of Science

To make sense of the microscopic scale, scientists use the convention of ‘powers of 10’. In this system, even very small lengths are related back to the metre. For instance, a micrometre is expressed as 10-6 m. This nomenclature helps scientists to compare the sizes of the objects they see down the microscope and to communicate clearly with others about what they have seen.

Useful links

This video clip (12 minutes) explores the size relationship between objects on the microscopic scale (and beyond).

This animation looks at the scale of the universe from the largest objects to the smallest. It’s helpful for visualising those objects that sit below the microscopic scale.

    Published 29 February 2012