Very small numbers have to be brought into play when considering the size of objects at the subatomic scale. We all know that the smallest measurement found on a common school ruler is one millimetre. But, what if we were to subdivide that millions and millions of times? We'll consider lengths going ever smaller, until we reach the smallest measurement possible.
More correctly spelt Ångström, as it is named after Swedish physicist Anders Ångström, this is a measurement used in describing the dimensions of atoms. It is one tenth the distance of a nanometre, or one 10 millionth of a millimetre.It is represented as 1x10-10m. The radius of a hydrogen atom is 0.25Å.
By now, we've reached one million millionth of a millimetre! But, unbelievably, there's a long way to go yet before we reach the limit of smallness.Next, we have the attometre, at 1x10-18, the zeptometre, at 1x10-21 and the yoctometre, a tiny 1x10-24.
At these levels, we're dealing with the sizes of things like quarks and neutrinos, some of the smallest possible particles.
Here, at long last, is the smallest measurable length possible. It is thought that any lengths smaller than this would cease to have any meaning.At an impressive 1.62x10-35, it is derived from the speed of light, Planck's constant and the cosmological constant. It deserves to be written out in full, to give you more of an idea how small it is.
To give you more of an idea, imagine a dot . that was expanded to be the size of the observable Universe. One Planck length within it would be the size of the original dot.
It is at the Planck length scale that interactions of the strings in string theory are thought to take place.