Hard & Soft

February 06, 2009


Photographer: Stu Witmer
Summary Author: Stu Witmer

What are the hardest and the softest substances known? The photo above illustrates both conditions in that the black volcanic rock is hard and the white billowy cloud is soft, but neither is at the extreme end of the scale. Frederich Mohs came up with a scale of mineral hardness in 1812 listing diamond as the hardest, and barring any new synthetics, that claim still stands.

But what is the softest? This question takes us into the realms of philosophy and quantum physics. The Tao Te Ching says water is the softest substance. If so, then a cloud would have to be softer since it is vaporized water. Some scientists say the softest “substance” is a vacuum.

Now that seems to ring true, what could be softer than nothing, right? The problem is that a vacuum is not truly empty. There are degrees of “emptiness” in a vacuum that can be measured in units called Pascal (Pa).

Unfortunately, we cannot just go to the end of the scale and find the “softest” substance because we run into quantum field theory in which the “vacuum state” has lowest possible energy but even this is not empty.

Perhaps we need to rephrase our question: Aside from a vacuum, what is the softest substance?

Photo taken at Craters of the Moon National Monument, Idaho, August 30, 2007 at 10:13 a.m. local time. Camera details: Nikon E5700 camera with a Nikkor ED 8.9 - 71.2 mm lens, f/3.7, ISO 100, 1/718 sec., 29.5 mm.