The Big and the Small - Part 2

At different scales, different forces have a predominate influence over matter

Jul 27, 2006

Last week we looked at how the four fundamental forces influence matter on the atomic and microscopic scales, this week we look at the macroscopic and cosmic scales.

At the macroscopic scale, the scale of everyday life, both electromagnetism and gravity hold sway. A spider can crawl along a ceiling with ease, but an elephant would find this impossible. The spider isn't equipped with anti-gravity boots, but is just still small enough that electromagnetism overcomes gravity. It actually uses barbs on it's feet to grip the texture of the ceiling, using stiction, which is a manifestation of the electromagnetic force.

You can see the effects of the changeover in dominance from electromagnetism to gravity at the macroscopic scale in the body plans of various organisms. Our spider for instance has a big body supported by slender legs. If it were as big as an elephant, it's legs would be unable to support its relative body mass. An elephant requires thick legs to support it's body. Even a large tree requires a thick trunk that is unnecessary for a blade of grass. The largest animals on Earth can be found in the oceans, where their massive bodies can be supported by water. The water is bound together in a liquid by the electromagnetic force and helps to counteract the force of gravity.

On the cosmic scale, gravity dominates. The solar system is held together by gravity, as is our galaxy, our local galactic cluster, the strings of galactic clusters, and the Universe itself. The effect of gravity is cumulative. Each subatomic particle that has mass contributes a little bit to the overall amount of gravity in a region. On the cosmic scale, vast clouds of gas and dust are pulled together by the mutual attraction of gravity, and coalesce to form massive structures - clusters, galaxies, stars, and planets. Where a structure forms in space is determined by the minutiae of where each constituent particle starts out, and what direction and speed they are moving. Over a long time, millions to billions of years, the structures gradually form, but are constantly changing due to the cumulative effect of gravity.

The copyright of the article The Big and the Small - Part 2 in Physics is owned by Katharine M. J. Osborne. Permission to republish The Big and the Small - Part 2 in print or online must be granted by the author in writing.