Descartes' Laws of Motion, Conservation and Vortices

Basic Laws of Cartesian Physics

Descartes invokes God to explain extension and motion: God is the creator of matter and of a certain amount of motion that remains constant, because God is unchangeable both in being and in operation. He therefore regards the universe as a closed system. He formulates three fundamental laws:

Three Fundamental Laws of Motion

1. Law of inertia: Every body tends to remain in its state of rest or of uniform motion in a straight line unless acted on by an external force.
2. Law of straight-line motion: Any body in motion tends to continue moving in a straight line unless an external force intervenes; otherwise there would be no reason to explain a deviation.
3. Law of conservation of motion: Motion is not lost in collisions between bodies; the total momentum remains constant.

Thus, all phenomena are reduced to a mathematical mechanism and the universe is treated as a closed system in which phenomena are explained by extension and motion.

Types of Matter and the Vacuum

Another important point is that there is no vacuum. Given that extension is the characteristic of bodies, it is not logical to posit something large but empty. Applied to the cosmos in general, Descartes argues that everything is filled with three types of matter:

• The thick stuff: The fundamental constituent of bodies we perceive directly through the senses.
• The ether: Matter composed of finer particles that fills much of space.
• Light particles: The finest of all, which can slip through the others and travel across the immensity of space.

Vortex Cosmology and Planetary Motion

Descartes also offers a provocative explanation of the organization and movement of the universe as a whole. The early material particles were equal in magnitude and motion, and moved both about their own axes and relative to one another. In the chaos, swirling fluids formed; early vortices focused particles into centers that became the Sun and the other planets. From these vortices comes the rotation of the planets around their axes. The whirlwinds of smaller planets are, in turn, contained within a larger vortex surrounding the Sun.

The same phenomenon occurs when wind swirls leaves and dust into a center, or when water drains from a tub and spins faster at the center than at the edges. For a similar reason, Descartes argued, the planets would rotate in the same direction, a claim that was plausible in his time.

The vortex in which the Earth moves also explains why, during its motion around the Sun, the atmosphere does not detach and why drafts and winds form. It would also provide an explanation for gravity, since bodies tend to fall toward the centers of vortical motion.

Limitations of Descartes' Theory

The weakness of Descartes's theory lies in its lack of mathematical development. It vaguely agreed with observed phenomena but could not yield calculable or measurable consequences. No one could deduce the shapes of the orbits or the times of revolution around the Sun, for example.