Critique of Practical Reason and Other Works on Ethics

As a universal property of matter, we cannot suppose the sun’s attractive force is limited only to our solar system. If this gravity extends to the nearest fixed stars, and if those stars (which are themselves suns) exert a similar force around them, they would eventually collide with each other unless they were prevented—just as the planets are—by a centrifugal force Centrifugal force: The outward force experienced by an object moving in a circle, which balances the inward pull of gravity to maintain an orbit.. From this, we may conclude that all the stars in the heavens have their own orbital motions. If we imagine our planetary system multiplied a thousand times over, and the various bodies within it were self-luminous, the appearance as seen from the Earth would resemble that of the Milky Way.

The structure of the heavens of the fixed stars, therefore, is on a large scale the result of the same systematic arrangement as our own solar system is on a small scale. In short, our sun and the other stars are the "planets" of a vaster system, which is, in fact, the Milky Way.¹ There may be many such systems, and some of these may appear to us as nebulae term: nebulae; historically, this referred to any faint, fuzzy patch in the sky. Kant correctly guessed that many were actually distant galaxies outside our own.. When these are viewed from an angle, they would appear to have an elliptical shape. The Milky Way, if seen from a great enough distance, would look exactly like one of these elliptical nebulae. Furthermore, these systems might themselves be related to one another, together forming an even more immeasurable system. This perspective opens a view into the infinite field of creation and provides a conception of God’s work that is suited to the infinity of the great Creator. If the magnitude of a planetary system—in which the Earth is like a grain of sand—fills our minds with wonder, how much more amazed must we be when we consider the vast multitude of worlds and systems which constitute...

¹ This suggestion by Kant anticipated a similar suggestion by Lambert Johann Heinrich Lambert (1728–1777), a Swiss-German mathematician and astronomer who independently proposed a hierarchical model of the universe. by six years.