Current Issue: Spring 2007 (Vol I)
Kant and Einstein: Reconciling Reason and Relativity
At first glance, physics and philosophy seem to be two realms of knowledge that are naturally unrelated. Generally speaking, the former deals with the workings of our physical universe, while the latter reasons abstractly about such diverse topics as logic, ethics, and the nature of the mind. Upon closer examination, however, there is no reason why the two might not share a similar approach to understanding the world around us. The 19th century philosopher Immanuel Kant explicitly sought such a common approach to knowledge when he deliberately applied the method of science to the study of metaphysics. In his Critique of Pure Reason, he argues for a more scientific approach to reason in order to limit the abstractness and ambiguity that often arise when dealing with questions on the nature of thought.
Kant urges a radical “Copernican Revolution” in our understanding of space and time: rather than realities which can be discovered among the objects of the universe, space and time are the inescapable structures (or forms) of our mind which condition how we perceive the objects of the universe. This description of space and time seems to have a firm (though abstract) philosophical foundation; yet what it might mean in the concrete reality of the physical world often eludes us. Still less does it seem to make sense in light of the relation between space and time discovered by modern physics. By engaging philosophy and physics in a genuine dialogue, however, incorporating Einstein’s general theory of relativity into Kant’s Critique of Pure Reason, we may come to a better understanding not only of the nature of space and time, but also of the relationship between these two fields of knowledge.
Kant’s philosophy bases reason upon theory and experiment, a methodical foundation already employed by physics and the sciences. He claims that “reason, holding in one hand its principles, according to which alone concordant appearances can be admitted as equivalent to laws, and in the other hand the experiment which has been devised in conformity with these principles, must approach nature in order to be taught by it.”1 In this way, Kant agrees completely with the method of the experimental physicist: begin with known principles, apply them to experiment, and then extract newfound answers to questions based on the results of experimentation. Indeed, it is the very success enjoyed and progress made by the scientific method which encourages Kant to incorporate this method into philosophical inquiry: “[Mathematics’ and physics’] success should incline us, at least by way of experiment, to imitate their procedure.”2 Kant’s idea of progress in metaphysics is based on the success of the scientific method in expanding the knowledge of physics.
Kant’s imitation of physics is adequate when limiting speculative reason to empirical phenomena. Things can be considered in two ways: as we perceive them through our senses, and as they are in and of themselves. Kant’s critique limits metaphysics to a consideration of things as objects of experience (phenomena), because he believes that objects as things in themselves (noumena) cannot be known to us. His critique is opposed to “the presumption that it is possible to make progress with pure knowledge, according to principles, from concepts alone (those that are philosophical) as reason has long been in the habit of doing.”3 By restricting our analysis to objects of experience, we are able to use the method of science to understand our relationship to the things around us.
By this approach, Kant is able to avoid unanswerable questions while simultaneously developing a better understanding of the relationship between our interior consciousness and what we sense empirically. Rather than attempt to determine our purpose or to define our existence, he defines objects and experiences through sensibility—something our minds can more easily grasp. In Kantian terms, sensibility is defined as “the capacity for receiving representations through the mode in which we are affected by objects,” that mode being our outer sense.4 Though he avoids defining existence, he uses sensibility to show that we can know that we and the things around us exist. He states:
Inner experience itself depends upon something permanent which is not in me, and consequently can be only in something outside me, to which I must regard myself as standing in relation. The reality of outer sense is thus necessarily bound up with inner sense, if experience in general is to be possible at all; that is, I am just as certainly conscious that there are things outside me, which are in relation to my sense, as I am conscious that I myself exist as determined in time.5
Thus our ability to experience the objects around us makes us confident that we and those outer objects coexist. The key word here is coexist—we cannot know those objects in and of themselves, but only in relation to us.
In order for us to be aware of the objects in our surroundings, Kant argues that they must exist as appearances within a representation which is already contained in our minds, and which we call space. This representation must be a pure form of sensible intuition, a structure of the mind which conditions how appearances of objects relate to one another and to the self: “Space is nothing but the form of all appearances of outer sense. It is the subjective condition of sensibility, under which alone outer intuition is possible for us.”6 The only way that we know the objects we encounter everyday is through their appearance under the form of space, an inescapable structure of the mind’s very knowing.
However, we may well ask Kant to describe how exactly the form of space relates to the objects considered in themselves. He claims that some representation of space in our mind is presupposed for outer objects to appear to us; is there also some physical reality which corresponds to the definition of space as a pure form of sensible intuition? And furthermore, exactly what attribute or alteration of space makes us know that an object appears to us? It seems that something must happen to space in order for an object to be sensed. His philosophical explanation, as it stands, remains abstract and lacks an empirical, scientific meaning. Perhaps a more physical description of space could hold the answers to these questions.
The classical, Newtonian model of the universe which was accepted in Kant’s day did not account for the curvature of space-time. In his general theory of relativity, Einstein proves that space and time conform to objects; the mass of objects causes space-time to warp. Although we may not always see the effect, all objects cause this warping; on greater scales of magnitude, however, we can actually observe the physical result of that space-time curvature. The warping is essentially the cause of gravitational attraction. We may illustrate this effect with an oft-used analogy. Imagine a bowling ball on a rubber surface: the ball causes the surface to sink in, so that if you were to roll a marble past the ball, the marble would roll toward it and then around it in a circle. Similarly, a massive object causes space-time to dramatically warp around it, and smaller objects are then “attracted” to it; they fall into the curve of space-time and get caught in orbit. Thus the presence of one object has a physical, relative effect on the other. Kant had reasoned that objects exist on relative terms on the basis of the structure of the mind’s knowledge, but he did not give an account of the physical significance of such a statement.
Einstein’s discovery of the curvature of space-time fills in the gaps of Kant’s description not only of space but of time as well. Kant claims that, similar to space, time must also be a structure of the mind, a form; while space is the form of outer sense, time is the form of inner sense. In his description, time deals with a particular relation of representations both in our inner state and in outer appearances. Kant states that “all representations… belong, in themselves, as determinations of the mind, to our inner state; and since this inner state stands under the formal condition of inner intuition, and so belongs to time; time is an a priori condition of all appearances whatsoever.”7 Thus, while space is limited to the form of all outer intuition, time is the form of all things, including our inner state. In summary, one may think of outer appearances existing in the form of space; these outer appearances, in turn, exist in our inner sense when they are known by us, and this inner sense is conditioned by the structure, or form, of time. Kant thus concludes that time, as an inner form of the mind, does not alter; rather, it is the phenomena which appear under the form of time that change.
But this description does not adequately take into account the physical realities of the relativity of time. For Einstein, relativity means that an object or person’s motion alters its own measurement of time. As a particle’s velocity approaches the speed of light, time for that particle runs slower than time for a stationary observer. This can be more vividly illustrated with humans: if we were to hypothetically replace the particle with a person rocketing through space at close to the speed of light (ignoring for the moment that humans are incapable of surviving motion at such high speeds), then that person would age more slowly than everyone else moving at “normal speed” on Earth. Einstein’s theory thus implies that all people and things possess individual internal clocks. Relativity here presents a physical reality that simply was unaccounted for in Kant’s philosophical notion of time.
The above comparisons suggest an interesting question: How would Kant’s descriptions of space and time be different if he had known the principles of Einstein’s general relativity? While Einstein finds all things to be physically relative—including space and time—Kant maintains that all objects are relative within the mind’s forms of space and time. One might guess that, if Kant had the knowledge of general relativity we possess today, his revolutionary critique would incorporate the modern revolution in physics. Kant seems to find value in the methods of science regarding principles and experiment, so it is likely that he would take these new scientific inquiries into consideration when formulating his Critique of Pure Reason. With a philosophy which describes objects as relative in some way to space and time, he is already on the right track toward concurring with modern physics. In physics, a commonly accepted description of space-time regards it as a four-dimensional fabric, one which allows for the curvature and warping that Einstein depicts. This description makes for an easy incorporation into Kant’s philosophy. He may still describe space and time as forms within the mind by which objects appear to us; the change would be in both the flexibility and physical reality of those forms. While Kant says that objects fit into these forms, he does not allow for the forms to modify themselves with respect to those objects. Kant’s critique would fit nicely with the space-time fabric description if he included the idea that those forms are flexible. With this slight change, the shape of the forms within our minds would be relative to the objects within them, just as our physical existence is determined relative to the objects we sense. Both externally and internally, relativity would hold in Kantian metaphysics as it does in modern physics.
By combining physics with philosophy, we have added some scientific content to Kant’s abstract conceptions of space and time. The structures in our mind by which objects of outer sense appear correspond to physical dimensions that can be altered like the objects themselves. In significant ways, Kant’s introspective inquiry into space and time anticipated much of what has been realized through scientific inquiry. Our understanding of the physical universe is ever-changing as new discoveries and strokes of genius arise, and those new physical discoveries can often change our philosophical perspectives of this world. Complimentarily, those philosophical conjectures spark the interest for exploring the physical realm. Together, the harmony between philosophy and physics allows us to develop new theories, expand our knowledge, and continue our quest to answer some of the universe’s greatest questions.
1. Immanuel Kant, Critique of Pure Reason, trans. Norman Kemp Smith (Boston: Palgrave MacMillan, 2003), 20.
2. Ibid., 22.
3. Ibid., 32.
4. Ibid., 65.
5. Ibid., 36.
6. Ibid., 71.
7. Ibid., 77.
Abigail Pillitteri is a junior in the school of Arts and Sciences majoring in Physics with a minor in Philosophy. She acquired the information on Kant and his Critique of Pure Reason in her Philosophy of the Person class. She recommends The Elegant Universe by Brian Greene for anyone interested in the physical workings of the universe, and based her general comments on Einstein’s relativity on sections of this book, as well as on knowledge she gained from the Modern Physics course at BC. Abby is currently studying abroad at the University of Liverpool, taking advantage of the university’s truly “stellar” astrophysics courses. She plans to obtain a Master’s degree in astronomy after graduating from BC, and dreams of one day studying the stars for a living.