y = a(1-r) to the power of x

This morning I awoke to look through myself in the mirror. This new symptom of my singular condition, although long theorized by better mathematicians than myself and manifesting on schedule, terrifies me. How could it not? As I type this now I find it difficult to impart the necessary force to depress the keys. I am with increasing frequency disintegrating. These are the last words of a man fading from existence. I will then attempt to be brief, in the hope that I may convey the core of my life's experience with these few words in the few moments I have remaining.
At the age of ten it first became evident that something was wrong with me. While I appeared outwardly healthy and continued to grow in size, I was in fact decreasing in mass. My volume remained constant and my density was stretched beyond the limits of understanding. A neighboring mathematician and close family friend, acting on a hunch that he would later call insane, began measuring me daily. Over time a pattern emerged and his most outrageous fears were confirmed, I was decaying exponentially.
He told me I was living half-lives and a time would come when there would be nothing left to halve. He then taught me the math, carefully and kindly illustrating the simple formula and function that would define my life. First I learned Archimedes' formula:

density = mass/volume

When I understood the formula and its components he patiently explained the function for exponential decay.

y = a(1-r)x

[Where a is the amount before decay begins (my initial density), r is the rate of decay (1/2) and x is the number of intervals (my half-lives).]

My decline continues to progress rapidly, but the rate of change will decrease over time as there is less and less to halve. A ghost of me may outlive you all. But that ghost's density will be so insignificant that it will not be able to interact with the physical world. In fact, it is likely that it will fall through the earth, a victim of gravity, to further reduce within its core.
I spent a life alone with mathematics. Feeding my diminishing whole with numbers; frantically searching for a different solution. And having failed to disprove the irrefutable, I now regret those years in the narrow halls of academia. The ghost that I will become will have nothing but time to remember, and very few memories.
Beyond the psychological, my condition cause some discomfort, but little pain. And even as I continue to fade, a strange calm pervades. We are not to know our future. The curve of my life was graphed and anticipated. With all my ability I could not alter it. Now that there is nothing more I can do, my mind is free to wander without the oppressive need for haste. I go willingly into the theoretical void. I am awake. At first, and at last.