My physician recently recommended that I have a stress test to determine the condition of my heart. I had no symptoms, but the doctor evidently detected a possible anomaly that needed checking. An arthritic knee prevented the use of a treadmill, so I was scheduled for a 'chemical stress test.' This involved a lot more than I had anticipated. The actual stress test is preceded by a preliminary viewing of the heart's function by means of nuclear imaging. An intravenous injection of a radioisotope makes it possible to actually observe the heart beating and the blood flow through the heart by means of a giant, million-dollar machine that photographs the radiation being emitted from the blood.
I was curious as to what isotope was being used and was told that it was thorium-201, and that the half-life was 73 hours. The half-life is the time it takes for one-half of the sample to decay radioactively by the emission of certain nuclear particles such as beta-particles (electrons), alpha-particles (helium nuclei), protons, or neutrons. This decay rate is called the 'decay constant' and is different for every radioisotope. One-half of the sample decays in the first half-life, but only one-fourth in the second half-life, and one eighth in the third half-life, etc. Since you can never reach zero by dividing by two, the number of atoms of the parent sample never reaches zero. The graph of the decay with time is not linear, but exponential, and it approaches the zero line asymptotically. This means that I will always have an infinitesimally small number of thorium-201 atoms in my body.
Not all elements are radioactive; all of those in the periodic table up to calcium are stable, those from calcium up to bismuth are prone to instability if they are externally stimulated, and from bismuth on up to uranium the elements are all unstable and are naturally radioactive. Some of the isotopes in this group are so unstable that they last only seconds; others, such as uranium-238, have an extremely long half-life of billions of years.
We as Christians are somewhat like that. There are some very stable Christians who are solidly grounded in a faith that cannot be shaken or influenced by environmental factors of unbelief or ridicule; there are some whose faith is weak and are easily influenced by their associates or discouragement, and they must be sheltered and nurtured or they will revert to the world; there are others whose faith is extremely unstable, and they continually emit seeds of doubt, fanaticism, or discord. Is your faith so solid that nothing in heaven or on earth can shake it? Do you let the world intrude on your faith and cause you to falter? Are you vacillating and contentious and constantly unhappy with your lot? What is your "spiritual half-life"?
