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“”There shall come in the last days scoffers, walking after their own lusts, and saying, Where is the promise of his coming? for since the fathers fell asleep, all things continue as they were from the beginning of the creation.
|—Biblical prophecy, foreshadowing the advent and motivation of Uniformitarianists in 2 Peter 3:3-4|
Uniformitarianism is a principle in science and in the philosophy of science. Essentially, uniformitarianism spells out the assumption that natural law has always operated as it operates at present. Although an assumption, it is considered a very good and reasonable assumption, and certainly produces theories which are self-consistent, plausible and which explain observed evidence well. However, its successes are often ignored as it leads to conclusions that certain groups dislike, and these groups sometimes go to some lengths to discredit uniformitarianism as a useful tool in the study of the natural world.
The principle of uniformitarianism makes the methodological naturalism of modern science much more useful. It allows scientists, such as geologists, to study the past without actually having been there to directly observe it unfolding.
The principle of uniformitarianism was first formulated by Charles Lyell in his seminal work, Principles of Geology published in 1830. This was built on the insight of "deep time" propounded by James Hutton to explain geological processes. However, the term 'uniformitarianism' was not coined by Lyell but by the Cambridge academic William Whewell who called Lyell a uniformitarian in contrast to his own catastrophism — catastrophism, of course, being a euphemism for the Biblical flood. The ensuing arguments between deep-time scientists and Biblical literalists brought the term catastrophism into disrepute. For a long time the idea of uniformity of physical processes and uniformity of geological processes and their rate of action was the accepted model for uniformitarianism; however, as more geological evidence was accrued it became obvious that there have been both major and minor catastrophic occurrences in the Earth's history which have left their mark in both the geological and biological records. These have been entirely natural, albeit rare, events which neither upset the principle of uniformity of physical processes nor support the Biblical account of a global flood.
 Why it's smart
Creationists often assert that real scientists have no justification for assuming that physical laws are constant over time, and therefore, any work which is based upon this assumption (such as radiometric dating) is invalid. In reality, this Creationist assertion is not just wrong twice over, but if it were valid, it would necessarily render all science (including the Creationist version) and learning a perfect and utter waste of time.
First, real scientists don't actually presume that physical laws are constant; rather, they presume that if physical laws really did change, that change would leave traces of itself which could be detected by an appropriate experiment or observation. As such, real scientists can and do look for evidence that physical laws have changed. Empirical observations have, in fact, established that the greatest possible change which could have occured in physical laws is on the order of 1 part in several billion over the gigayears-long lifetime of the Universe.
Second, if physical laws do change in an indetectable manner, how can you trust that anything is reliable? Perhaps gravity might become a repulsive force tomorrow morning. Perhaps the molecules of your Bible might have rearranged themselves, transforming it into a copy of The God Delusion when you weren't looking. Simply put, uniformitarianism is the simpler assumption — because assuming that everything can change as it pleases, without any evidence of these variations, is unnecessary and need not be believed to explain everything we know.
The history of the attitude of the Judeo-Christian Jahweh towards His human likenesses provides a good example of uniformitarianism in action — the loving God remains the same yesterday, today and forever (Hebrews 13:8). (Intermittent hissy-fits like expelling humankind from Eden, drowning almost all humanity, sanctioning the slaughter of the enemies of Israel, and switching the outpouring of Grace from Jewry to the Gentile Christians merely represent occasional bouts of catastrophism within the overarching context of the overall uniformitarian Divine Plan.)
 Criticism of uniformitarianism
 By young-Earth creationists
Uniformitarianism has come under much criticism from young Earth creationists and such types, who posit that natural law has changed over time; specifically, that it has been altered by God for the purpose of resolving some messy inconsistencies of observed phenomena with the Honest-To-God TruthTM found in Genesis.
An example is the challenge against radiocarbon dating taken up by the people of the RATE committee which in condensed form follows this format:
- Scientist: By measuring the decay of carbon-14 in organic material, one can ascribe dates to fossils up to 60,000 years old.
- Creationist: That contradicts the biblical account of creation, so it's false.
- Scientist: But the radiocarbon dates line up perfectly with dates we know from other sources back 4,000 years.
- Creationist: You're working from the false premise of uniformitarianism. The truth is that the rate of radioactive decay changed during the Great Flood, so hundreds of thousands of years' worth of radioactive decay happened in a few days.
- Scientist: Er, that level of radiation would have generated enough heat to vaporize the Earth and nuke Noah.
- Creationist: Oh, ye of little faith. Do you not see that God also expanded the universe at the same time to keep
everythingonly the radioactive elements cool?
(We told you it was messy.)
 Other criticisms
Another criticism takes the milder approach of positing that it is a very big step to assume that in the few thousand years humans have been observing natural law, they have captured with any accuracy the principles by which the universe has operated for some 13 billion years.
This shortcoming is illustrated in a story about Charles Babbage. In order to make a point about miracles, Babbage would set his Difference Engine to wind from 2 to 4 to 6 to 8 to 10 to 117; his point being that a supposed "miracle" (the departure from an arithmetic progression) might only be the operation of some higher natural law hitherto unknown (i.e., God did not need to meddle with the gears in the Difference Engine for the departure to happen).
 Answering criticisms
These criticisms may be answered by pointing out that a large number of predictions based on uniformitarianism (in astronomy, for example) have turned out to be very accurate, and thus there is absolutely no harm in assuming uniformity.
In addition to the fact that uniformitarianism as an assumption works, its premise is also a reasonable one when we shave its beard. To postulate that mechanisms and rates were different in the past would require a researcher to determine not only what those mechanisms were but why they are different from the mechanisms in operation today. Creationists will often claim that radioactive decay was different during "Creation Week", thus fudging the numbers to come up with any age they like, although not one shows any evidence of why they were faster or how the rates changed. Not to mention the side effects of extremely enhanced rates, such as where they claim millions of years radioactivity could happen in days, releasing enough energy to blow apart the planet (as mentioned above). On the other hand, the structure of rock strata, cratering and weathering and many other factors that scientists have looked at support uniformitarianism. Creationists are left with their one main handy escape hatch: Goddidit!
Modern uniformitarianism, unlike conceptions that existed in earlier times, accepts that exceptional and extreme events, unknown in the time frame of humans, may have occurred in the past. Examples include the Messinian Salinity Crises (during which the Mediterranean Sea closed and almost completely dried up), the almost unimaginably extreme volcanism of the American West during the early Cenozoic, and the astoundingly huge floods emanating from glacial lakes during the Ice Ages. However, Occam's Razor rules, and such events are to be invoked only when no more mundane ("uniform") explanation covers the observed facts.