Every so often there is a leap second. (Eight times in the 90s, 6 times in the 80s, and 9 times in the 70s when the practice started.) Now the young-earth creationists have noticed this. They claim it is because the Earth’s rotation is slowing down. (Which is correct.) They give the rate, based on these leap seconds to be that the day gets longer by 1.5 milliseconds per day. And thus the need for leap seconds. Then they calculate that if the Earth is millions of years old that it would have to have been spinning impossibly fast in the past. So fast that it would have produced 5000 mph winds when scientists think the dinosaurs lived among other things.
Kent Hovind’s web site has a short audio clip of him talking about this. It is not hard to find many other creationist web sites make similar claims. See this (#20), this, this, and that for a few examples.
Now why is this wrong?
Today we have atomic clocks. These are extremely precise (and accurate) timekeepers. Now since the earth is slowing down at a rate noticeable to these clocks one cannot use the usual definition of one day being x many seconds. The second, as defined for the atomic clock, is based on an atomic process and was defined in such a way that it matched the day as it was in 1900.
The Earth is really slowing down at about 1.5 milliseconds a day per century—not 1.5 milliseconds a day per day as the young-earth creationist state. Whoops!
Now a century has passed since 1900.
(1.5 milliseconds/day/century)(century)=1.5 milliseconds/day
Basically because of a century of the Earth’s rotation slowing down, the second as defined for atomic clocks is shorter than a second as defined by day/night cycle which we ordinary people use. So a discrepancy of about 1.5 milliseconds a day accumulates. To keep the two time systems within a second of each other the a leap second was invented. It is important to note that even if the Earth stopped slowing down and rotated at a constant speed, we would still need to have leap seconds because the second was defined to match the Earth’s rotation in 1900 when the Earth was rotating faster.
(Keep in mind that 1.5 milliseconds/day/century is an approximate figure and that the slow down of the Earth is not absolutely constant. I chose the value for the sake of simplicity.)
For more info on leap seconds see a site from the U.S. Naval Observatory, the agency which keeps time for the United States. Also see another debunking of this false claim. This site also debunks this claim and several other “proofs” that the Earth is young.
Now this one is a bit confusing at first until one sees what is going on. The creationists mistook the discrepancy between the second defined as one 86,400th of a day and the second as the physics people define it for the rate of which the Earth’s rotation is slowing down. I really don’t blame them for making this mistake initially. We are all entitled to a few mistakes. But this does not justify keeping this claim going for years and years. My question is, why is this claim still being made?