‘A Blink of an Eye, Astronomically’: What Does It Actually Mean?
Have humans only been around for "a blink of an eye"? How long did it take to form galaxies, blinkwise?
February 13, 2010 - 12:00 am
In a January 15 Science news item, Yudhijit Bhattacharjee reported that the earliest galaxies began to form around 300 million years after the Big Bang. He said this was:
A blink of an eye in astronomical time.
Of course that is just a figure of speech, but I thought we should figure that figure of speech out. Just what is a “blink of an eye” astronomically?
The best guess for the age of the universe is about 14 billion years, maybe a little less. There’s about 365 and a quarter days per year, accounting for leap years, and 24 hours to each day. Each hour has 60 minutes, and each hour has 60 seconds. Multiplying those together tells us that 14 billion years translates to a humongous number of seconds. How many?
Write down 44 and then write 16 zeros after it: the actual number is just over 440,000,000,000,000,000 seconds. That figure is — currently — larger than our budget deficit. So it’s pretty big.
A real blink of an eye takes 300 to 400 milliseconds. Since there’s 1,000 milliseconds in each second, a blink of an eye takes about 1/3 of a second.
Compared to the time span of one full second, a blink of an eye is an eternity. Thirty-three percent of that second is given over to blindness, after all. But if you’re measuring the length of the blink with respect to an hour, the disparity isn’t so dramatic. And still less dramatic is the time of a blink weighed against the time it takes the Earth to spin once around its axis (Berkeley High School graduates: that’s one day).
These comparisons are necessary because the blink of an eye is meaningful only when it is measured against some base, or when it is contrasted with some reference. The reference provides us with a ratio: the length of time of a blink to the length of time of the reference. Once we decide the reference, we’ll use it in calculating the ratio of the length of time for an “astronomical-blink” to the length of time the universe existed.
It works like this: We’ll know the reference time, the length of the blink, and the age of the universe. We can use those to solve for the length of the astro-blink by applying the beloved techniques of high school algebra. So what’s the best reference?