Billions and Billions...

Matt Lowry

I got to know Bob a few years ago during the summer of 2000 when I was doing electrical repair work for my school district. Bob is quite the handyman, and he's also a pleasantly curious fellow. He and I enjoyed many conversations on science and astronomy related topics in the two months I worked with him.

So, given our shared history and my reputation at school for being one of the pre-eminent science geeks, Bob recently came to me with an interesting question. In the email I got from Bob was a question about the frequency of Gamma Ray Bursts (GRBs) and their detection. He noted that the beams put out by GRBs are pretty narrow, comparatively speaking and he then went on to say...

"How often do we see these gamma bursts? Using their narrow beam theory, wouldn't giant stars need to burn out trillions of times a minute for us to see them ever? You would have to be a pretty good shot to hit our little tiny earth from 100 billion light years away."

This got me to thinking, and it was the perfect opportunity to illustrate to my friend how vast the observable universe really is. I responded that a GRB is discovered at the rate of roughly one per day (I looked it up on a NASA website), which comes out to about 365 per Earth year. And then I followed up with...

"There are about 100 billion stars in our galaxy alone (that's 10^11 - a 1 with 11 zeros behind it), and there are roughly 100 billion (10^11 again) galaxies in the observable universe - this comes out to a grand total of 10,000 billion billion (or 10^22) stars roughly in our observable universe. That's a bunch!

Now compare 10^22 stars with the number of detected GRBs in a year - a ratio of roughly 365 to 10^22, a number so small that your calculator couldn't even put it on the screen. True, these are only the GRBs that happen to be "aimed" in our particular direction, but in light of the numbers it starts to make sense."

Bob was impressed by these numbers, to say the least. Even those of us who are veteran stargazers and well-educated in the sciences are humbled by numbers such as these. They go far, far beyond the familiar-sounding "billions and billions" made famous by Carl Sagan. These sorts of numbers make Sagan's billions seem like nothing more than a speck of dust.

Ironically, the day after I dialoged with Bob, a similar topic came up in one of my introductory physics classes. We had been discussing the Doppler Effect and how astronomers have been using it to detect extra-solar planets. The idea is that large mass planets tug their home stars around in little circles, which causes the spectrum of that star's light to wobble between what is called a red-shift and blue-shift.

Using these techniques, I explained to my class, astronomers have indirectly detected roughly 150 extra-solar planets in the last 10 years. And these, I reminded them, are just among the stars within about 100 light-years of Earth. Of course, a curious student then asked, "Could there be life on those planets?" Why not, I said, with the disclaimer that it was probably nothing like Earth life, if in fact it existed.

"Do you think there's intelligent life out there in the universe somewhere, Mr. Lowry?" was the next question.

My response: "Well, think about how many stars there are out there in the universe. And we're just now discovering that a lot of them, the nearby ones at least, have planets around them. Statistically speaking, I think there's got to be extraterrestrial life in the universe."

"Folks, the universe is almost too big to imagine, and we are just one planet... cosmically speaking, a speck of dust."

Some kids seemed a little unsettled by the revelation, others, like my friend Bob, seemed excited. I suppose this is because there are those who like to have a na´ve, egocentric view of the universe, and when that is challenged they might feel threatened.

But for those of us who are not intimidated by Sagan's billions, or the even larger numbers (10^22 - wow!), 100 light-years away is just the tip of the cosmic iceberg, a universe full of splendor and discovery.

Ad Astra -- Matt Lowry

Published in the May 2005 issue of the NightTimes