Distances in space can be a very relative thing. After all, the universe is billions of light years1 across. So I had to laugh yesterday when reading a NASA news item2 that described a recently discovered black hole (named SN 1979C) as “in our cosmic neighborhood.”
Are we in danger from this nearby black hole? Since it is in our neighborhood, could it wander too close to Earth and sucks us all into oblivion? Well, not very likely. You see, the folks at NASA who deal on a daily basis with a universe that is billions of light years across, define “our neighborhood” a little differently than the average person would.
This newest black hole discovered by NASA is 50 million light years away, or roughly 293,500,000,000,000,000,000 miles. That is not in our solar system; it is not among the 1,000 nearest stars; it is not even in our galaxy. So is it really in our “neighborhood”?
Let’s do a quick thought experiment. (If you have a math aversion, feel free to skip the next paragraph!)
Imagine that before the dinosaurs became extinct 65 million years ago, a team of dinosaur scientists discovered how to travel at a significant fraction of the speed of light3 and then decided to visit the SN 1979C black hole. After leaving Earth 65 million years ago and traveling since then at 75% of the speed of light, today those dinosaur scientists STILL would have over 1 million years left in their journey before reaching SN 1979C.
Sorry NASA, but when I use the phrase “our neighborhood” in the context of Earth and outer space, I think it should be defined as a nearby area that is at least potentially accessible from Earth. For example, our solar system is definitely part of the neighborhood (and might even qualify as “our backyard”). Nearby stars (those within a couple of dozen or maybe even 100 light years) are in our neighborhood. If I really wanted to stretch the definition, I might even say everything in our Milky Way galaxy is in Earth’s neighborhood.4 But someplace that would take us millions of years of trip time to reach ... that’s just not in the neighborhood.
- A light year is the distance light travels in one year, or about 5.87 trillion miles. [↩]
- Youngest nearby black hole, NASA website, November 15, 2010 [↩]
- Based on our current knowledge of physics, it is either impossible — or so difficult as to be virtually impossible — to travel faster than the speed of light. In addition, as your speed approaches the speed of light, it takes exponentially more energy to move any faster, so even getting close to 100% of the speed of light become a nearly impossible goal. Given those limitations, we’ll assume these brainy dinosaurs were able to move at up to 75% the speed of light. Finally, yes I do realize there is no evidence for brainy dinosaurs that were able to build spaceships far beyond anything humans are capable of ... that’s why this is called a thought experiment! [↩]
- This would be something like saying that Seattle is in Los Angeles’ neighborhood — it’s a stretch, but in certain contexts you might be able to make the case. [↩]