Suppose it turns out that one in 1 million stars has a planet that at some point in its history is home to an advanced civilization. Then the total number of civilizations that have arisen in our galaxy would be closest to _________.

To find the total number of civilizations that have arisen in our galaxy based on the given supposition, we would follow these steps:

1. Estimate the total number of stars in our galaxy, the Milky Way. 2. Apply the given probability to determine the number of stars with planets hosting advanced civilizations.

The Milky Way is estimated to have approximately 100 to 400 billion stars. For simplification, let's choose a number in this range. A common estimate used is 200 billion stars.

Now, if one in 1 million stars has a planet with an advanced civilization, we can calculate the number of such planets:

Number of civilizations = (Number of stars in the galaxy) / (Frequency of stars with advanced civilizations)

Assuming 200 billion stars: Number of civilizations = 200,000,000,000 stars / 1,000,000 (for one in 1 million chance)

Number of civilizations = 200,000

Therefore, the total number of civilizations that have arisen in our galaxy would be closest to 200,000, given the assumption that one in 1 million stars has a planet where an advanced civilization has developed at some point in history.