Scientist: Given the human tendency to explore and colonize new areas, some people believe that the galaxy will event...

shunhe on December 27, 2019

Hi @Shiyi-Zhang,

The wording in this question stem can be a bit tricky. Essentially, what it's saying is that some people think the galaxy will eventually be colonized by trillions of humans (this is straightforward). When this happens, a majority of humans who ever lived would be alive during this time. Why? Because trillions of humans would be alive during that time, and up to now, there have been less than a trillion humans. So a majority would be alive during colonization of the galaxy. Let's say the galaxy is colonized by 3 trillion people and only 1 trillion people existed before the galaxy was colonized. Then 3/4 people were alive during colonization. This is what the scientist is saying in her somewhat confusing second sentence.

Then, the scientist tells us that probability-wise, it's likely we're alive during this period. Why? Because looking at it from a bird's eye view, we have a 3/4 chance of being alive during that period because theoretically, we have an equal chance at being any one of the 4 trillion people who have existed up to that point. The scientist finally concludes by saying that we aren't alive during this period (as the galaxy isn't being colonized), and so it's unlikely that the colonization will ever happen. In other words, the event hasn't occurred despite its high likeliness, so the hypothesis itself is likely false. Hope this helps!