OK, imagine you’ve heard about a phenomenon about invisible dodgeballs. You can’t see them, but you have evidence they’ve been around by leaving wet trails on the floor as they’ve passed by. This is how you can tell it’s direction and likely properties of the balls but not any other information. They haven’t been directly observed.
So now you want to get more information about these invisible dodgeballs. One way to do it is to roll a bag of baseballs to a likely spot where the balls are known to go by. Eventually you get a bunch of baseballs rolling back towards you and you measure the speed, direction they were going, etc. to gather more about the invisible dodgeballs. So you can calculate where it *was*, but not where it currently *is*. Now that the invisible dodgeballs have been observed, their conditions have been changed.
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