system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do we know the Pillars of Creation will be destroyed in 1000 years?

I mean, Light takes 7000(?) years to get to us from the Pillars, and we still have another 1000 years to see the (predicted) destruction. Now if light is the fastest object how could we possibly predict that they will be destroyed?
gpt
Imagine the newly enchanted Hubble Telescope happened to return images of a person 10,000 light years away swinging a sledgehammer at a plate glass window. The swinger is covering some distance, though, so the last image of the day is of the hammer making contact with the window, but we won't get images of the result until tomorrow. 

Based on the images, we have established that the hammer is moving very fast, and that the glass really is just regular glass, and we know there was an impact.  Even though, because of the limitations of the speed of light we won't actually *see* the glass break until tomorrow, we can be certain it will happen---or, at least, as certain as we can be based on our current understanding of how hammers and glass interact.  And it doesn't matter that it may have actually "happened" 10,000 years ago. 

Same with the Pillars.  We see something moving towards them that, based on what we know about the pillars, would destroy them. Could something else happen in the next thousand years to prevent it? Of course, but the fact that the pillars are far away doesn't prevent us from making that prediction with a level of confidence consistent with the facts at hand.