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>In Derek's example the switch and the bulb are 1 meter away from each other and therefore the time is 1/c seconds, i.e the time light takes to travel 1 meter.

Perhaps I didn't make my example clear. Imagine loop with 2 switches...one switch 1 LY away...another switch 1 meter away.

Derek flips the 1m switch and light instantly turns on: What does that tell you? Derek flips the 1m switch and light doesn't turn on: What does that tell you?

How were you able to find out that information before waiting 1 yr?

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It's explained in a comment from a few days ago:

https://news.ycombinator.com/item?id=29283101

From what I understand, in your setup the lightbulb will turn on and quickly turn off, irrespective of the state of the other switch which is 1 yr away. Then after 1 yr passes it will react according to the state of the other switch.