We know that light and even gravitational waves propagate at the speed of light.
So if something catastrophic happened to the black hole at the center of our galaxy (about 26,000 lightyears away), would there be any way for us to have advance knowledge of it before we could observe it with telescopes or before we could measure the gravitational changes?
Ludicrous example: say the black hole at the center of the galaxy disappeared 25,999 years ago. Is there a way we would have known about it by now, or do we just have to wait out another year to see if we’re all screwed?
This is what I thought - I just wanted to make sure I hadn’t failed to consider something obvious. Am meeting up with some old friends who are science geeks next month and wanted to throw out the line “for all we know, the center of the galaxy exploded 25,999.9 years ago and we could all die tomorrow” and I didn’t want anyone coming back with “well actually…we would have detected that by now thanks to technology xyz that was in ivented in 20XX”.
If the black hole specifically disappeared, it would have no effect on us. The solar system would not even be launched on a 100 million year trajectory out of the galaxy, as galactic rotation is dependent on the masses of stellar and interstellar matter in the disk and dark matter in the halo. The supermassive galactic black holes, despite being supermassive, still only make up a tiny percentage of total galactic mass.
If you want to wow your friends, tell them about false vacuum decay. We could have bubbles of true vacuum expanding out in space from multiple directions towards us at lightspeed, and no way of knowing about them, stopping them, or outrunning them. Any point in space could nucleate a new true vacuum bubble at any time, just like a given uranium atom could decay now or in 5 billion years or never. Even spookier, by principle of quantum immortality, the Earth could have been engulfed by vacuum bubbles many times before, and we are just the one tiny sliver of probability space where by luck alone we survived long enough to talk about it here and now.
Thankfully false vacuum is just an idea and there is currently no evidence that it is real.
