I'm pretty sure there's no way to know about it before ... information can't travel faster than the speed of light.
this post was submitted on 26 Jul 2023
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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.
I totally misread your post as you were meeting up with some old friends who are science geckos and I wanted the story behind all of that, but then I read it again and was disappointed in the lack of geckos.
Enjoy your boring gecko-free meet up.
i guess if you had some super crazy distant probe observing the black home and it's memory bits were quantum entangled with a receiver device near us, we might know instantly-ish? but would need to wait millions of years for that probe to be placed to begin with and hope the systems don't corrode or corrupt or fail in those millions of years. and what would you do with the info? tell everyone?
I thought FTL communication is just a fun typical science fiction understanding of quantum entanglement.
I thought we would still have to know what is going on at the probe via another means to know or decode the message sent by the entangled particles to their counterparts on Earth.
Kind of like putting two letters in two envelopes but we don't know what colour they are, just that they will always be opposite colours. Even the person arranging them doesn't know which colour they are. We don't know if a red letter is sent to London or a green one is sent to LA or what colour they'll be at all. But when we open the letter in London and see that it's the red one we know the other one in LA is green.
So no matter where or when the person with the red letter is, they'll always know the other person has the green one once they open the letter. But no information has been mysteriously transported across space and time, just the correlation between the two has been discovered.
This is correct. FTL communication using any form of quantum entanglement is provably mathematically impossible by the no-communication theorem. Most common sci-fi trope though.