if something happened to the black hole at the center of our galaxy, could we know about that problem before it affected us?

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?

Anticorp ,

Nothing will happen to the black hole, except for its continued growth. At least not anything on time scales that are meaningful for humanity. We’ll be long gone before any observable changes happens to any black holes.

AA5B ,

Yes, let me lawyer the question ….

We could know about it in only 26,000 years due to the speed of light and gravity waves. However I’m not sure how it would affect us at all …

  • Perhaps there’s a burst of particles going less than the speed of light. We would know about it before those particles got here.
  • Perhaps you mean the disappearance of the strong gravity well at the center might affect us: I imagine any changes to the structure of the galaxy or it’s movement would take much much much longer to affect us
Num10ck ,

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?

Kyle ,

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.

TauZero ,

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.

portifornia ,

No, as both gravitational and em waves travel at the speed of light, the “we’re all screwed” things we could ever observe would only ever be slowed-down/distorted (by things that could even do such a thing like a black hole) as they approach us.

So it’d be a happy little surprise (short of worm-holes or tachyons existing), on year 26,000.

That’s not too say life as we know it would end immediately. We might make it generations before the real chaos affected us on earth. On a smaller scale, if the sun blipped out of existence, sure, we’re 💯 doomed and we’d know it after 8.3 minutes, but some of us might make it a solid week before all life on earth was expunged 😅.

ghostface ,

I can not answer this question, but I suspect, that actual answer is yes and no. Due to the swpc they relay solar storm info to earth before it hits due to sensors.

Webwoupd need yo send probes out further yo.grab that data first

count_of_monte_carlo Mod ,

Any data is sent at or below the speed of light. Solar storms are charged particles (mostly protons) being ejected from the sun and eventually hitting the earth’s magnetic field, causing disruptions in the field (and potentially cool auroras).

Since these storms are just particles traveling from the sun to the earth, they travel slower than light speed, so our distant sensors can warn us in advance at/near the speed of light. This won’t work if the sun were to instantly disappear or change color though, that information would travel at light speed and the probe signals would arrive at the same time.

jmp242 ,

I’m pretty sure there’s no way to know about it before … information can’t travel faster than the speed of light.

krayj OP ,

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”.

clockwork_octopus ,

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.

TauZero ,

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.

WarmSoda ,

Many worlds is a fun idea, too. But also being regarded as not real for a while now. The cat in a poison box living or dying doesn’t mean it lives and dies.

I never heard about the false vacuum before, that’d be some good sci-fi

madcaesar ,

I was reading this clenching my butt, then got to the last line and unclenched.

Nomad ,

What about gravitational waves? Ligo can detect them and as they send ripples through spacetime they might be faster?

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