[jeffreyH (OP)]

These are force carriers critical to physics outside the black hole. If they are forced along a worldline towards a singularity, what would that mean for the integrity of atoms?

[Bored chemist]

It wouldn't matter if they turned into a marzipan model of the Titanic.
That change, inside the event horizon, could never affect something - be it atoms, or us, outside the event horizon.

If the hole was really big, and there was an observer inside the  EH then they would see the particles behaving in just the way particles normally do.

[jeffreyH (OP)]

It wouldn't matter if they turned into a marzipan model of the Titanic.

Now you are just being silly.

That change, inside the event horizon, could never affect something - be it atoms, or us, outside the event horizon.

Of course not. I never said it could..

If the hole was really big, and there was an observer inside the  EH then they would see the particles behaving in just the way particles normally do.

Well then, that is a very interesting comment. Worth discussing.

[Bored chemist]

Now you are just being silly.

Not really.
It's an absurd example- yes sure- that was the point.

But the underlying point is serious.
The rest of the universe is safe from any behaviour inside the hole.
So

what would that mean for the integrity of atoms?

Nothing.
It means absolutely nothing for any atom that I will ever observe.

[jeffreyH (OP)]

Ok, the integrity of atoms that cross the eh.

[jeffreyH (OP)]

You said "If the hole was really big, and there was an observer inside the  EH then they would see the particles behaving in just the way particles normally do."

Yet you also said "Nothing.
It means absolutely nothing for any atom that I will ever observe."

Have you been beyond the event horizon of a black hole? How do you come to your first conclusion? It is an important point. I am not trying to trip you up.

[Halc]

You said "If the hole was really big, and there was an observer inside the  EH then they would see the particles behaving in just the way particles normally do."

The answer is essentially correct.  An event horizon is a mathematical singularity, meaningful only to an outside perspective, not a local one.  A system crossing the event horizon defined by some distant observer O will simply cease to be a possible source of causal interaction to O, forever.  This is no different than a star crossing Earth's event horizon 16 BLY away.  That star can no longer have any effect on us, yet nothing physical happens to the star because it has done this.

Likewise, a molecule inside a black hole experiences similar physics like it always did.  Bosons and gravitons and such cannot cross back over the distant observer's EH, which is why the waves detected by LIGO from merging black holes abruptly switch off.

Large black holes do matter.  Small ones have insane tidal forces, and that is very much locally detectable.  Under strong enough tidal forces, molecules and even atoms can be ripped apart, which is empirically different physics than a relatively uniform gravitational field.

All the above answer is based on a mathematical model that presumes spacetime within a black hole.  There are some models that put such locations outside of spacetime, rendering it meaningless to discuss the physics within.

[Bored chemist]

Have you been beyond the event horizon of a black hole?

It's sort of possible that I have, but if I have, I still am.
A few decades ago it was reasonable to ponder the idea that the whole universe was a black hole and were all inside it.
Better measurements etc have ruled that out.
The point is that you might be in a black hole, but not know it.

[jeffreyH (OP)]

Have you been beyond the event horizon of a black hole?

It's sort of possible that I have, but if I have, I still am.
A few decades ago it was reasonable to ponder the idea that the whole universe was a black hole and were all inside it.
Better measurements etc have ruled that out.
The point is that you might be in a black hole, but not know it.

I agree with all the above. If we are all inside a vast black hole then at what point do all the world lines converge? Yes size matters, but ultimately everything should end up in a singularity. Whatever the size of the black hole. You are always traveling towards it (in theory).

[jeffreyH (OP)]

You said "If the hole was really big, and there was an observer inside the  EH then they would see the particles behaving in just the way particles normally do."

The answer is essentially correct.  An event horizon is a mathematical singularity, meaningful only to an outside perspective, not a local one.  A system crossing the event horizon defined by some distant observer O will simply cease to be a possible source of causal interaction to O, forever.  This is no different than a star crossing Earth's event horizon 16 BLY away.  That star can no longer have any effect on us, yet nothing physical happens to the star because it has done this.

Likewise, a molecule inside a black hole experiences similar physics like it always did.  Bosons and gravitons and such cannot cross back over the distant observer's EH, which is why the waves detected by LIGO from merging black holes abruptly switch off.

Large black holes do matter.  Small ones have insane tidal forces, and that is very much locally detectable.  Under strong enough tidal forces, molecules and even atoms can be ripped apart, which is empirically different physics than a relatively uniform gravitational field.

All the above answer is based on a mathematical model that presumes spacetime within a black hole.  There are some models that put such locations outside of spacetime, rendering it meaningless to discuss the physics within.

I agree with all the above statements.

[jeffreyH (OP)]

Sag A* has a diameter
of 44 million km. Not vast on cosmic scales. It also matters what the upper limit on a black hole is. It all depends on how much mass is available to feed it. The entire universe? Unlikely.