Viewing a single comment thread. View all comments

phantagom t1_j285l7s wrote

Reply to comment by WittyUnwittingly in What is our current "best guess" about how to observers that entered a black hole on opposite sides would look to each other once they crossed the event horizon? by WittyUnwittingly

No, "loss of causality information" and "infinitely blueshifted" is not the same thing.
The event horizon of a black hole acts as a "one-way membrane" that separates the region inside the black hole (the interior) from the region outside (the exterior). Once an object or particle crosses the event horizon, it becomes trapped inside the black hole and cannot escape. This means that, from the perspective of an observer outside the black hole, the interior of the black hole is causally disconnected from the exterior. This means that there is no way for an observer outside the black hole to receive information about what is happening inside the black hole, or to affect events that are occurring inside the black hole. This is what is meant by "loss of causality information."
The phenomenon of an object being infinitely blueshifted as it approaches the event horizon of a black hole is a consequence of the extreme gravitational forces present in the region. more extreme. In this sense, it is possible to say that the object is "infinitely blueshifted" as it approaches the singularity. However, this is not the same thing as a loss of causality information, as the object is not able to transmit any information about its experience to an outside observer once it crosses the event horizon.

The choice of coordinates used to describe a physical system is a matter of convenience, and different choices of coordinates can give rise to different perspectives on the same physical situation. It is generally more useful to choose coordinates that are well-behaved (e.g. that do not diverge or become singular at certain points) and that are adapted to the symmetries of the system (e.g. cylindrical coordinates for a cylindrically symmetric system).

3

WittyUnwittingly OP t1_j29tbcy wrote

Sorry. I did not mean to imply that blueshifted light observed from within an event horizon is what most mainstream scientists mean when they say "loss of causality information"

I understand that debate relatively well, and it pertains to recovery of information about what fell into the black hole from the outside.

I'm asking: is there something fundamental that I'm overlooking with my description of the "infinitely blueshifted" light? Seems to me that from the inside of a black hole you would be unable to deduce anything about the order of events outside using the photons falling in, because from your perspective, they would be arriving all at the same time.

1

phantagom t1_j2a17xx wrote

It is true that from the perspective of an observer inside the event horizon of a black hole, the photons falling into the black hole would appear to be infinitely blueshifted and would arrive at the singularity at the center of the black hole all at the same time. This is a consequence of the extreme gravitational forces present in the region, which cause the photons to be blueshifted and to follow highly curved paths as they fall towards the singularity.
However, from the perspective of an observer outside the event horizon, the photons falling into the black hole would not be infinitely blueshifted, and would not all arrive at the same time. From this perspective, the photons would follow paths that are determined by the curvature of spacetime, which would generally not be straight lines.

3