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While the previous assumption was that black holes are completely characterized by only three parameters - mass, electric charge, and angular momentum - which i

While the previous assumption was that black holes are completely characterized by only three parameters - mass, electric charge, and angular momentum - which is called the no-hair theorem [1]. This is at odds with the time-reversibility of physical laws as there are many ways to make a black hole with a certain mass, electrical charge, and angular momentum but given such a black hole it is not possible to go backwards in time and reconstruct the formation process of the black hole as you have only three numbers and therefore not enough information to figure out when, where and what was thrown into the black hole. [1] https://en.wikipedia.org/wiki/No-hair_theorem https://en.wikipedia.org/wiki/No-hair_theorem

Terry_Roll 5y ago
So space archaeology is dead before it got started?
- danbruc 5y ago
  Not sure if understand what you mean, but if you mean that black holes could eat up the traces of the past and make history inaccessible, then no, at least theoretically. I would assume that the current consensus is that black holes can not do this - which implies that the no-hair theorem is at best approximately true - but we only have unproven ideas which mechanism prevents black holes from destroying information. In practice recovering information from black holes is probably no easier than trying to recover the text of a book by inspecting the smoke of the fire you threw the book into.
  - Terry_Roll 5y ago
    It was a little joke about rooting around inside a blackhole discovering things from the past. ;-)
- simiones 5y ago
  "Dead" barely even begins to describe the horror of passing the event horizon of a black hole - essentially every particle of your body that gets closer to the center becomes unable to ever, in any possible future, communicate back to the parts that are farther away (according to the GR understanding, which to be fair is not consistent with what we know of QM).

Terry_Roll 5y ago

So space archaeology is dead before it got started?

danbruc 5y ago
Not sure if understand what you mean, but if you mean that black holes could eat up the traces of the past and make history inaccessible, then no, at least theoretically. I would assume that the current consensus is that black holes can not do this - which implies that the no-hair theorem is at best approximately true - but we only have unproven ideas which mechanism prevents black holes from destroying information. In practice recovering information from black holes is probably no easier than trying to recover the text of a book by inspecting the smoke of the fire you threw the book into.
- Terry_Roll 5y ago
  It was a little joke about rooting around inside a blackhole discovering things from the past. ;-)
simiones 5y ago
"Dead" barely even begins to describe the horror of passing the event horizon of a black hole - essentially every particle of your body that gets closer to the center becomes unable to ever, in any possible future, communicate back to the parts that are farther away (according to the GR understanding, which to be fair is not consistent with what we know of QM).