- #1
Elroch
- 138
- 12
Hawking and others suggest that it is a very special deal that macroscopic black holes lose quantum information, but I only partially agree.
It is clearly important that they do not preserve most quantum numbers - black holes may be a way to break a lot of conservation laws of particle physics. But as for other information about particles (eg dynamical variables) they don't seem very special at all.
To explain what I mean, compare two situations. In the first case you have some matter about which you know a great deal and drop it into a black hole. Soon it is characterised by a few quantum numbers. Lots of information lost.
Second case you have a lot of gas molecules and know a lot about their state. You vent the gas into a sealed box. After a very short while uncertainty means you have no predictive power about their special state. All the information that you have left is a temperature and a few other numbers.
Isn't this really rather similar?
Of course the second case is not so dramatic: you still have molecules. But if you ignore that detail there is a strong analogy.
The argument that black holes destroy information in a more radical way seems to come from the idea that if you know a wave function you have perfect predictive power about the wave function in the future. This is a red herring, because in the real world we never know the value of a wave function (except in some sense for a bound state), we just have some observations which give us partial uncertain knowledge about the quantum state. These observations allow us to make uncertain predictions which get increasingly inaccurate (without further observations).
[Note: the issue of virtual quantum black holes losing information (which Hawking wrote about) sounds intriguing and may be more significant to our understanding of what we can know and predict about the universe]
It is clearly important that they do not preserve most quantum numbers - black holes may be a way to break a lot of conservation laws of particle physics. But as for other information about particles (eg dynamical variables) they don't seem very special at all.
To explain what I mean, compare two situations. In the first case you have some matter about which you know a great deal and drop it into a black hole. Soon it is characterised by a few quantum numbers. Lots of information lost.
Second case you have a lot of gas molecules and know a lot about their state. You vent the gas into a sealed box. After a very short while uncertainty means you have no predictive power about their special state. All the information that you have left is a temperature and a few other numbers.
Isn't this really rather similar?
Of course the second case is not so dramatic: you still have molecules. But if you ignore that detail there is a strong analogy.
The argument that black holes destroy information in a more radical way seems to come from the idea that if you know a wave function you have perfect predictive power about the wave function in the future. This is a red herring, because in the real world we never know the value of a wave function (except in some sense for a bound state), we just have some observations which give us partial uncertain knowledge about the quantum state. These observations allow us to make uncertain predictions which get increasingly inaccurate (without further observations).
[Note: the issue of virtual quantum black holes losing information (which Hawking wrote about) sounds intriguing and may be more significant to our understanding of what we can know and predict about the universe]