5 ms·

Does physics have some "conservation of information" laws that I missed the memo about? Can anyone recommend some introductory reading about this?

T-A 11y ago
https://en.wikipedia.org/wiki/Black_hole_information_paradox https://en.wikipedia.org/wiki/Black_hole_information_paradox
danblick 11y ago
Here's another interesting one: https://en.wikipedia.org/wiki/Landauer's_principle https://en.wikipedia.org/wiki/Landauer's_principle Landauer's principle is a theoretical lower limit on the amount of energy required to perform a computation that destroys information.
Udo 11y ago
All known physical processes only transform information, it's never actually lost (although it may get "transformed" in a way that it's irretrievably scrambled). Black holes are the only known thing that may cause information to disappear from the universe - or not, that's the open question.
- chrischen 11y ago
  What about quantum mechanics? How can you get a true quantum random number generator if information is preserved?
  - gizmo686 11y ago
    The many worlds interpretations. Roughly speaking, if there is a quantum system that is in a superposition of states A and B, and we observe it, we then become entangled with it and are then in a superposition of having observed A and having observed B. No information has been lost from the universe, but there is no way for those of us living in the A state to observe anything about the B state.
  - deleted 11y ago
    [deleted]
  - eli_gottlieb 11y ago
    Quantum information is actually different from classical information (classical entropy). Quantum information is (believed to be?) a conserved quantity; classical is not (it never decreases). A quantum random number generator is just emitting quantum bits: without having had those qubits in the first place, you can't have computed them ahead-of-time, so they're random.
    - solipsism 11y ago
      Quantum information is (believed to be?) a conserved quantity No it's not. Why are so many people making things up? QM does not even define a concept of a quantity called "information".
danbruc 11y ago
The laws of physics conserve information in that sense that two initially distinct states will always remain, at least in principle, distinguishable for all times, i.e. two distinguishable states A and B will never evolve into the same state C. This is equivalent to the statement that the laws of physics are time reversible, i.e. if you would end up in state C you could not tell whether the system came from state A or B. If you, for example, start a pendulum with different initial displacements the pendulum will always end up at rest due to friction but if you could take into account the exact states of all the molecules in the air and the joint and so on you could in principle figure out in which exact positions you started the pendulum. You could actually just very precisely measure the temperature of a pendulum in a box and infer the initial displacement from that because different initial displacements imply different initial (potential) energies and therefore different final temperatures after all the energy became thermal energy and everything in the box had time to reach the equilibrium temperature. You just couldn't figure out whether the pendulum was started to the left or to the right of the rest position with this method.
- haberman 11y ago
  Fascinating. Do physicists generally believe this? The idea that both the infinite future and the infinite past are all encoded into any snapshot of the universe is blowing my mind. My layperson's understanding of QM always gave me the impression that it does the opposite: that it gives non-determinism a place to "hide," so-to-speak. My impression was that religious believers could use QM to argue that their unseen God, for example, does actually have a physically plausible mechanism by which he/it could intervene in the physical world. But if I'm understanding this theory correctly, unless God is a physical thing, there is no way for God or any other supernatural force to affect the physical world without itself being physical. This theory also would seem to deny the existence of free will.
  - solipsism 11y ago
    QM does away with any notion of conservation of information. Time reversibility (T symmetry) is usually talked about at macro scales where QMs effects are vanishingly small. IANAP Regarding free will -- rigorously define it for us, without evoking the supernatural, and as distinct from pure randomness and absolute determinism, and it should be easy to tell whether the law of conservation of information allows for it. Before spending too much time in e it, though, note that such a definition is widely considered impossible. IANAP
dogma1138 11y ago
Yes there is a principal in on of the "interpretations" (we really need a better word for it) of QM that the information carrier by a wave function cannot be destroyed, this present a problem in certain cases such as black holes. There's allot of weird stuff going on on the extreme edges of theoretical physics, to the point in which also a though that some areas of theoretical physics have moved into the "Metaphysics" and Philosophy domains and are distancing them selves from certain scientific principals. That said I like to treat black holes in the GR/SR manner they are simple massive objects not super dense hot balls of entropy, they don't have some universal cosmic powers, they are "black" simply because they red-shift all radiation to the point of invisibility, they can form, grow and break apart, and we never can see anything actually entering a black hole due to time dilation and anything that comes close to it will be red-shifted to a point in which we won't be able to see what or where it is either. Since nothing from out POV ever enters the black hole and everything is stuck on the event horizon nothing is lost, and since black holes can evaporate (Doesn't require hawking radiation altough it's the most common explanation since Yakov Zeldovich (which Stephen hawking based his work on) and others have proposed similar mechanisms which are more compatible with physics as it is measured and perceived by hmmm reality...), no firewalls or weird mechanism are needed to protect or explain other weirdness that happens around singularities. Singularities are well covered by GR and SR prevents naked singularities so we are good there too. But that's just me :)

T-A 11y ago

https://en.wikipedia.org/wiki/Black_hole_information_paradox https://en.wikipedia.org/wiki/Black_hole_information_paradox

danblick 11y ago

Here's another interesting one: https://en.wikipedia.org/wiki/Landauer's_principle https://en.wikipedia.org/wiki/Landauer's_principle Landauer's principle is a theoretical lower limit on the amount of energy required to perform a computation that destroys information.

Udo 11y ago

All known physical processes only transform information, it's never actually lost (although it may get "transformed" in a way that it's irretrievably scrambled). Black holes are the only known thing that may cause information to disappear from the universe - or not, that's the open question.

chrischen 11y ago
What about quantum mechanics? How can you get a true quantum random number generator if information is preserved?
- gizmo686 11y ago
  The many worlds interpretations. Roughly speaking, if there is a quantum system that is in a superposition of states A and B, and we observe it, we then become entangled with it and are then in a superposition of having observed A and having observed B. No information has been lost from the universe, but there is no way for those of us living in the A state to observe anything about the B state.
- deleted 11y ago
  [deleted]
- eli_gottlieb 11y ago
  Quantum information is actually different from classical information (classical entropy). Quantum information is (believed to be?) a conserved quantity; classical is not (it never decreases). A quantum random number generator is just emitting quantum bits: without having had those qubits in the first place, you can't have computed them ahead-of-time, so they're random.
  - solipsism 11y ago
    Quantum information is (believed to be?) a conserved quantity No it's not. Why are so many people making things up? QM does not even define a concept of a quantity called "information".

danbruc 11y ago

The laws of physics conserve information in that sense that two initially distinct states will always remain, at least in principle, distinguishable for all times, i.e. two distinguishable states A and B will never evolve into the same state C. This is equivalent to the statement that the laws of physics are time reversible, i.e. if you would end up in state C you could not tell whether the system came from state A or B. If you, for example, start a pendulum with different initial displacements the pendulum will always end up at rest due to friction but if you could take into account the exact states of all the molecules in the air and the joint and so on you could in principle figure out in which exact positions you started the pendulum. You could actually just very precisely measure the temperature of a pendulum in a box and infer the initial displacement from that because different initial displacements imply different initial (potential) energies and therefore different final temperatures after all the energy became thermal energy and everything in the box had time to reach the equilibrium temperature. You just couldn't figure out whether the pendulum was started to the left or to the right of the rest position with this method.

haberman 11y ago
Fascinating. Do physicists generally believe this? The idea that both the infinite future and the infinite past are all encoded into any snapshot of the universe is blowing my mind. My layperson's understanding of QM always gave me the impression that it does the opposite: that it gives non-determinism a place to "hide," so-to-speak. My impression was that religious believers could use QM to argue that their unseen God, for example, does actually have a physically plausible mechanism by which he/it could intervene in the physical world. But if I'm understanding this theory correctly, unless God is a physical thing, there is no way for God or any other supernatural force to affect the physical world without itself being physical. This theory also would seem to deny the existence of free will.
- solipsism 11y ago
  QM does away with any notion of conservation of information. Time reversibility (T symmetry) is usually talked about at macro scales where QMs effects are vanishingly small. IANAP Regarding free will -- rigorously define it for us, without evoking the supernatural, and as distinct from pure randomness and absolute determinism, and it should be easy to tell whether the law of conservation of information allows for it. Before spending too much time in e it, though, note that such a definition is widely considered impossible. IANAP

dogma1138 11y ago

Yes there is a principal in on of the "interpretations" (we really need a better word for it) of QM that the information carrier by a wave function cannot be destroyed, this present a problem in certain cases such as black holes. There's allot of weird stuff going on on the extreme edges of theoretical physics, to the point in which also a though that some areas of theoretical physics have moved into the "Metaphysics" and Philosophy domains and are distancing them selves from certain scientific principals. That said I like to treat black holes in the GR/SR manner they are simple massive objects not super dense hot balls of entropy, they don't have some universal cosmic powers, they are "black" simply because they red-shift all radiation to the point of invisibility, they can form, grow and break apart, and we never can see anything actually entering a black hole due to time dilation and anything that comes close to it will be red-shifted to a point in which we won't be able to see what or where it is either. Since nothing from out POV ever enters the black hole and everything is stuck on the event horizon nothing is lost, and since black holes can evaporate (Doesn't require hawking radiation altough it's the most common explanation since Yakov Zeldovich (which Stephen hawking based his work on) and others have proposed similar mechanisms which are more compatible with physics as it is measured and perceived by hmmm reality...), no firewalls or weird mechanism are needed to protect or explain other weirdness that happens around singularities. Singularities are well covered by GR and SR prevents naked singularities so we are good there too. But that's just me :)