- #1
- 8,142
- 1,756
I assume that some speed limit must exist that limits how often we can measure something - if is exists, perhaps the Plank time unit governs this? Do we know this answer? Does this relate to the speed of quantum computers?
Originally posted by jeff
Wave function collapse is irreversible:
The value of an observable once measured will not change in a system that remains otherwise undisturbed, and the fact that measured values of the same observable of a system that was disturbed in between measurements will not in general agree is not the result of some restorative process directly inverse to the initial collapse.
Originally posted by Ivan Seeking
Interesting. I thought it a basic principle of QM that we can only know that state of a system at the time of the measurement and immediately thereafter. After this, the state of the system cannot be known. This statement is false?
Originally posted by jeff
According to what the axioms of QM actually say, yep.
Originally posted by Ivan Seeking
I assume that some speed limit must exist that limits how often we can measure something - if is exists, perhaps the Plank time unit governs this? Do we know this answer? Does this relate to the speed of quantum computers?
Originally posted by Ivan Seeking
Still, it does seem that no truly isolated system can exist. Are we discussing an idealized system that cannot exist?
Gees. I read your answer and thought, great, we're done. But something has been nagging me and I finally realized what. Doesn't a fundamental argument exist that unique states only exist when measured? This is what I kept thinking was the motivation for the language of my old QM text. I am sure that I have heard this used as an escape clause for various paradoxes…say for example when we talk about the energy in a field. I will try to explain the violation of concepts that I am alluding to here.Originally posted by jeff
Yes: Whatever "apparent" deviation from these axioms we've seen in real systems have always been attributable to our inability to perform ideal experiments rather than to a failure of the axioms themselves.
Originally posted by ranyart
You are mis-interpreting the whole of shroedingers cat?..the cat is representative of a standing wave, It's inside of a box! You are external, the box forms a junction of where your observational limits are defined, and it works both ways, the cat inside cannot see you unless the box is removed, collapsed.
You cannot isolate the cat from the box, yourself from seeing the cat without the box, its the events that are always extended, there are always distructive obstacles in line's of sight when trying to isolate anything, even a single particle!
Originally posted by Ivan Seeking Doesn?t the whole idea of superposition fail if any measurement permanently collapses the wave function for an isolated wave/particle?
Originally posted by jeff
A collapsed wave function is still a wave function, since measurement of an observable must by the uncertainty principle leave us with a quantum superposition of all possible values of it's conjugate, i.e. if we know position we don't know momentum.
Originally posted by jeff
A collapsed wave function is still a wave function, since measurement of an observable must by the uncertainty principle leave us with a quantum superposition of all possible values of it's conjugate, i.e. if we know position we don't know momentum.
Originally posted by Ivan Seeking
Also, how do you feel about live-dead cats? Do you feel that a single qm entity can exist in a true superposition of states, or do you think this only applies to large populations of particles?
When a measurement is made on a quantum system, the wave function of the system collapses to a single eigenstate of the measured observable. This is known as the "collapse of the wave function" and is a fundamental concept in quantum mechanics.
In quantum mechanics, the observer plays a crucial role in the collapse of the wave function. The act of measurement by the observer causes the wave function to collapse, determining the state of the system.
The collapse of the wave function does not violate the principle of superposition. The superposition principle still holds, but after a measurement is made, the system is no longer in a superposition of states and will be in a single eigenstate.
The time it takes for a measurement to collapse a wave function is instantaneous. As soon as the measurement is made, the wave function collapses to a single state, and the system is in that state.
In most interpretations of quantum mechanics, a wave function can only collapse through measurement. However, some theories, such as the many-worlds interpretation, propose that alternative realities are created through the collapse of the wave function, even without measurement by an observer.