- #1
Robin
- 16
- 1
How do we know for sure that the photon's orientation isn't determined until we we measure it ?
Robin said:How do we know for sure that the photon's orientation isn't determined until we we measure it ?
If it's predetermined then no need for spooky action at a distance. So why the spooky action at a distance issue in Physics ?stevendaryl said:That's what Bell's inequality proves. The assumption that the photons have definite polarizations (we just don't know what they are) is a local hidden-variable theory, which Bell proved cannot reproduce the predictions of quantum mechanics.
Actually we don't know it. We just know that photon's polarization (if it has such a property) can't be the only thing that determines measurement results at different angles.Robin said:How do we know for sure that the photon's orientation isn't determined until we we measure it ?
Robin said:If it's predetermined then no need for spooky action at a distance. So why the spooky action at a distance issue in Physics ?
Look at this post: https://www.physicsforums.com/threads/a-simple-proof-of-bells-theorem.417173/#post-2817138Robin said:If it's predetermined then no need for spooky action at a distance. So why the spooky action at a distance issue in Physics ?
There isn't really a spooky issue in physics. It's just that you can interpret the Bell violations in various ways by rejecting different assumptions. Most people reject the non-contextuality assumption, since we know that it must be rejected anyway (for different reasons), but you can also reject the locality assumption (together with the non-contextuality assumption). That's what the hidden variables advocates do.Robin said:If it's predetermined then no need for spooky action at a distance. So why the spooky action at a distance issue in Physics ?
Yes. We have tried to explain this a number of times already in this thread. The reduced density matrix of the EPRB state is the (normalized) identity matrix. All the difficulties you are having in this thread (like partial traces and matrix multiplication) are really linear algebra difficulties and not quantum mechanics difficulties. Teaching these basics through an online forum is quite cumbersome, so I suggest you pick up a some introductory linear algebra textbook (for example Halmos FDVS) and then come back with specific questions.zonde said:So the tracing operation can produce mixed state corresponding to only one of these two martices, right?
Polarization is a quantum phenomenon that describes the alignment of electromagnetic waves in a specific direction. In quantum mechanics, the state of a system is described by a wavefunction, which contains all possible information about the system. However, until a measurement is made, the system exists in a superposition of all possible states, including both polarized and unpolarized states. Therefore, polarization is not evident until a measurement is made to collapse the wavefunction and determine the state of the system.
Measurement affects polarization by causing the wavefunction to collapse and the system to take on a specific polarization state. This is known as the "observer effect" in quantum mechanics. The measurement process involves interacting with the system, which disturbs it and causes it to take on a definite state. This is why polarization is not evident until it is measured.
In the quantum world, polarization only exists as a potential until it is measured. Without measurement, polarization is just one of the many possible states that the system could take on. However, in classical physics, polarization can exist without measurement because classical systems do not exhibit the same superposition and collapse of wavefunctions as quantum systems.
Measurement is necessary to determine polarization because it is a quantum phenomenon that exists in a superposition of states until a measurement is made to collapse the wavefunction and determine the state of the system. Without measurement, it is impossible to know which state the system is in and whether or not it is polarized.
The implications of polarization being undetectable until measurement are significant in the field of quantum mechanics. It means that the state of a system is not predetermined and can only be determined through measurement. This has led to debates and discussions about the role of the observer in quantum mechanics and the nature of reality. Additionally, it has practical applications in technologies such as quantum computing and communication, where the superposition of states plays a crucial role.