Entangled qubits measurement I have two entangled qubits. I measure one of the qubits and get a 1. Am I correct in saying that the second qubit instantaneously collapsed to a correlated state, even before I measured it? Or does the second qubit only collapse to a correlated state when I measured it?
 A: Quoting the example from wikipedia:

For example, the following is an entangled state:
$${\displaystyle {\tfrac {1}{\sqrt {2}}}\left(|0\rangle _{A} \otimes
>  |1 \rangle _{B}-|1\rangle _{A} \otimes |0 \rangle _{B}\right).} $$.
  Now suppose Alice is an observer for system A, and Bob is an observer
  for system B. If in the entangled state given above Alice makes a
  measurement in the ${\displaystyle \scriptstyle \{|0\rangle ,|1\rangle
> \}} \scriptstyle \{|0\rangle, |1\rangle\}$ eigenbasis of A, there are
  two possible outcomes, occurring with equal probability:
Alice measures 0, and the state of the system collapses to
  ${\displaystyle \scriptstyle |0\rangle _{A}|1\rangle _{B}}$
Alice measures 1, and the state of the system collapses to
  ${\displaystyle \scriptstyle |1\rangle _{A}|0\rangle _{B}}.$

So the state instantaneously collapses. 

If the former occurs, then any subsequent measurement performed by
  Bob, in the same basis, will always return 1. If the latter occurs,
  (Alice measures 1) then Bob's measurement will return 0 with
  certainty. Thus, system B has been altered by Alice performing a local
  measurement on system A. This remains true even if the systems A and B
  are spatially separated. This is the foundation of the EPR paradox.
The outcome of Alice's measurement is random. Alice cannot decide
  which state to collapse the composite system into, and therefore
  cannot transmit information to Bob by acting on her system. Causality
  is thus preserved, in this particular scheme. For the general
  argument, see no-communication theorem.

While it's discussed further here, the idea is that you can't use this instantaneous change to transfer information, because you can't control how it changes when you measure it. 
Some believe (in the many worlds interpretation of quantum mechanics) that the state itself does not instantaneously change, and that all of the possiblities still exist after measurement (that is, there's an alice that measures 0 and an alice that measures 1.) But by measuring the state alice is checking which of the alice's she is.  
