The next Q+ hangout is all set to run on 22nd April, 14:00 UTC+1. Surprisingly, the topic this time "On the Uncertainty of the Ordering of Nonlocal Wavefunction Collapse when Relativity is Considered", which I had earlier read through and found to be highly interesting and no less entangled, no pun.

In the EPR experiment, if Alice makes a measurement on her particle then the state of Bob’s particle collapses to the result anti-correlated to Alice’s measurement. This process is *said* to be happen instantaneously.

This 'instantaneous' gives rise to a paradox. For example, if in one reference frame Alice measures first then Bob’s state collapses. In a different inertial frame, an observer might say that Bob measured first leading to the collapse of Alice’s state. This leads to the identity paradox for *who* collapsed *whose *first!

This paper uses a type of clock device that functions on the laws of quantum-mechanics. This device in the experiment keeps the above paradox from occurring.

The bottom line being that in the experiment, Alice and Bob’s measurements cannot be made with infinite precision, rather they are constrained due to the energy-time uncertainty principle. Since energy and time are not relativistic invariant quantities, different observers in different reference frames must transform their uncertainty principles accordingly.

Concluding the paper rightfully claims the uncertainty principle in time always outruns the time difference induced by the change in reference frames. Neither Alice nor Bob will ever, with certainty, observe the two measurements swap temporal order. Furthermore, it can be said that if a time measurement performed an entangled biphoton is simultaneous in one shared reference frame then it can be considered simultaneous to all measuring observers who do not share a reference frame.

On a personal note, it was only while going through the paper I thought about the *time* it takes for a EPR photon to collapse when measurement taken on its pair. People have already calculated it *experimentally. *This hangout already sounds like exciting, fingers crossed that I can attend it uninterrupted this time, have a couple of questions for the presenter.

**Further Reading**

On the Uncertainty of the Ordering of Nonlocal Wavefunction Collapse when Relativity is Considered arXiv:1310.4956 [quant-ph]

The Uncertainty Relation Between Energy and Time in Non-relativistic Quantum Mechanics DOI: 10.1007/978-3-642-74626-0_8

Experimental test of relativistic quantum state collapse with moving reference frames DOI: 10.1088/0305-4470/34/35/334