[ExI] a clean well-lighted challenge

Anders Sandberg anders at aleph.se
Thu Sep 24 13:02:43 UTC 2015

I loved Adrian's stories. Especially the AI one - I did learn something 
from it.

This is a bit more experimental, but I always seem to end up with dialogue:

The argument was echoing down the hallway.
A: "It is just a convenience. It is not *real*."
B: "What do you mean by *real*? It has effects you can observe, right?"
A: "The effects are real, but then we just make up a convenient 
explanation for an unobservable cause."
B: "But you agree there *is* a cause. Something is making them fit 
A: "It could just be initial conditions making them correlated or 

C: "Are you guys talking about love again?"
They looked away from the whiteboard at the intruder, then quickly 
looked back and simultaneously pointed at an equation.
A: "The potential. He thinks it is real..."
B: "...while that postmodernist thinks it is just fiction."
C: "Do you think the electromagnetic field is real?"
A: "Sure, you can measure and interact with it."
B: "It is a tensor field associated with mass-energy."
C: "But you can derive the field equations from the potential, and vice 
versa. So the field and potential should be equally real or unreal."
A: "No! The potential is underdetermined: you can add anything that gets 
zeroed out when you differentiate it, and you get the same field."
B: "No! If you do any gauge transformation it leaves the field equations 
the same."
C: "So if potentials are unreal, then their exact form does not matter. 
If they are real, they have hidden degrees of freedom."
A: "Always unobservable. So they don't matter. They don't exist. Occham 
gets them."
B: "What about statistical mechanics? There degrees of freedom you 
cannot see matter: when you calculate something you count the number of 
possible states to make a partition function, and from that you get 
entropies and energies..."
A: "A mere convenience!"
C left the room. "Google the Aharonov–Bohm effect." They looked after 
him for a moment before whipping up their laptops.

A: "OK, charged particles change phase proportional to the vector 
potential they pass through. Great: wave function phase, *another* 
unobservable thing, is changed by the unobservable potential. It could 
just as well be spirits doing it."
B: "So two particles with the same phase starting from point A and going 
to point B will have a phase difference proportional to the magnetic 
flux through the area between the paths. That sounds observable."
A: "You can't see phase!"
B: "You can let the particles interfere. Do a standard double slit 
experiment, the phase will move the interference fringes. Observable. 
Done ages ago."
A: "Wait a moment... look at the diagram. The flux can be hidden inside 
a superconducting box. There is no magnetic field where the particles go."
B: "There you go. There is just potential outside the box."
A: "How can there be potential if there is no field?"
B: "He said that if potentials are real they have hidden freedoms. How 
come we get *that* interference pattern?"

The two began to hunt through the Wikipedia article for arguments they 
hoped would impress the potential of the absent third.

Anders Sandberg
Future of Humanity Institute
Oxford Martin School
Oxford University

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