RE: tautology

From: Niclas Thisell <>
Date: Fri, 10 Dec 1999 13:12:49 +0100

Marchal wrote in part
> OK. May be the measure (which is simple in QM, I agree) is
> simple also in relativistic QM (I have some doubt, here, though).

One common trait for all quantum mechanics models, including
relativistic ones, must be that they predict the probability of a
specific outcome of a measurement. The mathematical model is not
complete unless it can do so for a complex system, including a large
fraction of our universe, and over a long time, way past the Planck-time
of course.

Assuming we want to do a measurement where a scientist is part of the
experiment, the model must, of course, include the scientist in the
calculation. My view on the MWI is that, not only can we expect the
model to predict the probability of the outcome of the measurement, but
also give a measure to hypothetical measurements of the state of the
system before the actual 'physical' measurement takes place. This
clearly defines a measure of all worlds 'in between' measurements. And
it sounds likely that the measurement itself doesn't really affect this
third-person measure.

Now, unless the mathematical model explicitly introduces splits and
mergers, there is no reason to assume that we need to either. The
scientist may experience first-person splits or wave-function collapses
during the experiment, but that is, of course, exactly what Everett
wanted to explain.

So, in essence, the measure of a QM world is the probability of that
state at a hypothetical measurement.
Note that most readers of this list probably think of this the other way
around; the measure of a world defines the likelyhood of finding
ourselves in that world. But they are effectively equivalent, assuming
there is only QM. And that QM follows from the plenitude remains to be

Best regards,
Niclas Thisell
Received on Fri Dec 10 1999 - 04:11:07 PST

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