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From: Niclas Thisell <niclas.domain.name.hidden>

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

proven.

Best regards,

Niclas Thisell

Received on Fri Dec 10 1999 - 04:11:07 PST

Date: Fri, 10 Dec 1999 13:12:49 +0100

Marchal wrote in part

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

proven.

Best regards,

Niclas Thisell

Received on Fri Dec 10 1999 - 04:11:07 PST

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