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9 Mind, Life, and the Universe
as a scientist’s expectation of the outcome of his next experiment. As for D, it
represents data, that is, a fact or facts we get experimentally. Thus, P(H |D)
is the probability that our hypothesis is correct on the strength of the data D.
On the other hand, P(D|H ) is the probability of the observed data arising
from the hypothesis. This is known by the experimenter, because it expresses the
consequences which follow if the hypothesis is true. Likewise P(D) is known
experimentally, because it depends on the frequency with which the outcome
D arises when a certain experiment is performed. But P(H ) is different: It is
the scientist’s subjective estimate of how likely the hypothesis is to be true.
Every experiment yields some data D. As noted just above, P(H ) is the
scientist’s personal degree of confidence in the hypothesis. After the experiment
has been carried out, P(H ) is replaced by P(H |D), because the scientist’s
belief is no longer H but a version of H that has been updated by the data D.
You should notice, then, that in the Bayesian version, probability reflects
an experimenter’s subjective level of confidence in a hypothesis. A quantum
state changes when a measurement is made. However the change is not in the
physical world but results from the scientist’s updating his degree of belief in
a hypothesis after seeing new experimental data. Thus, the knowledge gained
from carrying out an experiment does not correspond to an objective reality of
the physical world, but to a scientist’s beliefs. New knowledge is not about the
unseen, unknown objective world, but about the scientist’s personal model of
reality, fine-tuned by experimental confirmation.
In particular, the collapse of the wave function when an observation is made
is simply the observer updating his beliefs after making a measurement. Thus,
the wave function is not a material reality of the physical world, but merely
the description of an observer’s knowledge. It is a remarkable fact that when
the wave function is viewed in this light, the famous paradoxes of quantum
theory disappear.
Despite the many impressive results of QBism, a weighty question hovers
over it: What kind of knowledge of the physical world does QBism give us? It is
said by scientists who are fully committed to it that at present there is no good
answer to that question, and for that reason, QBism remains an uncompleted
project.
The scheme presented in this book provides a foundation for quantum
bayesianism. As explained in the previous chapters, there is a radical divide
between the physical world removed from observation—that is, the universe
outside the range of any observer—and the aspects of reality created by the
minds of living observers. It has been argued that it is the mind that divides reality into distinct, separate objects and creates the shapes and structure of solids.
9 Mind, Life, and the Universe
as a scientist’s expectation of the outcome of his next experiment. As for D, it
represents data, that is, a fact or facts we get experimentally. Thus, P(H |D)
is the probability that our hypothesis is correct on the strength of the data D.
On the other hand, P(D|H ) is the probability of the observed data arising
from the hypothesis. This is known by the experimenter, because it expresses the
consequences which follow if the hypothesis is true. Likewise P(D) is known
experimentally, because it depends on the frequency with which the outcome
D arises when a certain experiment is performed. But P(H ) is different: It is
the scientist’s subjective estimate of how likely the hypothesis is to be true.
Every experiment yields some data D. As noted just above, P(H ) is the
scientist’s personal degree of confidence in the hypothesis. After the experiment
has been carried out, P(H ) is replaced by P(H |D), because the scientist’s
belief is no longer H but a version of H that has been updated by the data D.
You should notice, then, that in the Bayesian version, probability reflects
an experimenter’s subjective level of confidence in a hypothesis. A quantum
state changes when a measurement is made. However the change is not in the
physical world but results from the scientist’s updating his degree of belief in
a hypothesis after seeing new experimental data. Thus, the knowledge gained
from carrying out an experiment does not correspond to an objective reality of
the physical world, but to a scientist’s beliefs. New knowledge is not about the
unseen, unknown objective world, but about the scientist’s personal model of
reality, fine-tuned by experimental confirmation.
In particular, the collapse of the wave function when an observation is made
is simply the observer updating his beliefs after making a measurement. Thus,
the wave function is not a material reality of the physical world, but merely
the description of an observer’s knowledge. It is a remarkable fact that when
the wave function is viewed in this light, the famous paradoxes of quantum
theory disappear.
Despite the many impressive results of QBism, a weighty question hovers
over it: What kind of knowledge of the physical world does QBism give us? It is
said by scientists who are fully committed to it that at present there is no good
answer to that question, and for that reason, QBism remains an uncompleted
project.
The scheme presented in this book provides a foundation for quantum
bayesianism. As explained in the previous chapters, there is a radical divide
between the physical world removed from observation—that is, the universe
outside the range of any observer—and the aspects of reality created by the
minds of living observers. It has been argued that it is the mind that divides reality into distinct, separate objects and creates the shapes and structure of solids.