Predictions and Retrodictions

I have tried to reply to the QCD proton mass "prediction" post, but so
far there appears to be some sort of software glitch somewhere. As an
alternative method, I am sending the reply as a "new post", but it is
really a response to the Xanthian post.


PREDICTION: Making a definitive statement about what the empirical
answer will be BEFORE the answer is known.

RETRODICTION: Demonstrating that a theory can reproduce a KNOWN
ANSWER, elegantly or [as in this case] with heroic effort.

Woe be to science when the distinction between these very different
things is forgotten, obscured, etc. While both have scientific
usefulness, a true definitive prediction is many orders of magnitude
more challenging and important than the average retrodiction.

It is understandable that science writers, who are journalists more
than scientists, muddy the waters on this issue. It is important for
scientists to keep straightening them out until one day maybe they
will get it right.

Scientists who knowingly, or in the heat of enthusiasm, confuse
predictions and retrodictions have no excuse for their serious error.
When such mistakes are made, and they appear in the "best" journals
all too frequently, editors, reviewers and readers should raise
objections and demand that this type of fundamental error be corrected
before publication.

Yours in science,
Knecht
www.amherst.edu/~rloldershaw

Knecht wrote:
Woe be to science when the distinction between these very different
things is forgotten, obscured, etc. While both have scientific
usefulness, a true definitive prediction is many orders of magnitude
more challenging and important than the average retrodiction.

Not only are they both useful - they are part of the very
same scientific process, which goes like this:

- Make empirical observations
- Build a theory which "retropredicts" the observations
- Use the theory to make predictions
- Design experiments to test the predictions.

It is understandable that science writers, who are journalists more
than scientists, muddy the waters on this issue. It is important for
scientists to keep straightening them out until one day maybe they
will get it right.

Do you have specific examples ? Although I share your concern
about science reporting in general, while reading the articles
on the proton mass "retroprediction", I did not fell that the
authors were exagerating. All of them suggested that the
computational approach will be used to make useful predictions,
now that it has been validated against known results.

AC

IMO, "prediction" applied to physical theories just means the theory allows to
deduce a (possibly experimentally testable) value, and this is a -stable- and
-structural- property of the theory that does not depend on the value
experimentally being measured, on whether the theoretically provided value
agrees with the experimental value, or on that agreement being tested before or
after the formulation of the theory.

This corresponds to the verb usage "predicts" in the (continuing) present tense.

In contrast, your characterization would correspond to the common sense meaning
of "to predict", -and- it would require using not the present tense, but the
past tense, upon first measurement of the experimental fact (preferably in
association with either "rightly" or "wrongly").

Cheers, BB

Knecht wrote:
I have tried to reply to the QCD proton mass "prediction" post, but so
far there appears to be some sort of software glitch somewhere. As an
alternative method, I am sending the reply as a "new post", but it is
really a response to the Xanthian post.


PREDICTION: Making a definitive statement about what the empirical
answer will be BEFORE the answer is known.

RETRODICTION: Demonstrating that a theory can reproduce a KNOWN
ANSWER, elegantly or [as in this case] with heroic effort.

Woe be to science when the distinction between these very different
things is forgotten, obscured, etc. While both have scientific
usefulness, a true definitive prediction is many orders of magnitude
more challenging and important than the average retrodiction.

It is understandable that science writers, who are journalists more
than scientists, muddy the waters on this issue. It is important for
scientists to keep straightening them out until one day maybe they
will get it right.

Scientists who knowingly, or in the heat of enthusiasm, confuse
predictions and retrodictions have no excuse for their serious error.
When such mistakes are made, and they appear in the "best" journals
all too frequently, editors, reviewers and readers should raise
objections and demand that this type of fundamental error be corrected
before publication.

Yours in science,
Knecht
www.amherst.edu/~rloldershaw