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Experiments need a theory to even describe what is going on, or if their result is surprising, why it is surprising.
I don't agree. The results speak for themselves, whatever they are. When observations are published for posterity in journals and reports, it is with the understanding that the theory which is also included with the data might turn out to be wrong, but the data itself can be trusted (within experimental limits etc) and may be reused by others in future.

Why publish actual data otherwise? It would be sufficient to publish the theories, and just claim that they work.

However, you're entirely right that the choice of which experiments are significant (and therefore are the ones that should be carried out and published) depends on the theories of the day. So the succession of experiments is guided by the history of the theories. Is that what you mean?

It is physics that represents a small subset of human knowledge. In fact, the more physics we know the less we need to know as the theories become more and more generally applicable. But for the last 30 years theoretical physics has become largely divorced from experiment.
Now I think you're exaggerating too :) Physics is certainly a tiny subset of knowledge, but it's far from clear that we're close to a GUT. And if we were, so what? We still wouldn't be able to calculate a lot of systems for fundamental mathematical reasons. Paraphrasing Arnold: theoretical physics is the part of high energy physics where experiments are cheap.

The extent to which research in theoretical physics is directed by the likelihood of coming up with a publishable paper to put in one's CV for the next job placement 3 years down the line is positively postmodern.
Publish or perish is not just an issue in theoretical physics, yet even so good papers (though not all) will be cited, while the trash gets forgotten.

Finally, "my" Hegelian dialectic is not about "Knowledge" but about structural narratives/frames/myths of a society.
My calling it "your" dialectic was only intended as a light jab. However, I still don't see what postmodernism has to offer to experimental sciences.

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$E(X_t|F_s) = X_s,\quad t > s$
by martingale on Sat Sep 13th, 2008 at 04:17:02 AM EST
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At the risk of repeating myself, this diary is not about the experimental sciences, it's about the dominant narratives of society.

good papers (though not all) will be cited, while the trash gets forgotten

When you do a literature search properly you quickly encounter the reality of the plagiarizing of reference lists. Papers are not quoted because they are good, but because they are quoted by other papers. Then again, you're right, just because they are listed in the references doesn't mean they have been read by the authors so, yes, the trash is forgotten.

for the last 30 years theoretical physics has become largely divorced from experiment.
Now I think you're exaggerating too :)
Not one bit.
it's far from clear that we're close to a GUT. And if we were, so what? We still wouldn't be able to calculate a lot of systems for fundamental mathematical reasons
We don't need a GUT - we just need the standard model with a right-handed neutrino. And the fact that we can't calculate is why I said people needed to have left en masse towards mesoscopic physics.
The results speak for themselves, whatever they are.
No, the results of the LHC experiments don't speak for themselves except after a massive, massive theory-based massaging. And it is the theory that allows a narrow experiment to have a broadly applicable meaning.

A vivid image of what should exist acts as a surrogate for reality. Pursuit of the image then prevents pursuit of the reality -- John K. Galbraith
by Migeru (migeru at eurotrib dot com) on Sat Sep 13th, 2008 at 04:45:59 AM EST
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At the risk of repeating myself, this diary is not about the experimental sciences, it's about the dominant narratives of society.
Well I'm not trying to change the topic of this diary, so I don't mind leaving this thread for another time and place. We clearly don't agree on a number of things though.

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$E(X_t|F_s) = X_s,\quad t > s$
by martingale on Sat Sep 13th, 2008 at 05:32:36 AM EST
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I'm much more cynical about science than I once was.

But, seriously, most modern experiments make no sense without a theory.

A vivid image of what should exist acts as a surrogate for reality. Pursuit of the image then prevents pursuit of the reality -- John K. Galbraith

by Migeru (migeru at eurotrib dot com) on Sat Sep 13th, 2008 at 05:33:44 AM EST
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If an experiment is repeatable, the repeatability cannot depend on theoretical interpretations, surely? But no matter. I'm sure we'll have plenty of other occasions to settle this. Good fun :-)

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$E(X_t|F_s) = X_s,\quad t > s$
by martingale on Sat Sep 13th, 2008 at 05:51:06 AM EST
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Yes, but what does the experiment mean? Science is more than a collection of isolated facts. And knowledge is more than disorganised information (in, fact, doesn't a completely random signal have the most information? And must any information or entropy measure be computed with respect to a reference prior/null probability distribution?).

A vivid image of what should exist acts as a surrogate for reality. Pursuit of the image then prevents pursuit of the reality -- John K. Galbraith
by Migeru (migeru at eurotrib dot com) on Sat Sep 13th, 2008 at 06:06:13 AM EST
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And must any information or entropy measure not be computed with respect to a reference prior/null probability distribution?

(key word missing...)

A vivid image of what should exist acts as a surrogate for reality. Pursuit of the image then prevents pursuit of the reality -- John K. Galbraith

by Migeru (migeru at eurotrib dot com) on Sat Sep 13th, 2008 at 06:10:12 AM EST
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Well, the experiment only means that you've interacted with the world. It's the model which has a meaning, namely the interpretation it induces on the actual observations.

Information theoretically, the meaning is in the prior and the likelihood. The amount of surprise is, too, since entropy is an explicit function of the model, and for a given datapoint it can take any value as soon as you vary the model.

Is knowledge more than a collection of facts? Yes, but I would say it's a construct built on facts. If we lose the theories and the models, we can rebuild them, or substantially equivalent ones, from the facts. If we lose the facts, we can't just simulate new ones and call them real.

--
$E(X_t|F_s) = X_s,\quad t > s$

by martingale on Sat Sep 13th, 2008 at 07:20:09 AM EST
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What about observations which are not repeatable?

A vivid image of what should exist acts as a surrogate for reality. Pursuit of the image then prevents pursuit of the reality -- John K. Galbraith
by Migeru (migeru at eurotrib dot com) on Sat Sep 13th, 2008 at 07:26:12 AM EST
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That's the crucial difference between historical and experimental sciences, isn't it?

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$E(X_t|F_s) = X_s,\quad t > s$
by martingale on Sat Sep 13th, 2008 at 07:32:01 AM EST
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Right. So "repeatability" is a special quality that applies to a subset of human knowledge. It's not that "postmodern" "textual analysis" doesn't apply to physics, it is that when studying physics one has to take into account the repeatability. And, to a certain extent, stationarity and ergodicity are model-dependent features. Within physics you have astrophysics or cosmology which are also historical.

A vivid image of what should exist acts as a surrogate for reality. Pursuit of the image then prevents pursuit of the reality -- John K. Galbraith
by Migeru (migeru at eurotrib dot com) on Sat Sep 13th, 2008 at 07:39:25 AM EST
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Within physics you have astrophysics or cosmology which are also historical.
That would be a reasonable statement.

And, to a certain extent, stationarity and ergodicity are model-dependent features.
As a rule, stationarity and ergodicity are directly observable on experimental data if you have it, and vice versa. It's by no means a given in all theoretical models, but it's a real observable phenomenon regardless of subjective prior assumptions.

It's not that "postmodern" "textual analysis" doesn't apply to physics, it is that when studying physics one has to take into account the repeatability.
I never claimed it couldn't be applied to physics, rather I fail to see its value when an oracle exists which spits out facts for any well chosen question. Thus physics is not limited by the insights of postmodernism.

So "repeatability" is a special quality that applies to a subset of human knowledge.
Another good word is "interactivity". In an experimental science, we can choose the questions we want to ask, and receive answers from the world. In a "historical" science, we must accept the answers we are given, with little or no choice in the questions. In physics, much effort is spent designing experiments to isolate the bits we care about, in archaeology we cannot ask what the ancient Greeks would have been like if they had had television.

--
$E(X_t|F_s) = X_s,\quad t > s$
by martingale on Sat Sep 13th, 2008 at 08:10:12 AM EST
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Thus physics is not limited by the insights of postmodernism.

No, it is limited by the extent of repeatability.

A vivid image of what should exist acts as a surrogate for reality. Pursuit of the image then prevents pursuit of the reality -- John K. Galbraith

by Migeru (migeru at eurotrib dot com) on Sat Sep 13th, 2008 at 08:11:58 AM EST
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I agree.

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$E(X_t|F_s) = X_s,\quad t > s$
by martingale on Sat Sep 13th, 2008 at 08:18:06 AM EST
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Nonsense; your definition of experiment is overly restrictive. The observable universe is finite, but the number of stars, galaxies, clusters and so on is very large.
Just like the number of hadrons available for high speed collision, or elements to chemically combine, or bacterias to cultivate are technically finite, too.
Astronomers don't just point their scopes up randomly and write down what they see. They also design experiments. Some don't even require pointing a telescope, they just reuse existing images for analysis; see Galaxy Zoo.  Some experiments try to capture ephemeral events, see gamma ray burst: just because you don't decide when the event is going to happen doesn't make the experiment any less experimental. The results are reproducible, just not within a predetermined timeframe.
It is therefore fundamentally different from History, as a discipline; no matter how long you're willing to wait, you won't be able to reproduce a French Revolution. However, social psychology (see Miller, Cialdini ...) shows that you can obtain reproducible results by deriving abstractions and then designing experiments to test them. In other words, you can do science about anything as long as you're willing to get off your ass and do some real work.


A 'centrist' is someone who's neither on the left, nor on the left.
by nicta (nico@altiva․fr) on Thu Oct 2nd, 2008 at 10:36:58 AM EST
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