Wednesday, December 30, 2009

What is a scientific prediction?

After my bachelor's degree I changed field from mathematics to physics. I wanted to understand, at least to some extend, the world around me. Mathematics seemed to entail an infinite amount of possibilities whose each and every relevance wasn't clear to me while physics is tied to reality by experiment. Basically the reason why I'm a phenomenologist today is that I know how easy it is to get lost in the mathematical universe, and that this getting lost has clearly addictive qualities.

In the last decade in high energy physics one could notice a trend towards more phenomenology. While I welcome this for obvious reasons, here as in any aspect of life one can desire too much of a good thing. I've read quite a few of papers where the word "phenomenology" was used merely as decoration, and in other cases "phenomenological" is essentially an excuse for inconsistency. Such fashion trends in the community and their side-effects however aren't really surprising. What is surprising though is that the demand for "predictions" has been picked up by the public and has been used sometimes inappropriately as a measure for scientific quality. Thus I thought it would be worth clarifying what a scientific prediction is and isn't.

1. A scientific prediction is a statement about a future event.

That is to say the prediction was made without knowing whether it is correct. Strictly speaking this doesn't necessitate it to be about a future event, but it's hard to reliably show one didn't know about a measurement that was already made (a possible scenario is that available data wasn't analyzed with regard to a specific hypothesis). If you calculate the cosmological constant to be in agreement with the today measured value it's not a prediction, it's a postdiction. While it is certainly preferable to calculate the outcome of an experiment before it was done to avoid confirmation bias, this isn't always how it works. Sometimes theory is ahead, but sometimes the data is in already and awaits a theoretical explanation. Science is in the first line about understanding. Explanations, even if not predictions, are valuable. However, if there is something genuinely new about an explanation it will typically also imply new predictions.

2. A scientific prediction is based on a scientific theory. That means in particular it is reproducible (by everybody with the appropriate education), consistent, and the theory it is based on is not in conflict with available data already.

If you dreamed a meteoroid will crash into the White House on New Year's day, that's a prophecy, not a scientific prediction. Same for the recurring remark that the LHC might create angels at 14 TeV collision energy. That's funny, but not a scientific prediction. You may find it inconvenient that your theory be reproducible because this means other people must be able to understand it without your help. However, if you aren't able to communicate how your theory connects to state-of-the art science, it's your fault and not everybody else's fault. Likewise, if your theory comes with a prescription only to use it for this effect, but not for this effect because it doesn't work there for reasons only you understand, that's not a scientific theory. If your theory predicts a fourth lepton generation but has the side-effect that atoms are unstable, tough luck. See here for what it means for a theory to be consistent.

3. A scientific prediction is falsifiable. In practice this means often it's implausifiable.

Falsifiable means that your prediction can be shown to be wrong. This typically though not always implies the prediction has to be quantitative. "You will die" is not a scientific prediction: if you're still alive in 200 years, it could still be you will die someday. "At least 99.99% of people your age who smoke 1 pack per day will be dead 80 years from now," is a scientific prediction because 80 years from now you can look at the data and see whether I was correct (or rather somebody else will have to look, cough).

In physics, scientific theories often contain parameters and a measurement does not indeed falsify the theory but constrain the parameters until they are constrained so much it's point- and useless to consider a theory further. A good example is Brans-Dicke theory. If there are deviations from general relativity of the Brans-Dicke type, they are so small you can forget about them. Same for violations of Lorentz-invariance, time-variation of the structure constant, and so on. These are not falsified but tightly constrained. Reason why in high energy physics new theories are often not actually falsifiable is that for a new theory only small deviations from already extremely well confirmed theories are allowed. We know that our present theories are correct to high precision and new theories cannot differ by much or they are false already. If the deviation is too small however, it becomes unmeasurable.

As you can guess, implausibility is not binary but a continuous scale, thus people frequently disagree on exactly when to discard a theory. (MOND anybody?) As far as I am concerned everybody can decide for themselves how to waste the time of their life, as long as they don't waste other people's time.

That a theory is implausified rather than falsified is quite common if very good theories are available already as in theoretical physics. But in other fields falsification is easier. The dopamine level might just not correlate with schizophrenia. Holy water doesn't sanitize your hands. The world is older than 10,000 years, etc.

A statement is a scientific prediction if all three above explained requirements are fulfilled. If you you have suggestions for improvement of my definition, please leave in comments.

What you should have learned from this post:

  • Not every statement about a future event is a scientific prediction. More commonly it is a prophecy.

  • While making predictions is a merit of a theory, it's neither a substitute for scientific quality nor an indicator for promise.

  • Explanatory power of a theory can be valuable even if not predictive.

  • Theories in physics often have free parameters that can be constrained, rather than an ansatz being generally falsified.

108 comments:

Steven Colyer said...

How is MOND doing? Last I heard there was a prediction that if MOND were true tests in 2009 (almost over now) would reveal certain perturbations of planets (I'm guessing gas giants) in our solar system. Did those tests go down? What were the results if so?

I've always thought falsification was harder than proof. How can one falsify the multiverse, for example?

Neil' said...

Falsifiable? Tell that to people coming up with "interpretations" of quantum mechanics! One that bothers me a lot is the many-worlds interpretation. It is presumably not falsifiable, although Deutsch AFAIK has considered how. Proponents claim that it avoids the measurement problem: all outcomes are realized "somewhere", so the Schroedinger wave keeps evolving etc.

But they also say that it avoids measuring devices being "special." I don't agree. Take a Mach-Zehnder interferometer setup. A photon is "split" by BS1, goes around two paths, and recombined by BS2. Then the interference is observed per ensemble by the pattern of hits on detectors at each output face. I suppose MWIzards say, the detector output splits into "worlds" so both detectors each continue to receive and interact with the partial wave functions.

But wait a minute - why do the detectors do that, that far down the line? Why doesn't the "world" split occur way back in BS1, with each path taking place in a different "world"? But then, there would be no interference pattern (even looking at the past of any one world.) They claim, MDs aren't special, but have to treat them as the "instigator" for the MW split and no sooner. So really, MDs are either special as collapse instigators or special as world-splitters: the alleged democratic handling by MWI appears fallacious in a falsifiable way.

BTW, Thanks Bee for the Snowy Warmth Heart - the very name sounds paradoxical! I don't know if you got the one back I tried to send, my FB is acting flaky. Also folks, I am pleased at Google search for "quantum measurement paradox" - check it out. I am flattered, hope to deserve it. (I'm also planning to roll out a demonstration that the decoherence interpretation of collapse phenomena is flawed.)

Arun said...

A scientific prediction is based on a scientific theory. That means in particular it is reproducible (by everybody with the appropriate education), consistent, and the theory it is based on is not in conflict with available data already.

Billion-dollar experimental set-ups cannot be reproduced by everybody with the appropriate education. :)

For HEP, the above has to be changed to "in-principle reproducible".

CapitalistImperialistPig said...

Our models for what a scientific theory can or should be are the theories we have that work: Kepler, Newton, Maxwell, Darwin,etc. Most of them are not explicitly about prediction, but all embed immense predictive power.

The most distinctive feature of the theories of physics is that they are mathematical, which means that the predictions are quantitative. One virtue of this fact is that even small effects (perihelion shift and light deflection in GR, the Lamb shift and magnetic moment g-factor in QED).

CapitalistImperialistPig said...

I left off ... can be decisive.

Zephir said...

/*...sometimes the data is in already and awaits a theoretical explanation... versus ... if you calculate the cosmological constant to be in agreement with the today measured value it's not a prediction, it's a postdiction...*/
In general, this post is concise, informative and quite exact. I've still certain problem with some "minute" details with respect to symmetry of radiative time arrow, though. The explanation of existing things or their history in new ways is not always postdiction, but a prediction of new interpretations. The subject of evolutionary theory or big bang theory is whole about prediction from this perspective. For example, Heim's theory is reconcilling QM and gravity in such a way, mass of electron predicted agrees to more then seven digits with value observed (..a wet dream for every stringy/lqg theorist, btw). In such way, it predicts the explanation of electron mass for remote future.

Giotis said...

Regarding your requirements Bee, I have two points:

The axioms or the assumptions of a theory could be regarded as predictions?

Similarly, predictions which are made on general grounds (e.g. expectations based on general physical principles and the principles of the theory) could be regarded as predictions or predictions should be strictly the outcome of a precise mathematical calculation in the context of a strict mathematical framework?

Zephir said...

/*..predictions should be strictly the outcome of a precise mathematical calculation in the context of a strict mathematical framework..*/
They should be falsifiable and as such reproducible. This doesn't always mean exact. Sometimes underlying rigor is so poorly conditioned, the derivations based on fuzzy logics would become more relevant. But they still should remain falsifiable in context of this logics.

For example heliocentric model predicts order of Venus phases. This prediction is surprisingly difficult to formalize in language of formal math and it could be explained by geocentric model, too. The Occam's razor (a sorta Lagrangian in causal space) is the best criterion of falsifiability, after then.

Bee said...

Hi Giotis:

In general, axioms or assumptions are not themselves predictions, since they only set the base for a theory in which predictions are derived for a specific case. Eg the axioms of quantum mechanics don't assume the energy levels of the hydrogen atom, the axioms of general relativity don't assume the radar echo delay, etc. Best,

B.

Zephir said...

/*..the axioms or the assumptions of a theory could be regarded as predictions? .*/
This question illustrates the independence of implicate geometry and causal time arrow to local time arrow. The answer simply depends on time coordinate system choosed.

Bee said...

Zephir: I am glad you like my post.

"The explanation of existing things or their history in new ways is not always postdiction, but a prediction of new interpretations."

The explanation of existing facts is not a prediction if those making the prediction know about the facts. It's a matter of procedure. If you know what you want to have as outcome because you know the data already the risk is substantially higher you're biased by wishful thinking, that's the reason for the distinction between postdiction and prediction.

"The subject of evolutionary theory or big bang theory is whole about prediction from this perspective."

Maybe you were confused about what I meant with "event in the future." While the "event" big bang might have been in the past, what I was referring to would be statements about measurements that were made only to the future of the statement about its results. Best,

B.

Zephir said...

Is explanation of Big bang event the prediction or postdiction? It explains the process, which occurred in deep past, I mean so deep, so that the light perceived by observer still didn't travel to. We can assume, existing light would reach the event horizon in far future and from such perspective this postdiction becomes prediction, too.

Bee said...

Hi Neil',

As I said above, explanations can be valuable even if they don't make predictions. See, I think that science is in the first line about understanding. If a new interpretation improves the understanding of a theory, that should not be dismissed as useless, since it could provide a path to new insights. I don't find MWI much improves the understanding of QM though. However, what somebody finds improves understanding differs from one to the next. Best,

B.

Bee said...

Hi Arun,

I said the theory has to be reproducible by everybody with the appropriate education, not the experiment. Though the latter, as you say, should be reproducible at least in principle. Best,

B.

Bee said...

Zephir: Please read my above reply to your earlier comment. The point is not that the big bang was in the past, but that a measurement whose outcome you have calculated in your theory is in the future. The "event" for which you make a prediction is the observation. Best,

B.

Zephir said...

/*.if those making the prediction know about the facts. It's a matter of procedure...*/
I said the very same. For example special relativity is assuming constant speed of light. But we still don't know, whether speed of light is really constant under all circumstances. It's effectivelly prediction from this POV. So in my opionion the local reference frame isn't so crucial for consideration of reference frame of predictions and postdictions. It's simply independent on it.

Bee said...

CIP: I agree with you as far as physics is concerned. There are other fields of science though where a quantification of predictions is much harder. Best,

B.

Bee said...

Zephir: I already told you in the comments to this post that you do not need to assume the constancy of the speed of light to derive special relativity. You find the proof here. Last time, you refused to read it claiming that 4-dimensional space-time is bullshit and referred me to a Wikipedia entry that you evidently also hadn't read. I do not want to repeat this fruitless exchange here. You either show what is wrong with my proof or you shut up. Either way, this is not the place to discuss special relativity, so please omit further demonstrations of your misunderstandings. Best,

B.

Zephir said...

In principle, Popper's methodology is assuming, you can be never sure by anything (I mean both by observations, both by theories). From this point of view every assumption about reality is technically a sort of prediction.

AWT considers process of theory validation as a regression fit or patching of experience in causal space. Reality appears like space-time foam and theory appears like piece of causal foam. And we are just trying, whether our piece of foam fits the reality foam well. The local time frame of observer has nothing to do with it, because successful theory would fit reality tightly in atemporal way.

Are we looking for TOE just because it can explain all existing observations well, or because it could supply most of predictions possible? These two criterions aren't quite equivalent.

Giotis said...

Hi Bee,

Yes ok, but my point is that I don't understand this distinction between derived results or consequences and the general principles/axioms.

Strings are not a prediction of String theory?

The quantizized space-time is not a prediction of QG theories?

The dynamical metric field is not a prediction of GR?

The only reason we are looking for physical consequences and side effects to verify a theory (what we call predictions), is because it's very hard to falsify the general axioms of a theory. There is no other reason.

Bottom line my point is that it's hard to determine what constitutes a prediction and give a formal definition for it. More or less the theory itself is a prediction. What we have come to call a prediction is a result of our inability in practice to verify a theory.

Uncle Al said...

http://www.mazepath.com/uncleal/boojum.pdf

Somebody should look.

Zephir said...

/*..Strings are not a prediction of String theory?..*/
One of the reasons (if not the main one) of fact, science distinguishes logical (causual) time arrow is in point, this arrow may be different from other time arrow definitions.

If it's so, I wouldn't mix the "prediction" concept from perspective of radiative (or whatever else) arrow of local time and the "prediction" concept in context of causual implicate geometry of predicate logics, which is completelly abstract and independent to physical time arrows.

In implicate/explicate geometry the causuality and time arrow is defined by orientation of scalar components (antecedent and consequent) of implication tensor, not by physical time arrow.

Plato said...

Bee:I've read quite a few of papers where the word "phenomenology" was used merely as decoration, and in other cases "phenomenological" is essentially an excuse for inconsistency.

Thanks for moving forward here in explanations.

When Jo-Anne on Cosmic Variance spoke it reminded me of what you are saying here, as when the scientists gather together for opinion about direction, what funding should be allocated too, the question of which experiments to fund become an important question with regards to the research that has gone on and the direction they want to go.

As a lay person I am not sure that I could be excluded from the assessment because of the number and types of experiments going on which have similarities involved that demonstrate a scientific principal in terms of signal to noise ratios for specific calculation on particle outlays, according too, cosmic particle considerations.

I had seen here where Stefan and your self moved toward estimates of the Fly's eye experiment to consider "high energy particle" scenarios.


Pierre Auger on Cosmic Rays

"For in 1938, I showed the presence in primary cosmic rays of particles of a million Gigavolts -- a million times more energetic than accelerators of that day could produce. Even now, when accelerators have far surpassed the Gigavolt mark, they still have not attained the energy of 1020eV, the highest observed energy for cosmic rays. Thus, cosmic rays have not been dethroned as far as energy goes, and the study of cosmic rays has a bright future, if only to learn where these particles come from and how they are accelerated. You know that Fermi made a very interesting proposal that particles are progressively accelerated by bouncing off moving magnetic fields, gaining a little energy each time. In this way, given a certain number of "kicks," one could perhaps account for particles of 1018 -- 1020 electron volts. As yet, however, we have no good theory to explain the production of the very-high-energy particles that make the air showers that my students and I discovered in 1938 at Jean Perrin's laboratory on a ridge of the Jungfrau."

-- Pierre Auger, Journal de Physique, 43, 12, 1982


While you were seeking validations here the work of neutrino research was ongoing as was John Ellis experiments.

What would you say in terms of your classifying extra dimensions leading too, new psychics, where the "given space" has not be understood?

Is such a space predicted or a post diction?

Best,

Gordon said...

Yes, but mathematics lets you dream.
Falsifiability now seems to belong to the infancy of physics as experiments to falsify seem to be more and more outside the range of our capabilities. That doesn't mean that the theory is wrong about reality.

Arun said...

Dear Bee,

We humans "know" what we're talking about, and so your essay works. However, if we were to try to educate a machine, we'd have to be much more careful - else, e.g., we'd make musicology into a science with scientific predictions.

E.g., when I press this key on the piano tomorrow, I will get a middle C note (440 Hz) - is a statement about a future event, is based on a theory (of music scales) is reproducible, consistent, and is not in conflict with the data available, and is falsifiable.

:)


However, we are not into such philosophical hair-splitting here, and I agree with all you wrote.

Best,
-Arun

Michael said...

Hi Bee,

thanks for the nice post, I agree with your definition of a scientific prediction. In my world of experimental high-energy physics, the distinction between a prediction and a post-diction is clear and useful. Explaining the meson mass spectrum via an application of string theory would be wonderful, and is clearly a post-diction since we know that spectrum very well. Stating the mass of the neutralino and confirming it in terrestrial dark-matter scattering experiments would be an impressive prediction.

Perhaps to dispel some misunderstanding, one could say that a scientific prediction is a statement about the outcome of a controlled experiment - one that has not yet been done. This avoids discussion of the arrow of time, and makes a distinction with striking a piano key.

anyway, nice post. :)
Michael

Bee said...

Hi Giotis:

No, "strings" are not a prediction of string theory. What kind of a prediction is that? What does it predict? A prediction of string theory would tell you eg at what energy a cross-section has a resonance, what signature a string-ball has etc. "Quantized spacetime" is neither an axiom nor a prediction - the problem is to consistently make sense of the expression to begin with. A "dynamical metric field" is not a prediction of GR: a prediction is a statement about a measurement derived by use of the axioms. Best,

B.

Bee said...

Zephir: I have deleted several of your comments. I already told you about half a dozen times that your argument is faulty because for every theory are many different axiom systems that are equivalent to each other. If one of us is "violating" any "principles of discussion" its you since you're not replying to any of the arguments I raise to explain the mistakes in your thoughts, you just repeat nonsense like a broken record. I had to notice that this doesn't only annoy and tire Stefan and me but also several of our frequent visitors whose constructive comments I value very much. I will thus continue to delete your repetitions that do not offer any new information, as well as any further mentioning of your own theory of something. As our comment rules say, if you want to discuss something else than the topic if this post, please get your own blog. Thanks,

B.

Bee said...

Dear Arun,

I would argue that your musical example is a scientific prediction. It just isn't particularly interesting or insightful. What is interesting for humans I guess would indeed be very hard to explain to a machine. Best,

B.

Giotis said...

"a prediction is a statement about a measurement derived by use of the axioms"

What about extra dimensions then? There is no statement for a specific measurement regarding extra dimensions from the String theory point of view but nevertheless it's a prediction of the theory. If evidence of extra dimensions are discovered during an experiment then I suppose it would be a verification of a prediction after all.

So theories make statements about the physical world in general. Whether these statements could be translated to statements about a specific measurement, now or after a thousand years is relative and uncertain and it depends on many factors. This doesn't mean that the theory make no predictions.

You see my point?

Plato said...

Machine or human, are the matter distinctions separated while trying to extend our perception into the basis of reality "about a given a space?"

So the resonance would be "a possibility in connecting one level of that matter state of machine to another(human), according to what stage we want to assign the machine for calibration of focus, versus, the human, as to a standard measure of thought, and thoughts to use if for further measures?

All roads lead too?

Using cosmic particle scenarios in relation too, while, man made distinctive measures lead too? A "point" possibly holding the infinite?

How strange, has reductionism runs it course or is there something yet to be found?

Predict then, what you shall find?

Best,

Plato said...

Oh Steven has a link to the New York times article on Frank Wilczek in regards to the "strong force" and how we might identify some of that space?:)

Christine said...

Giotis wrote:

There is no statement for a specific measurement regarding extra dimensions from the String theory point of view but nevertheless it's a prediction of the theory.

No, they are not. Extra-dimensions are an assumption (hypothesis; postulate) or perhaps a requirement of string theory, but not a prediction. If it turns out that extra-dimensions are verified then it only means that the considered assumptions are valid.

A prediction must be an outcome of the theory, like, for instance, the bending of light around the sun, predicted by the general theory of relativity. OTOH, its assumptions (hypothesis; postulates) are based on general principles such as the principle of equivalence and the principle of general covariance. It also assumes that SR is locally valid for inertial frames.

So if a prediction is measured/observed, it means that the assumptions of the theory are valid under the probed regime, and by consequence the theory is regarded as acceptable under the assumptions and domain of validity analysed.

I think that Bee is refering to the assumptions/hypothesis/postulates of a theory as axioms, if I am not mistaken. However, I would call axiom as some proposition regarded as generally accepted or self-evident.

Best,
Christine

Giotis said...

Christine,

Extra dimensions are definitely not an assumption/hypothesis/postulate or axiom; They are a derived result/outcome of the theory based on SR, QM, conformal symmetry, SUSY and of course the existence of dimensional objects at Planck scales. Their number is the outcome of a specific, strict mathematical calculation.

Arun said...

Dear Bee,

That prediction is very important to the musician who expects the piano to produce the right notes; and very important to the piano-tuner who derives his income from the times when the prediction fails :)

Anyway, the reason why philosophical reasoning gets so involved is precisely because it has to be explainable in principle to machines or to aliens from outer space.

I'm not sure any useful insight has come from extra precision but maybe some reader here has an example?


Best,
-Arun

Anonymous said...

Hmmm, most interesting!

One imagines a certain amount of squirming in chairs, perspiration on the brows and arm-waving justifications.

Doth she protest too much?

Methinks the Xtasy bash is just about over. What fun it will be to watch the most enthusiastic celebrants try to explain their unfortunate behavior.

Golly good show of rigor and right-thinking!

Ulrich

Plato said...

Vernon Barger-perspectives on neutrino physics Posted by dorigo

Barger then mentioned the idea of mapping the universe with neutrinos: the idea is that active galactic nuclei (AGN) produce hadronic interactions with pions decaying to neutrinos, and there is a whole range of experiments looking at this. You could study the neutrinos coming from AGN and their flavor composition.

So while Fermi lets us look at the universe in one way what do we have to look forward too?

Galactic Neutrino Communication by John G. Learned, Sandip Pakvasa, A. Zee

We examine the possibility to employ neutrinos to communicate within the galaxy. We discuss various issues associated with transmission and reception, and suggest that the resonant neutrino energy near 6.3 PeV may be most appropriate. In one scheme we propose to make Z^o particles in an overtaking e^+ - e^- collider such that the resulting decay neutrinos are near the W^- resonance on electrons in the laboratory. Information is encoded via time structure of the beam. In another scheme we propose to use a 30 PeV pion accelerator to create neutrino or anti-neutrino beams. The latter encodes information via the particle/anti-particle content of the beam, as well as timing. Moreover, the latter beam requires far less power, and can be accomplished with presently foreseeable technology. Such signals from an advanced civilization, should they exist, will be eminently detectable in neutrino detectors now under construction.

How alien is that?:)

Bee said...

Christine, Giotis:

Giotis is right, extra dimensions are not an assumptions of string theory, they are a conclusion arising from requiring the theory to be physically meaningful. Best,

B.

Bee said...

Hi Giotis,

I don't see your point, sorry. I certainly don't want to dictate other people how to use specific words, but in my understanding (which I expressed in this post) "extra dimensions" is not a prediction. "Extra dimensions" is not even a statement whatsoever, not to mention that it's not a statement about a future measurment. "The existence of extra dimensions" is a consequence of string theory. A prediction tells you what is going to happen in a measurement. The correct formulation would be that "String theory requires the existence of extra dimensions and some models with extra dimensions make predictions that are testable at the LHC." It's exactly because this has frequently been formulated very sloppily that now people seem to think the LHC tests string theory. Best,

B.

Bee said...

Dear Arun,

I doubt there is a good definition for what is "interesting" and what not, because it's individually different. In any case, what I've tried to sketch is what a scientific prediction is and not what an interesting scientific prediction is. Being pressed I'd argue with revealed preferences. Best,

B.

Bee said...

Hi Michael,

Frequently when I hear talks from experimentalists about a running measurement (cosmic rays, dark matter, etc) I am impressed how careful they are to decide in advance how to analyze the data. In other fields, e.g. medicine the awareness for the importance of this seems to be low. I was stunned to read in that paper that after a study is performed it seems to happen quite frequently that researchers "search" for correlations by "post hoc subgroup analysis" or "serendipitous inclusion or exclusion of patients." I'm not sure exactly what the latter is supposed to mean, but my interpretation is basically if you haven't found a correlation you sample subgroups till one shows a correlation which will happen just by chance of you sample sufficiently. The result of such a postiori tempering is of the sort: in the subgroup of people where everybody died, the mortality was 100%. Best,

B.

Giotis said...

Ok I can accept that extra dimensions is not a prediction according to your definition but my point is that whether extra dimensions is a prediction or not has nothing to do with the theory itself. The prediction lies outside the theory. People often use the fact that certain theories currently don't make "predictions" to attack the core of these theories. My scope is to demote predictions to a peripheral secondary issue. It's relative, dynamical and it depends mostly on factors outside the theory.

Let's say for example that GR had appeared before the discovery of the problem with the precession of the perihelion of Mercury.
Then It wouldn't be a prediction of GR until its discovery. This has nothing to do with GR itself though. The prediction lies outside the theory itself.

So the phrase usually used "The theory makes no predictions" is vacant and pointless. As I said previously and I repeat here:

"Theories make statements about the physical world in general. Whether these statements could be translated to statements about a specific measurement, now or after a thousand years is relative and uncertain and it depends on many factors."

To that I would add now that it's not within the scope of a theory to make predictions. The scope of a theory is to explain the physical world. Whether they would be predictions or not has nothing to do with the theory itself.

In that respect I would very much agree with the with points 2 and 3 at the end of your post.

Christine said...

I previously wrote:

Extra-dimensions are an assumption (hypothesis; postulate) or perhaps a requirement of string theory, but not a prediction.

If you are willing to make sense of supersymmetric string theory, 10 dimensions are required. It turns out that "making sense" is a mathematical consistency requirement. Not a physical one. Then you must introduce the hypothesis that the physical world has extra-dimensions in order to proceed in the theory. I believe I stand correct.

Giotis said...

Extra dimensions are introduced because the Weyl Symmetry which is a gauge symmetry at classical level is anomalous when the theory is quantized. In order to eliminate the gauge anomaly, extra dimensions are introduced in the critical String theory. The fact that a gauge symmetry at classical level should be retained after quantization in order the theory to make sense is a physical requirement not a mathematical.

Christine said...

Giotis wrote:

--begin quote--

"Theories make statements about the physical world in general. Whether these statements could be translated to statements about a specific measurement, now or after a thousand years is relative and uncertain and it depends on many factors."

To that I would add now that it's not within the scope of a theory to make predictions. The scope of a theory is to explain the physical world. Whether they would be predictions or not has nothing to do with the theory itself.


--end quote--

Any scientific theory *must* have at least one logical consequence derived from its assertions. Otherwise it is completely vacuous. Any logical consequence of a theory *is* a prediction.

A theory that cannot be tested in principle, that is, one which the scientific method cannot be applied, is *not* a scientific theory. It is a speculation.

And do not confuse prediction with forecast.

Finally, please, people, stop trying to change the meaning of the scientific method in order to accommodate one's wishes. Nature does not care about that. This is why we need the rigorousness of the scientific method; otherwise we are just being deceptive to ourselves. This brings a high cost.

Steven Colyer said...

3. A scientific prediction is falsifiable. In practice this means often its implausifiable.

Bee, the most common mistake in writing in English is to write "its" when you mean "it's" and vice versa. I make that mistake all the time so it's not just you. Pls correct then delete this post as well, thanks, because you know it's only a matter of time before dear old Lubos gets wind of this thread and starts dumping on you, yet again (especially now that String Theory has been raised here).

Christine said...

In any case, if you go back enough, the 2D worldsheet describing the embedding of the string in spacetime is a mathematical hypothesis of the theory.

You may encode physical requirements (like gauge fields) conformally on the worldsheet. Yet, you are still working with mathematical consistency all the way.

(And if you advance into supersymmetry, you are also using an hypothesis, so you have at least 2 hypothesis in superstring theory).

Extra-dimensions are firmly dependent on hypotheses. This is my understanding of course.

Phil Warnell said...
This comment has been removed by the author.
Phil Warnell said...

Hi Bee,

Thanks again for a well written and thoughtful post, which along with many of the others is now forming to be quite a valuable resource for those who may be curious as to what the practice of science brings in terms of methods and subsequent demands. There is little that is found here that could be argued not to represent how doubt is expected to be addressed from the scientific perspective and that being with having it to remain only objectively dispelled, as to be able to relieve it as opposed to methods that often serve to increase the reason it remain.

The only thing I would wish to point out or rather clarify, is that despite how much science struggles to be totally objective, it has never discovered how it can be without the omission of some measure of the subjective to enable the process to begin. However even though this be true, what I find that is so often confused, being although this may not seem to fit with the demands of science, that this seeming contradiction is certainly resolved by way of its greatest demand, which being what’s to be considered as proof.

That’s to recognize it is better to have an incomplete picture of nature in regards to substance and action, rather than be tempted to think they can be known by only reason of undemonstrated or undemonstratable logical assumption(s). The unfortunate result is if one does or thinks it can be so modified, is they no longer hold true to the foundations of the philosophy, as to have it any longer be science. So although this may disappoint the expectation of some, when adhered to science's value by virtue of its utility will remain as being uncompromised.

Best,

Phil

Giotis said...

Christine said:

"Any scientific theory *must* have at least one logical consequence derived from its assertions. Otherwise it is completely vacuous. Any logical consequence of a theory *is* a prediction."

This definition is different from Bee's definition. According to Bee: "A prediction tells you what is going to happen in a measurement."

In my post I was referring to Bee's definition.

According to your definition extra dimensions is a prediction after all because it's a logical consequence of the theory; which contradicts your previous statement that extra dimensions is not a prediction.

Christine said...

Yes, Giotis, you are right; I should have more appropriately have said that any logical consequence resulting from a theory must describable in terms of a measurement, in accordance to Bee's definition, otherwise it is also vacuous. My position still is that extra-dimensions are not a prediction.

Steven Colyer said...

"My position still is that extra-dimensions are not a prediction."
... Christine

It's a good position; one of my favorites. THAT extra-dimensions pop out of String Theory as a logical consequence to making the Math fit the Theory fit Reality, etc., seems VERY ad-hoc to me. That ST predicts an infinite number of particle types and masses ALONE makes me want to kick Strings to the curb and then do further horrible things to it as well, aside, but ... we may be talking about the Anthropic version here, which isn't fair to David Gross and other Theorists who believe in Strings but reject the Anthropic version, so I'll say no more until I master Quantum Field Theory and can talk shop properly, other than I openly ask how many have seriously considered the possibility that Ted Kaluza was right but Oskar Klein was wrong (albeit well-intentioned). We all know or should know that Klein-Gordon was a failed but noble first attempt at SR-QM unification, and thank God for Paul Dirac, but that wasn't my point. My point was Kaluza-Klein theory. We've gotten so deep into the debate over small rolled up extra directions, have we lost sight that there may be just one large extra spatial one, and the implications thereof?

Phil wrote:

"The only thing I would wish to point out or rather clarify, is that despite how much science struggles to be totally objective, it has never discovered how it can be without the omission of some measure of the subjective to enable the process to begin."
... Phil Warnell

Good point as usual, Phil. Is this not the Double-Blind technique as taught to us from that 3rd youngest major field of study known as Psychology? One example I can think of is experiments designed to identify the fundamentals as either particles as waves. You get what you came for, so to speak. :-)

I echo Phil's sentiments, Bee, regarding the quality and importance of this discussion. Thanks to Giotis and Christine for their contribution and intelligent debate/discussion; it's fascinating and keep up the good thoughts.

Bee said...

Hi Steven,

Thanks, I've fixed that. Best,

B.

Plato said...

Where a dictionary proceeds in a circular manner, defining a word by reference to another, the basic concepts of mathematics are infinitely closer to an indecomposable element", a kind of elementary particle" of thought with a minimal amount of ambiguity in their definition. Alain Connes

Are there no good trackers anymore?:)

If you have been taken to a certain point in time, you have narrowed the circumference of the perspective "to a point" that directs the understanding of the collision process as a point of where such things meet, yet, contain a greater space for consideration then the one you started with.

How can a speck of a universe be physically identical to the great expanse we view in the heavens above? (Greene, The Elegant Universe, pages 248-249).

Ultimately, you are lead there.

This is not fiction or hypothetical and is very real.

Pointing toward the QGP "is directional" in that this regression to a point in time, is a dynamical relation to the substance of the interaction.

Sheesh!

Best,

Plato said...

Might I revert for a minute to the subjectively quality that is inline with directing our mechanical means toward an objective and goal and the understanding that the "time value" is set according to how far back we can go toward directing "our own subjective interpretation?"

You all understand the science here.

Yes subjectively, Phil is right to that point?:)You really have to understand the correlation Greene and Fudjack marry up for perspective.

The Structure of Consciousness John Fudjack - September, 1999

By 'dilating' and 'expanding' the scope of our attention we not only discover that 'form is emptiness' (the donut has a hole), but also that 'emptiness is form' (objects precipitate out of the larger 'space') - to use Buddhist terminology. The emptiness that we arrive at by narrowing our focus on the innermost is identical to the emptiness that we arrive at by expanding our focus to the outermost. The 'infinitely large' is identical to the 'infinitesimally small'.


I wouldn't necessarily say that space was empty though, would you?:)

Reveals a very dynamical relation with the reality around you. You can become "very fixated" much as one would think of as myself.

Trying to remain "very fluid" is "very hard" there is no doubt about this.:)

Best,

Best,

Plato said...

If you can find other correlation to this demonstration then do not be upset according to the time you might perceive subjectively as a functioning relationship to the world around in this demonstrative way.

Again, I know you know what science is.


Figure 8 [replaced by our Figure 2] is to be conceived three-dimensionally, the circles being cross-sections of spherical shells in the plane of the drawing. A man is climbing about on the huge spherical surface 1; by measurements with rigid rods he recognizes it as a spherical shell, i.e. he finds the geometry of the surface of a sphere. Since the third dimension is at his disposal, he goes to spherical shell 2. Does the second shell lie inside the first one, or does it enclose the first shell? He can answer this question by measuring 2. Assume that he finds 2 to be the smaller surface; he will say that 2 is situated inside of 1. He goes now to 3 and finds that 3 is as large as 1.

How is this possible? Should 3 not be smaller than 2? ...

He goes on to the next shell and finds that 4 is larger than 3, and thus larger than 1. ... 5 he finds to be as large as 3 and 1.

But here he makes a strange observation. He finds that in 5 everything is familiar to him; he even recognizes his own room which was built into shell 1 at a certain point. This correspondence manifests itself in every detail; ... He is quite dumbfounded since he is certain that he is separated from surface 1 by the intervening shells. He must assume that two identical worlds exist, and that every event on surface 1 happens in an identical manner on surface 5. (Reichenbach 1958, 63-64)


Happy New Year to you all.

Zephir said...

/*..your argument is faulty because for every theory are many different axiom systems that are equivalent to each other...*/
It's possible - but did you prove, Minkovski space postulate can replace the constant speed of light postulate completely under all circumstances thinkable? Is it possible to give such evidence in general case at all?

Anyway, your tendency to simply delete comments, which you don't agree with (and even attempting to reply) makes you equivalent to Motl and another arrogant troll in my eyes. As one of commenter's noticed already, under stress you're acting quite cowardly. You cannot face the arguments.

stefan said...

Zephir,

which arguments are you talking about? Yours? Did you ever have any? The comparison to the guy from Pilsen is an insult, by the way ;-). And, if you ever try to run a blog in a serious manner, I promise you, I will make you delete my pseudonymous comments faster than you believe - it's no big problem to either ruin a blog or to urge the owner to hit the delete button...

Anyway, have a Happy New Year though, and as a resolution, what about just not to bother anymore about backreaction?

Bee said...

Zephir:

"under stress you're acting quite cowardly."

*lmfao* It's called "projection," Zephir. As anyone can easily check it has been you who has insulted me when you came "under stress" and noticed you couln't counter my arguments. It is great progress that you have at least understood now it is possible to derive special relativity without assuming the constancy of the speed of ligh. And yes, I did prove it, please read the post that I referred you to several times already. It does of course hold for all circumstances since the outcome is just the usual special relativity with all its usual effects and predictions. Let me add that this proof is a completely standard construction and can be found in many textbook on mathematical physics. The Lorentz-Group is the symmetry group of Minkowski-Space, SO(3,1), that's it. That the speed of massless particles is constant follows from the kinematics in that space. Why don't you finally just go and read what I wrote?

That I deleted your comments has nothing to do with my alledged "cowardice" but that your repetitions of faulty arguments is useless, doesn't add new information, and just clogs the comment sections. Let me repeat once again that this post is not about special relativity, so please think about what I said and digest it quietly.
Happy New Year,

B.

Low Math, Meekly Interacting said...

I struggle with the existence of theories which are testable/falsifiable in principle, but in practice would require virtually god-like resources to actually do the experiment. What should be the status of theories that can only be distinguished from others with the assistance of instruments that are light years across, or require the conversion of stellar masses to pure energy?

This is a rare problem in science, and one that only seems to afflict the frontiers of high-energy physics and cosmology profoundly.

I also struggle with anthropism. In principle, multiversal landscapes that are finite can be explored using no more sophistication than empirical corroboration with our vacuum, in the complete absence of a selection principle to narrow the search. However, if the number of vacua to be considered is so large that even a fraction of a second spent on each would take trillions of years to perform a thorough search, then of what practical use is such a theory? Even with a selection principle, unless it is very stringent, the process of elimination may not be nearly sufficient to reduce the exploration time to the average lifespan of solar systems. That's not much better.

I see no easy solution. On the one hand, you can set an arbitrary standard for practicality, e.g. experiments it would take a god to do don't count, which is, well, arbitrary. Or you live with the current situation, which, in my mind, inevitably is about downgrading the importance of experimentation in defining what constitutes "scientific" exploration.

Zephir said...

/*...what about just not to bother anymore about backreaction.. */
??? ..another attempt for censorship?

/*..the Lorentz-Group is the symmetry group of Minkowski-Space, SO(3,1)...*/
But special relativity is invariant to Poincaré group, not just Lorentz group. The above claim is valid only locally, as the Poincaré group could lead into a much more complex and higher-dimensional, then just 4D space-time.

Common aspect of both models still doesn't mean the evidence, both models are equivalent. Your cowardice was proven experimentally by deleting of my posts, which you answered for at the same moment - so that the reader has no possibility to reconstruct flow of discussion. It's a pitty, I must learn you about so trivial principles of dialectic discussion, Bee.

Bee said...

Zephir: As I said above, I deleted your comments because they were entirely superfluous and just repetitions of your faulty earlier arguments. I had explained to you where your mistake is, you continued to repeat the same thing, my deletion was made to avoid our readers would have to read the same nonsense, which also doesn't belong into this comment section, some dozen times. Even this discussion we have already had before, and also here you are not able to understand what I am saying. This blog is not for you alone. If you don't respect the rules, I'll act on it. If you don't like that, good bye.

Yes, sorry, you are right, I meant Poincaré group. This part of the proof is trivial since Minkowski-spacetime is translation invariant. Best,

B.

Bee said...

Hi Low Math,

Yes, it's an important issue and one that I avoided to address because I don't really have much intelligent to say about it. I guess the underlying question is why do we pursue science? Best,

B.

Anonymous said...

Christine:"Yes, Giotis, you are right; I should have more appropriately have said that any logical consequence resulting from a theory must describable in terms of a measurement, in accordance to Bee's definition, otherwise it is also vacuous. My position still is that extra-dimensions are not a prediction."

Dear Christine, if you are genuinly interested to learn about this topic (experimental stringy signatures for "large" extra dimensional scenarios) you can find the relevant information in this paper:
"String Phenomenology at the LHC"
http://arxiv.org/abs/0909.2216

There are very specific predictions such as, e.g. the emergence of Regge excitations of the quarks and the gluons. These features clearly distinguish the extra-dimensional stringy physics from the Kaluza-Klein scenario.

Anonymous said...

Low Math Meekly Interacting,

The best science has always been testable. Sometimes it takes a long time [e.g., to actually observe the atomic basis of matter], but the prediction can sill be made. It was not easy to test General Relativity, but it made testable predictions, and eventually was tested many times over.

The farther physics gets from feasible perdictions/testing the more bizarre the theoretical physics becomes and the more pressure there is for physicists to come back to reality.

Just watch; it will happen in your lifetime.

Ulrich

Bee said...

Zephir: This time it was Stefan who deleted your comment. You already accused me of lying here, and I replied to it here, quoting this comment of yours to which you had nothing more to say. That's exactly why we're deleting your comments, because you just repeat what you already said without taking into account other's replies. You are not even trying to lead a dialogue, Zephir, you're leading a monologue, and a repetitive one in addition. The comments we deleted were pretty much exact reproductions of earlier comments, and nothing is lost with deleting them. Your elaborations are thus a waste of my and our readers time, which is why we are deleting them. As I already said many times, if you don't like that, go and dump your comments elsewhere. Best,

B.

Anonymous said...

The man without qualities does not do well at staying on other people's topics, far less at jumping through their hoops.

He also has an unfortunate weakness for smirking at human weaknesses.

But he is honest and honorable enough to recognize that this is your blog, and wish you and all a productive and illuminating 2010.

Sincerely,
Ulrich

Phil Warnell said...
This comment has been removed by the author.
Phil Warnell said...

Hi Bee,

In you drawing attention to phenomenology and its role in scientific discovery, it had me to become mindful of a paper I read of J.S. Bell some time ago entitled ‘How to teach special relativity’, where he reviews the route taken by Lorentz, Poincare and Fitzgerald in their efforts to explain the phenomenology presented in the Michaelson- Morley experiments. What I find this paper so amply does is to show that while such examination may not lead one to the realization that Einstein came to, in having such things encompassed by a principle synopsised as two characters of nature, it does show however by simply attempting to explain the phenomena in terms of its actions, can have one arrive at a place that predicatively accounts for such never the less.

After reading this paper the thing that stood out for me was to ask which of the two routes stands as being the better in terms as representing what science is. With the Lorentz, Poincare and Fitzgerald approach all the actions of nature are described as a series of recipes if you will, where a fixed reference frame is still considered as real although undetectable, while for Einstein this undetectably had it become so irrelevant that it was denied. However, from the practical standpoint in terms of being able to make predictions about nature in its demonstrated action the two are indistinguishable. So you come to ask yourself if to think strictly as Einstein’s precursors thought, is it more legitimate as to have explained a set of phenomena with simply mathematically consistent rules or to have it be explained in the terms of nature having qualities, which in this instance is to say it has no preferred reverence frame where for which anyone arbitrarily chosen all the laws of nature will remain the same.

So for me the question comes down to asking oneself, is nature a collection of arbitrarily chosen yet set actions, explainable only as a series of interlinked and interdependent recipes or rather a structure that is a consequence of reason leaving no choice at all as to how and why it must be. For me it comes to ask, is there is only one or many ways what is known as reality can come to be real; which I answer to myself in the affirmative, as to have all the other choices simply as what cannot be, by reason of them physically unable to be demonstrated as such.

So with all this considered I would ask, what is phenomenology’s true role in physics? That is it to have us simply able to make predictions in regards to the actions of our world or to find the reason(s) behind what mandates such actions. When I consider my first insistence as those things can only be real in one way, as reason would dictate being to me , I would say physics is to have answered, with the aid of phenomenology the latter question, rather than the first. Of course having such an opinion finds me to be in the minority these days; as such things are concerned, which demotes reason to being anything that can be imagined and sometimes for no reason assignable to it at all.

So I would finally ask, are the importance of demonstrated things like symmetry, conservation, least action, invariance and covariance, all able to be explained away by the seeming purposeless randomness of uncertainty, as most now believe, or is it also just another necessity for nature to have reality present itself only as it is, rather than one of just many ways.

Best,

Phil

Anonymous said...

One possibility is that "randomness" is an artificial concept, applicable to human mathematical models but not to nature.

I think Spinoza said that.

If the world is strictly deterministic, all the quantum weirdness vanishes like a mist.

I think J.S. Bell, himself, said that.

Happy new year, decade and century,

Ulrich

William, Boston said...

Ulrich said: "One possibility is that "randomness" is an artificial concept, applicable to human mathematical models but not to nature. ... I think Spinoza said that. ... If the world is strictly deterministic, all the quantum weirdness vanishes like a mist. ... I think J.S. Bell, himself, said that."

And it was Einstein who refused to believe in quantum indeterminism and steadfastly argued for "hidden variables" behind the hypothetical probabilistic-nature of quantum mechanics.

I agree with all three of them. It seems obvious to me that determinism must be true, and that random or probabilistic descriptions in physics simply reflect factors and forces which have not been properly accounted for.

Truly random events seem to me to be quite bizarre concepts, since they demand that something happens for no reason, with no cause and without any possible explanation.

Thinking of Einstein's metaphor of god not rolling dice ... is that to say that most physicists actually believe that the outcome of a roll of dice is not completely determined and is not, in principle, calculable, simply because it has a probabilistic outcome?

Steven Colyer said...

Hi Ulrich,

Lottery players would agree randomness is artificial, as they sure that THIS time they will buck the odds and win.

Casino owners who cheat (no!) by stacking the odds in their favor definitely know that randomness is artificial, for they made it so. Please don't tell the authorities.

I'm not sure, but my intuition tells me nonlinear dynamics holds the key to randomness in the quantum world. Who is working on that, if anyone?

Steven Colyer said...

Hi William, Boston

We all, like Einstein, WANT Determinism to be true, because we see nothing else on the length scale, the macroscopic scale, in which we exist.

But that's just not the way it works down at the length scale of quantum particles, like it or not. Einstein didn't like it, I don't like it, you don't like it, nobody likes it, but that's the way it is.

To his credit, Einstein accepted the basic tenets of Quantum Mechanics eventually; he did seek as you seek though a causal deterministic explanation. He did not succeed, and neither has anyone else.

But, good news time, we get closer every day.

Hidden variables however has been found to be unnecessary. See David Bohm and John Stewart Bell for more on that. Is that weird? Yes. But is it true? Also yes.

Phil Warnell said...

Hi Steven,William & Ulrich,

I hope no one took my argument as to what phenomenology should reveal in science to deny uncertainty in quantum process, as it surely wasn’t. I’m not even making an argument against randomness for that matter, since in actuality it’s not something that can be reproduced mathematically, yet in systems that are driven by it can be calculated. Actually, the only point I was making is many have come to believe that the apparent randomness of nature brings with it no predictable results or outcomes, which of course isn’t true, since often it’s only the part of process that assures all opinions are made available to have an end result that’s favourable or favoured.

The best example I can think of being evolution, where random is used as part of the process to best assure the continuance of life, yet not of any particular species, but rather often at their expense. To me it’s like saying to stir a cake’s ingredients as to have them evenly mixed, indicates the cake having then no purpose or have us not be certain it will be a cake after baking, solely because random was used as an element of the process. That’s simply to say that randomness leading to uncertainty is not the same as randomness leaving things always as uncertain. Another way to look at is if one is uncertain how to accomplish something the only way to arrive there is to try everything, yet this still doesn’t say there is anymore then only one way something can be had, like reality perhaps:-)

“Moreover, among the seeds anything must have come to be at random. But the person who asserts this entirely does away with 'nature' and what exists 'by nature'. For those things are natural which, by a continuous movement originated from an internal principle, arrive at some completion: the same completion is not reached from every principle; nor any chance completion, but always the tendency in each is towards the same end, if there is no impediment.”

-Aristotle

Best,

Phil

Steven Colyer said...

So Phil I guess what Aristotle was saying was that there is a deterministic reason for everything, but since we have not perfect knowledge of all the initial conditions (which exist although we lack knowledge of them), the results then "appear" to be random? I.e., the "illusion" of randomness?

I believe that was Heisenberg's take on his own Uncertainty Principle. I also believe Bohr had the better take.

Phil Warnell said...

Hi Steven,

Well I wouldn’t even say I be certain of that, no pun intended. Rather as I said in the outset, random is not something that can be reproduced mathematically, yet only what the likelihood of outcomes are in things that indicates it’s manifested in. For instance the definition of randomness from the mathematical perspective in relation to set theory is to have a set where the elements needed to describe it can be no smaller then the set it describes. No, rather what I’m saying is that if the system doesn’t incorporate random that having something that’s required to have it be be possible could be missed as a result.

That’s to say for me I find all existence and with it what’s called reality so incredible that I see random is more indicative that it might require considering all possible outcomes for it to be arrived at. That’s sort of to have the whole argument as to what random indicates of nature turned completely around, as to say random is a process to assure a particular outcome, rather than to have it uncertain. In the quantum mechanical perspective it was Heisenberg’s uncertainty principle that assured the stability of atomic structure, rather than not to have it so assured. So all I’m saying is people should not be so certain as to think they know what random is as it relates to process as meaning it indicates there being endless possible ways to assure in having reality.

Best,

Phil

Anonymous said...

William of Boston,

If you have not read Ian Stewart's entertaining and highly enlightening book: Does God Play Dice?, I highly recommend it.

My bet is that nonlinear dynamical systems theory, when combined with a better understanding of the hierarchical organization of nature, will be able to reproduce all empirically-tested quantum phenomena in a completely deterministic manner [note to the uninitiated: "causally determined" and "unpredictable" are not mutually exclusive concepts - and that can be proven logically].

Steve Colyer,

Sigh. Bohr was a great mathematical physicist, but he was a very confused natural philosopher.
You are just going to have to process that and learn to live with it.

Keep smiling
Ulrich

Neil B said...

Unfortunately, many of the issues concerning "quantum interpretation" are not testable - and therefore, not scientific "predictions." Some say, the decoherence interpretation is testable since we can calculate how long decoherence should take and then of course we find only one state when we look. Yeah, we already know we always *see* one state (or what about those experiments to keep things superposed for awhile?) They also claim to avoid "true" randomness, since each state evolves deterinistically albeit in "another world." However, I bring up complaints like the one upthread: why doesn't the first beam splitter in a MZ separate waves into two different worlds, in which case there'd be no interference at all?

In any case, I worked out a test for DI using an interferometer. It would experimentally disprove the DI claim that scrambling the phases between originally coherent states converts them into a "mixture." Such a mixture is claimed to be like classical occurrences of one state or the other by themselves. Phil W. it well at my own blog:
"... although the experimental setup should have destroyed the wave function, information can still be gathered about it after the fact and thus decoherence just can’t serve as an actual explanation of the observations." Check the post "Decoherence Interpretation Falsified?"

BTW, I changed my blog handle to "Neil B" to help distinguish me.

Plato said...

I have an image here that might help Bee remember the one she made in regards to "a triangle?"

The post itself might be interesting for some.

What use Twistor Theory, if it cannot be correlated to the way in which some views are seen as useful in science today??

Best,

Plato said...

Ah here it is.

Perhaps within the context of "Scientific prediction" a mind map might be useful and with refence to this article?

Precursors to the "Manhattan economic project" had to derive it's basis from "some framework" for an outcome in society, or why would you attempt to offer a new methods for consideration? Economists crying foul?:)

My own inclination, "is an arch" depicting "a relationship between what can descend into mind and what Aristotle could gather from around him." You had to understand that Plato's finger was more then exclaiming the "One thing" which might ring as to Curlies Gold, is more the direction of all the possibilities could marry up with the hand that outlays what exists here on earth.:)

So ya, Raphael's painting of the School of Athens can be used as a mind map.

Best,

William, Boston said...

Plato,

Thanks for links. The Penrose sketch http://photos1.blogger.com/blogger/6460/633/1600/Roger%20Penrose.jpg is curious in that the text on the Physical World in straight, as written on a flat ruled sheet of paper; on the Mental World is curved with the circumference, as if written on a 2-D disk; and on the Platonic World is curved anti-circumferentially, along geodesics, as if written on a 3-D sphere!

I wonder if that has any predictive value to Penrose's thinking. Haha.

Also, I guess the arrows represent the status of the understanding of phenomena .. since they become some solid and well-defined as they progress from Physical world, from Mental world and from Platonic world. I would have that last arrow go back to the Mental World though, and then have added a different type of arrow from the Mental World back to the Physical World.

That motivated to create a graphic version that made sense to me, and it became bigger and bigger, until it included factors like sex, god, war, consumerism, CO2, hawking-like radiation of vital human mental energy, entropy and more ... with a lot of annotation, on a graphic model with 5 Worlds. Although one of the Worlds, the "Fucked-Up-Mind World" is unstable and is noted to be subject to black-hole collapse or to going super-nova.

I plan to clean it up and submit it to RIA NOVOSTI as an Infographic, since I like their Infographics. http://en.rian.ru/infographics/

I predict they reject it, but that is an unscientific prediction, I believe. O,o

Wishes, William of Boston

Plato said...

Hi William,

Better a question then, as to the descriptor of the "Nature of Time and Space?":)

I would hope that I could placed before any scientist the question as to how each individual would "draw this diagram" as to the nature of prediction, is a dance of sorts between them self and the world.

We are of course asking for responsibility in this process as to the "best image" that could possibly be deduced, that I would if could, place it before the edge.org as a question to all on the nature of this responsibility toward prediction.

I gave two examples by way of Penrose and Bee, as seeing the topological explanation in terms of relativity, is ever the question dynamically on where exactly we are in relation to the natural world, geometrically described by example toward identifying our relationship with the world.

Now I just given my example and now throw it out there for others to show how they would describe this "process to truth," as I have attempted to do.

Best,

Anonymous said...

Predicting the existence of superparters by string theory definitely qualifies as a scientific prediction. Just because there is no definite result about the mass spectrum does not in any way undermine this fact. Discovery of supersymmetry at the LHC will be the first confirmed prediction of string theory.

Bee said...

Anonymous: Oh yes, it does undermine this fact. And if you had read what I wrote you'd be wiser now. Show me that you can't have supersymmetry without string theory. Best,

B.

Anonymous said...

"Show me that you can't have supersymmetry without string theory."

Suppose the LHC discovered superpartners. We know that the scale of supersymmetry breaking is directly related to the mass of the gravitino - the superpartner of the graviton. (In gravity mediation the gravitino mass sets the scale of superpartner masses whereas in gauge mediation the gravitino is typically the LSP) The presence of the gravitino automatically implies not just global SUSY but its local extension - N=1 D=4 supergravity. N=1 D=4 supergravity is not a UV complete theory but arises as the low energy limit in string compactifications.

Back in 1973 Maskawa and Kobayashi's theory required that there be at least three families of quarks, a prediction that was confirmed experimentally. Note that they did not predict the masses of top and bottom quarks, only that they must exist!
The fact that Kobatashi and Maskawa's theory did not predict the masses of the third generation did not prevent them from getting the 2008 Nobel Prize, awarded in large part for predicting the existence of the third generation.

The fact that string theory requires (an therefore predicts) the existence of superpartners is definitely from the same catogory.

Bee said...

Anonymous: You didn't show what I asked you to (and if you could, I suggest you write a paper about it and just post the link here.) Besides this, Maskawa and Kobayashi knew there was CP violation, there was real data. If the LHC sees supersymmetry it means... there's supersymmetry. Not more and not less. This would clearly be good news for string theory, but that's about it. Your above argument is equivalent to the following: Consider that for whatever reasons people had worked on LQG before Newton had been around. Then they go and recover Newton's law, make a prediction, this prediction is found to be correct and they conclude fundamentally our spacetime is a string network. Oh. Wiat. There was a logical gap in this argument, no? If you really don't understand what I'm saying, ask yourself if you actually need string theory to compute any SUSY cross-section. Best,

B.

Bee said...

*lol* I meant spin network!

Anonymous said...

"If you really don't understand what I'm saying, ask yourself if you actually need string theory to compute any SUSY cross-section."

OK, in case you missed what I said, discovery of susy at the LHC automatically implies supergravity. Supergravity by itself is not a UV complete theory. Strings are the only known UV completion. So, for example, if you have some gauge mediated scenario, any process involving the gravitino LSP beyond the tree-level would require the knowledge of a UV complete theory. You don't suggest that it's ok to use N=1 D=4supergravity to compute multiloop amplitudes, do you?

Furthermore, in many SUSY models
people rely on higher order corrections to e.g. the Kahler potential, in order to find vacua with spontaneously broken SUSY, such corrections can only be computed if one knows the UV theory, i.e. string theory. There are plenty of papers where people are using s.t. tools to extract such corrections.
Writing a paper about this would be silly because what I'm saying is common knowledge. Some models of SUSY breaking are less sensitive to the UV physics than others but it's always there.

Bee said...

Anonymous: I did not miss what you said but you evidently didn't understand my reply. That one theory is the only UV completion of an observed feature you know doesn't proof it is. It's a logical gap. Consequently, observation of the feature does not allow you to draw the conclusion you want to draw. To make that very clear Strings => SUSY. For your claim to be true what's needed is SUSY => Strings. I'll repeat: saying it's the only known game in town is not a proof. You seem to know what you're talking about, so take a deep breath and notice there's a missing link in your argument. Finally, hiding behind anonymity is to me nothing but an expression of cowardice. Best,

B.

Anonymous said...

"I'll repeat: saying it's the only known game in town is not a proof."

Using this type of logic it's not a proof but until there are several alternative self-consistent frameworks that UV complete supergravity, other than string theory, your statement is empty. What you are saying is logically true but it's content free.

You can apply this logic to many phenomena, not just supersymmetry, and argue that the only existing known explanation/model is not the only possibility and therefore there is no proof that it is the "true" explanation. So, what?

BTW, thanks for the compliment, I'd suspected it was coming :)

Bee said...

My empty statement is simply that your claim is logically false, which you just agreed on. Thanks,

B.

Anonymous said...

But this logic, while logically sound, is completely empty because it's based on a hypothetical assumption. Look where your logic leads:

"To make that very clear BCS theory => low TC. For your claim to be true what's needed is low TC => BCS theory."

Hence, by the same logic one can always make the claim that there may exist yet another alternative to the BCS theory that reproduces low TC. So what? The above claim, just like your claim about string theory not being the only possible UV completion of supergravity is empty, unless you come up with a viable alternative that allows you to perform actual computations in order to answer some specific questions (e.g. higher order corrections to the tree-level Kahler potential in N=1 D=4 supergravity). But then again, someone can come and apply your logic again and again to any theory/model by saying that there may be yet another alternative that may reproduce the same corrections, spectrum, etc.

But this is not physics, it's pure sophistry!

stefan said...

To make a constructive suggestion, maybe anonymous could try to make his point without recourse to the "we all know..." rhetoric? - I, as a nuclear theorist, do not know.

Is it possible to explain why "we" know, what gives "us" the confidence, and why "we" can safely dismiss other options?

Phil Warnell said...
This comment has been removed by the author.
Phil Warnell said...

Hi Stefan.

Good point and thanks, for if you don’t know, how would those like me stand a chance to have it understood. It reminds me of what case law represents as being in the US, where things are thought fair to be decided based on precedent, rather than actual situational and circumstantial reasoning.

However, I think the greater problem Bee is facing in such situation is analogous to a concept found in some eastern philosophies where one is warned that the tallest nail is pounded down. That has our Anonymous friend rendered safe as leaving him not recognized as who be the pounder, while also not having it be known how tall he/she stands. Bee cites this as simply cowardice, yet I find there to be a difference between a foolish coward and a clever one, as the latter certainly represents to be the most ethically vacuous and therein the more dangerous kind. That’s why lady justice is shown to be wearing the blindfold, rather than the accused and/or the jury.

Best,

Phil

Anonymous said...

First of all, my previous post has not been displayed so I'm not sure if it makes sense to post again but I'll respond to Stefan anyway.

1) The only person who used "we all know" in this thread is Steven and you never objected to his usage of "We all know", so why are you criticizing my choice of words and not his?

2) If you prefer passive voice just replace "we know" to "it is known".

3) If something is not known to you personally it does not nullify any of the statements I made. If this topic is of any interest to you, all you need to do is pick up a texbook on supersymmetry/supergravity and look things up, or use Google.

4) When I said "common knowledge" I really meant that everything I had said is known to people working in this area and it would be ridiculous to publish a paper about it, as Bee had suggested.

5) If you are interested in the physics content of my posts fire away any questions you have but please don't pick on the choice of words. I'm not a lawyer :)

"Is it possible to explain why "we" know, what gives "us" the confidence, and why "we" can safely dismiss other options?"

I'm not working on formal string theory. I'd rather describe myself as a Beyond the Standard Model particle phenomenologist. However, as a matter of practice, string theory is the only AVAILABLE tool that allows to perform very specific computations in N=1 D=4 supergravity. There are no "other options" available that would allow to perform such computations. None! So there is NOTHING to dismiss. Until such options appear string theory is the only known way to compute certain quantities that are sensitive to the UV physics.

Anonymous said...

Let me give you one specific example of the type of a computation I'm talking about, which one would not be able to perform in the effective N=1 D=4 supergravity and where string theory can give you the answer.

So,here we go:
Suppose you want to compute the kinetic term for charged chiral matter multiplets (quarks or leptons).

If you read the literature on susy/supergravity you'll notice that often it is assumed that such kinetic terms are canonical (this is where mSUGRA (minimal supergravity) comes from). However, this assumption is often made because it makes the analysis easier, not because of some underlying symmetry reason.


In general, in N=1 D=4 supergravity such terms are non-canonical and depend on certain scalar fields called moduli. However, charged chiral matter fields are not part of the supergravity multiplet (in string theory they come from open strings), so their kinetic terms are not computable by doing any type of dimensional reduction of some higher dimensional supergravity theory. Note that I'm not even talking about some higher order corrections here, just tree-level. The only known way to obtain these is to use the worldsheet CFT methods. In particular, one needs to compute a scatting amplitude involving the moduli (closed string modes) and charged chiral matter (open string modes). Here is one example: http://arxiv.org/abs/hep-th/0404134

Anonymous said...

Sorry, this is the last point, related to the example I gave in the previous post. The importance of knowing the precise form of the kinetic terms for charged chiral matter fields is huge because it is directly related to the so-called flavor problem in gravity-mediated susy breaking scenarios. Any kind of kinetic mixing between sfermions from different families generically leads to Flavor Changing Neutral Currents. These are highly constrained by experiment, which makes one of the most popular scenarios of susy breaking, i.e. gravity mediation, highly sensitive to the UV physics. String worldsheet CFT techniques are the only known way to compute such couplings while supergravity alone has nothing to say about them. None of the "alternatives" come anywhere close to answering such questions.

Bee said...

Anonymous, Stefan, Phil:

As you probably noticed we have comment moderation on for all threads (like this) older than 14 days.

That's because 99.5% of all comments we get on posts older than 2 weeks are spam, and they typically come in bulks of 5-10 (some script I believe), sometimes several such bulks per day. Before blogger offered this feature of selective comment moderation we had to go and visit every single site, deleting these comments. Now they get piped into a comment moderation queue that I can visit when I like and hit "delete all." This has virtually limited the number of spam comments on this blog to zero and saves me a lot of time.

It has the disadvantage that your comments only appear when I have time to publish them. It wasn't clear to me that comments from blog administrators (Stefan and me) don't end in the moderation queue. Thus, it might have been confusing that Stefan's comment appeared and Anonymous'/Phil's didn't. I see however that now that I published them they are in the correct time order.

Bee said...

Anonymous:

Your example about BCS theory unfortunately shows that you still didn't understand what I've been telling you. If I relate that example to your initial claim, BCS theory is the analogue of SUSY, not string theory. BCS theory doesn't force on you a whole bulk of untestable "sophistry". (Wait, BSC is a prediction of string theory, or is it?)

Since my above example about Newton's law was evidently too abstract for you, I'll give you a different example. Why hasn't Higgs gotten the Nobelprize yet? We know that particles have masses. Arguably the Higgs mechanism is THE commonly accepted explanation. We know it is. Clearly though, there's no proof that particle masses => Higgs (let's not dwell on what different Higgses are possible, that's not the point). Consequently, before the committee gives out a Nobelprize they want to see a Higgs (rspt any decent signature, you know what I mean). Similarly, before you can claim we have evidence for strings, you'll have to show me a string. Not a susy particle. I hope you notice that your later elaborations pulling on computations of specific processes are already very far off your initial claim. Your initial claim was "The existence of superparters is a scientific prediction by string theory." Meanwhile we're at "In some currently investigated scenarions string theory techniques are used to compute certain cross-sections."

Best,

B.

Bee said...

Hi Phil,

Yes, and that's exactly why every anonymous coward like this one gets me a step closer to disabling anonymous comments. While I am here signing with my name, if he finally understands why he's wrong he can just walk around continuing to spread his mistaken beliefs. For him, it's a win-win situation, while I lose (at the very least I lose time) anyway. And that's exactly why it is nothing but cowardice: our anonymous friend is clearly afraid to be shown wrong, he's afraid of damaging his reputation. Best,

B.

Bee said...

Anonymous,
Forgot: You said "it would be ridiculous to publish a paper about it, as Bee had suggested." What I asked you to publish a paper about is what you then figured out to be logically false. Best,

B.

stefan said...

I had not seen that there is a comment by anonymous in the queue.

BCS theory seems to be, actually, a very instructive example. As we know, superconductivity was an experimentally thoroughly studied phenomenon by the 1950s, and BCS theory was the long searched-for explanation, which turned out to be much wider in scope than just to explain conventional superconductivity.

Let's suppose some nuclear theorists had come up with BCS before the phenomenon of superconductivity was established (as we know, BCS applies to nuclear structure) and hence, predicted its existence. Let's further suppose the liquid-nitrogen cuprate superconductors were discovered before the conventional superconductors. What would this have told us about BCS? At least, it should not have been discarded as a theory of superconductivity.

Bee said...

I never said or even hinted at "discarding" string theory. What I'm saying is: suppose somebody explained electrons are actually noiseless subsystems in spin-foams and these electrons can form Cooper-pairs and lead to the phenomenon of superconductivity. Now you observe superconductivity. Can you conclude the world is a spin-foam network? No, because you haven't actually tested anything particular for the underlying theory. That this might at the time being be the only known explanation for what an electron "is" is entirely irrelevant. Same thing with supersymmetry. If you observe SUSY partners at the LHC you have evidence that SUSY is realized in Nature. Not more and not less. What anonymous is further saying is that if you carefully measure cross-sections you should further be able to pin down details of the model/SUSY-breaking etc. That's certainly true but quite far off his original bold statement that "Discovery of supersymmetry at the LHC will be the first confirmed prediction of string theory." (Finally, let me ask the obvious question: If the LHC sees no evidence for SUSY, can we consider string theory it falsified?)

Steven Colyer said...

I would consider ST on the ropes if SUSY particles are not found at the energies string theorists predict, especially Vafa's prediction of the stau, but ... you know String Theorists! Backed against a wall as they have been many times since '68 and bosonic strings, they find a way out. :-P

Nevertheless Bee's point is well taken. The discovery of SUSY's will not validate Strings, it merely won't INvalidate them. Superstring theory is far from the only one for which SUSY is applicable.

14 posts up, anonymous wrote:

"I'll repeat: saying it's the only known game in town is not a proof."
Using this type of logic it's not a proof but until there are several alternative self-consistent frameworks that UV complete supergravity, other than string theory, your statement is empty. What you are saying is logically true but it's content free.


From Wiki under UV completion:

In theoretical physics, UV completion of a quantum field theory A is another quantum field theory (or a more generalized theory) B that reduces to A below some energy scale (the cutoff of A). However, theory B must be, unlike theory A, well-defined at arbitrarily high energies; i.e. in the ultraviolet regime (this is the origin of the adjective "UV").

The theory B must be renormalizable; it can have no Landau poles; and most typically, B enjoys asymptotic freedom in the case that B is a quantum field theory (or at least has a nontrivial UV fixed point). However, B may also be a background of string theory whose UV behavior is at least as good as that of renormalizable quantum field theories. Besides these two known examples (QFT and string theory), it could be a completely different theory than string theory that behaves well at very high energies.

from Wiki under Hořava gravity:

The theory relies on the theory of foliations to produce its causal structure. It is related to topologically massive gravity and the Cotton tensor. It is a possible UV completion of general relativity.

pawned. ;-p

Phil Warnell said...

Hi Bee & Stefan,

Personally that’s the difficulty I have with these new theories that appear to have a grab bag of things they can account for, rather than serving to minimize what they should and can be. Of course the current consensus would say that’s my problem, as insisting our reality being only one possible outcome out of many equally viable ones. I’m then left to wonder whether qualities of nature such as action principle, invariance, covariance , entropy and conservation are themselves optional in terms of what can be and what cannot? That’s to say our reality seems to be very restrictive from the standpoint of order and outcome, while some of the new theories having few if any at all. Perhaps all this is reasonable yet I never could imagine how, as to me it is not only to insist you don’t need a chicken to have an egg, yet even if you have the egg you’re not guaranteed ending up with a chicken. Then again perhaps I’m just showing my age :-)

Best,

Phil

Tracy Allison Altman said...

Great food for thought. Especially pleased that you're emphasizing the *explanatory* power of scientific theory & prediction. We wrote about your post on our site ExplanationScience.org - where we are dedicated to the science of explaining. (Explaining is one of the most important things people do, but it hasn't received enough attention. We’re changing that.)

Paco Ahlgren said...

How Can String Theory Be Science if it Isn’t Falsifiable?
I’m not throwing string theory out the window yet, but when even its leading proponents — and the people who claim to understand it best — admit they can’t prove any of its major tenets (contextually, of course), well… that’s a big problem.