Is String Theory Is String Theory Scientific?Scientific?

Keizo.Matsubara@filosofi.uu.Keizo.Matsubara@filosofi.uu.sese

andand

Lars-Goran.Johansson@filosofLars-Goran.Johansson@filosofi.uu.sei.uu.se

A quote from the works of A quote from the works of Richard P. FeynmanRichard P. Feynman

“ “Philosophers say a great deal about Philosophers say a great deal about what is absolutely necessary for what is absolutely necessary for science, and it is always, so far as science, and it is always, so far as one can see, rather naïve, and one can see, rather naïve, and probably wrong.”probably wrong.”

The Feynman Lectures on PhysicsThe Feynman Lectures on Physics. . Ch. 1, Vol. I Ch. 1, Vol. I

There is no real consensus There is no real consensus among philosophers among philosophers

Philosophers disagree about almost Philosophers disagree about almost everything!everything!

Our business as philosophers is to Our business as philosophers is to question presuppositions usually made question presuppositions usually made by scientists, philosophers and people in by scientists, philosophers and people in general. general.

When one criticizes philosophy in When one criticizes philosophy in general it is very hard to avoid general it is very hard to avoid formulating a new philosophical position.formulating a new philosophical position.

A few comments on the A few comments on the discussion discussion

There have been opponents to string There have been opponents to string theory for a long time. Many theory for a long time. Many experimentalists have been skeptical. experimentalists have been skeptical. Criticism have also been expressed by Criticism have also been expressed by philosophers of science.philosophers of science.

The books by Smolin and Woit caused The books by Smolin and Woit caused further debate.further debate.

The discussion has partly been too The discussion has partly been too simplistic and held as if though Popper simplistic and held as if though Popper was the only relevant philosopher to was the only relevant philosopher to discuss.discuss.

Many perspectivesMany perspectives

We will look at how string theory would be We will look at how string theory would be evaluated according to the following evaluated according to the following different perspectives:different perspectives:

Logical PositivistsLogical Positivists PopperPopper Kuhn Kuhn LakatosLakatos Feyerabend Feyerabend

Different answers will be given. Different answers will be given.

Logical positivistsLogical positivists

The Vienna circleThe Vienna circle Empiricist views on scienceEmpiricist views on science Verification criterion for meaningVerification criterion for meaning InstrumentalistInstrumentalist AntimetaphysicalAntimetaphysical Stressed the use of strict logical Stressed the use of strict logical

methodsmethods Inductive methodInductive method

Logical positivism and Logical positivism and string theorystring theory

String theory would be considered strictly String theory would be considered strictly speaking meaningless since it does not speaking meaningless since it does not connect to experiment. connect to experiment.

Since they are basically supporting Since they are basically supporting induction as the basis for scientific method induction as the basis for scientific method they conceived of the development of a they conceived of the development of a theory coming after the data. theory coming after the data.

The “work in progress”- argument can be The “work in progress”- argument can be made, but that would be questionable made, but that would be questionable given the assumptions. given the assumptions.

NoteNote

There are really no philosophers who There are really no philosophers who defend traditional logical positivism. defend traditional logical positivism.

Some of their views, however, remain Some of their views, however, remain influential to the way scientists and influential to the way scientists and philosophers think about science.philosophers think about science.

Internal problems with the position and Internal problems with the position and severe criticism has destroyed it. severe criticism has destroyed it.

PopperPopper

Hypothetico-deductive method.Hypothetico-deductive method. A scientific theory needs to be falsifiable.A scientific theory needs to be falsifiable. A theory could be meaningful although A theory could be meaningful although

not falsifiable, thus not scientific.not falsifiable, thus not scientific. Popper have nothing against speculations Popper have nothing against speculations

and metaphysical assumptions in and metaphysical assumptions in principle, but it is only when a theory is principle, but it is only when a theory is put into a falsifiable formulation that a put into a falsifiable formulation that a theory is scientific.theory is scientific.

Hypothetico-deductive Hypothetico-deductive methodmethod

H=hypothesisH=hypothesis

E=empirical consequenceE=empirical consequence

HHE HE HEE

Not E ENot E E

______ ------------______ ------------

H falsified H supported H falsified H supported /corroborated /corroborated

Popperazzi?Popperazzi?

Susskind mentions the Feynman Susskind mentions the Feynman statement, quoted earlier, which statement, quoted earlier, which expressed a less than favorable expressed a less than favorable description of philosophers. He clearly description of philosophers. He clearly implies that the criticism directed implies that the criticism directed towards philosophers in general towards philosophers in general applied to Popper in particular.applied to Popper in particular.

But what was Feynman’s own views on But what was Feynman’s own views on scientific method?scientific method?

Scientific Method according Scientific Method according to Feynmanto Feynman

““In general we look for a new law by the In general we look for a new law by the following process. First we guess it. Then we following process. First we guess it. Then we compute the consequences of the guess to see compute the consequences of the guess to see what would be implied if this law that we what would be implied if this law that we guessed is right. Then we compare the result guessed is right. Then we compare the result of the computation to nature, with experiment of the computation to nature, with experiment or experience, compare it directly with or experience, compare it directly with observation, to see if it works. If it disagrees observation, to see if it works. If it disagrees with experiment it is wrong. In that simple with experiment it is wrong. In that simple statement is the key to science. It does not statement is the key to science. It does not make any difference how beautiful your guess make any difference how beautiful your guess is. It does not make any difference how smart is. It does not make any difference how smart you are, who made the guess or what his name you are, who made the guess or what his name is – if it disagrees with experiment it is wrong.”is – if it disagrees with experiment it is wrong.”

Scientific Method according Scientific Method according to Feynman, continuedto Feynman, continued

““You can see of course, that with this You can see of course, that with this method we can attempt to disprove any method we can attempt to disprove any definite theory. If we have a definite definite theory. If we have a definite theory, a real guess, from which we can theory, a real guess, from which we can conveniently compute consequences conveniently compute consequences which can be compared with experiment which can be compared with experiment then in principle we can get rid of any then in principle we can get rid of any theory. There is always the possibility of theory. There is always the possibility of proving a definite theory wrong; but proving a definite theory wrong; but notice that we can never prove it right.”notice that we can never prove it right.”

Scientific Method according Scientific Method according to Feynman, continuedto Feynman, continued

““Suppose that you invent a guess, calculate Suppose that you invent a guess, calculate the consequences, and discover every time the consequences, and discover every time that the consequences you have calculated that the consequences you have calculated agree with experiment. The theory is then agree with experiment. The theory is then right? No, it is simply not proved wrong. In right? No, it is simply not proved wrong. In the future you could compute a wider range the future you could compute a wider range of consequences, there could be a wider of consequences, there could be a wider range of experiments and you might then range of experiments and you might then discover that the thing is wrong”discover that the thing is wrong”

The Character of Physical Law pp. 156-158The Character of Physical Law pp. 156-158

What does this show?What does this show? Not very much; only that Susskind can not Not very much; only that Susskind can not

claim to have an ally in Feynman when claim to have an ally in Feynman when defending string theory against the defending string theory against the “Popperazzi”.“Popperazzi”.

It should also be noted that Feynman was It should also be noted that Feynman was highly critical of string theory, to a large highly critical of string theory, to a large extent for Popperian reasons. Since extent for Popperian reasons. Since Feynman died in 1988 all he said regarding Feynman died in 1988 all he said regarding string theory refers to the theory before string theory refers to the theory before that but it is hard to think that he would that but it is hard to think that he would have changed his assessment. have changed his assessment.

A Popperian evaluation of A Popperian evaluation of String theory String theory

String theory is not meaninglessString theory is not meaningless String theory is not yet falsifiable and is String theory is not yet falsifiable and is

hence not yet a scientific theory.hence not yet a scientific theory. The “work in progress”- argument can more The “work in progress”- argument can more

plausibly be used here to defend research in plausibly be used here to defend research in string theory as legitimate, as long as one string theory as legitimate, as long as one admits that one has not yet succeeded in admits that one has not yet succeeded in formulating a scientific theory.formulating a scientific theory.

Comparison should be made with the Comparison should be made with the examples Popper criticized viz. examples Popper criticized viz. Psychoanalysis and Marxism. The situation is Psychoanalysis and Marxism. The situation is NOT the same as the one for string theory…NOT the same as the one for string theory…

There are problems with There are problems with Popper’s views on science!Popper’s views on science!

To derive consequences from a To derive consequences from a hypothesis one typically need to use a hypothesis one typically need to use a host of different auxiliary assumptions host of different auxiliary assumptions and when things do not turn out as and when things do not turn out as expected one can blame the auxiliary expected one can blame the auxiliary assumptions.assumptions.

When modifying auxiliary assumptions When modifying auxiliary assumptions one is supposed to avoid modifications one is supposed to avoid modifications that are that are ad hocad hoc..

It is however not at all easy to define ad It is however not at all easy to define ad hocness clearly. hocness clearly.

KuhnKuhn

ParadigmsParadigms Normal Science vs. Revolutionary Normal Science vs. Revolutionary

ScienceScience Puzzle SolvingPuzzle Solving IncommensurabilityIncommensurability

Normal science in string Normal science in string theory?theory?

String theory is clearly so well defined String theory is clearly so well defined so that puzzles and problems can be so that puzzles and problems can be formulated and solved within the formulated and solved within the framework. The puzzles are however framework. The puzzles are however only of a theoretical nature and does only of a theoretical nature and does that really count?that really count?

String theory has many of the features String theory has many of the features expected by a mature science but since expected by a mature science but since it does not yet solve puzzles connected it does not yet solve puzzles connected with experiment it is not clear how Kuhn with experiment it is not clear how Kuhn would have described that.would have described that.

A Kuhnian evaluation of A Kuhnian evaluation of string theorystring theory

It is not completely clear whether or not It is not completely clear whether or not Kuhn’s analysis applies.Kuhn’s analysis applies.

String theory has some features of normal String theory has some features of normal science.science.

Kuhn’s position is largely descriptive and Kuhn’s position is largely descriptive and not particularly normative. A point might not particularly normative. A point might be made that the dominance of a paradigm be made that the dominance of a paradigm might have occurred even when there are might have occurred even when there are no experiments, and the processes behind no experiments, and the processes behind this might be more or less the same… this might be more or less the same…

LakatosLakatos Lakatos’ position is to some extent similar to Lakatos’ position is to some extent similar to

Kuhn’s but he denies incommensurability.Kuhn’s but he denies incommensurability. He uses the term “research program” instead He uses the term “research program” instead

of “paradigm” but what they refer to is roughly of “paradigm” but what they refer to is roughly similar.similar.

A research program have basic assumptions in A research program have basic assumptions in the “hard core” these should not be questioned the “hard core” these should not be questioned within the program. If you abandon them you within the program. If you abandon them you have abandoned the program.have abandoned the program.

Lakatos basic norm is that it is rational to Lakatos basic norm is that it is rational to leave a degenerate program in favor of a leave a degenerate program in favor of a progressive one. (This is not a strict rule…but progressive one. (This is not a strict rule…but rather a rule of thumb.) rather a rule of thumb.)

A Lakatosian evaluation of A Lakatosian evaluation of string theorystring theory

String theory could be considered String theory could be considered theoretically progressive but not theoretically progressive but not progressive in the way Lakatos intended, progressive in the way Lakatos intended, since it is only solving theoretical puzzles. since it is only solving theoretical puzzles.

One should not abandon a research One should not abandon a research program unless there is a better program unless there is a better alternative. alternative.

String Theory roughly fits into Lakatos String Theory roughly fits into Lakatos conception of a scientific research program conception of a scientific research program and can thus be considered scientific. and can thus be considered scientific.

A new norm?A new norm?

According to a Lakatosian view String According to a Lakatosian view String Theory would be respectable. But so Theory would be respectable. But so would other approaches. If a research would other approaches. If a research program becomes empirically progressive program becomes empirically progressive it would be rational to focus on that. But it would be rational to focus on that. But when programs that are only theoretically when programs that are only theoretically progressive to various degrees are progressive to various degrees are competing which strategy would be best competing which strategy would be best to use? Is there a risk with having a to use? Is there a risk with having a dominant program such as string theory?dominant program such as string theory?

Another quote from Another quote from FeynmanFeynman

“ “ If every individual student follows the If every individual student follows the same current fashion in expressing and same current fashion in expressing and thinking about [the generally understood thinking about [the generally understood areas], then the variety of hypotheses areas], then the variety of hypotheses being generated to understand [the still being generated to understand [the still open problems] is limited. Perhaps open problems] is limited. Perhaps rightly so, for possibly the chance is high rightly so, for possibly the chance is high the truth lies in the fashionable the truth lies in the fashionable direction. But [if] it is another direction direction. But [if] it is another direction … who will find it? ”… who will find it? ”

From the Nobel Lecture 1965.From the Nobel Lecture 1965.

FeyerabendFeyerabend

Since no strict effective rules can be Since no strict effective rules can be specified that once and for all define specified that once and for all define scientific method there really is no scientific method there really is no scientific method.scientific method.

““Anything goes!”. What did he mean?Anything goes!”. What did he mean? Feyerabend have said things to the Feyerabend have said things to the

effect that there is no real difference effect that there is no real difference between science compared with voodoo, between science compared with voodoo, astrology or any other theories or astrology or any other theories or worldviews.worldviews.

A Feyerabendian evaluation A Feyerabendian evaluation of of

String TheoryString Theory Since Feyerabend abandons the Since Feyerabend abandons the

question to even try to find criteria question to even try to find criteria for scientific method he basically for scientific method he basically allows anything and would of course allows anything and would of course also accept string theory.also accept string theory.

Of course Feyerabend’s radical Of course Feyerabend’s radical position is probably not acceptable position is probably not acceptable to most scientists.to most scientists.

Should philosophers dictate Should philosophers dictate scientific method?scientific method?

The point is not that philosophers dictate The point is not that philosophers dictate questions of method. What methods are questions of method. What methods are applied is decided by the practicing applied is decided by the practicing scientists but there is a constant debate scientists but there is a constant debate on the issues and the philosophers are on the issues and the philosophers are participants in this debate. participants in this debate.

We believe that it is beneficial for We believe that it is beneficial for scientists to be at least aware of how scientists to be at least aware of how these problems are discussed and the these problems are discussed and the different philosophical position there different philosophical position there are.are.

Conclusions: Is String Conclusions: Is String Theory Scientific?Theory Scientific?

Logical Positivism : No, but…Logical Positivism : No, but… Popper : Not yet, but… Popper : Not yet, but… Kuhn : Well maybe, Kuhn : Well maybe,

but… but… Lakatos : Yes, but…Lakatos : Yes, but… Feyerabend : Who cares?! Feyerabend : Who cares?!