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SELECTED READINGS FOR ESSAY 3 (IV)

SELECTED READINGS FOR ESSAY 3 (IV)

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String theory and its experimental foundation

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In spite of the significant effort that string theorists have made to gain credibility and respect from other physicists there is still no global consensus regarding the way they conceive science. Criticisms concerning the lack of a concrete link between mathematical formulae and the empirical physical world are abound, especially from physicists with a more experimental orientation. In the previous section I have shown how diverse interpretations of the past, made by groups with different traditions, are often exploited in order to promote a certain way of doing science. This is the case with the connection between the concept of beauty as seen by string theorists and the experimental tradition of science.

One group of detractors, educated in the experimental tradition, argue that it is absurd to talk about the mathematical beauty of a physical theory before any experimental verification. As they see it, there might be many beautiful theories but there can only be one that accurately describes reality. It is the goal of the experiment to determine the right one. If Maxwell’s theory is correct it is because it predicted the electromagnetic waves then discovered by Hertz; Dirac’s equation is exact for the simple reason that positrons were discovered in the early thirties by Carl Anderson; the standard model is correct since its prediction of the existence and precise properties of the intermediate bosons W and Z was confirmed at CERN in 1983 (in addition to this, the last quark, the top or truth, was discovered in 1995 at Fermilab); and Einstein’s general theory of relativity is truthful only because the bending of light was conclusively confirmed in 1919 by Arthur Eddington. To them, string theorists reply that they are proceeding in the same exemplary way as Einstein and Dirac did: ‘‘In a certain sense, therefore, I hold it true that pure [mathematical] thought can grasp [the unique] reality, as the ancients dreamed.’’ In this famous sentence Einstein implicitly assumed that there is a one to one relationship between the natural and the mathematical world. To ‘‘grasp’’ the mathematical world means to understand nature. Then, there cannot be many beautiful theories for a unique natural world, as some string theory critics maintain; rather, there is one unique beautiful and simple theory for a unique physical reality. And, string theorists sustain, in the same way as general relativity is the unique theory precisely describing gravitational phenomena, superstring theory is the unique consistent theory describing the whole physical world. This belief is shared by many contemporary theoretical gravitational physicists: ‘‘Within theoretical physics, the search for logical self-consistency has been always more important for progress than experimental results.’’[source] This confidence is their motivation for pushing onward with the theory.

As it was proved a posteriori that Einstein had been right to remain optimistic regarding his general theory of relativity, string theorists believe that the ‘‘beautiful structure’’ of their theory will be someday verified in the laboratories. Every physicist knows that when Einstein was asked about the possibility that Eddington’s observations could have disproved his gravitational theory he replied: ‘‘I would have felt sorry of the dear Lord, because the theory is correct.’’ Similarly, David Gross says: ‘‘Never, never, never, never give up!’’ For string theorists, the validity of the theory cannot solely rely on the results of future ‘‘crucial experiments.’’ If a theory is beautiful, that is, correct, experiments cannot change that. When John Schwarz was asked about the risk of superstring theory being invalidated by experiments, he emphatically replied:

The above argument can be summarized in one single phrase: string theorists, by means of mathematical beauty and simplicity, discover rather than invent.

Another common criticism, also coming from the experimental tradition, asserts that the development of the theory has ignored the most recent experimental data. Philip Anderson, a distinguished condensed matter physicist, is one of these critics and is convinced that string theory is taking us back to the pre-scientific era:

To these attacks, string theorists are prompt to respond that Newton did not require any observational data to discover his gravitational law (he was isolated from everything else due to the plague hitting Europe) neither did Einstein need any to discover the theory of relativity (in fact, during his ‘‘annus mirabilis’’ he was confined in a gloomy patent office). It is thus currently claimed that if physicists are sufficiently smart, ‘‘pure thought’’ is more than enough to unravel the ‘‘ultimate truths of the universe.’’

Even though theoretical physicists differ on certain points with colleagues who have a more experimentalist disposition, there is fundamental agreement on one point: the existence of an ordered world governed by simple laws which are there to be ‘‘dis-covered.’’ Both groups are convinced that nature is ruled by simple mathematical laws. The main difference between them is that one thinks that these laws can be discovered only by means of experience, and the other group believes that they can bypass natural experience and reach reality through pure thought. However, they concur with each other that nature and its mathematical description is beautiful. Modern physics would be inconceivable without this premise.

Recently, Leonard Susskind has proposed the possibility, within string theory, that the laws of physics may not be as elegant as it has been proclaimed:

It is impossible to know the transcendence that Susskind’s words will have in the near future in the realm of theoretical physics and superstring theory. Maybe none. Nevertheless, one thing is certain: Western science will look completely different the day it stops believing in and searching for beautiful physical laws.

One group of detractors, educated in the experimental tradition, argue that it is absurd to talk about the mathematical beauty of a physical theory before any experimental verification. As they see it, there might be many beautiful theories but there can only be one that accurately describes reality. It is the goal of the experiment to determine the right one. If Maxwell’s theory is correct it is because it predicted the electromagnetic waves then discovered by Hertz; Dirac’s equation is exact for the simple reason that positrons were discovered in the early thirties by Carl Anderson; the standard model is correct since its prediction of the existence and precise properties of the intermediate bosons W and Z was confirmed at CERN in 1983 (in addition to this, the last quark, the top or truth, was discovered in 1995 at Fermilab); and Einstein’s general theory of relativity is truthful only because the bending of light was conclusively confirmed in 1919 by Arthur Eddington. To them, string theorists reply that they are proceeding in the same exemplary way as Einstein and Dirac did: ‘‘In a certain sense, therefore, I hold it true that pure [mathematical] thought can grasp [the unique] reality, as the ancients dreamed.’’ In this famous sentence Einstein implicitly assumed that there is a one to one relationship between the natural and the mathematical world. To ‘‘grasp’’ the mathematical world means to understand nature. Then, there cannot be many beautiful theories for a unique natural world, as some string theory critics maintain; rather, there is one unique beautiful and simple theory for a unique physical reality. And, string theorists sustain, in the same way as general relativity is the unique theory precisely describing gravitational phenomena, superstring theory is the unique consistent theory describing the whole physical world. This belief is shared by many contemporary theoretical gravitational physicists: ‘‘Within theoretical physics, the search for logical self-consistency has been always more important for progress than experimental results.’’[source] This confidence is their motivation for pushing onward with the theory.

As it was proved a posteriori that Einstein had been right to remain optimistic regarding his general theory of relativity, string theorists believe that the ‘‘beautiful structure’’ of their theory will be someday verified in the laboratories. Every physicist knows that when Einstein was asked about the possibility that Eddington’s observations could have disproved his gravitational theory he replied: ‘‘I would have felt sorry of the dear Lord, because the theory is correct.’’ Similarly, David Gross says: ‘‘Never, never, never, never give up!’’ For string theorists, the validity of the theory cannot solely rely on the results of future ‘‘crucial experiments.’’ If a theory is beautiful, that is, correct, experiments cannot change that. When John Schwarz was asked about the risk of superstring theory being invalidated by experiments, he emphatically replied:

I believe that we have found the unique mathematical structure that consistently combines quantum mechanics and general relativity. So it must almost certainly be correct. For this reason, even though I do expect supersymmetry to be found, I would not abandon this theory if supersymmetry turns out to be absent.[source]

The above argument can be summarized in one single phrase: string theorists, by means of mathematical beauty and simplicity, discover rather than invent.

Another common criticism, also coming from the experimental tradition, asserts that the development of the theory has ignored the most recent experimental data. Philip Anderson, a distinguished condensed matter physicist, is one of these critics and is convinced that string theory is taking us back to the pre-scientific era:

My belief is based on the fact that string theory is the first science in hundreds of years to be pursued in pre-Baconian fashion, without any adequate experimental guidance. It proposes that Nature is the way we would like it to be rather than the way we see it to be; and it is improbable that Nature thinks the same way we do.[source]

To these attacks, string theorists are prompt to respond that Newton did not require any observational data to discover his gravitational law (he was isolated from everything else due to the plague hitting Europe) neither did Einstein need any to discover the theory of relativity (in fact, during his ‘‘annus mirabilis’’ he was confined in a gloomy patent office). It is thus currently claimed that if physicists are sufficiently smart, ‘‘pure thought’’ is more than enough to unravel the ‘‘ultimate truths of the universe.’’

Even though theoretical physicists differ on certain points with colleagues who have a more experimentalist disposition, there is fundamental agreement on one point: the existence of an ordered world governed by simple laws which are there to be ‘‘dis-covered.’’ Both groups are convinced that nature is ruled by simple mathematical laws. The main difference between them is that one thinks that these laws can be discovered only by means of experience, and the other group believes that they can bypass natural experience and reach reality through pure thought. However, they concur with each other that nature and its mathematical description is beautiful. Modern physics would be inconceivable without this premise.

Recently, Leonard Susskind has proposed the possibility, within string theory, that the laws of physics may not be as elegant as it has been proclaimed:

Physicists, particularly theoretical physicists, have a very strong sense of beauty, elegance, and uniqueness. They have always believed that the laws of nature are the unique inevitable consequence of some elegant mathematical principle. The belief is so deeply ingrained that most of my colleagues would feel an immense sense of loss and disappointment if this uniqueness and elegance turned out to be absent-if the Laws of Physics are “ugly” … . Despite the protestations of physicists that the laws of elementary particles are elegant, the empirical evidence points much more convincingly to the opposite conclusion.[source]

It is impossible to know the transcendence that Susskind’s words will have in the near future in the realm of theoretical physics and superstring theory. Maybe none. Nevertheless, one thing is certain: Western science will look completely different the day it stops believing in and searching for beautiful physical laws.

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SELECTED READINGS FOR ESSAY 3 (IV)

SELECTED READINGS FOR ESSAY 3 (IV)

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