08/20/2018

Long and Winding Road: A Conversation with String Theory Pioneer

John Schwarz discusses the history and evolution of superstring theory

The decades-long quest for a theory that would unify all the known forces—from the microscopic quantum realm to the macroscopic world where gravity dominates—has had many twists and turns. The current leading theory, known as superstring theory and more informally as string theory, grew out of an approach to theoretical particle physics, called S-matrix theory, which was popular in the 1960s. Caltech's John H. Schwarz, the Harold Brown Professor of Theoretical Physics, Emeritus, began working on the problem in 1971, while a junior faculty member at Princeton University. He moved to Caltech in 1972, where he continued his research with various collaborators from other universities. Their studies in the 1970s and 1980s would dramatically shift the evolution of the theory and, in 1984, usher in what's known as the first superstring revolution.

Essentially, string theory postulates that our universe is made up, at its most fundamental level, of infinitesimal tiny vibrating strings and contains 10 dimensions—three for space, one for time, and six other spatial dimensions curled up in such a way that we don't perceive them in everyday life or even with the most sensitive experimental searches to date. One of the many states of a string is thought to correspond to the particle that carries the gravitational force, the graviton, thereby linking the two pillars of fundamental physics—quantum mechanics and the general theory of relativity, which includes gravity.

We sat down with Schwarz to discuss the history and evolution of string theory and how the theory itself might have moved past strings.

What are the earliest origins of string theory?

The first study often regarded as the beginning of string theory came from an Italian physicist named Gabriele Veneziano in 1968. He discovered a mathematical formula that had many of the properties that people were trying to incorporate in a fundamental theory of the strong nuclear force [a fundamental force that holds nuclei together]. This formula was kind of pulled out of the blue, and ultimately Veneziano and others realized, within a couple years, that it was actually describing a quantum theory of a string—a one-dimensional extended object.

How did the field grow after this paper?

In the early '70s, there were several hundred people worldwide working on string theory. But then everything changed when quantum chromodynamics, or QCD—which was developed by Caltech's Murray Gell-Mann [Nobel Laureate, 1969] and others—became the favored theory of the strong nuclear force. Almost everyone was convinced QCD was the right way to go and stopped working on string theory. The field shrank down to just a handful of people in the course of a year or two. I was one of the ones who remained.

How did Gell-Mann become interested in your work?

Gell-Mann is the one who brought me to Caltech and was very supportive of my work. He took an interest in studies I had done with a French physicist, André Neveu, when we were at Princeton. Neveu and I introduced a second string theory. The initial Veneziano version had many problems. There are two kinds of fundamental particles called bosons and fermions, and the Veneziano theory only described bosons. The one I developed with Neveu included fermions. And not only did it include fermions but it led to the discovery of a new kind of symmetry that relates bosons and fermions, which is called supersymmetry. Because of that discovery, this version of string theory is called superstring theory.

When did the field take off again?

A pivotal change happened after work I did with another French physicist, Joël Scherk, whom Gell-Mann and I had brought to Caltech as a visitor in 1974. During that period, we realized that many of the problems we were having with string theory could be turned into advantages if we changed the purpose. Instead of insisting on constructing a theory of the strong nuclear force, we took this beautiful theory and asked what it was good for. And it turned out it was good for gravity. Neither of us had worked on gravity. It wasn't something we were especially interested in but we realized that this theory, which was having trouble describing the strong nuclear force, gives rise to gravity. Once we realized this, I knew what I would be doing for the rest of my career. And I believe Joël felt the same way. Unfortunately, he died six years later. He made several important discoveries during those six years, including a supergravity theory in 11 dimensions.

Surprisingly, the community didn't respond very much to our papers and lectures. We were generally respected and never had a problem getting our papers published, but there wasn't much interest in the idea. We were proposing a quantum theory of gravity, but in that era physicists who worked on quantum theory weren't interested in gravity, and physicists who worked on gravity weren't interested in quantum theory.

That changed after I met Michael Green [a theoretical physicist then at the University of London and now at the University of Cambridge], at the CERN cafeteria in Switzerland in the summer of 1979. Our collaboration was very successful, and Michael visited Caltech for several extended visits over the next few years. We published a number of papers during that period, which are much cited, but our most famous work was something we did in 1984, which had to do with a problem known as anomalies.

What are anomalies in string theory?

One of the facts of nature is that there is what's called parity violation, which means that the fundamental laws are not invariant under mirror reflection. For example, a neutrino always spins clockwise and not counterclockwise, so it would look wrong viewed in a mirror. When you try to write down a fundamental theory with parity violation, mathematical inconsistencies often arise when you take account of quantum effects. This is referred to as the anomaly problem. It appeared that one couldn't make a theory based on strings without encountering these anomalies, which, if that were the case, would mean strings couldn't give a realistic theory. Green and I discovered that these anomalies cancel one another in very special situations.

When we released our results in 1984, the field exploded. That's when Edward Witten [a theoretical physicist at the Institute for Advanced Study in Princeton], probably the most influential theoretical physicist in the world, got interested. Witten and three collaborators wrote a paper early in 1985 making a particular proposal for what to do with the six extra dimensions, the ones other than the four for space and time. That proposal looked, at the time, as if it could give a theory that is quite realistic. These developments, together with the discovery of another version of superstring theory, constituted the first superstring revolution.

Richard Feynman was here at Caltech during that time, before he passed away in 1988. What did he think about string theory?

After the 1984 to 1985 breakthroughs in our understanding of superstring theory, the subject no longer could be ignored. At that time it acquired some prominent critics, including Richard Feynman and Stephen Hawking. Feynman's skepticism of superstring theory was based mostly on the concern that it could not be tested experimentally. This was a valid concern, which my collaborators and I shared. However, Feynman did want to learn more, so I spent several hours explaining the essential ideas to him. Thirty years later, it is still true that there is no smoking-gun experimental confirmation of superstring theory, though it has proved its value in other ways. The most likely possibility for experimental support in the foreseeable future would be the discovery of supersymmetry particles. So far, they have not shown up.

What was the second superstring revolution about?

The second superstring revolution occurred 10 years later in the mid '90s. What happened then is that string theorists discovered what happens when particle interactions become strong. Before, we had been studying weakly interacting systems. But as you crank up the strength of the interaction, a 10th dimension of space can emerge. New objects called branes also emerge. Strings are one dimensional; branes have all sorts of dimensions ranging from zero to nine. An important class of these branes, called D-branes, was discovered by the late Joseph Polchinski [BS '75]. Strings do have a special role, but when the system is strongly interacting, then the strings become less fundamental. It's possible that in the future the subject will get a new name but until we understand better what the theory is, which we're still struggling with, it's premature to invent a new name.

What can we say now about the future of string theory?

It's now over 30 years since a large community of scientists began pooling their talents, and there's been enormous progress in those 30 years. But the more big problems we solve, the more new questions arise. So, you don't even know the right questions to ask until you solve the previous questions. Interestingly, some of the biggest spin-offs of our efforts to find the most fundamental theory of nature are in pure mathematics.

Do you think string theory will ultimately unify the forces of nature?

Yes, but I don't think we'll have a final answer in my lifetime. The journey has been worth it, even if it did take some unusual twists and turns. I'm convinced that, in other intelligent civilizations throughout the galaxy, similar discoveries will occur, or already have occurred, in a different sequence than ours. We'll find the same result and reach the same conclusions as other civilizations, but we'll get there by a very different route.

Written by Whitney Clavinhttp://www.caltech.edu/news/long-and-winding-road-conversation-string-theory-pioneer-83209

ゼロ除算の発見は日本です：

∞？？？

∞は定まった数ではない///

人工知能はゼロ除算ができるでしょうか：

とても興味深く読みました：2014年2月2日

ゼロ除算の発見と重要性を指摘した：日本、再生核研究所

ゼロ除算関係論文・本

https://ameblo.jp/syoshinoris/entry-12370797278.html

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\title{\bf Announcement 448:\\ Division by Zero;\\

Funny History and New World}

\author{再生核研究所}

\date{2018.08.20}

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{\bf Abstract: } Our division by zero research group wonder why our elementary results may still not be accepted by some wide world and very recently in our Announcements: 434 (2018.7.28),

437 (2018.7.30),

438(2018.8.6), \\

441(2018.8.9),

442(2018.8.10),

443(2018.8.11),

444(2018.8.14),

in Japanese, we stated their reasons and the importance of our elementary results. Here, we would like to state their essences. As some essential reasons, we found fundamental misunderstandings on the division by zero and so we would like to state the essences and the importance of our new results to human beings over mathematics.

We hope that:

close the mysterious and long history of division by zero that may be considered as a symbol of the stupidity of the human race and open the new world since Aristotle-Eulcid.

From the funny history of the division by zero, we will be able to realize that

human beings are full of prejudice and prejudice, and are narrow-minded, essentially.

\medskip

\section{Division by zero}

The division by zero with mysterious and long history was indeed trivial and clear as in the followings:

\medskip

By the concept of the Moore-Penrose generalized solution of the fundamental equation $az=b$, the division by zero was trivial and clear as $b/0=0$ in the {\bf generalized fraction} that is defined by the generalized solution of the equation $az=b$.

Note, in particular, that there exists a uniquely determined solution for any case of the equation $az=b$ containing the case $a=0$.

People, of course, consider as the division $b/a$ that it is the solution of the equation $ az =b$ and if $a=0$ then $0 \cdot z =0$ and so, for $b\ne0$ we can not consider the fraction $a/b$. We have been considered that the division by zero $b/0$ is impossible for mysteriously long years, since the document of zero in India in AD 628. In particular, note that Brahmagupta (598 -668 ?) established four arithmetic operations by introducing $0$ and at the same time he defined as $0/0=0$ in Brhmasphuasiddhnta. Our world history, however, stated that his definition $0/0=0$ is wrong over 1300 years, but, we will see that his definition is right and suitable. However, he did not give its reason and did not consider the importance case $1/0$ and the general fractions $b/0$. The division by zero was a symbol for {\bf impossibility} or to consider the division by zero was {\bf not permitted}. For this simple and clear conclusion, we did not definitely consider more on the division by zero. However, we see many and many formulas appearing the zero in denominators, one simple and typical example is in the function $w=1/z$ for $z=0$.

We did not consider the function at the origin $z=0$.

In this case, however, the serious interest happens in many physical problems and also in computer sciences, as we know.

When we can not find the solution of the fundamental equation $az=b$, it is fairly clear to consider the Moore-Penrose generalized solution in mathematics. Its basic idea and beautiful mathematics will be definite.

Therefore, we should consider the generalized fractions following the Moore-Penrose generalized inverse. Therefore, with its meaning and definition we should consider that $b/0=0$.

It will be very curious that we know very well the Moore-Penrose generalized inverse as a very fundamental and important concept, however, we did not consider the simplest case $ az =b$.

Its reason may be considered as follows: We will consider or imagine that the fraction $1/0$ may be like infinity or ideal one.

For the fundamental function $W =1/ z $ we did not consider any value at the origin $z = 0$. Many and many people consider its value by the limiting like $+\infty $ and $- \infty$ or the

point at infinity as $\infty$. However, their basic idea comes from {\bf continuity} with the common sense or

based on the basic idea of Aristotle. --

For the related Greece philosophy, see \cite{a,b,c}. However, as the division by zero we have to consider its value of

the function $W =1 /z$ as zero at $z = 0$. We will see that this new definition is valid widely in

mathematics and mathematical sciences, see (\cite{mos,osm}) for example. Therefore, the division by zero will give great impacts to calculus, Euclidian geometry, analytic geometry, complex analysis and the theory of differential equations in an undergraduate level and furthermore to our basic ideas for the space and universe.

For the extended complex plane, we consider its stereographic projection mapping as the Riemann sphere and the point at infinity is realized as the north pole in the Alexsandroff's one point compactification.

The Riemann sphere model gives a beautiful and complete realization of the extended complex plane through the stereographic projection mapping and the mapping has beautiful properties like isogonal (equiangular) and circle to circle correspondence (circle transformation). Therefore, the Riemann sphere is a very classical concept \cite{ahlfors}.

\medskip

Now, with the division by zero we have to admit the strong discontinuity at the point at infinity. To accept this strong discontinuity seems to be very difficult, and therefore we showed many and many examples for giving the evidences over $800$ items.

\medskip

We back to our general fractions $1/0=0/0=z/0=0$ for its importances.

\medskip

H. Michiwaki and his 6 years old daughter Eko Michiwaki stated that in about three weeks after the discovery of the division by zero that

division by zero is trivial and clear from the concept of repeated subtraction and they showed the detailed interpretation of the general fractions. Their method is a basic one and it will give a good introduction of division and their calculation method of divisions.

We can say that division by zero, say $100/0$ means that we do not divide $100$ and so the number of the divided ones is zero.

\medskip

Furthermore,

recall the uniqueness theorem by S. Takahasi on the division by zero:

\medskip

{\bf Proposition 1.1 }{\it Let F be a function from ${\bf C }\times {\bf C }$ to ${\bf C }$ satisfying

$$

F (b, a)F (c, d)= F (bc, ad)

$$

for all

$$

a, b, c, d \in {\bf C }

$$

and

$$

F (b, a) = \frac {b}{a }, \quad a, b \in {\bf C }, a \ne 0.

$$

Then, we obtain, for any $b \in {\bf C } $

$$

F (b, 0) = 0.

$$

}

Note that the complete proof of this proposition is simply given by 2 or 3 lines.

In the long mysterious history of the division by zero, this proposition seems to be decisive.

Indeed, Takahasi's assumption for the product property should be accepted for any generalization of fraction (division). Without the product property, we will not be able to consider any reasonable fraction (division).

Following Proposition 1.1, we should {\bf define}

$$

F (b, 0) = \frac{b}{0} =0,

$$

and consider, for any complex number $b$, as $0$;

that is, for the mapping

\begin{equation}

W = f(z) = \frac{1}{z},

\end{equation}

the image of $z=0$ is $W=0$ ({\bf should be defined from the form}).

\medskip

Furthermore,

the simple field structure containing division by zero was established by M. Yamada.

\medskip

In addition, for the fundamental function $f(z) = 1/z$, note that

the function is odd function

$$

f(z) = - f(-z)

$$

and if the function may be extended as an odd function at the origin $z=0$, then the identity $f(0) = 1/0 =0$ has to be satisfied. Further, if the equation

$$

\frac{1}{z} =0

$$

has a solution, then the solution has to be $z=0$.

\medskip

\section{Division by zero calculus}

As the number system containing the division by zero, the Yamada field structure is complete.

However, for applications of the division by zero to {\bf functions}, we need the concept of the division by zero calculus for the sake of uniquely determinations of the results and for other reasons.

For example, for the typical linear mapping

\begin{equation}

W = \frac{z - i}{z + i},

\end{equation}

it gives a conformal mapping on $\{{\bf C} \setminus \{-i\}\}$ onto $\{{\bf C} \setminus \{1\}\}$ in one to one and from \begin{equation}

W = 1 + \frac{-2i}{ z - (-i)},

\end{equation}

we see that $-i$ corresponds to $1$ and so the function maps the whole $\{{\bf C} \}$ onto $\{{\bf C} \}$ in one to one.

Meanwhile, note that for

\begin{equation}

W = (z - i) \cdot \frac{1}{z + i},

\end{equation}

if we enter $z= -i$ in the way

\begin{equation}

[(z - i)]_{z =-i} \cdot \left[ \frac{1}{z + i}\right]_{z =-i} = (-2i) \cdot 0= 0,

\end{equation}

we have another value.

\medskip

In many cases, the above two results will have practical meanings and so, we will need to consider many ways for the application of the division by zero and we will need to check the results obtained, in some practical viewpoints. We referred to this delicate problem with many examples.

Therefore, we will introduce the division by zero calculus that give important values for functions. For any Laurent expansion around $z=a$,

\begin{equation}

f(z) = \sum_{n=-\infty}^{-1} C_n (z - a)^n + C_0 + \sum_{n=1}^{\infty} C_n (z - a)^n,

\end{equation}

we obtain the identity, by the division by zero

\begin{equation}

f(a) = C_0.

\end{equation}

Note that here, there is no problem on any convergence of the expansion (2.5) at the point $z = a$, because all the terms $(z - a)^n$ are zero at $z=a$ for $n \ne 0$.

\medskip

For the correspondence (2.6) for the function $f(z)$, we will call it {\bf the division by zero calculus}. By considering the formal derivatives in (2.5), we {\bf can define any order derivatives of the function} $f$ at the singular point $a$; that is,

$$

f^{(n)}(a) = n! C_n.

$$

\medskip

{\bf Apart from the motivation, we define the division by zero calculus by (2.6).}

With this assumption, we can obtain many new results and new ideas. However, for this assumption we have to check the results obtained whether they are reasonable or not. By this idea, we can avoid any logical problems. -- In this point, the division by zero calculus may be considered as an axiom.

\medskip

This paragraph is very important. Our division by zero is just definition and the division by zero is an assumption. Only with the assumption and definition of the division by zero calculus, we can create and enjoy our new mathematics. Therefore, the division by zero calculus may be considered as a new axiom.

Of course, its strong motivations were given. We did not consider any value {\bf at the singular point} $a$ for the Laurent expansion (2.5). Therefore, our division by zero is a new mathematics entirely and isolated singular points are a new world for our mathematics.

We had been considered properties of analytic functions {\bf around their isolated singular points.}

The typical example of the division zero calculus is $\tan (\pi/2) = 0$ and the result gives great impacts to analysis and geometry.

See the references for the materials.

\medskip

For an identity, when we multiply zero, we obtain the zero identity that is a trivial.

We will consider the division by zero to an equation.

For example, for the simple example for the line equation on the $x, y$ plane

$$

ax + by + c=0

$$

we have, formally

$$

x + \frac{by + c}{a} =0,

$$

and so, by the division by zero, we have, for $a=0$, the reasonable result

$$

x = 0.

$$

However, from

$$

\frac{ax + by}{c} + 1 =0,

$$

for $c=0$, we have the contradiction, by the division by zero

$$

1 =0.

$$

For this case, we can consider that

$$

\frac{ax + by}{c} + \frac{c}{c} =0,

$$

that is always valid. {\bf In this sense, we can divide an equation by zero.}

\section{Conclusion}

Apparently, the common sense on the division by zero with a long and mysterious history is wrong and our basic idea on the space around the point at infinity is also wrong since Euclid. On the gradient or on derivatives we have a great missing since $\tan (\pi/2) = 0$. Our mathematics is also wrong in elementary mathematics on the division by zero.

We have to arrange globally our modern mathematics with our division by zero in our undergraduate level.

We have to change our basic ideas for our space and world.

We have to change globally our textbooks and scientific books on the division by zero.

From the mysterious history of the division by zero, we will be able to study what are human beings and about our narrow-minded.

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\end{document}