**Lee Smolin**

Because of the non-locality of quantum entanglement, realist approaches to completing quantum mechanics have implications for our conception of space. Quantum gravity also is expected to predict phenomena in which the locality of classical spacetime is modified or disordered. It is then possible that the right quantum theory of gravity will also be a completion of quantum mechanics in which the foundational puzzles in both are addressed together. I review here the results of a program, developed with Roberto Mangabeira Unger, Marina Cortes and other collaborators, which aims to do just that. The results so far include energetic causal set models, time asymmetric extensions of general relativity and relational hidden variables theories, including real ensemble approaches to quantum mechanics. These models share two assumptions: that physics is relational and that time and causality are fundamental.

Read more at https://arxiv.org/pdf/1805.12468.pdf

# Category Archives: History and Philosophy of Physics

# Memories of a Theoretical Physicist

**Joseph Polchinski**

While I was dealing with a brain injury and finding it difficult to work, two friends (Derek Westen, a friend of the KITP, and Steve Shenker, with whom I was recently collaborating), suggested that a new direction might be good. Steve in particular regarded me as a good writer and suggested that I try that. I quickly took to Steve’s suggestion. Having only two bodies of knowledge, myself and physics, I decided to write an autobiography about my development as a theoretical physicist.

This is not written for any particular audience, but just to give myself a goal. It will probably have too much physics for a nontechnical reader, and too little for a physicist, but perhaps there with be different things for each. Parts may be tedious. But it is somewhat unique, I think, a blow-by-blow history of where I started and where I got to.

Probably the target audience is theoretical physicists, especially young ones, who may enjoy comparing my struggles with their own. Some disclaimers: This is based on my own memories, jogged by the arXiv and Inspire. There will surely be errors and omissions. And note the title: this is about my memories, which will be different for other people. Also, it would not be possible for me to mention all the authors whose work might intersect mine, so this should not be treated as a reference work.

Read more at https://arxiv.org/pdf/1708.09093.pdf

# Nietzsche for physicists

**J. C. S. Neves**

One of the most important philosophers in the history, the German Friedrich Nietzsche, is almost ignored by physicists. The author who stated the death of God in 19th century was a science enthusiast, mainly during the second part of his work. With the aid of the physical concept of force, Nietzsche created his concept of will to power. Thinking about the energy conservation, the German philosopher had some inspiration for creating his concept of the eternal recurrence.

In this article, one points out some influences of physics on Nietzsche and discusses the topicality of his epistemological position, the perspectivism. From the concept of will to power, I propose that the perspectivism leads to the interpretation where physics, and science in general, is viewed as a game.

Read more at https://arxiv.org/pdf/1611.08193v1.pdf

# Eugene Paul Wigner’s Nobel Prize

**Y.S. Kim**

In 1963, Eugene Paul Wigner was awarded the Nobel Prize in Physics for his contributions to the theory of the atomic nucleus and the elementary particles, particularly through the discovery and application of fundamental symmetry principles. There are no disputes about this statement. On the other hand, there still is a question of why the statement did not mention Wigner’s 1939 paper on the Lorentz group, which was regarded by Wigner and many others as his most important contribution in physics. By many physicists, this paper was regarded as a mathematical exposition having nothing to do with physics. However, it has been more than one half century since 1963, and it is of interest to see what progress has been made toward understanding physical implications of this paper and its historical role in physics. Wigner in his 1963 paper defined the subgroups of the Lorentz group whose transformations do not change the four-momentum of a given particle, and he called them the little groups. Thus, Wigner’s little groups are for internal space-time symmetries of particles in the Lorentz-covariant world. Indeed, this subgroup can explain the electron spin and spins of other massive particles. However, for massless particles, there was a gap between his little group and electromagnetic waves derivable Maxwell’s equations. This gap was not completely removed until 1990. The purpose of this report is to review the stormy historical process in which this gap is cleared. It is concluded that Wigner’s little groups indeed can be combined into one Lorentz-covariant formula which can dictate the symmetry of the internal space-time time symmetries of massive and massless particles in the Lorentz covariant world, just like Einstein’s energy-momentum relation applicable to both slow and massless particles.

Read more at https://arxiv.org/pdf/1610.01740v1.pdf

# Werner Heisenberg and the German Uranium Project 1939 – 1945

## Myths and Facts

**Klaus Gottstein**

The results of a careful analysis of all the available information on the activities of Heisenberg and of his talks during the years 1939 to 1945 can be summarized in the following way. Like several other German physicists Heisenberg was drafted by German Army Ordnance when war began in Europe in September 1939 to investigate whether the energy from splitting Uranium nuclei by neutrons could be used for technical and military purposes. Heisenberg found that this is possible in principle but that military use would require such enormous industrial expenditures that it would take many years and would be impracticable while the war lasted. The project was therefore dropped by the Nazi government in 1942. Heisenberg even refrained from calculating a precise value for the critical mass of U 235. He was relieved that he was thus spared a moral decision between obeying an order to build the bomb or risking his life by refusing to be involved in the project or sabotaging it. He was happy to be confined to a project of building a small test reactor under civilian administration that the government had approved. In 1941 Heisenberg tried to get the opinion of Niels Bohr in Copenhagen on what the international community of nuclear physicist could possibly do or prevent regarding the long-range technical feasibility of making nuclear weapons. Bohr completely misunderstood the cautious approach of Heisenberg.

read more at https://arxiv.org/ftp/arxiv/papers/1609/1609.02775.pdf

# The dangers of non-empirical confirmation

**Carlo Rovelli**

In the book “String Theory and the Scientific Method”, Richard Dawid describes a few of the many non-empirical arguments that motivate theoretical physicists’ confidence in a theory, taking string theory as case study. I argue that excessive reliance on non-empirical evidence compromises the reliability of science, and that precisely the case of string theory well illustrates this danger.

Read more at http://arxiv.org/pdf/1609.01966v1.pdf

# Bringing quantum mechanics to life: from Schrödinger’s cat to Schrödinger’s microbe

**Zhang-qi Yin, Tongcang Li**

The question whether quantum mechanics is complete and the nature of the transition between quantum mechanics and classical mechanics have intrigued physicists for decades. There have been many experimental breakthroughs in creating larger and larger quantum superposition and entangled states since Erwin Schr\”{o}dinger proposed his famous thought experiment of putting a cat in a superposition of both alive and dead states in 1935. Remarkably, recent developments in quantum optomechanics and electromechanics may lead to the realization of quantum superposition of living microbes soon. Recent evidences also suggest that quantum coherence may play an important role in several biological processes. In this review, we first give a brief introduction to basic concepts in quantum mechanics and the Schr\”{o}dinger’s cat thought experiment. We then review developments in creating quantum superposition and entangled states and the realization of quantum teleportation. Non-trivial quantum effects in photosynthetic light harvesting and avian magnetoreception are also discussed. At last, we review recent proposals to realize quantum superposition, entanglement and state teleportation of microorganisms, such as viruses and bacteria.

Read more at http://arxiv.org/pdf/1608.05322v1.pdf