Lin T. (Ed.) Alice and Bob Meet the Wall of Fire: The Biggest Ideas in Science from Quanta

The Simons Foundation, Inc., 2018. — xx+308 p. — ISBN: 978-0262536349.The present collection consists of 38 texts, grouped in eight parts. Clearly it is not possible to cover each of the subjects here in detail, but the titles of the eight parts can give an idea of what is covered. Note that they are all formulated as questions, which reflects that they relate to some of the "big questions" that humans naturally ask and that scientists have been trying to solve, often replacing them by new, even more challenging ones.
– Why doesn't our universe make sense?
This is all about cosmology, space-time, multiverse collision, etc. It contains the article that delivered the book's title. Alice and Bob are the usual persons used in thought experiments. The wall of fire is how an outside observer would see the event horizon of a black hole, if Hawking radiation is accepted, but there are still paradoxes connected to black holes that could not be solved yet.
– What is quantum reality, really?
Although quantum theory was conceived about a century ago, it is still not completely understood. It is very real as confirmed by experiments over and over again. So there are still attempts to provide new explanations or old ones are revived. For example various multiverse concepts have their believers and non-believers based on different arguments. We can read about the amplituhedron, a geometrical object that should simplify the quantum field theoretical computations, a considerable improvement over Feynman diagrams. Noteworthy is also a text by Nobel Prize winner Frank Wilczek about quantum entanglement (he also had a contribution in the previous part about Feynman diagrams). He is one of the three authoring scientists in this collection (Robbert Dijkgraaf, director of the IAS in Princetion is another exception, with a contribution in the last part).
– What is time?
Time is in many aspects an "outsider" in physical quantities. Physicists have developed several theories about what it is and what is causing it. It is intimately related to an increase of entropy described by the second law of thermodynamics. Entropy is a measure of information. It quantifies the amount of uncertainty, and hence directly links to quantum theory. The preferred laboratory to investigate time (and other quantum physical effects) in extreme circumstances are black holes. Mathematically, time just stops at the singularity of a black hole like it popped into existence with the Big Bang. Quantum entanglement comes into the picture because entanglement happens in space-time, and hence there can also be this "spooky action" at a distance in time which makes causality questionable, but it may explain the evaporation of black holes that Hawking predicted.
– What is life?
A lot of progress has been made in cell biology up to the tiniest scale, and that has sparked some hypotheses about the origin of life. Life seems to counteract the second law of thermodynamics, creating structure from chaos. Again, the intimate relation between entropy and information can bring insight. External energy can make self-replication possible, but is it life? Should a sharp boundary between living and non-living be erased? Artificial life, editing and generating new DNA became reality. Animal life with asexual self-replication was discovered. And there is debate when in the course of evolution neurons where developed. All of these questions are discussed in this part.
– What makes us human?
The brain is still one of the most complex and least understood organs. There are speculations of why about 3 million years ago the brain of humans started to quadruple in size although size is not the only thing that counts. Why do we have an evolutionary aversion to loneliness? Why do we sometimes make bad decisions, and neuroscientists investigate how the brain of a child changes into the brain of an adult. This part is connected to the next one where machines simulate how the brain operates.
– How do machines learn?
Here it is explained how computers are programmed to win in chess or Go from humans. However, this is a machine programmed by humans who feed the rules of the game. In this setting a machine can beat a human only because it is faster. The proper learning machine is however obtained by neural nets where deep learning and reinforced learning are the driving mechanisms that make the machine learn on its own. It will be clumsy in the beginning, but it never gets tired and hence can learn much faster than humans.
– How will we learn more?
Here we are back into cosmology and quantum theory. Since the LIGO has measured gravitational waves, a whole new area has opened to scientists. The waves emerge from colliding black holes, but how did these black holes come about and why did they collide? Also a pair of neutron stars can collapse and how did that happen?
– Where do we go from here?
It was hoped or expected that the LHC at CERN would detect new particles, but except for the Higgs boson, which was predicted, none other new particle has been observed. So what about the speculative string theory? Will there ever be evidence for some of the, by now many, versions of string theory? Can we ever arrive at a Theory of Everything, and at explaining quantum gravity, or will a completely new vision emerge? Hawking was very optimistic at first to have a ToE at the beginning of the 21st century, but he eventually had admit that it will take a while longer.Foreword
Sean CarrollThomas LinWhy doesn't Our Universe Make Sense?
Is Nature Unnatural?
Natalie Wolchover
Alice and Bob Meet the Wall of Fire
Jennifer Ouellette
Wormholes Untangle a Black Hole Paradox
K.C. Cole
How Quantum Pairs Stitch Space-Time
Jennifer Ouellette
In a Multiverse, What are the Odds?
Natalie Wolchover
Multiverse Collisions May Dot the Sky
Jennifer Ouellette
How Feynman Diagrams Almost Saved Space
Frank WilczekWhat is Quantum Reality, really?
A Jewel at the Heart of Quantum Physics
Natalie Wolchover
New Support for Alternative Quantum View
Dan Falk
Entanglement Made Simple
Frank Wilczek
Quantum Theory Rebuilt from Simple Physical Principles
Philip BallWhat is Time?
Time’s Arrow Traced to Quantum Source
Natalie Wolchover
Quantum Weirdness Now a Matter of Time
George Musser
A Debate over the Physics of Time
Dan FalkWhat is Life?
A New Physics Theory of Life
Natalie Wolchover
How Life (and Death) Spring from Disorder
Philip Ball
In Newly Created Life-Form, a Major Mystery
Emily Singer
Breakthrough DNA Editor Born of Bacteria
Carl Zimmer
New Letters Added to the Genetic Alphabet
Emily Singer
The Surprising Origins of Life’s Complexity
Carl Zimmer
Ancient Survivors Could Redefine Sex
Emily Singer
Did Neurons Evolve Twice?
Emily SingerWhat Makes Us Human?
How Humans Evolved Supersize Brains
Ferris Jabr
New Evidence for the Necessity of Loneliness
Emily Singer
How Neanderthal DNA Helps Humanity
Emily Singer
The Neuroscience Behind Bad Decisions
Emily Singer
Infant Brains Reveal How the Mind Gets Built
Courtney HumphriesHow Do Machines Learn?
Is Alphago Really Such a Big Deal?
Michael Nielsen
New Theory Cracks Open the Black Box of Deep Learning
Natalie Wolchover
A Brain Built from Atomic Switches Can Learn
Andreas von Bubnoff
Clever Machines Learn How to Be Curious
John PavlusHow Will We Learn More?
Gravitational Waves Discovered at Long Last
Natalie Wolchover
Colliding Black Holes Tell New Story of Stars
Natalie Wolchover
Neutron-Star Collision Shakes Space-Time and Lights up the Sky
Katia MoskvitchWhere Do We Go from Here?
What No New Particles Means for Physics
Natalie Wolchover
To Solve the Biggest Mystery in Physics, Join Two Kinds of Law
Robbert Dijkgraaf
The Strange Second Life of String Theory
K.C. Cole
A Fight for the Soul of Science
Natalie WolchoverAcknowledgments

Notes
Index