Alice and Bob Meet the Wall of Fire
Thomas Lin was science editor for the online New York Times before he decided in 2012 to become the founder and editor in chief of the online Quanta Magazine. By now it has become a highly appreciated freely available online source for journalists to find information about (hard) science: physics, biology, computer science, and mathematics. Quanta is sponsored by the Simons Foundation, an organization for the promotion of science created by James Simons, the billionaire mathematician and hedge-fund founder. The editorial policy is to cover in about five to ten pages the cutting edge topics that fall somewhat outside the interest of the mainstream media. The texts are engaging newspaper style stories that are rigorous without being really technical. It should catch the attention of any science minded reader. The authors are mostly reporters that have talked to or interviewed the scientists. Only in very exceptional cases, it is written by the scientists themselves.
After the first five years of Quanta's existence, Lin has made a "Best of"-selection of the texts in two volumes. One is entitled The prime number conspiracy and collects papers dealing with mathematical subjects. That involves obviously prime numbers, but is not restricted to number theory. The remaining subjects (physics, computer science, and biology) is covered in the present volume. The texts are only slightly edited to add the latest news. Clearly some are older while others are more recent. By reading subsequent texts on the same or a closely related topic it is seen how science advances.
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. What follows is a selective survey.
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.
Of course most of the topics covered in this book rely on mathematics, fundamental or applied. However, because of the purpose of these texts is to inform the non-specialist about the latest developments, the mathematics are left out and reference to the underlying mathematics is only rarely made. Nevertheless, I believe that also mathematicians, certainly mathematicians, will and should be interested. These applied topics is where mathematical tools are needed that may not be available yet. Here models and simulations of ever higher complexity are required, and more complex abstract tools should be developed. Anyone can read this to stay informed about recent developments in science, but young mathematicians may find here inspiration on which applied direction they want to build their career.