Physics

The black hole information paradox is a contradiction between fundamental principles which has puzzled physicists for over forty years. The crux of the problem lies in an assumption about the structure of entanglement across the event horizon, namely, that the Hilbert space factorizes. While valid in quantum mechanics, this fails drastically in quantum field theory, and hence a deeper understanding of entanglement is required if further progress is to be made. Recently, ideas from algebraic quantum field theory have provided new insight into this issue, and show promise for elucidating the connection between entropy and horizons that underlies black hole thermodynamics.

This paper explores the physics of the what-if question "what if the entire Earth was instantaneously replaced with an equal volume of closely packed, but uncompressed blueberries?" While the assumption may be absurd, the consequences can be explored rigorously using elementary physics. The result is not entirely dissimilar to a small ocean-world exoplanet.

Before they met, David Bohm and Roger Penrose each puzzled over the paradox of the arrow of time. After they met, the case for projective physical space became clearer.

Some physical aspects of Chinese cuisine are discussed. We start from the cultural and historical particularities of the Chinese cuisine and technologies of food production. What is the difference between raw and boiled meat? What is the difference in the physical processes of heat transfer during steaming of dumplings and their cooking in boiling water? Why is it possible to cook meat stripes in a "hot pot" in ten seconds, while baking a turkey requires several hours? This article is devoted to discussion of these questions.

Satyendra Nath Bose's attempt to describe the quantum statistical aspects of light consistently in terms of particles, and Einstein's generalisation, lead to the concept of Bosons as a class of quanta obeying `Bose-Einstein statistics'. Their identity as a class came in sharp contrast when the Pauli exclusion principle and the Dirac equation revealed the other class called Fermions, obeying `Fermi-Dirac statistics'. Spin, and spin alone, is the determining factor of the multiparticle behaviour of fundamental quanta. This is the basis of the Spin-Statistics Connection. While it is known that the overall theoretical picture is consistent, the physical reason for the connection is unknown. Further, the class difference is sensitive only to the total spin in a quantum aggregate, as spectacularly seen in superconductivity and superfluidity, and in the Bose-Einstein condensation of neutral atomic gas. Can we grasp the true reason behind the difference in the collective behaviour of Bosons and Fermions? An explorer's journey demanding logical and physical consistency of what we already know takes us to the hidden factors in the relation between spin and the statistics of quanta. The surprising answer is in the domain of gravity, that too, on a cosmic scale.

Stars form from large clouds of gas and dust that contract under their own gravity. The birth of a star occurred when a fusion reaction of hydrogen into helium has ignited in its core. The key variable that determines the formation of a star is mass. If the mass of the contracting cloud is below certain minimum value, instead of a star, a substelar object -- known as a brown dwarf -- will form. How much mass is required for a star to form? This article aims to answer this question by means of a simple heuristic argument. The found value is 0.016 solar masses, which is of the same order of magnitude as the accepted value 0.08 solar masses. This article may be useful as pedagogical material in an introductory undergraduate astronomy course.

The results of experimental tests of a novel method for moving large (pyramid construction size) stone blocks by rolling them are presented. The method is implemented by tying 12 identical rods of appropriately chosen radius to the faces of the block forming a rough dodecagon prism. Experiments using a 1,000 kg block show that it can be moved across level open ground with a dynamic coefficient of friction of less than 0.06. This value is a factor of five lower than that obtained for dragging the block, and the best values reported for dragging by others, at 0.3. the results are more dramatic than those obtained on smaller scale experiments on a 29.6 kg block, also reported here. For full scale pyramid blocks, the wooden "rods" woudl need to be posts of order 30 cm in diameter, similar in size to those used as masts on ships in the Nile.

That water expands when freezing is a well-known fact, and it is at the basis of an experiment that is often involuntary performed with beer bottles in freezers. But why does the water behave this way? And, more difficult, how can one illustrate this phenomenon in simple terms?

The tumuli of Newgrange and Knowth in Ireland are among the most monumental heritages of the Neolithic era. The megalithic constructions date back to around 3'200 BC, centuries before the completion of Stonehenge and the Egyptian pyramids. Passageways inside the mounds have been shown to be aligned such as the rising sun illuminates the interior chambers on the winter solstice at Newgrange and around the equinoxes at Knowth. Many of the kerb and interior stones are covered with petroglyphs, in particular with spiral motifs. Despite several attempts to classify and interpret them, they remain enigmatic. Here we show that some of the most elaborated spirals are likely calendrical representations. We use a new, 'dynamic' approach adding a temporal dimension to the rock art. We identify in the detailed spiral motifs up to five different manifestations of the solar and lunar cycles, which could easily be observed in prehistoric Ireland. Corroborating evidence comes from adjacent motifs or a special location of the stone. Although the work is speculative by nature, many clues give confidence in the interpretation. If correct, it would imply that one or a few individuals developed skills for celestial observations, the design of complex motifs and their preservation on the rock. This resembles a scientific process, but is more likely the expression of a ritual engagement with the sky.

Space settlement represents a long-term human effort that requires unprecedented coordination across successive generations. In this chapter, I develop a comparative hierarchy for the value of long-term projects based upon their benefits to culture, their development of infrastructure, and their contributions to lasting information. I next draw upon the concept of the time capsule as an analogy, which enables a comparison of historical examples of projects across generational, intergenerational, and deep time. The concept of deep altruism can then be defined as the selfless pursuit of informational value for the well-being of others in the distant future. The first steps toward supporting an effort like space settlement through deep altruism would establish governance and funding models that begin to support ambitions with intergenerational succession.