4) Here are the final letters by Leonard Susskind' and Lee Smolin in their email debate re the Anthropic Principle.

Smolin: ... My main point is that string theory will have much more explanatory power if the dominant mode of reproduction is through black holes, as is the case in the original version of CNS. This is the key point I would hope to convince Susskind and his colleagues about, because I am sure that the case they want to make is very much weakened if they rely on the Anthropic Principle (AP) and eternal inflation. ...

Susskind: ... Finally let me quote a remark of Smolin's that I find revealing. He says "It was worry about the possibility that string theory would lead to the present situation, which Susskind has so ably described in his recent papers, that led me to invent the Cosmological Natural Selection (CNS) idea and to write my first book. My motive, then as now, is to prevent a split in the community of theoretical physicists in which different groups of smart people believe different things, with no recourse to come to consensus by rational argument from the evidence." First of all, preventing a "split in the community of theoretical physicists" is an absurdly ridiculous reason for putting forward a scientific hypothesis.

But what I find especially mystifying is Smolin's tendency to set himself up as an arbiter of good and bad science. Among the people who feel that the anthropic principle deserves to be taken seriously, are some very famous physicists and cosmologists with extraordinary histories of scientific accomplishment. They include Steven Weinberg [2], Joseph Polchinski [3], Andrei Linde [4], and Sir Martin Rees [5]. These people are not fools, nor do they need to be told what constitutes good science. ...    more »

The Hubble Space Telescope has discovered the first organic molecule on a planet that's not in our solar system. According to NASA, this breakthrough could be a major step toward discovering life on other planets. Scientists believe that the organic compound detected, methane, can be an integral part in the chemical reactions considered necessary to form life as we know it. ...   more »

3) Here's Leonard Susskind's #2 to Lee Smolin #2:

...The issue here is not whether the usual phenomenological inflation was of the eternal kind although that is relevant. Eternal inflation taking place in any false vacuum minimum on the landscape would favor [in Smolin's sense] the maximum cosmological constant. But for the sake of argument I will agree to ignore eternal inflation as a reproduction mechanism.

The question of how many black holes are formed is somewhat ambiguous. What if two black holes coalesce to form a single one. Does that count as one black hole or two? Strictly speaking, given that black holes are defined by the global geometry, it is only one black hole. What happens if all the stars in the galaxy eventually fall into the central black hole? That severely diminishes the counting. So we better assume that the bigger the black hole, the more babies it will have. Perhaps one huge black hole spawns more offspring than 10^22 stellar black holes.

That raises the question of what exactly is a black hole? One of the deepest lessons that we have learned over the past decade is that there is no fundamental difference between elementary particles and black holes. As repeatedly emphasized by 't Hooft [10][11][12], black holes are the natural extension of the elementary particle spectrum. This is especially clear in string theory where black holes are simply highly excited string states. Does that mean that we should count every particle as a black hole? ...   more »

...if antimatter is, from a physics standpoint, the mirror image of matter, why is there so little antimatter in the universe? What happened early in the universe’s history to favor—if by only a small amount—the creation of matter instead of antimatter?

Particle physics has, like other scientific fields, its own lexicon that can be baffling to outsiders, and while reading 'The Mystery of the Missing Antimatter' one runs the risk of getting lost among terms like CP violation, J/psi particles, and leptogenesis. The authors do their best, though, to explain non-intuitive physics with plain language and analogies... For those curious about why the universe is the way it is, this book is a reminder of how much we have learned about physics at its smallest and largest scales, but also how much more we have yet to understand. ...   more »

It’s easy to forget that until recently cosmology was largely a theoretical science. Thanks in particular to the Wilkinson Microwave Anisotropy Probe (WMAP), which was launched by NASA in 2001 to study the cosmic microwave background, researchers are now able to talk about the first instants of the universe with the kind of certainty normally associated with a bench-top experiment.

With the analysis of two further years of WMAP data announced last week, that view of the early universe has just got even more detailed. As well as placing tighter constraints on parameters such as the age and content of the universe, the five-year WMAP data provide new, independent evidence for a cosmic neutrino background. The detection of such low-energy neutrinos, wrote Steven Weinberg in 1977 in his famous book The First Three Minutes, “would provide the most dramatic possible confirmation of the standard model of the early universe” — yet at the time no-one knew how to detect such a signal.   more »

Faced with the difficulty of observing Hawking radiation from astrophysical black holes, some physicists have attempted to make artificial ones in the lab that have a higher characteristic temperature. Clearly, generating huge amounts of gravity is both dangerous and next to impossible. But artificial black holes could be based on an analogous system in which the curved space–time of a gravitational field is enacted by another varying parameter that affects the propagation of a wave. “We cannot change the laws of gravity at our will,” Ulf Leonhardt at the University of St Andrews in the UK tells physicsworld.com. “But we can change analogous parameters in a condensed-matter system.” Leonhardt’s group at St Andrews is the first to create an artificial black-hole system in which Hawking radiation could be detected (Science 319 1367). ...   more »

Mysteriously, four spacecraft that flew past the Earth have each displayed unexpected anomalies in their motions. -- These newfound enigmas join the so-called "Pioneer anomaly" as hints that unexplained forces may appear to act on spacecraft.

A decade ago, after rigorous analyses, anomalies were seen with the identical Pioneer 10 and 11 spacecraft as they hurtled out of the solar system. Both seemed to experience a tiny but unexplained constant acceleration toward the sun. -- A host of explanations have been bandied about for the Pioneer anomaly. At times these are rooted in conventional science — perhaps leaks from the spacecraft have affected their trajectories. At times these are rooted in more speculative physics — maybe the law of gravity itself needs to be modified.

Now Jet Propulsion Laboratory astronomer John Anderson and his colleagues — who originally helped uncover the Pioneer anomaly — have discovered that four spacecraft each raced either a tiny bit faster or slower than expected when they flew past the Earth en route to other parts of the solar system. ...   more »