2) And here's Lee Smolin's #2 to Leonard Susskind #1:
I am grateful to Lenny for taking the time to respond to my paper. I will be as brief as I can in replying, especially as the key points are already presented in detail in my paper hep-th/0407213 ["Scientific alternatives to the anthropic principle"] or in my book, Life of the Cosmos or previous papers on the subject. -- For clarity I had in section 5.1.6 identified two arguments in Weinberg's papers. The first is the one I criticized in the summary. Susskind reponds, reasonably, by agreeing, and then raising the second argument. This argument is also criticized in detail in my paper, and it was perhaps a mistake not to include this in the summary I sent to Susskind.
This second argument is based on a version of the AP called the "Principle of Mediocrity" by Garriga and Vilenkin, who have done the most to develop it. Their version states that, "...our civilization is typical in the ensemble of all civilizations in the universe." -- This argument is discussed in full in sections 5.1.5 and 5.1.6. There I argue that the mediocrity principle cannot yield falsifiable predictions because it depends on the definition of the ensemble within which our civilization is taken to be typical as well as on assumptions about the probability distribution. I establish this by general argument as well as by reference to specific examples including Weinberg's use of it.
Can this be right if, as Susskind claims, Weinberg's prediction was found to hold? In fact, Weinberg's prediction did not work all that well. In the form that he made it, it led to an expectation of a cosmological constant larger than the observed value. Depending on the ensemble chosen and the assumptions made about the probability distribution, the probability that Lambda be as small as observed ranges between about 10 % and a few parts in ten thousand. In fact, the less probable values are the more reasonable, as they come from an ensemble where Q, the scale of the density fluctuations, is allowed to vary. While I am not an expert here, it appears from a reading of the literature [references in the paper] that to make the probability for the present value as large as 10% one has to assume that Q is frozen and fixed by fundamental theory. It is hard to imagine a theory where the parameters vary but Q does not, as it depends on parameters in the inflation potential. ... more »
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Friday, February 29
2) The Anthropic Principle: Lee Smolin's #2 to Leonard Susskind #1
by
ronjon
on February 29, 2008 08:26PM (PST)
Thursday, February 28
1) The Anthropic Principle: Leonard Susskind's Reply #1 to Lee Smolin #1
by
ronjon
on February 28, 2008 01:23PM (PST)
1) Here's Leonard Susskind's answer to Lee Smolin's first email:
Yesterday I received an email message from Lee Smolin asking for my comments about a paper he had posted the previous day [1]. Having not had a chance to read the paper I asked if he would summarize the arguments. He was kind enough to do so in an admirably concise and clear summary. (See above). -- I took a quick look at the paper just to make sure that there was not more that I might have missed in the summary. -- I noticed that in the paper Smolin quotes the philosopher, Karl Popper. Personally I don't think these are deep philosophical issues requiring a heavyweight like Popper. Weinberg was just using good old fashioned common sense. Weinberg's argument, which is clearly stated in his general audience book Dreams of a Final Theory is not that the cosmological constant has to be smaller than the limit from galaxy formation. If it were, then Smolin would be correct: the Anthropic Principle doesn't add much to the observed fact that galaxies exist. What Weinberg argued was that if the Anthropic Principle is correct, then the cosmological constant will probably not be much smaller than the galaxy formation limit. Weinberg was just expressing the common sense opinion that if anthropics is the only reason the cosmological constant is small, then it is unlikely that it will be orders of magnitude smaller than the anthropic limit. -- Was it a prediction that could be proved wrong? Most people thought so. Just about everyone I know was certain that the cosmological constant was exactly zero. Smolin's next argument involves what he calls a scientific alternative to the Anthropic Principle. He argues for a Darwinian natural selection principle. Smolin believes, as I do, that universes can reproduce and give rise to mutated offspring that differ in the values of the constants of nature. He believes the mechanism involves black holes while I believe it involves eternal inflation and Coleman de Luccia bubble nucleation. But either will do. ... more » Wednesday, February 27
0) Smolin vs. Susskind: The Anthropic Principle. Lee Smolin's first letter to Leonard Susskind
by
ronjon
on February 27, 2008 02:11AM (PST)
Introduction
Recently, I received a copy of an email sent by Leonard Susskind to a group of physicists which included an attached file entitled "Answer to Smolin". This was the opening salvo of an intense email exchange between Susskind and Smolin concerning Smolin's argument that "the Anthropic Principle (AP) cannot yield any falsifiable predictions, and therefore cannot be a part of science". After reading several postings by each of the physicists, I asked each if (a) they would consider posting the comments on Edge, and (b) if they would write a new, and final "letter". -- Both agreed, but only after a negotiation: (1) No more than 1 letter each; (2) Neither sees the other's letter in advance; (3) No changes after the fact. A physics shoot-out. While this is a conversation written by physicists for physicists, it should nonetheless be of interest for Edge readers as it's in the context of previous Edge features with the authors, it's instructive as to how science is done, and it's a debate that clarifies, not detracts. And finally it's a good example of what Edge is all about, where contributors share the boundaries of their knowledge and experience with each other and respond to challenges, comments, criticisms, and insights. The constant shifting of metaphors, the intensity with which we advance our ideas to each other — this is what intellectuals do. Edge draws attention to the larger context of intellectual life. ... more » Friday, February 22
Google $20 million lunar challenge gets under way
by
ronjon
on February 22, 2008 10:22PM (PST)
...the X Prize Foundation announced the first 10 teams entered in the Google Lunar X Prize. Unveiled in September 2007, the Google Lunar X Prize requires contestants to land a privately funded robotic spacecraft on the moon, explore the terrain for at least 500 meters, and transmit results of the trip back to Earth. The grand prize is $20 million, with a second prize of $5 million and bonuses of $5 million. ... more »
Thursday, February 21
Nobel Laureate Queries Point To Postmodern Dark Matter Theory, Big Bang
by
ronjon
on February 21, 2008 02:00AM (PST)
"How inflation happened a split second after the Big Bang." "Identify the exact sources of these cosmic rays and how they accelerate particles." Two different Nobel Laureates raised these two unrelated queries in cosmology publicly in November and December 2007. The timing of these queries is close to the fourth anniversary of a postmodern Big Bang cosmology theory published Dec. 15, 2003, in a cosmology book, "How Dark Matter Created Dark Energy and the Sun," authored by Jerome Drexler.
There is the possibility that plausible answers or helpful responses to both of these queries can be derived from a recent cosmology paper utilizing Drexler's dark matter theory and Big Bang cosmology... The paper argues that the Big Bang, which occurred at the beginning of time, must have satisfied the Second Law of Thermodynamics. Thus, immediately after the Big Bang the entropy of the universe would be at the lowest level it would reach throughout all time. Therefore, the Big Bang should not be characterized, as it has been for over 40 years, as a chaotic fireball explosion associated with a high level of disorder and high entropy. The very low entropy could be achieved by the Big Bang firing out, in all directions, high-velocity ultra-high-energy (UHE) relativistic protons and helium nuclei in the well-known ratio of 12 to 1. A very high percentage of their energies would be available to do work since their entropy, a measure of the percentage of their energy unavailable to do work, would be very low. Such a Big Bang, characterized by a dispersion of UHE relativistic nuclei, would be highly efficient and could create very high usable energy and very low entropy, and might be designated a Relativistic Big Bang. This concept is fundamental to Drexler's dark matter theory and his postmodern Big Bang cosmology. ... more » Wednesday, February 20
Military Hopes to Bring Down [Potentially Dangerous] Satellite
by
ronjon
on February 20, 2008 04:39PM (PST)
The Pentagon counted down Wednesday toward an unprecedented effort to shoot down a dying and potentially deadly U.S. spy satellite, using a souped-up missile fired from a ship in the Pacific.
The timing was tricky. For the best chance to succeed, the military awaited a combination of favorable factors: steady seas around the Navy cruiser that would fire the missile, optimum positioning of the satellite as it passed in polar orbit and the readiness of an array of space- and ground-based sensors to help cue the missile and track the results. The operation was so extraordinary, with such intense international publicity and political ramifications, that Defense Secretary Robert Gates — not a military commander — was to make the final decision to pull the trigger. The government organized hazardous materials teams, under the code name "Burnt Frost," to be flown to the site of any dangerous or otherwise sensitive debris that might land in the United States or elsewhere. ... more » Tuesday, February 19
Potentially Habitable Planets Are Common, Study Says
by
ronjon
on February 19, 2008 02:49PM (PST)
More than half of the sunlike stars in the galaxy could have terrestrial planets with the potential to harbor life, a new study suggests.
The research, announced yesterday at a meeting of the American Association for the Advancement of Science in Boston, Massachusetts, is just one of a set of recent findings that suggest the roster of potential life-harboring worlds is huge—even in our own solar system. "Our observations suggest that between 20 percent and 60 percent of sunlike stars form rocky planets like our solar system's," said Michael Meyer, an astronomer at the University of Arizona, at a press briefing Sunday. Meyer and his team used NASA's Spitzer Space Telescope to study heat from the dust around sunlike stars of various ages, much like looking at "the smoke you see rising from chimneys in Boston on a cold day." ... more » Monday, February 18
Superfluids could create a 'universe in a bucket'
by
ronjon
on February 18, 2008 02:00AM (PST)
IT'S an ambitious task, recreating the universe in a bucket. But if it is successful, the experiment could help solve the twin puzzles of why we're made of matter rather than antimatter and where the huge magnetic fields that span galaxies come from.
At last month's Cosmology Meets Condensed Matter conference in London, it emerged that space-time could be simulated in the lab using weird substances known as "superfluids", which flow without resistance and can even climb up the walls of jars. Intriguingly, the equations governing the particles inside superfluids are similar to those that represent the early universe, says Ray Rivers at Imperial College London. "We hope that we can use these to check things in the lab that frankly we don't have any hope of seeing through astrophysical observations." ... more » Sunday, February 17
Laser Light Creates [first?] Black Holes In The Lab
by
ronjon
on February 17, 2008 09:57PM (PST)
Imagine being able to peek inside a black hole and even perform experiments there. It may not be as far-fetched as it sounds, thanks to a team which claims to have simulated a black hole’s event horizon in the lab. -- Ulf Leonhardt at the University of St Andrews, UK, and his colleagues accomplished the feat by firing lasers down an optical fiber, exploiting the fact that different wavelengths of light move at different speeds within an optical fiber.
They first shot a relatively slowmoving laser pulse through the fibre, and then sent a faster “probe wave” chasing after it. The first pulse distorts the optical properties of the fibre simply by travelling through it. This distortion forces the speedy probe wave to slow down dramatically when it catches up with the slower pulse and tries to move through it. In fact, the probe wave becomes trapped and can never overtake the pulse’s leading edge, which effectively becomes a black hole event horizon, beyond which light cannot escape. This “laser black hole” could allow physicists to examine what happens to light on both sides of a event horizon – “a feat that is utterly impossible in astrophysics”, the authors note in their paper. ... more » Saturday, February 16
New frontiers in space propulsion sciences
by
ronjon
on February 16, 2008 02:00AM (PST)
Abstract
Mankind's destiny points toward a quest for the stars. Realistically, it is difficult to achieve this using current space propulsion science and develop the prerequisite technologies, which for the most part requires the use of massive amounts of propellant to be expelled from the system. Therefore, creative approaches are needed to reduce or eliminate the need for a propellant. Many researchers have identified several unusual approaches that represent immature theories based upon highly advanced concepts. These theories and concepts could lead to creating the enabling technologies and forward thinking necessary to eventually result in developing new directions in space propulsion science. In this paper, some of these theoretical and technological concepts are examined approaches based upon Einstein's General Theory of Relativity, spacetime curvature, superconductivity, and newer ideas where questions are raised regarding conservation theorems and if some of the governing laws of physics, as we know them, could be violated or are even valid. These conceptual ideas vary from traversable wormholes, Krasnikov tubes and Alcubierre's warpdrive to Electromagnetic (EM) field propulsion with possible hybrid systems that incorporate our current limited understanding of zero point fields and quantum mechanics. ... more » Sunday, February 10
[Most] Biofuels Deemed a Greenhouse Threat
by
ronjon
on February 10, 2008 02:00AM (PST)
Almost all biofuels used today cause more greenhouse gas emissions than conventional fuels if the full emissions costs of producing these “green” fuels are taken into account, two studies published Thursday have concluded...
Together the two studies offer sweeping conclusions: It does not matter if it is rain forest or scrubland that is cleared, the greenhouse gas contribution is significant. More important, they discovered that, taken globally, the production of almost all biofuels resulted, directly or indirectly, intentionally or not, in new lands being cleared, either for food or fuel. “When you take this into account, most of the biofuel that people are using or planning to use would probably increase greenhouse gasses substantially,” said Timothy Searchinger, lead author of one of the studies and a researcher in environment and economics at Princeton University. “Previously there’s been an accounting error: land use change has been left out of prior analysis.” ... more » Thursday, February 7
"We Should Take the 'Posthuman' Era Seriously," by Martin Rees (Pres. of the Royal Society)
by
ronjon
on February 7, 2008 01:03PM (PST)
Public discourse on very long-term planning is riddled with inconsistencies. Mostly we discount the future very heavily — investment decisions are expected to pay off within a decade or two. But when we do look further ahead — in discussions of energy policy, global warming and so forth — we underestimate the possible pace of transformational change. In particular, we need to keep our minds open — or at least ajar — to the possibility that humans themselves could change drastically within a few centuries.
Our medieval forebears in Europe had a cosmic perspective that was a million-fold more constricted than ours. Their entire cosmology — from creation to apocalypse — spanned only a few thousand years. Today, the stupendous time spans of the evolutionary past are part of common culture — except among some creationists and fundamentalists. Moreover, we are mindful of immense future potential. It seems absurd to regard humans as the culmination of the evolutionary tree. Any creatures witnessing the Sun's demise 6 billion years hence won't be human — they could be as different from us as we are from slime mould... Human-induced changes are occurring with runaway speed. It's hard to predict a mere century from now, because what will happen depends on us — this is the first century where humans can collectively transform, or even ravage, the entire biosphere. Humanity will soon itself be malleable, to an extent that's qualitatively new in the history of our species. New drugs (and perhaps even implants into our brains) could change human character; the cyberworld has potential that is both exhilarating and frightening. We can't confidently guess lifestyles, attitudes, social structures, or population sizes a century hence. Indeed, it's not even clear for how long our descendants would remain distinctively 'human'. Darwin himself noted that "not one living species will transmit its unaltered likeness to a distant futurity". Our own species will surely change and diversify faster than any predecessor —— via human-induced modifications (whether intelligently-controlled or unintended), not by natural selection alone... more » Wednesday, February 6
Galaxy without dark matter puzzles astronomers
by
ronjon
on February 6, 2008 05:23PM (PST)
...In the outer regions of most galaxies, stars orbit around the centre so fast that they should fly away. The combined mass of all the observable inner stars and gas does not exert strong enough gravity to hold onto these speeding outliers, suggesting some mass is missing. -- Most astronomers believe that the missing mass is made up of some exotic invisible substance, labelled dark matter, which forms vast spherical halos around each galaxy. Another possibility is that the force of gravity behaves in an unexpected way, a theory known as modified Newtonian dynamics, or MOND.
In the spiral galaxy NGC 4736, however, the rotation slows down as you move farther out from the crowded inner reaches of the galaxy. At first glance, that declining rotation curve is just what you would expect if there is no extended halo of dark matter, and no modification to gravity. As you move far away from the swarming stars of the inner galaxy, gravity becomes weaker, and so motions become more sedate. ...one exceptional dark-matter-less galaxy would be a great puzzle. "The current picture is that galaxies form inside of dark matter halos," Diemand told New Scientist. The dark matter's gravity attracts ordinary gas, which can then coagulate into stars. -- It is unclear how one would form a galaxy without a dark halo, or how one could remove the halo without destroying the galaxy," says Diemand. "A galaxy without dark matter really does not fit into our current understanding of cosmology and galaxy formation." ... more » Tuesday, February 5
Human DNA, the Ultimate Spot for Secret Messages (Are Some There Now?)
by
ronjon
on February 5, 2008 02:00AM (PST)
...a team of Japanese geneticists...announced that they had taught relativity to a bacterium, sort of.
Using the same code that computer keyboards use, the Japanese group, led by Masaru Tomita of Keio University, wrote four copies of Albert Einstein’s famous formula, E=mc2, along with “1905,” the date that the young Einstein derived it, into the bacterium’s genome, the 4.2-million-long string of A’s, G’s, T’s and C’s that determine everything the little bug is and everything it’s ever going to be. The point was not to celebrate Einstein. The feat, they said in a paper published in the journal Biotechnology Progress, was a demonstration of DNA as the ultimate information storage material, able to withstand floods, terrorism, time and the changing fashions in technology, not to mention the ability to be imprinted with little unobtrusive trademark labels — little “Made by Monsanto” tags, say. ... more » Monday, February 4
NASA to beam Beatles' song 'Across the Universe' to deep space on Feb.4,2008
by
ronjon
on February 4, 2008 02:00AM (PST)
...at 7 p.m. Eastern time on Monday, Feb. 4...NASA will be celebrating the 50th anniversary of its first space mission — the launch of the Explorer 1 satellite — by using the system of huge antennas that usually listen for inbound signals from space to send one outbound instead: the Beatles’ song “Across the Universe,” which as it happens was mostly recorded exactly 40 years earlier, on Feb. 4, 1968.
Reception will be best in the general direction of Polaris, 431 lightyears away, which is where NASA is aiming the signal. (That would be the North Star to us laymen.) But it ought to be audible in plenty of places on Earth as well, at least by imitation: NASA is encouraging space fans and Beatle fans alike to play the song themselves at the same time. NASA’s press release includes some perfectly in-character comments from Sir Paul McCartney (”Amazing! Well done, NASA! Send my love to the aliens. All the best, Paul.”) and from Yoko Ono, widow of John Lennon, the song’s main author (”I see that this is the beginning of the new age in which we will communicate with billions of planets across the universe.”). ... more » |
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