Wednesday, December 26, 2012

Slipher data was before Hubble

I have posted papers showing that Hubble does not deserve credit for discovering the big bang. Now Cormac O. Raifeartaigh posts a new paper:
A brief history of the discovery of the expanding universe is presented, with an emphasis on the seminal contribution of VM Slipher. It is suggested that the well-known Hubble graph of 1929 could also be known as the Hubble-Slipher graph. It is also argued that the discovery of the expanding universe matches the traditional view of scientific advance as a gradual process of discovery and acceptance, and does not concur with the Kuhnian view of science progressing via abrupt paradigm shifts.
He explains how Lemaitre and others did the theoretical work, and Hubble relied on Slipher, in part, for experimental work. The paper also says that Hubble never really accepted the big bang, and left open the possibility that his data might be consistent with other models.

The paper also argues that the discovery of the big bang was nothing like a Kuhnian paradigm shift. If there were any merit to Kuhn's philosophy, then the big bang should have been a paradigm shift. The whole concept of a paradigm shift is bogus.

Update: Another new paper says:
Much debate has ensued recently over who deserves credit for being first to discover the Universe is expanding. Lemaître’s theoretical discovery of expansion in 1927 was not translated into English until two years after Hubble’s observational discovery of expansion in 1929 (Lemaître 1927b, translated 1931). Further, that translation omitted the Hubble constant of expansion that Lemaître calculated in 1927. That omission, only recently revealed in these pages by frequent contributor to JRASC Sidney van den Bergh of the Dominion Astrophysical Observatory, peaked the debate (see van den Bergh 2011, JRASC 105,151). At least a dozen papers regarding Hubble’s priority in the discovery of expansion have been published in the last two years alone, more papers regarding Hubble’s priority than were written in all the years since 1929 combined.

Monday, December 24, 2012

Incinerated by a black hole firewall

Jennifer Ouellette writes in SciAm:
Conventionally, physicists have assumed that if the black hole is large enough, Alice won’t notice anything unusual as she crosses the horizon. In this scenario, colorfully dubbed “No Drama,” the gravitational forces won’t become extreme until she approaches a point inside the black hole called the singularity. There, the gravitational pull will be so much stronger on her feet than on her head that Alice will be “spaghettified.”

Now a new hypothesis is giving poor Alice even more drama than she bargained for. If this alternative is correct, as the unsuspecting Alice crosses the event horizon, she will encounter a massive wall of fire that will incinerate her on the spot. As unfair as this seems for Alice, the scenario would also mean that at least one of three cherished notions in theoretical physics must be wrong. ...

Paradoxes in physics have a way of clarifying key issues. At the heart of this particular puzzle lies a conflict between three fundamental postulates beloved by many physicists. The first, based on the equivalence principle of general relativity, leads to the No Drama scenario: Because Alice is in free fall as she crosses the horizon, and there is no difference between free fall and inertial motion, she shouldn’t feel extreme effects of gravity. The second postulate is unitarity, the assumption, in keeping with a fundamental tenet of quantum mechanics, that information that falls into a black hole is not irretrievably lost. Lastly, there is what might be best described as “normality,” namely, that physics works as expected far away from a black hole even if it breaks down at some point within the black hole — either at the singularity or at the event horizon.
I haven't read these papers, but this conflict sounds crazy to me. Unitarity is not a fundamental tenet of quantum mechanics. It is not a physical principle at all, and there is no physical evidence for it. It is only thought to be important by those with some philosophical disagreement with wave function collapse.

The idea that Alice will be incinerated by a massive wall of fire upon entering a black hole sounds a little bit like the story of Lot's wife in the Bible.

A comment gives the source for Einstein's "spooky action at a distance":
"I cannot make a case for my attitude in physics which you would consider at all reasonable. I admit, of course, that there is a considerable amount of validity in the statistical approach which you were the first to recognise clearly as necessary given the framework of the existing formalism. I cannot seriously believe in it because the theory cannot be reconciled with the idea that physics should represent a reality in time and space, free from spooky actions at a distance. I am, however, not yet firmly convinced it can really be achieved with a continuous field theory, although I have discovered a possible way of doing this which so far seems quite reasonable...But I am quite convinced that someone will eventually come up with a theory whose objects, connected by laws, are not probabilities but considered facts, as used to be taken for granted until quite recently. I cannot however, base this conviction on logical reasons, but can only produce my little finger as witness, that is I offer no authority which would be able to command any kind of respect outside of my own hand." (Einstein to Born, 2 Mar. 1947.)

Born comments: "I too had considered this postulate [that physics should represent a reality in time and space] to be one which could claim absolute validity. But the realities of physical experience had taught me that this postulate is not an a priori principle but a time-dependent rule which must be, and can be, replaced by a more general one."
Einstein wants to reject quantum mechanics in favor of some sort of hidden variable theory, and his buddy Max Born cannot convince him that the probabilities are essential. In my opinion, they were both wrong.

String theorist Lumo adds his criticism of Ouellette's article:
Well, more precisely, it's nice and informative if you assume that her task was to uncritically promote the views of Joe Polchinski, Leonard Susskind, Raphael Bousso, and a few others. From a more objective viewpoint, the article's main message is wrong and the text misinterprets the state of the research, too.

Over the last decade or so, my great respect for some of the most famous names in high-energy physics was diminishing and this trend has become undeniable by now. It seems to me that my previous worries about the apparent deterioration of meritocracy within the field have turned out to be a tangible reality.

Saturday, December 22, 2012

String theory races for Kuhnian glory

Chemist Ashutosh (Ash) Jogalekar writes in SciAm:
Freeman Dyson has a perspective in this week’s Science magazine in which he provides a summary of a theme he has explored in his book “The Sun, the Genome and the Internet”. Dyson’s central thesis is that scientific revolutions are driven as much or even more by tools than by ideas. This view runs somewhat contrary to the generally accepted belief regarding the dominance of Kuhnian revolutions – described famously by Thomas Kuhn in his seminal book “The Structure of Scientific Revolutions” – which are engineered by ideas and shifting paradigms. In contrast, in reference to Harvard university historian of science Peter Galison, Dyson emphasizes the importance of Galisonian revolutions which are driven mainly by experimental tools.

As a chemist I find myself in almost complete agreement with the idea of tool-driven Galisonian revolutions.
Dyson writes:
Thomas Kuhn was a theoretical physicist before he became a historian. He saw the history of science through the eyes of a theorist. He gave us an accurate view of events in the world of ideas. His favorite word, “paradigm,” means a system of ideas that dominate the science of a particular place and time. A scientific revolution is a discontinuous shift from one paradigm to another. The shift happens suddenly because new ideas explode with a barrage of new insights and new questions that push old ideas into oblivion. I remember the joy of reading Kuhn's book, The Structure of Scientific Revolutions, when it first appeared in 1962. It made sense of the relativity and quantum revolutions that had happened just before the theoretical physicists of my generation were born. Those were revolutions led by deep thinkers — Einstein and Heisenberg and Schrödinger and Dirac — who guessed nature's secrets by dreaming dreams of mathematical beauty. Their new paradigms were created out of abstract ideas. In those revolutionary years from 1900 to 1930, ideas led the way to understanding.
These guys are badly confused. A Kuhnian paradigm shifts is a reformulation of a scientific theory that is has no measurable advantage to the previous theory. The canonical examples are Copernican heliocentrism and Einstein's 1905 relativity paper. Kuhn wrote a whole book on the dawn of quantum mechanics, and did not say that it was a revolution or paradigm shift.

The term paradigm shift is also used by crackpots who complain that the science establishment is ignoring their silly ideas.

The Copernican revolution was the Earth revolving around the Sun. It was a different point of view, but did not approximate the observable orbits any more accurately.

Einstein's 1905 relativity was essentially the same as Lorentz's, with minor technical differences.

Dyson ends up concluding that string theory and multiverse speculations are entirely Kuhnian:
At the beginning of the 21st century, we find ourselves in a situation reminiscent of the 1950s. Once again, the community of physi-cists is split into Kuhnians and Galisonians. The most ambitious of the Kuhnian programs is string theory, building a grand and beauti-ful structure out of abstract mathematics and hoping to find it somehow mirrored in the architecture of the universe. This program is not an isolated one-man show like Einstein’s unified field theory. String theory is a collec-tive enterprise combining the efforts of thou-sands of people in hundreds of universities. These people are the best and the brightest of their generation, most of them young and many of them brilliant. Their work is admired by the pure mathematicians who share their ideas and speak their language. String theory, as a solid part of modern mathematics, is here to stay. But meanwhile, Galisonian science is continuing to forge ahead, exploring nature without paying attention to string theory. The great recent discoveries in the physical sci-ences were dark matter and dark energy, two mysterious monsters together constituting 97% of the mass of the universe. These dis-coveries did not give rise to new paradigms. ...

We are standing now as we stood in the 1950s, between a Kuhnian dream of sudden illumination and a Galisonian reality of labo-rious exploring. On one side are string theory and speculations about multiverses; on the other are all-sky surveys and observations of real black holes. The balance today is more even than it was in the 1950s. String theory is a far more promising venture than Einstein’s unified field theory. Kuhn and Galison are running neck and neck in the race for glory. We are lucky to live in a time when both are going strong.
I agree that string theory and multiverse theory are Kuhnian in that they have no hope of making any measurable progress in our understanding of the world, and that belief in them is not rational. It is only because of Einsteinian-Kuhnian thinking that there is any glory in such activity.

In a companion essay (also behind a paywall), molecular biologist Sydney Brenner argues:
It seems remark-able that historians once thought that science
progressed by the steady addition of knowl-edge, building the edifice of scientific truth, brick by brick. In his 1962 book The Struc-ture of Scientific Revolutions, Thomas Kuhn argued that progress occurs in revolutionary steps by the introduction of new paradigms, which may be new theories—new ways of looking at the world—or new technical meth-ods that enhance observation and analysis. Between Kuhn’s revolutions, scientific knowledge does advance by accretion, as there is much to do to consolidate the new sci-ence. But then, inevitably, unsolved problems accumulate and, in many cases, the inconsis-tencies have been put to one side and every-body hopes that they will quietly go away. The edifice becomes rickety; some of its founda-tions are insecure and many of the bricks have not been well-baked. This is when a new rev-olutionary wave in the form of new ideas or new techniques appears, which allows us to condemn and demolish the unsafe or corrupt parts of the edifice and rebuild truth. Often there is great resistance to the new wave, but as Max Planck pointed out, it succeeds because the opponents grow old and die. The process is then repeated: The radicals become liberals, the liberals become conservatives, the conservatives become reactionaries, and the reactionaries disappear. Students of evolu-tion will recognize this process in the theory of punctuated equilibrium: Organisms stay much the same for very long periods of time; this is interrupted by bursts of change when novelty appears, followed again by stasis. The life sciences have undergone a radical revolution in my lifetime, and it is interesting to view this from the vantage point of the pres-ent to understand its full meaning and impact. In the first half of the 20th century, physics underwent two revolutions: Einstein’s theory of relativity, connected with large scales of time and space, and quantum mechanics, con-cerned with the very small and dealing with fundamental questions of matter and energy. ...

We can now see exactly what consti-tuted the new paradigm in the life sci-ences: It was the introduction of the idea of information and its physical embodiment in DNA sequences of four different bases. Thus, although the components of DNA are simple chemicals, the complexity that can be generated by different sequences is enormous. In 1953, biochemists were pre-occupied only with questions of matter and energy, but now they had to add informa-tion.
It is amazing how otherwise-intelligent scientists fall for this nonsense. The discovery of DNA sequences was not like what Kuhn described as a paradigm shift. It was not just an incommensurable new view on an old theory. It did not succeed because the opponents grew old and die. The first Nobel prize for relativity was in 1902 to Lorentz and for quantum mechanics in 1918 (Planck) and 1922 (Bohr). Heisenberg, Schrödinger, and Dirac got their prizes in 1932-33 for work done only about 5 years earlier. Compare that to string theory and multiverse theory, where no one has ever gotten a Nobel prize.

Thursday, December 20, 2012

Not living in the matrix

Physicist Silas Beane explains:
The idea that we live in a simulation is just science fiction, isn't it?
There is a famous argument that we probably do live in a simulation. The idea is that in future, humans will be able to simulate entire universes quite easily. And given the vastness of time ahead, the number of these simulations is likely to be huge. So if you ask the question: 'do we live in the one true reality or in one of the many simulations?', the answer, statistically speaking, is that we're more likely to be living in a simulation. ...

But can we improve our own simulations?
The size of the universe we simulate is a just fermi, that's a box with sides 10-15 metres long. But we can use Moore's Law to imagine what we might be able to simulate in future. If the current trends in computing continue, we should be simulating a universe the size of a human within a century and within five centuries, we could manage a box 1026 metres big. That's the size of the observable universe.
This is a pretty crazy extrapolation of Moore's Law. The law might be good for another 10 years, but that's all. Yes, the idea that we are living in a simulation is pure science fiction.

I also don't know how to reconcile this with the recent SciAm claim that fermions cannot be simulated on a computer. How can we hope to simulate the universe if we cannot even simulate a single proton?

Wednesday, December 19, 2012

History of twin paradox

This new paper on the history of the relativity twin paradox has this amusing argument for the psychological significance of using twins to illustrate time dilation:
II 5 Why Twins?
As mentioned above, although the idea of twins was given by Weyl 1922, it is only around the fifties of the preceding century that the name twin paradox was very often used. To find the hidden reason for this habit, I propose to investigate the collective image of twinship as it was elaborated trough myths and religions and to relate it to the use of the word.

I begin by quoting B.Beit_Hallahmi and M.Paluszny (1974) from their paper on twinship:
"…there are common psychological elements in both mythological and scientific approaches to twinship. The major elements are fascination and ambivalence. Fascination with twin births has always been combined with a great deal of apprehension and ambivalence. In both primitive and modern societies, multiple births have been viewed as a potential source of familial and social conflict and complication."

Effectively one finds in the Bible and several mythologies frequent situations of conflict between twins. In the Bible one can mention Cain and Abel with the murder of Abel and also Jacob and Esau. Esau wants to kill his twin brother Jacob but Jacob has time to escape.

In the Greek mythology (See the works of Aeschylus (1966)), the fight between Atreus
(preferred by Zeus) and Thyestes (preferred by the people) with all the successive conflicts in the Atrides family is well known. In the roman mythology, the two twins Remus and Romulus (see the details of the story in Plutarch) who are the founders of Rome, are fighting for the government of the city. It results that Romulus kills his twin Remus.

In a complete different context, Levi-Strauss (1995) analyzed the myths of some North
America and South America Indians and considers the antagonism between twins as a
source of disequilibrium. In fact, the twins' conflict is not completely general since there are also some cases where the twins manage their life in peace. For example in the Greek mythology the twins Castor and Pollux are in good relationship and there are taken as example of a peaceful twinship. Nevertheless the collective image of twins is frequently related to conflict and violence. This double presence of two identical persons is seen as something scandalous and abnormal. One of them must disappear or at least put in a bad position.

I propose to adopt this point of view considering the twins of the paradox. In the unconscious mind, the twinship must be destroyed and in the paradox this is what happened: one of the twins remains young and the other old, when young is better than old. I propose to interpret the habit to give the name "twin paradox" to the clock paradox as an intrusion of the subconscious in the language of physicists. All the efforts of the physicists are to show the asymmetry in the twins as it must be.
It should not be so surprising for one twin to be older than the other. Even without relativistic effects, if one twin went on a long trip and was put in cryogenic hibernation as in 2001: A Space Odyssey, then he would return noticeably younger just like the twin paradox.

Monday, December 17, 2012

Aether no more than a metaphysical construct

Steve Carlip and Philip Gibbs summarize the history of special relativity:
In 1879 it was thought that light must propagate through a medium in space just as sound propagates through the air and other substances. The two scientists Michelson and Morley set up an experiment to attempt to detect the ether, by observing relative changes in the speed of light as the Earth changed its direction of travel relative to the sun during the year. To their surprise, they failed to detect any change in the speed of light.

Fitzgerald then suggested that this might be because the experimental apparatus contracted as it passed through the ether, in such a way as to countermand the attempt to detect the change in velocity. Lorentz extended this idea to changes in the rates of clocks to ensure complete undetectability of the ether. Einstein then argued that those transformations should be understood as changes of space and time rather than of physical objects, and that the absoluteness of space and time introduced by Newton should be discarded. Just after that, the mathematician Minkowski showed that Einstein's theory of relativity could be understood in terms of a four dimensional non-euclidean geometry that considered space and time as one entity, ever after called spacetime.

This refers to Fitzgerald 1889, Lorentz 1895, Einstein 1905, and Minkowski 1908. It ignores the 1899-1905 work of Lorentz and Poincare, where they perfected the Lorentz transformations and applied them to space and time more generally than Einstein, and before Einstein.
But what if we pursued the original theory of Fitzgerald and Lorentz, who proposed that the ether is there, but is undetectable because of physical changes in the lengths of material objects and the rates of clocks, rather than changes in space and time? For such a theory to be consistent with observation, the ether would need to be completely undetectable using clocks and rulers. Everything, including the observer, would have to contract and slow down by just the right amounts. Such a theory could make exactly the same prediction in all experiments as the theory of relativity; but in that case the ether would be no more than a metaphysical construct unless there was some other way of detecting it — which nobody has found. In the view of Einstein, such a construct would be an unnecessary complication, to be best eliminated from the theory.
That is correct about Lorentz aether theory, and it is what Poincare always said. As early as 1889, he said:
Whether the ether exists or not matters little - let us leave that to the metaphysicians; what is essential for us is, that everything happens as if it existed, and that this hypothesis is found to be suitable for the explanation of phenomena. After all, have we any other reason for believing in the existence of material objects? That, too, is only a convenient hypothesis; only, it will never cease to be so, while some day, no doubt, the ether will be thrown aside as useless.
Poincare also said this in his popular 1902 book, which Einstein read with his physicist friends. They say that he was greatly fascinated by it.

Sometimes Einstein fans imply that Lorentz and Poincare had an inferior understanding of relativity because they did not realize that experiments had reduced the aether to an undetectable metaphysical construct. But that is exactly how Poincare described it. Einstein was not as clear about it, and used language similar to Lorentz.

I explain these points in my book.

Thursday, December 13, 2012

Essay winners not so contrarian

I am disappointed in the winners of the FQXi essay contest. Maybe I am just a sore loser, because my essay is not one of the 20 winners, out of 271 submissions. But I do not think that the winners followed the contest objectives very well.

Most of the submissions violated this rule:
The instructions say this:

“Successful and interesting essays will not use this topic as an opportunity to trot out their pet theories simply because those theories reject assumptions of some other or established theory. Rather, the challenge here is to create new and insightful questions or analysis about basic, often tacit, assumptions that can be questioned but often are not”
Most essays just promoted some crackpot theory without really explaining how or why the textbook theories are wrong.

Unfortunately, FQXi has taken down the page with these rules. You can find most of them here, or maybe in your browser cache.

Of the winning essays, most of them promote some completely mainstream and accepted idea, but try to make it sound original by attacking some silly straw man. Other essays presented some vague and speculative ideas about quantum gravity or some similar field where ideas cannot be tested.

In 2nd place, Ellis gives examples of causation being more easily understood with a top-down view, such as entropy increasing. Weinstein suggests that action-at-a-distance might explain some quantum mechanics and cosmology.

In 3rd place, Barbour doubts that reductionism will explain entanglement. Dribus rejects spacetime in favor of a "causal metric hypothesis". Hossenfelder speculates about quantum gravity. Wharton says the universe is not a computer.

My essay got a lot of attention, and many favorable comments. I have some much more provocative statements than the winning essays, but I thought that was the point. Most of the essays don't actually say Which of Our Basic Physical assumptions are Wrong.

The rules also say:
Interesting: An interesting essay is:
  • Original and Creative: Foremost, the intellectual content of the essay must push forward understanding of the topic in a fresh way or with new perspective. While the essay may or may not constitute original research, if the core ideas are largely contained in published works, those works should be the author's. At the same time, the entry should differ substantially from any previously published piece by the author.
  • Technically correct and rigorously argued, to the degree of a published work or grant proposal.
  • Well and clearly written, so that it is comprehensible and enjoyable to read.
  • Accessible to a diverse, well-educated but non-specialist audience, aiming in the range between the level of Scientific American and a review article in Science or Nature.
So perhaps the judges thought that my essay was not "Technically correct and rigorously argued". If so, then I would have preferred them to say so in the online comments, so I could defend myself. As it is, I do not know what they disliked. If I had submitted it to a journal, at least I would have gotten a rejection report. I guess I could still submit it somewhere else, but it is not really a technical physics advance. It is an essay suited for this contest.

Saturday, December 8, 2012

Lundmark also predated Hubble

I posted last year (and previously) that Lemaitre discovered the expanding universe, and was the real father of the big bang.

Now Ian Steer posts Who discovered Universe expansion?:
Swedish astronomer, Knut Lundmark, were much more advanced than formerly appreciated. ...

Lundmark was the first person to find observational evidence for expansion, in 1924 — three years before Lemaître and five years before Hubble. Lundmark’s extragalactic distance estimates were far more accurate than Hubble’s, consistent with an expansion rate (Hubble constant) that was within 1% of the best measurements today. ...

Hubble’s research in 1929 yielded a value for the Hubble constant that was inaccurate by almost an order of magnitude. It was adopted because it was derived from multiple methods — including one still in use (brightest stars) — and was cross-checked with multiple galaxies with distances based on proven Cepheid star variables.
I credit Lemaitre because he was the first to publish a cosmological model with red-shift proportional to distance, and to publish observational data to back it up. I don't know how Hubble stole the credit.

Friday, December 7, 2012

Physics essay winners announced

The 2012 Questioning the Foundations Winning Essays were just announced. The winning essay presents a distinction between kinematics and dynamics, with the main difference being that a dynamical theory tries to explain change under time. It argues that this distinction is not so important, and that it is better to think about the causal structure for how variables are influenced by variables at earlier times. Its preferred examples involve strange interpretations of quantum mechanics that violate local causality.

General relativity is an example of a theory that has a causal structure but does not really distinguish between kinematics and dynamics. But the paper says:
While proponents of diff erent interpretations of quantum theory and proponents of diff erent approaches to quan-tizing gravity may disagree about the correct kinematics and dynamics, they typically agree that any proposal must
be described in these terms.
No, I very much doubt that any proponents of quantum gravity agree that the kinematics and dynamics must be separated, because everyone has said for a century that they are not separate for gravity.

The object of the essay contest was to answer the question: "Which of Our Basic Physical Assumptions Are Wrong?" I was disappointed that most of the essays do not really answer the question.

Thursday, December 6, 2012

String theory defense published

Peter Woit writes that you can now get a state-of-the-art defense of the theory:
The journal Foundations of Physics has been promising a special issue on “Forty Years of String Theory: Reflecting on the Foundations” for quite a while now, with a contribution first appearing back when it really was 40 years since the beginnings (more like 43 now). The final contribution has now appeared, an introductory essay by the editors (’t Hooft, Erik Verlinde, Sebastian de Haro and Dennis Dieks).

The overall tone of the collection is one of defensive promotion of the subject. The fact that string theory’s massively overhyped claims to give a unified theory of particle physics have led to miserable failure is mostly completely ignored.
Bob Jones adds:
Most people would say that string theory is an idea about quantum gravity. ... You can complain all you want about the lack of testable predictions in particle physics, but these objections seem pretty irrelevant since most string theorists aren’t trying to do phenomenology and since string theory has achieved so much success in other areas…
I may be stupid, but I fail to see that string theory has anything to do with quantum gravity.

The best theory of gravity is general relativity. String theorists nearly always assume that no gravity is present. To account for gravity, they sometimes just say that the underlying space could satisfy the equations of general relativity. Relativity uses a 4-dimensional spacetime, and string theorists use 10 or 11 dimensions, so they extend the equations. But that's all. They do not quantize gravity. They claim to have a theory of everything with quantum field theory have gravity, but they have no quantum gravitational fields. They say that the theory has a graviton, but quantum mechanics is about observables and the graviton is impossible to observe.

I wonder how a non-physicist would understand the excuse that "string theorists aren’t trying to do phenomenology". Wikipedia defines:
The term phenomenology in science is used to describe a body of knowledge that relates empirical observations of phenomena to each other, in a way that is consistent with fundamental theory, but is not directly derived from theory.
Someone might ask how one could be a scientist and not care about phenomenology. The answer is that string theorists have never been able to relate their theories to phenomena, so they ignore phenomena.

Leonard Susskind writes:
Just to be precise about what constitutes string theory, let me give a narrow definition — no doubt much too narrow for many string theorists. But it has the virtue that we know that it mathematically exists. By string theory I will mean the theory of supersymmetric string backgrounds including 11-dimensional M-theory and com-pactifications that preserve some degree of supersymmetry. These backrounds are generally either flat (zero cosmological constant) or anti de Sitter space with negative cosmological constant.

With that definition of string theory, there is no doubt: string theory is not the theory of nature — the world is not supersymmetric, and it has positive cosmolog-ical constant. Exactly how the definition has to be expanded in order to describe the observed universe is not known. Nevertheless string theory has had a pro-found, and I believe lasting, influence on how gravity and quantum mechanics fit together.
Steven B. Giddings tries to summarize the outlook for making string theory a quantum gravity theory:
To summarize the situation, string theory has been a continuous source of new ideas in mathematics and physics, and showed a lot of initial promise for resolving the problems of quantum gravity. However, the more profound problems are yet to be convincingly addressed, and there are deep puzzles about how they might be addressed by string theory. ...

We seek a consistent framework for describing quantum processes, in which spacetime locality emerges in an approximation. This, together with the requirement that it produce an S-matrix (and other local dynamics) with familiar properties of gravity seems a very tall order. This is actually encouraging, as it suggests the problem is sufficiently constrained to guide the resolution of this profoundly challenging set of problems. It remains to be seen what role string theory plays in this, and whether it can provide further clues.
Keep in mind that these are top string theorists trying to defend the theory. But it is painfully that any connection between string theory and quantum gravity is wildly speculative.

Update: I see Lumo has a long tortured explanation of whether string theory makes presumptions about gravitational fields. There is no simple answer.

Sunday, December 2, 2012

New translation of anti-Galileo argument

Christopher M. Graney has just posted this paper:
In January of 1616, the month before before the Roman Inquisition would infamously condemn the Copernican theory as being "foolish and absurd in philosophy", Monsignor Francesco Ingoli addressed Galileo Galilei with an essay entitled "Disputation concerning the location and rest of Earth against the system of Copernicus". A rendition of this essay into English, along with the full text of the essay in the original Latin, is provided in this paper. The essay, upon which the Inquisition condemnation was likely based, lists mathematical, physical, and theological arguments against the Copernican theory. Ingoli asks Galileo to respond to those mathematical and physical arguments that are "more weighty", and does not ask him to respond to the theological arguments at all. The mathematical and physical arguments Ingoli presents are largely the anti-Copernican arguments of the great Danish astronomer Tycho Brahe; one of these (an argument based on measurements of the apparent sizes of stars) was all but unanswerable. Ingoli's emphasis on the scientific arguments of Brahe, and his lack of emphasis on theological arguments, raises the question of whether the condemnation of the Copernican theory was, in contrast to how it is usually viewed, essentially scientific in nature, following the ideas of Brahe.
Galileo is always the proof that religion is anti-science, such as in this recent
episode of Rationally Speaking. Sometimes the Pope is ridiculed for refusing to look into a telescope to see Galileo's proof of the Earth's motion. But it is hard to see how the Church could be blamed for using Tycho's arguments, as Tycho was a more accomplished astronomer than Galileo.