"Yevgeniy Brikman shares key lessons from the “Infrastructure Cookbook” they developed at Gruntwork while creating and maintaining a library of over 300,000 lines of infrastructure code used in production by hundreds of companies. Topics include how to design infrastructure APIs, automated tests for infrastructure code, patterns for reuse and composition, refactoring, namespacing, and more."
Brikman gives a sobering presentation about the reality of DevOps rather than the hype.
"Brikman: Thank you all for coming. This is a talk, as Jonas mentioned, of the ugly layer beneath your microservices, all the infrastructure under the hood that it's going to take to make them work and some of the lessons we learned. There's not a great term for this. I'm just going to use the word DevOps, although it's not super well-defined. And one of the things I want to share is a confession about DevOps to start the talk off.
Hey, there it is. There's a limited range on this thing. So here's the confession - the DevOps industry is very much in the stone ages, and I don't say that to be mean or to insult anybody. I just mean, literally, we are still new to this. We have only been doing DevOps, at least as a term, for a few years. Still figuring out how to do it. But what's scary about that is we're being asked to build things that are very modern. We're being asked to put together these amazing, cutting edge infrastructures, but I feel like the tooling we're using to do it looks something like that.
Now, you wouldn't know that if all you did was read blog posts, read the headlines, everything sounds really cutting edge. Half the talks here, half the blog posts out there, they're going to be about, oh my God, Kurbernetes, and Docker, and microservices, and service meshes, and all these unbelievable things that sound really cutting edge. But for me as a developer, on a day to day basis, it doesn't feel quite so cutting edge, right? That's not what my day-to-day experience feels like. My day-to-day experience with DevOps feels a little more like that. You're cooking pizza on an iron with a blow dryer. This is your hashtag for this talk, #thisisdevops. This is what it feels like.
"The Gremlin team has announced "Gremlin Free", which provides the ability to run chaos engineering experiments on a free tier of their failure-as-a-service SaaS platform. The current version of the free tier allows the execution of shutdown and CPU attacks on a host or container, which can be controlled via a simple web-based user interface, API or CLI.
At the end of 2017 the Gremlin team announced the first release of their chaos experimentation SaaS product that supported the coordination of multiple attacks on hosts and the associated infrastructure. In 2018 application-level failure injection (ALFI) was also added, which supported running attacks on individual application services or functions. One of the primary attacks throughout the evolution of the product has been the shutdown of instances, which was partly inspired by the Netflix Chaos Monkey -- one of the first chaos engineering tools within the cloud computing domain.
The Gremlin team has argued that although the Chaos Monkey tool is useful, it does require time to learn how to safely operate. The original tool also only supported AWS (although additional tooling has emerged that offers similar instance shutdown abilities within Azure and Google Cloud Platform). With the launch of Gremlin Free, the Gremlin team is aiming to reduce these barriers to running chaos experiments, and facilitate teams in quickly seeing the value from doing so.
For engineers looking to explore the new free tier, Tammy Butow, principal SRE at Gremlin, has created a "Shutdown Experiment Pack" that is available on the Gremlin website. This provides a detailed walkthrough for running five chaos experiments that shutdown cloud infrastructure hosts and containers on AWS, Azure, and GCP (for which cloud vendor accounts are required), and also shutdown containers running locally with Docker.
InfoQ recently sat down with Lorne Kligerman, director of product, and discussed the motivations and future plans with Gremlin Free."
"Diane Craig Davis is an astrodynamicist and principal systems engineer with NASA and USAF aerospace industry leader AI solutions. She designs spacecraft orbits with the Gateway trajectory team at Johnson Space Center in Houston, TX, and previously navigated spacecraft to Mars and comets at the Jet Propulsion Laboratory. She is the lead researcher for the Deep Space Trajectory Explorer." (from QCon)
The talk was about Deep Space Trajectory Explorer, a JavaFX-based trajectory design and visualization software package that features a mix of custom 2D and 3D visualizations.
Astrodynamicist Diane Craig Davis worked with JavaFX developer Sean Phillips to find a way to visualise possible space trajectories of 3 body systems like the Earth, Moon and a space craft.
3 body systems are inherently chaotic.
The closest approach in an orbit is called a periapsis point. A collection of potential periapsis points is called a Poincaré map. Deep Space Trajectory Explorer enables a scientist to quickly and simply see a million possible orbits using a Poincaré map, and then whittle them down to find the best path for a trajectory.
Here are another 2 videos by Diane Craig Davis and Sean Phillips found on YouTube.
Sean Phillips also gave a great 2 hour talk and demo at Java User Group Dahlgren on JavaFX and NetBeans IDE.
This is 3 part of a series of 3 posts that reprint articles that cover the crisis in particle physics that have emerged since the failure of scientists at CERN to discover a whole range of new particles as predicted by string theorists.
In my opinion, string theory is complete bollocks as is multi-universes. Nature is a book to be read not written. Maths is largely an invention rather than discovery. Theory needs to be tested and proven by experimentation. Below is an article about a panel discussion which takes up many of the issues confronting particle physics, the nature of mathematics etc. The video of the panel discussion is well worth watching. Natalie Wolchover in her panel comments discusses the issues raised at the workshop she previously wrote about in A Fight for the Soul of Science.
On November 16, more than 200 readers joined writers and editors from Quanta Magazine for a panel discussion exploring the latest ideas in fundamental physics, biology and mathematics research.
From left: Thomas Lin, Natalie Wolchover, John Rennie, Kevin Hartnett and Robbert Dijkgraaf.
Why doesn’t our universe make sense? What is time? What is life? On Friday, more than 200 readers joined writers and editors from Quanta Magazine at the Simons Foundation for a wide-ranging panel discussion that examined the newest ideas in fundamental physics, biology and mathematics research, including the questions of whether our universe is “natural,” the nature of time, the origin and evolution of life, whether mathematics is invented or discovered and what role it plays in science and society. These are just some of the topics presented in Quanta’s two new books published by The MIT Press: Alice and Bob Meet the Wall of Fire and The Prime Number Conspiracy.
Robbert Dijkgraaf, director of the Institute for Advanced Study
Kevin Hartnett, senior writer at Quanta Magazine
John Rennie, deputy editor at Quanta Magazine
Natalie Wolchover, senior writer and editor at Quanta Magazine
This is 2 part of a series of 3 posts that reprint articles that cover the crisis in particle physics that have emerged since the failure of scientists at CERN to discover a whole range of new particles as predicted by string theorists.
In my opinion, string theory is complete bollocks as is multi-universes. Nature is a book to be read not written. Maths is largely an invention rather than discovery. Theory needs to be tested and proven by experimentation. The article below is a report from a 3-day workshop in Germany. The workshop was held in response to the article in Nature, Scientific Method: Defend the integrity of physics.
By Natalie Wolchover
Senior Writer/Editor Quanta Magazine
December 16, 2015.
String theory, the multiverse and other ideas of modern physics are potentially untestable. At a historic meeting in Munich, scientists and philosophers asked: should we trust them anyway?
Physicists typically think they “need philosophers and historians of science like birds need ornithologists,” the Nobel laureate David Gross told a roomful of philosophers, historians and physicists last week in Munich, Germany, paraphrasing Richard Feynman.
Physicists George Ellis (center) and Joe Silk (right) at Ludwig Maximilian University in Munich on Dec. 7.
Laetitia Vancon for Quanta Magazine
But desperate times call for desperate measures.
Fundamental physics faces a problem, Gross explained — one dire enough to call for outsiders’ perspectives. “I’m not sure that we don’t need each other at this point in time,” he said.
It was the opening session of a three-day workshop, held in a Romanesque-style lecture hall at Ludwig Maximilian University (LMU Munich) one year after George Ellis and Joe Silk, two white-haired physicists now sitting in the front row, called for such a conference in an incendiary opinion piece in Nature. One hundred attendees had descended on a land with a celebrated tradition in both physics and the philosophy of science to wage what Ellis and Silk declared a “battle for the heart and soul of physics.”
The crisis, as Ellis and Silk tell it, is the wildly speculative nature of modern physics theories, which they say reflects a dangerous departure from the scientific method. Many of today’s theorists — chief among them the proponents of string theory and the multiverse hypothesis — appear convinced of their ideas on the grounds that they are beautiful or logically compelling, despite the impossibility of testing them. Ellis and Silk accused these theorists of “moving the goalposts” of science and blurring the line between physics and pseudoscience. “The imprimatur of science should be awarded only to a theory that is testable,” Ellis and Silk wrote, thereby disqualifying most of the leading theories of the past 40 years. “Only then can we defend science from attack.”
They were reacting, in part, to the controversial ideas of Richard Dawid, an Austrian philosopher whose 2013 book String Theory and the Scientific Method identified three kinds of “non-empirical” evidence that Dawid says can help build trust in scientific theories absent empirical data. Dawid, a researcher at LMU Munich, answered Ellis and Silk’s battle cry and assembled far-flung scholars anchoring all sides of the argument for the high-profile event last week.
David Gross, a theoretical physicist at the University of California, Santa Barbara.
Laetitia Vancon for Quanta Magazine
Gross, a supporter of string theory who won the 2004 Nobel Prize in Physics for his work on the force that glues atoms together, kicked off the workshop by asserting that the problem lies not with physicists but with a “fact of nature” — one that we have been approaching inevitably for four centuries.
The dogged pursuit of a fundamental theory governing all forces of nature requires physicists to inspect the universe more and more closely — to examine, for instance, the atoms within matter, the protons and neutrons within those atoms, and the quarks within those protons and neutrons. But this zooming in demands evermore energy, and the difficulty and cost of building new machines increases exponentially relative to the energy requirement, Gross said. “It hasn’t been a problem so much for the last 400 years, where we’ve gone from centimeters to millionths of a millionth of a millionth of a centimeter” — the current resolving power of the Large Hadron Collider (LHC) in Switzerland, he said. “We’ve gone very far, but this energy-squared is killing us.”
As we approach the practical limits of our ability to probe nature’s underlying principles, the minds of theorists have wandered far beyond the tiniest observable distances and highest possible energies. Strong clues indicate that the truly fundamental constituents of the universe lie at a distance scale 10 million billion times smaller than the resolving power of the LHC. This is the domain of nature that string theory, a candidate “theory of everything,” attempts to describe. But it’s a domain that no one has the faintest idea how to access.
The problem also hampers physicists’ quest to understand the universe on a cosmic scale: No telescope will ever manage to peer past our universe’s cosmic horizon and glimpse the other universes posited by the multiverse hypothesis. Yet modern theories of cosmology lead logically to the possibility that our universe is just one of many.
Tynan DeBold for Quanta Magazine; Icons via Freepik
Whether the fault lies with theorists for getting carried away, or with nature, for burying its best secrets, the conclusion is the same: Theory has detached itself from experiment. The objects of theoretical speculation are now too far away, too small, too energetic or too far in the past to reach or rule out with our earthly instruments. So, what is to be done? As Ellis and Silk wrote, “Physicists, philosophers and other scientists should hammer out a new narrative for the scientific method that can deal with the scope of modern physics.”
“The issue in confronting the next step,” said Gross, “is not one of ideology but strategy: What is the most useful way of doing science?”
Over three mild winter days, scholars grappled with the meaning of theory, confirmation and truth; how science works; and whether, in this day and age, philosophy should guide research in physics or the other way around. Over the course of these pressing yet timeless discussions, a degree of consensus took shape.
Rules of the Game
Throughout history, the rules of science have been written on the fly, only to be revised to fit evolving circumstances. The ancients believed they could reason their way toward scientific truth. Then, in the 17th century, Isaac Newton ignited modern science by breaking with this “rationalist” philosophy, adopting instead the “empiricist” view that scientific knowledge derives only from empirical observation. In other words, a theory must be proved experimentally to enter the book of knowledge.
But what requirements must an untested theory meet to be considered scientific? Theorists guide the scientific enterprise by dreaming up the ideas to be put to the test and then interpreting the experimental results; what keeps theorists within the bounds of science?
Today, most physicists judge the soundness of a theory by using the Austrian-British philosopher Karl Popper’s rule of thumb. In the 1930s, Popper drew a line between science and nonscience in comparing the work of Albert Einstein with that of Sigmund Freud. Einstein’s theory of general relativity, which cast the force of gravity as curves in space and time, made risky predictions — ones that, if they hadn’t succeeded so brilliantly, would have failed miserably, falsifying the theory. But Freudian psychoanalysis was slippery: Any fault of your mother’s could be worked into your diagnosis. The theory wasn’t falsifiable, and so, Popper decided, it wasn’t science.
Paul Teller (by window), a philosopher and professor emeritus at the University of California, Davis.
Laetitia Vancon for Quanta Magazine
Critics accuse string theory and the multiverse hypothesis, as well as cosmic inflation — the leading theory of how the universe began — of falling on the wrong side of Popper’s line of demarcation. To borrow the title of the Columbia University physicist Peter Woit’s 2006 book on string theory, these ideas are “not even wrong,” say critics. In their editorial, Ellis and Silk invoked the spirit of Popper: “A theory must be falsifiable to be scientific.”
But, as many in Munich were surprised to learn, falsificationism is no longer the reigning philosophy of science. Massimo Pigliucci, a philosopher at the Graduate Center of the City University of New York, pointed out that falsifiability is woefully inadequate as a separator of science and nonscience, as Popper himself recognized. Astrology, for instance, is falsifiable — indeed, it has been falsified ad nauseam — and yet it isn’t science. Physicists’ preoccupation with Popper “is really something that needs to stop,” Pigliucci said. “We need to talk about current philosophy of science. We don’t talk about something that was current 50 years ago.”
Nowadays, as several philosophers at the workshop said, Popperian falsificationism has been supplanted by Bayesian confirmation theory, or Bayesianism, a modern framework based on the 18th-century probability theory of the English statistician and minister Thomas Bayes. Bayesianism allows for the fact that modern scientific theories typically make claims far beyond what can be directly observed — no one has ever seen an atom — and so today’s theories often resist a falsified-unfalsified dichotomy. Instead, trust in a theory often falls somewhere along a continuum, sliding up or down between 0 and 100 percent as new information becomes available. “The Bayesian framework is much more flexible” than Popper’s theory, said Stephan Hartmann, a Bayesian philosopher at LMU. “It also connects nicely to the psychology of reasoning.”
Gross concurred, saying that, upon learning about Bayesian confirmation theory from Dawid’s book, he felt “somewhat like the Molière character who said, ‘Oh my God, I’ve been talking prose all my life!’”
Another advantage of Bayesianism, Hartmann said, is that it is enabling philosophers like Dawid to figure out “how this non-empirical evidence fits in, or can be fit in.”
Another Kind of Evidence
Dawid, who is 49, mild-mannered and smiley with floppy brown hair, started his career as a theoretical physicist. In the late 1990s, during a stint at the University of California, Berkeley, a hub of string-theory research, Dawid became fascinated by how confident many string theorists seemed to be that they were on the right track, despite string theory’s complete lack of empirical support. “Why do they trust the theory?” he recalls wondering. “Do they have different ways of thinking about it than the canonical understanding?”
String theory says that elementary particles have dimensionality when viewed close-up, appearing as wiggling loops (or “strings”) and membranes at nature’s highest zoom level. According to the theory, extra dimensions also materialize in the fabric of space itself. The different vibrational modes of the strings in this higher-dimensional space give rise to the spectrum of particles that make up the observable world. In particular, one of the vibrational modes fits the profile of the “graviton” — the hypothetical particle associated with the force of gravity. Thus, string theory unifies gravity, now described by Einstein’s theory of general relativity, with the rest of particle physics.
Video: Richard Dawid, a physicist-turned-philosopher at Ludwig Maximilian University in Munich.
Laetitia Vancon for Quanta Magazine
However string theory, which has its roots in ideas developed in the late 1960s, has made no testable predictions about the observable universe. To understand why so many researchers trust it anyway, Dawid signed up for some classes in philosophy of science, and upon discovering how little study had been devoted to the phenomenon, he switched fields.
In the early 2000s, he identified three non-empirical arguments that generate trust in string theory among its proponents. First, there appears to be only one version of string theory capable of achieving unification in a consistent way (though it has many different mathematical representations); furthermore, no other “theory of everything” capable of unifying all the fundamental forces has been found, despite immense effort. (A rival approach called loop quantum gravity describes gravity at the quantum scale, but makes no attempt to unify it with the other forces.) This “no-alternatives” argument, colloquially known as “string theory is the only game in town,” boosts theorists’ confidence that few or no other possible unifications of the four fundamental forces exist, making it more likely that string theory is the right approach.
Second, string theory grew out of the Standard Model — the accepted, empirically validated theory incorporating all known fundamental particles and forces (apart from gravity) in a single mathematical structure — and the Standard Model also had no alternatives during its formative years. This “meta-inductive” argument, as Dawid calls it, buttresses the no-alternatives argument by showing that it has worked before in similar contexts, countering the possibility that physicists simply aren’t clever enough to find the alternatives that exist.
Emily Fuhrman for Quanta Magazine, with text by Natalie Wolchover and art direction by Olena Shmahalo.
The third non-empirical argument is that string theory has unexpectedly delivered explanations for several other theoretical problems aside from the unification problem it was intended to address. The staunch string theorist Joe Polchinski of the University of California, Santa Barbara, presented several examples of these “unexpected explanatory interconnections,” as Dawid has termed them, in a paper read in Munich in his absence. String theory explains the entropy of black holes, for example, and, in a surprising discovery that has caused a surge of research in the past 15 years, is mathematically translatable into a theory of particles, such as the theory describing the nuclei of atoms.
Polchinski concludes that, considering how far away we are from the exceptionally fine grain of nature’s fundamental distance scale, we should count ourselves lucky: “String theory exists, and we have found it.” (Polchinski also used Dawid’s non-empirical arguments to calculate the Bayesian odds that the multiverse exists as 94 percent — a value that has been ridiculed by the Internet’s vocal multiverse critics.)
One concern with including non-empirical arguments in Bayesian confirmation theory, Dawid acknowledged in his talk, is “that it opens the floodgates to abandoning all scientific principles.” One can come up with all kinds of non-empirical virtues when arguing in favor of a pet idea. “Clearly the risk is there, and clearly one has to be careful about this kind of reasoning,” Dawid said. “But acknowledging that non-empirical confirmation is part of science, and has been part of science for quite some time, provides a better basis for having that discussion than pretending that it wasn’t there, and only implicitly using it, and then saying I haven’t done it. Once it’s out in the open, one can discuss the pros and cons of those arguments within a specific context.”
The Munich Debate
Laetitia Vancon for Quanta Magazine
The trash heap of history is littered with beautiful theories. The Danish historian of cosmology Helge Kragh, who detailed a number of these failures in his 2011 book, Higher Speculations, spoke in Munich about the 19th-century vortex theory of atoms. This “Victorian theory of everything,” developed by the Scots Peter Tait and Lord Kelvin, postulated that atoms are microscopic vortexes in the ether, the fluid medium that was believed at the time to fill space. Hydrogen, oxygen and all other atoms were, deep down, just different types of vortical knots. At first, the theory “seemed to be highly promising,” Kragh said. “People were fascinated by the richness of the mathematics, which could keep mathematicians busy for centuries, as was said at the time.” Alas, atoms are not vortexes, the ether does not exist, and theoretical beauty is not always truth.
Except sometimes it is. Rationalism guided Einstein toward his theory of relativity, which he believed in wholeheartedly on rational grounds before it was ever tested. “I hold it true that pure thought can grasp reality, as the ancients dreamed,” Einstein said in 1933, years after his theory had been confirmed by observations of starlight bending around the sun.
The question for the philosophers is: Without experiments, is there any way to distinguish between the non-empirical virtues of vortex theory and those of Einstein’s theory? Can we ever really trust a theory on non-empirical grounds?
In discussions on the third afternoon of the workshop, the LMU philosopher Radin Dardashti asserted that Dawid’s philosophy specifically aims to pinpoint which non-empirical arguments should carry weight, allowing scientists to “make an assessment that is not based on simplicity, which is not based on beauty.” Dawidian assessment is meant to be more objective than these measures, Dardashti explained — and more revealing of a theory’s true promise.
Gross said Dawid has “described beautifully” the strategies physicists use “to gain confidence in a speculation, a new idea, a new theory.”
“You mean confidence that it’s true?” asked Peter Achinstein, an 80-year-old philosopher and historian of science at Johns Hopkins University. “Confidence that it’s useful? confidence that …”
“Let’s give an operational definition of confidence: I will continue to work on it,” Gross said.
“That’s pretty low,” Achinstein said.
“Not for science,” Gross said. “That’s the question that matters.”
Kragh pointed out that even Popper saw value in the kind of thinking that motivates string theorists today. Popper called speculation that did not yield testable predictions “metaphysics,” but he considered such activity worthwhile, since it might become testable in the future. This was true of atomic theory, which many 19th-century physicists feared would never be empirically confirmed. “Popper was not a naive Popperian,” Kragh said. “If a theory is not falsifiable,” Kragh said, channeling Popper, “it should not be given up. We have to wait.”
But several workshop participants raised qualms about Bayesian confirmation theory, and about Dawid’s non-empirical arguments in particular.
Carlo Rovelli, a proponent of loop quantum gravity (string theory’s rival) who is based at Aix-Marseille University in France, objected that Bayesian confirmation theory does not allow for an important distinction that exists in science between theories that scientists are certain about and those that are still being tested. The Bayesian “confirmation” that atoms exist is essentially 100 percent, as a result of countless experiments. But Rovelli says that the degree of confirmation of atomic theory shouldn’t even be measured in the same units as that of string theory. String theory is not, say, 10 percent as confirmed as atomic theory; the two have different statuses entirely. “The problem with Dawid’s ‘non-empirical confirmation’ is that it muddles the point,” Rovelli said. “And of course some string theorists are happy of muddling it this way, because they can then say that string theory is ‘confirmed,’ equivocating.”
The German physicist Sabine Hossenfelder, in her talk, argued that progress in fundamental physics very often comes from abandoning cherished prejudices (such as, perhaps, the assumption that the forces of nature must be unified). Echoing this point, Rovelli said “Dawid’s idea of non-empirical confirmation [forms] an obstacle to this possibility of progress, because it bases our credence on our own previous credences.” It “takes away one of the tools — maybe the soul itself — of scientific thinking,” he continued, “which is ‘do not trust your own thinking.’”
The Munich proceedings will be compiled and published, probably as a book, in 2017. As for what was accomplished, one important outcome, according to Ellis, was an acknowledgment by participating string theorists that the theory is not “confirmed” in the sense of being verified. “David Gross made his position clear: Dawid’s criteria are good for justifying working on the theory, not for saying the theory is validated in a non-empirical way,” Ellis wrote in an email. “That seems to me a good position — and explicitly stating that is progress.”
In considering how theorists should proceed, many attendees expressed the view that work on string theory and other as-yet-untestable ideas should continue. “Keep speculating,” Achinstein wrote in an email after the workshop, but “give your motivation for speculating, give your explanations, but admit that they are only possible explanations.”
“Maybe someday things will change,” Achinstein added, “and the speculations will become testable; and maybe not, maybe never.” We may never know for sure the way the universe works at all distances and all times, “but perhaps you can narrow the live possibilities to just a few,” he said. “I think that would be some progress.”
This is part 1 of a series of 3 posts that reprint articles that cover the crisis in particle physics that have emerged since the failure of scientists at CERN to discover a whole range of new particles as predicted by string theorists.
In my opinion, string theory is complete bollocks as is multi-universes. Nature is a book to be read not written. Maths is largely an invention rather than discovery. Theory needs to be tested and proven by experimentation.
The article below is a stirring defence of science. I agree with it completely.
Attempts to exempt speculative theories of the Universe from experimental verification undermine science, argue George Ellis and Joe Silk.
This year, debates in physics circles took a worrying turn. Faced with difficulties in applying fundamental theories to the observed Universe, some researchers called for a change in how theoretical physics is done. They began to argue — explicitly — that if a theory is sufficiently elegant and explanatory, it need not be tested experimentally, breaking with centuries of philosophical tradition of defining scientific knowledge as empirical. We disagree. As the philosopher of science Karl Popper argued: a theory must be falsifiable to be scientific.
Chief among the 'elegance will suffice' advocates are some string theorists. Because string theory is supposedly the 'only game in town' capable of unifying the four fundamental forces, they believe that it must contain a grain of truth even though it relies on extra dimensions that we can never observe. Some cosmologists, too, are seeking to abandon experimental verification of grand hypotheses that invoke imperceptible domains such as the kaleidoscopic multiverse (comprising myriad universes), the 'many worlds' version of quantum reality (in which observations spawn parallel branches of reality) and pre-Big Bang concepts.
These unprovable hypotheses are quite different from those that relate directly to the real world and that are testable through observations — such as the standard model of particle physics and the existence of dark matter and dark energy. As we see it, theoretical physics risks becoming a no-man's-land between mathematics, physics and philosophy that does not truly meet the requirements of any.
The issue of testability has been lurking for a decade. String theory and multiverse theory have been criticized in popular books and articles, including some by one of us. In March, theorist Paul Steinhardt wrote in this journal that the theory of inflationary cosmology is no longer scientific because it is so flexible that it can accommodate any observational result. Theorist and philosopher Richard Dawid and cosmologist Sean Carroll have countered those criticisms with a philosophical case to weaken the testability requirement for fundamental physics.
We applaud the fact that Dawid, Carroll and other physicists have brought the problem out into the open. But the drastic step that they are advocating needs careful debate. This battle for the heart and soul of physics is opening up at a time when scientific results — in topics from climate change to the theory of evolution — are being questioned by some politicians and religious fundamentalists. Potential damage to public confidence in science and to the nature of fundamental physics needs to be contained by deeper dialogue between scientists and philosophers.
String theory is an elaborate proposal for how minuscule strings (one-dimensional space entities) and membranes (higher-dimensional extensions) existing in higher-dimensional spaces underlie all of physics. The higher dimensions are wound so tightly that they are too small to observe at energies accessible through collisions in any practicable future particle detector.
Some aspects of string theory can be tested experimentally in principle. For example, a hypothesized symmetry between fermions and bosons central to string theory — supersymmetry — predicts that each kind of particle has an as-yet-unseen partner. No such partners have yet been detected by the Large Hadron Collider at CERN, Europe's particle-physics laboratory near Geneva, Switzerland, limiting the range of energies at which supersymmetry might exist. If these partners continue to elude detection, then we may never know whether they exist. Proponents could always claim that the particles' masses are higher than the energies probed.
“The consequences of overclaiming the significance of certain theories are profound.”
Dawid argues6 that the veracity of string theory can be established through philosophical and probabilistic arguments about the research process. Citing Bayesian analysis, a statistical method for inferring the likelihood that an explanation fits a set of facts, Dawid equates confirmation with the increase of the probability that a theory is true or viable. But that increase of probability can be purely theoretical. Because “no-one has found a good alternative” and “theories without alternatives tended to be viable in the past”, he reasons that string theory should be taken to be valid.
In our opinion, this is moving the goalposts. Instead of belief in a scientific theory increasing when observational evidence arises to support it, he suggests that theoretical discoveries bolster belief. But conclusions arising logically from mathematics need not apply to the real world. Experiments have proved many beautiful and simple theories wrong, from the steady-state theory of cosmology to the SU(5) Grand Unified Theory of particle physics, which aimed to unify the electroweak force and the strong force. The idea that preconceived truths about the world can be inferred beyond established facts (inductivism) was overturned by Popper and other twentieth-century philosophers.
We cannot know that there are no alternative theories. We may not have found them yet. Or the premise might be wrong. There may be no need for an overarching theory of four fundamental forces and particles if gravity, an effect of space-time curvature, differs from the strong, weak and electromagnetic forces that govern particles. And with its many variants, string theory is not even well defined: in our view, it is a promissory note that there might be such a unified theory.
The multiverse is motivated by a puzzle: why fundamental constants of nature, such as the fine-structure constant that characterizes the strength of electromagnetic interactions between particles and the cosmological constant associated with the acceleration of the expansion of the Universe, have values that lie in the small range that allows life to exist. Multiverse theory claims that there are billions of unobservable sister universes out there in which all possible values of these constants can occur. So somewhere there will be a bio-friendly universe like ours, however improbable that is.
Some physicists consider that the multiverse has no challenger as an explanation of many otherwise bizarre coincidences. The low value of the cosmological constant — known to be 120 factors of 10 smaller than the value predicted by quantum field theory — is difficult to explain, for instance.
Earlier this year, championing the multiverse and the many-worlds hypothesis, Carroll dismissed Popper's falsifiability criterion as a “blunt instrument” (see go.nature.com/nuj39z). He offered two other requirements: a scientific theory should be “definite” and “empirical”. By definite, Carroll means that the theory says “something clear and unambiguous about how reality functions”. By empirical, he agrees with the customary definition that a theory should be judged a success or failure by its ability to explain the data.
He argues that inaccessible domains can have a “dramatic effect” in our cosmic back-yard, explaining why the cosmological constant is so small in the part we see. But in multiverse theory, that explanation could be given no matter what astronomers observe. All possible combinations of cosmological parameters would exist somewhere, and the theory has many variables that can be tweaked. Other theories, such as unimodular gravity, a modified version of Einstein's general theory of relativity, can also explain why the cosmological constant is not huge7.
Some people have devised forms of multiverse theory that are susceptible to tests: physicist Leonard Susskind's version can be falsified if negative spatial curvature of the Universe is ever demonstrated. But such a finding would prove nothing about the many other versions. Fundamentally, the multiverse explanation relies on string theory, which is as yet unverified, and on speculative mechanisms for realizing different physics in different sister universes. It is not, in our opinion, robust, let alone testable.
The many-worlds theory of quantum reality posed by physicist Hugh Everett is the ultimate quantum multiverse, where quantum probabilities affect the macroscopic. According to Everett, each of Schrödinger's famous cats, the dead and the live, poisoned or not in its closed box by random radioactive decays, is real in its own universe. Each time you make a choice, even one as mundane as whether to go left or right, an alternative universe pops out of the quantum vacuum to accommodate the other action.
Billions of universes — and of galaxies and copies of each of us — accumulate with no possibility of communication between them or of testing their reality. But if a duplicate self exists in every multiverse domain and there are infinitely many, which is the real 'me' that I experience now? Is any version of oneself preferred over any other? How could 'I' ever know what the 'true' nature of reality is if one self favours the multiverse and another does not?
In our view, cosmologists should heed mathematician David Hilbert's warning: although infinity is needed to complete mathematics, it occurs nowhere in the physical Universe.
Pass the test
We agree with theoretical physicist Sabine Hossenfelder: post-empirical science is an oxymoron (see go.nature.com/p3upwp and go.nature.com/68rijj). Theories such as quantum mechanics and relativity turned out well because they made predictions that survived testing. Yet numerous historical examples point to how, in the absence of adequate data, elegant and compelling ideas led researchers in the wrong direction, from Ptolemy's geocentric theories of the cosmos to Lord Kelvin's 'vortex theory' of the atom and Fred Hoyle's perpetual steady-state Universe.
The consequences of overclaiming the significance of certain theories are profound — the scientific method is at stake (see go.nature.com/hh7mm6). To state that a theory is so good that its existence supplants the need for data and testing in our opinion risks misleading students and the public as to how science should be done and could open the door for pseudoscientists to claim that their ideas meet similar requirements.
What to do about it? Physicists, philosophers and other scientists should hammer out a new narrative for the scientific method that can deal with the scope of modern physics. In our view, the issue boils down to clarifying one question: what potential observational or experimental evidence is there that would persuade you that the theory is wrong and lead you to abandoning it? If there is none, it is not a scientific theory.
Such a case must be made in formal philosophical terms. A conference should be convened next year to take the first steps. People from both sides of the testability debate must be involved.
In the meantime, journal editors and publishers could assign speculative work to other research categories — such as mathematical rather than physical cosmology — according to its potential testability. And the domination of some physics departments and institutes by such activities could be rethought.
The imprimatur of science should be awarded only to a theory that is testable. Only then can we defend science from attack.
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