Wednesday, 26 October 2016

The Universe, “Branes,” and the Science of Multiple Dimensions


How a needle, a shower curtain, and a New England clam explain the possibility of parallel universes.

“The mystery of being is a permanent mystery,” John Updike once observed in pondering why the universe exists, and yet of equal permanence is the allure this mystery exerts upon the scientists, philosophers, and artists of any given era. The Universe: Leading Scientists Explore the Origin, Mysteries, and Future of the Cosmos (public library | IndieBound) collects twenty-one illuminating, mind-expanding meditations on various aspects of that mystery, from multiple dimensions to quantum monkeys to why the universe looks the way it does, by some of the greatest scientific thinkers of our time. It is the fourth installment in an ongoing series by Edge editor John Brockman, following Thinking (2013), Culture (2011), and The Mind (2011).
In one of the essays, theoretical physicist Leonard Suskind marvels at the unique precipice we’re fortunate to witness:
The beginning of the 21st century is a watershed in modern science, a time that will forever change our understanding of the universe. Something is happening which is far more than the discovery of new facts or new equations. This is one of those rare moments when our entire outlook, our framework for thinking, and the whole epistemology of physics and cosmology are suddenly undergoing real upheaval. The narrow 20th-century view of a unique universe, about 10 billion years old and 10 billion light years across with a unique set of physical laws, is giving way to something far bigger and pregnant with new possibilities.
Gradually physicists and cosmologists are coming to see our ten billion light years as an infinitesimal pocket of a stupendous megaverse.
Here, an inevitable note on a different kind of human narrowness: I am not one to advocate for a blind quota-filling approach, where there must be equal representation on all levels at all cost. And yet it’s rather disappointing to see only one female scientist alongside her twenty-two male peers. (One of the twenty-one essays has three authors.) To be sure, Edge itself is far from gender-balanced — one could rationalize that this is simply the state of science still — but the site’s vast archive, spanning fifteen years of conversations and essays, does feature a number of female scientists, which renders the 5% female representation in this collection editorially lamentable.
This gender gap lends double meaning to Susskind’s reflections on the progress of science in the twenty-first century as he notes: “Man’s place in the universe is also being reexamined and challenged.” Woman’s, evidently, is not.
Lisa Randall (Photograph: Phil Knott)
And yet, it’s perhaps not coincidental that the sole female contributor is none other than Harvard’s Lisa Randall, one of the most influential theoretical physicists of our time, and her essay is the most intensely interesting in the entire collection. (Perchance Brockman considered its weighted quotient equal to several of the male essays combined. No, not really, but when the skies of equality get particularly cloudy, what is one to do but squint for silver linings?)
Randall’s essay explores her work on the physics of extra dimensions of space, particularly the concept of “branes” — membrane-like two-dimensional objects that exist in a higher-dimensional space. (Randall illustrates this with the visual metaphor of a shower curtain, “virtually a two-dimensional object in a three-dimensional space.”) To understand why branes matter — more than that, why they are so infinitely interesting — we first need a primer on the physics of what is known as the “TeV scale.” Randall explains:
Particle physicists measure energy in units of electron volts. “TeV” means “a trillion electron volts.” This is a very high energy and challenges the limits of current technology, but it’s low from the perspective of quantum gravity, whose consequences are likely to show up only at energies 16 orders of magnitude higher. This energy scale is interesting, because we know that the as-yet-undiscovered part of the theory associated with giving elementary particles their masses should be found there… Back at the very beginning, the entire universe could have been squeezed to the size of an elementary particle. Quantum fluctuations could shake the entire universe, and there would be an essential link between cosmology and the microworld.
This ghostly playground of particles raises the question of whether “space and time are so complicated and screwed up that we can’t really talk about a beginning in time” — which brings us to string theory and its peculiar predicament. Randall writes:
The one thing that’s rather unusual about string theory from the viewpoint of the sociology and history of science is that it’s one of the few instances where physics has been held up by a lack of the relevant mathematics. In the past, physicists have generally taken fairly old-fashioned mathematics off the shelf. Einstein used 19th-century non-Euclidean geometry, and the pioneers in quantum theory used group theory and differential equations that had essentially been worked out long beforehand. But string theory poses mathematical problems that aren’t yet solved, and has actually brought math and physics closer together.
String theory is the dominant approach right now, and it has some successes already, but the question is whether it will develop to the stage where we can actually solve problems that can be tested observationally. If we can’t bridge the gap between this ten-dimensional theory and anything that we can observe, it will grind to a halt. In most versions of string theory, the extra dimensions above the normal three are all wrapped up very tightly, so that each point in our ordinary space is like a tightly wrapped origami in six dimensions. We see just three dimensions; the rest are invisible to us because they are wrapped up very tightly. If you look at a needle, it looks like a one-dimensional line from a long distance, but really it’s three-dimensional. Likewise, the extra dimensions could be seen if you looked at things very closely. Space on a very tiny scale is grainy and complicated — its smoothness is an illusion of the large scale. That’s the conventional view in these string theories.
The Cat’s Eye Nebula, from ‘Hubble: Imaging Space and Time.’ Click image for more.
This is where Randall’s work on branes comes in as a promising contender for a better solution. She writes:
According to this theory, there could be other universes, perhaps separated from ours by just a microscopic distance; however, that distance is measured in some fourth spatial dimension, of which we are not aware. Because we are imprisoned in our three dimensions, we can’t directly detect these other universes. It’s rather like a whole lot of bugs crawling around on a big two-dimensional sheet of paper, who would be unaware of another set of bugs that might be crawling around on another sheet of paper that could be only a short distance away in the third dimension.
Of course, the concepts of multiple dimensions and parallel universes are far from new and can be traced as far back as another trailblazing woman in scientific thought, Margaret Cavendish, Duchess of Newcastle — her 1666 book The Blazing World features a heroine who passes into a world with different stars through a space-time portal near the North Pole.
Randall takes us into her own time machine to trace the history of multiple dimensions in contextualizing what makes branes so special:
People entertained the idea of extra dimensions before string theory came along, although such speculations were soon forgotten or ignored. It’s natural to ask what would happen if there were different dimensions of space; after all, the fact that we see only three spatial dimensions doesn’t necessarily mean that only three exist, and Einstein’s general relativity doesn’t treat a three-dimensional universe preferentially. There could be many unseen ingredients to the universe. However, it was first believed that if additional dimensions existed they would have to be very small in order to have escaped our notice. The standard supposition in string theory was that the extra dimensions were curled up into incredibly tiny scales — 1033 centimeters, the so-called Planck length and the scale associated with quantum effects becoming relevant. In that sense, this scale is the obvious candidate: If there are extra dimensions, which are obviously important to gravitational structure, they’d be characterized by this particular distance scale. But if so, there would be very few implications for our world. Such dimensions would have no impact whatsoever on anything we see or experience.
Branes are special, particularly in the context of string theory, because there’s a natural mechanism to confine particles to the brane; thus not everything need travel in the extra dimensions, even if those dimensions exist. Particles confined to the brane would have momentum and motion only along the brane, like water spots on the surface of your shower curtain. Branes allow for an entirely new set of possibilities in the physics of extra dimensions, because particles confined to the brane would look more or less as they would in a three-plus-one-dimension world; they never venture beyond it. Protons, electrons, quarks, all sorts of fundamental particles could be stuck on the brane. In that case, you may wonder why we should care about extra dimensions at all, since despite their existence the particles that make up our world do not traverse them. However, although all known standard-model particles stick to the brane, this is not true of gravity. The mechanisms for confining particles and forces mediated by the photon or electrogauge proton to the brane do not apply to gravity. Gravity, according to the theory of general relativity, must necessarily exist in the full geometry of space. Furthermore, a consistent gravitational theory requires that the graviton, the particle that mediates gravity, has to couple to any source of energy, whether that source is confined to the brane or not. Therefore, the graviton would also have to be out there in the region encompassing the full geometry of higher dimensions—a region known as the bulk—because there might be sources of energy there. Finally, there’s a string-theory explanation of why the graviton is not stuck to any brane: The graviton is associated with the closed string, and only open strings can be anchored to a brane.
Meanwhile, scientists haven’t studied gravity as intensely as they have other particles, largely because gravity is an extremely weak force. (It might not seem so every time you trip and fall, but as Randall points out, that’s because the entire Earth is pulling you down at that moment, whereas “the result of coupling an individual graviton to an individual particle is quite small.”) What makes branes especially intriguing is that including them into string theory allows us to contemplate, to use Randall’s technical term, “crazily large extra dimensions.” These, in turn, might explain why gravity is so weak — if its force is spread out across these gigantic dimensions, no wonder it would be this diluted on any one brane.
But it gets even more interesting — citing her work with Johns Hopkins scientist Raman Sundrum, Randall writes:
A more natural explanation for the weakness of gravity could be the direct result of the gravitational attraction associated with the brane itself. In addition to trapping particles, branes carry energy. We showed that from the perspective of general relativity this means that the brane curves the space around it, changing gravity in its vicinity. When the energy in space is correlated with the energy on the brane so that a large flat three-dimensional brane sits in the higher-dimensional space, the graviton — the particle communicating the gravitational force — is highly attracted to the brane. Rather than spreading uniformly in an extra dimension, gravity stays localized, very close to the brane.
René Descartes’s 1644 model of the universe, from ‘The Book of Trees.’ Click image for more.
Randall’s discoveries get even more mind-bending. Outlining a finding that calls to mind the legendary Victorian allegory Flatland: A Romance of Many Dimensions (which in turn inspired Norton Juster’s brilliant 1963 book and film The Dot and the Line: A Romance in Lower Mathematics, she writes:
Conventionally, it was thought that extra dimensions must be curled up or bounded between two branes, or else we would observe higher-dimensional gravity. The aforementioned second brane appeared to serve two purposes: It explained the hierarchy problem because of the small probability for the graviton to be there, and it was also responsible for bounding the extra dimension so that at long distances, bigger than the dimension’s size, only three dimensions are seen.
The concentration of the graviton near the Planck brane can, however, have an entirely different implication. If we forget the hierarchy problem for the moment, the second brane is unnecessary. That is, even if there’s an infinite extra dimension and we live on the Planck brane in this infinite dimension, we wouldn’t know about it. In this “warped geometry,” as the space with exponentially decreasing graviton amplitude is known, we would see things as if this dimension did not exist and the world were only three-dimensional.
Because the graviton makes only infrequent excursions into the bulk, a second brane or a curled-up dimension isn’t necessary to get a theory that describes our three-dimensional world, as had previously been thought. We might live on the Planck brane and address the hierarchy problem in some other manner—or we might live on a second brane out in the bulk, but this brane would not be the boundary of the now infinite space. It doesn’t matter that the graviton occasionally leaks away from the Planck brane; it’s so highly localized there that the Planck brane essentially mimics a world of three dimensions, as though an extra dimension didn’t exist at all. A four-spatial-dimensions world, say, would look almost identical to one with three spatial dimensions. Thus all the evidence we have for three spatial dimensions could equally well be evidence for a theory in which there are four spatial dimensions of infinite extent.
So why does any of this matter, this “exciting but frustrating game” of speculation, as Randall elegantly puts it? For one thing, there might be subtle but important differences between these different dimensions and different worlds — for instance, black holes may not behave the same way in each of them. If energy leaks off a brane, a black hole might spit out particles into an extra dimension as it perishes. (If you’ve ever steamed a New England clam, you may have noticed it “spitting” water at you in its final moments — perhaps this is somewhat akin to what Randall describes.) Most importantly, multiple dimensions offer endless possibilities for the very structure of space. Randall writes:
There can be different numbers of dimensions and there might be arbitrary numbers of branes contained within. Branes don’t even all have to be three-plus-one-dimensional; maybe there are other dimensions of branes in addition to those that look like ours and are parallel to ours. This presents an interesting question about the global structure of space, since how space evolves with time would be different in the context of the presence of many branes. It’s possible that there are all sorts of forces and particles we don’t know about that are concentrated on branes and can affect cosmology.
Lisa Randall
So where does this leave us? Randall echoes Marie Curie’s famous words upon receiving her second graduate degree — a sentiment no doubt common to any great scientist who understands that not-knowing is the currency of meaningful work — and concludes:
In general, the problems that get solved, although they seem very complicated, are in many ways simple problems. There’s much more work to be done; exciting discoveries await, and they will have implications for other fields… It’s my hope that time and experiments will distinguish among the possibilities.
Randall’s essay is a spectacular, mind-bending read in its entirety, as are the rest of the contributions in The Universe. Complement it with Brockman’s compendium of leading scientists’ selections of the most elegant theory of how the world works and the single most important concept to make you smarter.



From Wikipedia, the free encyclopedia/Blogger Ref
The following article may have some relevance to Multi-Dimensional Science which is really concerned with the possibility of non-physical, or para-physical universes..But it is always good to see how some scientists are seeing to speak...
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For other uses, see Multiverse (disambiguation).
The multiverse (or meta-universe) is the hypothetical set of finite and infinite possible universes, including the universe in which we live. Together, these universes comprise everything that exists: the entirety of space, time, matter, energy, and the physical laws and constants that describe them.
The various universes within the multiverse are called "parallel universes", "other universes" or "alternate universes."

Origin of the concept[edit]

In Dublin in 1952, Erwin Schrödinger gave a lecture in which he jocularly warned his audience that what he was about to say might "seem lunatic." He said that, when his Nobel equations seemed to describe several different histories, these were "not alternatives, but all really happen simultaneously." This is the earliest known reference to the multiverse.[1]
The American philosopher and psychologist William James used the term multiverse in 1895, but in a different context.[2]


The structure of the multiverse, the nature of each universe within it, and the relationships among these universes differ from one multiverse hypothesis to another.
Multiple universes have been hypothesized in cosmology, physics, astronomy, religion, philosophy, transpersonal psychology, and literature, particularly in science fiction and fantasy. In these contexts, parallel universes are also called "alternate universes", "quantum universes", "interpenetrating dimensions", "parallel dimensions", "parallel worlds", "alternate realities", "alternate timelines", and "dimensional planes".
The physics community continues to debate the multiverse hypothesis. Prominent physicists disagree about whether the multiverse exists.
Some physicists say the multiverse is not a legitimate topic of scientific inquiry.[3] Concerns have been raised about whether attempts to exempt the multiverse from experimental verification could erode public confidence in science and ultimately damage the study of fundamental physics.[4] Some have argued that the multiverse is a philosophical rather than a scientific hypothesis because it cannot be falsified. The ability to disprove a theory by means of scientific experiment has always been part of the accepted scientific method.[5] Paul Steinhardt has famously argued that no experiment can rule out a theory if the theory provides for all possible outcomes.[6]
In 2007, Nobel laureate Steven Weinberg suggested that if the multiverse existed, "the hope of finding a rational explanation for the precise values of quark masses and other constants of the standard model that we observe in our Big Bang is doomed, for their values would be an accident of the particular part of the multiverse in which we live."[7]

Search for evidence[edit]

Around 2010, scientists such as Stephen M. Feeney analyzed Wilkinson Microwave Anisotropy Probe (WMAP) data and claimed to find evidence suggesting that our universe collided with other (parallel) universes in the distant past.[8][unreliable source?][9][10][11] However, a more thorough analysis of data from the WMAP and from the Planck satellite, which has a resolution 3 times higher than WMAP, did not reveal any statistically significant evidence of such a bubble universe collision.[12][13] In addition, there was no evidence of any gravitational pull of other universes on ours.[14][15]

Proponents and skeptics[edit]

Proponents of one of the multiverse hypotheses include Stephen Hawking,[16] Brian Greene,[17][18] Max Tegmark,[19] Alan Guth,[20] Andrei Linde,[21] Michio Kaku,[22] David Deutsch,[23] Leonard Susskind,[24] Alexander Vilenkin,[25] Yasunori Nomura,[26] Raj Pathria,[27] Laura Mersini-Houghton,[28][29] Neil deGrasse Tyson,[30] and Sean Carroll.[31]
Scientists who are generally skeptical of the multiverse hypothesis include: Nobel laureate Steven Weinberg,[32] Nobel laureate David Gross,[33] Paul Steinhardt,[34] Neil Turok,[35] Viatcheslav Mukhanov,[36] Michael S. Turner,[37] Roger Penrose,[38] George Ellis,[39][40] Joe Silk,[41] Carlo Rovelli, [42] Adam Frank,[43] Marcelo Gleiser,[43] Jim Baggott,[44] and Paul Davies.[45]

Arguments against multiverse theories[edit]

In his 2003 New York Times opinion piece, A Brief History of the Multiverse, the author and cosmologist Paul Davies offered a variety of arguments that multiverse theories are non-scientific :[46]
For a start, how is the existence of the other universes to be tested? To be sure, all cosmologists accept that there are some regions of the universe that lie beyond the reach of our telescopes, but somewhere on the slippery slope between that and the idea that there are an infinite number of universes, credibility reaches a limit. As one slips down that slope, more and more must be accepted on faith, and less and less is open to scientific verification. Extreme multiverse explanations are therefore reminiscent of theological discussions. Indeed, invoking an infinity of unseen universes to explain the unusual features of the one we do see is just as ad hoc as invoking an unseen Creator. The multiverse theory may be dressed up in scientific language, but in essence it requires the same leap of faith.
— Paul Davies, A Brief History of the Multiverse
Taking cosmic inflation as a popular case in point, George Ellis, writing in August 2011, provided a balanced criticism of not only the science but, as he suggested, the scientific philosophy by which multiverse theories are generally substantiated.
He, like most cosmologists, accepts Tegmark's level-I "domains", even though they lie far beyond the cosmological horizon. Likewise, the multiverse of cosmic inflation is said to exist very far away. It would be so far away, however, that it's very unlikely any evidence of an early interaction will be found. He argues that, for many theorists, the lack of empirical testability or falsifiability is not a major concern.
Many physicists who talk about the multiverse, especially advocates of the string landscape, do not care much about parallel universes per se. For them, objections to the multiverse as a concept are unimportant. Their theories live or die based on internal consistency and, one hopes, eventual laboratory testing.
Although he believes there's little hope that laboratory testing will ever be possible, he grants that the theories on which speculation is based have some scientific merit. He concluded that multiverse theory is a "productive research program":[47]
As skeptical as I am, I think the contemplation of the multiverse is an excellent opportunity to reflect on the nature of science and on the ultimate nature of existence: why we are here.... In looking at this concept, we need an open mind, though not too open. It is a delicate path to tread. Parallel universes may or may not exist; the case is unproved. We are going to have to live with that uncertainty. Nothing is wrong with scientifically based philosophical speculation, which is what multiverse proposals are. But we should name it for what it is.
— George Ellis, Scientific American, Does the Multiverse Really Exist?

Classification schemes[edit]

Max Tegmark and Brian Greene have devised classification schemes for the various theoretical types of multiverse, or for the types of universe that a multiverse might comprise.

Max Tegmark's four levels[edit]

Cosmologist Max Tegmark has provided a taxonomy of universes beyond the familiar observable universe. The four levels of Tegmark's classification are arranged such that subsequent levels can be understood to encompass and expand upon previous levels. They are briefly described below.[48][49]

Level I: An extension of our Universe[edit]

A prediction of chaotic inflation is the existence of an infinite ergodic universe, which, being infinite, must contain Hubble volumes realizing all initial conditions.
Accordingly, an infinite universe will contain an infinite number of Hubble volumes, all having the same physical laws and physical constants. In regard to configurations such as the distribution of matter, almost all will differ from our Hubble volume. However, because there are infinitely many, far beyond the cosmological horizon, there will eventually be Hubble volumes with similar, and even identical, configurations. Tegmark estimates that an identical volume to ours should be about 1010115 meters away from us.[19]
Given infinite space, there would, in fact, be an infinite number of Hubble volumes identical to ours in the universe.[50] This follows directly from the cosmological principle, wherein it is assumed that our Hubble volume is not special or unique.

Level II: Universes with different physical constants[edit]

Bubble universes — every disk represents a bubble universe. Our universe is represented by one of the disks.
Universe 1 to Universe 6 represent bubble universes. Five of them have different physical constants than our universe has.
In the chaotic inflation theory, a variant of the cosmic inflation theory, the multiverse as a whole is stretching and will continue doing so forever,[51] but some regions of space stop stretching and form distinct bubbles (like gas pockets in a loaf of rising bread). Such bubbles are embryonic level I multiverses.
Different bubbles may experience different spontaneous symmetry breaking, which results in different properties, such as different physical constants.[50]
Level II also includes John Archibald Wheeler's oscillatory universe theory and Lee Smolin's fecund universes theory.

Level III: Many-worlds interpretation of quantum mechanics[edit]

Hugh Everett's many-worlds interpretation (MWI) is one of several mainstream interpretations of quantum mechanics.
In brief, one aspect of quantum mechanics is that certain observations cannot be predicted absolutely. Instead, there is a range of possible observations, each with a different probability. According to the MWI, each of these possible observations corresponds to a different universe. Suppose a six-sided die is thrown and that the result of the throw corresponds to a quantum mechanics observable. All six possible ways the die can fall correspond to six different universes.
Tegmark argues that a Level III multiverse does not contain more possibilities in the Hubble volume than a Level I or Level II multiverse. In effect, all the different "worlds" created by "splits" in a Level III multiverse with the same physical constants can be found in some Hubble volume in a Level I multiverse. Tegmark writes that, "The only difference between Level I and Level III is where your doppelgängers reside. In Level I they live elsewhere in good old three-dimensional space. In Level III they live on another quantum branch in infinite-dimensional Hilbert space."
Similarly, all Level II bubble universes with different physical constants can, in effect, be found as "worlds" created by "splits" at the moment of spontaneous symmetry breaking in a Level III multiverse.[50] According to Yasunori Nomura,[26] Raphael Bousso, and Leonard Susskind,[24] this is because global spacetime appearing in the (eternally) inflating multiverse is a redundant concept. This implies that the multiverses of Levels I, II, and III are, in fact, the same thing. This hypothesis is referred to as "Multiverse = Quantum Many Worlds".
Related to the many-worlds idea are Richard Feynman's multiple histories interpretation and H. Dieter Zeh's many-minds interpretation.

Level IV: Ultimate ensemble[edit]

The ultimate mathematical universe hypothesis is Tegmark's own hypothesis.[52]
This level considers all universes to be equally real which can be described by different mathematical structures.
Tegmark writes that:
Abstract mathematics is so general that any Theory Of Everything (TOE) which is definable in purely formal terms (independent of vague human terminology) is also a mathematical structure. For instance, a TOE involving a set of different types of entities (denoted by words, say) and relations between them (denoted by additional words) is nothing but what mathematicians call a set-theoretical model, and one can generally find a formal system that it is a model of.
He argues that this "implies that any conceivable parallel universe theory can be described at Level IV" and "subsumes all other ensembles, therefore brings closure to the hierarchy of multiverses, and there cannot be, say, a Level V."[19]
Jürgen Schmidhuber, however, says that the set of mathematical structures is not even well-defined and that it admits only universe representations describable by constructive mathematics — that is, computer programs.
Schmidhuber explicitly includes universe representations describable by non-halting programs whose output bits converge after finite time, although the convergence time itself may not be predictable by a halting program, due to the undecidability of the halting problem.[53][54][55] He also explicitly discusses the more restricted ensemble of quickly computable universes.[56]

Brian Greene's nine types[edit]

The American theoretical physicist and string theorist, Brian Greene, discussed nine types of parallel universes:[57]
The quilted multiverse works only in an infinite universe. With an infinite amount of space, every possible event will occur an infinite number of times. However, the speed of light prevents us from being aware of these other identical areas.
The inflationary multiverse is composed of various pockets in which inflation fields collapse and form new universes.
The brane multiverse follows from M-theory and states that our universe is a 3-dimensional brane that exists with many others on a higher-dimensional brane or "bulk". Particles are bound to their respective branes except for gravity.
The cyclic multiverse (via the ekpyrotic scenario) has multiple branes (each a universe) that have collided, causing Big Bangs. The universes bounce back and pass through time until they are pulled back together and again collide, destroying the old contents and creating them anew.
The landscape multiverse relies on string theory's Calabi–Yau spaces. Quantum fluctuations drop the shapes to a lower energy level, creating a pocket with a set of laws different from that of the surrounding space.
The quantum multiverse creates a new universe when a diversion in events occurs, as in the many-worlds interpretation of quantum mechanics.
The holographic multiverse is derived from the theory that the surface area of a space can simulate the volume of the region.
The simulated multiverse exists on complex computer systems that simulate entire universes.
The ultimate multiverse contains every mathematically possible universe under different laws of physics.

Cyclic theories[edit]

Main article: Cyclic model
In several theories, there is a series of infinite, self-sustaining cycles (for example, an eternity of Big Bangs, Big Crunches, and/or Big Freezes).


A multiverse of a somewhat different kind has been envisaged within string theory and its higher-dimensional extension, M-theory.[58]
These theories require the presence of 10 or 11 spacetime dimensions respectively. The extra 6 or 7 dimensions may either be compactified on a very small scale, or our universe may simply be localized on a dynamical (3+1)-dimensional object, a D3-brane. This opens up the possibility that there are other branes which could support other universes.[59][60] This is unlike the universes in the quantum multiverse, but both concepts can operate at the same time.[citation needed]
Some scenarios postulate that our Big Bang was created, along with our universe, by the collision of two branes.[59][60]

Black-hole cosmology[edit]

Main article: Black-hole cosmology
A black-hole cosmology is a cosmological model in which the observable universe is the interior of a black hole existing as one of possibly many universes inside a larger universe. This includes the theory of white holes, which are on the opposite side of space-time.
While a black hole sucks everything in, including light, a white hole releases matter and light. Hence the name "white hole".

Anthropic principle[edit]

Main article: Anthropic principle
The concept of other universes has been proposed to explain how our own universe appears to be fine-tuned for conscious life as we experience it.
If there were a large (possibly infinite) number of universes, each with possibly different physical laws (or different fundamental physical constants), then some of these universes (even if very few) would have the combination of laws and fundamental parameters that are suitable for the development of matter, astronomical structures, elemental diversity, stars, and planets that can exist long enough for life to emerge and evolve.
The weak anthropic principle could then be applied to conclude that we (as conscious beings) would only exist in one of those few universes that happened to be finely tuned, permitting the existence of life with developed consciousness. Thus, while the probability might be extremely small that any particular universe would have the requisite conditions for life (as we understand life), those conditions do not require intelligent design as an explanation for the conditions in the Universe that promote our existence in it.
An early form of this reasoning is evident in Arthur Schopenhauer's 1844 work "Von der Nichtigkeit und dem Leiden des Lebens", where he argues that our world must be the worst of all possible worlds, because if it were significantly worse in any respect it could not continue to exist.[61]

Occam's Razor[edit]

Proponents and critics disagree about how to apply Occam's Razor. Critics argue that to postulate an almost infinite number of unobservable universes, just to explain our own universe, is contrary to Occam's Razor.[62] But proponents argue that, in terms of Kolmogorov complexity, the proposed multiverse is simpler than a single idiosyncratic universe.[50]
For example, multiverse proponent Max Tegmark argues:
[A]n entire ensemble is often much simpler than one of its members. This principle can be stated more formally using the notion of algorithmic information content. The algorithmic information content in a number is, roughly speaking, the length of the shortest computer program that will produce that number as output. For example, consider the set of all integers. Which is simpler, the whole set or just one number? Naively, you might think that a single number is simpler, but the entire set can be generated by quite a trivial computer program, whereas a single number can be hugely long. Therefore, the whole set is actually simpler... (Similarly), the higher-level multiverses are simpler. Going from our universe to the Level I multiverse eliminates the need to specify initial conditions, upgrading to Level II eliminates the need to specify physical constants, and the Level IV multiverse eliminates the need to specify anything at all.... A common feature of all four multiverse levels is that the simplest and arguably most elegant theory involves parallel universes by default. To deny the existence of those universes, one needs to complicate the theory by adding experimentally unsupported processes and ad hoc postulates: finite space, wave function collapse and ontological asymmetry. Our judgment therefore comes down to which we find more wasteful and inelegant: many worlds or many words. Perhaps we will gradually get used to the weird ways of our cosmos and find its strangeness to be part of its charm.[50]
— Max Tegmark, "Parallel universes. Not just a staple of science fiction, other universes are a direct implication of cosmological observations". Scientific American. 288 (5): 40–51. May 2003. doi:10.1038/scientificamerican0503-40. PMID 12701329. 
Princeton cosmologist Paul Steinhardt used the 2014 Annual Edge Foundation Question to state his opposition to multiverse theories:
A pervasive idea in fundamental physics and cosmology that should be retired: the notion that we live in a multiverse in which the laws of physics and the properties of the cosmos vary randomly from one patch of space to another. According to this view, the laws and properties within our observable universe cannot be explained or predicted because they are set by chance. Different regions of space too distant to ever be observed have different laws and properties, according to this picture. Over the entire multiverse, there are infinitely many distinct patches. Among these patches, in the words of Alan Guth, "anything that can happen will happen—and it will happen infinitely many times". Hence, I refer to this concept as a Theory of Anything. Any observation or combination of observations is consistent with a Theory of Anything. No observation or combination of observations can disprove it. Proponents seem to revel in the fact that the Theory cannot be falsified. The rest of the scientific community should be up in arms since an unfalsifiable idea lies beyond the bounds of normal science. Yet, except for a few voices, there has been surprising complacency and, in some cases, grudging acceptance of a Theory of Anything as a logical possibility. The scientific journals are full of papers treating the Theory of Anything seriously. What is going on?[34]
— Paul Steinhardt, "Theories of Anything"
Steinhardt claims that multiverse theories have gained currency mostly because too much has been invested in theories that have failed (e.g., inflation theory and string theory). He sees in them an attempt to redefine the values of science, to which he objects even more strongly:
A Theory of Anything is useless because it does not rule out any possibility and worthless because it submits to no do-or-die tests. (Many papers discuss potential observable consequences, but these are only possibilities, not certainties, so the Theory is never really put at risk.)[34]
— Paul Steinhardt, "Theories of Anything"

Modal realism[edit]

Possible worlds are a way of explaining probability and hypothetical statements. Some philosophers, such as David Lewis, believe that all possible worlds exist and that they are just as real as the world we live in (a position known as modal realism).[63]

Trans-world identity[edit]

A metaphysical issue which crops up in multiverse theories that posit infinite identical copies of any given universe, is the notion that there can be identical objects in different possible worlds. According to the counterpart theory of David Lewis, the objects should be regarded as similar rather than identical.[64][65]

See also[edit]


  1. Jump up ^ David Deutsch, The Beginning of Infinity, page 310.
  2. Jump up ^ James, William, The Will to Believe, 1895; and earlier in 1895, as cited in OED's new 2003 entry for "multiverse": James, William (October 1895), "Is Life Worth Living?", Internat. Jrnl. Ethics, 6: 10, doi:10.1086/205378, Visible nature is all plasticity and indifference, a multiverse, as one might call it, and not a universe. 
  3. Jump up ^ Kragh, H. (2009). "Contemporary History of Cosmology and the Controversy over the Multiverse". Annals of Science. 66 (4): 529–551. doi:10.1080/00033790903047725. 
  4. Jump up ^ Ellis, George; Silk, Joe (December 16, 2014). "Scientific Method: Defend the Integrity of Physics". Nature. 516: 321–323. Bibcode:2014Natur.516..321E. doi:10.1038/516321a. 
  5. Jump up ^ "Feynman on Scientific Method". YouTube. Retrieved July 28, 2012. 
  6. Jump up ^ Steinhardt, Paul (June 3, 2014). "Big Bang blunder bursts the Multiverse bubble". Nature. 510: 9. Bibcode:2014Natur.510....9S. doi:10.1038/510009a. 
  7. Jump up ^ Weinberg, Steven (November 20, 2007). "Physics: What we do and don't know". The New York Review of Books. 
  8. Jump up ^ Lisa Zyga (December 17, 2010). "Scientists find first evidence that many universes exist". Retrieved 12 October 2013. 
  9. Jump up ^ "Astronomers Find First Evidence Of Other Universe". December 13, 2010. Retrieved 12 October 2013. 
  10. Jump up ^ Max Tegmark; Alexander Vilenkin (July 19, 2011). "The Case for Parallel Universes". Retrieved 12 October 2013. 
  11. Jump up ^ "Is Our Universe Inside a Bubble? First Observational Test of the 'Multiverse'". Science Daily. Aug 3, 2011. Retrieved 12 October 2013. 
  12. Jump up ^ Feeney, Stephen M.; et al. (2011). "First observational tests of eternal inflation: Analysis methods and WMAP 7-year results". Physical Review D. 84 (4): 43507. arXiv:1012.3667free to read. Bibcode:2011PhRvD..84d3507F. doi:10.1103/PhysRevD.84.043507. 
  13. Jump up ^ Feeney; et al. (2011). "First observational tests of eternal inflation". Physical Review Letters. 107 (7): 071301. arXiv:1012.1995free to read. Bibcode:2011PhRvL.107g1301F. doi:10.1103/PhysRevLett.107.071301. PMID 21902380. . Bousso, Raphael; Harlow, Daniel; Senatore, Leonardo (2013). "Inflation after False Vacuum Decay: Observational Prospects after Planck". Physical Review D. 91 (8): 083527. arXiv:1309.4060free to read. Bibcode:2015PhRvD..91h3527B. doi:10.1103/PhysRevD.91.083527. 
  14. Jump up ^ Collaboration, Planck; Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Balbi, A.; Banday, A. J.; Barreiro, R. B.; Battaner, E.; Benabed, K.; Benoit-Levy, A.; Bernard, J. -P.; Bersanelli, M.; Bielewicz, P.; Bikmaev, I.; Bobin, J.; Bock, J. J.; Bonaldi, A.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Burigana, C.; Butler, R. C.; Cabella, P.; Cardoso, J. -F.; Catalano, A.; Chamballu, A.; et al. (2013-03-20). "Planck intermediate results. XIII. Constraints on peculiar velocities". Astronomy & Astrophysics. 561: A97. arXiv:1303.5090free to read. Bibcode:2014A&A...561A..97P. doi:10.1051/0004-6361/201321299. 
  15. Jump up ^ "Blow for 'dark flow' in Planck's new view of the cosmos". New Scientist. 3 April 2013. Retrieved 10 March 2014. 
  16. Jump up ^ Universe or Multiverse. p. 19. ISBN 9780521848411. Some physicists would prefer to believe that string theory, or M-theory, will answer these questions and uniquely predict the features of the Universe. Others adopt the view that the initial state of the Universe is prescribed by an outside agency, code-named God, or that there are many universes, with ours being picked out by the anthropic principle. Hawking argues that string theory is unlikely to predict the distinctive features of the Universe. But neither is he is an advocate of God. He therefore opts for the last approach, favoring the type of multiverse which arises naturally within the context of his own work in quantum cosmology. 
  17. Jump up ^ Greene, Brian (January 24, 2011). A Physicist Explains Why Parallel Universes May Exist. Interview with Terry Gross. Archived from the original on September 12, 2014. Retrieved September 12, 2014. 
  18. Jump up ^ Greene, Brian (January 24, 2011). Transcript:A Physicist Explains Why Parallel Universes May Exist. Interview with Terry Gross. Archived from the original on September 12, 2014. Retrieved September 12, 2014. 
  19. ^ Jump up to: a b c Tegmark, Max (2003). "Parallel Universes". In "Science and Ultimate Reality: from Quantum to Cosmos", honoring John Wheeler's th birthday. J. D. Barrow, P.C.W. Davies, & C.L. Harper eds. v1. Cambridge University Press. arXiv:astro-ph/0302131free to read. Bibcode:2003SciAm.288e..40T. doi:10.1038/scientificamerican0503-40.  "Parallel universes. Not just a staple of science fiction, other universes are a direct implication of cosmological observations". Scientific American. 288: 40–51. May 2003. arXiv:astro-ph/0302131free to read. Bibcode:2003SciAm.288e..40T. doi:10.1038/scientificamerican0503-40. PMID 12701329. 
  20. Jump up ^ "Alan Guth: Inflationary Cosmology: Is Our Universe Part of a Multiverse?". YouTube. Retrieved 6 October 2014. 
  21. Jump up ^ Linde, Andrei (January 27, 2012). "Inflation in Supergravity and String Theory: Brief History of the Multiverse" (PDF). Archived (PDF) from the original on September 13, 2014. Retrieved September 13, 2014. 
  22. Jump up ^ Parallel Worlds: A Journey Through Creation, Higher Dimensions, and the Future of the Cosmos
  23. Jump up ^ David Deutsch (1997). "The Ends of the Universe". The Fabric of Reality: The Science of Parallel Universes—and Its Implications. London: Penguin Press. ISBN 0-7139-9061-9.
  24. ^ Jump up to: a b Bousso, R.; Susskind, L. (2012). "Multiverse interpretation of quantum mechanics". Physical Review D. 85 (4). arXiv:1105.3796free to read. Bibcode:2012PhRvD..85d5007B. doi:10.1103/PhysRevD.85.045007. 
  25. Jump up ^ Vilenkin, Alex (2007). Many Worlds in One: The Search for Other Universes. ISBN 9780374707149. 
  26. ^ Jump up to: a b Nomura, Y. (2011). "Physical theories, eternal inflation, and the quantum universe". Journal of High Energy Physics. 2011 (11). arXiv:1104.2324free to read. Bibcode:2011JHEP...11..063N. doi:10.1007/JHEP11(2011)063. 
  27. Jump up ^ Pathria, R. K. (1972). "The Universe as a Black Hole". Nature. 240 (5379): 298–299. Bibcode:1972Natur.240..298P. doi:10.1038/240298a0. 
  28. Jump up ^ Catchpole, Heather (November 24, 2009). "Weird data suggests something big beyond the edge of the universe". Cosmos (magazine). Archived from the original on 14 July 2014. Retrieved July 27, 2014. 
  29. Jump up ^ Moon, Timur (May 19, 2013). "Planck Space Data Yields Evidence of Universes Beyond Our Own". International Business Times. Retrieved July 27, 2014. 
  30. Jump up ^ Freeman, David (March 4, 2014). "Why Revive 'Cosmos?' Neil DeGrasse Tyson Says Just About Everything We Know Has Changed". Archived from the original on September 12, 2014. Retrieved September 12, 2014. 
  31. Jump up ^ Sean Carroll (October 18, 2011). "Welcome to the Multiverse". Discover (magazine). Retrieved May 5, 2015. 
  32. Jump up ^ Falk, Dan (March 17, 2015). "Science's Path from Myth to Multiverse". Quanta Magazine. New York: Simons Foundation. 
  33. Jump up ^ Davies, Paul (2008). "Many Scientists Hate the Multiverse Idea". The Goldilocks Enigma: Why Is the Universe Just Right for Life?. Houghton Mifflin Harcourt. p. 207. ISBN 9780547348469. 
  34. ^ Jump up to: a b c Steinhardt, Paul (March 9, 2014). "Theories of Anything". 2014 : WHAT SCIENTIFIC IDEA IS READY FOR RETIREMENT?. Archived from the original on March 9, 2014. Retrieved March 9, 2014. 
  35. Jump up ^ Gibbons, G.W.; Turok, Neil (2008). "The Measure Problem in Cosmology". Phys. Rev. D. 77 (6): 063516. arXiv:hep-th/0609095free to read. Bibcode:2008PhRvD..77f3516G. doi:10.1103/PhysRevD.77.063516. 
  36. Jump up ^ Mukhanov, Viatcheslav (2014). "Inflation without Selfreproduction". Fortschritte der Physik. 63 (1): 36–41. arXiv:1409.2335free to read. Bibcode:2015ForPh..63...36M. doi:10.1002/prop.201400074. 
  37. Jump up ^ Woit, Peter (June 9, 2015). "A Crisis at the (Western) Edge of Physics". Not Even Wrong. 
  38. Jump up ^ Woit, Peter (June 14, 2015). "CMB @ 50". Not Even Wrong. 
  39. Jump up ^ Ellis, George F. R. (August 1, 2011). "Does the Multiverse Really Exist?". Scientific American. New York: Nature Publishing Group. 305 (2): 38–43. doi:10.1038/scientificamerican0811-38. ISSN 0036-8733. LCCN 04017574. OCLC 828582568. Retrieved September 12, 2014. (subscription required (help)). 
  40. Jump up ^ Ellis, George (2012). "The Multiverse: Conjecture, Proof, and Science" (PDF). Slides for a talk at Nicolai Fest Golm 2012. Archived (PDF) from the original on September 12, 2014. Retrieved September 12, 2014. 
  41. Jump up ^ Ellis, George; Silk, Joe (December 16, 2014), "Scientific Method: Defend the Integrity of Physics", Nature, 516: 321–323, Bibcode:2014Natur.516..321E, doi:10.1038/516321a 
  42. Jump up ^ Scoles; Sarah (April 19, 2016), "Can Physics Ever Prove the Multiverse is Real", 
  43. ^ Jump up to: a b Frank, Adam; Gleiser, Marcelo (June 5, 2015). "A Crisis at the Edge of Physics". New York Times. 
  44. Jump up ^ Baggott, Jim (August 1, 2013). Farewell to Reality: How Modern Physics Has Betrayed the Search for Scientific Truth. Pegasus. ISBN 978-1-60598-472-8. ISBN 978-1-60598-574-9. 
  45. Jump up ^ Davies, Paul (April 12, 2003). "A Brief History of the Multiverse". New York Times. 
  46. Jump up ^ Davies, Paul (12 April 2003). "A Brief History of the Multiverse". New York Times. Retrieved 16 August 2011. 
  47. Jump up ^ Ellis, George F. R. (August 1, 2011). "Does the Multiverse Really Exist?". Scientific American. New York: Nature Publishing Group. 305 (2): 38–43. doi:10.1038/scientificamerican0811-38. ISSN 0036-8733. LCCN 04017574. OCLC 828582568. Retrieved August 16, 2011. (subscription required (help)). 
  48. Jump up ^ Tegmark, Max (May 2003). "Parallel Universes". Scientific American. 288: 40–51. doi:10.1038/scientificamerican0503-40. PMID 12701329. 
  49. Jump up ^ Tegmark, Max (23 January 2003). Parallel Universes (PDF). Retrieved 7 February 2006. 
  50. ^ Jump up to: a b c d e "Parallel universes. Not just a staple of science fiction, other universes are a direct implication of cosmological observations.", Tegmark M., Sci Am. 2003 May;288(5):40–51.
  51. Jump up ^ "First Second of the Big Bang". How The Universe Works 3. 2014. Discovery Science. 
  52. Jump up ^ Tegmark, Max (2014). Our Mathematical Universe: My Quest for the Ultimate Nature of Reality. Knopf Doubleday Publishing Group. ISBN 9780307599803. 
  53. Jump up ^ J. Schmidhuber (1997): A Computer Scientist's View of Life, the Universe, and Everything. Lecture Notes in Computer Science, pp. 201–208, Springer: IDSIA – Dalle Molle Institute for Artificial Intelligence
  54. Jump up ^ Schmidhuber, Juergen (2000). "Algorithmic Theories of Everything". Sections in: Hierarchies of generalized Kolmogorov complexities and nonenumerable universal measures computable in the limit. International Journal of Foundations of Computer Science ():587-612 (2002). Section 6 in: the Speed Prior: A New Simplicity Measure Yielding Near-Optimal Computable Predictions. in J. Kivinen and R. H. Sloan, editors, Proceedings of the 15th Annual Conference on Computational Learning Theory(COLT 2002), Sydney, Australia, Lecture Notes in Artificial Intelligence, pages 216-228. Springer, 2002. 13 (4): 1–5. arXiv:quant-ph/0011122free to read. 
  55. Jump up ^ J. Schmidhuber (2002): Hierarchies of generalized Kolmogorov complexities and nonenumerable universal measures computable in the limit. International Journal of Foundations of Computer Science 13(4):587–612 IDSIA – Dalle Molle Institute for Artificial Intelligence
  56. Jump up ^ J. Schmidhuber (2002): The Speed Prior: A New Simplicity Measure Yielding Near-Optimal Computable Predictions. Proc. 15th Annual Conference on Computational Learning Theory (COLT 2002), Sydney, Australia, Lecture Notes in Artificial Intelligence, pp. 216–228. Springer: IDSIA – Dalle Molle Institute for Artificial Intelligence
  57. Jump up ^ In The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos, 2011
  58. Jump up ^ Weinberg, Steven (2005). "Living in the Multiverse". arXiv:hep-th/0511037v1free to read. 
  59. ^ Jump up to: a b Richard J Szabo, An introduction to string theory and D-brane dynamics (2004)
  60. ^ Jump up to: a b Maurizio Gasperini, Elements of String Cosmology (2007)
  61. Jump up ^ Arthur Schopenhauer, "Die Welt als Wille und Vorstellung," supplement to the 4th book "Von der Nichtigkeit und dem Leiden des Lebens". see also R.B. Haldane and J. Kemp's translation "On the Vanity and Suffering of Life" pp 395-6
  62. Jump up ^ Trinh, Xuan Thuan (2006). Staune, Jean, ed. Science & the Search for Meaning: Perspectives from International Scientists. West Conshohocken, PA: Templeton Foundation. p. 186. ISBN 1-59947-102-7. 
  63. Jump up ^ Lewis, David (1986). On the Plurality of Worlds. Basil Blackwell. ISBN 0-631-22426-2. 
  64. Jump up ^ Deutsch, Harry (Summer 2002). Edward N. Zalta, ed. "Relative Identity". The Stanford Encyclopedia of Philosophy. Retrieved 6 October 2014. 
  65. Jump up ^ "Paul B. Kantor "The Interpretation of Cultures and Possible Worlds", 1 October 2002". Retrieved 6 October 2014. 


  • Surya-Siddhanta: A Text Book of Hindu Astronomy by Ebenezer Burgess, ed. Phanindralal Gangooly (1989/1997) with a 45-page commentary by P. C. Sengupta (1935).

External links[edit]