the cosmic landscape pdf free download

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Susskind claims in his recent book The Cosmic Landscape that evidence for the existence and nature of `pocket universes' in a multiverse would be available in the detailed nature of the Cosmic Blackbody Background Radiation that constantly bathes all parts of our observable universe. I point out that acceptance of the complex chain of argument involved does not imply possible experimental verification of multiverses at the present time. Rather this claim relates only to theoretically possible observations in the very far future of the universe. Comment: Revised to clarify claims; essential substance unchanged

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arXiv:astro-ph/0603266v2 15 Mar 2006

COMMENT

On horizons and the cosmic landscape

George F R Ellis

Mathematics Department, University of Cape Town,

Rondebosch, Cape Town, South Africa.

Abstract

Susskind claims in his recent book The Cosmic Landscape that evi-

dence for the existence and nature of 'pocket universes' in a multiverse

would be available in the detailed nature of the Cosmic Blackbody Back-

ground Radiation that constantly bathes all parts of our observable uni-

verse. I point out that acceptance of the complex chain of argument

involved does not imply possible experimental veriﬁcation of multiverses

at the present time. Rather this claim relates only to theoretically possible

observations in the very far future of the universe.

A recent book by Susskind [1] presents interesting arguments for the exis-

tence of multiverses. Much of that argument is based on quantum ﬁeld theory

and the non-zero but small value for the cosmological constant, and is not the

concern of this comment, which focuses on issues to do with the nature of hori-

zons in cosmology. The point I wish to make is that Susskinds' contentions

about information ﬂows and the Cosmic Background Radiation ('CBR') in his

book do not imply possible astronomical conﬁrmation of multiverses at any

ﬁnite time in the history of the universe.

The multiverse proposal Susskind espouses states that there exist in a single

big megaverse a vast number of "pocket universes" like the expanding universe

domain we see around us, all beyond our observational reach as they are hidden

behind the cosmological horizon. "Our cosmic horizon is about ﬁfteen billion

light-years away, where things are moving so rapidly away from us that light

from there can never reach us, nor can any other signal. It is exactly the same as

a black hole horizon - a point of no return. The only diﬀerence is that the cosmic

horizon surrounds us, whereas we surround a black hole horizon. In either case

nothing from beyond the horizon can inﬂuence us, or so it was thought. Ac-

cording to classical physics, those other worlds are forever completely sealed oﬀ

from our world".1 The signiﬁcance is that this apparently means that claims of

a multiverse are not susceptible to observational veriﬁcation or disproof; hence

their scientiﬁc status is open to question: "Unfortunately the rest of the mega-

verse of pocket universes is all in this never-never land beyond the horizon.

According to the classical principles of general relativity, we can wonder all we

want about the existence and reality of these other worlds, but we can never

know. They are metaphysics, not physics" ([1], p.340; and see also [2]).

1This quote from [1] is taken from the Introduction, available on the web at http :

//www.twbookmark.com/books/28/0316155799/chapter−excerpt22014 .html .

Susskind counters this objection on the basis of what he terms "the Black

Hole War" - the battle over the fate of information that falls behind the event

horizon of a black hole. He states that the standard view that all information

falling behind the event horizon is irretrievably lost, has turned out to be wrong.

On the basis of a complex discourse involving the No Quantum Xerox Principle,

Black Hole Complementarity, and The Holographic Principle, he makes the

major claim that is the sub ject of this comment:1 "The very same arguments

that won the Black Hole War can be adapted to cosmological horizons. The

existence and details of all the other pocket universes are contained in the subtle

features of the cosmic radiation that constantly bathes all parts of our observable

universe" (my italics).

Now I do not aim to adjudicate here as to whether the Black Hole War

is won or lost: I simply accept for the sake of the rest of the discussion that

information may not after all be lost when it has fallen behind the event horizon.

The key point is that if this is so, it does not have the implications set out in

the italicized statement in the previous paragraph, because the limits on our

present day causal connectivity in cosmology are due to the particle horizon, not

the event horizon [3, 4, 5, 6].

While it is true that "the cosmic event horizon of an eternally inﬂating uni-

verse is mathematically very similar to the horizon of a black hole" ([1], p.340),

this has nothing to do with limits on information available to astronomers to-

day; these are based on the cosmic particle horizon, which is quite diﬀerent. The

particle horizon in cosmology (limiting the 'particles' we can see at the present

time) is deﬁned in terms of world lines of matter, and depends on the epoch

of observation; it strictly limits what information about matter we can access

at the present time. Furthermore, it exists in any realistic (almost Friedmann-

Lemaˆıtre) universe. By contrast, the event horizon in either cosmology or a

black hole context (limiting the events we will ever be able to see at any time

in our history) is deﬁned by a limiting past null cone, and relates to the entire

world line of the observer, not any particular observational epoch; whether it

exists or not in a cosmological context is determined by the nature of the end

of our history in the far future [3]. An event horizon will not occur in a cosmol-

ogy that expands forever with cosmological constant Λ = 0 in the far future; it

exists either at a 'Big Crunch' a ﬁnite time from now in the future in a k = +1

universe that recollapses, or at an inﬁnite time in the future in a universe that

expands forever with a non-zero cosmological constant (in each case there is a

spacelike future inﬁnity leading to the existence of the event horizon2 [4, 5, 6]).

The criteria for existence of the two kinds of horizon in a Robertson-Walker

universe with scale factor a (t ) are as follows [3]:

- a particle horizon exists if and only if at an arbitrary time t0 in the uni-

verse's history, either the integral R t 0

0dt/a(t ) converges (if the universe started

at time t = 0 where a (t )→ 0), or the integral R t 0

−∞ dt/a(t ) converges (if the

2In the black hole case, the event horizon is independent of the world line chosen, whereas

in the cosmological case, diﬀerent event horizons occur for world lines ending at diﬀerent

points on this spacelike future inﬁnity.

universe has existed forever),

- an event horizon exists if and only if at an arbitrary time t0 in the universe's

history, the integral R ∞

t0 dt/a(t ) converges (if the universe expands forever in the

future) or the integral R t f inal

t0 dt/a(t ) converges (if the universe comes to an end

at a ﬁnite time t f inal in the future where a (t )→ 0).

These expressions show how the event horizon relates to the future (obser-

vational events yet to take place), whereas the particle horizon relates to the

past (events that can send signals to be received by us today).

It is the event horizon that is at the centre of the Black Hole information

loss paradox; if the resolution of this problem described by the author is correct,

observers would become aware of any information escaping from their event

horizon as they approached it in the far future of their histories. If information

about what lies beyond a cosmological event horizon were indeed to emerge, this

information would be available to us only at the very end of the universe. This

possibility does not aﬀect present day observations, which are fundamentally

limited not by the event horizon but by the particle horizon - which excludes all

information from other pocket universes in a supposed megaverse from reaching

us at the present time (in essence: there has not been enough time since they

were formed for light from them to reach us).

In reality, the limit is even stronger: no signiﬁcant cosmological information

reaches us at the present time from beyond the visual horizon - deﬁned by the

world-lines of the furthest matter from which we receive electromagnetic radi-

ation today [7, 8].3 This matter is seen by us as the matter that emitted the

observed CBR at the time of decoupling of matter and radiation in the early

universe. The possible far future occurrence of an event horizon in the uni-

verse will not inﬂuence CBR data available to us today, inter alia because that

information is shaped by the interactions taking place in the primeval plasma

after inﬂation and before decoupling, see e.g. [11]. Prior information is largely

forgotten during this era - thermalization will destroy any subtle correlations

that may exist at earlier times - and occurrence of an event horizon in the far

future of this epoch is irrelevant. Possible other 'pocket universes' do not enter

the calculations [11] of CBR anisotropies.4

In summary: The ESA-NASA Planck Surveyor data on CBR anisotropies

will not have coded into it the nature of multiverse regions enormously more dis-

tant from us than a Hubble radius. Attempts to decipher information about far

distant regions of a megaverse supposedly hidden in that data will not succeed.

The black hole arguments of [1] potentially become relevant only at the end of

our destiny when our past light cone merges with the event horizon, either at

future inﬁnity (t → ∞ on our world line, with Λ 6 = 0 in that limit), or at the

ﬁnal crunch in a recollapsing universe (t→ t f inal on our world line, necessarily

with k = +1); they do not aﬀect present day astronomy.

3This is not related to the matter moving away from us at the speed of light, as is often

supposed (see [9, 10]).

4Discussions of 'super-horizon modes' and 'trans-Planckian eﬀects', see e.g. [12], are all

carried out in the context of a single Robertson-Walker universe domain.

References

[1] L Susskind: The Cosmic Landscape: String Theory and the Illusion of Intelligent

Design (Litle Brown, New York. 2005).

[2] G F R Ellis: "Philosophy of cosmology". To appear in Handbook in Philoso-

phy of Physics, Ed J Butterﬁeld and J Earman (Elsevier, 2006), Section 9.2.

(http://arxiv.org/abs/astro-ph/06022) .

[3] W Rindler, "Visual horizons in world models". Mon Not Roy Ast Soc 116 662

(1956).

[4] R Penrose, "Conformal treatment of inﬁnity". Relativity, Groups and Topology

ed C M DeWitt and B S DeWitt (New York: Gordon and Breach, 1963), 565.

[5] S W Hawking and G F R Ellis,The Large Scale Structure of Space-Time . (Cam-

bridge: Cambridge University Press, 1973), pp. 127-130.

[6] F J Tipler, C J S Clarke and G F R Ellis, "Singularities and horizons: A review

article". In General Relativity and Gravitation: One Hundred Years after the

Birth of Albert Einstein, Vol. 2 ed A Held (New York: Plenum Press, 1980),

97.

[7] G F R Ellis and W R Stoeger, "Horizons in inﬂationary universes". Class Qu

Grav 5, 207 (1988).

[8] G F R Ellis and R M Williams. Flat and Curved Space Times. (Oxford University

Press, 2000), Section 7.5.

[9] G F R Ellis and T Rothman, "Lost Horizons". Am. J. Phys . 61 , 93 (1993).

[10] T M Davis and C H Lineweaver, "Expanding Confusion: common miscon-

ceptions of cosmological horizons and the superluminal expansion of the Uni-

verse". Publications of the Astronomical Society of Australia, 21, 97-109 (2004).

(http://arxiv.org/abs/astro-ph/0310808) .

[11] S Dodelson, Modern Cosmology. (Academic Press, 2003).

[12] J Martin and R H Brandenberger, "The Trans-Planckian Problem of Inﬂationary

Cosmology" (2005). Phys.Rev. D63 (2001) 123501 (http:/arxiv.org/abs/hep-

th/0005209) .

Version 2007-03-15.

... Through quantum cosmology arguments [5]? Is the string landscape scenario compatible with predictability [6]? Do the universes of the multiverse interact [7] (see also Ref. [8])? ...

We examine a new multiverse scenario in which the component universes interact. We focus our attention to the process of "true" vacuum nucleation in the false vacuum within one single element of the multiverse. It is shown that the interactions lead to a collective behaviour that might lead, under specific conditions, to a pre-inflationary phase and ensued distinguishable imprints in the comic microwave background radiation.

... Through quantum cosmology arguments [65]? Is the string landscape scenario compatible with predictability [66]? Do the universes of the multiverse interact [67]? ...

Orfeu Bertolami

We present a general discussion about the so-called emergent properties and discuss whether space-time and gravity can be regarded as emergent features of underlying more fundamental structures. Finally, we discuss some ideas about the multiverse, and speculate on how our universe might arise from the multiverse.

... It has been pointed out, for instance, that the impossibility of observing a multiuniverse implies that its scientific status is questionable. It is in the realm of metaphysics, rather than of physics [45]. It has also been argued that selection criteria like the anthropic landscape must be necessarily supplemented by arguments based on dynamics and symmetry, as only these lead to a real "enlightenment", the former are actually a "temptation" [46]. ...

Orfeu Bertolami

Since the nineteenth century, it is known, through the work of Lobatchevski, Riemann, and Gauss, that spaces do not need to have a vanishing curvature. This was for sure a revolution on its own, however, from the point of view of these mathematicians, the space of our day to day experience, the physical space, was still an essentially a priori concept that preceded all experience and was independent of any physical phenomena. Actually, that was also the view of Newton and Kant with respect to time, even though, for these two space-time explorers, the world was Euclidean.

... One refers to the anthropic landscape, when the vacuum selection is based on anthropic considerations. This interpretation is not free from criticism: indeed, it has been pointed out, for instance, that the impossibility of observing a multiverse implies that its scientific status is questionable — It is in the realm of metaphysics, rather than of physics [58]. This situation could be altered if the universes could interact. ...

Orfeu Bertolami

We review, in a historical perspective, developments in physics which led to the emergence of unifying ideas and theories. Some attention is paid to the theoretical programme that started in the second decade of the XXth century and whose objective was to reach a unified description of gravity and electromagnetism. These attempts can be regarded as conceptually akin to the contemporary "theories of everything" which aim to unify all interactions of Nature. Comment: Latex, 29 pages. Based on talk delivered at the "Mira Fernandes and his age: An historical Conference in honour of Aureliano de Mira Fernandes (1884-1958)", 17 June 2009, Instituto Superior T\'ecnico, Lisbon, Portugal. Typos corrected

Orfeu Bertolami

We discuss how developments in physics often imply in the need that spacetime acquires an increasingly richer and complex structure. General Relativity was the first theory to show us the way to connect space and time with the physical world. Since then, scrutinizing the ways spacetime might exist is, in a way, the very essence of physics. Physics has thus given substance to the pioneering work of scores of brilliant mathematicians who speculated on the geometry and topology of spaces.

... The statistical equality of widely separated regions was set up in the early universe when they were in causal contact, so the particle horizon is much larger than the visual horizon. (For clarification of the different horizons, see [109,110].) In spacetimes which are not statistically homogeneous and isotropic, the averaging procedure would not be expected to be useful, and a description in terms of an overall scale factor would probably not make sense. For example, this would be the case if the size of typical non-linear structures were a sizeable fraction of the visual horizon. ...

Syksy Rasanen

The International School for Advanced Studies (SISSA) was founded in 1978 and was the first institution in Italy to promote post-graduate courses leading to a Doctor Philosophiae (or PhD) degree. A centre of excellence among Italian and international universities, the school has around 65 teachers, 100 post docs and 245 PhD students, and is located in Trieste, in a campus of more than 10 hectares with wonderful views over the Gulf of Trieste. SISSA hosts a very high-ranking, large and multidisciplinary scientific research output. The scientific papers produced by its researchers are published in high impact factor, well-known international journals, and in many cases in the world's most prestigious scientific journals such as Nature and Science. Over 900 students have so far started their careers in the field of mathematics, physics and neuroscience research at SISSA. Visit www.sissa.it.

This article reviews the properties and limitations associated with the existence of particle, visual, and event horizons in cosmology in general and in inflationary universes in particular, carefully distinguishing them from 'Hubble horizons'. It explores to what extent one might be able to probe conditions beyond the visual horizon (which is close in size to the present Hubble radius), thereby showing that visual horizons place major limits on what are observationally testable aspects of a multiverse, if such exists. Indeed these limits largely prevent us from observationally proving a multiverse either does or does not exist. We emphasize that event horizons play no role at all in observational cosmology, even in the multiverse context, despite some claims to the contrary in the literature.

A.N. Schellekens

If the results of the first LHC run are not betraying us, many decades of particle physics are culminating in a complete and consistent theory for all non-gravitational physics: the Standard Model. But despite this monumental achievement there is a clear sense of disappointment: many questions remain unanswered. Remarkably, most unanswered questions could just be environmental, and disturbingly (to some) the existence of life may depend on that environment. Meanwhile there has been increasing evidence that the seemingly ideal candidate for answering these questions, String Theory, gives an answer few people initially expected: a huge "landscape" of possibilities, that can be realized in a multiverse and populated by eternal inflation. At the interface of "bottom-up" and "top-down" physics, a discussion of anthropic arguments becomes unavoidable. We review developments in this area, focusing especially on the last decade.

Orfeu Bertolami
Victor Herdeiro

It has been recently proposed that the multiverse of eternal inflation and the many-worlds interpretation of quantum mechanics can be identified, yielding a new view on the measure and measurement problems. In the present note, we argue that a non-linear evolution of observables in the quantum multiverse would be an obstacle for such a description and that these non-linearities are expected from quite general arguments.

George F. R. Ellis

This chapter discusses the issues related to the philosophy of cosmology. Cosmology is the study of the large-scale structure of the Universe, where "the Universe" means all that exists in a physical sense. A unique role of the universe is in creating the environment in which galaxies, stars, and planets develop, thus providing a setting in which local physics and chemistry can function in a way that enables the evolution of life on planets such as the Earth Thus cosmology considers the vast domain of galaxies, clusters of galaxies, and quasi-stellar objects--observable in the sky by use of telescopes of all kinds, examining their nature, distribution, origins, and relation to their larger environment. After a substantial outline of present day cosmology, issues are explored in the chapter based on a series of thirty-four "Theses" clustered around nine key aspects of the nature of cosmology--related to geometry, physics, and philosophy that frame the context of the philosophical issues facing cosmology and its relation to local physics.

Cosmological horizons play an essential role in determining the causal structure of spacetime and are of central importance in the inflationary universe scenario. We review the topic of horizons in simple language, pointing out a number of widespread misconceptions. The use of spacetime diagrams plotted in terms of proper time and proper distance coordinates helps sort out some of these difficulties. They complement the widely used conformal diagrams, which show causal relations clearly but severely distort proper distances.

For the first edition, published in 1988, see Abstr. 46.003.044. Contents: 1. Space-time diagrams and the foundations of special relativity. 2. Fundamentals of measurement. 3. Measurements in flat space-times. 4. The Lorentz transformation and the invariant interval. 5. Curved space-times. 6. Spherical and stellar collapse. 7. Simple cosmological models.

Scott Dodelson

Modern Cosmology begins with an introduction to the smooth, homogeneous universe described by a Friedmann-Robertson-Walker metric, including careful treatments of dark energy, big bang nucleosynthesis, recombination, and dark matter. From this starting point, the reader is introduced to perturbations about an FRW universe: their evolution with the Einstein-Boltzmann equations, their generation by primordial inflation, and their observational consequences. These consequences include the anisotropy spectrum of the cosmic microwave background (CMB) featuring acoustic peaks and polarization, the matter power spectrum with baryonic wiggles, and their detection via photometric galaxy surveys, redshift distortions, cluster abundances, and Modern Cosmology is the first book to explain in detail the structure of the acoustic peaks in the CMB, the E/B decomposition in polarization which may allow for detection of primordial gravity waves, and the modern analysis techniques used on increasingly large cosmological data sets. Readers will gain the tools needed to work in cosmology and learn how modern observations are rapidly revolutionizing our picture of the universe.

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the cosmic landscape pdf free download