A Perspective on the Landscape Problem

Abstract

I discuss the historical roots of the landscape problem and propose criteria for its successful resolution. This provides a perspective to evaluate the possibility to solve it in several of the speculative cosmological scenarios under study including eternal inflation, cosmological natural selection and cyclic cosmologies.

Invited contribution for a special issue of Foundations of Physics titled Forty Years Of String Theory: Reflecting On the Foundations.

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Notes

  1. 1.

    For several reasons this cannot be the AdS/CFT correspondence. One reason is that the cosmological constant has the wrong sign, another is that a cosmological theory cannot have boundaries or asymptotic regions, for reasons I will discuss below.

  2. 2.

    This partly reflects conclusions reached in joint work with Roberto Mangabeira Unger [80].

  3. 3.

    Which he named.

  4. 4.

    The evidence that quantum gravity effects eliminate singularities in this way has become much stronger recently. Compare older papers on bounces which employ mainly semiclassical methods [3436] to the newer literature on loop quantum cosmology which shows that bounces are generic in exact quantum evolutions of a class of quantum cosmological models [3741]. A study of modifications of coupling constants during bounces is in [42].

  5. 5.

    Claims by Penrose and Gurzadyan [1416] that these have been observed are presently controversial [1719].

  6. 6.

    Critiques of cosmological natural selection were published in [4851]. These have been all answered in the recent papers [27, 28] and book [1] (see especially the appendix and end notes).

  7. 7.

    Indeed, the use of the word landscape was meant to suggest the analogy to the fitness landscapes of evolutionary biology [1].

  8. 8.

    This prediction was pointed to in [1], which was published in 1997, just before the discovery of dark energy. “This means that we may expect that when all the observations have been sorted out, there will be a small cosmological constant, there will be a neutrino mass and Omega will not be exactly equal to one.” [1], p. 315.

  9. 9.

    An excellent historical and critical survey of the anthropic principle and related developments is in [73].

  10. 10.

    I am grateful to Ben Freivogel for conversations on this issue.

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Acknowledgements

I am grateful to Roberto Mangabeira Unger for proposing a collaboration on evolving laws of nature which stimulated and sharpened many of the ideas and arguments contained here. Results of our joint work, on which this essay is partially based, will be published in [80]. I am grateful to many colleagues at Perimeter Institute including Niayesh Afshordi, Latham Bole, Matt Johnson and Neil Turok for conversations on these issues. I have also learned a great deal from the opportunity to listen to conferences where various attempts to resolve the landscape problem were critically examined. Research at Perimeter Institute for Theoretical Physics is supported in part by the Government of Canada through NSERC and by the Province of Ontario through MRI.

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Smolin, L. A Perspective on the Landscape Problem. Found Phys 43, 21–45 (2013). https://doi.org/10.1007/s10701-012-9652-x

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Keywords

  • String theory
  • Landscape