Is Quantum Gravity Necessary?

Mattingly, James

doi:10.1007/0-8176-4454-7_17

Cited by 43 publications

(54 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…I concur with Callender andHuggett (2001a, 2001b) and with Mattingly (1999) that this question must be answered in the negative. The mere existence of approaches to quantum gravity which do not involve the quantization of gravity implies that quantization is a contingent matter.…”

Section: Why Quantize Gravity?supporting

confidence: 55%

To Quantize or Not to Quantize: Fact and Folklore in Quantum Gravity

Wüthrich¹

2005

Philos. of Sci.

View full text Add to dashboard Cite

Does the need to find a quantum theory of gravity imply that the gravitational field must be quantized? Physicists working in quantum gravity routinely assume an affirmative answer, often without being aware of the metaphysical commitments that tend to underlie this assumption. The ambition of this article is to probe these commitments and to analyze some recently adduced arguments pertinent to the issue of quantization. While there exist good reasons to quantize gravity, as this analysis will show, alternative approaches to gravity challenge the received wisdom. These renegade approaches do not regard gravity as a fundamental force, but rather as effective, i.e. as merely supervening on fundamental physics. I will urge that these alternative accounts at least prove the tenability of an opposition to quantization. IntroductionAll major approaches to quantum gravity endorse, implicitly or explicitly, the view that gravity must be "quantized" in order to be amenable to a description at the fundamental level. To be sure, different approaches propose to execute this task in radically different manners. But they agree * I wish to thank

show abstract

Section: Why Quantize Gravity?supporting

confidence: 55%

To Quantize or Not to Quantize: Fact and Folklore in Quantum Gravity

Wüthrich¹

2005

Philos. of Sci.

View full text Add to dashboard Cite

show abstract

“…The last term is the contribution of Ĥ int given in equation (15). In the last term on the right-hand side of the above equation, the infinite terms with i = j are treated by standard renormalization and regularization techniques at the second-quantized level and they appear as a mass renormalization.…”

Section: The Schrödinger-newton Equation As a Hartree Approximationmentioning

confidence: 99%

“…The Schrödinger-Newton equation does follow from a theory in which only matter fields are quantized, while the gravitational field remains classical even at the fundamental level. This is what we will refer to as semi-classical gravity in the following, thereby adopting the notation of [14][15][16]. One possible candidate for such a theory is a coupling of gravity to matter by means of the semiclassical Einstein equations π Ψ Ψ + = | | μν μν μν physics [19,20] but these arguments turn out to be inconclusive [15,16,21,22].…”

mentioning

confidence: 99%

The Schrödinger–Newton equation and its foundations

et al. 2014

View full text Add to dashboard Cite

The necessity of quantising the gravitational field is still subject to an open debate. In this paper we compare the approach of quantum gravity, with that of a fundamentally semi-classical theory of gravity, in the weak-field non-relativistic limit. We show that, while in the former case the Schrödinger equation stays linear, in the latter case one ends up with the so-called Schrödinger-Newton equation, which involves a nonlinear, non-local gravitational contribution. We further discuss that the Schrödinger-Newton equation does not describe the collapse of the wave-function, although it was initially proposed for exactly this purpose. Together with the standard collapse postulate, fundamentally semiclassical gravity gives rise to superluminal signalling. A consistent fundamentally semi-classical theory of gravity can therefore only be achieved together with a suitable prescription of the wave-function collapse. We further discuss, how collapse models avoid such superluminal signalling and compare the nonlinearities appearing in these models with those in the Schrödinger-Newton equation.4 that is by replacing the classical energy-momentum tensor in Einsteinʼs equations by the expectation value of the corresponding quantum operator in a given quantum state Ψ. This idea has a long history, dating back to the works of Møller [17] and Rosenfeld [18]. It has been commented repeatedly that such a theory would be incompatible with established principles of 3 The self-interactions present in the classical theory would then be treated in the same way as in quantum electrodynamics, namely, through the normal ordering and renormalization prescription. They would lead to a mass-renormalization of the theory rather than a potential term in the Schrödinger equation [9,10]. 4 The term quantum gravity here is restricted to any such theory which, at least in its low energy limit, treats the gravitational field in the linearized Einstein equations as a linear quantum operator. 5 Apart from this, the Schrödinger-Newton equation also follows uncontroversially from a gravitating classical matter field [13]. 2 New J. Phys. 16 (2014) 115007 M Bahrami et al

show abstract

“…Remarkably, the evidence for these claims is extremely thin, and indeed what there is is extremely dubious. For general analyses of the failure to establish the case for quantization, see Mattingly's discussion [4,5], and Calender and Huggett's editorial introduction [1] to their (2001).…”

Section: Introductionmentioning

confidence: 99%

“…While Page and Geilker do carry out their experiment, the significance of their result was called into question even before the experiment was performed, by the very person (Kibble [3]) who suggested the experiment in the first place. I will not here discuss their experiment since its significance has been decisively undermined [1,3,4,5], and because it applies only to one specific version of semiclassical gravity, semiclassical general relativity.…”

Section: Introductionmentioning

confidence: 99%

Why Eppley and Hannah’s thought experiment fails

Mattingly

2006

Phys. Rev. D

Self Cite

108

View full text Add to dashboard Cite

It is shown that Eppley and Hannah's thought experiment establishing that gravity must be quantized is fatally flawed. The device they propose, even if built, cannot establish their claims, nor is it plausible that it can be built with any materials compatible with the values of c, , G. Finally the device, and any reasonable modification of it, would be so massive as to be within its own Schwarzschild radius-a fatal flaw for any thought experiment.

show abstract

Is Quantum Gravity Necessary?

Cited by 43 publications

References 8 publications

To Quantize or Not to Quantize: Fact and Folklore in Quantum Gravity

To Quantize or Not to Quantize: Fact and Folklore in Quantum Gravity

The Schrödinger–Newton equation and its foundations

Why Eppley and Hannah’s thought experiment fails

Contact Info

Product

Resources

About