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Sabine Hossenfelder

Publications and source records attributed to Sabine Hossenfelder.

At least 55 records · Page 3Linked to original sources
arXiv2013

Minimal Length Scale Scenarios for Quantum Gravity

We review the question of whether the fundamental laws of nature limit our ability to probe arbitrarily short distances. First, we examine what insights can be gained from thought experiments for probes of shortest distances, and summarize what can be learned from different approaches to a theory of quantum gravity. Then we discuss some models that have been developed to implement a minimal length scale in quantum mechanics and quantum field theory. These models have entered the literature as the generalized uncertainty principle or the modified dispersion relation, and have allowed the study of the effects of a minimal length scale in quantum mechanics, quantum electrodynamics, thermodynamics, black-hole physics and cosmology. Finally, we touch upon the question of ways to circumvent the manifestation of a minimal length scale in short-distance physics.

gr-qc↗
arXiv2012

Gravity can be neither classical nor quantized

I argue that it is possible for a theory to be neither quantized nor classical. We should therefore give up the assumption that the fundamental theory which describes gravity at shortest distances must either be quantized, or quantization must emerge from a fundamentally classical theory. To illustrate my point I will discuss an example for a theory that is neither classical nor quantized, and argue that it has the potential to resolve the tensions between the quantum field theories of the standard model and general relativity.

gr-qc↗
arXiv2012

Comment on the black hole firewall

Recently, it has been argued that black hole complementarity is inconsistent by showing that, for an infalling observer, it would lead to the existence of a firewall near the black hole horizon, thereby violating the equivalence principle. If true, this would necessitate to give up on at least one of the postulates of black hole complementarity. In this comment I want to address an additional assumption that went into the conclusion, that the early outgoing Hawking radiation is entangled with the late radiation.

gr-qc↗
arXiv2012

Quantum superpositions of the speed of light

While it has often been proposed that, fundamentally, Lorentz-invariance is not respected in a quantum theory of gravity, it has been difficult to reconcile deviations from Lorentz-invariance with quantum field theory. The most commonly used mechanisms either break Lorentz-invariance explicitly or deform it at high energies. However, the former option is very tightly constrained by experiment already, the latter generically leads to problems with locality. We show here that there exists a third way to integrate deviations from Lorentz-invariance into quantum field theory that circumvents the problems of the other approaches. The way this is achieved is an extension of the standard model in which photons can have different speeds without singling out a preferred restframe, but only as long as they are in a quantum superposition. Once a measurement has been made, observables are subject to the laws of special relativity, and the process of measurement introduces a preferred frame. The speed of light can take on different values, both superluminal and subluminal (with respect to the usual value of the speed of light), without the need for Lorentz-invariance violating operators and without tachyons. We briefly discuss the relation to deformations of special relativity and phenomenological consequences.

gr-qc↗
arXiv2012

Can we measure structures to a precision better than the Planck length?

It was recently claimed that the Planck length is not a limit to the precision by which we can measure distances, but that instead it is merely the Planck volume that limits the precision by which we can measure volumes. Here, we investigate this claim and show that the argument does not support the conclusion.

gr-qc↗
arXiv2012

Emission spectra of self-dual black holes

We calculate the particle spectra of evaporating self-dual black holes that are potential dark matter candidates. We first estimate the relevant mass and temperature range and find that the masses are below the Planck mass, and the temperature of the black holes is small compared to their mass. In this limit, we then derive the number-density of the primary emission particles, and, by studying the wave-equation of a scalar field in the background metric of the black hole, show that we can use the low energy approximation for the greybody factors. We finally arrive at the expression for the spectrum of secondary particle emission from a dark matter halo constituted of self-dual black holes.

gr-qc↗
arXiv2012

The Free Will Function

It is argued that it is possible to give operational meaning to free will and the process of making a choice without employing metaphysics.

physics.hist-ph↗
arXiv2011

Testing super-deterministic hidden variables theories

We propose to experimentally test non-deterministic time evolution in quantum mechanics by consecutive measurements of non-commuting observables on the same prepared state. While in the standard theory the measurement outcomes are uncorrelated, in a super-deterministic hidden variables theory the measurements would be correlated. We estimate that for macroscopic experiments the correlation time is too short to have been noticed yet, but that it may be possible with a suitably designed microscopic experiment to reach a parameter range where one would expect a super-deterministic modification of quantum mechanics to become relevant.

quant-ph↗
arXiv2010

Deformed Special Relativity from Asymptotically Safe Gravity

By studying the notion of a fundamentally minimal length scale in asymptotically safe gravity we find that a specific version of deformed special relativity (DSR) naturally arises in this approach. We then consider two thought experiments to examine the interpretation of the scenario and discuss similarities and differences to other approaches to DSR.

gr-qc↗
arXiv2010

Experimental Search for Quantum Gravity

We offer a brief survey of existent and planned experimental tests for quantum gravity. First, we outline the questions we wish to address, and then introduce some of the phenomenological models that are currently used in quantum gravity, both with and without a lowered Planck scale. After that, we summarize experimental areas where these models can be tested or constrained and discuss the status of the field.

gr-qc↗
arXiv2010

Comment on arXiv:1007.0718 by Lee Smolin

In a recent paper it was suggested a novel interpretation of deformed special relativity. In that new approach, nonlocal effects that had previously been shown to occur and be incompatible with experiment to high precision, are interpreted as coordinate artifacts that do not lead to real physical consequences. It is argued here that if one follows through the consequences of this thought, one finds that the theory one is dealing with needs to be ordinary special relativity to precision even better than the bound on nonlocal effect already requires. Consequently, the new approach cannot be understood as a version of deformed special relativity that circumvents the bound.

gr-qc↗
arXiv2010

Reply to arXiv:1006.2126 by Giovanni Amelino-Camelia et al

It was previously shown that models with deformations of special relativity that have an energy-dependent yet observer-independent speed of light suffer from nonlocal effects that are in conflict with observation to very high precision. In a recent preprint it has been claimed that this conclusion is false. This claim was made by writing down expressions for modified Lorentz-transformations the use of which does not reproduce the result. I will show here that the failure to reproduce the result is not a consequence of a novel and improved calculation, but a consequence of repeating the same calculation but making an assumption that is in conflict with the assumptions made to produce the original scenario. I will here explain what the physical meaning of either assumption is and why the original assumption is the physically meaningful one. I will then further explain why even making the differing assumption does not remove but merely shift the problem and why the bound derived by Amelino-Camelia et al is wrong.

gr-qc↗
arXiv2010

Comments on Nonlocality in Deformed Special Relativity, in reply to arXiv:1004.0664 by Lee Smolin and arXiv:1004.0575 by Jacob et al

It was previously shown that models with deformations of special relativity that have an energy-dependent yet observer-independent speed of light suffer from nonlocal effects that are in conflict with observation to very high precision. In a recent paper it has been proposed that these paradoxa arise only in the classical limit and can be prevented by an ad-hoc introduction of a quantum uncertainty that would serve to hide the nonlocality. We will show here that the proposed ansatz for this resolution is inconsistent with observer-independence and, when corrected, is in agreement with the earlier argument that revealed the troublesome nonlocality. We further offer an alternative derivation for the energy-dependent speed of light in the model used.

gr-qc↗
arXiv2010

Comments on and Comments on Comments on Verlinde's paper "On the Origin of Gravity and the Laws of Newton"

We offer some, hopefully clarifying, comments on Verlinde's recent claim that gravity is an entropic force. A suitable identification of quantities shows that both formulations of Newtonian gravity, the classical and the thermodynamical one, are actually equivalent. It turns out that some additional assumptions made by Verlinde are unnecessary. However, when it comes to General Relativity there remain some gaps in the argument. We comment on whether this identification can be done also for electrostatics. Finally, some thoughts on the use of this reinterpretation are offered.

gr-qc↗
arXiv2010

A model for non-singular black hole collapse and evaporation

We study the formation of a black hole and its subsequent evaporation in a model employing a minisuperspace approach to loop quantum gravity. In previous work the static solution was obtained and shown to be singularity-free. Here, we examine the more realistic dynamical case by generalizing the static case with help of the Vaidya metric. We track the formation and evolution of trapped surfaces during collapse and evaporation and examine the buildup of quantum gravitationally caused stress-energy preventing the formation of a singularity.

gr-qc↗
arXiv2010

At the Frontier of Knowledge

At any time, there are areas of science where we are standing at the frontier of knowledge, and can wonder whether we have reached a fundamental limit to human understanding. What is ultimately possible in physics? I will argue here that it is ultimately impossible to answer this question. For this, I will first distinguish three different reasons why the possibility of progress is doubted and offer examples for these cases. Based on this, one can then identify three reasons for why progress might indeed be impossible, and finally conclude that it is impossible to decide which case we are facing.

physics.pop-ph↗