Sean M. Carroll

We consider emergence from the perspective of dynamics: states of a system evolving with time. We focus on the role of a decomposition of wholes into parts, and attempt to characterize relationships between levels without reference to whether higher-level properties are "novel" or "unexpected." We offer a classification of different varieties of emergence, with and without new ontological elements at higher levels.

The holographic principle suggests that regions of space contain fewer physical degrees of freedom than would be implied by conventional quantum field theory. Meanwhile, in Hilbert spaces of large dimension 2 ⁿ , it is possible to define N ≫ n Pauli algebras that are nearly anti-commuting (but not quite) and which can be thought of as ‘overlapping degrees of freedom’. We propose to model the phenomenology of holographic theories by allowing field-theory modes to be overlapping, and derive potential observational consequences. In particular, we build a Fermionic quantum field whose effective degrees of freedom approximately obey area scaling and satisfy a cosmic Bekenstein bound, and compare predictions of that model to cosmic neutrino observations. Our implementation of holography implies a finite lifetime of plane waves, which depends on the overall UV cutoff of the theory. To allow for neutrino flux from blazar TXS 0506+056 to be observable, our model needs to have a cutoff Λ UV ≲ 500 Λ LHC . This is broadly consistent with current bounds on the energy spectrum of cosmic neutrinos from IceCube, but high energy neutrinos are a potential challenge for our model of holography. We motivate our construction via quantum mereology, i.e. using the idea that EFT degrees of freedom should emerge from an abstract theory of quantum gravity by finding quasi-classical Hilbert space decompositions. We also discuss how to extend the framework to Bosons. Finally, using results from random matrix theory we derive an analytical understanding of the energy spectrum of our theory. The numerical tools used in this work are publicly available within the GPUniverse package, https://github.com/OliverFHD/GPUniverse.

I propose a version of quantum mechanics featuring a discrete and finite number of states that is plausibly a model of the real world. The model is based on standard unitary quantum theory of a closed system with a finite-dimensional Hilbert space. Given certain simple conditions on the spectrum of the Hamiltonian, Schrödinger evolution is periodic, and it is straightforward to replace continuous time with a discrete version, with the result that the system only visits a discrete and finite set of state vectors. The biggest challenges to the viability of such a model come from cosmological considerations. The theory may have implications for questions of mathematical realism and finitism.

We argue that if axions are the dark matter, their coupling to electromagnetism results in exponential growth of a helical magnetic field when the axion field first rolls down its potential. After an inverse cascade, the relevant length scales to day are of order 10-100 kpc, of astrophysical interest. Our mechanism for allowing the field to grow relies on a nuance of MHD. Faraday's Law says that an electric field is needed to create a magnetic field. Previous authors relied on conventional Ohm's law to calculate E, but the resistivity is negligible and therefore they assume E is as well. We use a modified Ohm's Law that includes the effects of self-induction in limiting the current driven by a given E, which allows a magnetic field to grow.

Laparoscopy can improve outcomes and patient re- covery times compared to open surgery. However, the minimally-invasive nature of these procedures deprives clinicians of tactile feedback which, when coupled with pinching graspers that deliver high-stress concentrations, increases the likelihood of inflicting iatrogenic trauma upon tissues, especially the small intestine [1]–[4]. Retraction of the small intestine is often necessary to vi- sualize and access nearby tissues [5], [6]. Commercially- available devices rely on passive structures to hold intestinal segments and do not embed compliance [7]. Prior research on surgical retractors has focused on granular jamming [5], pneumatic balloons [6], and either cable-driven [8] or vacuum [9] graspers. However, these devices are challenging to integrate into surgical work- flows, require auxiliary instruments, and do not provide feedback regarding tissue interaction forces. We introduce a laparoscopic grasper capable of passing through an 18 mm trocar, expanding to a controllable width once inside the abdominal cavity, and safely enveloping the small intestine to enable retraction. Upon entry into the abdominal cavity, the grasper estab- lishes an initial hold on a target intestinal segment by pulling vacuum through the suction unit on its distal tip (Fig. 1[a]); this functionality helps the surgeon isolate the target intestinal segment from surrounding bundles. Once a preliminary suction hold has been established, the grasper envelops the intestine by inflating a pair of pneumatic fiber-reinforced soft actuators (FRSAs) (Fig. 1[b]-[c]), whose separation can be modulated up to 40 mm using a miniaturized scissor lift mechanism (MSLM). This approach distributes the force necessary to grasp and hold the intestine over a large surface area (i.e., the whole surface of the FRSAs) rather than concentrating it in a small region, allowing safe, robust grasps even on dilated intestinal segments. Inflation of the FRSAs and suction are controlled using two buttons (Fig. 1 [d]). The horizontal position of the FRSAs and the separation between them are independently actuated via two linear motors, which the surgeon controls using a rocker switch and trigger, respectively (Fig. 1 [d]). Each actuator is equipped with two soft sensors to interpret 3D interaction forces via a machine learning algorithm.