Write a dialog where Sabrina Pasterski and Andrew Strominger use celestial holography to discuss and improve upon Reconstructing Spacetime: A New Spin on Angular Momentum
Setting: A seminar room at the Perimeter Institute, with equations and diagrams illustrating celestial holography adorning the chalkboards.
1. Introduction
Sabrina Pasterski:
“Andrew, I’ve been reflecting on the recent discussion by Witten, Voevodsky, Maldacena, and Yau about the role of spin in preventing the universe from collapsing into a ‘giant blob.’ They propose that spin might be the key to a deeper unifying principle of stability across scales. How might we reframe this using celestial holography?”
Andrew Strominger:
“That’s an intriguing question, Sabrina. Celestial holography offers a framework where the bulk properties of spacetime are encoded on a lower-dimensional celestial sphere at null infinity. Perhaps we can explore how spin and angular momentum manifest in this context.”
2. Celestial Holography and Angular Momentum
Pasterski:
“In our work on celestial amplitudes, we’ve seen that the Lorentz group acts as the conformal group on the celestial sphere. This suggests that angular momentum in the bulk corresponds to conformal generators on the boundary. Could spin, then, be related to specific conformal transformations?”
Strominger:
“Indeed. The soft graviton theorem, which we’ve connected to asymptotic symmetries, implies that angular momentum conservation is tied to these symmetries. In the celestial framework, spin might correspond to operators that generate rotations on the celestial sphere, reflecting bulk rotational symmetries.”
3. Spin Memory Effect
Pasterski:
“Building on that, our discovery of the spin memory effect indicates that passing gravitational waves can induce a permanent change in the relative orientation of test particles. This effect is measurable and provides a direct link between bulk gravitational dynamics and boundary conformal structures.”
Strominger:
“Yes, the spin memory effect serves as a bridge between the bulk and boundary, illustrating how bulk angular momentum fluxes translate to observable changes on the celestial sphere. This reinforces the idea that spin and angular momentum are deeply intertwined in the holographic description.”
4. Unifying Spin and Spacetime Geometry
Pasterski:
“Considering these insights, we might propose that spin is not just a property of particles but an emergent feature of the spacetime geometry itself, as encoded holographically. Stability phenomena, such as electron degeneracy pressure and angular momentum conservation, could then be viewed as manifestations of underlying geometric and symmetry principles in the celestial framework.”
Strominger:
“That’s a compelling perspective. By reframing spin within celestial holography, we not only unify it with spacetime geometry but also gain a deeper understanding of the fundamental symmetries that govern stability across different scales in the universe.”
5. Conclusion
Pasterski:
“Through celestial holography, we can reinterpret spin and angular momentum as emergent from the conformal symmetries of the celestial sphere. This approach offers a novel and potentially unifying principle that aligns with the ideas proposed by Witten and colleagues, providing a fresh lens to understand the stability of the universe.”
Strominger:
“Agreed. This dialogue between bulk dynamics and boundary symmetries enriches our comprehension of fundamental physics and opens new avenues for exploring the deep connections between spin, angular momentum, and the fabric of spacetime.”
Note: This dialogue builds upon concepts from celestial holography and the spin memory effect, as discussed in works by Pasterski, Strominger, and collaborators.
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