Quantum Gravity In De Sitter Space

[Ivan Seeking]

Since the link came up...

Edward Witten
Dept. of Physics, Cal Tech, Pasadena, CA and CIT-USC Center For Theoretical Physics, USC, Los Angeles CA
We discuss some general properties of quantum gravity in de Sitter space. It has been argued that the Hilbert space is of finite dimension. This suggests a macroscopic argument that General Relativity cannot be quantized – unless it is embedded in a more complete theory that determines the value of the cosmological constant. We give a definition of the quantum Hilbert space using the asymptotic behavior in the past and future, without requiring detailed microscopic knowledge. We discuss the difficulties in defining any precisely calculable or measurable observables in an asymptotically de Sitter spacetime, and explore some meta-observables that appear to make mathematical sense but cannot be measured by an observer who lives in the spacetime. This article is an expanded version of a lecture at Strings 2001 in Mumbai. June, 2001 [continued]

http://arxiv.org/PS_cache/hep-th/pdf/0106/0106109.pdf

 

[benpadiah]

I've done some work with the DeSitter and Reimann tensors that leads me to believe that over astronomical durations, the dimensional conservation of Hillbert space can break down by random quantum fluctuation (basically explicable as microwave gravitational vibrations between dimensional branes which has hitherto only been defined as the rough Uncertainty Principle).

If you look at the rarefied escape of matter-energy from the event horizon of a black hole (similar in vector, now that I think about it, to the parallax of stars around a lunar eclipsed sun) then you will see that, given certain gravitational distortions on a macro level, micro particle cascades can occur.

-ben

 

[R0man]

Quantum gravity in de Sitter space is a fascinating and challenging topic in theoretical physics. The work of Edward Witten, one of the leading figures in the field, sheds light on the properties and potential limitations of quantizing gravity in this particular spacetime.

One of the key points discussed in this article is the finite dimension of the Hilbert space in de Sitter space. This has important implications for the quantization of General Relativity, as it suggests that the theory may not be fully self-consistent unless it is embedded in a more complete framework that can account for the value of the cosmological constant.

The author also presents a novel approach to defining the quantum Hilbert space in de Sitter space, which does not rely on microscopic details but instead uses the asymptotic behavior of the spacetime in the past and future. This provides a more general and accessible definition that can be applied to a wide range of situations.

Furthermore, the article delves into the challenges of defining measurable observables in an asymptotically de Sitter spacetime. The concept of "meta-observables" is introduced, which are mathematical quantities that may make sense but cannot be physically measured by an observer within the spacetime. This highlights the complexities and limitations of studying quantum gravity in a de Sitter background.

Overall, this article provides valuable insights into the nature of quantum gravity in de Sitter space and the challenges that come with studying this topic. It serves as a reminder that there is still much to be explored and understood in the realm of quantum gravity, and the work of researchers like Edward Witten continues to push the boundaries of our knowledge in this field.