Friday, June 27, 2008

Reduce Everything to Space-time?

[UPDATED 25 Sept.2009: Fixed Links]
I want to quickly comment on an interesting post by Justin at Panexperientialism. In it he reviews a book by Freya Mathews (called The Ecological Self) and also discusses a draft paper by Jonathan Schaffer (Spacetime the One Substance). Please check out his post, which discusses many aspects of Mathews’ ideas in particular beyond what I’m picking up on here (I have not read the book).

Both Mathews and Schaffer advocate a monistic metaphysical view where matter is effectively reduced to space-time.

I agree with these authors that the dual scheme of {space-time container plus material objects} must be rejected, but think they are slightly off-track in wanting to reduce the properties of matter fields to space-time (at least space-time anything like we currently think of it).

These brief comments focus on the relationship of this idea to the work of theoretical physicists. Mathews acknowledges that an early attempt to derive this reduction from general relativity failed (Wheeler’s Geometrodynamics), but still likes the metaphysical vision for philosophical reasons. In his paper Schaffer argues toward a similar goal, but along the way I think he overstates the degree to which GR and (especially) quantum field theory as we know them are congenial to this vision. QFT has matter fields housed in a separate space-time container. In GR the matter and space-time are dynamically intertwined, but the fact that you can model the geometry while leaving out matter shows that they remain distinct.

In some ways the quest for a theory of quantum gravity can (should?) be viewed as a quest for a monistic theory which is rid of the dual scheme. I continue to try to follow the different theories as a layperson to see how they come down on this issue.

String theory: originally an extension of QFT which retained the feature of having fields on a background space-time. Has evolved in many ways over the years and maybe can overcome this starting point (?).

Loop Quantum Gravity and Causal Dynamical Triangulations: these seek to formulate a quantum version of space-time with the promise of integrating matter into the picture later. I’m not sure if this promised integration would be more monistic than GR.

Causal Sets; Quantum Causal Histories/Geometrogenesis; Internal Relativity; Quantum Computing and Condensed Matter-based approaches: these programs seem best on this question as they try to specify a monistic underlying micro-theory from which space-time and matter fields as we know them may simultaneously emerge.

I would note that if the latter sort of approach works, it doesn’t support Schaffer’s advocacy of priority monism (see my previous post on this topic). The underlying network would not be a very coherent whole, but a fairly ill-behaved evolving pluralism of micro-events. Even though Schaffer wants to overcome the container/object scheme, his view of space-time as the holistic fundamental object still has a bit of a hangover from the container idea in my opinion.


brad4d said...

Energy= mass, like in space, location, & the speed of light, squared is duration, so yeah, I like how relativity has natural reference.

Steve said...

Thanks for stopping by here brad4d. - Steve