Myth of spacetime (Gomes Koslowski)

[marcus]

http://arxiv.org/abs/1110.3837

A smooth classical spacetime manifold can no more exist than can a smooth classical trajectory of a moving particle. Spacetime as a classical 4D manifold is a myth, sometimes a very useful one. Many PF people must already realize this so clearly that one hardly needs to say it.

Henrique Gomes and Tim Koslowski just posted a very interesting paper that among other things carries this idea further. They manage to make do with a 3D manifold, so there is no 4D "general covariance", and still get something that is equivalent to 1915 GRavity. The idea has been brewing a long time, it's not new with them.

And they put matter there---what looks to me like standard matter fields. See what you think.

Their time is not fundamental but instead is something that emerges----emerges like temperature emerges from a dungheap (Misthaufen). In the heap there are only molecules, nothing at a fundamental level called "temperature" Yet one can stick a thermometer into the compost pile and see the temperature rising: Time for them is a socalled emergent phenomenon.

They start the paper--it's a really good one, I think--with a quote from an article on spectral geometry by Tom Kopf and Mario Paschke:

“Spacetime is the fairy tale of a classical manifold. It is irreconcilable with quantum effects in gravity and most likely, in a strict sense, it does not exist. But to dismiss a mythical being that has inspired generations just because it does not really exist is foolish. Rather it should be understood together with the story-tellers through whom and in whom the being exist. ”​

That is beginning to look like the THEME of some new theories contending for the honor of replacing 1915 classical GR. Simply put, the theme is:

"Spacetime is a fairy tale."

 

[marcus]

I also like very much how Bianchi has realized Loop gravity as the dynamics of topological defects in a 3D manifold.
He gave a PIRSA talk on it in September.

Now, a month later, we see that Freidel and two collaborators has translated the phase space of this topological defects Bianchi version of Loop into that of the more familiar formulation using graph Hilbert spaces.
http://arxiv.org/abs/1110.4833

That's good. Two seemingly different versions of Loop turning out to be closely related.

 

[czes]

Thank you Marcus for interesting links. It encourages me because it seems the reality is built of "+" and "-" defined information and nothing more.
The question is how the information is defined and how are the relation (configuration structure) between the information.
The relations between information create a spacetime and the configuration of the spacetime creates particle of matter.
There are more and more papers toward this information physics.

 

[marcus]

But Czes by your standards these authors are not very radical. They are only skeptical of spacetime, not space.

I think the basic perception goes back quite a long time (perhaps to Dirac, or Wheeler, my knowledge of history is embarrassingly weak on this point, I'm sorry to say.) Rovelli gave a simpe explanation in his 2006 essay "Unfinished Revolution". You can google it. I echoed one step at the beginning of post #1 here.

Feynman, among other people, taught us that a moving particle does not have a smooth trajectory. Assuming it does will lead to contradictions. One can only make a finite number of measurements along the the way. Spacetime is just another trajectory---of the changing geometry of space.
If a particle does not have a smooth trajectory then neither does the geometry of space.
If trajectories are not for real, neither is spacetime.

But Gomes Koslowski are clearly within the bounds of conventional physics. Space is real for them and so is spatial geometry, which after all we are constantly experiencing and measuring. They merely take seriously the long-understood idea that spacetime is not.
And so they apply conventional physics analysis to study geometry. They study geometry (which exists for them) interacting with matter. Nature in other words.

It is completely traditional, no leaps. This is how I see it anyway, and why I find it interesting. But perhaps you see this in a more radical light, and I fail to understand.

 

[czes]

You are right but I want to learn all ideas how the time emerges and space as well. They explain that time is emergent.
I have read Rovelli's essay "Forget time"
http://fqxi.org/data/essay-contest-files/Rovelli_Time.pdf
In holographic universe the space is emergent and time is emergent too. Therefore it is interesting for me.