Expansion of quantised space

  • #1

Main Question or Discussion Point

First post on here, so don't be too savage. I'm a recovering chemist who is developing an interest in physics/maths on the side.

My question concerns the idea of cosmic inflation, in which it is suggested that space itself may be stretched/expanded between distant objects in space.

If this idea is combined with space-time being quantised, then where do the extra quanta of space-time between the two objects come from?

Could it be related to particle-antiparticle formation/destruction? Maybe when a pair is formed they need to take up new/separate space-time quanta. Could this process potentially expand the space between two distant objects?

This model throws up extra issues. What is the geometry of expanding space-time quanta? Is there a link to the passing of time or to gravity? Thoughts?
 

Answers and Replies

  • #2
bcrowell
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Welcome to PF!

My question concerns the idea of cosmic inflation, in which it is suggested that space itself may be stretched/expanded between distant objects in space.
Cosmic inflation not the same thing as expansion of space. Cosmological expansion dates back 85 years, and has been empirically well established for decades. Inflation is a much more recent and speculative idea; AFAIK there is little empirical support for it. Anyway, I think your question can be phrased simply by replacing "cosmic inflation" with "cosmological expansion."

If this idea is combined with space-time being quantised, then where do the extra quanta of space-time between the two objects come from?

Could it be related to particle-antiparticle formation/destruction? Maybe when a pair is formed they need to take up new/separate space-time quanta. Could this process potentially expand the space between two distant objects?
When we talk about particles and antiparticles, we basically mean things that have all the same properties except for opposite charge (or opposite values of some other property such as lepton number). Spacetime isn't electrically charged, so I don't think the particle-antiparticle concept applies here.
 
  • #3
atyy
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As an approximation, presumably yes. Take a look at figures 4 and 6 of http://arxiv.org/abs/0906.3947 .

But the Causal Dynamical Triangulations approach is supposed to be an approximation to some sort of continuum limit, ie. a quantum field theory (maybe even a string field theory?), in which case I don't know what happens to all the little triangles.
 
  • #4
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If this idea is combined with space-time being quantised, then where do the extra quanta of space-time between the two objects come from?
In the LQG picture, I believe that the Hamiltonian operator can change the number of nodes in a spin network. Since the nodes are associated with the volume operator, it's not too difficult to imagine the volume of a three space evolving in time (once we've agreed on how the classical limit is retrieved). I get the impression that there is still some unfinished business in defining the Hamiltonian though.....
 
  • #5
Thanks for the excellent replies. The paper on dynamic space geometry was very interesting.

I was also looking for any suggestions of a possible link between having an irregular geometry in a dynamic (expanding) space-time with the actual microstructure of Einsteinian "warped space-time" under the influence of gravity.

Surely the two ideas go hand in hand. You can't warp space time if it is built of some basic building block unless the building block has some kind of variable geometry.

Is this connected to the idea that our apparent 3 dimensional space is merely an emergent approximation, and that in fact it is more like a fractal that is close to 3-dimensional? Light speed travel or intense gravity seem to reduce the dimensionality of the space from what I understand.
 
  • #6
tom.stoer
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LQC (as a kind of approximation to LQG) provides some insights how space is created during inflation. It is basically due to the fact that a very small length scales the interaction between spacetime and matter becomes strong which a) prevents spacetime to form singularites like the big bang or black holes and b) let's the interaction of matter and spacetime "create" new spacetime.

This does not work w/o any matter field, but it does not require some artificial insflaton field but should work with any matter content; so its rather generic - but still work in progress
 

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