Can Unification of Forces Coexist with an Eternally Inflating Universe?

[Ranku]

Is the possibility of unification of gravitation with the other three fundamental forces compatible with the idea of an 'eternally existing self-replicating inflationary universe' as proposed by Linde? In other words, for unification of the four fundamental forces, is it necessary for the universe to have a finite beginning, or can it have an 'infinite' origin?

 

[Chalnoth]

Is the possibility of unification of gravitation with the other three fundamental forces compatible with the idea of an 'eternally existing self-replicating inflationary universe' as proposed by Linde? In other words, for unification of the four fundamental forces, is it necessary for the universe to have a finite beginning, or can it have an 'infinite' origin?

I don't think there's any reason to suspect that these ideas are incompatible, no. Especially as the precise way in which gravity and quantum mechanics can be reconciled isn't yet known.

 

[bapowell]

It's also worth pointing out that eternal inflation does not avoid the initial singularity.

 

[PeterDonis]

eternal inflation does not avoid the initial singularity

Can you elaborate?

 

[bapowell]

Can you elaborate?

Sure, check out: http://arxiv.org/abs/gr-qc/0110012 and http://arxiv.org/abs/gr-qc/9312022.

 

[windy miller]

Bapowell, I notice both papers are by the same authors, something that always makes me suspicious.
I am not qualified to assess the validity of the argument, so I generally look to see if other cosmologists agree and it seem they don't agree
https://arxiv.org/abs/0712.0571
https://arxiv.org/abs/1204.5385
i doubt there is any to test between the two notions, but happy to be proven wrong.

 

[bapowell]

Well, we need to do more than just find dissenting viewpoints. Rather than assume that inflation is past-eternal until proven otherwise, why not withhold judgement either way until you can understand the merits of the various arguments?

Thanks for posting the references: I'll try to have a look this weekend and determine where the disagreement lies.

For what it's worth, and not to blindly appeal to authority, but Alex Vilenkin and Alan Guth are two of the original architects of quantum cosmology and inflation theory and have generally well-reasoned arguments. We'll see if they withstand the challenge.

 

[windy miller]

I agree. My thinking when assessing these things, is if a theorist claims something and I am not in a position to assess if they are right i can ask two questions
1) is there a consensus amongst other theorists ? are the dissenters respected int the field?
2) is there a way to experimentally confirm their statements?
I know Guth and Vilenkin are big names in the field but Susskind and Aguirre are also quite well respected, are they not?
heres another dissenter
http://arxiv.org/abs/1205.5550
I look forward to your comments and Yes I do withhold judgement. On the second point, I think we would be very lucky to find some direct probe of eternal inflation happening maybe something like bubble collisions or some other means, but even in such an optimistic scenario how we could test the claim that it not past eternal?

 

[Ranku]

In the paper "Eternally Existing..." Linde says: "its (eternally inflating universe) global geometry has nothing in common neither with the geometry of an open or flat homogeneous universe with a gradually decreasing energy density, nor with the geometry of a closed universe.." Also: "There may exist an initial global singular spacelike hypersurface. In this case the universe as a whole emerges from a state with a Planck density ρ ~ M_P⁴ at some moment t = t_P at which it becomes possible to speak about the universe in terms of classical spacetime."

So what does this mean in terms of the similarity and difference between eternal inflation and finite inflation, apart from the rolling potential in the latter? For instance, is the dynamics of eternal inflation described by the Friedmann equation?

 

[windy miller]

Mu impression is that eternal inflation is eternal in at least one direction of time, not necessarily both, although some have argued it is both, see above posts.