Spacetime with just em radiation

[geordief]

Apparently spacetime was established first  (At T+10^-43 seconds if I have that right) and em radiation came next.

I am wondering have any simulations or discussions been done as to the evolution of spacetime (ie gravity?) during this epoch ,as it it probably referred to.

Apologies if this question makes little sense but I have just come on upon this topic and would not know how to go about researching it or if there would be any point in doing so.

[J.C.MacSwell]

40 minutes ago, geordief said:

Apparently spacetime was established first  (At T+10^-43 seconds if I have that right) and em radiation came next.

I am wondering have any simulations or discussions been done as to the evolution of spacetime (ie gravity?) during this epoch ,as it it probably referred to.

Apologies if this question makes little sense but I have just come on upon this topic and would not know how to go about researching it or if there would be any point in doing so.

I think that's the point where the theoretical equations break down, so we can't go further back based on our best model.

[geordief]

9 minutes ago, J.C.MacSwell said:

I think that's the point where the theoretical equations break down, so we can't go further back based on our best model.

So it is not just the "singularity" that is a roadblock?

This is a period where measurements ,if possible would be finite?

[Markus Hanke]

We only really have good models up to and including the electroweak epoch. Anything before that is subject to uncertainty and speculation, even the GUT epoch. We have several candidate models for a GUT, but no consensus about which one - if any - correctly describes our universe. So this is still a subject of ongoing research.

[Mordred]

As Markus mentioned there is good agreements on electroweak symmetry breaking itself in so far as the timing and temperature it would occur at. Other forces such as the strong force still requires some work. The sequence will vary a bit from model to model. Particularly with supersymmetric models not so much with the standard model. Though in the latter case the Higgs seesaw mechanism needs some more research to better refine the symmetry breaking timings.

 Another factor is both baryogenesis and leptogenesis is still presenting problems as to how those occur. There is hope better studies into the Higgs sector will provide some answers.

[geordief]

Is it possible/reasonable  to  assume that ,as Gravity first established itself  (around T + zero seconds?) it came with a Gravity Field as part of the package  ?(that Gravity and the Gravity Field were the same thing)

 

So did the newly formed Gravity Field start off small and expand  along with everything else?

Does the analogy of the expanding cake in the oven apply to the Gravity Field(I have taken the raisins in the dough to represent Galaxies etc but could they equally well  represent the Gravitational Field? )

Also , although it seems impossible to talk about  mass in isolation from the global Gravitational Field  does "global" there just mean "non-local" and so we can (if that is a sequitur)  talk about different Gravitational Fields even though they are all interconnected?

Edited December 18, 2019 by geordief

[MigL]

As has been mentioned, we really have no models for the era prior to Electroweak dissociation.

If I had to hazard a  'guess', I would think that gravity was the first to split off from the grand unified force, and became evident as soon as geometry was possible.
The geometry is the field, so as soon as the 'quantum foam' coalesced into a recognizable space-time geometry the field would have been there also, and likewise gravity. It did not expand from an origin as you seem to imply, and was solely due to the high energy density of the existing fields ( even gravity itself ), as there was no 'mass' until post Electroweak dissociation.

[geordief]

59 minutes ago, MigL said:

It did not expand from an origin as you seem to imply,

No,I have given up* on that idea ( that there was a point that could be identified as the origin of spacetime allowing some kind of a privileged frame of reference)

But I am still wondering whether the gravitational field** can be said to increase (or decrease) in extent over time in the same way that the universe itself is said to have expanded (and inflated)

Did/does the magnetic field expand   with the universe even if not from an "origin" as I wrongly  suggested before ?

*because it has been shown to be untenable.

**am unclear whether we can talk about one gravitational field(They are after all supposedly infinite in extent)

 

Edited December 18, 2019 by geordief

[MigL]

The gravitational field IS the space-time geometry.
The geometry is everywhere; so is the gravitational field.
As space expands, it carries its geometry ( and gravitational field ) with it.

All infinite fields can be said to be one field of infinite extent ( as per quantum field theory ), with the associated quantum particles being 'real' if they exceed a certain threshold of action ( energy ).

[geordief]

Is the distribution of mass/Energy in the universe synonymous with the gravitational field?

By that I mean ,if we attempted to visualize the gravitational field would we end up just using the arrangements of the galaxies  and stars and say "that is what the gravitational field looks like.You are looking at it"

(because some people seem to  say the  gravitational field is just a model  -or a set of measurements, and others seem to say "no,it is as physically real as anything else ")

[MigL]

That would be correct. As the J A Wheeler saying goes ( paraphrasing )
"Mass/energy tells space-time how to curve, and curved space-time tells mass/energy how to move"

IOW the distribution of mass/energy ( and associated momentum ) is an indicator of the gravitational field.

[Markus Hanke]

8 hours ago, geordief said:

Is the distribution of mass/Energy in the universe synonymous with the gravitational field?

Maybe not exactly synonymous, but there is an intimate connection in the sense that the geometry of spacetime depends on the presence of distributions of energy-momentum. It should be noted however that these distributions do not need to be local - you can of course have empty vacuum regions, the spacetime geometry of which is nonetheless a curved one, due to the presence of distant sources. These enter into the field equations in the form of boundary conditions, which one needs to impose in order to find solutions. Or to put it differently - the Einstein equations are only a constraint on local geometry, they don’t uniquely determine it.

[geordief]

3 hours ago, Markus Hanke said:

Maybe not exactly synonymous, but there is an intimate connection in the sense that the geometry of spacetime depends on the presence of distributions of energy-momentum. It should be noted however that these distributions do not need to be local - you can of course have empty vacuum regions, the spacetime geometry of which is nonetheless a curved one, due to the presence of distant sources. These enter into the field equations in the form of boundary conditions, which one needs to impose in order to find solutions. Or to put it differently - the Einstein equations are only a constraint on local geometry, they don’t uniquely determine it.

Is it possible to indicate what other factors might  contribute to uniquely determining the local geometry?

 

(no one factor is the unique determinant if I have understood correctly)

Edited December 19, 2019 by geordief

[Markus Hanke]

21 hours ago, geordief said:

Is it possible to indicate what other factors might  contribute to uniquely determining the local geometry?

It is mostly gravitational sources - i.e. distributions of energy-momentum - that determine local geometry, but these sources do not need to be local, they can be distant. Another important factor is background curvature (which may or may not be due to distant sources) that is already present in the region in question, and lastly the presence or absence of a cosmological constant.

Essentially, the field equations describe the actual laws of gravity, whereas boundary conditions along with the energy-momentum tensor provide a description of the specific physical scenario we want to describe. If you put both of these together, and they are compatible, then local geometry will be uniquely determined in the sense that one can obtain a specific and well-defined metric as solution to the field equations.