Big Bang starting reference point

[geordief]

55 minutes ago, sethoflagos said:

Probably the wrong word to choose. 

'Pointlike' may be better. Suggesting that an instantaneous 'now' of zero duration doesn't exist. So a unit of Planck time, say, wouldn't have any clearly definable start or endpoint.

I wonder ,does the Planck unit of time  also dilate along with spacetime curvature(under extreme conditions, of course)?

[Mordred]

Rather meaningless to describe time as diluting. How one measures time is observer dependant. However you do not get time dilation due to expansion.

[geordief]

3 minutes ago, Mordred said:

There was an older multiverse model that has matter in one universe with antimatter and time reversal in the other universe. It long ago fell out of any research interest. ( due to better understanding of anti-matter in that the time reversal is a mathematical treatment for symmetry purposes and not actuality)

1s it considered at all plausible that two ( more?) universes could be created from a shared event?

Or is that just "intellectual incontinence" 

[Mordred]

Yes it's plausible the model I just mentioned had the same BB origin point. Matter and forward time in one universe. Antimatter and reverse time in the other universe. Both resulting from the same BB event.

However as stated that model essentially died though you do come across attempts to renew the model.

Here is a brief description of the model

https://physicsworld.com/a/our-universe-has-antimatter-partner-on-the-other-side-of-the-big-bang-say-physicists/

Edited May 17 by Mordred

[sethoflagos]

1 hour ago, Mordred said:

There was an older multiverse model that has matter in one universe with antimatter and time reversal in the other universe. It long ago fell out of any research interest. ( due to better understanding of anti-matter in that the time reversal is a mathematical treatment for symmetry purposes and not actuality)

I'm struggling a little to recollect beer mediated musings from 30-odd years ago, so please bear with me.

Am I correct in understanding your last point as CPT symmetry reversal is not a physically realisable phase change in contrast to say electroweak symmetry breaking or recombination?

[Mordred]

No that's not what I'm stating. The time reversal for anti particles results from the negative frequency modes. It doesn't mean the antiparticle travels back in time. That particular model suggested it did.

One detail though electroweak symmetry breaking isn't really about CPT. That's more relation to baryogenesis and leptogenesis.

 Electroweak symmetry breaking describes when particles acquire mass and lose symmetry with other particles aka drops out of thermo equilibrium. This corresponds to the relevant  force couplings. Strong, weak and EM force  couplings. ( yes this includes Higgs  Dirac and Yukawa couplings of the SM model).

There's two very similar named processes that can get confused (Electroweak Baryogenesis) and (electroweak phase transition). The latter is the thermal equilibrium dropout. The former is suggested to occur during  the EWPT (electroweak phase transition) happens. The (EWBG) electroweak baryogenesis is where the CPT relations are involved.

Leptogenesis would occur just prior to EWBG. Once again involves CPT.

Edited May 18 by Mordred