Alcubierre Metric: York Time Cause and Effect

[MattRob]

So, there's a paper here that I'm a bit confused about. On pages 3 and 4, it talks about energy density magnitude and York time.

What I'm a bit confused about, is in the article that linked me to it, the scientist makes mention of eventually generating negative vacuum energy.

However, from reading the paper, I get the impression that the energy density distribution is the cause: That by creating this toroidal geomoetry of energy density, the York time magnitudes will come as a result. At least, that's the impression the paper gives me.

To quote:

... While this line of reason seems to resolve the paradox, it also suggests that the York Time may not be the driving phenomenon, rather a secondary result. In this physical explanation of the mathematics, the York Time might be thought of as perhaps a Doppler strain on space as this spherical region is propelled through space. A pedestrian analog to use to help envision this concept would be to consider the hydrodynamic pressure gradients that form around a spherical body moving through a fluid – the front hemisphere has a high pressure region while the rear hemisphere has a low pressure region. Analogously, the warp bubble traveling through space-time causes space to pile up (contract) in front of the bubble, and stretch out (expand) behind the bubble.

But if that's the case, then why is generating negative vacuum energy necessary: Is that just to better understand negative York time, or is it necessary? Which causes which? Does the York time geometry result in the energy density distribution, or does the energy density distribution cause the York time geometry?

Because while it seems to really heavily indicate that the toroidal placement of energy density causes the York time curvature, I'm left puzzled as to why it would be necessary, then, to invoke negative energy density to generate this "warp field"?

Because if the York time is a result of the toroidal energy density, then wouldn't negative energy density be unnecessary to generate the "warp field", but rather come as a consequence of generating it with positive energy density?

 

[pinball1970]

https://link.springer.com/content/pdf/10.1140/epjc/s10052-021-09484-z

from last year

@Orodruin may be able to have a look?

 

[PAllen]

Harold White's work is not generally accepted in the GR community. Matt Visser and many others have published multiple different proofs that negative energy is required to create any warp drive or any stable wormhole.

 

[PAllen]

So, there's a paper here that I'm a bit confused about. On pages 3 and 4, it talks about energy density magnitude and York time.

In the pdf at the bottom of this link, it states everywhere that negative energy is required. How do conclude it says otherwise?