Recent content by Jaime Rudas

Yes, although it seems that it wasn't an unexpected surprise for everyone: https://tritonstation.com/2019/01/28/a-personal-recollection-of-how-we-learned-to-stop-worrying-and-love-the-lambda/

Are you talking about expansion or accelerating expansion?

If we designate the distance to the event horizon as ##D_{eh}## (which, by the way, is not 5 Mpc, but about 5 Gpc), then the maximal comoving distance that can be reached at speed ##v## is ##\frac {v}{c} D_{eh}##

Equation 18 is Hubble's law (or, more precisely, the Hubble-Lemaître law). Yes

The total velocity is equal to the recession velocity plus the peculiar velocity, which is what includes the derivative of ##\chi##, as shown in equations 19 and 20: $$ \dot D= \dot R \chi +R \dot \chi $$ $$ v_{tot} = v_{rec} + v_{pec} $$

Orodruin said in another thread that "the spacetime of a spatially flat universe generally has curvature". Is the expansion (or contraction) of a spatially flat universe the manifestation of the curvature of its spacetime? If so, does the expansion correspond to a positive or negative curvature?

The "curvature density parameter" ##\Omega_k## is more of an indicator of how far from flatness a space is, than a true indicator of density.

It seems to me that this interpretation is not entirely correct because it would imply that, for example, a positive curvature contributes negatively to the density parameter, while dark energy, mass and radiation, added together, contribute more than 100% of the total.

And, specifically, to the geometry of space.

In addition to what was explained by Orodruin, it is worth clarifying that the "curvature density parameter" ##\Omega_k## is, by definition, equal to 1-(##\Omega_M##+##\Omega_\Lambda##+##\Omega_R##), so its value is not restricted to being 0, 1 or -1. In fact, with that definition, a negative...

Yes, that's precisely why I wrote "at least" in bold.

According to what was calculated here, the radius of curvature of the universe is at least about 10 times larger than the radius of the observable universe, which means that its volume is at least about 4700 times larger.

And the superluminal velocity with which he did it. Well, with his "normally I don't answer", I wouldn't want to abuse his kindness.

Regarding this, I asked Miguel Alcubierre the following: Alcubierre answered:

By dealing with the Alcubierre bubble, we are implicitly assuming its characteristics, one of which is having this space behind. Furthermore, The original post talks about the distance from Earth to Alpha Centuari following a path through the Alcubierre bubble. Saying "through" implies that...