4 ms·

you have to show that it's physically valid. I strongly doubt that the paper can do that, for reasons which are too long to fit in the margin of this post. I'd

you have to show that it's physically valid. I strongly doubt that the paper can do that, for reasons which are too long to fit in the margin of this post. I'd love to hear about it if you have some time.

pdonis 14y ago
I'll try to give the short version. Look at the Figure 2 diagram on the ScienceDirect page. That is a diagram of a solution to the Einstein Field Equation, which is the central equation of General Relativity. In that diagram, B and C are not the same event; the curve A-B-C-D is disconnected. That's not physically valid as it stands. The paper, as far as I can tell, is claiming that it is somehow physically possible for the curve A-B-C-D to be connected, so that it can be a physically valid worldline for an observer. For that to be the case, we would have to be able to obtain another solution to the Einstein Field Equation by cutting the Figure 2 diagram along the "southwest-northeast" diagonal (the one on which B and C lie), and sliding one half of the diagram along that diagonal until B and C coincide. I strongly doubt that the spacetime described by the resulting diagram is a solution of the Einstein Field Equation; and if it isn't, then the paper's claim is incorrect. [Edit: someone downthread posted a link to an arxiv preprint of the paper; I'll take a look and respond further there.]
- deleted 14y ago
  [deleted]
  - deleted 14y ago
    [deleted]
- pdonis 14y ago
  cutting the Figure 2 diagram along the "southwest-northeast" diagonal (the one on which B and C lie), and sliding one half of the diagram along that diagonal until B and C coincide. After reading through the paper, that I think the transformation the author intends is somewhat different than what I described: what he is doing is cutting the Figure 2 diagram along the diagonal containing B and C, then flipping the top half over so that C coincides with B. This is not a valid solution of the vacuum Einstein Field Equation (neither is the transformed spacetime I originally described, where the top half is "slid" along the diagonal), which the original spacetime diagrammed in Figure 2 (before any transformations to move C around) is. But the author is claiming that it is a solution if we put an infinitely dense sheet of lightlike radiation on the diagonal. This may be true mathematically speaking (I haven't verified it), but that doesn't make it physically reasonable. So I still think the paper's claims are not physically valid; they may describe a mathematically consistent solution, but it's not something that would ever happen in the real universe.

pdonis 14y ago

I'll try to give the short version. Look at the Figure 2 diagram on the ScienceDirect page. That is a diagram of a solution to the Einstein Field Equation, which is the central equation of General Relativity. In that diagram, B and C are not the same event; the curve A-B-C-D is disconnected. That's not physically valid as it stands. The paper, as far as I can tell, is claiming that it is somehow physically possible for the curve A-B-C-D to be connected, so that it can be a physically valid worldline for an observer. For that to be the case, we would have to be able to obtain another solution to the Einstein Field Equation by cutting the Figure 2 diagram along the "southwest-northeast" diagonal (the one on which B and C lie), and sliding one half of the diagram along that diagonal until B and C coincide. I strongly doubt that the spacetime described by the resulting diagram is a solution of the Einstein Field Equation; and if it isn't, then the paper's claim is incorrect. [Edit: someone downthread posted a link to an arxiv preprint of the paper; I'll take a look and respond further there.]

deleted 14y ago
[deleted]
- deleted 14y ago
  [deleted]
pdonis 14y ago
cutting the Figure 2 diagram along the "southwest-northeast" diagonal (the one on which B and C lie), and sliding one half of the diagram along that diagonal until B and C coincide. After reading through the paper, that I think the transformation the author intends is somewhat different than what I described: what he is doing is cutting the Figure 2 diagram along the diagonal containing B and C, then flipping the top half over so that C coincides with B. This is not a valid solution of the vacuum Einstein Field Equation (neither is the transformed spacetime I originally described, where the top half is "slid" along the diagonal), which the original spacetime diagrammed in Figure 2 (before any transformations to move C around) is. But the author is claiming that it is a solution if we put an infinitely dense sheet of lightlike radiation on the diagonal. This may be true mathematically speaking (I haven't verified it), but that doesn't make it physically reasonable. So I still think the paper's claims are not physically valid; they may describe a mathematically consistent solution, but it's not something that would ever happen in the real universe.