Daniel65 wrote:
R Kym Horsell wrote on 17/2/21 11:37 pm:
In alt.astronomy Andrew W wrote:
...
Bragalia said it was a "stunning admission" from the US government and the
documents reveal that some of the retrieved debris possesses "extraordinary
capabilities" including the potential to make things invisible or even slow
down the speed of light.

It's disheartening to hear this last bit.

Many materials "slow down the speed of light". E.g. glass. The "refractive
index" of various glases on which optical instruments depend is the ratio of
the speed of light in the material to the speed of light in air.

Slowing down the speed of light in a vaccum would be the trick.

.... whereas slowing down the speed of light with a sheet of Lead is
quite easily done!!

What is lead's refractive index?