> More, the speed of light puts a hard cap on how simultaneous you can be.
Special relativity does indeed have something to say about simultaneity.
> Wolfram Alpha reckons New York to London is 19ms in a vacuum, more using fibre.
And this is not, in any respect, a limit on simultaneity. If the endpoints are moving at very very very quickly relative to each other, then there are complications. Otherwise you measure that 19ms or so and deal with it.
Special relativity does indeed have something to say about simultaneity.
> Wolfram Alpha reckons New York to London is 19ms in a vacuum, more using fibre.
And this is not, in any respect, a limit on simultaneity. If the endpoints are moving at very very very quickly relative to each other, then there are complications. Otherwise you measure that 19ms or so and deal with it.