The existence of a Multiverse has many philosophical consequences (and it just makes so much more physical sense than having us living in a Goldilocks Universe). And as the Multiverse has been postulated from actual observations, we can almost say we can test its existence.
Of course it would be all much more interesting if we could talk to a parallel universe.
Or would it? Communication between Universes may actually be made rather difficult by a “crowding echo effect“.
Imagine I were to try send a message via a quantum interference pattern, for example.
Obviously, all my quasi-identical copies from “nearby” parallel universes quasi-identical to my own Universe, would be trying to send quasi-identical information via quasi-identical ways at quasi-identical times: so we could all be creating so much noise as to make the reception of any message next-to-impossible.
Even more paradoxically, we could actually be reading each other’s message: but since those messages would all be quasi-identical to each other, we could mistakenly convince ourselves that we were listening each one only to his own echo.
After all what meaningful information could anybody exchange with a quasi-identical copy?
It may take a very very long time to figure out the minute differences between the two and those may as well be undetectable or absolutely irrelevant.
If the effect of clouds on climate is “obscure” and “little is currently known about where [aerosols] end up in the atmosphere” (as recognised on The Economist’s “Grey-sky thinking”, July 5, 2007), what kind of hubris is necessary to state, as at the beginning of the article, that “the general trends [of climate] are clear”?
Late-XIX-century physics looked pretty much complete too, apart from the obscure problem of black-body radiation, solved by Planck in 1900 by discovering the hitherto completely unknown world of quantum physics.