Dan,

He did say 'truths' and not facts.

Einstein's relativity theory was not provable right away. But it was correct - so it was always a truth.

So truths exist that cannot be proven - doesn'tmean they will always be unprovable - doesn't mean they aren't truths.

Of course you can prove relativity theory in a lab with pencil lead (graphene) now :-)

Blacknad.