What indicates that Interstellar travel requires a technological level that includes arbitrary transmutation? It seems to me travelling these distances is much simpler, it basically just requires current technology plus organisations that can hold together for more than a century or so. If you take the only known civilisation as an example: Ever since the invention of atomic bombs we have the propulsion part of what's required to go to ~40% the speed of light (or ~20% and then break). The most difficult challenge yet to overcome would probably be the front shield (at relativistic speeds, space dust can really mess things up), but that seems far from unsolvable. The main thing missing is political will to take the required risks. We were well on a path to such a machine in the 60ies, what failed was mainly politics in the two organisations large and advanced enough to do it (USGov/UdSSR).

Chemical reactions are a subset of atomic transmutation. Arbitrary atomic transmutation is likely a superset of all possible atomic transmutations

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