I don't understand. Is consciousness a feeling or an external manifestation? It's something purely internal or something also visible on the outside? If it's only internal you cannot, by defition, say if a machine is conscious, but also every other human. If tomorrow we would discover an alien civilization and start a meaningful communication, would you question their consciousness?

Personally, I don't think that all the discussion about consciousness is meaningful. Consciousness could be the human feeling of abstract reasoning, like cold is the human feeling of registering a lower temperature. A machine could reproduce abstract reasoning, and asking about its consciousness would be like asking if a thermostat feels cold.