You are correct to question your understanding of patents if you thought it was a government stamp of approval. The patent office does not do its own research and testing on patents. Unless something is claimed to be a perpetual motion machine the scientific feasibility is not questioned. Patents are examined for novelty and obviousness. There is a utility requirement but that means utility of the face of it.
A patent is not a government blessing that something works, although fear of that misunderstanding is probably why perpetual motion is not patentable without scientific demonstration (impossible of course).
A patent is something one can use to try to stop others from making or doing something, not a license to do anything. If something is impossible, I suppose it doesn't matter that a patent keeps people from making it, selling it, offering it for sale, using it or importing it.
One downside of an impossible patent is that a granted patent is assumed to be "enabled" by its specification. That means that a subsequent application with more modest claims can be deemed as not novel in light of the impossible patent. At that point the new applicant needs to somehow overcome the presumption that the impossible patent is workable. You can attack that by affidavits from experts.