The cosmic inflation. Yes, the universe is smooth but how is that enough to justify this unimaginable expansion? There seem to be no proof or possible experimen

The cosmic inflation. Yes, the universe is smooth but how is that enough to justify this unimaginable expansion? There seem to be no proof or possible experiment yet the scientific community apparently accepted this theory with its abrupt start and abrupt end, only secondary to the big bang itself in its scale and energy.