The latest cosmological observations strongly suggest the surprising fact that the Universe is undergoing an accelerated expansion at two very different times, immediately after the birth of the Universe and at the present time. However, this fact is incompatible with the property that gravity is an attractive force. An interesting fact is that the latest observational results suggest that a modification of general relativity may be manifested in the very early and current Universe. I believe that the key to the search for essentially new observables is to observe the “Dark Ages” and “Cosmic Dawn”, in which information about the very early Universe is preserved. Through radio observations that can probe these epochs, I aim to unravel the detailed history of the Universe.