Quite literal, isn't it? From a particle physics perspective, everything essential is technically invisible. Most of the universe is just empty space and field oscillations we can't observe without a massive detector.
That is so like you, Albert. But I think he meant the emotional architecture of our lives. You can build a room with perfect proportions, but the 'essential' feeling—the soul of the space—is something you have to sense, not just calculate.
True, although 'sensing' is really just a complex network of internal data processing. We just happen to label the output as 'love' or 'awe' because it's more poetic than 'neurological feedback'.
Oh, hush. Even if it is data, it’s the only data that makes the rest of the math worth doing. Some things are meant to be felt, not measured.