"As far as extra dimensions are concerned, very tiny extra dimensions wouldn't be perceived in everyday life, just as atoms aren't: we see many atoms together but we don't see atoms individually"

This quote by Edward Witten is describing the idea of additional measurements in physics. He is suggesting that simply as we can not see individual atoms, we would not have the ability to view really small extra measurements in daily life. This is due to the fact that the additional measurements would be too small to be found by our senses. Witten is suggesting that although extra measurements may exist, they would be too little to be seen in our everyday lives. This resembles atoms, which are too little to be seen separately, however can be seen when they are organized together. Witten's quote is a suggestion that although additional dimensions may exist, they are too small to be seen in our everyday lives.