The longest timescale that we can possibly observe is the age of the universe, which is approximately 14 billion years, or 4 1017 s. With the emergence of attosecond optics in the twenty-first century (1 as¼ 1018 s), it is now possible to ‘‘see’’ things that happen in extremely short timescales. To imagine how short, just think that comparing 1 as to 1 s is equivalent to comparing 1 s to the age of our universe. Attosecond optics is a subfield of ultrafast optics and strong field physics.