We tend to treat time as a quantifiable commodity — something that can be managed, saved and retrieved for future use, like a stick of butter in the freezer. But our perceptions of past and present are often not so solid.
Archaeologists try to reconstruct ancient history from artifacts, and those clues often allow enough leeway to imagine alternative pasts. Take the current controversy over whether the ancient Clovis people, who lived in North America around 13,000 years ago, killed mammoths and other large mammals. Dioramas of these brave hunters felling massive beasts with stone-tipped spears have been a staple of natural history museums for decades.