Albert Einstein decided there must be a fourth dimension outside of the three dimensions we see. The fourth dimension is time, or spacetime, since Einstein said space and time cannot be separated.
We understand what time is from our 3-D perspective. Thus, we can see the fourth dimension the way someone in the second dimension could see us—only partially.
Famed astronomer Carl Sagan explained on his TV show “Cosmos” that a 2-D creature could see a 3-D creature as “only a plain, only a cross-section.”
Left: Cross-section of a cucumber (Eivaisla/iStock/Thinkstock) Center: Cucumbers Siraphol/iStock/Thinkstock
