The Universe Is Not as We Perceive It

A Conversation with Michelle Thaller

The Milky Way galaxy, if the Sun were the size of the dot of an eye on a page of text, would be larger than the Earth itself. That is the scale Michelle Thaller, former NASA astrophysicist, uses to help people grasp what a galaxy actually is. "Nobody can visualize what a galaxy really is," she says. "You can take pictures of them, you can say the word galaxy, but people have no idea what monsters these are."

Thaller spent her career at NASA as a science communicator and astrophysicist, and the conversation quickly moves from scale to the deeper strangeness of what we have actually measured about the universe.

Time Is Not What It Feels Like

One of the most concrete demonstrations that time is not absolute comes from GPS satellites. They orbit at about 9,000 miles per hour, and they are far enough from Earth that gravity's pull on them is weaker than it is on the surface. Both effects matter: the satellites' speed slows their time slightly, but their distance from Earth's gravity speeds it up more. The net result is that their clocks run faster than clocks on the ground. If engineers did not correct for this relativistic effect, GPS positions would drift by about six miles within a single day.