Examining the Big Questions of Time

While most of us measure time in hours or days as we plan our activities, these units are not nearly small enough—nor large enough—for those who work at the edges of discovery. Explore how some scientists use attoseconds and others use billion-year increments to study the often baffling revelations of spacetime.

Just a few decades ago, scientists were absolute in their determination that time began with the Big Bang. But that’s all been turned on its head with the rise of string theory and other fascinating developments in theoretical physics. Learn how those advances brought the pre-Bang universe to the forefront of cosmology.

Right now, you are reading these words. True enough, right? But all that certainty erodes when we look at the concept of “now” through the lens of modern physics. Although we perceive “now” as being unique—our present moment always seeming to separate the knowable past from the unknowable future—you’ll learn why “now” slips from our grasp when we try to actually define it.

While we’ve all heard that time is money, the two terms might turn out to be more similar than we ever knew. Could time, like money, be just an invented convenience with no fundamental existence in the natural world? Discover the many ways in which philosophers have helped physicists grapple with this question—and the answers they’ve come to so far.

In a thought experiment called the twin paradox, Einstein illustrated that two observers moving at different speeds would experience different durations between the same two events. See how this time dilation has been proven and measured since Einstein’s life, and why your GPS wouldn’t work without accounting for it. Time travel, anyone?

From the ancient Egyptians to the 13th-century inventors of the mechanical clock to the atomic clocks of the last century, people keep striving to measure time more accurately. Understand why accuracy in timekeeping was important for the agriculturists of the Nile and why it still matters for those of us today who use navigation systems, cell phones, and electricity from the power grid.

Modern timekeeping has allowed us to measure differences in the passage of time as affected by motion and gravity to such a degree that relatively itself can now be measured in the lab. Learn about the development and precision of atomic clocks—and the myriad ways they benefit us—and about the optical clocks that can keep time to within one second in roughly 3.7 billion years.

Our circadian rhythm is hardwired into every cell in our bodies. Even under constant lighting, human cells in a petri dish will continue to follow 24-hour cycles of gene activity, hormone secretion, and energy production. Explore neurologists’ latest thinking about the brain’s internal timekeeping systems, and how those systems affect our health.

While our internal clocks regulate our physical processes, our mind has a clock of its own. Explore what scientists mean by “mind time,” and how we organize our thoughts about events in the passage of time. Uncover how mind time is linked to our ability to make and store memories, and reveal the interesting differences between anterograde and retrograde amnesia.

Almost all our scientific knowledge is possible because we rely on a few very basic constants—such as the velocity of light and the mass of the electron. Discover how string theory brings the possibility of a vast number of other worlds with different self-consistent laws and constants, and whether or not those worlds could possibly include biological entities like ourselves.

In the field of quantum mechanics, physicists have suggested for almost a century that light is made of energy packets that can behave like both a particle and a wave, a phenomenon known as photons. But could gravity also be made of discrete packets—gravitons? Explore the concept of loop quantum gravity and learn how physicists use spin networks to gain a deeper understanding of our universe.

As we experience life, time never ends. Even after death, our molecules will be recycled, and both time and matter will continue. But if time can slow down and speed up—as Einstein predicted, and later confirmed by observation—could it also end? Explore what the equations of modern physics tell us about the possibility of an end with no rebirth.