Time isn't what it used to be—and that's a good thing.
Think about the last time you complained there weren't enough hours in the day. What if those hours themselves weren't as stable as you thought? For centuries, we've treated time as a constant, unyielding force—but that understanding is now being fundamentally rewritten.
These aren't just abstract concepts—they're discoveries that could revolutionize everything from GPS navigation to our understanding of the universe's very fabric.
For over five decades, the global standard for timekeeping has relied on cesium atomic clocks, which measure the vibration of cesium atoms when exposed to microwave energy. While remarkably accurate for their time, a new generation of timekeepers—optical clocks—is poised to make them obsolete 1 .
So what makes optical clocks different? These incredible instruments measure the frequency of atoms after they've been excited by lasers. The atoms are first cooled to near absolute zero, then lasers detect their vibrations. Those vibrations, called frequency ratios, correspond to the "tick" of a second 1 .
Researchers estimate an optical clock would not gain or lose a second for billions of years. To put that in perspective, you could wait the current age of the universe four times over, and an optical clock would still be off by less than a minute 1 .
Atoms are cooled to near absolute zero using lasers to minimize thermal motion.
Precisely tuned lasers excite the atoms to higher energy states.
Lasers detect atomic vibrations (frequency ratios) that define the "tick" of a second.
The process achieves accuracy to within one second over billions of years.
Despite their potential, optical clocks remain incredibly complex instruments. There are only about 100 of them worldwide because they're difficult to build, operate, and maintain 1 . Different clocks also measure the frequencies of different types of atoms, each with its unique frequency. The only way to establish a consistent global standard is to directly compare these clocks with one another 1 .
This challenge prompted a groundbreaking international collaboration called the ROCIT project, involving researchers from Finland, France, Germany, Italy, the UK, and Japan 1 . In 2022, over a 45-day period, scientists simultaneously compared measurements from 10 different optical clocks—the largest coordinated comparison of its kind 1 .
Used for long-distance clock comparisons across continents with high precision timing signals.
Spanning thousands of miles across Europe, providing more stable and precise comparison data.
"Comparing multiple clocks at the same time and using more than one type of link technology provides far more information than the mostly pairwise clock comparisons that have been carried out to date."
The results were remarkable: the comparison produced 38 different frequency ratios measured simultaneously, four of them for the first time. The remaining ratios were measured with greater accuracy than ever before 1 .
| Timekeeping Technology | Estimated Accuracy | Time Drift Over 1 Billion Years |
|---|---|---|
| Mechanical Wristwatch | Loses/Gains seconds per month | Would be off by thousands of years |
| Cesium Atomic Clock (Current Standard) | Loses/Gains 1 second every 100 million years | Would be off by approximately 10 seconds |
| Optical Clock (Next Generation) | Would not lose/gain a second in billions of years | Would be off by less than 1 minute |
Table 1: Estimated Performance Comparison of Timekeeping Technologies
Just as optical clocks are revolutionizing how we measure time, groundbreaking theoretical work is challenging our understanding of time's fundamental nature. For centuries, we've experienced time as moving inexorably forward—the "arrow of time" concept that distinguishes past from future. But at the quantum level, this may not be the whole story.
A team of physicists in England spent over two years theoretically investigating time's arrow in open quantum systems—systems that interact with their environment, as opposed to closed systems isolated from outside influence 8 .
Researchers discovered something astonishing: two arrows of time spontaneously arising, moving in opposite directions from a given moment 8 .
The key to understanding this phenomenon lies in entropy—the measure of disorder in a system that tends to increase over time. The second law of thermodynamics states that entropy always increases, which is why we remember the past but not the future, and why spilled milk doesn't unspill itself 8 .
Crucially, the team found that this fundamental law is preserved even with two time arrows. Entropy still increases—but it can increase toward the past instead of the future from a given starting point.
"You'd still see the milk spilling on the table, but your clock would go the other way around."
| System Type | Definition | Relationship with Time |
|---|---|---|
| Closed Quantum System | Isolated from environmental influence | Unchanging, protected from time's effects |
| Open Quantum System | Interacts with surrounding environment | Changes over time through energy dissipation |
| Open Quantum System with Twin Arrows | Interacts with environment with modified equations | Features two spontaneous arrows of time moving in opposite directions |
Table 2: Comparison of Quantum System Types and Their Relationship with Time
Rocco is quick to clarify that this isn't about time travel: "This has absolutely nothing to do with time travel or constructing a time machine" 8 . Rather, it suggests that from any given moment, "two trajectories are equally possible: one going forward and the other one going backwards from that moment" 8 . Once the arrow chooses a direction, familiar dynamics like entropy take over, and the arrow continues in that direction.
The revolution in understanding time isn't limited to quantum labs and metrology institutes—it's also playing out in the very practical arena of public health policy. The debate over daylight saving time versus standard time has taken on new urgency as research reveals significant health implications tied to our time policies.
A study from Stanford Medicine published in the journal PNAS compared three different time policies: permanent standard time, permanent daylight saving time, and the current system of biannual switching 4 . The findings were clear: changing clocks twice a year is the worst option for our circadian rhythms 4 . But between the two permanent options, permanent standard time appeared to benefit more people 4 .
Our circadian cycles—the body's innate clock regulating numerous functions—aren't exactly 24 hours. For most people, it's closer to 24 hours and 12 minutes, and light exposure helps regulate this cycle 4 .
Speeds up our circadian cycle
Slows down our circadian cycle
"The more light exposure you get at the wrong times, the weaker the circadian clock. All of these things that are downstream—for example, your immune system, your energy—don't match up quite as well."
The Stanford team modeled how permanent standard time could prevent approximately 300,000 cases of stroke and reduce obesity prevalence by 0.78 percent nationwide, amounting to about 2.6 million fewer people with obesity 4 . Permanent daylight saving time would achieve about two-thirds of these same effects 4 .
| Health Outcome | Permanent Standard Time | Permanent Daylight Saving Time | Current System (Baseline) |
|---|---|---|---|
| Obesity Cases Prevented | 2.6 million | 1.7 million | 0 |
| Stroke Cases Prevented | 300,000 | 220,000 | 0 |
| Effect on Circadian Rhythms | Best for most people | Better for early-risers (15% of population) | Worst option |
Table 3: Projected Annual U.S. Health Impacts of Different Time Policies
As impressive as optical clocks are, scientists are already looking beyond them to the next frontier in timekeeping: nuclear clocks. Last year, the National Institute of Standards and Technology (NIST) reported they were close to completing a nuclear clock prototype that focuses on vibrations not from a single atom, but from a single nucleus 1 .
"Imagine a wristwatch that wouldn't lose a second even if you left it running for billions of years. While we're not quite there yet, this research brings us closer to that level of precision."
Meanwhile, the discovery of twin arrows of time in quantum systems raises profound questions about cosmology and the origin of our universe. Rocco mentions that some scientists speculate whether at the moment of the Big Bang, two universes emerged—traveling in opposite directions in time 8 . While his team's results don't confirm this speculation, the theoretical framework they developed could help reassess our assumptions of time's function in the universe 8 .
What makes these discoveries particularly exciting is their potential convergence. As timekeeping becomes more precise, it provides better tools for testing extraordinary theoretical concepts like time's dual arrows. The same optical clocks that might redefine the second could potentially detect subtle quantum temporal effects that were previously unimaginable.
More precise timing improves location accuracy
Better transaction timestamps and security
Testing relativity and exploring dark matter
Time, we're discovering, is far more complex and fascinating than the steady tick of a clock. From optical clocks that measure vibrations of laser-cooled atoms with unimaginable precision, to quantum systems where time's arrow points in two directions, to health policies that recognize how our bodies respond to temporal shifts—our understanding of time is evolving dramatically.
These developments remind us that even the most fundamental aspects of our experience are ripe for rediscovery. The second—that basic unit of time we take for granted—may soon be redefined, with ripple effects across science, technology, and daily life. Meanwhile, theoretical work continues to challenge our assumptions about time's very nature, suggesting that reality might be far stranger than we imagined.