General and special relativity are two of the more mind bending theories in modern science. According to them, space and time are a singular entity that is warped by mass, where measurements completely depend on how the person doing the measuring is moving. People generally believe that relativity has no effect in everyday life, since it's generally discussed in terms of things going very fast or objects in highly warped spacetime.

This belief is not entirely true—GPS equipment would not work if the times measured by the satellites were not corrected for time dilation that arises from the rapid motion of the satellites relative to your car. In general, though, most people go about their day without experiencing any ill- (or odd-) effects due to relativity. However, it turns out that, if you can measure accurately enough, the effects of relativity are indeed all around us.

Using the most accurate clocks in existence, a team of researchers at NIST in Boulder, CO have shown that relativity all around us—even on everyday lab scales. The team used an optical "quantum logic clock" that is based on an electron's oscillations between the 1s and 3p quantum energy levels of an 27Al+ ion. A pair of these clocks—each of which will lose less than one second every 3.7 billion years—were tethered together by a special optical cable connecting two adjacent labs. The clocks were then manipulated so that time dilation occurred.

The first experiment had one clock moving relative to the other, a situation that is used to introduce the concept of time dilation to introductory physics students—faster moving clocks will tick away more slowly. In this case, one clock's ion was put in motion relative to the other, and the frequency shift that resulted was measured. Even when the clocks were moving apart at 22.4 miles per hour, it was possible to observe a change in frequency of approximately 45x10-17. This is exactly in agreement with the predictions of special relativity.

A lesser known consequence of general relativity is that time will move slower in a stronger gravitational field. On Earth, one implication of this is that a clock on the second floor of an office building will move faster than one on the first floor. Using the ultra-precise clock setup, the NIST researchers tested this as well. One of the optical clocks was placed about a foot above the other and measurements were taken. They found a fractional frequency change of (4.1±1.6)x10-17; plugging this number back into relativity's formulas produced an equivalent height differential gave 14.5±5.9 inches, a result that nicely bracketed the 12 inch difference in the experimental setup.

Science, 2010. DOI: 10.1126/science.1192720