Atomic Optical Clocks Demonstrate Slowing and Speeding of Time per Relative Speed or Proximity to Mass

© 2010 Peter Free

 

01 November 2010

 

I did not think researchers would pull this kind of precision off in my lifetime using “clocks” sitting virtually side by side, but they did

 

Observers in relative motion or at different gravitational potentials measure disparate clock rates. These predictions of relativity have previously been observed with atomic clocks at high velocities and with large changes in elevation.

 

We observed time dilation from relative speeds of less than 10 meters per second by comparing two optical atomic clocks connected by a 75-meter length of optical fiber. We can now also detect time dilation due to a change in height near Earth’s surface of less than 1 meter [actually 0.33 m].

 

 

© 2010 C.W. Chou et al., Optical Clocks and Relativity, Science 329(5999): 1630-1633 (24 September 2010) (paragraph split)

 

Impressive experimental technique

 

Chou’s Time and Frequency Division group, at the National Institute of Standards, wrote that, in the past, detecting these relativistic effects was most accurately done at speeds close to that of light or changes in elevation of 104 to 107 meters.  Tiny shifts (10-16) over short distances were previously detected with atom interferometry and gamma ray Mössbauer spectroscopy.  (Where’s the fun in that?)

 

His group was able demonstrate relativistic temporal effects using optical clocks based on the harmonic vibration of aluminum cations (Al+).

 

Instead of literally zooming one clock around the “room” to attain speed relative to the other, the group applied an electrical field to its ion, so as to shift it off its null point.

 

“In the language of the twin paradox, the moving Al+ ion is the traveling twin, and its harmonic motion amounts to many round trips.”

 

“Traveling twin,” as used here, refers to the school kid example of comparing the relativity effects of aging between a twin on the ground and another traveling in a super-fast rocket.

 

Why aluminum ions?

 

According to Chou, inherent uncertainties in aluminum ion frequencies have been reported at between 8.6 x 10-18 (smaller) to 2.3 x 10-17 (small).  These uncertainties are smaller than cesium fountain clocks (3.4 x 10-16).  (Reduced uncertainty means greater measurement precision.)

 

Just how small are the relative time differences?

 

Relativity dictates that higher speed, or closer proximity to large mass, slows time between relative observational points.

 

For example, if two identical clocks are separated vertically by 1 km [kilometer] near the surface of Earth, the higher clock emits about three more second-ticks than the lower one in a million years.

 

© 2010 C.W. Chou et al., Optical Clocks and Relativity, Science 329(5999): 1630-1633 (24 September 2010)

 

 

Here’s the “wow”

 

Using the 33 centimeter (0.33 meter) difference in height that the researchers used, it would take very roughly 800,000 years just to demonstrate a one-second difference between the lower clock and the elevated one.

 

No “live longer” therapy here

 

But it’s still a cool effect that illustrates the Universe’s often unseen dynamism.