Featured Research

from universities, journals, and other organizations

Clock Comparison Yields Clues To 'Constant' Change

Date:
February 18, 2007
Source:
National Institute of Standards and Technology
Summary:
Years of comparisons among the world's best atomic clocks -- based on different atoms -- have established the most precise limits ever achieved in the laboratory for detecting possible changes in so-called 'constants' of nature. The comparisons at NIST may help scientists test the latest theories in physics and develop a more complete understanding of the history of the universe.

Years of comparisons among the world's best atomic clocks--based on different atoms--have established the most precise limits ever achieved in the laboratory for detecting possible changes in so-called "constants" of nature. The comparisons at the National Institute of Standards and Technology (NIST) may help scientists test the latest theories in physics and develop a more complete understanding of the history of the universe.

Related Articles


Some astronomical and geological studies suggest there might have been very small changes in the values of fundamental constants over billions of years, although the results have been inconsistent and controversial. If fundamental constants are changing, the present-day rates of change are too small to be measured using conventional methods. However, a new comparison of NIST's cesium fountain and mercury ion clocks, scheduled to appear in this week's issue of Physical Review Letters,* has narrowed the range in which one of them--the "fine-structure constant"-- possibly could be changing by a factor of 20. Widely used in physical theory and experiments, the fine-structure constant, represents the strength of the interaction between electrons and photons.

Astronomers and geologists have attempted to detect changes in natural constants by examining phenomena dating back billions of years. The NIST experiments attained the same level of precision by comparing the relative drifts in the "ticks" of an experimental mercury ion clock, which operates at optical frequencies, and NIST-F1, the national standard cesium clock, which operates at lower microwave frequencies. These data can be plugged into equations to obtain upper limits for possible rates of change of the fine structure constant in recent times.

A second study, based on seven years of comparisons of cesium and hydrogen clocks at NIST and in Europe,** achieved record limits on Local Position Invariance, the principle that two clocks based on natural frequencies of different atoms should undergo proportional frequency shifts when subjected to the same changes in gravitational field. The new experiments lowered the upper limit for a possible violation of LPI, by more than 20 times.

Changes in physical constants such as the fine structure constant or the gravitational constant would violate Albert Einstein's original theory of general relativity. Such violations are predicted in recent theories aimed at unifying gravitation and quantum mechanics. NIST scientists now plan an all-optical-frequency comparison of the mercury ion clock with an aluminum ion atomic clock, which could increase measurement precision further, offering a more stringent test of the theoretically predicted changes. Conducting such tests with many different types of atomic clocks offers the best chance of eliminating extraneous factors to clearly identify which, if any, of the fundamental "constants" are changing over time.

Partial support for staff and equipment was provided by Los Alamos National Laboratory.

* T.M. Fortier, N. Ashby, J.C. Bergquist, M.J. Delaney, S.A. Diddams, T.P. Heavner, L. Hollberg, W.M. Itano, S.R. Jefferts, K. Kim, F. Levi, L. Lorini, W.H. Oskay, T.E. Parker, J. Shirley and J.E. Stalnaker. Precision atomic spectroscopy for improved limits on variation of the fine structure constant and local position invariance. Physical Review Letters. Feb. 16, 2007.

** N. Ashby, T. P. Heavner, S. R. Jefferts, T. E. Parker, A. G. Radnaev and Y. O. Dudin. Testing local position invariance with four cesium-fountain primary frequency standards and four NIST hydrogen masers. Physical Review Letters. Feb. 16, 2007.


Story Source:

The above story is based on materials provided by National Institute of Standards and Technology. Note: Materials may be edited for content and length.


Cite This Page:

National Institute of Standards and Technology. "Clock Comparison Yields Clues To 'Constant' Change." ScienceDaily. ScienceDaily, 18 February 2007. <www.sciencedaily.com/releases/2007/02/070215180952.htm>.
National Institute of Standards and Technology. (2007, February 18). Clock Comparison Yields Clues To 'Constant' Change. ScienceDaily. Retrieved November 22, 2014 from www.sciencedaily.com/releases/2007/02/070215180952.htm
National Institute of Standards and Technology. "Clock Comparison Yields Clues To 'Constant' Change." ScienceDaily. www.sciencedaily.com/releases/2007/02/070215180952.htm (accessed November 22, 2014).

Share This


More From ScienceDaily



More Matter & Energy News

Saturday, November 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Toyota's Hydrogen Fuel-Cell Green Car Soon Available in the US

Toyota's Hydrogen Fuel-Cell Green Car Soon Available in the US

AFP (Nov. 21, 2014) Toyota presented its hydrogen fuel-cell compact car called "Mirai" to US consumers at the Los Angeles auto show. The car should go on sale in 2015 for around $60.000. It combines stored hydrogen with oxygen to generate its own power. Duration: 01:18 Video provided by AFP
Powered by NewsLook.com
Google Announces Improvements To Balloon-Borne Wi-Fi Project

Google Announces Improvements To Balloon-Borne Wi-Fi Project

Newsy (Nov. 21, 2014) In a blog post, Google said its balloons have traveled 3 million kilometers since the start of Project Loon. Video provided by Newsy
Powered by NewsLook.com
NSA Director: China Can Damage US Power Grid

NSA Director: China Can Damage US Power Grid

AP (Nov. 20, 2014) China and "one or two" other countries are capable of mounting cyberattacks that would shut down the electric grid and other critical systems in parts of the United States, according to Adm. Michael Rogers, director of the National Security Agency and hea Video provided by AP
Powered by NewsLook.com
Latest Minivan Crash Tests Aren't Pretty

Latest Minivan Crash Tests Aren't Pretty

Newsy (Nov. 20, 2014) Five minivans were put to the test in head-on crash simulations by the Insurance Institute for Highway Safety. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins