Editing Fine-structure constant (section)

=== Present rate of change ===
In 2008, Rosenband ''et al.''<ref>
{{cite journal
 |last1=Rosenband |first1=T.            |last2=Hume       |first2=D. B.
 |last3=Schmidt   |first3=P. O.          |last4=Chou       |first4=C. W.
 |last5=Brusch    |first5=A.            |last6=Lorini     |first6=L.
 |last7=Oskay     |first7=W. H.          |last8=Drullinger |first8=R. E.
 |last9=Fortier   |first9=T. M.          |last10=Stalnaker |first10=J. E.
 |last11=Diddams  |first11=S. A.         |last12=Swann     |first12=W. C.
 |last13=Newbury  |first13=N. R.         |last14=Itano     |first14=W. M.
 |last15=Wineland |first15=D. J.         |last16=Bergquist |first16=J. C.
 |display-authors=6
 |date=28 March 2008
 |title=Frequency ratio of Al{{sup|+}} and Hg{{sup|+}} single-ion optical clocks; metrology at the 17th&nbsp;decimal place
 |journal=Science
 |volume=319 |issue=5871 |pages=1808–1812
 |doi=10.1126/science.1154622 |pmid=18323415
 |bibcode=2008Sci...319.1808R |s2cid=206511320
 |url=https://zenodo.org/record/1230892
 |doi-access=free}}</ref>
used the frequency ratio of {{chem2|Al+}} and {{chem2|Hg+}} in single-ion optical atomic clocks to place a very stringent constraint on the present-time temporal variation of {{mvar|α}}, namely {{sfrac| {{math|Δ}}{{mvar|α}} | {{mvar|α}} }} = {{val|-1.6|2.3|e=-17}} per year. A present day null constraint on the time variation of alpha does not necessarily rule out time variation in the past. Indeed, some theories<ref>
{{cite journal
 |last1=Barrow   |first1=John D.
 |last2=Sandvik  |first2=Håvard Bunes
 |last3=Magueijo |first3=João
 |date=21 February 2002
 |title=Behavior of varying-alpha cosmologies
 |journal=[[Physical Review D]]
 |volume=65  |issue=6  |pages=063504
 |doi=10.1103/PhysRevD.65.063504  |arxiv=astro-ph/0109414
 |bibcode=2002PhRvD..65f3504B  |s2cid=118077783
}}</ref>
that predict a variable fine-structure constant also predict that the value of the fine-structure constant should become practically fixed in its value once the universe enters its current [[dark energy]]-dominated epoch.