Despite breathless reports by non scientist reporters may say scientist at NIST have not warped time or even really done much that has to do with General Relativity directly. What Toby Bothwell et. al did accomplish is as one peer reviewer put it is an “Impressive result in time keeping and Time and Frequency metrology.” In normal plain English they managed to measure smaller units of time than before with smaller uncertainty of measurement than before. What they did was improve on the methods that could be used to measure effects on time at scales where quantum mechanics would be relevant. If we can improve on this enough it will open up an avenue for direct experimental testing of theories of quantum gravity OR will reveal data that might inform such theories.

 This is NOT to downplay the technical achievement involved. It does not need to be ground breaking general relativity  and quantum mechanics to be important.    What is important is where this will lead especially in context of the overall cannon of research that is out there. 

Ultimately theory tells us that we need to measure time scales as short as the Planck Time. 10^-43 seconds.  What they tried to measure was gravitational redshift and in the trying they were able to measure very small lengths of time about 10^-22

Measuring Gravity At Small Scales

Taken with work like the following we can gain insights into the limits where General Relativity will break and quantum mechanics might come into play. The crucial things to minimize are the masses involved and the distances involved as well as the times.  

Westphal et al have measured gravitational fields of milligram sized masses.  The Planck mass is a mass of 2.1X10^-8 kg.  We know that these masses are sensitive to the gravitational fields of larger bodies, but it is an open question if such small masses even have their own gravitational field.  Most attempts at quantum gravity lead to the conclusion, by simple analyses that a mass smaller than that cannot have a gravitational field.  That it would take that much mass to warp space by one Planck length-time.

As Budrikis writes at small length scales but masses larger compared to the Planck mass gravity seems to obey Newton (and hence Einstein) exactly. 


The current work being misreported is magnificent work.  It is important work but the media is sensationalizing it.  Taken with these other works and similar works it will be a great small-scale probe of General Relativity. 

This work will complement work by LIGO VIRGO and LISA which measure gravitational waves, waves in space time, created by the interactions of the most massive things there are.   As a theoretical astrophysicist my job will be to understand, analyze, and propose theories which can explain gravity on all of these scales.  It may be that Einstein is exactly right from the scale of atoms to the scale of the Universe.  It may be that his theory needs modification to be right on all of those scales.  

Via all of this work we, humanity, can learn how the universe really works. 
If you enjoyed this news article take a look at the other great writers here at science2.0.  To hear from me early and support my work consider subscribing to my substack.  It is free at least for now. 


Bothwell, T., Kennedy, C.J., Aeppli, A. et al. Resolving the gravitational redshift across a millimetre-scale atomic sample. Nature 602, 420–424 (2022).

Westphal, T., Hepach, H., Pfaff, J. et al. Measurement of gravitational coupling between millimetre-sized masses. Nature 591, 225–228 (2021).

Budrikis, Z. Even at short range, Newton’s law still rules. Nat Rev Phys 2, 174 (2020).