Physics · the experiment
Close the two clocks' error budget
One clock in Teddington, the other in Braunschweig, 2,220 km of fibre between them. You hold their uncertainty budget: find what dominates it, and what it would take to do better.
1 · Find the centimetres
Beginner
What is the largest item in the comparison's uncertainty budget?
The items add in quadrature. Set the uncertainty on the clocks' height to recover the paper's total uncertainty, 4.8 × 10⁻¹⁸.
2 · Move a clock up one floor
The gravity shift is proportional to the height difference: the paper equates 3.5 × 10⁻¹⁸ with just over 3 cm.
Intermediate
By how much does a clock's frequency change if you raise it by 3 m?
3 · Erase the gravity error
The authors want better knowledge of the gravity field at both sites. Imagine it were known perfectly.
Expert
What would the total uncertainty, 4.8 × 10⁻¹⁸ today, become?
Check it: bring the height uncertainty down to zero.
Budget closed
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