3 ms·
Yes, people have already measured the gravitational redshift in many other contexts. That should not take away from this impressive achievement. The team here
by ISL 5y ago
Yes, people have already measured the gravitational redshift in many other contexts. That should not take away from this impressive achievement.
The team here measured the gravitational redshift by comparing the clock-rates inferred from atoms at the top and bottom of a cloud of atoms that was itself smaller than a grain of rice.
I've spent much of my career building precision gravity-sensing systems -- I'm happy to assure you that this news is very cool. Clocks are an awesome way to learn a lot of new things about gravity, particularly because they measure differences in potential, rather than differences in acceleration. In the past two decades, we have seen atomic clocks begin to become sensitive to terrestrial gravity. In the next two decades, we are likely to see clocks begin to open up previously-impossible measurements.
The measurement described here is a wonderful stepping-stone on that path.
- lordnacho 5y agoHow are such precise measurements possible? Have you got an intro reading? I just don't get how we could have found and cancelled all the sources of noise on something like this.
- omgwtfbyobbq 5y ago>The specific way they measured the shift — comparing two parts of the same cloud — allowed them to cancel out a lot of noise that was common to both parts. It’s like measuring a sailboat in rough seas. Even as it lurches up and down unpredictably, the distance between the keel and mast will always stay constant. While a clock made of a cloud of atoms can drift due to any number of things — electric fields, magnetic fields, the laser light itself, heat from the environment — the difference in frequencies between the top and bottom of the cloud remains the same. Measuring that difference revealed the effect of gravity. “That’s not trivial to do,” said Andrew Ludlow, an atomic clock expert at the National Institute of Standards and Technology, who was not involved with the research.
- lordnacho 5y agoBut if the difference you're measuring is absolutely tiny, you would imagine that the differential cooling of the mast when the wind is blowing/not blowing would have an effect on the height?
- raattgift 5y ago> this news is very cool 800 nanokelvins down to 100 nK! Brrr! [https://arxiv.org/abs/2109.12238 https://arxiv.org/abs/2109.12238 "Atomic sample preparation", pdf p. 16, and top of p. 3] Maybe it's soon time to plan updates to PARCS/ACES/SAGAS.