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Monday, August 5, 2024
Nuclear breakthrough at UCLA
Scientists: please explain this to a non-scientist. Thank you!
Photons are oscillations of the electromagnetic field, and an oscillation or periodic motion can be used to construct a clock : just as a quartz crystal in an ordinary watch provides timekeeping. The original such device was the ammonia maser or atomic clock demonstrated in the 1950's which used microwave photons emitted by ammonia molecules -- I recall this is described in Volume 3 of the Feynman Lectures on Physics.
This is a particular scheme involving ultraviolet photons emitted by nuclei (rather than atoms, molecules, or crystalline defects) which for technical reasons can be produced with a very well-defined energy, and thus a well-defined frequency.
More accurate metrology has a number of possible applications, including precision tests of general relativity and quantum electrodynamics, any deviation from which could lead to new physics.
By the way, correct me if I'm wrong but 28855 days have elasped between the bombing of Hiroshima and the supposed anniversary this year on August 6th.
Because the calendar year is 365.242198 days which is compensated by various leap day rules in the Gregorian calendar, and the bomb was dropped in the morning, it seems to me that August 5th was the actual anniversary of the event, not the 6th as the calendar would suggest.
This is a an improved method to do precision measurements. The more fined tuned you can get timings you can also looks for deviations which could be caused changes in space time distortions, get a better numbers of physical constants, look at deviations from the standard model and so on. I would also guess it could be bused to create better measures standards. Poster 11.35 am got it right. I think by embedding in to a solid it is much easier to controll than if it was in atomic gas.
However this is just a demonstration it needs to be very repeatable and the it needs to give strong signals so it could easier to use in other laboratories.
6:57 -- I think embedding in a solid gives a higher density of the active nuclei per unit volume, and the band gap allows passage of the light and also suppresses other decay modes of the excited nuclei which is also advantageous in this case, giving the excited states a longer lifetime. There are some environmental effects on the frequency of course, requiring no doubt thermal control of the solid matrix, and careful preparation. And there is the obvious benefit a solid may be easier and more practical to work with.
Nuclei embedded in a crystal also can have recoilless emission in some cases by the way, whereby the entire crystal recoils rather than the nucleus in question at least some of the time, but I'm not sure whether this is the goal here or important. This is known as the Mossbauer effect, and was used in a previous test of General Relativity namely the Pound-Rebka experiment.
Accurate timekeeping does have particular uses in navigation, communications, and synchronizing or operating certain computer and electronic systems. This was actually very important when ships used celestial navigation historically and needed to carry accurate timepieces to determine longitude:
https://en.wikipedia.org/wiki/Marine_chronometer
GPS satellites of course, also contain accurate time and frequency standards, which are necessary for their operation, and can be used I think, to obtain accurate timekeeping information on earth.
There have been of course, previous experiments to use accurate clocks for tests of General Relativity such as Gravity Probe A:
https://en.wikipedia.org/wiki/Gravity_Probe_A
By the way "precision quartz watches" are available and have been for quite some time as well as well as watches which of course, set themselves using radio signals such as those provided by NIST or GPS, or using time obtained from cellular networks:
There are a lot of very sophisticated analog watch mechanisms of course, but of course the Rolex designs are mechanically simpler but able to stay accurate and reliable under actual use conditions. Eisenhower owned one in fact, which was solid gold and given to him as a special gift,
Part of the reason for the 9:25 observation I made previously turns out to be because of 2000 being a leap year, years divisible by 100 are not leap years unless they are also divisible by 400. So a lot of anniversary dates that cross that century line will then be potentially incorrect at least in a very technical sense, that is in terms of alignment with seasons, solstices, or the equinox.
There is a separate sidereal year of course, that governs the return of the Earth in its orbit relative to fixed stars, it is the actual orbital period, which differs by 20 minutes longer due to the procession of the equinoxes.
In terms of sidereal years of course, that would mean that the anniversary was indeed correct, of course.
8 comments:
Photons are oscillations of the electromagnetic field, and an oscillation or periodic motion can be used to construct a clock : just as a quartz crystal in an ordinary watch provides timekeeping. The original such device was the ammonia maser or atomic clock demonstrated in the 1950's which used microwave photons emitted by ammonia molecules -- I recall this is described in Volume 3 of the Feynman Lectures on Physics.
This is a particular scheme involving ultraviolet photons emitted by nuclei (rather than atoms, molecules, or crystalline defects) which for technical reasons can be produced with a very well-defined energy, and thus a well-defined frequency.
More accurate metrology has a number of possible applications, including precision tests of general relativity and quantum electrodynamics, any deviation from which could lead to new physics.
I guess it is time to sell my Caesium stock.
By the way, correct me if I'm wrong but 28855 days have elasped between the bombing of Hiroshima and the supposed anniversary this year on August 6th.
Because the calendar year is 365.242198 days which is compensated by various leap day rules in the Gregorian calendar, and the bomb was dropped in the morning, it seems to me that August 5th was the actual anniversary of the event, not the 6th as the calendar would suggest.
This is a an improved method to do precision measurements. The more fined tuned you can get timings you can also looks for deviations which could be caused changes in space time distortions, get a better numbers of physical constants, look at deviations from the standard model and so on. I would also guess it could be bused to create better measures standards. Poster 11.35 am got it right. I think by embedding in to a solid it is much easier to controll than if it was in atomic gas.
However this is just a demonstration it needs to be very repeatable and the it needs to give strong signals so it could easier to use in other laboratories.
I and ,I am sure other readers, appreciate your scientific input on this
6:57 -- I think embedding in a solid gives a higher density of the active nuclei per unit volume, and the band gap allows passage of the light and also suppresses other decay modes of the excited nuclei which is also advantageous in this case, giving the excited states a longer lifetime. There are some environmental effects on the frequency of course, requiring no doubt thermal control of the solid matrix, and careful preparation. And there is the obvious benefit a solid may be easier and more practical to work with.
Nuclei embedded in a crystal also can have recoilless emission in some cases by the way, whereby the entire crystal recoils rather than the nucleus in question at least some of the time, but I'm not sure whether this is the goal here or important. This is known as the Mossbauer effect, and was used in a previous test of General Relativity namely the Pound-Rebka experiment.
Accurate timekeeping does have particular uses in navigation, communications, and synchronizing or operating certain computer and electronic systems. This was actually very important when ships used celestial navigation historically and needed to carry accurate timepieces to determine longitude:
https://en.wikipedia.org/wiki/Marine_chronometer
GPS satellites of course, also contain accurate time and frequency standards, which are necessary for their operation, and can be used I think, to obtain accurate timekeeping information on earth.
There have been of course, previous experiments to use accurate clocks for tests of General Relativity such as Gravity Probe A:
https://en.wikipedia.org/wiki/Gravity_Probe_A
By the way "precision quartz watches" are available and have been for quite some time as well as well as watches which of course, set themselves using radio signals such as those provided by NIST or GPS, or using time obtained from cellular networks:
https://www.watchtime.com/featured/high-accuracy-quartz-guide-longines-vhp-breitling-bulova-citizen-chronomaster-omega-grand-seiko-9f/
There are a lot of very sophisticated analog watch mechanisms of course, but of course the Rolex designs are mechanically simpler but able to stay accurate and reliable under actual use conditions. Eisenhower owned one in fact, which was solid gold and given to him as a special gift,
https://www.bobswatches.com/rolex-blog/watch-review/presidents-dwight-d-eisenhowers-rolex.html
Mechanical watches can be adjusted when serviced to be highly accurate at the time of service, there are internal adjustments to zero out the drift.
Part of the reason for the 9:25 observation I made previously turns out to be because of 2000 being a leap year, years divisible by 100 are not leap years unless they are also divisible by 400. So a lot of anniversary dates that cross that century line will then be potentially incorrect at least in a very technical sense, that is in terms of alignment with seasons, solstices, or the equinox.
There is a separate sidereal year of course, that governs the return of the Earth in its orbit relative to fixed stars, it is the actual orbital period, which differs by 20 minutes longer due to the procession of the equinoxes.
In terms of sidereal years of course, that would mean that the anniversary was indeed correct, of course.
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