While both teams have used fluorite crystals doped with Th229, which was the most obvious choice for the active medium, they have used different kinds of optical frequency multipliers in order to generate the ultraviolet light required to probe the thorium nuclei.
For now, the frequency multiplication method used by the Chinese team is superior, allowing a greater output power, which ensures a better signal-to-noise ratio.
The team from Austria intends to use a better frequency multiplier in the future, to increase their output power, and they are evaluating several methods, one of which is the 4-wave mixing in cadmium vapor, already demonstrated by the Chinese team.
I would in general agree with you, but having read through the journal paper: I think the fraction of general audience newspaper readers who could actually read that paper is very low. I come from a science background, spent time dabbling in time and frequency measurement enough to understand some of the concepts, and still found it a painful slog. (I am very much not a physicist!)
I still think it's the right practice for newspapers to always link to the primary source, but in this particular case I understand why they might make an editorial decision not to.
Is there evidence that is the actual reasoning, because I find it ridiculous. People who don’t care about the primary source are not going to follow a link to, e.g., a court ruling, government report, fed minutes, a leaked document, a research paper, etc; but those who are interested are going to immediately leave the site and likely not come back for a long while.
To address some of the most pressing open questions in fundamental physics, such as the origin and properties of dark matter...
Owing to unknown nuclear parameters, precise values of these sensitivity factors cannot at present be calculated, but it is predicted that they will exceed those of the most sensitive atomic clock transitions by several orders of magnitude.
So when you achieve FTL, the Vulcans show up.
Who (or what) shows up when you solve the riddle of dark matter?
According to Wikipedia thorium is probably created from neutron stars or supernovae making it one of the rarest elements in the galaxy. But, it’s quite abundant on Earth, maybe 3x as abundant as Uranium on earths crust. Because of this abundance it is, along with Radon, the primary constituent of earths natural background radiation.
Iron is the last element that can form through a sustaining fusion process. All elements above iron are formed in super nova or neutron star collisions. Specifically gold and platinum are thought to be formed primarily in neutron star collisions
While it's correct that fusion stops producing energy once the fusion product is iron, it is not true that all elements beyond iron are only produced in cataclysmic events (supernovae / neutron star collisions).
Stars can function as "breeder reactors", where the natural
flow of neutrons produced as intermediate / side effect of the various fusion reactions going on in a later-stage-life star get absorbed by nuclei and then (by beta decay) produce beyond-iron elements. This is called the "s-Process" (slow), and responsible for a large range of elements into the Lanthanides or so. And stellar winds, or the planetary nebula stage at the end, will return some of this to the interstellar medium.
It's correct that the heaviest "naturally present" elements require the so-called "r-Process", heavy overabundance of neutrons / extremely high neutron flow as in supernovae, or direct fusion of beyond-iron nuclei as in neutron star collisions.
There is rather active research happening here, both astronomical (trying to detect various nuclei from x ray spectroscopy of cataclysmic events) and theoretical (because r-Process cannot be simulated in labs since the neutron fluxes needed are not within our reach).
That said, it remains
true that many "transition groups" elements are bred via s-Process in relatively-ordinary stars.
It is kind of astonishing (well, not really if you think about it - more violent stuff actually happens faster with stars, and energy density was higher in the early universe) that every stable element exists on earth even if some are very rare. That means that earth's materials have had quite a lot of stuff happening to them before forming earth.
Iron 56 is the isotope with the highest nuclear binding energy per nucleon, so it can form from the fusion of any lighter nuclei.
After iron 56, the binding energy decreases slowly, so the next heavier nuclei can still form from the fusion of certain lighter nuclei, but not from any of them, but only from pairs with a lower average binding energy.
So the following heavier nuclei after iron 56 can still form through fusion, but with increasing atomic mass the probability of their formation decreases quickly, until it becomes negligible.
Relatively large amounts of cobalt, nickel, copper, zinc, gallium and germanium still form through the fusion of lighter elements, but after germanium the amount of chemical elements formed through fusion becomes extremely low. Already the amount of germanium formed through fusion is almost ten thousand times less than the amount of iron.
The binding energy per nucleon decreases very slowly, so even uranium has a higher binding energy per nucleon than helium, so energetically it could form through the fusion of hydrogen or helium, but such an event has a completely negligible probability (because there is a negligible chance for so many hydrogen or helium nuclei to collide simultaneously and if they fuse into nuclei of intermediate mass those block the propagation of the fusion reaction by having higher binding energies than the heavier nuclei).
The elements heavier than germanium form almost only through neutron capture, with the exception of some proton-rich isotopes, which form through collisions with protons. There are several kinds of environments with abundant neutrons where heavy elements can form, where the concentrations of neutrons and their energy distributions are different, so in any of these environments there are different classes of isotopes that form preferentially there.
In a relatively young stellar system like ours, the matter from which the star and the planets have condensed is a mixture of chemical elements coming from different sources.
In environments with extremely high neutron abundances (which include the nuclear explosions on Earth, not only supernova explosions, neutron star collisions and the like), all chemical elements up to fermium (Z = 100) are formed. Nonetheless, while the matter composed of these elements travels through space until the formation of a new stellar system, most of the trans-uranium elements, except the plutonium, decay. When the Solar System was formed, it still contained relatively large amounts of plutonium, not only thorium and uranium, as the heaviest elements, but since then until now the plutonium has decayed, like also most of the uranium 235 that is used now in nuclear reactors.
How do they know the accuracy of the clock? Eg: 2s of drift in 65M years.
Naively, measuring that seems more difficult than the clock. Wouldn’t you need a perfect clock as a baseline? There must be something really clever here.
They measured the stability by comparing the nuclear clocks with more stable conventional atomic clocks. In Vienna, they used a commercial single-ion optical clock [1], and in Beijing they used a hydrogen maser (a type of microwave atomic clocks) that was calibrated to the International Atomic Time scale via GNSS satellites.
By adding up the uncertainties of all intermediate measurements they made.
As a parallel, for a regular clock, you'd measure and compute the uncertainties of:
- The distance between the axis of rotation and the center of mass of the pendulum,
- The local acceleration of gravity.
And deduce the pendulum period and its uncertainty by calculus.
In that case I'm not sure you can build (and measure) a pendulum that's more precise than a previous realization of the second (because the meter is defined from the speed of light and the second, and gravimeters probably depend on the definition of the second too).
That's why the definition of base units is carefully chosen to not depend on previous realization. IIRC time is the most fundamental of base units, because other base units depend on it.
Standard atomic clocks probe outer-shell electrons sensitive to stray EM noise; locking directly to the nucleus is how you actually kill environment drift.
Spot on. Shielding electron transitions from stray thermal and magnetic shifts takes brutal trapping setups. The nucleus provides that isolation for free.
The hope is that with nuclear clocks there will be no need for the very complex single-ion traps or optical lattices required for clocks that use ionic or atomic energy levels.
Even with the atoms of thorium contained in a small crystal, the frequency of their clock transitions should not be influenced by the environment.
Unfortunately, for now no other suitable nucleus has been found, because the frequency corresponding to nuclear energy levels is normally too high for the current or near future technology.
With thorium 229, the potential simplicity of the clock is counterbalanced by the great expense required for producing this artificial isotope.
I may be completely ignorant, but aren't these strictly inferior to optical lattice atomic clocks? Maybe they have a better form factor/are more transportable?
The actual journal article, since NYT didn't bother linking to it: https://www.nature.com/articles/s41586-026-11084-4
There are 2 Nature articles, for the 2 independent teams who have built such nuclear clocks with thorium 229.
This is the other article, from the Chinese team:
https://www.nature.com/articles/s41586-026-11122-1
While both teams have used fluorite crystals doped with Th229, which was the most obvious choice for the active medium, they have used different kinds of optical frequency multipliers in order to generate the ultraviolet light required to probe the thorium nuclei.
For now, the frequency multiplication method used by the Chinese team is superior, allowing a greater output power, which ensures a better signal-to-noise ratio.
The team from Austria intends to use a better frequency multiplier in the future, to increase their output power, and they are evaluating several methods, one of which is the 4-wave mixing in cadmium vapor, already demonstrated by the Chinese team.
It's unfortunately not a case of bothering but rather intent: Keep the user on the site even at cost of quality
I would in general agree with you, but having read through the journal paper: I think the fraction of general audience newspaper readers who could actually read that paper is very low. I come from a science background, spent time dabbling in time and frequency measurement enough to understand some of the concepts, and still found it a painful slog. (I am very much not a physicist!)
I still think it's the right practice for newspapers to always link to the primary source, but in this particular case I understand why they might make an editorial decision not to.
Is there evidence that is the actual reasoning, because I find it ridiculous. People who don’t care about the primary source are not going to follow a link to, e.g., a court ruling, government report, fed minutes, a leaked document, a research paper, etc; but those who are interested are going to immediately leave the site and likely not come back for a long while.
Am I missing something?
3 replies →
To address some of the most pressing open questions in fundamental physics, such as the origin and properties of dark matter...
Owing to unknown nuclear parameters, precise values of these sensitivity factors cannot at present be calculated, but it is predicted that they will exceed those of the most sensitive atomic clock transitions by several orders of magnitude.
So when you achieve FTL, the Vulcans show up.
Who (or what) shows up when you solve the riddle of dark matter?
The Langoliers of course.
According to Wikipedia thorium is probably created from neutron stars or supernovae making it one of the rarest elements in the galaxy. But, it’s quite abundant on Earth, maybe 3x as abundant as Uranium on earths crust. Because of this abundance it is, along with Radon, the primary constituent of earths natural background radiation.
Iron is the last element that can form through a sustaining fusion process. All elements above iron are formed in super nova or neutron star collisions. Specifically gold and platinum are thought to be formed primarily in neutron star collisions
Reality is amazing!!
While it's correct that fusion stops producing energy once the fusion product is iron, it is not true that all elements beyond iron are only produced in cataclysmic events (supernovae / neutron star collisions).
Stars can function as "breeder reactors", where the natural flow of neutrons produced as intermediate / side effect of the various fusion reactions going on in a later-stage-life star get absorbed by nuclei and then (by beta decay) produce beyond-iron elements. This is called the "s-Process" (slow), and responsible for a large range of elements into the Lanthanides or so. And stellar winds, or the planetary nebula stage at the end, will return some of this to the interstellar medium.
It's correct that the heaviest "naturally present" elements require the so-called "r-Process", heavy overabundance of neutrons / extremely high neutron flow as in supernovae, or direct fusion of beyond-iron nuclei as in neutron star collisions.
There is rather active research happening here, both astronomical (trying to detect various nuclei from x ray spectroscopy of cataclysmic events) and theoretical (because r-Process cannot be simulated in labs since the neutron fluxes needed are not within our reach).
That said, it remains true that many "transition groups" elements are bred via s-Process in relatively-ordinary stars.
It is kind of astonishing (well, not really if you think about it - more violent stuff actually happens faster with stars, and energy density was higher in the early universe) that every stable element exists on earth even if some are very rare. That means that earth's materials have had quite a lot of stuff happening to them before forming earth.
This is only approximately correct.
Iron 56 is the isotope with the highest nuclear binding energy per nucleon, so it can form from the fusion of any lighter nuclei.
After iron 56, the binding energy decreases slowly, so the next heavier nuclei can still form from the fusion of certain lighter nuclei, but not from any of them, but only from pairs with a lower average binding energy.
So the following heavier nuclei after iron 56 can still form through fusion, but with increasing atomic mass the probability of their formation decreases quickly, until it becomes negligible.
Relatively large amounts of cobalt, nickel, copper, zinc, gallium and germanium still form through the fusion of lighter elements, but after germanium the amount of chemical elements formed through fusion becomes extremely low. Already the amount of germanium formed through fusion is almost ten thousand times less than the amount of iron.
The binding energy per nucleon decreases very slowly, so even uranium has a higher binding energy per nucleon than helium, so energetically it could form through the fusion of hydrogen or helium, but such an event has a completely negligible probability (because there is a negligible chance for so many hydrogen or helium nuclei to collide simultaneously and if they fuse into nuclei of intermediate mass those block the propagation of the fusion reaction by having higher binding energies than the heavier nuclei).
The elements heavier than germanium form almost only through neutron capture, with the exception of some proton-rich isotopes, which form through collisions with protons. There are several kinds of environments with abundant neutrons where heavy elements can form, where the concentrations of neutrons and their energy distributions are different, so in any of these environments there are different classes of isotopes that form preferentially there.
In a relatively young stellar system like ours, the matter from which the star and the planets have condensed is a mixture of chemical elements coming from different sources.
In environments with extremely high neutron abundances (which include the nuclear explosions on Earth, not only supernova explosions, neutron star collisions and the like), all chemical elements up to fermium (Z = 100) are formed. Nonetheless, while the matter composed of these elements travels through space until the formation of a new stellar system, most of the trans-uranium elements, except the plutonium, decay. When the Solar System was formed, it still contained relatively large amounts of plutonium, not only thorium and uranium, as the heaviest elements, but since then until now the plutonium has decayed, like also most of the uranium 235 that is used now in nuclear reactors.
The nuclear clock uses 229Th though which has an 8000 year half life and does not occur in nature at all.
Yes, it is produced artificially in nuclear reactors, thus it is much more expensive than any natural isotope.
The amount used in a nuclear clock would be very small, but even so, its availability would be a problem.
Wikipedia says that potassium-40 has the largest contribution to background radiation, about 10x as much as thorium: https://en.wikipedia.org/wiki/Environmental_radioactivity
This article says it’s all about the thorium and radon. https://en.wikipedia.org/wiki/Background_radiation
I have no idea which of these articles is more correct.
1 reply →
Where does the potassium come from?
6 replies →
"We are star stuff", Carl Sagan [1]
[1] https://www.youtube.com/watch?v=LNqqFhFa4dI
Much better use than for toothpaste.
https://en.wikipedia.org/wiki/Doramad_Radioactive_Toothpaste
How do they know the accuracy of the clock? Eg: 2s of drift in 65M years.
Naively, measuring that seems more difficult than the clock. Wouldn’t you need a perfect clock as a baseline? There must be something really clever here.
They measured the stability by comparing the nuclear clocks with more stable conventional atomic clocks. In Vienna, they used a commercial single-ion optical clock [1], and in Beijing they used a hydrogen maser (a type of microwave atomic clocks) that was calibrated to the International Atomic Time scale via GNSS satellites.
[1] https://www.toptica.com/products/optical-quantum-clocks/topt...
By adding up the uncertainties of all intermediate measurements they made.
As a parallel, for a regular clock, you'd measure and compute the uncertainties of:
- The distance between the axis of rotation and the center of mass of the pendulum,
- The local acceleration of gravity.
And deduce the pendulum period and its uncertainty by calculus.
In that case I'm not sure you can build (and measure) a pendulum that's more precise than a previous realization of the second (because the meter is defined from the speed of light and the second, and gravimeters probably depend on the definition of the second too).
That's why the definition of base units is carefully chosen to not depend on previous realization. IIRC time is the most fundamental of base units, because other base units depend on it.
You measure precision with frequency combs and relative beat notes against an optical lattice clock
https://unwall.app/www.nytimes.com/2026/10/07/science/first-...
Standard atomic clocks probe outer-shell electrons sensitive to stray EM noise; locking directly to the nucleus is how you actually kill environment drift.
TIL an atomic clock is not a nuclear clock.
the former brings (cesium) atoms, including their electrons, into resonance.
the latter brings (thorium) _nuclei_ into resonance.
both then "just like any clock" measure that oscillation. "simples" ;-)
and I learned "environment" creating drift is temperature, magnetism, anything that influences electrons.
Spot on. Shielding electron transitions from stray thermal and magnetic shifts takes brutal trapping setups. The nucleus provides that isolation for free.
The hope is that with nuclear clocks there will be no need for the very complex single-ion traps or optical lattices required for clocks that use ionic or atomic energy levels.
Even with the atoms of thorium contained in a small crystal, the frequency of their clock transitions should not be influenced by the environment.
Unfortunately, for now no other suitable nucleus has been found, because the frequency corresponding to nuclear energy levels is normally too high for the current or near future technology.
With thorium 229, the potential simplicity of the clock is counterbalanced by the great expense required for producing this artificial isotope.
archived no paywall: https://nonograph.com/in-vienna-and-beijing-the-first-nuclea...
I may be completely ignorant, but aren't these strictly inferior to optical lattice atomic clocks? Maybe they have a better form factor/are more transportable?
https://archive.ph/1PBHj