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How to make a nuclear clock tick

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While not primarily useful for telling the time, nuclear clocks could allow scientists to test humankind’s fundamental understanding of how reality works.

By Caleb Davies

Thorsten Schumm is a clockmaker, but not the kind who sits at a workbench covered with springs and cogs, a magnifying loupe jammed into one eye. No, he is making a timepiece that is in an entirely different league.

Atomic clocks may sound familiar enough – but if Schumm’s research goes to plan, it could result in a nuclear clock. And far from just telling the time, it could help crack some of the universe’s most closely guarded secrets.

‘This is still a dream,’ said Schumm, a professor at the Vienna University of Technology in Austria. ‘No one knows how to do it.’

He intends to change that and, in the process, to shed light on some of the fundamental forces of nature.

Split second

A clock can be based on anything that oscillates at regular intervals and can be read. The first clocks were mechanical. Many wristwatches today use the electromechanical oscillations of a quartz crystal.

But clock technology moved up a gear in the 1950s with the advent of atomic clocks.

Atoms are made up of a nucleus surrounded by an orbiting cloud of electrons. The tick of an atomic clock depends on the “quantum transitions” these electrons make.

It works like this. Electrons can absorb a packet of energy, which moves them from a “ground state” to an “excited state” of higher energy. Then they can fall back to the ground state, releasing that packet of energy on their way down.

These energy transitions occur with a particular frequency that can be used for timekeeping. This all happens astonishingly fast.

For instance, one second is officially defined as 9 192 631 770 oscillations of an energy packet that excites a caesium-133 atom. Atomic clocks are so precise because they produce an awful lot of oscillations, or ticks. So, if the readout mechanism misses one or two of them, it generally isn’t much of a problem when there are more than 9 billion per second.

Nuclear clocks are different. The tick wouldn’t depend on electrons but rather on the vibrations of the nucleus itself. These are many times faster than the ticks of the electron transitions.

But, as Schumm says, work continues on getting a nuclear clock up and running.

Happy coincidence

He got interested in solving this nuclear mystery partly out of serendipity.

It turns out that a rare isotope of the element thorium-229 is by far the easiest material from which a nuclear clock might be built. That’s because it is thought to have the slowest ticks of any nucleus. Plus, the institute where Schumm works is one of the few places that can access this material.

Thorium-229 isn’t naturally occurring. It is produced only through the nuclear decay of certain types of uranium. The Vienna University of Technology has an agreement with Oakridge National Laboratory in the US that allows it to obtain some thorium-229 from leftover uranium used in nuclear tests decades ago. It wasn’t lost on Schumm that his first name and the name of the element are both derived from the mythical Norse god, Thor. ‘That tickled me,’ he said.

It’s about time

Since 2020, Schumm has been conducting basic research on creating a nuclear clock under the EU-funded ThoriumNuclearClock project running until early 2026.

He and his colleague Professor Ekkehard Peik of Germany’s National Metrology Institute in Braunschweig share the project’s role of principal investigators, along with Marianna Safronova from the University of Delaware in the US and Peter Thirolf from LMU Munich in Germany.

To set a nuclear clock ticking, it needs a nudge with a laser set to exactly the right energy level. But for most nuclei, the energy frequency required is nowhere near accessible with current laser technology.

Thorium-229 is one of the largest stable nuclei that exist. It was thought it could adopt a state with a very low energy that current lasers could reach – though no one really understands how or why it does this.

‘To begin with, it wasn’t even really clear that this state of thorium-229 existed,’ said Schumm.

Now it’s known that it does exist. In 2020, Schumm and his colleagues published a measurement of the isotope’s energy level. Since then, they have continued to build on that knowledge. All of that opens the way to testing the clock for real. Schumm and his fellow researchers have been working on building a laser that is custom-designed to tickle the thorium at exactly the right frequency. Soon they plan to direct this laser at some trapped thorium atoms for the first time in a bid to start them ticking.

‘We are very excited about the outcome of this experiment because it is something that has never been done before,’ said Peik. ‘We and others have tried related experiments with thorium-229 in the past without success. This time we feel we are much better prepared.’

Crystal clear

For those experiments, the thorium atoms will be held in atomic traps – a very finicky business. So, while ThoriumNuclearClock was already under way, Schumm also lead a two-year EU-funded project called CRYSTALCLOCK, which aimed to develop a simpler design and readout mechanism for a nuclear clock.

The idea here was to grow a crystal consisting of calcium fluoride and have a scattering of thorium-229 atoms distributed through the material. This provides a solid material that is far easier to work with than the atomic traps.

Schumm and his colleagues, including Dr Tomas Sikorsky, published a paper demonstrating that these thorium-doped crystals could be grown in 2022. The next step will be to start working out how the tick of these crystals can be read.

Schumm says that a technique called nuclear tomography could be adapted for this purpose and the whole process would be much easier than using thorium atoms in traps.

Forces of nature

This is worth all the bother not because more precise clocks are needed but rather because humankind’s fundamental understanding of how reality works can be tested.

The best theories of physics explain that the universe has four fundamental forces: gravity, electromagnetism, the weak nuclear force and the strong nuclear force. The strength of these forces is known and those numbers are often referred to as fundamental “constants”.

But it isn’t know whether the strength of these forces has been, and will always be, the same. There are indications that the forces were much stronger in the distant past, close to the Big Bang, and they may even still be changing by the merest amount.

Atomic and nuclear clocks may make it possible to put that to the test. The tick of an atomic clock is predominantly affected by the strength of electromagnetism, so if the speed of the tick began to change that would suggest a drift in the underlying force.

However, electromagnetism is very weak, so atomic clocks, despite their breathtaking precision, may never be able to pick up any change to it.

Nuclear clock ticks are, by contrast, influenced by the strong force. So, if and when a working nuclear clock were to be created, it could be used to monitor whether there are any changes to the strong force over periods of time.

‘Going from atoms to nuclei isn’t about getting a better clock,’ said Schumm. ‘In fact, it’s likely that the first nuclear clock won’t be as good as the best atomic clocks. The point is more about having a completely new kind of technology that could basically test the strong force.’

Research in this article was funded via the EU’s European Research Council and the Marie Skłodowska-Curie Actions (MSCA). This article was originally published in Horizon, the EU Research and Innovation Magazine. 

World News

TIME: Will China create a better world?

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China is everywhere in global politics. China is “ubiquitous,” a retired Senior Colonel Zhou Bo of China’s PLA told in a conversation with TIME magazine. On March 10, in an agreement brokered by Beijing, Iran and Saudi Arabia agreed to normalize relations, after seven years of bitter rivalry in a deal that sidelined the U.S. Earlier, on February 24, China put forward a 12-point proposal for peace in Ukraine. On March 20, President Xi Jinping arrived in Moscow, where he discussed the situation in Ukraine with Vladimir Putin.

Senior Colonel Zhou Bo spoke about what the “watershed moment” means for China and the world. He said:

– For Beijing, the war in Ukraine is a trigger for new security arrangements in Europe that will have to be made before peace returns. China’s proposal on peace in Ukraine is a big step forward. The success on mediation between Iran and Saudi Arabia will encourage China to make more proposals, but the challenge is always to find road maps. With reform and opening up, as Deng Xiaoping said, China was trying to get across the river by feeling the stones on the riverbed, but now China is entering the ocean.

– We are talking about Global China. When Boris Johnson talked about Global Britain, it was probably more rhetorical. But Global China is definitely real. China is ubiquitous. China’s influence is everywhere. The PLA’s operations overseas are carefully chosen to be humanitarian in nature, but as your strength grows, people have higher expectations for you. We are talking about the world. This is the ocean we are wading in.

– China does have some sympathy with Russia on how this war came about because of NATO expansion, despite NATO’s promises on no expansion from time to time. China understands why Russia is resentful. When China stresses sovereignty must be respected, it also tries to look at it from a more comprehensive perspective. Countries like South Africa, Brazil, or India are taking similar positions like China on this.

– There is no doubt that China wants to see a ceasefire because China’s interests were damaged in Europe. Because of China’s neutrality, China’s relations with Western capitals have soured. This is ludicrous because China has nothing to do with this war.

– It does not make any sense that China, which has not provided weapons to Russia since the outbreak of the war, would change its mind, especially at a time when they have actually announced a peace plan. Why would Antony Blinken say that? By saying it, Blinken was actually giving a pre-emptive warning because China providing military support would be the worst fear of the U.S. But it’s totally impossible.

– The American presence in the region is not as strong as before, but the U.S. will not go away. But on this issue China is doing what the U.S. cannot do. Why? Because the U.S. doesn’t even have diplomatic relations with Iran. It cannot become a mediator between the two sides. The U.S. has allies in the region. It has to adopt double standards. Therefore, China can do a better job, but this is not an attempt to replace the U.S.

– If there were a war between Saudi and Iran, this would damage China’s interests, both economic interests and energy security, profoundly. So China needs to prevent a war and that may explain its new role.

– China depends on energy imports from the Middle East, which make up 40-50% of Chinese energy imports. We are trying to diversify, but that is the situation for now… At the same time, China’s activity in the Middle East now comprises almost everything, from building infrastructure to launching satellites to energy imports, therefore its stake on peace and stability in the Middle East has become higher.

– This is the first time China becomes directly involved in regional security. The biggest question of the 21st century is, if China’s rise is inevitable, will China create a better world? My answer is, at least it can make a safer world. At least it will make much less harm than the U.S.

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World News

War in Ukraine: Congress adopts a declaration of condemnation

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Image source: Czech Presidency

The Congress of Local and Regional Authorities of the Council of Europe unanimously adopted on 21 March 2023 a Declaration to mark the one-year anniversary of Russia’s war against Ukraine, presented by the Congress President and Rapporteur on The Russian Federation’s war against Ukraine, Leendert Verbeek (Netherlands, SOC/G/PD).

President Verbeek said that the Congress declaration is a clear message of condemnation of this brutal war and a strong reaffirmation of the Congress’ unwavering solidarity with Ukraine, its people and communities : “we must continue to show our Ukrainian friends, colleagues and peers – the elected leaders that are engaged in a battle for their lives, their citizens, their towns and their futures – that they are NOT forgotten and that we will do everything in our power now, and in the future, to support them.” President Verbeek also stressed that the declaration reiterated the Congress’ resolute support for Ukraine’s sovereignty, political independence and territorial integrity within its internationally recognised borders.

The debate was preceded by a video message from the Ukrainian Commissioner for Human Rights, Dmytro Lubinets. “The solidarity of our partners strengthens the stability of our resistance to the aggressor and our strong confidence in victory”, he underlined while speaking about the difficult humanitarian situation in Ukraine. He also stressed the importance of mechanisms for the protection of citizens’ rights on the local level for everybody. He described how his office was implementing this approach by opening representative offices of the Commissioner in each region.

In his speech, the Congress President praised the “extraordinary courage and resilience of the Ukrainians and their leadership as they relentlessly defend their country at the frontline and the home front. “The Congress commends the solidarity and unity of Europeans, their cities and regions. We call on all to continue to mobilise and provide large-scale financial, security and humanitarian assistance to their Ukrainian counterparts”, he highlighted.

During the debate, Congress members supported the creation of a special international tribunal for the crime of aggression against Ukraine and the setting up of an international compensation mechanism for the injury, damage and loss incurred by the State of Ukraine as well as natural and legal persons in Ukraine. “It is imperative to hold Russia accountable for all crimes and justice must be done for all the victims.”, stressed President Verbeek.

“The Congress stands by the Ukrainian people at this historically decisive time for Ukraine and the world and believes in a common, democratic future based on respect for international law and a just peace.”, he concluded.

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World News

The strategic situation in the Persian Gulf region has dramatically changed

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photo: Xinhua/Liu Weibing

The China-brokered Saudi-Iranian normalisation of diplomatic relations. What has happened is an epochal event, writes M.K. Bhadrakumar, Indian Ambassador and prominent international observer.

Henry Kissinger drew the analogy of his own accomplishment in an extraordinary diplomatic career when, as Secretary of State in the Richard Nixon administration, he helped achieve rapprochement with Beijing amidst its tensions with Moscow.

One aspect of the Saudi-Iranian deal that has implications for India’s immediate external environment is that the strategic situation in the Persian Gulf region, India’s extended neighbourhood, has dramatically changed.

This can only be seen as the culmination of a series of repositioning on the part of the regional states that have been underway in the regional politics, as they increasingly took to diversifying their foreign policies away from the preponderant dependency on the West historically, and steadily and unmistakably began asserting their strategic autonomy with a newfound self-assuredness — be it Saudi Arabia, the UAE, Egypt or Turkey.

Today, Israel stares at strategic isolation in its region and America, its mentor-cum-benefactor-cum-guardian-cum-protector, stands diminished.

Kissinger noted that ‘China has in recent years declared that it needs to be a participant in the creation of the world order. It has now made a significant move in that direction.’

Of course, Chinese President Xi Jinping himself stated last week that Beijing should ‘actively participate in the reform and construction of the global governance system’ and promote ‘global security initiatives’.

India cannot but be wary that the Biden administration’s main thrust is military deterrence fuelling an Asian arms race, with which India can identify only at the risk of grave consequences.

NATO’s defeat in Ukraine will seriously damage the transatlantic system and the US’ hopes that casting China as enemy might rally Europe are unrealistic. Besides, the China-Russia quasi-alliance will resist. Should India get sucked into the maelstrom?

The US strategies seriously impact peace and stability in the Indo-Pacific, as they are anchored on bloc politics and confrontation, and their self-serving geopolitical agenda is to create a NATO-replica in the Asian continent.

The Anglo-Saxon clique known as AUKUS — comprising the US, Britain and Australia—opens a Pandora’s box as other countries will likely follow suit, which will seriously impact the international nuclear non-proliferation regime and even lead to its collapse. Will that serve Indian interests?

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