Physicists are on the brink of redefining time
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Around the world, we are all controlled by the same, invisible force that tells us when to wake up, when to work, and even when to socialize: time. After this past year, the concept of time may seem less real than ever, but according to a team of physicists in Colorado, that couldn’t be further from the truth. The team used three different elements to measure the length of a second.
To date, atomic clocks (which absorb and emit photons at regular frequencies to keep time) are the most accurate way to measure the passage of time in seconds, but their accuracy has been stagnated for more than a decade.
Using both optical fibres and invisible laser transmission of data, the research team measured the meaning of a second more accurately than ever before. They did it by looking at minute (the measure of size, not time) differences between time kept by the atoms — a crucial step toward redefining time itself.
What is time?
Previous attempts to measure these minute differences between how atoms keep time — also referred to the ratio between them — had only ever delivered an accuracy of up to 17 digits.
But now using their new model, which includes the first-ever use of a ‘free-space link’ for this purpose (essentially, laser pulses of data going through the air instead of a cable,) the University of Colorado’s BACON team (Boulder Atomic Clock Optical Network) has now measured this ratio reliably out to 18 digits.
The research was published Wednesday in the journal Nature.
Why it matters
One digit might not make or break a grade on your final exam or even your credit score, but for extremely tiny measurements in physics, this is a big deal.
Rachel Godun is a senior research scientist in the Time and Frequency group at the National Physical Laboratory in the U.K. She wrote an unaffiliated essay on this work also published this week in Nature. She says that the kind of precision demonstrated in this study is literally astronomical.
“Such frequency-ratio measurements are no mean feat, and are equivalent to determining the distance from Earth to the Moon to within a few nanometres,” says Godun in the essay.
The research team reports continued refinement of atomic clock measurements using this model has the potential to redefine the second as we know it and can help physicists test fundamental theories of the universe — including relativity and dark matter — by measuring atomic perturbations even more precisely.
How do we define a second?
Here’s the background.
The first atomic clock began ticking in 1949. It was powered by an ammonia molecule, but a cesium isotope quickly became the standard only a few years after.
Since then, scientists have relied on these incredibly precise clocks, which are largely immune to earthly headaches like earthquakes, to help keep precise time. This measurement is used to not only define time itself, but to guide satellites in orbit via GPS as well.
Such a clock, called the “Master Clock,” resides at the U.S. Naval Observatory (USNO) in D.C. In addition to its role as a historic scientific institution, the USNO is also the residence for the vice president of the United States — meaning it’s where Vice President Kamala Harris will live once renovations are complete.
Historically, atomic clocks have worked used cesium to measure fractions of time by counting the jumps the atoms make between different energy states when exposed to certain radio-wave frequencies. Since 1967, the official definition of a second has been “the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom.”
In other words, there are just over 9 billion cesium energy jumps in one second.
While this method has worked for decades, it is still far from perfect. The oscillation frequency of cesium clocks is in the microwave region of the electromagnetic spectrum (the rainbow that stretches from low energy radio waves to high energy gamma rays and describes all possible frequencies of incoming light.)
Newer designs for atomic clocks instead focus on elements whose frequencies would in the optical spectrum (the part we can see) instead. These frequencies would be 100,000 times faster than the microwave range ones emitted from cesium clocks and in turn 100 times more accurate.
But before scientists can think about replacing the cesium in our atomic clocks, they have to prove that other elements would work even better. That’s what the team in Colorado set out to do.
What they did — To better measure time, the researchers used three elemental clocks:
- an aluminium-ion atomic clock
- one made using ytterbium
- the third using strontium
To take their measurements, the research team set up the aluminium-ion and ytterbium clocks at a National Institute of Standards and Technology lab in Boulder and the strontium clock roughly a mile away at the University of Colorado’s JILA lab.
The idea is to measure how transmitting measurement data between these distances would impact its accuracy. The data was transmitted using both a 2.2-mile long optical fibre and a .9-mile stretch of free-space link communication via laser pulses.
Over several months the team pinged this atomic data back and forth between the institutions (stopping only briefly for a snowstorm) to determine how reproducible and accurate their measurements were. The goal was not to choose the best element for a new atomic clock, but to instead perfect the ways these elements’ time-keeping accuracy was compared. With those new standards established, it would then be possible to find a replacement for cesium.
From their experiments, the research team was able to make the most accurate measurement to date of these ratios between the clocks and also determined that the free-space link provided the same level of uncertainty as the longer, bulkier optical fibre.
“The authors’ demonstration that high accuracy clocks can be connected by free-space links, without needing an optical-fibre infrastructure, is exciting because it opens up possibilities for applications outside the laboratory, such as land surveying,” says Godun.
What’s next
This new research has not yet shaken the longstanding definition of a second, but it has made serious progress toward ushering in a new era of atomic time-keeping. Continuing to refine and test these models could one day soon transform the meaning of a second — improving not only international timekeeping but boosting the accuracy of everything from self-driving cars to your FitBit as well via GPS.
Abstract:
Atomic clocks are vital in a wide array of technologies and experiments, including tests of fundamental physics. Clocks operating at optical frequencies have now demonstrated fractional stability and reproducibility at the 10^−18 level, two orders of magnitude beyond their microwave predecessors. Frequency ratio measurements between optical clocks are the basis for many of the applications that take advantage of this remarkable precision.
However, the highest reported accuracy for frequency ratio measurements has remained largely unchanged for more than a decade. Here we operate a network of optical clocks based on 27Al+ (ref. 6), 87Sr (ref. 7) and 171Yb (ref. 8), and measure their frequency ratios with fractional uncertainties at or below 8 × 10^−18. Exploiting this precision, we derive improved constraints on the potential coupling of ultralight bosonic dark matter to standard model fields.
Our optical clock network utilizes not just optical fibre, but also a 1.5-kilometre free-space link. This advance in frequency ratio measurements lays the groundwork for future networks of mobile, airborne and remote optical clocks that will be used to test physical laws, perform relativistic geodesy and substantially improve international timekeeping.
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Herb Rose
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If time varies with velocity and gravity why are they trying to measure so precisely a variable?
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Jerry Krause
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Hi Herb,
I agree with your comment but I would write: Why are they ignoring Heisenberg’s UNCERTAINTY PRINCIPLE???
Have a good day, Jerry
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T. C. Clark
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Uh, to have a standard…for comparison purposes…for research purposes …. just like there is a standard one meter length…one gram weight…..one liter volume.
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Ken Hughes
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Here we go again, yet another article asking the question “What IS time?”, but never getting close to answering it. I have never seen any article, post, or paper defining what time IS.
Time is a process, the process of evolution of any system, and the rate of this process can vary with your speed or proximity to massive objects. Now there’s two very good clues needing investigation to get some idea of WHAT time is, but no one, it seems, has even made an attempt in over a century !
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Robert Beatty
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From Futurism: “In 2013, a group of researchers working out of France took the measurement of the gravitational constant, using the same machine that they’d used some 2 years earlier. Improvements were made on the machine to improve the sensitivity and give a more accurate result. The machine, which uses two independent methods to calculate the constant, averages the results of the two. This, in theory, should help reduce systematic errors. What did they find? A different result!”
So if G varies why would not time vary? The logic here is if the value for G changes, because the Gravitational Field Strength varies, then time should also vary with GFS. My relationship between time dilation and G is given by: Time Dilation T = 1/G
See https://principia-scientific.com/publications/PROM/PROM-Beatty-Gravispheres.pdf
If time can be measured to 18 decimal places at a specific time and place on earth, then G’s accuracy should be similarly available. But if the time can be shown to be changing over a period, this will prove that G is not a constant either.
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Herb Rose
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Hi Robert,
According to current theory gravity is a function of both mass and distance and is affected by the mass and distance of other objects. This would mean that gravity and the size of time would continually change depending on time of day (position of the sun), month (position of the moon), the position of the planets, and the position of the solar system in the galaxy. Every measurement of time and G would be different. According to Einstein the only constant is the speed of light but because both the size of time and the size of a unit of distance vary you can never know the value of that constant or any other constant (like pi).
As I’ve said before, time is just a unit (like a meter or gram) created to provide a common reference of the energy (rate of change) of objects, just as a meter or a gram provides an artificial common reference for the physical characteristics of objects.
Herb
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Robert Beatty
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Hi Herb,
T.C. Clark says it best.
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Robert Beatty
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Hi Herb,
You state: “According to current theory gravity is a function of both mass and distance and is affected by the mass and distance of other objects. This would mean that gravity and the size of time would continually change depending on time of day (position of the sun), month (position of the moon), the position of the planets, and the position of the solar system in the galaxy”
IMO gravity is caused by the concentration of Gravitons associated with the local solar system material. That concentration is very slow to change, because it is a function of the distance to the barycentre of our Gravisphere, as previously discussed. Does this make sense to you?
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Herb Rose
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Hi Robert,
I believe that energy1/Gravitons are attracted to positive matter (protons) and create the compression force (strong nuclear force) that holds the nucleus of the atom together, overcoming the repelling electric force between protons. This force radiates out from the nucleus (unlike the strong nuclear force which magically stops) and becomes the attractive gravity and magnetic (directional force) fields which decrease with distance as the concentration of energy1/gravitons decrease. The barycenter is the point between two objects where the attractive force/concentration between the two objects are equal.and there may be no matter there, as in the case of binary asteroids. What would cause your gravitons to concentrate there?
Herb
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Robert Beatty
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Hi Herb,
“The barycenter is the point between two objects where the attractive force/concentration between the two objects are equal.and there may be no matter there, as in the case of binary asteroids. What would cause your gravitons to concentrate there?”
Good question. Gravitons, according to QM theory, attach to elements with equal numbers of neutrons and protons. See https://bosmin.com/PSL/NEGATRONS.pdf page 9.
This is similar to magnetic fields only being present in elements having magnetic properties.
So Gravitons can attach to a much wider range of elements than magnetism, and provides the attractive property between mass we know as gravity. It seems the concentration of Gravitons follows an inverse square relationship from the centre of our Gravisphere – at black hole V616.
Our understanding of magnetism, gravity, and entangled particles is still very basic, but we seem to be on the right track.
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Herb Rose
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Hi Robert,
The only atom I am aware of that has equal number of protons and neutrons is deuterium.with one of each. All atoms have magnetic fields associated with them, that is how molecules are held together and atoms emit light (electromagnetic waves). In some cases we cannot detect them because the magnetic force is internal rather than radiated. When you force the similar poles of two magnets together the radiated magnetic field disappears as the internal repelling force increases.It is opposite to the electric force where when you force two electrons together the radiated negative field increases.
Hrrb
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Robert Beatty
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Hi Herb,
Of the 59 Graviton amenable elements listed on referenced page 9, the lightest is Helium with an atomic number of 2 being two protons with He isotopes possible including one or two neutrons.
Otherwise, the number of protons and neutrons are calculated by assuming one of each makes up one pair. Deuterium only has one pair of proton with a neutron, thereby excluding it from the QM Graviton association. Molecules can also produce pairs which extends the range of Graviton associated mass particles indefinitely.
Do your comments about magnetism have any basis QM theory?
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Herb Rose
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Hi Robert,
My comments on magnetism are a result of experiment.
If you place a permanent magnet, M1, on a scale and fix another magnet, M2, above it, you will lift some of the weight of M1 off the scale, When you position another magnet, M3, over the lifting magnet, M2, with like poles facing each other, the lifting power of the magnet, M2, decreases and the weight of the magnet on the scale, M1, increases as M2 and M3 approach each other. This shows the radiated magnetic field of M2 is deceasing as the repelling force (internal force) between M2 and M3 increases..
Herb
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Herb Rose
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Hi Robert,
I will take this opportunity to explain why I don’t believe that a neutron is a neutral subatomic particle but a subatomic molecule formed from a proton and electron with both a positive and negative charge. Perhaps you can answer the question I have asked others and never gotten an answer.
Beta decay is where the nucleus of an atom emits an electron and gamma radiation and the atomic number (number of protons) increases by one, creating a positive ion of the next larger element. First question: If the creation of the proton is the changing of one quark from an up to a down eliminating a neutron, where does the electron come from?
When a neutron is not within a nucleus it will spontaneously split into an electron, a proton, and gamma radiation in ten minutes. Second question: Since this is an energy producing reaction and the creation of a neutron by the combining of an electron and a proton to form a neutron is also an energy producing reaction, how does this not violate the first law of thermodynamics?
Herb
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