A rock is a clock: Physicists use matter to measure time

Jan 10, 2013
A rock is a clock: Physicist uses matter to tell time
Quantum mechanically, mass can be used to measure time and vice versa. Credit: Holger Müller lab

What is the simplest, most fundamental clock? Physicist Holger Müller and his UC Berkeley colleagues have shown that a single atom is sufficient to measure time using its high-frequency matter wave. Conversely, the frequency of matter can be used to define its mass. The feat is a fundamental demonstration of wave-particle duality central to quantum mechanics.

Ever since he was a kid growing up in Germany, Holger Müller has been asking himself a fundamental question: What is time?

That question has now led Müller, today an associate professor of physics at the University of California, Berkeley, to a fundamentally new way of measuring time.

Taking advantage of the fact that, in nature, matter can be both a particle and a wave, he has discovered a way to tell time by counting the oscillations of a matter wave. A matter wave's frequency is 10 billion times higher than that of visible light.

"A rock is a clock, so to speak," Müller said.

In a paper appearing in the Jan. 11 issue of Science, Müller and his UC Berkeley colleagues describe how to tell time using only the matter wave of a . He refers to his method as a Compton clock because it is based on the so-called Compton frequency of a matter wave.

"When I was very young and reading science books, I always wondered why there was so little explanation of what time is," said Müller, who is also a guest scientist at Lawrence Berkeley National Laboratory. "Since then, I've often asked myself, 'What is the simplest thing that can measure time, the simplest system that feels the passage of time?' Now we have an upper limit: one single massive particle is enough."

While Müller's Compton clock is still 100 million times less precise than today's best , which employ aluminum ions, improvements in the technique could boost its precision to that of atomic clocks, including the cesium clocks now used to define the second, he said.

"This is a beautiful experiment and cleverly designed, but it is going to be controversial and hotly debated," said John Close, a at The Australian National University in Canberra. "The question is, 'Is the Compton frequency of atoms a clock or not a clock?' Holger's point is now made. It is a clock. I've made one, it works."

Müller welcomes debate, since his experiment deals with a basic concept of quantum mechanics – the wave-particle duality of matter – that has befuddled students for nearly 90 years.

"We are talking about some really fundamental ideas," Close said. "The discussion will create a deeper understanding of quantum physics."

Müller can also turn the technique around to use time to measure mass. The reference mass today is a platinum-iridium cylinder defined as weighing one kilogram and kept under lock and key in a vault in France, with precise copies sparingly dispersed around the world. Using Müller's matter wave technique provides a new way for researchers to build their own kilogram reference.

De Broglie's "crazy" idea

The idea that matter can be viewed as a wave was the subject of the 1924 Ph.D. thesis by Louis de Broglie, who took Albert Einstein's idea that mass and energy are equivalent (E=mc2) and combined it with Ernst Planck's idea that every energy is associated with a frequency. De Broglie's idea that matter can act as a wave was honored with the Nobel Prize in Physics in 1929.

Using matter as a clock, however, seemed far-fetched because the frequency of the wave, called the Compton, or de Broglie, frequency, might be unobservable. And even if it could be seen, the oscillations would be too fast to measure.

Müller, however, found a way two years ago to use to confirm Einstein's gravitational redshift – that is, that time slows down in a gravitational field. To do this, he built an atom interferometer that treats atoms as waves and measures their interference.

"At that time, I thought that this very, very specialized application of matter waves as clocks was it," Müller said. "When you make a grandfather clock, there is a pendulum and a clockwork that counts the pendulum oscillations. So you need something that swings and a clockwork to make a clock. There was no way to make a clockwork for matter waves, because their oscillation frequency is 10 billion times higher than even the oscillations of visible light."

One morning last year, however, he realized that he might be able to combine two well-known techniques to create such a clockwork and explicitly demonstrate that the Compton frequency of a single particle is, in fact, useful as a reference for a clock. In relativity, time slows down for moving objects, so that a twin who flies off to a distant star and returns will be younger than the twin who stayed behind. This is the so-called twin paradox.

Similarly, a cesium atom that moves away and then returns is younger than one that stands still. As a result, the moving cesium matter wave will have oscillated fewer times. The difference frequency, which would be around 100,000 fewer oscillations per second out of 10 million billion billion oscillations (3 x 1025 for a cesium atom), might be measurable.

In the lab, Müller showed that he could measure this difference by allowing the matter waves of the fixed and moving cesium atoms to interfere in an atom interferometer. The motion was caused by bouncing photons from a laser off the cesium atoms. Using an optical frequency comb, he synchronized the laser beam in the interferometer with the difference frequency between the matter waves so that all frequencies were referenced solely to the matter wave itself.

"Our clock is accurate to within 7 parts per billion," he said. "That's like measuring one second out of eight years, about as good as the very first cesium atomic clock about 60 years ago. Maybe we can develop it further and one day define the second as so many of the Compton frequency for a certain particle."

Müller's proposal to make a mass standard based on time provides a new way to realize plans by the international General Conference on Weights and Measures to replace the standard kilogram with a more fundamental measure. It will involve an incredibly pure crystal of silicon, dubbed an Avogadro sphere, which is manufactured so precisely that the number of atoms inside is known to high accuracy.

"Our clock and the current best Avogadro spheres would make one of the best realizations of the newly defined kilogram," he said. "Knowing the ticking rate of our clock is equivalent to knowing the mass of the particle, and once the mass of one atom is known, the masses of others can be related to it."

And what about the question, What is time? Müller says that "I don't think that anyone will ever have a final answer, but we know a bit more about its properties. Time is physical as soon as there is one massive particle, but it definitely is something that doesn't require more than one massive particle for its existence. We know that a massless particle, like a photon, is not sufficient."

Müller hopes to push his technique to even smaller particles, such as electrons or even positrons, in the latter case creating an antimatter . He is hopeful that someday he'll be able to tell using quantum fluctuations in a vacuum.

Müller's coauthors are post-doctoral fellows Shau-Yu Lan, Michael A. Hohensee and Damon English; graduate students Pei-Chen Kuan and Brian Estey; and Miller Postdoctoral fellow Justin M. Brown. All are in UC Berkeley's Department of Physics. The work was supported by the Alfred P. Sloan Foundation, the David and Lucile Packard Foundation, the National Institute of Standards and Technology, the National Science Foundation and the National Aeronautics and Space Administration.

Explore further: Rice physicist emerges as leader in quantum materials research

More information: "A Clock Directly Linking Time to a Particle's Mass," by S.-Y. Lan et al., Science, 2013.

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User comments : 19

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tadchem
5 / 5 (3) Jan 10, 2013
What we call a 'particle' or a 'wave' is actually only our interpretation of the observations we make on an object. The object itself is something that can appear to have the properties of either.
The closest analogy to an object in mathematics is a tensor field. Depending on which operators are applied to the tensor various properties of the tensor can be 'extracted' according to interactions with other 'objects.' These may be particle properties or wave properties, depending on the operator applied (mass, charge, frequency, wavelength, etc.) If two different operators commute, then the properties each represents can be independently determined. As is often the case, if the operators do not commute, the properties cannot be determined independently - à la Heisenberg's Unbestimmtheit.
Tausch
1 / 5 (2) Jan 10, 2013
We know that a massless particle, like a photon, is not sufficient." - author


Let there be light.
And low and behold it was insufficient.

Ice breaker for hot debate.
vacuum-mechanics
1 / 5 (8) Jan 10, 2013
Taking advantage of the fact that, in nature, matter can be both a particle and a wave, he has discovered a way to tell time by counting the oscillations of a matter wave. A matter wave's frequency is 10 billion times higher than that of visible light.
"A rock is a clock, so to speak," Müller said.

This seems be a great idea, anyway the problem is that nowadays conventional quantum mechanics still cannot explain the how matter can be both a particle and a wave work! Understand the mechanism (below) could give us more confident about the idea mentioned.
http://www.vacuum...17〈=en
nuge
5 / 5 (1) Jan 10, 2013
Now we have an upper limit: one single massive particle is enough


I hate to be "that guy", but technically we've always had the upper limit. It's the lower limit that would be pretty fundamentally interesting.
AmritSorli
2 / 5 (4) Jan 11, 2013
Time is the only physical quantity which has no material existence. Time we measure with clocks is only a mathematical quantity, namely a numerical order of material change.
http://physicsess...xt=sorli

Torbjorn_Larsson_OM
3.7 / 5 (3) Jan 11, 2013
As long as they use different clocks to measure time and mass...

@AmritSorli: That is what Dennett calls a deepity.

We don't have a complete understanding of time, but we have plenty of physical measures, material existence, of time in the form of clocks and more generically processes.

In Susskind's form of eternal inflation, the asymmetry of time comes from symmetry breaking when inflation proceeds into terminal vacuum sinks. This is then a complete prediction of time (clocks/processes, asymmetry, causality).

@vm, AmritSorli, natello: This is a science website, not a place for crackpot ideas, you have your own sites for that. Also, the very first comment describes how one can predict particles and wavelike behavior out of quantum field. Also, aether was rejected over a century ago.
prof-art
not rated yet Jan 11, 2013
Possibly this may never have the best accuracy for clocks, due to the extreme difficulty of holding an atom still...

Great concept, brilliant idea!! I really like it!
ValeriaT
1 / 5 (1) Jan 11, 2013
the asymmetry of time comes from symmetry breaking when inflation proceeds into terminal vacuum sinks
I'll keep the dense aether model concept for myself, as it sounds far less crackpotish, than "terminal vacuum sinks".. Anyway, it's definitely not accepted more, than whatever aether stuff of mine. In dense aether model the time is asymmetric by its definition with gradient of space-time.
PhyOrgSux
1 / 5 (3) Jan 11, 2013
so since matter "is" a "wave" perhaps it is possible to create a matter cloak for it? A cloak that is invisible to all(?) matter would be able to pass through matter, I would think.
Sean_W
1 / 5 (3) Jan 12, 2013
Is this related:
http://phys.org/n...806.html
?
Mass and time converting to length and space.
ValeriaT
1 / 5 (2) Jan 12, 2013
No, until you want to hear the opposite..;-)
Sean_W
1 / 5 (3) Jan 12, 2013
http://arxiv.org/ftp/arxiv/papers/1007/1007.1750.pdf, until you want to hear the opposite..;-)


Too bad. I was hoping to convert some of my mass into time so I could live longer and length so I could... Uh, never mind.
jartsa
not rated yet Jan 12, 2013
The frequency of the cecium atom increased by the same amount that the frequency of the photon that pushed the cecium atom decreased.

A Compton wave is not a clock, because Compton waves are waving rapidly in a fast moving space ship, while clocks are running slowly in a fast moving space ship.
ValeriaT
1 / 5 (2) Jan 13, 2013
Have our fundamental theories got time right? Does size really matter? Or is physics all in the eyes of the beholder? Right about time?
ValeriaT
1 / 5 (2) Jan 13, 2013
A Compton wave is not a clock, because Compton waves are waving rapidly in a fast moving space ship, while clocks are running slowly in a fast moving space ship.
It's just manifestation of time arrow duality. The duality of entropic time arrow is considered in many contemporary theories and it follows from the definition of space-time as a density gradient of particle environment. In dense aether model we as a human observers are living at the anthropocentric boundary of two time arrows: relativistic and quantum mechanics one. The objects larger than the wavelength of CMBR are collapsing with gravity and their entropy decreases. The smaller objects tend to evaporate with pressure of radiation instead. The same duality exists at all scales at the local space-time density gradients of aether: inside of particles the relativistic time arrow exists in form of quantum wave, outside of them is running backward as a Compton wave.
Moebius
1 / 5 (2) Jan 13, 2013
This is why our understanding of time is wrong. Time doesn't slow down near a black hole, just the clocks do.
ValeriaT
1 / 5 (2) Jan 13, 2013
More exactly the clocks based on motion of vacuum OUTSIDE of particles. The clocks based on motion of vacuum INSIDE of massive particles will accelerate instead. This dichotomy can be perceived as a testable consequence of so-called complementarity of black holes. Recently a theory based on this duality has been proposed - it predicts, that in higher gravity field the electronic transitions within atoms will be accelerated, because the energy of fundamental quantum state will be lowered there.

It's easy to imagine it with dense aether model. Inside of dense vacuum around black hole all phenomena mediated with transverse waves will run slower, because of slower energy transfer. But because the more dense vacuum balances the density of vacuum inside of particles, the phenomena mediated with longitudinal waves (radioactive decay) will run faster instea
rkolter
not rated yet Jan 15, 2013
A Compton wave is not a clock, because Compton waves are waving rapidly in a fast moving space ship, while clocks are running slowly in a fast moving space ship.


wait...

Are you saying that if I took a compton clock and an atomic clock of equal accuracy, put them on a space ship, verified they were set to the same time, and launched the ship, when it returned, the compton clock would read a dramatically different time than the Atomic clock?
jartsa
not rated yet Jan 17, 2013

wait...

Are you saying that if I took a compton clock and an atomic clock of equal accuracy, put them on a space ship, verified they were set to the same time, and launched the ship, when it returned, the compton clock would read a dramatically different time than the Atomic clock?


Yes.

The Berkeley guys say that cesium atom that took a trip resembles a cesium atom that spent some time downstairs.

I say it resembles a cesium atom that spent some time upstairs.

Maybe the Berkeley physicists should check which way it is. They have already experimented with gravitational time dilation of compton clocks.