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  • richardmitnick 2:19 pm on May 24, 2019 Permalink | Reply
    Tags: ACES clock: French space agency engineers working on the Pharao atomic space clock., Atomic Clocks, Comparing time down to a stability of hundreds femtoseconds – one millionth of a billionth of a second – requires techniques that push the limits of current technology., Einstein-Eddington eclipse experiment, , Pound-Rebka experiment first measured the redshift effect induced by gravity in a laboratory   

    From European Space Agency: “Clocks, gravity, and the limits of relativity” 

    ESA Space For Europe Banner

    From European Space Agency

    1

    23 May 2019

    The International Space Station will host the most precise clocks ever to leave Earth. Accurate to a second in 300 million years the clocks will push the measurement of time to test the limits of the theory of relativity and our understanding of gravity.

    Albert Einstein’s general theory of relativity predicted that gravity and speed influences time, the faster you travel the more time slows down, but also the more gravity pulling on you the more time slows down.

    On 29 May 1919 Einstein’s theory was first put to the test when Arthur Eddington observed light “bending” around the Sun during a solar eclipse.

    Eddington/Einstein exibition of gravitational lensing solar eclipse of 29 May 1919

    Forty years later, the Pound-Rebka experiment first measured the redshift effect induced by gravity in a laboratory – but a century later scientists are still searching for the limits of the theory.

    Pound-Rebka Experiment

    “The theory of relativity describes our Universe on the large scale, but on the border with the infinitesimally small scale the theory does not jibe and it remains inconsistent with quantum mechanics,” explains Luigi Cacciapuoti, ESA’s Atomic Clock Ensemble in Space (ACES) project scientist. “Today’s attempts at unifying general relativity and quantum mechanics predict violations of the Einstein’s equivalence principle.”

    Einstein’s principle details how gravity interferes with time and space. One of its most interesting manifestations is time dilation due to gravity. This effect has been proven by comparing clocks at different altitudes such as on mountains, in valleys and in space. Clocks at higher altitude show time passes faster with respect to a clock on the Earth surface as there is less gravity from Earth the farther you are from our planet.

    Flying at 400 km altitude on the Space Station, the Atomic Clock Ensemble in Space will make more precise measurements than ever before.

    Internet of Clocks

    3
    ACES clock: French space agency engineers working on the Pharao atomic space clock. Pharao is part of the Atomic Clock Ensemble in Space, ACES, that will fly to the International Space Station. Pharao is accurate to a second in 300 million years. This will allow scientists to test fundamental theories first proposed by Albert Einstein to an accuracy that is impossible in laboratories on Earth. The final 375 kg experiment will be installed on a platform outside Europe’s Columbus space laboratory. Credit CNES

    ACES will create an “internet of clocks”, connecting the most accurate atomic timepieces the world over and compare their timekeeping with the ones on humankind’s weightless laboratory as it flies overhead.

    Comparing time down to a stability of hundreds femtoseconds – one millionth of a billionth of a second – requires techniques that push the limits of current technology. ACES has two ways for the clocks to transmit their data, a microwave link and an optical link. Both connections exchange two-way timing signals between the ground stations and the space terminal, when the timing signal heads upwards to the Space Station and when it returns down to Earth.

    The unprecedented accuracy this setup offers brings some nice bonuses to the ACES experiment. Clocks on the ground will be compared among themselves providing local measurements of geopotential differences, helping scientists to study our planet and its gravity.

    The frequencies of the laser and microwave links will help understand how light and radio waves propagate through the troposphere and ionosphere thus providing information on climate. Finally, the internet of clocks will allow scientists to distribute time and to synchronise their clocks worldwide for large-scale Earth-based experiments and for other applications that require precise timing.

    “The next generation of atomic clocks and the link techniques that we are developing could one-day be used to observe gravitational waves themselves as ESA’s proposed LISA mission,” adds Luigi, “but right now ACES will help us test as best we can Einstein’s theory of general relativity, searching for tiny violations that, if found, might open a window to a new theory of physics that must come.”

    The clocks have been tested and integrated on the ACES payload and the microwave link for ACES is undergoing tests before final integration with the full experiment. ACES will be ready for launch to the Space Station by 2020.

    See the full article here .


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    The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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  • richardmitnick 8:56 am on March 17, 2019 Permalink | Reply
    Tags: A single ion of ytterbium, , Atomic Clocks, Einstein’s special theory of relativity,   

    From Science News: “Ultraprecise atomic clocks put Einstein’s special relativity to the test” 

    From Science News

    March 13, 2019
    Emily Conover

    An experiment tested a foundational principle of physics known as Lorentz symmetry.

    1
    WATCHING THE CLOCK Scientists monitored two atomic clocks for six months in order to test a tenet of Einstein’s special theory of relativity. Each clock, like the one shown, contained a single ion of ytterbium. PTB

    The ticktock of two ultraprecise clocks has proven Einstein right, once again.

    A pair of atomic clocks made of single ions of ytterbium kept pace with one another over six months, scientists report March 13 in Nature. The timepieces’ reliability supports a principle known as Lorentz symmetry. That principle was the foundation for Einstein’s special theory of relativity, which describes the physics of voyagers dashing along at nearly the speed of light.

    Lorentz symmetry states that the rules of physics should remain the same whether you’re standing still or moving at a breakneck speed, and no matter what direction you’re facing (SN: 7/8/17, p. 14). The clocks kept up with one another as the Earth rotated, confirming that idea.

    The two ytterbium ions — positively charged atoms — absorbed and emitted light at a particular frequency, functioning like the ticking of a clock hand. The ions, which were oriented in different directions, rotated as the Earth turned, making a full cycle each day. If the atomic clocks’ ticks varied based on their orientation in space, the experiment would reveal a daily variation in the relative frequencies from the two clocks — a violation of Lorentz symmetry. But the atomic clocks agreed within about a tenth of a quadrillionth of a percent, confirming with about 100 times the precision of previous tests that Lorentz symmetry held.

    Although Lorentz symmetry has been confirmed repeatedly, some scientists predict that it won’t hold up to increasingly precise tests. Some theories of quantum gravity, which aim to unite scientists’ understanding of gravity with the theory of very small objects (SN: 10/17/15, p. 28), suggest that Lorentz symmetry’s days are numbered. But so far, there’s no hint of its demise.

    See the full article here .


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  • richardmitnick 12:44 pm on November 29, 2018 Permalink | Reply
    Tags: , Atomic Clocks,   

    From NIST: “NIST Atomic Clocks Now Keep Time Well Enough to Improve Models of Earth” 


    From NIST

    November 28, 2018

    Experimental atomic clocks at the National Institute of Standards and Technology (NIST) have achieved three new performance records, now ticking precisely enough to not only improve timekeeping and navigation, but also detect faint signals from gravity, the early universe and perhaps even dark matter.

    The clocks each trap a thousand ytterbium atoms in optical lattices, grids made of laser beams. The atoms tick by vibrating or switching between two energy levels. By comparing two independent clocks, NIST physicists achieved record performance in three important measures: systematic uncertainty, stability and reproducibility.

    2

    NIST physicist Andrew Ludlow and colleagues achieved new atomic clock performance records in a comparison of two ytterbium optical lattice clocks. Laser systems used in both clocks are visible in the foreground, and the main apparatus for one of the clocks is located behind Ludlow.
    Credit: Burrus/NIST

    Published online today in the journal Nature, the new NIST clock records are:

    Systematic uncertainty: How well the clock represents the natural vibrations, or frequency, of the atoms. NIST researchers found that each clock ticked at a rate matching the natural frequency to within a possible error of just 1.4 parts in 1018—about one billionth of a billionth.
    Stability: How much the clock’s frequency changes over a specified time interval, measured to a level of 3.2 parts in 1019 (or 0.00000000000000000032) over a day.
    Reproducibility: How closely the two clocks tick at the same frequency, shown by 10 comparisons of the clock pair, yielding a frequency difference below the 10-18 level (again, less than one billionth of a billionth).

    “Systematic uncertainty, stability, and reproducibility can be considered the ‘royal flush’ of performance for these clocks,” project leader Andrew Ludlow said. “The agreement of the two clocks at this unprecedented level, which we call reproducibility, is perhaps the single most important result, because it essentially requires and substantiates the other two results.”

    “This is especially true because the demonstrated reproducibility shows that the clocks’ total error drops below our general ability to account for gravity’s effect on time here on Earth. Hence, as we envision clocks like these being used around the country or world, their relative performance would be, for the first time, limited by Earth’s gravitational effects.”

    Einstein’s theory of relativity predicts that an atomic clock’s ticking, that is, the frequency of the atoms’ vibrations, is reduced—shifted toward the red end of the electromagnetic spectrum—when observed in stronger gravity. That is, time passes more slowly at lower elevations.

    While these so-called redshifts degrade a clock’s timekeeping, this same sensitivity can be turned on its head to exquisitely measure gravity. Super-sensitive clocks can map the gravitational distortion of space-time more precisely than ever. Applications include relativistic geodesy, which measures the Earth’s gravitational shape, and detecting signals from the early universe such as gravitational waves and perhaps even as-yet-unexplained dark matter.

    NIST’s ytterbium clocks now exceed the conventional capability to measure the geoid, or the shape of the Earth based on tidal gauge surveys of sea level. Comparisons of such clocks located far apart such as on different continents could resolve geodetic measurements to within 1 centimeter, better than the current state of the art of several centimeters.

    In the past decade of new clock performance records announced by NIST and other labs around the world, this latest paper showcases reproducibility at a high level, the researchers say. Furthermore, the comparison of two clocks is the traditional method of evaluating performance.

    Among the improvements in NIST’s latest ytterbium clocks was the inclusion of thermal and electric shielding, which surround the atoms to protect them from stray electric fields and enable researchers to better characterize and correct for frequency shifts caused by heat radiation.

    The ytterbium atom is among potential candidates for the future redefinition of the second—the international unit of time—in terms of optical frequencies. NIST’s new clock records meet one of the international redefinition roadmap’s requirements, a 100-fold improvement in validated accuracy over the best clocks based on the current standard, the cesium atom, which vibrates at lower microwave frequencies.

    NIST is building a portable ytterbium lattice clock with state-of-the-art performance that could be transported to other labs around the world for clock comparisons and to other locations to explore relativistic geodesy techniques.

    The work is supported by NIST, the National Aeronautics and Space Administration and the Defense Advanced Research Projects Agency.

    See the full article here.

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    NIST Campus, Gaitherberg, MD, USA

    NIST Mission, Vision, Core Competencies, and Core Values

    NIST’s mission

    To promote U.S. innovation and industrial competitiveness by advancing measurement science, standards, and technology in ways that enhance economic security and improve our quality of life.
    NIST’s vision

    NIST will be the world’s leader in creating critical measurement solutions and promoting equitable standards. Our efforts stimulate innovation, foster industrial competitiveness, and improve the quality of life.
    NIST’s core competencies

    Measurement science
    Rigorous traceability
    Development and use of standards

    NIST’s core values

    NIST is an organization with strong values, reflected both in our history and our current work. NIST leadership and staff will uphold these values to ensure a high performing environment that is safe and respectful of all.

    Perseverance: We take the long view, planning the future with scientific knowledge and imagination to ensure continued impact and relevance for our stakeholders.
    Integrity: We are ethical, honest, independent, and provide an objective perspective.
    Inclusivity: We work collaboratively to harness the diversity of people and ideas, both inside and outside of NIST, to attain the best solutions to multidisciplinary challenges.
    Excellence: We apply rigor and critical thinking to achieve world-class results and continuous improvement in everything we do.

     
  • richardmitnick 9:10 pm on October 7, 2017 Permalink | Reply
    Tags: (3-D) quantum gas atomic clock, , Atomic Clocks, JILA physicists have created an entirely new design for an atomic clock, , , , Quantum gas,   

    From NIST: “JILA’s 3-D Quantum Gas Atomic Clock Offers New Dimensions in Measurement” 


    NIST

    October 05, 2017

    Laura Ost
    laura.ost@nist.gov
    (303) 497-4880

    1
    JILA

    4
    CU Boulder

    1
    JILA’s three-dimensional (3-D) quantum gas atomic clock consists of a grid of light formed by three pairs of laser beams. A stack of two tables is used to configure optical components around a vacuum chamber. Shown here is the upper table, where lenses and other optics are mounted. A blue laser beam excites a cube-shaped cloud of strontium atoms located behind the round window in the middle of the table. Strontium atoms fluorescence strongly when excited with blue light. Credit: G.E. Marti/JILA

    JILA physicists have created an entirely new design for an atomic clock, in which strontium atoms are packed into a tiny three-dimensional (3-D) cube at 1,000 times the density of previous one-dimensional (1-D) clocks. In doing so, they are the first to harness the ultra-controlled behavior of a so-called “quantum gas” to make a practical measurement device.

    With so many atoms completely immobilized in place, JILA’s cubic quantum gas clock sets a record for a value called “quality factor” and the resulting measurement precision. A large quality factor translates into a high level of synchronization between the atoms and the lasers used to probe them, and makes the clock’s “ticks” pure and stable for an unusually long time, thus achieving higher precision.

    Until now, each of the thousands of “ticking” atoms in advanced clocks behave and are measured largely independently. In contrast, the new cubic quantum gas clock uses a globally interacting collection of atoms to constrain collisions and improve measurements. The new approach promises to usher in an era of dramatically improved measurements and technologies across many areas based on controlled quantum systems.

    The new clock is described in the Oct. 6 issue of Science.

    “We are entering a really exciting time when we can quantum engineer a state of matter for a particular measurement purpose,” said physicist Jun Ye of the National Institute of Standards and Technology (NIST). Ye works at JILA, which is jointly operated by NIST and the University of Colorado Boulder.

    The clock’s centerpiece is an unusual state of matter called a degenerate Fermi gas (a quantum gas for Fermi particles), first created in 1999 by Ye’s late colleague Deborah Jin. All prior atomic clocks have used thermal gases. The use of a quantum gas enables all of the atoms’ properties to be quantized, or restricted to specific values, for the first time.

    “The most important potential of the 3-D quantum gas clock is the ability to scale up the atom numbers, which will lead to a huge gain in stability,” Ye said. “Also, we could reach the ideal condition of running the clock with its full coherence time, which refers to how long a series of ticks can remain stable. The ability to scale up both the atom number and coherence time will make this new-generation clock qualitatively different from the previous generation.”

    Until now, atomic clocks have treated each atom as a separate quantum particle, and interactions among the atoms posed measurement problems. But an engineered and controlled collection, a “quantum many-body system,” arranges all its atoms in a particular pattern, or correlation, to create the lowest overall energy state. The atoms then avoid each other, regardless of how many atoms are added to the clock. The gas of atoms effectively turns itself into an insulator, which blocks interactions between constituents.

    The result is an atomic clock that can outperform all predecessors. For example, stability can be thought of as how precisely the duration of each tick matches every other tick, which is directly linked to the clock’s measurement precision. Compared with Ye’s previous 1-D clocks, the new 3-D quantum gas clock can reach the same level of precision more than 20 times faster due to the large number of atoms and longer coherence times.

    The experimental data show the 3-D quantum gas clock achieved a precision of just 3.5 parts error in 10 quintillion (1 followed by 19 zeros) in about 2 hours, making it the first atomic clock to ever reach that threshold (19 zeros). “This represents a significant improvement over any previous demonstrations,” Ye said.

    The older, 1-D version of the JILA clock was, until now, the world’s most precise clock. This clock holds strontium atoms in a linear array of pancake-shaped traps formed by laser beams, called an optical lattice. The new 3-D quantum gas clock uses additional lasers to trap atoms along three axes so that the atoms are held in a cubic arrangement. This clock can maintain stable ticks for nearly 10 seconds with 10,000 strontium atoms trapped at a density above 10 trillion atoms per cubic centimeter. In the future, the clock may be able to probe millions of atoms for more than 100 seconds at a time.

    Optical lattice clocks, despite their high levels of performance in 1-D, have to deal with a tradeoff. Clock stability could be improved further by increasing the number of atoms, but a higher density of atoms also encourages collisions, shifting the frequencies at which the atoms tick and reducing clock accuracy. Coherence times are also limited by collisions. This is where the benefits of the many-body correlation can help.

    The 3-D lattice design—imagine a large egg carton—eliminates that tradeoff by holding the atoms in place. The atoms are fermions, a class of particles that cannot be in the same quantum state and location at once. For a Fermi quantum gas under this clock’s operating conditions, quantum mechanics favors a configuration where each individual lattice site is occupied by only one atom, which prevents the frequency shifts induced by atomic interactions in the 1-D version of the clock.

    JILA researchers used an ultra-stable laser to achieve a record level of synchronization between the atoms and lasers, reaching a record-high quality factor of 5.2 quadrillion (5.2 followed by 15 zeros). Quality factor refers to how long an oscillation or waveform can persist without dissipating. The researchers found that atom collisions were reduced such that their contribution to frequency shifts in the clock was much less than in previous experiments.

    “This new strontium clock using a quantum gas is an early and astounding success in the practical application of the ‘new quantum revolution,’ sometimes called ‘quantum 2.0’,” said Thomas O’Brian, chief of the NIST Quantum Physics Division and Ye’s supervisor. “This approach holds enormous promise for NIST and JILA to harness quantum correlations for a broad range of measurements and new technologies, far beyond timing.”

    Depending on measurement goals and applications, JILA researchers can optimize the clock’s parameters such as operational temperature (10 to 50 nanokelvins), atom number (10,000 to 100,000), and physical size of the cube (20 to 60 micrometers, or millionths of a meter).

    Atomic clocks have long been advancing the frontier of measurement science, not only in timekeeping and navigation but also in definitions of other measurement units and other areas of research such as in tabletop searches for the missing “dark matter” in the universe.

    The National Bureau of Standards, now NIST, invented the first atomic clock in 1948.

    3
    Dr. Harold Lyons (right), inventor of the ammonia absorption cell atomic clock, observes, while Dr. Edward U. Condon, the director of the National Bureau of Standards, examines a model of the ammonia molecule (1949).

    The work is supported by NIST, the Defense Advanced Research Projects Agency and the National Science Foundation.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    NIST Campus, Gaitherberg, MD, USA

    NIST Mission, Vision, Core Competencies, and Core Values

    NIST’s mission

    To promote U.S. innovation and industrial competitiveness by advancing measurement science, standards, and technology in ways that enhance economic security and improve our quality of life.
    NIST’s vision

    NIST will be the world’s leader in creating critical measurement solutions and promoting equitable standards. Our efforts stimulate innovation, foster industrial competitiveness, and improve the quality of life.
    NIST’s core competencies

    Measurement science
    Rigorous traceability
    Development and use of standards

    NIST’s core values

    NIST is an organization with strong values, reflected both in our history and our current work. NIST leadership and staff will uphold these values to ensure a high performing environment that is safe and respectful of all.

    Perseverance: We take the long view, planning the future with scientific knowledge and imagination to ensure continued impact and relevance for our stakeholders.
    Integrity: We are ethical, honest, independent, and provide an objective perspective.
    Inclusivity: We work collaboratively to harness the diversity of people and ideas, both inside and outside of NIST, to attain the best solutions to multidisciplinary challenges.
    Excellence: We apply rigor and critical thinking to achieve world-class results and continuous improvement in everything we do.

     
  • richardmitnick 11:30 am on August 6, 2017 Permalink | Reply
    Tags: and Why Does It Seem to Flow?, Atomic Clocks, , China to launch world’s first ‘cold’ atomic clock in space ... and it’ll stay accurate for a billion years., , , Where Did Time Come From   

    From Nautilus: “Where Did Time Come From, and Why Does It Seem to Flow?” 

    Nautilus

    Nautilus

    Jul 18, 2017
    John Steele

    1
    We say a river flows because it moves through space with respect to time. But time can’t move with respect to time—time is time.Image by violscraper / Flickr.


    NASA Deep Space Atomic Clock

    1
    NIST-F2 atomic clock operated by America’s National Institute of Standards and Technology in Boulder, Colorado.

    3
    China to launch world’s first ‘cold’ atomic clock in space … and it’ll stay accurate for a billion years.

    Paul Davies has a lot on his mind—or perhaps more accurate to say in his mind. A physicist at Arizona State University, he does research on a wide range of topics, from the abstract fields of theoretical physics and cosmology to the more concrete realm of astrobiology, the study of life in places beyond Earth. Nautilus sat down for a chat with Davies, and the discussion naturally drifted to the subject of time, a long-standing research interest of his. Here is a partial transcript of the interview, edited lightly for length and clarity.

    Is the flow of time real or an illusion?

    The flow of time is an illusion, and I don’t know very many scientists and philosophers who would disagree with that, to be perfectly honest. The reason that it is an illusion is when you stop to think, what does it even mean that time is flowing? When we say something flows like a river, what you mean is an element of the river at one moment is in a different place of an earlier moment. In other words, it moves with respect to time. But time can’t move with respect to time—time is time. A lot of people make the mistake of thinking that the claim that time does not flow means that there is no time, that time does not exist. That’s nonsense. Time of course exists. We measure it with clocks. Clocks don’t measure the flow of time, they measure intervals of time. Of course there are intervals of time between different events; that’s what clocks measure.

    So where does this impression of flow come from?

    Well, I like to give an analogy. Suppose I stand up, twirl around a few times, and stop. Then I have the overwhelming impression that the entire universe is rotating. I feel it to be rotating—of course I know it’s not. In the same way, I feel time is flowing, but of course I know it’s not. And presumably the explanation for this illusion has to do with something up here [in your head] and is connected with memory I guess—laying down of memories and so on. So it’s a feeling we have, but it’s not a property of time itself.

    And the other thing people contemplate: They think denying the flow of time is denying time asymmetry of the world. Of course events in the world follow a directional sequence. Drop an egg on the floor and it breaks. You don’t see eggs assembling themselves. Buildings fall down after earthquakes; they don’t rise up from heaps of rubble. [There are] many, many examples in daily life of the asymmetry of the world in time; that’s a property of the world. It’s not a property of time itself, and the explanation for that is to be sought in the very early universe and its initial conditions. It’s a whole different and perfectly respectable subject.

    Is time fundamental to the Universe?

    Time and space are the framework in which we formulate all of our current theories of the universe, but there is some question as to whether these might be emergent or secondary qualities of the universe. It could be that fundamentally the laws of the universe are formulated in terms of some sort of pre-space and time, and that space-time comes out of something more fundamental.

    Now obviously in daily life we experience a three-dimensional world and one dimension of time. But back in the Big Bang—we don’t really understand exactly how the universe was born in the Big Bang, but we think that quantum physics had something to do with it—it may be that this notion of what we would call a classical space-time, where everything seems to be sort of well-defined, maybe that was all closed out. And so maybe not just the world of matter and energy, but even space-time itself is a product of the special early stage of the universe. We don’t know that. That’s work under investigation.

    So time could be emergent?

    This dichotomy between space-time being emergent, a secondary quality—that something comes out of something more primitive, or something that is at the rock bottom of our description of nature—has been floating around since before my career. John Wheeler believed in and wrote about this in the 1950s—that there might be some pre-geometry, that would give rise to geometry just like atoms give rise to the continuum of elastic bodies—and people play around with that.

    The problem is that we don’t have any sort of experimental hands on that. You can dream up mathematical models that do this for you, but testing them looks to be pretty hopeless. I think the reason for that is that most people feel that if there is anything funny sort of underpinning space and time, any departure from our notion of a continuous space and time, that probably it would manifest itself only at the so-called Planck scale, which is [20 orders of magnitude] smaller than an atomic nucleus, and our best instruments at the moment are probing scales which are many orders of magnitude above that. It’s very hard to see how we could get at anything at the Planck scale in a controllable way.

    If multiple universes exist, do they have a common clock?

    The inter-comparison of time between different observers and different places is a delicate business even within one universe. When you talk about what is the rate of a clock, say, near the surface of a black hole, it’s going to be quite different from the rate of a clock here on Earth. So there isn’t even a common time in the entire universe.

    But now if we have a multiverse with other universes, whether each one in a sense comes with its own time—you can only do an inter-comparison between the two if there was some way of sending signals from one to the other. It depends on your multiverse model. There are many on offer, but on the one that cosmologists often talk about—where you have bubbles appearing in a sort of an inflating superstructure—then there’s no direct way of comparing a clock rate in one bubble from clock rates in another bubble.

    What do you think are the most exciting recent advances in understanding time?

    I’m particularly drawn to the work that is done in the lab on perception of time, because I think that has the ability to make rapid advances in the coming years. For example, there are famous experiments in which people apparently make free decisions at certain moments and yet it’s found that the decision was actually made a little bit earlier, but their own perception of time and their actions within time have been sort of edited after the event. When we observe the world, what we see is an apparently consistent and smooth narrative, but actually the brain is just being bombarded with sense data from different senses and puts all this together. It integrates it and then presents a consistent narrative as it were the conscious self. And so we have this impression that we’re in charge and everything is all smoothly put together. But as a matter of fact, most of this is, is a narrative that’s recreated after the event.

    Where it’s particularly striking of course is when people respond appropriately much faster than the speed of thought. You need only think of a piano player or a tennis player to see that the impression that they are making a conscious decision—“that ball is coming in this direction; I’d better move over here and hit it”—couldn’t possibly be. The time it takes for the signals to get to the brain and then through the motor system, back to the response, couldn’t work. And yet they still have this overwhelming impression that they’re observing the world in real time and are in control. I think all of this is pretty fascinating stuff.

    In terms of fundamental physics, is there anything especially new about time? I think the answer is not really. There are new ideas that are out there. I think there are still fundamental problems; we’ve talked about one of them: Is time an emergent property or a fundamental property? And the ultimate origin of the arrow of time, which is the asymmetry of the world in time, is still a bit contentious. We know we have to trace it back to the Big Bang, but there are still different issues swirling around there that we haven’t completely resolved. But these are sort of airy-fairy philosophical and theoretical issues in terms of measurement of time or anything being exposed about the nature of time.

    Then of course we’re always looking to our experimental colleagues to improve time measurements. At some stage these will become so good that we’ll no doubt see some peculiar effects showing up. There’s still an outstanding fundamental issue that although the laws of physics are symmetric in time, for the most part, there is one set of processes having to do with the weak interaction where there is apparently a fundamental breakdown of this time-reversal symmetry of a small amount. But it seems to play a crucial role and exactly how that fits into the broader picture in the universe. I think there’s still something to be played out there. So there’s still experiments can be done in particle physics that might disclose this time-reversal asymmetry which is there in the weak interaction, and how that fits in with the arrow of time.

    See the full article here .

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    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 4:44 pm on May 16, 2017 Permalink | Reply
    Tags: , Atomic Clocks,   

    From ars technica: “Atomic clocks and solid walls: New tools in the search for dark matter” 

    Ars Technica
    ars technica

    5/15/2017
    Jennifer Ouellette

    1
    An atomic clock based on a fountain of atoms. NSF

    Countless experiments around the world are hoping to reap scientific glory for the first detection of dark matter particles. Usually, they do this by watching for dark matter to bump into normal matter or by slamming particles into other particles and hoping for some dark stuff to pop out. But what if the dark matter behaves more like a wave?

    That’s the intriguing possibility championed by Asimina Arvanitaki, a theoretical physicist at the Perimeter Institute in Waterloo, Ontario, Canada, where she holds the Aristarchus Chair in Theoretical Physics—the first woman to hold a research chair at the institute. Detecting these hypothetical dark matter waves requires a bit of experimental ingenuity. So she and her collaborators are adapting a broad range of radically different techniques to the search: atomic clocks and resonating bars originally designed to hunt for gravitational waves—and even lasers shined at walls in hopes that a bit of dark matter might seep through to the other side.

    “Progress in particle physics for the last 50 years has been focused on colliders, and rightfully so, because whenever we went to a new energy scale, we found something new,” says Arvanitaki. That focus is beginning to shift. To reach higher and higher energies, physicists must build ever-larger colliders—an expensive proposition when funding for science is in decline. There is now more interest in smaller, cheaper options. “These are things that usually fit in the lab, and the turnaround time for results is much shorter than that of the collider,” says Arvanitaki, admitting, “I’ve done this for a long time, and it hasn’t always been popular.”

    The end of the WIMP?

    While most dark matter physicists have focused on hunting for weakly interacting massive particles, or WIMPs, Arvanitaki is one of a growing number who are focusing on less well-known alternatives, such as axions—hypothetical ultralight particles with masses that could be as little as ten thousand trillion trillion times smaller than the mass of the electron. The masses of WIMPs, by contrast, would be larger than the mass of the proton.

    Cosmology gave us very good reason to be excited about WIMPs and focus initial searches in their mass range, according to David Kaplan, a theorist at Johns Hopkins University (and producer of the 2013 documentary Particle Fever). But the WIMP’s dominance in the field to date has also been due, in part, to excitement over the idea of supersymmetry. That model requires every known particle in the Standard Model—whether fermion or boson—to have a superpartner that is heavier and in the opposite class. So an electron, which is a fermion, would have a boson superpartner called the selectron, and so on.

    Physicists suspect one or more of those unseen superpartners might make up dark matter. Supersymmetry predicts not just the existence of dark matter, but how much of it there should be. That fits neatly within a WIMP scenario. Dark matter could be any number of things, after all, and the supersymmetry mass range seemed like a good place to start the search, given the compelling theory behind it.

    But in the ensuing decades, experiment after experiment has come up empty. With each null result, the parameter space where WIMPs might be lurking shrinks. This makes distinguishing a possible signal from background noise in the data increasingly difficult.

    “We’re about to bump up against what’s called the ‘neutrino floor,’” says Kaplan. “All the technology we use to discover WIMPs will soon be sensitive to random neutrinos flying through the Universe. Once it gets there, it becomes a much messier signal and harder to see.”

    Particles are waves

    Despite its momentous discovery of the Higgs boson in 2012, the Large Hadron Collider has yet to find any evidence of supersymmetry. So we shouldn’t wonder that physicists are turning their attention to alternative dark matter candidates outside of the mass ranges of WIMPs. “It’s now a fishing expedition,” says Kaplan. “If you’re going on a fishing expedition, you want to search as broadly as possible, and the WIMP search is narrow and deep.”

    Enter Asimina Arvanitaki—“Mina” for short. She grew up in a small Greek Village called Koklas, and, since her parents were teachers, she grew up with no shortage of books around the house. Arvanitaki excelled in math and physics—at a very young age, she calculated the time light takes to travel from the Earth to the Sun. While she briefly considered becoming a car mechanic in high school because she loved cars, she decided, “I was more interested in why things are the way they are, not in how to make them work.” So she majored in physics instead.

    Similar reasoning convinced her to switch her graduate-school focus at Stanford from experimental condensed matter physics to theory: she found her quantum field theory course more scintillating than any experimental results she produced in the laboratory.

    Central to Arvanitaki’s approach is a theoretical reimagining of dark matter as more than just a simple particle. A peculiar quirk of quantum mechanics is that particles exhibit both particle- and wave-like behavior, so we’re really talking about something more akin to a wavepacket, according to Arvanitaki. The size of those wave packets is inversely proportional to their mass. “So the elementary particles in our theory don’t have to be tiny,” she says. “They can be super light, which means they can be as big as the room or as big as the entire Universe.”

    Axions fit the bill as a dark matter candidate, but they interact so weakly with regular matter that they cannot be produced in colliders. Arvanitaki has proposed several smaller experiments that might succeed in detecting them in ways that colliders cannot.

    Walls, clocks, and bars

    One of her experiments relies on atomic clocks—the most accurate timekeeping devices we have, in which the natural frequency oscillations of atoms serve the same purpose as the pendulum in a grandfather clock. An average wristwatch loses roughly one second every year; atomic clocks are so precise that the best would only lose one second every age of the Universe.

    Within her theoretical framework, dark matter particles (including axions) would behave like waves and oscillate at specific frequencies determined by the mass of the particles. Dark matter waves would cause the atoms in an atomic clock to oscillate as well. The effect is very tiny, but it should be possible to see such oscillations in the data. A trial search of existing data from atomic clocks came up empty, but Arvanitaki suspects that a more dedicated analysis would prove more fruitful.

    Then there are so-called “Weber bars,” which are solid aluminum cylinders that Arvanitaki says should ring like a tuning fork should a dark matter wavelet hit them at just the right frequency. The bars get their name from physicist Joseph Weber, who used them in the 1960s to search for gravitational waves. He claimed to have detected those waves, but nobody could replicate his findings, and his scientific reputation never quite recovered from the controversy.

    Weber died in 2000, but chances are he’d be pleased that his bars have found a new use. Since we don’t know the precise frequency of the dark matter particles we’re hunting, Arvanitaki suggests building a kind of xylophone out of Weber bars. Each bar would be tuned to a different frequency to scan for many different frequencies at once.

    Walking through walls

    Yet another inventive approach involves sending axions through walls. Photons (light) can’t pass through walls—shine a flashlight onto a wall, and someone on the other side won’t be able to see that light. But axions are so weakly interacting that they can pass through a solid wall. Arvanitaki’s experiment exploits the fact that it should be possible to turn photons into axions and then reverse the process to restore the photons. Place a strong magnetic field in front of that wall and then shine a laser onto it. Some of the photons will become axions and pass through the wall. A second magnetic field on the other side of the wall then converts those axions back into photons, which should be easily detected.

    This is a new kind of dark matter detection relying on small, lab-based experiments that are easier to perform (and hence easier to replicate). They’re also much cheaper than setting up detectors deep underground or trying to produce dark matter particles at the LHC—the biggest, most complicated scientific machine ever built, and the most expensive.

    “I think this is the future of dark matter detection,” says Kaplan, although both he and Arvanitaki are adamant that this should complement, not replace, the many ongoing efforts to hunt for WIMPs, whether deep underground or at the LHC.

    “You have to look everywhere, because there are no guarantees. This is what research is all about,” says Arvanitaki. “What we think is correct, and what Nature does, may be two different things.”

    See the full article here .

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