Changing Concepts of Light and Matter
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Lindau Nobel Laureate Meetings242 / 340
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MorgenLichtMessungVorlesung/Konferenz
00:38
Elle <Maßeinheit>TeilchenNewton, IsaacLichtNewton, IsaacSonnenstrahlungBuntheitGleitsichtglasVorlesung/KonferenzBesprechung/Interview
01:44
BuntheitPhotonWelle <Maschinenbau>LichtYoung, ThomasInterferenzerscheinungSchwingungsphaseProfilwalzenSichtweiteDrehenWocheVorlesung/KonferenzBesprechung/Interview
02:25
WellenlängeFiat 500WellenlängeOptisches SpektrumLichtLichtgeschwindigkeitViolettAmperemeterComputeranimationVorlesung/Konferenz
02:51
WellenlängeFiat 500Michelson, Albert AbrahamEinstein, AlbertLichtOptisches SpektrumStandardzelleFunkgerätHochfrequenzübertragungNegativer WiderstandMichelson-InterferometerBuick CenturyWerkzeugMessungInterferometrieErderInterferenzerscheinungLichtgeschwindigkeitModellbauerComputeranimationVorlesung/KonferenzBesprechung/Interview
03:50
Schwarzes LochMehrfachsternInterferometrieSensorSternwarteSchwarzes LochGigant <Bagger>Vorlesung/KonferenzBesprechung/Interview
04:21
BerlinePlanck-MasseStrahlungOptisches SpektrumFeldeffekttransistorBeleuchtungSource <Elektronik>LichtBuick CenturyOptisches SpektrumMessungSatz <Drucktechnik>ModellbauerPlanck-Masse
05:12
PhotonTeilchenEmissionsvermögenAbsorptionPhotonClosed Loop IdentificationHochfrequenzübertragungElementarteilchenInterferenzerscheinungSensorLichtWocheArmbanduhrTonschlickerPhototechnikAbstandsmessungVorlesung/KonferenzBesprechung/Interview
06:00
PhotonQuantenkryptologieQuantencomputerQuanteninformatikPhotonAbstandsmessungFeldquantSensorWerkzeugSS-20Besprechung/Interview
06:29
InfrarotlaserOptische KohärenzSource <Elektronik>VideotechnikKombiQuantenelektronikFunkgerätLaserErwärmungErsatzteilBlatt <Papier>VC 10Discovery <Raumtransporter>Planck-MasseLichtDrehmasseNegativer WiderstandOptische Kohärenz
07:16
LaserPlanck-MasseOptisches InstrumentDampfbügeleisenMessgerätQuantenelektronikImpaktTransistorMikroskopSpiel <Technik>Besprechung/Interview
07:47
LaserImpaktAtomistikFACTS-AnlageLichtSpiel <Technik>SensorMikroskopTunneldiodeBuick CenturyMessgerätZylinderblockLaserKalenderjahrSichtweiteComputeranimation
08:48
Stoff <Textilien>SonnenenergieVideotechnikOptisches SpektrumAbsorptionBuick CenturySonnenstrahlungAtomistikAtmosphäreSonnenenergieSteckverbinderLithium-Ionen-AkkumulatorSternatmosphäreMolekülmasseSpeckle-InterferometrieSpektrographBahnelementProfilwalzenAbsorptionslinieGewichtsstückIonComputeranimation
09:49
SonnenenergieOptisches SpektrumVideotechnikWasserstoffatomRestkernRutherford, ErnestFlorettKernstrahlungBlattgoldLichtAtomistikZentralsternMasse <Physik>LichtstreuungVideotechnikSichtweiteWellenlängeWerkzeugWolkengattungAbsorptionslinieElektronAlphazerfallOptisches SpektrumRestkernWasserstoffatomKompendium <Photographie>SchusswaffeDeckSurround-SystemPlanetarischer NebelSteinzeugModellbauerBasis <Elektrotechnik>Rosetta <Raumsonde>
11:33
Planetarischer NebelWasserstoffatomBohr, NielsModellbauerPlanck-MassePlanetarischer NebelUmlaufbahnLichtgeschwindigkeitStrahlungBroglie, Louis deElektronFeldquantTheodolitColourMasse <Physik>EisElementarteilchenVorlesung/KonferenzBesprechung/InterviewComputeranimation
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Schrödinger, ErwinOptisches SpektrumWellenlängeWasserstoffatomUmlaufbahnFernordnungDrehenPaarerzeugungProfilwalzenVorlesung/Konferenz
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FestkörperB-2ErderBuchdruckVorlesung/Konferenz
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DigitalelektronikGleichstrom
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Flavour <Elementarteilchen>KalenderjahrRelativistischer EffektKristallgitterPositronWasserstoffatomVideotechnikElektronLungenautomatBesprechung/Interview
15:11
Polarisierte StrahlungQuantenfluktuationVakuumphysikRotverschiebungVirtuelles PhotonEnergieniveauDiscovery <Raumtransporter>AM-Herculis-SternKlangeffektFACTS-AnlageElektronDurchführung <Elektrotechnik>Angeregter ZustandKristallgitterWasserstoffatomVideotechnikVakuumphysikPaarerzeugungRestkernKosmische StrahlungQuantenfluktuationFeldquant
16:03
StandardzelleModellbauerElementarteilchenKlassifikationsgesellschaftAntiquarkKristallgitterFeynman-GraphBeschleunigungLeptonBosonWasserstoffatomZylinderblockModellbauerAntiquarkFeldquantRestkernPostkutscheGluonLuftstromVorlesung/KonferenzBesprechung/Interview
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VermittlungseinrichtungAntiquarkKristallgitterHalo <Atmosphärische Optik>WasserstoffatomSchlichte <Textiltechnik>LaserInfrarotlaserFarbstofflaserWerkzeugOptische SpektroskopieTrenntechnikWeltraumComputeranimation
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RotverschiebungBuntheitOptisches SpektrumRadarmeteorologieOptisches InstrumentWasserstoffatomOptische SpektroskopieLaserMessungBlei-209SchiffsmastOptische SpektroskopieWasserstoffatomSensorLichtDigitales FernsehenColourAngeregter ZustandTheodolitH-alpha-LinieRadarmeteorologieGleitsichtglasLaserElektronisches BauelementAntiwasserstoffKalenderjahrVideotechnikWarmumformenSättigungsspektroskopieAbsorptionslinieTagKristallgitterLaserkühlungSchmiedenGasDiagramm
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RadarmeteorologieOptische SpektroskopieLaserLuftkühlungOptisches InstrumentWasserstoffatomLaserkühlungOptische SpektroskopieGasOptischer FrequenzkammDrechselnWasserstoffatomGleitlagerWerkzeugLichtSensorVorlesung/KonferenzBesprechung/Interview
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FunkgerätOptisches InstrumentUhrMessungWerkzeugOptische KohärenzKette <Zugmittel>SchwingungsphaseMechanismus <Maschinendynamik>LaserWerkzeugSchwingungsphaseOptisches InstrumentOptische KohärenzOptischer FrequenzkammKette <Zugmittel>FunkgerätOptisches SpektrumSource <Elektronik>ThekeMechanikerinLaserWarmumformenAtomuhrComputeranimationVorlesung/KonferenzBesprechung/Interview
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SpektrometerKämmen <Textiltechnik>Optisches InstrumentSynthesizerKämmen <Textiltechnik>VideotechnikSAPHIR <Spektrometer>Optischer FrequenzkammBuntheitSpektrographWarmumformenInterferenzerscheinungSchnittmusterOptisches SpektrumDauerstrichbetriebTextilfaserDPSKDiffraktometerLichtRelaisLaserAbsorptionslinieIntervallWerkstattNivellierlatteDipolLithium-Ionen-AkkumulatorOptische KohärenzKalenderjahrErdefunkstelle
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BriefumschlagVideotechnikFlugzeugträgerSchwingungsphaseFront <Meteorologie>MessungFarbeKristallwachstumDrehen
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TextilfaserLaserPolysiliciumSource <Elektronik>Kämmen <Textiltechnik>Dreidimensionale IntegrationVideotechnikMessgerätKalenderjahrWarmumformenSource <Elektronik>Kämmen <Textiltechnik>AmperemeterZahnradbahnNichtlineare OptikLithographieOptisches InstrumentInfrarotlaserKristallwachstumReglerDigitales FernsehenAnzeige <Technik>Energieniveau
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SynthesizerFunkgerätStörgrößenaufschaltungOptische SpektroskopieGleichstromOptische KohärenzHöchstfrequenztechnikOptisches InstrumentFadingWasserstoffatomPhotonGrundzustandSchärfenUhrDrechselnAtomistikLichtSchreibwareAngeregter ZustandTheodolitUltraviolett BWasserstoffatomMetastabiler ZustandMessung
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WasserstoffatomUhrMessungKette <Zugmittel>TheodolitTelefonDigitales FernsehenAtomuhrTextilfaserZeitskalaVorlesung/Konferenz
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StandardzelleGrundfrequenzKompendium <Photographie>Optische SpektroskopieWasserstoffatomDigitales FernsehenSchlichte <Textiltechnik>WasserstoffatomEnergieniveauColourBogenlampeRotverschiebungQuantenzahlTheodolitGrundzustandGleitsichtglasElektronBeschleunigungMaßstab <Messtechnik>MessungPassatSchusswaffePorzellanVorlesung/KonferenzComputeranimation
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WasserstoffatomRotverschiebungKonfektionsgrößeLaserRootsgebläseRotverschiebungBogenlampeMaßstab <Messtechnik>Patrone <Munition>PolradMyonAtomistikLaserElektronErsatzteilSchlichte <Textiltechnik>ColourRestkernFront <Meteorologie>WasserstoffatomTheodolitUrkilogrammH-alpha-LinieLeistungssteuerungAngeregter ZustandVorlesung/Konferenz
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LichtstreuungWasserstoffatomResonanzenergieRotverschiebungResonanzenergieKopfstützeBlei-209WasserstoffatomZylinderkopfErderIonBogenlampeBeschleunigungFehlprägung
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MyonElektronOptische SpektroskopieEisWasserstoffatomElektronSchlichte <Textiltechnik>SIGMA <Radioteleskop>MyonOptische SpektroskopieWerkstattTheodolitMessungVorlesung/Konferenz
29:33
KombinationskraftwerkOptische SpektroskopieSchärfenFehlprägungKlangeffektFACTS-AnlageTheodolitWasserstoffatomGauß-BündelFörderleistungFuß <Maßeinheit>
30:09
WasserstoffatomOptische SpektroskopieMinuteFiat 500AntiteilchenPhotonTheodolitMetastabiler ZustandBetazerfallAtomistikFehlprägungGauß-BündelAtmosphäreGrundfrequenzKommandobrückeDigitales FernsehenWasserstoffatomFunkgerätTissueNatürliche RadioaktivitätOptische SpektroskopieAbendMessungPatrone <Munition>Schlichte <Textiltechnik>Optischer FrequenzkammAntiwasserstoffMyonKalenderjahrComputeranimationVorlesung/Konferenz
32:19
PlanetWeltraumBasis <Elektrotechnik>SpektrographSternwarteGrundfrequenzSonnenstrahlungPlanetZentralsternErderVorlesung/Konferenz
32:53
PlanetRotverschiebungWeltraumGleitsichtglasWirtsgitterDunkle MaterieVorlesung/Konferenz
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Vorlesung/KonferenzComputeranimation
Transkript: Englisch(automatisch erzeugt)
00:15
Good morning, it's always a pleasure to be here in Lindau and you know that I'm an
00:25
experimental physicist working with lasers and light and with a passion for precise measurements which have taught us much about light and matter in the past and which might teach us more in the future.
00:42
So today I thought I would talk about how our concepts of light and matter have evolved over time and how they are still changing. Light and matter are of course intertwined with the concepts of space and time and these
01:02
are central not just to physics but to life. They are essential for survival and so evolution has hardwired very strong intuitive concepts in our brain which are so compelling that they can actually hinder scientific progress.
01:25
Let's look at what was discovered in the scientific exploration of light which started probably when Sir Isaac Newton sent a ray of sunlight through a prison and he saw how
01:43
the light is dispersed into a rainbow of colours and he argued that these different colours must correspond to different kinds of light particles. Then came Thomas Young who showed that light is a wave, just like water waves going
02:01
through a double slit you can observe interference fringes, two waves oscillating in phase reinforce each other, two waves oscillating out of phase can cancel each other through interference. Fresnel came up with a mathematical formulation of this kind of wave theory even though at
02:21
a time it was not known what kind of wave light is but from interference experiments Young was able to measure the wavelengths of light and so he determined that in the visible spectrum the wavelength ranges between 700 nm in the red and 400 nm in the
02:43
violet and once you know the wavelength and the speed of light of course you can calculate the frequency of light. So in the middle of the spectrum we are talking about something like five times 10 to the 14 oscillations per second. Nowadays of course we know that light is an electromagnetic wave, there is a huge
03:13
interference can be used as a tool for very precise measurements. One important such measurement was made by Abraham Michelson in the late 19th century
03:26
using his famous Michelson interferometer. He could show that the speed of light does not change with the motion of earth and of course Einstein was the one who came up with his brilliant spatial theory of relativity
03:45
to explain this and at least to model it and then as we heard yesterday of course also with general relativity that thoroughly changed our understanding of space and time. And David Gross yesterday has of course already pointed out the latest triumph of this kind
04:07
of interferometry is the detection of gravitational waves from two coalescing black holes using essentially a giant and sophisticated Michelson interferometry, the LIGO observatory.
04:23
So much for waves and so people were happy that they understood what light is. But there were some worrisome observations in the late 19th century. People in Germany at the PDB, it was at that time not yet called PDB but they in
04:42
Berlin carefully measured the spectrum emitted by black hot bodies because they wanted to understand how to make more efficient electric light sources. And the spectrum measure could not be explained in any classical model. Planck was the one who showed that if you make the assumption that light is emitted
05:06
only in packets, emitted and absorbed in light packets of quantity Planck's constant times frequency, then one can model this type of black body spectrum very well. And Einstein then postulated 1905 that it's not just absorption and emission but the
05:26
nature of light itself is quantized. The term photon was coined much later in the 1920s. But today we have positioned sensitive photon detectors where you can watch how an interference
05:42
pattern builds up photon by photon in a double slit experiment. So we know that light can act as if it were made of particles. It can act as if it was an electromagnetic wave. It can act as if it were made of particles, not classical particles, but particles that
06:03
show these strange correlations over a distance called entanglement, which indicate that you cannot assume that a photon that you detect already has its properties before detection. This has become a tool for applications such as quantum cryptography, quantum information
06:28
processing, quantum computing, and the pioneers there are Jean Klaus and Alan Aspey. An even more momentous discovery or invention was that of the laser that you can make a
06:47
source of coherent light waves that acts much like a classical radio frequency oscillator. The race to build the first laser was triggered by Art Schawlow and Charlie Towns
07:01
with a seminal paper published in 1958. The very first laser was realized by Ted Mayman in 1960. Here are the parts of his original laser that are right now in our Max Planck Institute
07:20
of Quantum Optics in Garching, thanks to Kathleen Mayman, the widow of Ted Mayman. What I find charming is that it's really very simple. It's a simple device that could have been realized much earlier. It also shows that the largest impact is not always from big and sophisticated instruments.
07:47
It can be simple instruments that are game changers. Other examples, of course, are the transistor, the scanning tunneling microscope. This is, I think, the kind of invention that I am really very excited about.
08:03
Of course, the impact in science is illustrated by the fact that there are now 26 Nobel Prizes around the laser, or enabled by the laser, and not counting yet the detection of gravitational waves that surely will be included in the future.
08:24
OK, so much for light. What about matter? The question, what is matter, of course, is a natural question to ask. Old philosophers speculate that maybe there are small, indivisible building blocks of matter, atoms.
08:43
But these ideas were soon forgotten, but they revived in the 18th and 19th century by a chemist, Doughton, showed that if you make this assumption that matter consists
09:03
of atoms, then one can naturally understand the proportion in which elements react to form molecules, and one can even determine relative molecular weights. And of course, we see even absolute atomic weights. But nobody had any idea how these atoms are composed.
09:25
There were some hints that they must be complex. Fraunhofer, with his spectrographs, looking at the solar spectrum, discovered the dark absorption lines due to atoms or ions in the solar atmosphere or Earth's atmosphere, and
09:50
this kind of spectroscopy soon became a tool to chemists, like Bunsen or Kirchhoff, used it to identify atoms by their spectrum, like a fingerprint.
10:05
But how these spectral lines came about remained obscure. The very simplest of the atom and the very simplest of the spectra, in the end, provided the Rosetta Stone for having a deeper look into how atoms work.
10:25
There is the visible bounder spectrum that was first observed in astronomy in the light of distant stars. And you know that Jacob Ballmer was the first to come up with an empirical formula for
10:40
the wavelengths of this very simple line spectrum that was later generalized by Rydberg, who introduced the empirical Rydberg constant. But still, one didn't know how these lines could come about. One had even no idea what was going on inside an atom until radioactivity was discovered
11:05
and until Rutherford used scattering of radioactive alpha rays from a gold foil to discover that all the mass of an atom must be confined to very small, heavy nucleus, and the light
11:21
electrons are surrounding these nucleus like a cloud. So with this insight, Bohr tried to model the hydrogen atom, the simplest atom with just a single electron, as some sort of planetary system, and he tried to see what
11:42
could give the Ballmer spectrum, and he realized that no classical model would work. He had to make some radical assumptions like Planck that there are only certain stationary orbits which are allowed and that radiation is emitted in transitions, in jumps between
12:03
these orbits, these early quantum postulates, hard to swallow, but they allowed Bohr to calculate the Rydberg constant in terms of the electron mass, electron charge, Planck's
12:22
constant, and the speed of light to fairly high accuracy, so people realized there must be something to it, even though it made no sense. Puzzling about it, Louis de Broglie showed that if you make the assumption that electrons, particles, can also have wave properties, and if you wonder what would be the orbits
12:44
where you have resonant waves, where an integer number of wavelengths fits around, that you could reproduce the Ballmer spectrum. Schrodinger came up with a wave equation for these matter waves, which is perhaps one of the most successful and best tested equations in physics.
13:04
As the Schrodinger equation for the hydrogen atom could be solved in closed form, one can draw pictures of orbitals, still it's a question that has not been definitely answered until today. What is it that this Schrodinger equation or the Schrodinger wave function describes?
13:24
There is infinite room for speculation for philosophy, but if we want to stay on the solid ground of science, I think all we can say for sure is that this equation describes our information about the probabilities of clicks and meter readings.
13:42
It doesn't say anything about the true microscopic world. So this is the essence, the spirit of the Copenhagen interpretation, which has been sharpened and made more consistent with the interpretation of cubism, a minimal interpretation that interprets probabilities in the Bayesian spirit, as we have heard
14:06
from Saoirse Roche, so in particular different physicists can assign different probabilities depending on the information they have. So this is still some frontier where we hope one of you maybe will have some insights
14:26
how we can go beyond this phenomenological description. Nonetheless it works very well, Dirac two years later was able to generalize the Schrodinger equation to include relativistic effects and this Dirac equation was miraculous
14:46
because it not only contained relativistic effects, it also predicted the existence of anti-electrons of positrons, and it was so beautiful that people felt this
15:01
must now be the ultimate truth. There were nagging uncertainties where Dirac could really describe the fine structure of hydrogen lines very well, and since the Second World War we know that the Dirac equation is not complete, it is not able to describe the fine structure of hydrogen lines
15:22
because there are effects that were not included, in particular the effect of the vacuum fluctuations and vacuum polarization. Lamb, with his discovery of the Lamb shift, the fact that there are two energy levels in hydrogen, the 2s state where the electron comes close to the nucleus, the 2p state
15:44
where it stays away, two levels that should be precisely the same, they should be degenerate according to Dirac, but in reality they are split by about 1000 MHz and this was the beginning of quantum electrodynamics and modern quantum field theories
16:03
In 1965 the Nobel prize for the developments in quantum electrodynamics was given to Tomo and Ager, Schwinger and Feynman. Of course since then we have, thanks to Gelman, found that there is a scheme
16:27
how we can classify the building blocks of all matter in terms of quarks and leptons bosons and we believe that this is a complete description of matter as we understand it today.
16:45
Of course one is eager to look beyond the standard model and we see new accelerator experiments at CERN, maybe one will discover new things, but so this is considered a very successful model of matter and its interactions.
17:06
According to the standard model, the proton, the nucleus of the hydrogen atom is a composite system made up of quarks and gluons, there is the theory of quantum
17:20
chromodynamics that attempts to model this, but it's still at an early stage, we cannot for instance predict the size of the proton and this question, how small is the proton, is something that has become important experimentally, partly because of lasers and precision spectroscopy.
17:42
So my own encounter with hydrogen started in the early 1970s when I was a postdoc at Stanford University, Art Schawlow co-inventor of the laser was my host and mentor and he gave good advice to young people, he said if you like to discover something new,
18:04
try to look where no one has looked before and actually we had a tool where we could do this very nicely in the early 70s because we had the first tunable dye laser that was at the same time highly monochromatic so one could use it to study spectral lines free of Doppler broadening
18:23
using nonlinear saturation spectroscopy and so we succeeded to for the first time resolve individual fine structure components of the red palmar alpha line, whereas before spectroscopists were dealing with a blend of unresolved lines due to the
18:43
very large Doppler broadening of the light hydrogen atoms and this has been the start of a long adventure studying hydrogen with ever higher resolution and ever higher precision in the hope that if we look closely enough maybe one day we will find a surprise
19:05
and only if we find a disagreement with existing theory can we hope to make progress and so over the years and this adventure is continuing today we have advanced the fractional frequency uncertainty with which we can study transitions in hydrogen from something like six
19:25
or seven decimal digits in classical spectroscopy to 15 digits today and to make progress beyond 10 digits we had to learn how to measure the frequency of light so
19:41
motivation for doing this kind of work is we want to test bound state QED look for possible discrepancies but we can also measure fundamental constants in particular the Rydberg constant and the proton charge radius one can ask the question are constants really constant or might they be slowly changing with time there is anti hydrogen so one can
20:05
hope to compare matter and anti-matter and all together maybe discover some new physics and so this quest has motivated inventions in the 1970s techniques of Doppler free laser
20:22
spectroscopy also the idea of laser cooling of atomic gases was inspired by this quest for higher resolution and accuracy in hydrogen and in the 1990s finally a tool the femtosecond frequency comb that makes it now easy but had been impossible or extremely difficult before
20:44
namely to count the ripples of a light wave so at the turn of the millennium various newspapers and journals reported on these frequency combs because they had been cited when the Nobel
21:01
Prize was awarded in 2005 to Jen Hall and myself and so the frequency comb is for the first time a simple tool for measuring optical frequencies of hundreds or even thousands of terahertz it provides a phase coherent link between the optical and the
21:21
radio frequency region and it's a clockwork mechanism a counter for optical atomic clocks so how does a frequency comb work typically you have a laser or some kind of source that emits very short pulses with a broad spectrum if you have a single such pulse you get a broad
21:44
spectrum if you have not a single pulse but two pulses in succession they interfere in the spectrum so it's similar to the young double slit experiment but now interference in the spectrum or in the spectrograph and you get a fringe pattern so in essence you have
22:02
already a frequency comb a comb of lines not very sharp the more distant the pulses are the more comb lines you get and the frequency spacing between these comb lines is just precisely
22:21
the inverse time interval between the two pulses so if I have not two pulses but many pulses then they can interfere like we get interference in the diffraction gradient we have multi-wave interference if we can build up sharp lines the longer we wait the sharper the
22:42
lines and they can be as sharp as any continuous wave laser but only if you have precisely controlled timing otherwise of course this doesn't work so these are extremely elementary principles according to Fourier still most people didn't expect that this could actually
23:04
work to measure the frequency of light they didn't anticipate how far these principles could be pushed that you could take a motlock titanium sapphire laser send its light through a non-linear fiber to broaden it by self phase modulation to a rainbow of colors and still have a frequency
23:28
comb so you can get a hundred thousand or a million sharp spectral lines very equally spaced by precisely the pulse repetition frequency the only thing that was still a problem
23:43
was that we don't know the absolute position of these lines we know the spacing but the absolute positions depend on the slippage of the phase of the carrier wave relative to the pulse envelope the so-called carrier envelope offset frequency but once you have an octave spanning comb it's extremely simple to measure this offset frequency you can take
24:04
comb lines from the red and send them through a non-linear crystal to frequency double get comb lines in the blue and look at a collective beat note and you can measure it and if you measure it you can use server controls to make it go away or you simply take it into account
24:24
and so now you can buy instruments optical frequency meters and there are hundreds of these in different laboratories they're being miniaturized or can have an instrument that was my dream 30 years ago something that you put on a desktop or in a rack and you have an input for a laser
24:46
light and on a digital display you can measure the frequency you can read out the frequency to as many digits as you like there is work going on on miniaturized comb sources based on micro toroids fabricated by lithography and one of the reasons for growing interest in these combs is
25:09
that there is an evolutionary tree of applications but we have no time I'm looking at the clock and I see that I really need to speed up but let's look at the original purpose
25:24
a frequency measurement so there is this extremely sharp transition in atomic hydrogen two-photon transition from the ground state to the metastable 2s state which has a natural line rates of only one hertz or so you can excite it with ultraviolet light the earliest
25:42
experiments were done in 1975 with carl weyman who is actually here at this meeting I haven't seen now we are able to measure the frequency of this transition to something like 15
26:01
decimal digits for the measurement we need a comparison our comparison was the national cesium fountain clock time standard at the pdb and we had a fiber link linking uh laboratories about a thousand kilometers away so if I have that frequency can I determine the
26:28
rittberg constant yes by comparison with theory but there is one problem we don't know the proton size waiver and so that's why the frequency is known to 15 digits but the rittberg
26:41
constant only to 12 digits so to make progress we need a better value of the proton charge radius how is the proton charge radius measured the electron scattering experiments at accelerators and there is also the possibility to measure it by comparing different transitions in hydrogen
27:00
if you look at the energies of s levels they scale this rittberg constant over principal quantum number square plus lamp shift of the ground state divided by the cube of the principal number and this lamp shift traditionally includes a term that scales with the root mean squared charge radius of the proton so by comparing two different transitions you can measure
27:26
the proton size you can do it much better by looking at artificial man-made atoms of bionic hydrogen where you have a instead of the electron a negative muon 200 times heavier that comes 200 times closer to the nucleus in this case the lamp shift is actually in the
27:45
mid infrared at six micron but you can by capturing muons in hydrogen gas you can populate the metastable to acetate and induce transitions with a laser and look for lamin alpha which in this case is a two kilo electron volt in the soft x-ray region so this kind of experiment
28:07
was done was finally successful here you see the part of the international team in front of the laboratory at the powell sharer institute in switzerland and so in 2010 and 2013 we could
28:25
publish results with randolph poll really as the leader of the team at of observing such resonances lamp shift resonances in ionic hydrogen and the big surprise was that it wasn't where it was expected to be there are two positions where the resonance should be
28:48
according to the official code data value and where it should be according to accelerator experiment so it wasn't there and if we look at the error bars we see that the
29:03
proton size determined from the muonic hydrogen is almost eight sigma away from the size determined by scattering electrons we're looking at electronic hydrogen this is known as the proton size puzzle it has not been completely resolved our suspicion is that the muonic hydrogen
29:28
experiments are right and maybe the hydrogen spectroscopy wasn't right this has to do with the fact that we have one way sharp transition the one is two ways
29:41
but they're auxiliary transitions that are not so sharp and that are more easily uh perturbed by electric fields and other effect so if one looks at all the hydrogen spectroscopic data that flow into the value of the proton radius one sees that each individual one has
30:01
big error bars and only if we average over all of them do we get the small error but maybe one is not allowed to do that there are some new experiments carried out in our laboratory with axel beyer studying one photon transition in a cold beam of metastable 2s atoms from 2s to 4p this is
30:26
essentially balmer beta and he went through great pains to eliminate any conceivable systematic error and so he now has some result which is on the other side actually of the proton radius
30:48
determined from muonic hydrogen i don't know if this is really conclusive but it suggests that maybe that would be the solution that we are not discovering new physics but we are discovering old errors in spectroscopy of hydrogen nonetheless so if we for a moment
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assume that the muonic hydrogen gives us the right proton size then we can see how will this affect the rydberg constant and so here we have the official value of the rydberg constant according to the most recent co-data adjustment of the fundamental constants and if
31:25
we take the bionic hydrogen radius we see that the error bars shrink quite a bit almost in order of magnitude which is a major step for a fundamental constant but we also move the rydberg constant which has of course consequences in all kinds of precise predictions
31:45
i have to come to an end let me just briefly mention way soon maybe even this year i expect to uh see the first results of laser spectroscopy of anti-hydrogen and of course the question whether
32:02
hydrogen and anti-hydrogen are precisely the same or if there is a tiny difference is very monumental for our understanding of nature and even the tiniest difference would be important therefore the more digits you can get in measurements the better uh also in astronomy frequency combs are now being installed in large observatories with
32:28
highly resolving spectrographs and there are a number of areas where maybe one can discover more about light and matter so first you can use it to search for earth-like planets around sun-like stars but of course you can test for general relativity you can maybe get
32:47
observational evidence for possible changes in fundamental constants there is also the question are these cosmic red shifts that we observe are they shifting are they changing with time can we get earthbound observation evidence for the continuing accelerated expansion of the
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universe and it looks like this might be possible and of course how little we know about the universe is illustrated here where we assume that 68 percent is totally unknown dark energy
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and 26.8 percent are dark matter of unknown composition so there is still a lot to be discovered and the progress that we have made in our own lab was really not so much
33:41
motivated by this important question but more by curiosity and by having fun in the laboratory