Whenever we open a new window on the  universe we discover something new.

Whether it's figuring out how to see to  greater distances like with telescopes,   or down to smaller size-scales like with  microscopes, or perhaps expanding our vision   to new wavelengths of light or via exotic means  such as in neutrinos or gravitational waves.

Well,   the 2023 Nobel prize in physics has been awarded  to three physicists for opening just such a new   window—but it's not a window to a new size scale  or a new mode of seeing—-it’s for a new window in   time.

It’s for attosecond physics—the billionth  of a billionth of a second that represents the   timescale of the insides of atoms.

This year’s  Nobel in physics is for a microscope in time Every 230 million years the solar system  completes one orbit around the Milky Way.

Every 243 years Venus passes between the Sun and the Earth.

Every year monarch butterflies migrate between the United States and Mexico.

Every 3  seconds a Kinesin protein travels down  one of your cytoskeletal filaments.

As we look to smaller and smaller scales,  we find faster and faster processes.

Makes   intuitive sense—big things surely have a hard  time moving faster than their constituents.

The   trend continues to the smallest scales—the motion  of individual atoms during chemical reactions,   or of individual electrons moving in atoms.

The timescale of their motion is not measured   in microseconds nor nanoseconds, they're  measured in attoseconds.

And this is a very   small amount of time indeed.

There are as  many attoseconds in a second as there are   seconds in the entire history of the universe.

Probably there are some things to be discovered   buried in that universe of phenomena  that play out in every single second.

And this is why the Swedish Academy of  Sciences made a very reasonable choice   in awarding Anne L'Hullier, Pierre  Agostini and Ferenc Krausz the 2023   Nobel Prize in Physics for bringing into  existence the field of attosecond physics.

Before we get to how our newly minted laureates  managed this, let’s talk about why it was so   difficult in the first place.

Think about what it takes to observe  something.

Observing means watching things bounce   off other things, whether it’s light bouncing off  an apple into our eyes or electrons bouncing off   a tardigrade into our electron microscope.

The smaller the object you want to observe,   the smaller the particle you need to fling  at it.

For example, you could get a rough   idea of my shape by hurling beach balls  at me and seeing how they scattered.

But   you’d get a better picture pelting me with  ping pong balls.

Or even better, photons.

Resolving small distances requires scattering  many particles with small spatial separation,   into a well-defined spatial location.

Resolving very small times requires scattering   many particles with small separations in  time and well-defined temporal locations.

Imagine you want to take a video of a fast  process—say, a hovering hummingbird.

If   your camera aperture stays open too long you’ll  only capture a blur over the span of the wings’   motion.

The aperture opening needs to have a  well-defined temporal location—in other words,   it needs to be quick.

But quick exposures aren’t  going to give you a very good movie of the   humminbird if they aren’t separated by less than  a wing beat.

Then you’ll only get a random seeming   collection of stills.

You need short temporal  separation to get a meaningful sequence.

So how   do you get tight temporal location and short  temporal separation down to the attometer?

Let’s start by thinking about the temporal  location of a photon.

That’s limited by its   period—you can’t clock a photon to any time  smaller than a single up-down cycle of its   electromagnetic wave Light with a period  of attoseconds is in the X-ray part of   the electromagnetic spectrum.

We routinely use  X-rays in imaging, so we should be fine there,   right?

Not quite.

A typical laser fires one  photon every few femtoseconds - that’s 1000   times longer than an attosecond.

So even if  you make a movie of attosecond motion with   a conventional laser, the abysmal frame rate  would turn the motion into a hopeless blur.

It is possible to build extremely fast lasers—for  example, Free-Electron lasers… But they require   an electron accelerator to work,  and they are honestly too powerful   and way too dangerous to give to the  average physicist to play around with,   and besides, blasting your sample with an  X-ray laser of the power required would be   like taking an x-ray using a nuclear  explosion, it's just not practical.

Enter our first Nobel laureate.

Back in the  1980s Anne L’Huillier and her colleagues   were playing around with irradiating Argon gas  with infrared lasers.

They observed something   pretty weird.

Normally, when you irradiate  a gas you’ll get different types of light   out.

That includes some of the light you put  in, some light corresponding to the electron   transitions of the atom, as well as some  random thermal light from the jiggling of   the atoms.

But L’Huillier’s team noticed that  the outgoing beam consisted of the original   in-going frequency plus some higher frequencies  that didn’t correspond to any known process.

So where did these other frequencies come from?

It’s pretty cool actually.

As a laser pulse passes   by a gas atom, it can nudge the electromagnetic  field holding the electrons in place in such a way   that electron escapes by quantum  tunneling.

The electron can then be pulled straight back to its atom and will release the energy it   gained in a single photon, think of it like a  stretching a spring and letting it go.

That one   photon will have a higher energy than each of the many photons that made up the laser pulse.

In fact it’ll have a frequency that’s some  integer multiple of the laser photons, and   a cool detail is that it'll be an odd  multiple, for complex reasons regarding symmetry This process is called high harmonic generation,  and it basically adds overtones to the laser beam.

Play a note on any musical instrument and  you’ll get the fundamental frequency plus   higher frequency overtones.

The fundamental  corresponds to the longest wavelength standing   wave that can fit along the resonating string  or air column, while the overtones correspond   to all shorter wavelength standing waves that  also fit.

The balance of the strength of the   overtones determines the precise character  of the sound of an instrument—its timbre.

So, the timbre of the laser was altered  by the argon cloud.

That’s a cute effect,   but we’re not quite at Nobel-level science just yet.

To get to attosecond physics, we need one more   analogy with acoustics.

Listen to this.

It’s  a very low G note.

And this is a very low A.

Individually there’s nothing unusual, but if we  play them together we hear a sort of "wawawa".

This is known as a "beat" in acoustics, and it’s  due to the fact that the sine waves of the G and   the A line up perfectly at certain points, making  them louder with constructive interference, while   they’re perfectly out of alignment elsewhere,  and so cancel out with destructive interference.

For a pair of waves the  beats are quite spread out,   with a lower frequency than both of its  parents.

But if you add more and more waves,   it’s possible to narrow the width of the beats  so you end up with sharp pulses and very little   in between.

For that you need a large number of  frequencies of similar intensity—for example,   the rich spectrum of overtones produced  in Anne L’Huillier’s experiment.

In fact,   it proved possible to get pulses that were mere  hundreds of attoseconds in their temporal width.

Our new attosecond-resolved pulses weren’t  ready for application just yet.

The potential   value is that they would allow us to measure  attosecond-scale events.

But if the pulses   themselves are attosecond-scale events, how  can we calibrate them to start with?

It's   like trying to measure your height with a series  of rules whose individual length you don’t know.

And here we get to our second Nobel  Laureate, Pierre Agostini.

Agostini   was able to calibrate the pulse train by  again using constructive and destructive   interference—this time in reference to  the ingoing laser beam.

He did this by   deflecting part of the beam and adding a  delay to it before recombining it with the   now-frequency-multiplied beam.

In this way he  could measure the width of the pulses—clocking   them at 250 attoseconds.

He also found that  the pulses were what we call phase locked,   which means the beats were nice and consistent and  just what we needed for attosecond measurements.

These pulse trains provided pulses with  attosecond temporal locality and separation,   just as we required.

But for some applications  it would be preferable to have single,   isolated attosecond pulses.

And that  effort is thanks to our third Laureate,   Ferenc Krausz.

I won’t go into the gory details,  but for your viewing pleasure here’s their   Rube-Goldberg experimental setup.

With intricate  phase and amplitude manipulation, they were able   to create isolated pulses of 650 attoseconds,  whose width was known to 150 attosecond precision.

OK, attosecond resolution achieved.

So what can we do with it?

As Krausz himself states   in an interview, they invented this  technology because looking at Nature   in a new way is wonderful, literally, it  fills you with wonder.

But we did just   give ourselves a new superpower,  so it’d be a shame not to use it.

The first application of attosecond pulses  was to look at electron motion in atoms and   molecules.

Electrons travel the breadth of  their orbitals in a handful of attoseconds,   or rather the fuzzy quantum clouds that define the  electron in an atom change on that timescale.

By   hitting these clouds with attosecond pulses we can  study the shapes and dynamics of these electrons.

Attosecond pulses can also be used to  manipulate electrons on tiny timescales,   which has a number of powerful applications.

One  effort that Ferenc Krausz’s team is working on   at the Max Planck institute for Quantum  Optics is in molecular fingerprinting,   in which attosecond pulses are frequency-tuned  to cause vibrations in specific molecules.

In   this way the detailed molecular composition  of a sample can potentially be cataloged.

The   Krausz team are using this to develop molecular  fingerprinting devices for medical diagnosis.

Another very exciting possibility is the creation  of ultrafast electronics.

If we have two metal   plates with opposite electric charge and we  shoot an isolated attosecond pulse at one of   the plates it can be absorbed by an electron,  which hops to the second plate.

This is the   photoelectric effect, and we’ve known about it for  120 years.

But in the configuration I described   it’s also a transistor, a key component in most  of our technology.

Regular transistors control   the flow of electricity between two charged  plates by changing the charge in a third plate,   but this new type of transistor controls  the flow using light itself, which can in   principle be much, much faster—especially if  the pulse width is measured in attoseconds.

Krausz claims that it may be possible  to increase the power of computers by a   factor of 100,000 this way.

That sounds …  optimistic.

But even if we get a fraction   of that it’s an incredible achievement, and  may save Moore's law for a few more decades.

Those are just a couple of applications in  medicine and electronics, but as we look at   the universe with this new tool we are bound to  find new applications and to make new discoveries.

After all, every time we open a new window to  the universe new mysteries are revealed—whether   that window is to the largest, the smallest,  and now the fastest phenomena in Space Time