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Einstein, Time, and Cool Stuff

William D. Phillips

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What does NIST do?

length

time

mass

Images Copyright Shutterstock

Among other responsibilities, the National Institute of Standards and Technology is

the keeper of the the standards of measurements for the United States.

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Time and Einstein

What is time?

Images Copyright Shutterstock

Time is what a clock measures.

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Clocks “tick”…

… and different clocks have different “tickers.”

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The best tickers are atoms.

Every quartz watch crystal vibrates at a rate

different from every other one.

Every 133Cs atom is absolutely identical to every other one.

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Spring forward

Cesium atom clocks like the one in this cartoon are accurate to one second in 3

million years.

Copyright Nick Downs

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Spring forward

Cesium atom clocks like the one in this cartoon are accurate to one second in 3

million years.

Copyright Nick Downs

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Spring forward

Cesium atom clocks like the one in this cartoon are accurate to one second in 3

million years.

Copyright Nick Downs

Who needs a clock this

good?

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My goodness, it’s 12:15:0936420175. Time for lunch

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Who cares?

One reason we need atomic clocks is the Global Positioning System.

Atomic clocks in satellites guide cars, planes, backpackers, even golfers.

Image Copyright ShutterstockImage NASA

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How GPS WorksAll the satellite clocks are synchronized.

They broadcast their time and their location.

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By the time the time signal reaches you, your clock has advanced a little, so you know how far away that satellite is.

How GPS Works 2

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Each satellite, at a different distance, shows a different delay.

How GPS Works 3

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Knowing how far you are from two satellites tells you where you are (if you, and the satellites were on a flat

sheet.

How GPS Works 4

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In a 3-dimensional world, you need three satellites in view (four if you

don’t have your own clock) to tell where you

are.

How GPS Works 5

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# 1: Atoms Animations

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#2: Hot & Cold Animation

18Demonstrations

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The Absolute or “Kelvin” temperature scale

0 K => absolute zero

300 K => room temperature

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The Absolute or “Kelvin” temperature scale

300 K => room temperature273 K => ice melts

0 K => absolute zero

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The Absolute or “Kelvin” temperature scale

0 K => absolute zero

300 K => room temperature

195 K => dry ice

273 K => ice melts

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The Absolute or “Kelvin” temperature scale

0 K => absolute zero

300 K => room temperature

195 K => dry ice

273 K => ice melts

185 K => a cold day in Antarctica

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The Absolute or “Kelvin” temperature scale

0 K => absolute zero

300 K => room temperature

195 K => dry ice

77 K => liquid nitrogen

273 K => ice melts

185 K => a cold day in Antarctica

24pull out balloons

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#3: balloon animation

Hot gas—atoms are free and isolated, but

fast.

Condensed “gas”—atoms are frozen, stuck to each other and the container.

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Comet photo courtesy NASA

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#4: Comet animation

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Na Optical Molasses

How cold are these atoms?

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The Absolute or “Kelvin” temperature scale

0 K => Absolute Zero

300 K => room temperature

195 K => dry ice

77 K => liquid nitrogen

273 K => ice melts

185 K => a cold day in Antarctica

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The Absolute or “Kelvin” temperature scale

0 K => Absolute Zero

300 K => room temperature

195 K => dry ice

77 K => liquid nitrogen

3 K => outer space

273 K => ice melts

185 K => a cold day in Antarctica

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T = 700 nK (Vthermal < 1 cm/s)

100 million times colder than liquid nitrogen

4 million times colder than outer space.

We have gotten cesium atoms as cold as:

Atoms this cold make great clocks.

This was 200 time COLDER than everybody thought was

possible!

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This clock is accurate to one second in 80 million years…

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Clocks with laser cooled ions (electrically charged atoms) are good to 1 second in a

billion years…

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Clocks with laser cooled ions (electrically charged atoms) are good to 1 second in a

billion years…

… close enough for government work.

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But where do you keep the coldest gas in the universe?

No ordinary container will do.

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But where do you keep the coldest gas in the universe?

No ordinary container will do.

We use a magnetic bottle.

Use a magnetic bottle

38Trapping-levitation

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laser cooled clock performance

Using a magnetic bottle as a container for ultra-cold atoms…

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laser cooled clock performance

…and evaporating atoms from the magnetic container, gets to even colder temperatures—less than one billionth of a degree.

Einstein drawing by Bülent Atalay

Using a magnetic bottle as a container for ultra-cold atoms…

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10 000 K

100 K

1 K

10-2 K

10-4 K

10-6 K

10-8 K

10-10 K

10-12 K

surface of the sun: 5000 Kroom temperature: 300 K

outer space: 3 K

liquid nitrogen: 77 K

laser cooling: 0.7 K

Bose-Einstein Condensation: 1 nK

BEC in space (the future):1 pK

logarithmicthermometer

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What’s Next?• Better clocks

• Better tests of Einstein’s theories of time and gravity

• Ultra-cold collisions

• New kinds of materials

• Better understanding of superconductivity

• Quantum computers

• More . . .

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Laser cooling group

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The End

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Atoms in a gas are moving really fast,

and that makes it hard to measure their ticking.

Fast gas atoms make a

fast atomic beam.

about 200 meters/sec

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COLD:

slow atoms

HOT:

fast atoms

Hot and Cold

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How do we cool something without touching it?

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Comet photo courtesy NASA

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We use the pressure of light to push on atoms and slow them down.

Comet photo courtesy NASA