Name: 5 of the Best Measurements In Science
Uploaded: 2020-03-30T03:22:27.000Z
Duration: 14 min 7 s
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Relative clauses (Restrictive vs. nonrestrictive)

If you take all the humans who have ever lived,

have probably witnessed around a quadrillion sunrises --

That's a quadrillion tests of the hypothesis that the sun rises in the morning.

to predict just about everything that happens in the subatomic world.

And, coincidentally, it also was tested about a quadrillion times.

we have more evidence for the predictions of the Standard Model

than for the prediction that sunrise will happen tomorrow.

That is what it means for an idea to be well-tested in physics.

But proving something right isn't just about quantity.

scientists have made measurements proving

that we understand ridiculously well how the universe works.

If a GPS's clock is off by a millionth of a second,

it will think you're a few hundred meters away from where you actually are.

So clocks in your phone and elsewhere are based on ones that measure very rapid shifts,

Those electrons oscillate at a reliable rate:

While tiny counting uncertainties mean that cesium clocks aren't perfect,

the best ones will take about 300 million years to be off by as much as a second.

the best mechanical watches in the world gain or lose a second after a day or two.

In strontium, electrons oscillate about fifty thousand times faster than in cesium.

If you can keep track of the darn things,

you can use them to make an even more accurate clock.

The technology for measuring such quick changes

is only a couple decades old, and it's still being perfected.

But in 2018, a team was able to watch strontium atoms so closely

that their clock wouldn't gain or lose a single second in over a hundred billion years

in the neighborhood of ten times the age of the universe.

They did it by cooling about ten thousand strontium atoms down to just fifteen nanokelvins

fifteen billionths of a degree Celsius above the coldest possible temperature.

atoms don't get in each others' way as much,

which allowed the team to more easily zero in and count those bounces

The clock is so accurate that they're not just thinking about using it to keep us all

But it is useful for a reason General relativity is the name of our modern theory of gravity,

and one of its weirdest features is that time itself should tick

at slightly different rates at different elevations above Earth's surface.

We've measured this effect in satellites --

GPS wouldn't work if we didn't account for it --

but we've never had clocks that were precise enough to check general relativity's odd

temporal effects down here on the surface.

though, these clocks might be our way of doing it.

Scientists don't expect to see anything too shocking

Because general relativity has passed some pretty incredible tests of its own.

When physicists talk about something's mass,

they're really talking about two very slightly different things.

It measures how hard something is to get moving:

the harder it is to accelerate an object.

That's the one you're technically measuring when you use a balance.

that measures how much something interacts with the force of gravity

-- so it's like a sort of gravitational “charge”.

Electrically charged objects respond more to electric fields than uncharged ones.

So if gravitational mass is akin to charge, objects with more gravitational charge --

that is, mass -- feel the gravitational force more.

Viewed this way, there's no reason inertial and gravitational mass

should have anything to do with each other.

But every time we use an object's inertial mass to predict how it interacts with gravity,

The classic test is to see if everything falls at the same rate regardless of its mass.

If they didn't, things with more inertial than gravitational mass would fall more sluggishly

to Galileo supposedly dropping two cannonballs off the Leaning Tower of Pisa,

and all the way forward to astronauts actually dropping a hammer and a feather on the Moon.

These and other tests established the equivalence of inertial and gravitational mass so thoroughly

that in general relativity -- that modern theory of gravity I mentioned earlier -- they

General relativity is the best explanation of gravity that we have, and it completely

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5 of the Best Measurements In Science

equivalent

incredibly

constant

slightly