5 of the Best Measurements In Science

5 of the Best Measurements In Science


[ intro ] If you take all the humans who have ever lived, then, all told, members of our species have probably witnessed around a quadrillion
sunrises — give or take. That’s a quadrillion tests of the hypothesis
that the sun rises in the morning. Today’s humans use what’s called the Standard Model of particle physics to predict just about everything that happens
in the subatomic world. And, coincidentally, it also was tested about
a quadrillion times. … At one single experiment: The Large Hadron Collider. … And in one single year: 2016. We’ve tested it plenty of other times, in plenty of other places. Which means that, in some sense, 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. It’s also about quality. And over the years, scientists have made measurements proving that we understand ridiculously well how the
universe works. [1. Time] 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. And that’s no way to get around. So clocks in your phone and elsewhere are
based on ones that measure very rapid shifts, or oscillations, in electrons within atoms of cesium. Those electrons oscillate at a reliable rate: After this many oscillations, we say a single second has passed. 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. For comparison, the best mechanical watches in the world gain
or lose a second after a day or two. But we can do even better. 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. When it’s that cold, atoms don’t get in each others’ way as
much, which allowed the team to more easily zero
in and count those bounces more clearly than ever before. The clock is so accurate that they’re not
just thinking about using it to keep us all in sync. 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. Once they become more portable, though, these clocks might be our way of doing
it. Scientists don’t expect to see anything
too shocking from these new tests, though. 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. First, there’s its inertial mass. It measures how hard something is to get moving: The more inertial mass, the harder it is to accelerate an object. That’s the one you’re technically measuring
when you use a balance. Then there’s gravitational mass. 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. One is a kind of charge; the other is how much stuff there is. But every time we use an object’s inertial
mass to predict how it interacts with gravity, we get the right answer anyway. The two seem exactly equivalent. 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 — and vice versa. These tests go all the way back 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 can’t be different from each other. General relativity is the best explanation
of gravity that we have, and it completely breaks if inertial and gravitational masses
aren’t equal. Enter the MicroSCOPE satellite, which held
two cylinders that were the same size but different inertial masses. The cylinders floated freely inside the satellite, which orbited Earth 120 times and measured
how Earth’s gravity tugged on both of them during the trip. According to the MicroSCOPE results, if inertial and gravitational mass aren’t
equal, the difference between them has to be incredibly
tiny: About one part in a hundred trillion. For comparison, that’s the equivalent of
measuring the distance to the Moon to within the width of a single red blood cell. That number is all the more remarkable because
gravity is actually really weak by the standards of fundamental forces. So measuring its detailed effects requires
a lot of effort. And MicroSCOPE and other experiments are part
of why astronomers can be so confident that they understand gravity — even when it makes us think there’s weird
stuff like dark matter out there. Compared to gravity, measuring electromagnetic
effects is a snap. Which has helped us find the Rydberg Constant
— one of the best-verified numbers in all of
science. It lets you predict an atom’s spectrum: The colors of light that can come out when
its electrons have a little extra energy. If you can see an object’s spectrum, you can
tell what elements it contains. Scientists use spectra all over the place: doctors use them to measure lead in people’s
bodies; astronomers use them to discover what stars
are made of; and they’re everywhere in between. This light show happens when the electrons
around the atoms lose a bit of energy. That energy has to be shed in an incredibly
specific quantity, which takes the form of a photon of light. And that photon will have a wavelength that
corresponds to its energy. Which is a fancy way of saying it’ll be
a specific color. But to predict these things, we need a constant for the math to work out. If you can measure the energy of the light
that’s emitted, and you know the extra energy the electrons
had in the first place, then you can reverse engineer yourself the
Rydberg Constant. Except that of course it’s not quite that
simple. Electrons get in their own way, stretching
out and altering the light that they emit. So you can’t just measure the light from
a single atom, or even a single kind of atom. To measure the Rydberg Constant, scientists have to study three different kinds
of small atoms: Regular hydrogen; helium; and deuterium, which is hydrogen with an extra neutron. Scientists give the atoms a little extra energy, split the light that comes back out into its
constituent colors, and use those colors to measure the Rydberg
Constant. And the number they get looks like this, where those last two numbers in parentheses are how much the very last digits could be
wrong. That quantity is technically called the uncertainty. And as a fraction of the overall number, it’s telling us that we know the Rydberg
Constant with as much error as we’d know the distance
from your eye to the Moon if we had to worry about blinking. Because the thickness of your eyelid changes
that distance by about ten times more than the uncertainty
we have in the Rydberg constant. Yes, that’s thicker than a red blood cell
— but in a way, this number is actually more impressive than
knowing two masses are the same. It tends to be easier to compare two things
— like masses — than to come up with a number like the Rydberg
constant out of the blue. So the fact that it’s so precise is pretty
nifty. The Rydberg Constant might be one of the most
precise measurements out there, but there’s at least one that beats it. It’s called the electron g factor, and its value is arguably the best match between a prediction and a measurement in the history of science. The g factor has to do with an electron’s
anomalous magnetic moment, which is one of those names that sounds more
complicated than it is. Electrons are the tiny negatively charged
particles in atoms that have already come up a couple times in
this video. They behave as if they’re spinning, and spinning things with electric charge make
magnetic fields — that’s where the “magnetic” part comes
from. And “moment” is the word physicists use
to describe how strong a magnetic field is. Putting that all together, the electron’s magnetic moment is the strength
of its magnetic field. And it’s anomalous because it’s weird. It’s not exactly what you’d expect if
you imagine the electron as a tiny spinning ball of charge, because electrons aren’t little spheres
and they also interact with the empty space around them. Hence: The electron’s anomalous magnetic
moment. The g factor is a measure of just how anomalous
it is. The great thing about the g factor is that,
like the Rydberg Constant, it’s fairly straightforward to measure it
in an experiment. But it’s also possible to directly predict
what it should be based on parts of the Standard Model of particle
physics. So it’s another place where we can directly
check if our theories match reality. And with the g factor, they don’t just match. They really match. The g factor gets measured by using an outside magnetic field to split
up electrons whose own magnetic fields point in different directions. There are a bunch of different ways this is
done in practice, but altogether they’ve given us a measured
g factor that looks like this — where, again, the parentheses are the amount
the last couple digits could be wrong. And by calculating based on the Standard Model, scientists get a number that looks like this. The precision of that measurement is like knowing the distance to Mars to within
the length of a couple thumbtacks. And it’s part of what people mean when they
say that the Standard Model is one of the best-verified
ideas in human history. Better verified than knowing the sun will
come up tomorrow! In chemistry, we learn that if an atom has the same number
of positively charged protons and negatively charged electrons, it’s electrically “neutral”: From far away, it looks like there’s no
charge there at all. But that’s only true if protons and electrons
have exactly opposite charges: Protons are plus one; electrons are minus
one. There are good reasons to think this is true: If it weren’t, even a tiny difference would
add up across the trillions and trillions of protons
and electrons in just about anything around you. We’d definitely notice like constant lightning
bolts shooting out of everything. But that was a little too hand-wavy for a
pair of physicists in the seventies, who verified that if electrons and protons
don’t have exactly opposite charges, they can only be different by less than about
one part in a billion trillion — that’s a one with twenty zeros after it. Which is something like knowing the distance
to the Sun to within the diameter of your DNA. What they did was put a bunch of a heavy gas called sulfur hexafluoride into a container
about 20 centimeters wide. They put the gas in an electric field that
flipped back and forth. If protons and electrons didn’t exactly
cancel, the electric field would make the gas particles
start to push each other around. Flipping the field back and forth would then
make the gas start vibrating, creating sound waves that could be picked
up on microphones around the experiment. They did that, and the mics didn’t hear
anything, and that told them that electrons and protons
must have exactly matching charges — or, at least, very close to it. Scientists don’t make these absurdly precise
measurements just to one-up each other. Ultimately, we want to understand the universe
— especially the parts we’re clueless about
like dark matter and dark energy. They have no place in our current models,
which means those models have something wrong with them. Every one of these ultra-precise measurements
is an opportunity to find where those models fail. And every time a team finds exactly what they
expect, it gets harder to make room for something
brand-new to sneak in. Because if you know the distance to the Moon
to within a red blood cell, you can be pretty sure there’s not an elephant
standing there. Modern physicists hear thumping feet and trumpeting
trunks. But when they look closely, there’s no elephant. Not yet. Thanks for watching this episode of SciShow, writing episodes like this is not easy and We have amazing community of supporters that
allow us to do it, and if you want to join them, you can get
started at patreon.comscishow. [ outro ]

100 thoughts to “5 of the Best Measurements In Science”

  1. So… 111 thumbs down… I can never understand why someone would even think of doing that! Or do they just not "like" Hank?

  2. To be clear, the clocks in our phones and computers are not "based on cesium" clocks in terms of their design. They are based on crystals and in some cases MEMS devices. Better to say, "the time kept in our phones is based on time kept by cesium clock". Clock refers to the mechanism of time keeping, not the time value itself.

  3. Black Widow kicking some poor HYDRA agent off the roof. Saying "Oops, I thought gravity is a very week force…"

  4. 3:50 – a balance scale measures inertial mass, not gravitational mass.
    Woh-woh-woh-woh-woh!
    You can’t just do that as a hit-and-run.

  5. One minute in, and I'm pausing to tell you that this is pseudoscience, complete with ironically condescending douche-bag hipster.

    "The sun rises in the morning" as a hypothesis? First of all, no. This is a bit of definitional tomfoolery. The morning is either defined as the time around the sunrise, in which case the "hypothesis" is silly; or else it's defined around a specific period of time in the day, in which case you're either adjusting that time with something like time zones (in which case it's just the same as "the time around sunrise") or else you're just wrong, because the sunrise is constantly happening, just at different places during the day.

    Secondly, watching the sun rise in the morning is not a test of a hypothesis because it's a confirmation of an expectation rather than a test for falsification.

    Learn to science.

  6. “The sun will rise tomorrow” doesn’t even need to be tested. It will always 100% be true. Because if it doesn’t rise, then it’s not “tomorrow” yet.
    Those 2 are not just correlation but actually causation. Which makes it always true. In the past, now, and in the future. 🙂

  7. It's childish, but go to google translate, select Dutch as your source language, English as your target language and type in stront OR
    https://translate.google.com/#view=home&op=translate&sl=nl&tl=en&text=stront
    I'm so sorry, but for once I had a laugh because Dutch is my mother tongue

  8. National science day is celebrated in India on 28th February each year to mark the discovery of the Raman effect by Indian 🇮🇳 physician sir C V Raman on 28 Feb 1928.The celebration also includes public speeches radio TV shows science movies science exhibitions based on themselves and concepts watching the night sky live project research demonstration debates quiz competitions lecturs science model exhibitions and many activities

  9. first minute:
    the "thorough testing" of the standard model of particle physics is Done by whom tho?
    they are not people – that do the testing, that are in any way under our control at all
    even tho it was probably we that paid for the dam LHC

  10. 2nd minute: so they can actually see an electron now then?
    "the team watched strontium atoms very closely" they must! that's new

  11. 9:47 so electrons move as a wave as well as in straight lines and presumably
    the electrons move in circles around the nucleus, don't they?
    they can't be seen, can they? electrons

  12. How can the GPS get an error of a few hundred meters for just a milionth of a second? Intuitively, it makes sense to for the distance measurement to be off by the satellite's speed divided by the delay time

  13. You can't comment directly on ads, but I think you guys will understand. I just had an ad for "Lego Friends", which started "What's that? It's a cube!" but it was clearly *not a cube*. It was like 10x10x6 cm, and the corners and edges were extremely rounded. It made me upset. There, I said it.

  14. Everything in science is based on the concepts of Standardization & Measurement . In fact, it's pretty much impossible to do scientific experimentation without them.

    The impact that these two concepts have had upon everything that makes up our modern world is so staggeringly vast that it's almost (paradoxically) immeasurable, yet they're so banal that most people haven't a clue how important they truly are.

    When you pick up a specific type of screw that was manufactured in China in 2019 & insert it into the threaded socket of a piece of machinery made in 1975 , you can be completely confident that it will fit because of Standardisation. (You can thank British Engineer Joseph Whitworth for beginning the standardization of screws way back in 1841 , btw.)

    Throughout the majority of humanity's time on this planet, this simply hasn't been the case, with the components of a specific piece of technology (of whichever era) often being made by a singlular skilled craftsman. Try to imagine building the Egyptian Pyramids if each group of masons had a radically different standard for the size of the blocks to carve. A precision flintlock rifle made by one studio of British artisans in the 1700s , would have slight variations in the dimensions of components to another (despite being made by the same manufacturer, likely with the same jigs/templates), making repairs, & especially disseminating improvements, very difficult indeed. (Most of the time parts needed to be modified to fit, or even made from scratch – & necessarily by another skilled gunsmith. Now anyone can replace a standardized worn or defective tech component in minutes.) Incidentally, this is one of those things which makes the Antikythera Mechanism (a primitive analog computer made of bronze gears & levers) all the more extraordinary: so much of it's design & manufacture had to come from one single genius craftsman (or perhaps a studio of various craftspeople working together), all in approximately 150BC ! (Some people can be said to be "Ahead of Their Time" by a few years/decades, but how many are advanced by Millennia !?)

    ~ ~ ~

    Right now there is an International Organisation with the sole purpose of clearly defining the standards of damn near everything. The International Organization for Standardization is known by the letters ISO & it has been utterly invaluable in the development of our Tech driven world. Note that the US has it's own standards organisation (which works with the ISO ). It's called The American National Standards Institute ( ANSI ).

    ~ ~ ~

    As an exercise, try to think of how much of an impact that one single tech standard: Universal Serial Bus , or USB , has had on your life, personally.

  15. Nah the g factor is definitely more complicated than it sounds, whatever you call it. If you think it's simple then you don't understand it.

  16. The strontium clock is so accurate that you can measure how much it speeds up when you raise it out of earth's gravity well a fraction of a meter. That makes it the world's most expensive altimeter.

  17. My understanding is that more-recent atomic clocks in GPS satellites are the Rubidium type, not cesium. https://www.satellitetoday.com/uncategorized/2020/01/10/frequency-electronics-rubidium-atomic-clock-completes-critical-design-review/ and
    https://apps.dtic.mil/dtic/tr/fulltext/u2/a427869.pdf

  18. @3m20s

    https://www.nist.gov/news-events/news/2010/09/nist-pair-aluminum-atomic-clocks-reveal-einsteins-relativity-personal-scale

  19. Nice, those are great measurements indeed! A few minor remarks: 1. LHC is not the experiment, ATLAS is (in this case). The LHC is "just" the apparatus to accelerate the particles. 2. The clocks in phones and such are based on oscillations in a piezoelectric crystal, which is a different kind of timekeeping that atomic clocks do

  20. Funny how when the models AND all real world observations can't prove dark matter's existence that it must be faulty models and equipment. It couldn't possibly be that someone with a PHD is wrong. Couldn't possibly be that 'dark matter' is simply dust and wispy gasses that you can't see with current telescope technology. Nope. It must be some new wild and exotic material that behaves in bizarre ways, is ubiquitous, and imperceptible. Makes sense.
    While I have no interest in being the first man to open a hot dog stand on the Sun I fully support your efforts to do so.

  21. The clock in your phone is not based on vibrations of cesium, the clocks in navigation-satellites are. I'm kinda surprised SciShow would make this sort of mistake

  22. What would be the implications of the charges of the proton and election weren't evenly matched? Is there an explanation for why they are exactly the same? Are they connected at the fundamental level? Could there be an alternate universe where they aren't the same?

  23. I presume you guys factored in the fact that the distance from the earth (um, which exact part of Earth..? I expect the highest elevation of rock and/or plus snow (which itself is variable) / or maybe sea-level (but then, during which tide?).. or the outer most reach of the atmosphere? .. (which is nebulous) – then again we're talking about the width of a red blood cell, or thickness of a strand of DNA… right?), to the moon and sun changes over time? … nevermind. (Too many nested parentheses… (..and ellipses..)).

  24. Measurement of time or calculating when a specific thing will happen is impossible when relativist equations come into play. Space and time are related to one another. The more that the universe expands and the speed that it expands, plays a role in what "time" is.

  25. 5:03 ah Apollo program and its XIX century quality of most important shots… hehe
    https://en.wikipedia.org/wiki/Color_photography#/media/File:Prokudin-Gorskii-12.jpg

  26. That was cool. I wonder if current physics will be looked upon like general relativity looks upon Newton's laws. It's not wrong or small, but looks like foundation stones to a building. You can't fathom the greatness of the later by looking at the first.

  27. Fundamentally flawed I’m afraid. It implies that time is a constant when it’s anything but. Mass itself equals time. thus one second or say Planck second could be the lifetime of the universe.

  28. "Welcome to the Scishow writing staff! What are your qualifications?"
    "Well, I like measuring how far stuff is to other stuff."

    "For instance, how far away is this guillotine to a trio of very wealthy orphans?"

  29. Great episode, thanks for posting. I would like to point out one small error. At around 3:15 you mention that the gravitational effects on time dilation at earth's surface are waiting for more precise clocks (if I understood you correctly). But this has long been demonstrated by the Pound-Rebka experiment back in 1959, with detection of a slight change of light wavelength over the height of a building. Mathematically, this directly correlates to time dilation. Other tests have shown this effect over a few meters in a lab.

  30. the standard model explains 4% of the universe…that's it…research the electric universe theory and you will see exactly what BS the standard model is

  31. They "don't want to one-up each other"?Then why do they have names like "very large array", "even bigger array" and such? Come up with something like "12 meter array" or "one eagle per basketball field array" if you need to use a measurement that americans understand. Like thumbtacks.

  32. "They put the [sulphur hexafluoride] gas in a container…" then breathed it and had fun singing the bass line of popular songs.

  33. Its the ether. It cant be measured. Trying to measure it is like trying to follow one specific atom of oxygen or hydrogen in the ocean. No matter how close you look you won't see it. And by the time you can see it, it wouldnt be the ocean you're looking at anymore.

  34. Four of the five segments contain things that are either wrong or misleading.
    1. My phone doesn't have an atomic clock in it.
    2. When I use a balance I'm measuring gravitational mass, not inertial mass.
    3.
    4. Those two numbers are written with different precision. This makes it look like the measurement is 14 times more accurate than the prediction, while in fact it's only 1.4 times more accurate.
    5. A billion trillion is 10^21, not 10^20 (and also one of those horrible things americans say that only makes things harder to understand).

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