WEBVTT

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how do you measure something that's really really small

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well first you might try a measuring tape then calipers and if you've got a

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big budget you might treat yourself to a scanning electron microscope

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but there is one very clear problem with

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all of those solutions a they're too small and b

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they don't use lasers at lago they had the right idea so by

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shooting a laser four kilometers down this tube they're able to get an

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accuracy of one ten thousandth the charge diameter of proton

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that's like measuring from here to the closest star with the accuracy of a hair

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which i don't know i still don't have context for that but it got them a noble

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prize for physics and they were the first ones to get gravitational waves

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detected so awesome

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glasswire lets you instantly see your current and past network activity you

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can detect malware and block badly behaving apps on your pc and Android

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device and you can use offer code Linus to get 25 off glasswire at the link

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below

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gravitational waves happen all the time every time a mass accelerates waves

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ripple through space time so like i'm actually waving space time right now

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but it only really becomes noticeable when crazy massive things start

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accelerating like black holes colliding when einstein first predicted

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gravitational waves in 1916 he thought they were a problem with his algebra and

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then later when he believed that they were real he figured it would still be

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impossible to detect them but of course that hasn't stopped people from trying

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in the 50s joseph weber first tried to detect gravitational waves using the 6

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000 pound chunk of aluminum the idea is that it would resonate

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when gravitational waves went through it and that would be picked up by these piezoelectric crystals on the top

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unfortunately it just wasn't possible to get the precision needed

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in 1972 though ray vice wrote a paper

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detailing just how an interferometer could be used to detect gravitational

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waves basically he wrote a laser beam could go

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through a beam splitter and then down two four kilometer long tubes at the end

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of each of these tubes would be a mirror that sends the beam back where it would

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be recombined by the beam splitter and then measured

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normally when recombined in this manner the two beams would destructively

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interfere but if a gravitational wave were to pass

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through the detector it should physically distort space and time

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causing the length of the two arms to very slightly change compared to each

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other this would change the interference of the two beams ultimately changing the

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signal on the photo detector at the end

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in 2002 then caltech and mit joined

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forces to create iligo a proof that this

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could work and after extensive research and an upgrade to advanced ligo we were

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able to successfully detect gravitational waves in 2015.

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and by we of course i mean humans as a as a species not me i i

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wasn't involved so behind us is the beam

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splitter so it comes from the laser room back there which is why we have to have

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these laser glasses on it gets split right around here and then gets sent off

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the arms that way and that way it then travels back in and is detected

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over there somewhere unsurprisingly taking measurements that precisely in

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the real world is a lot easier said than done any particles in the air will cause

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the laser to scatter and although they're only sending in 20 watts of

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laser power the way it works is to have the beam trapped as a standing wave

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inside so after 300 bounces or so that

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amplifies it to about a hundred kilowatts with power like that even a

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tiny speck of dust on the mirror could absorb enough heat to permanently damage

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it meaning that the four kilometer tubes or arms have to be under an ultra high

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vacuum so this is the concrete that goes around the ARM it doesn't actually help

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with the laser tube but it's just to protect it from like cars animals stray

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bullets or whatever

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the real magic though happens in this three millimeter thick stainless steel

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tube which is hold to one trillionth of an atm

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even the vacuum outside the international space station can't hold a

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candle to what they've got going on in here so how did they build it

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well first they cooked or more accurately

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baked now if regular stainless steel was used for this hydrogen and other

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particles on the metal could contaminate the vacuum so to combat this every

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inside surface needs to be heated to at least 170 degrees celsius and held there for

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an extended amount of time now for the nuts and bolts that's pretty simple i

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mean i could do that with my toaster oven at home but for something this

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large what they had to do was pump a

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quadrant of it full of electricity effectively using the resistance of the

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metal to turn it into a heater and hold it at 170 for a month with the vacuum

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pumps running to remove all the contaminants i guess that's probably why

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they wouldn't let us inside we are the contaminants

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so that's cool now the laser can make its way from one end to the other but

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what about the mirrors on the end even something as small as a truck on

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the highway or an earthquake in taiwan would create too much vibration for

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gravitational wave detection which i guess is probably why they put

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their air conditioner way off away from the building rather than up on top of it

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like normal people this is one of the mirrors from iligo to

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reduce the high frequency vibrations the mirror is hung like a pendulum by this

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steel wire and the lower frequency vibrations are decreased by the springs

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on the lower base but they obviously weren't done there in the

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newer version the mirror is hung from four pendulums by glass fibers

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and that is far from the end on the bottom of the table there's actually a

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seismometer that measures any movement in the ground and then uses that

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information to manipulate voice coils and static electricity to actively

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cancel out the vibrations coming from the ground

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at this point then the mirrors are basically perfectly still

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but they still aren't done yet

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for some frequencies their level of accuracy is being determined by quantum

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mechanics and the heisenberg uncertainty principle but even this can be reduced

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using quantum squeezing on a very basic level they can only know

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so much about the amplitude or phase of the laser light but for this application

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the amplitude of the light being detected matters a lot less

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so they're able to perform a quantum squeeze and get better accuracy out of

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the phase detection so they're using a ktp crystal that is a

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potassium titanal phosphate crystal and this is able to transform one green

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photon into two infrared photons or vice

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versa energy is conserved here because the infrared light has less energy than the

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green light so what they do here is pump a crystal

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full of infrared light this is just to get a lot of green light and high

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powered infrared lasers are easier to get and then that green light is sent

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into another ktp crystal but when those photons are emitted they

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are quantumly entangled now in a vacuum there naturally exists a

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lot of noise particularly when there is very little light like around the dark

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end of the detector so by injecting these entangled photons they're able to

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remove the completely random vacuum noise and replace it with the entangled

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photons that produce noise that they like

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now you're probably thinking i am too holy sweet crap

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how could they even verify that these are actually gravitational waves they're

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detecting and the answer is by building another

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detector on the other side of the country so that if a gravitational wave

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is detected they can confirm that it isn't just a localized movement oh and

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also by using two observatories to try and find where the astronomical event is

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happening so with the accuracy of the

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interferometer mostly figured out how the heck do they acquire all the data

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and process it ah yes my friends we are finally getting to the computery part of

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the video in here they collect data from 250

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000 channels simultaneously and then to isolate the signals being created by the

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detector from the computers they actually put the noisy bits of the

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computer cpus power etc in another room

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150 feet down the hall and they connect them using fiber optic pci express

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extenders the most important thing with the computing here though is timing so every

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processor's clock in this server room is

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synced using a custom built system since the processor's timing has to be

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precisely known in order to calculate the time of the events in the

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interferometer but it's not just synced in this room there are also computers at

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the very ends of the laser arms four kilometers away with their clocks

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perfectly synchronized too and the 22 microsecond transmission time

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delay taken into account oh and that second gravitational wave

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observatory in louisiana you guessed right the processor clocks are perfectly

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synchronized there too once the data is collected it gets sent

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over to their server warehouse for analysis and very quick analysis is

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important since if there's a large astronomical event taking place they'll

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detect it here first and then they need to be able to tell their astronomers

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where to point the telescopes in a timely manner

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so all that processing is handled in here where they've got 6

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000 processing cores 64 gpus almost 4

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terabytes of RAM and close to 5 and a half petabytes of data stored on SSD

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spinning and tape storage the data is then copied from here to

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caltech servers where it is further analyzed and made available to more

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scientists and then eventually the armchair physicists at home

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and they're still not done future plans to improve their accuracy involve using

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cryogenics to reduce the movement of the molecules on the mirrors detecting

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changes in the earth's gravity to remove noise from movement below the earth's

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crust implementing quantum squeeze that can be changed throughout the frequency

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band and even building a space-based

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gravitational wave observatory the goal is that with every little

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adjustment they should be able to see even further into space collecting a bit

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more data about how our universe works

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so a huge thanks to ligo and particularly amber you rock for letting

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us come and hang out in the observatory and a huge thanks to you guys for

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