Why are there giant concrete tunnels in the desert?

this is going to be you know one of the next huge discoveries and it happened [Music] there's this place in the Washington desert where giant concrete tunnels run for miles out into the sand for 20 years they protected a strange technology that will become humanity's first glimpse into an unseen universe hey I'm Diana and you're watching physics girl last month we traveled to Hanford Washington to see the site where gravitational waves were first detected because gravitational waves are one of my obsessions gravitational waves are invisible inaudible waves in space itself and time rippling through the universe through earth through us all the time it turns out space-time can stretch like a slinky and can carry waves across the universe my professors told away net we don't know when we're gonna discover gravitationally is it could be the next ten years could be the next 50 we don't know if this detector is gonna work and then when the enough so is they did 2015 which was only like four years after I graduated I was like what gravity is cool it's also weird it doesn't affect space instantaneously if the Sun suddenly disappeared poof the earth would continue on orbiting as if the Sun were still there for eight minutes and twenty more seconds until that information about the change in the gravitational field would get to us and then earth would fly off into space but at that same instant light would reach us too and we would see that the Sun is gone but you know what that means the speed of gravity and the speed of light are the same that's one of the many things that we've confirmed down to the order of ten to the minus 15 from the detection of gravitational waves and those giant concrete tunnels those are the exoskeleton of two giant arms of the first gravitational wave detector LIGO gravitational wave detectors has to be huge because they need to detect waves coming from billions of light-years away they're so sensitive that trucks nearby affect the signal when we were there they told us to accelerate and decelerate slowly so as not to disturb the detector and so the AC unit is not even connected to the building they had to put it in a separate enclosure on Springs so that it wouldn't mess with the signal and then there's this those liquid nitrogen tanks tubes that go inside they carry the liquid nitrogen inside yeah and they were getting ice around those - yeah the Ravens were coming out and pecking at that oh my god and that little bit of vibration coupled back into the interferometer but that insane sensitivity allowed us to detect an entirely new type of phenomenon I should tell you how the detector works so this is like a cross-section of what the cement tunnel would look like this is one of the sections of the concrete structure yeah beam tube cover the concrete tunnels house two four kilometer long tubes made of metal that are actually under vacuum which is surprising because the metal is pretty thin so that is holding in that hand a powerful laser is shot out and split into two beams and each is sent off into the X&Y arms of the detector that's what they call them then depending on the distance of those laser beams travel when they meet back up again the waves add and they interfere and make patterns like waves that overlap in water making patterns if space is stretched or squeezed in one of the directions bypassing gravitational waves the laser beam in that arm will travel a shorter or longer distance affecting how the two waves the two beams add up when they're recombined and we can tell space has been stretched by a gravitational wave we're trying to do everything possible to keep any particulate up we're just hairnet and into the experiment home from what I remember because I've been here before this is the laser that like that enclosure over there is the belief that infrared laser beam came comes out of that big building thing over there and through here and then this is where it splits into the two beams and then when they come back and they merge here as well go down this way we come to where we've got the photo diodes this is where the gravitational wave signal is detecting that was the photodiode that detected the actual first gravitational wave and I got to hold it kind of I I got close to it Wow you tell me not to touch it now the next thing to consider is where to put one of these detectors you can't just put it anywhere they have to be far away from earthquakes or people because they they move too much some people can't stop moving you can't even have the laser going through the air because there's too much noise and just the gas in the atmosphere so the tubes of the detector arms are completely evacuated of everything plus there are other crazy considerations the tunnels are so long that they have to correct for the curvature of Earth over four kilometers the earth drops about a meter in half the detector is so sensitive it's affected by quantum fluctuations which is essentially randomness caused by quantum mechanics in the mirrors some of the problems that arise from noise are solved by having an identical detector nearly 2,000 miles away doing the exact same thing there's another LIGO in Livingston Louisiana and when a gravitational wave passes through both detectors the signals line up perfectly and one more thing both detectors have four kilometer long arms but they're actually effectively 1,200 kilometers and the light bounces back and forth on average about 300 times so that makes the arm length not just four kilometers but effectively 1,200 kilometers long and length matters here you need the longer the arm the larger the overall effect that the gravitational wave has on your arms you know what clever way to get an even bigger detector put it in space this is a real plan I was like how are they gonna launch vacuum tubes long enough up into space isn't that hard and then they politely reminded me that space is a vacuum excellent point space scientists now what kinds of things do you see with these detectors oh just super violent events like neutron stars smashing into each other the first detection was to giant enormous black holes colliding 1.3 billion light years away two black holes take the first event you can tell from the waves on that on the ring town that this thing was 62 solar masses so three in that process three times the mass of the Sun were converted into gravitational wave energy at the time it was the most powerful astronomical event known to human beings because of that conversion three times the mass of the Sun in a quarter second that outshines all the stars in the known universe for that car second night of its coming out of light so I'll come out in gravitational waves that makes it super exotic object right many people asking you to set off a nuclear bomb and measure the gravitational waves there it's still a paltry amount compared to what you need to actually see them you heard him right a nuclear bomb puts out an insignificant meager amount of energy compared to what is measurable with gravitational waves I wonder how many nuclear bombs this actually is can you hand me my laptop thank you it's those three solar masses 5 times 7 to the 47th joules versus 2 times 10 to the 10 to the 17 joules the number of nuclear bombs in this collision to about 2 times 10 to the 30th that's 2 with 30 zeros okay that's not even a number I can fathom thank you the only reason they're so small when they get to us is they've been traveling through the universe for a billion years when they first happen they were very concentrated here right yeah and as they start radiating outward they don't attenuate as they go through matter but as it goes out you're now covering up their volume the whole wave together would have this energy right but the amplitude has to go down because it's been spread out so much more so by the time it comes to us a billion years after the collision there in seemingly small one of the reasons that the waves are so small is that space is really really stiff it resists being stretched by a lot it's the stiffest strongest stuff thing I'm not really sure what word to use to describe space but it's the stiffest medium that we know of if you look at what is the in general ativy is effectively the young's modulus of space-time ya which in materials young modulus tells you like how compressible is something is you could say oh here's the link Young's modulus of space-time and let's compare that to steel the young's modulus is kind of a funny number to use as a reference for the stiffness of space because it's usually a number that describes how stiff materials are so for example if you compared space to steel space is 10 to the 20 times 20 orders of magnitude stiffer than steel the numbers we're dealing with here are just unbelievable that's why we need you know black holes and neutron stars stars exploding the birth of the universe these are the kind of things that are actually going to create vibrations in space that will be large enough in amplitude for us to see that first collision event was 1.3 billion light years away which means that it took 1.3 billion years to get to us that's why when it finally got here it only changed the length of one of the arms of detector by one one thousandth the width of a proton if you can wrap your head around how small that is then you're saying to yourself right now no no that's not possible that's too small and if you can't wrap your head around how small that is congratulations you are human it's so small I'm I'm just laughs dude you talked about breaking our brains right like the melting of our brains just thinking about scale alone and I think it helps us understand our place in the universe yeah and then helping people see that it's this beautiful science that explains so much yeah I know you're a better job I really so I relate to all of it since the first collision laga has detected 30 more collisions of black holes neutron stars violent events powerful enough to create gravitational waves that we could detect and we've learned such incredible things from these collisions because this is a new type of astronomy we're able to learn that when two black holes collide which are usually very spiracle objects they have a ring down phase where they turn into this lumpy weird thing that rings down like a bell and what we see at the end of the signal is that ring down we can learn something about a phenomenon that we would never be able to see with our current technology with a telescope whoa LIGO is so freaking cool and the people at LIGO were so amazing I feel incredibly lucky to haven't been able to go on back there cuz I actually went once before for the stellar episode from with PBS you may have seen that went out a couple months ago but this time I brought a bunch of your questions from Twitter and asked them to dr. Michael Landry who was the head of LIGO Hanford and I was so fascinated by his answers that we're gonna make an entire video with just that interview so you can look out for that next week it's gonna feed all of your curiosity but mostly my curiosity on gravitational waves and LIGO and space check back in for that next week but in the meantime thank you so much for watching and happy physics Inge [Music]

Channel: Physics Girl

Views: 2,522,732

Rating: 4.8244896 out of 5

Keywords: physics girl, dianna cowern, ligo, gravitational waves, mystery, science, physics, cosmology, black hole, desert, why are there giant concrete tunnels in the desert, tunnels in the desert, giant tunnels, michael landry, amber strunk, physicsgirl, observatory, what are gravitational waves, how are gravitational waves detected, space, space science, invisible, science mystery

Id: DjcS1kRkc6M

Length: 11min 25sec (685 seconds)

Published: Fri Aug 23 2019

Reddit Comments

[u/ElectricMoose]

At least as of a few years ago the LIGO in Washington offers free tours. Definitely worth a visit if you're in the area.

[u/MC_Knight24]

TIL: Gravity moves at the same speed as light. Did not know this, very interesting.

[u/XxNinjaInMyCerealxX]

TLDW?

[u/tridentgum]

I thought the answer was gonna be water or oil.

This was definitely a nice surprise; wasn't expecting it.

[u/SonWutRUdoin]

I still don't get this experiment.

If spacetime is being warped, how can you measure it as we exist within the confines of spacetime as does the laser..

So if it's warped, everything is warped, so nothing changes?

[u/NightHawkCanada]

I dropped by for a tour of LIGO Hanford when I was travelling for the 2017 Solar Eclipse. Really amazing to see and talk to professionals working on this science.

[u/IL_is_not_ItaLy]

When she said that if the sun disappeared it would take 8 minutes for us on Earth to feel the effect of the gravity and also 8 minutes for us to see the event. So it means that light travels at exactly the same speed gravitational waves travel? Then should we be able to see with a good enough telescope an event like two black holes merging?

[u/el-cuko]

I understood some of those words

[u/speaktothamasses]

hmmmm interesting