1
00:00:00,160 --> 00:00:06,240
how do you measure something that's really really small

2
00:00:04,400 --> 00:00:10,400
well first you might try a measuring tape then calipers and if you've got a

3
00:00:08,639 --> 00:00:15,599
big budget you might treat yourself to a scanning electron microscope

4
00:00:12,480 --> 00:00:17,199
but there is one very clear problem with

5
00:00:15,599 --> 00:00:22,960
all of those solutions a they're too small and b

6
00:00:20,640 --> 00:00:26,800
they don't use lasers at lago they had the right idea so by

7
00:00:25,119 --> 00:00:30,080
shooting a laser four kilometers down this tube they're able to get an

8
00:00:28,240 --> 00:00:33,520
accuracy of one ten thousandth the charge diameter of proton

9
00:00:32,079 --> 00:00:38,079
that's like measuring from here to the closest star with the accuracy of a hair

10
00:00:36,640 --> 00:00:42,320
which i don't know i still don't have context for that but it got them a noble

11
00:00:40,399 --> 00:00:46,079
prize for physics and they were the first ones to get gravitational waves

12
00:00:44,000 --> 00:00:49,280
detected so awesome

13
00:00:47,360 --> 00:00:53,039
glasswire lets you instantly see your current and past network activity you

14
00:00:51,440 --> 00:00:56,399
can detect malware and block badly behaving apps on your pc and Android

15
00:00:54,559 --> 00:01:00,310
device and you can use offer code Linus to get 25 off glasswire at the link

16
00:00:58,640 --> 00:01:08,400
below

17
00:01:08,400 --> 00:01:16,479
gravitational waves happen all the time every time a mass accelerates waves

18
00:01:13,680 --> 00:01:22,400
ripple through space time so like i'm actually waving space time right now

19
00:01:20,240 --> 00:01:28,080
but it only really becomes noticeable when crazy massive things start

20
00:01:25,200 --> 00:01:32,400
accelerating like black holes colliding when einstein first predicted

21
00:01:29,600 --> 00:01:37,119
gravitational waves in 1916 he thought they were a problem with his algebra and

22
00:01:34,880 --> 00:01:42,079
then later when he believed that they were real he figured it would still be

23
00:01:39,439 --> 00:01:46,880
impossible to detect them but of course that hasn't stopped people from trying

24
00:01:44,880 --> 00:01:51,119
in the 50s joseph weber first tried to detect gravitational waves using the 6

25
00:01:48,799 --> 00:01:54,799
000 pound chunk of aluminum the idea is that it would resonate

26
00:01:53,119 --> 00:02:00,399
when gravitational waves went through it and that would be picked up by these piezoelectric crystals on the top

27
00:01:58,000 --> 00:02:06,000
unfortunately it just wasn't possible to get the precision needed

28
00:02:02,159 --> 00:02:08,879
in 1972 though ray vice wrote a paper

29
00:02:06,000 --> 00:02:12,480
detailing just how an interferometer could be used to detect gravitational

30
00:02:11,440 --> 00:02:18,239
waves basically he wrote a laser beam could go

31
00:02:15,760 --> 00:02:23,200
through a beam splitter and then down two four kilometer long tubes at the end

32
00:02:21,040 --> 00:02:27,440
of each of these tubes would be a mirror that sends the beam back where it would

33
00:02:25,200 --> 00:02:30,879
be recombined by the beam splitter and then measured

34
00:02:28,959 --> 00:02:33,920
normally when recombined in this manner the two beams would destructively

35
00:02:32,640 --> 00:02:38,800
interfere but if a gravitational wave were to pass

36
00:02:36,400 --> 00:02:43,920
through the detector it should physically distort space and time

37
00:02:41,519 --> 00:02:47,280
causing the length of the two arms to very slightly change compared to each

38
00:02:46,480 --> 00:02:54,480
other this would change the interference of the two beams ultimately changing the

39
00:02:51,440 --> 00:02:57,760
signal on the photo detector at the end

40
00:02:54,480 --> 00:03:01,599
in 2002 then caltech and mit joined

41
00:02:57,760 --> 00:03:04,319
forces to create iligo a proof that this

42
00:03:01,599 --> 00:03:08,800
could work and after extensive research and an upgrade to advanced ligo we were

43
00:03:07,120 --> 00:03:14,080
able to successfully detect gravitational waves in 2015.

44
00:03:11,680 --> 00:03:20,239
and by we of course i mean humans as a as a species not me i i

45
00:03:17,120 --> 00:03:22,239
wasn't involved so behind us is the beam

46
00:03:20,239 --> 00:03:25,920
splitter so it comes from the laser room back there which is why we have to have

47
00:03:23,440 --> 00:03:30,560
these laser glasses on it gets split right around here and then gets sent off

48
00:03:28,239 --> 00:03:35,840
the arms that way and that way it then travels back in and is detected

49
00:03:33,040 --> 00:03:41,040
over there somewhere unsurprisingly taking measurements that precisely in

50
00:03:38,159 --> 00:03:45,200
the real world is a lot easier said than done any particles in the air will cause

51
00:03:43,519 --> 00:03:49,760
the laser to scatter and although they're only sending in 20 watts of

52
00:03:47,120 --> 00:03:55,040
laser power the way it works is to have the beam trapped as a standing wave

53
00:03:51,920 --> 00:03:57,439
inside so after 300 bounces or so that

54
00:03:55,040 --> 00:04:02,799
amplifies it to about a hundred kilowatts with power like that even a

55
00:04:00,720 --> 00:04:07,920
tiny speck of dust on the mirror could absorb enough heat to permanently damage

56
00:04:05,599 --> 00:04:13,280
it meaning that the four kilometer tubes or arms have to be under an ultra high

57
00:04:11,040 --> 00:04:17,359
vacuum so this is the concrete that goes around the ARM it doesn't actually help

58
00:04:15,840 --> 00:04:21,510
with the laser tube but it's just to protect it from like cars animals stray

59
00:04:20,239 --> 00:04:23,600
bullets or whatever

60
00:04:23,600 --> 00:04:28,639
the real magic though happens in this three millimeter thick stainless steel

61
00:04:26,960 --> 00:04:32,880
tube which is hold to one trillionth of an atm

62
00:04:31,199 --> 00:04:37,440
even the vacuum outside the international space station can't hold a

63
00:04:35,600 --> 00:04:43,600
candle to what they've got going on in here so how did they build it

64
00:04:41,040 --> 00:04:48,160
well first they cooked or more accurately

65
00:04:45,440 --> 00:04:52,639
baked now if regular stainless steel was used for this hydrogen and other

66
00:04:50,560 --> 00:04:57,840
particles on the metal could contaminate the vacuum so to combat this every

67
00:04:55,680 --> 00:05:04,560
inside surface needs to be heated to at least 170 degrees celsius and held there for

68
00:05:01,840 --> 00:05:08,479
an extended amount of time now for the nuts and bolts that's pretty simple i

69
00:05:06,960 --> 00:05:14,000
mean i could do that with my toaster oven at home but for something this

70
00:05:10,880 --> 00:05:16,400
large what they had to do was pump a

71
00:05:14,000 --> 00:05:21,280
quadrant of it full of electricity effectively using the resistance of the

72
00:05:18,479 --> 00:05:26,240
metal to turn it into a heater and hold it at 170 for a month with the vacuum

73
00:05:24,560 --> 00:05:30,560
pumps running to remove all the contaminants i guess that's probably why

74
00:05:28,639 --> 00:05:35,280
they wouldn't let us inside we are the contaminants

75
00:05:32,880 --> 00:05:40,560
so that's cool now the laser can make its way from one end to the other but

76
00:05:38,240 --> 00:05:45,360
what about the mirrors on the end even something as small as a truck on

77
00:05:42,720 --> 00:05:49,600
the highway or an earthquake in taiwan would create too much vibration for

78
00:05:47,520 --> 00:05:53,360
gravitational wave detection which i guess is probably why they put

79
00:05:51,280 --> 00:05:57,360
their air conditioner way off away from the building rather than up on top of it

80
00:05:55,039 --> 00:06:02,880
like normal people this is one of the mirrors from iligo to

81
00:06:00,320 --> 00:06:07,600
reduce the high frequency vibrations the mirror is hung like a pendulum by this

82
00:06:05,199 --> 00:06:11,440
steel wire and the lower frequency vibrations are decreased by the springs

83
00:06:09,759 --> 00:06:16,880
on the lower base but they obviously weren't done there in the

84
00:06:14,560 --> 00:06:22,880
newer version the mirror is hung from four pendulums by glass fibers

85
00:06:20,560 --> 00:06:27,280
and that is far from the end on the bottom of the table there's actually a

86
00:06:24,800 --> 00:06:32,000
seismometer that measures any movement in the ground and then uses that

87
00:06:29,440 --> 00:06:36,560
information to manipulate voice coils and static electricity to actively

88
00:06:34,720 --> 00:06:40,479
cancel out the vibrations coming from the ground

89
00:06:38,240 --> 00:06:46,479
at this point then the mirrors are basically perfectly still

90
00:06:43,280 --> 00:06:48,800
but they still aren't done yet

91
00:06:46,479 --> 00:06:52,960
for some frequencies their level of accuracy is being determined by quantum

92
00:06:51,199 --> 00:06:57,600
mechanics and the heisenberg uncertainty principle but even this can be reduced

93
00:06:55,440 --> 00:07:02,240
using quantum squeezing on a very basic level they can only know

94
00:06:59,919 --> 00:07:06,240
so much about the amplitude or phase of the laser light but for this application

95
00:07:04,800 --> 00:07:10,960
the amplitude of the light being detected matters a lot less

96
00:07:08,560 --> 00:07:14,960
so they're able to perform a quantum squeeze and get better accuracy out of

97
00:07:13,360 --> 00:07:20,160
the phase detection so they're using a ktp crystal that is a

98
00:07:17,599 --> 00:07:26,400
potassium titanal phosphate crystal and this is able to transform one green

99
00:07:22,639 --> 00:07:27,360
photon into two infrared photons or vice

100
00:07:26,400 --> 00:07:32,080
versa energy is conserved here because the infrared light has less energy than the

101
00:07:31,039 --> 00:07:36,479
green light so what they do here is pump a crystal

102
00:07:34,400 --> 00:07:39,840
full of infrared light this is just to get a lot of green light and high

103
00:07:38,400 --> 00:07:44,479
powered infrared lasers are easier to get and then that green light is sent

104
00:07:42,080 --> 00:07:48,960
into another ktp crystal but when those photons are emitted they

105
00:07:46,720 --> 00:07:53,919
are quantumly entangled now in a vacuum there naturally exists a

106
00:07:51,280 --> 00:07:58,479
lot of noise particularly when there is very little light like around the dark

107
00:07:56,000 --> 00:08:03,440
end of the detector so by injecting these entangled photons they're able to

108
00:08:00,960 --> 00:08:08,240
remove the completely random vacuum noise and replace it with the entangled

109
00:08:06,080 --> 00:08:11,440
photons that produce noise that they like

110
00:08:09,759 --> 00:08:16,639
now you're probably thinking i am too holy sweet crap

111
00:08:14,240 --> 00:08:19,840
how could they even verify that these are actually gravitational waves they're

112
00:08:18,639 --> 00:08:24,000
detecting and the answer is by building another

113
00:08:22,479 --> 00:08:28,879
detector on the other side of the country so that if a gravitational wave

114
00:08:26,560 --> 00:08:34,399
is detected they can confirm that it isn't just a localized movement oh and

115
00:08:31,520 --> 00:08:39,279
also by using two observatories to try and find where the astronomical event is

116
00:08:37,519 --> 00:08:43,599
happening so with the accuracy of the

117
00:08:41,039 --> 00:08:48,880
interferometer mostly figured out how the heck do they acquire all the data

118
00:08:46,160 --> 00:08:51,760
and process it ah yes my friends we are finally getting to the computery part of

119
00:08:50,640 --> 00:08:59,120
the video in here they collect data from 250

120
00:08:56,320 --> 00:09:03,519
000 channels simultaneously and then to isolate the signals being created by the

121
00:09:01,040 --> 00:09:09,680
detector from the computers they actually put the noisy bits of the

122
00:09:05,519 --> 00:09:12,560
computer cpus power etc in another room

123
00:09:09,680 --> 00:09:16,480
150 feet down the hall and they connect them using fiber optic pci express

124
00:09:15,200 --> 00:09:24,399
extenders the most important thing with the computing here though is timing so every

125
00:09:21,360 --> 00:09:26,640
processor's clock in this server room is

126
00:09:24,399 --> 00:09:31,680
synced using a custom built system since the processor's timing has to be

127
00:09:29,040 --> 00:09:35,680
precisely known in order to calculate the time of the events in the

128
00:09:32,959 --> 00:09:41,279
interferometer but it's not just synced in this room there are also computers at

129
00:09:38,560 --> 00:09:45,760
the very ends of the laser arms four kilometers away with their clocks

130
00:09:43,760 --> 00:09:50,480
perfectly synchronized too and the 22 microsecond transmission time

131
00:09:48,480 --> 00:09:55,360
delay taken into account oh and that second gravitational wave

132
00:09:52,880 --> 00:10:00,080
observatory in louisiana you guessed right the processor clocks are perfectly

133
00:09:57,519 --> 00:10:03,920
synchronized there too once the data is collected it gets sent

134
00:10:02,240 --> 00:10:09,040
over to their server warehouse for analysis and very quick analysis is

135
00:10:06,880 --> 00:10:13,600
important since if there's a large astronomical event taking place they'll

136
00:10:11,200 --> 00:10:17,360
detect it here first and then they need to be able to tell their astronomers

137
00:10:15,600 --> 00:10:20,880
where to point the telescopes in a timely manner

138
00:10:18,720 --> 00:10:27,360
so all that processing is handled in here where they've got 6

139
00:10:23,440 --> 00:10:29,760
000 processing cores 64 gpus almost 4

140
00:10:27,360 --> 00:10:36,000
terabytes of RAM and close to 5 and a half petabytes of data stored on SSD

141
00:10:33,279 --> 00:10:40,640
spinning and tape storage the data is then copied from here to

142
00:10:38,560 --> 00:10:44,560
caltech servers where it is further analyzed and made available to more

143
00:10:42,560 --> 00:10:49,920
scientists and then eventually the armchair physicists at home

144
00:10:47,040 --> 00:10:54,000
and they're still not done future plans to improve their accuracy involve using

145
00:10:51,760 --> 00:10:58,800
cryogenics to reduce the movement of the molecules on the mirrors detecting

146
00:10:56,320 --> 00:11:03,519
changes in the earth's gravity to remove noise from movement below the earth's

147
00:11:00,959 --> 00:11:08,880
crust implementing quantum squeeze that can be changed throughout the frequency

148
00:11:05,839 --> 00:11:11,120
band and even building a space-based

149
00:11:08,880 --> 00:11:15,200
gravitational wave observatory the goal is that with every little

150
00:11:13,279 --> 00:11:21,120
adjustment they should be able to see even further into space collecting a bit

151
00:11:17,519 --> 00:11:22,880
more data about how our universe works

152
00:11:21,120 --> 00:11:26,959
so a huge thanks to ligo and particularly amber you rock for letting

153
00:11:25,279 --> 00:11:29,279
us come and hang out in the observatory and a huge thanks to you guys for

154
00:11:28,320 --> 00:11:36,079
watching this video is brought to you by ting ting does rates not plans for your cell

155
00:11:34,000 --> 00:11:40,800
phones you pay just six dollars per phone line plus the minutes messages and

156
00:11:38,160 --> 00:11:45,279
data you actually use each month usage gets shared across all your devices so

157
00:11:43,360 --> 00:11:49,040
the more phones on one ting account the less you end up paying per phone and

158
00:11:47,120 --> 00:11:52,959
with an average bill of just 23 bucks a month per phone ting is the smarter

159
00:11:50,959 --> 00:11:57,279
choice for mobile they offer service on two nationwide lte networks so the phone

160
00:11:55,519 --> 00:12:01,440
that you already own will likely work with ting and there are no contracts and

161
00:11:59,360 --> 00:12:07,279
no overage fees so you can try ting for a month with no commitments so check out

162
00:12:04,000 --> 00:12:10,399
our link below it's linus2018.ting.com

163
00:12:07,279 --> 00:12:11,519
to get 25 off your bill or towards a new

164
00:12:10,399 --> 00:12:16,399
device so thanks for watching guys if this video sucked or you're a member of the

165
00:12:14,399 --> 00:12:19,519
flat earth society you know what to do but if it was awesome get subscribed hit

166
00:12:18,240 --> 00:12:24,000
that like button or check out the link to where to buy the stuff we featured in the video description right also linked

167
00:12:22,720 --> 00:12:30,200
in the description is our merge storage has cool shirts like this one and our community forum which you should totally

168
00:12:27,200 --> 00:12:30,200
join