[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.00,0:00:18.02,Default,,0000,0000,0000,,{\i1}35c3 preroll music{\i0}
Dialogue: 0,0:00:18.02,0:00:27.45,Default,,0000,0000,0000,,Herald: Our speaker is Jost Migenda and he\Nis PhD student in astroparticle physics
Dialogue: 0,0:00:27.45,0:00:34.98,Default,,0000,0000,0000,,from the University of Sheffield in the UK\Nand Jost is going to talk about going deep
Dialogue: 0,0:00:34.98,0:00:41.50,Default,,0000,0000,0000,,underground to watch the stars. Please\Ngive a huge round of applause for Jost
Dialogue: 0,0:00:41.50,0:00:42.53,Default,,0000,0000,0000,,Migenda.
Dialogue: 0,0:00:42.53,0:00:50.86,Default,,0000,0000,0000,,{\i1}applause{\i0}
Dialogue: 0,0:00:50.86,0:00:56.22,Default,,0000,0000,0000,,J: Good morning everybody. I'm glad you\Nmanaged the first day of congress. Now
Dialogue: 0,0:00:56.22,0:01:02.30,Default,,0000,0000,0000,,physics rarely makes highlight news. And\Nif and when it does it is often treated a
Dialogue: 0,0:01:02.30,0:01:09.50,Default,,0000,0000,0000,,black box, where you pourd in money and\Nscientist on one end, you wait a while and
Dialogue: 0,0:01:09.50,0:01:16.24,Default,,0000,0000,0000,,knowledge drops out. So today in this talk\NI want to do this a bit differently. I
Dialogue: 0,0:01:16.24,0:01:20.25,Default,,0000,0000,0000,,want to give you a glimpse behind the\Nscenes of an experiment, I have been
Dialogue: 0,0:01:20.25,0:01:26.29,Default,,0000,0000,0000,,working on for over 4 years now. First as\Npart of my master's thesis and then as a
Dialogue: 0,0:01:26.29,0:01:33.92,Default,,0000,0000,0000,,PhD student. Now earlier this year we\Npublished a design report which is over
Dialogue: 0,0:01:33.92,0:01:38.03,Default,,0000,0000,0000,,300 pages long and contains much more\Ndetail about the experiment than you
Dialogue: 0,0:01:38.03,0:01:45.24,Default,,0000,0000,0000,,probably want to know. So I'll focus on\Njust some of the highlights in this talk.
Dialogue: 0,0:01:45.24,0:01:48.72,Default,,0000,0000,0000,,But before we actually talk about the\Ndetector I'll have to introduce you to the
Dialogue: 0,0:01:48.72,0:01:55.39,Default,,0000,0000,0000,,particles we're looking for. And that\Nstory begins over 100 years ago with
Dialogue: 0,0:01:55.39,0:02:02.28,Default,,0000,0000,0000,,radioactive beta decay. Now in radioactive\Nbeta decay, you have a nucleus of one
Dialogue: 0,0:02:02.28,0:02:07.85,Default,,0000,0000,0000,,chemical element that turns into a nucleus\Nof a different element and emits an
Dialogue: 0,0:02:07.85,0:02:16.06,Default,,0000,0000,0000,,electron or in modern language we would\Nsay a neutron decays into a proton and an
Dialogue: 0,0:02:16.06,0:02:21.92,Default,,0000,0000,0000,,electron. Now after that was discovered\Nthere were lots of experiments done to
Dialogue: 0,0:02:21.92,0:02:26.57,Default,,0000,0000,0000,,measure the energy of the outgoing\Nelectron and experiment after experiment
Dialogue: 0,0:02:26.57,0:02:34.91,Default,,0000,0000,0000,,found that there was some variance in\Nenergy but was always lower than expected.
Dialogue: 0,0:02:34.91,0:02:39.81,Default,,0000,0000,0000,,And physicists at the time came up with\Nall sorts of possible explanations for
Dialogue: 0,0:02:39.81,0:02:45.65,Default,,0000,0000,0000,,what might be going wrong with these\Nexperiments but they excluded those
Dialogue: 0,0:02:45.65,0:02:51.87,Default,,0000,0000,0000,,explanations very quickly as well. So\Nafter a while physicists became desperate
Dialogue: 0,0:02:51.87,0:02:56.25,Default,,0000,0000,0000,,and some pretty well-known physicists\Nactually thought: "Well, maybe we'll just
Dialogue: 0,0:02:56.25,0:03:04.07,Default,,0000,0000,0000,,have to give up on conservation of\Nenergy". So in this desperate situation a
Dialogue: 0,0:03:04.07,0:03:09.26,Default,,0000,0000,0000,,guy called Wolfgang Pauli came up with\Nwhat he himself call "a desperate way
Dialogue: 0,0:03:09.26,0:03:14.54,Default,,0000,0000,0000,,out". So in this letter to a group of his\Ncolleagues which he addressed as "Dear
Dialogue: 0,0:03:14.54,0:03:21.42,Default,,0000,0000,0000,,radioactive ladies and gentlemen", Pauli\Nsuggested that maybe there's another
Dialogue: 0,0:03:21.42,0:03:28.57,Default,,0000,0000,0000,,particle created in this beta decay. And\NPauli originally called this particle
Dialogue: 0,0:03:28.57,0:03:33.56,Default,,0000,0000,0000,,neutron but of course two years later the\Nparticle we nowadays know as Neutron was
Dialogue: 0,0:03:33.56,0:03:40.34,Default,,0000,0000,0000,,discovered. So Pauli's particle was re-\Nnamed neutrino. Now you might be wondering
Dialogue: 0,0:03:40.34,0:03:46.72,Default,,0000,0000,0000,,well why didn't they observe this particle\Nalready. And the answer is very simple.
Dialogue: 0,0:03:46.72,0:03:52.16,Default,,0000,0000,0000,,Neutrinos are like ghosts. So what I mean\Nby there is they can quite literally, you
Dialogue: 0,0:03:52.16,0:03:58.62,Default,,0000,0000,0000,,know, go through walls or through your\Nbody. And in effect we can do a little
Dialogue: 0,0:03:58.62,0:04:03.74,Default,,0000,0000,0000,,experiment right now to try and detect\Nneutrinos. So to help me with this
Dialogue: 0,0:04:03.74,0:04:12.81,Default,,0000,0000,0000,,experiment, please give me thumb's up.\NEveryone? Okay so there's two things
Dialogue: 0,0:04:12.81,0:04:16.75,Default,,0000,0000,0000,,happening right now. First thing of all\Nyou're giving me a massive confidence
Dialogue: 0,0:04:16.75,0:04:23.56,Default,,0000,0000,0000,,boost. But, you know, more importantly\Nsomewhere out there the sun is shining and
Dialogue: 0,0:04:23.56,0:04:28.04,Default,,0000,0000,0000,,it's producing a lot of neutrinos and\Nnuclear fusion. Now these neutrinos are
Dialogue: 0,0:04:28.04,0:04:35.48,Default,,0000,0000,0000,,flying to Earth through the roof of this\Nbuilding and then through your thumbnail.
Dialogue: 0,0:04:35.48,0:04:43.06,Default,,0000,0000,0000,,And right now as you're listening to me\Naround 60 billion neutrinos are flying
Dialogue: 0,0:04:43.06,0:04:49.18,Default,,0000,0000,0000,,through your thumbnail. 60 billion\Nneutrinos flying through your thumbnail
Dialogue: 0,0:04:49.18,0:04:57.97,Default,,0000,0000,0000,,every second. How does that feel? Hmm? You\Ndon't feel any of them? Right, so that's
Dialogue: 0,0:04:57.97,0:05:02.74,Default,,0000,0000,0000,,how ghost-like neutrinos are. And of\Ncourse physicists are clever and shortly
Dialogue: 0,0:05:02.74,0:05:08.21,Default,,0000,0000,0000,,after Pauli had this idea some of them\Nestimated that how often neutrinos
Dialogue: 0,0:05:08.21,0:05:13.57,Default,,0000,0000,0000,,interact with normal matter and they found\Nthat there is no practically possible way
Dialogue: 0,0:05:13.57,0:05:18.41,Default,,0000,0000,0000,,of observing the neutrino. And that\Nremained true for over 20 years
Dialogue: 0,0:05:18.41,0:05:28.44,Default,,0000,0000,0000,,afterwards. So now that I have introduced\Nyou to neutrinos. Let's talk about
Dialogue: 0,0:05:28.44,0:05:36.37,Default,,0000,0000,0000,,building a detector to actually detect\Nthem. And the original motivation for
Dialogue: 0,0:05:36.37,0:05:44.15,Default,,0000,0000,0000,,building this detector was something a bit\Ndifferent. I talked about beta decay and
Dialogue: 0,0:05:44.15,0:05:48.58,Default,,0000,0000,0000,,over the next decades physicists slowly\Ndiscovered more particles. They discovered
Dialogue: 0,0:05:48.58,0:05:55.62,Default,,0000,0000,0000,,that protons and neutrons are made up out\Nof quarks and in the 1970s theoretical
Dialogue: 0,0:05:55.62,0:06:00.96,Default,,0000,0000,0000,,physicists came up was are some Grand\NUnified Theories basically precursors to
Dialogue: 0,0:06:00.96,0:06:06.80,Default,,0000,0000,0000,,string theory. And these theories\Npredicted that the proton should decay as
Dialogue: 0,0:06:06.80,0:06:14.82,Default,,0000,0000,0000,,well. So of course you know we build\Ndetectors to look for that and a group in
Dialogue: 0,0:06:14.82,0:06:20.61,Default,,0000,0000,0000,,Japan built a detector near the town of\NKamioka which they called the Kamioka
Dialogue: 0,0:06:20.61,0:06:27.29,Default,,0000,0000,0000,,Nucleon Decay Experiment or Kamiokande for\Nshort. Now they didn't observe any proton
Dialogue: 0,0:06:27.29,0:06:33.03,Default,,0000,0000,0000,,decay but shortly after they built it\Nsomebody had a suggestion that if we
Dialogue: 0,0:06:33.03,0:06:37.13,Default,,0000,0000,0000,,changed just a little bit above their\Ndetector, if we modified just a little, we
Dialogue: 0,0:06:37.13,0:06:44.65,Default,,0000,0000,0000,,would also be able to detect neutrinos\Nwith that. So they modified the detector
Dialogue: 0,0:06:44.65,0:06:49.29,Default,,0000,0000,0000,,switched it back on and just a couple of\Nweeks later they actually observe
Dialogue: 0,0:06:49.29,0:06:57.77,Default,,0000,0000,0000,,neutrinos from an exploding star just\Noutside our Milky Way. And that was the
Dialogue: 0,0:06:57.77,0:07:03.54,Default,,0000,0000,0000,,birth of neutrino astronomy. And for that\Nthe then-leader of the experiment received
Dialogue: 0,0:07:03.54,0:07:11.86,Default,,0000,0000,0000,,the Nobel Prize in 2002. Now after over a\Ndecade of running physicists were
Dialogue: 0,0:07:11.86,0:07:15.86,Default,,0000,0000,0000,,basically hitting the limits of what we\Ncould do with a detector of their size. So
Dialogue: 0,0:07:15.86,0:07:22.47,Default,,0000,0000,0000,,we needed to build a bigger detector and\Nthat one was very creatively named Super-
Dialogue: 0,0:07:22.47,0:07:29.36,Default,,0000,0000,0000,,Kamiokande. And it's about 20 times\Nbigger, started running in 1996 and still
Dialogue: 0,0:07:29.36,0:07:39.68,Default,,0000,0000,0000,,running to this day. Now Super-K did not\Ndiscover proton decay but did detect a lot
Dialogue: 0,0:07:39.68,0:07:43.89,Default,,0000,0000,0000,,of neutrinos and made very fascinating\Ndiscoveries. For example, they discovered
Dialogue: 0,0:07:43.89,0:07:49.07,Default,,0000,0000,0000,,that different types of neutrinos can\Nchange into each other back and forth as
Dialogue: 0,0:07:49.07,0:07:55.26,Default,,0000,0000,0000,,they travel. That's like you buying a cone\Nof vanilla ice cream and then as you walk
Dialogue: 0,0:07:55.26,0:08:01.57,Default,,0000,0000,0000,,out it suddenly turns into chocolate ice\Ncream. That's really weird. And for their
Dialogue: 0,0:08:01.57,0:08:08.86,Default,,0000,0000,0000,,discovery just a few years ago they\Nreceived the Nobel Prize again. But today
Dialogue: 0,0:08:08.86,0:08:12.58,Default,,0000,0000,0000,,we are again hitting the limit of you know\Nwhat we can learn from a detector that
Dialogue: 0,0:08:12.58,0:08:18.52,Default,,0000,0000,0000,,size. So of course the next step is to\Nbuild an even bigger detector and we're
Dialogue: 0,0:08:18.52,0:08:26.28,Default,,0000,0000,0000,,calling it Hyper-Kamiokande. By the way\N"super" and "hyper" mean exactly the same
Dialogue: 0,0:08:26.28,0:08:34.10,Default,,0000,0000,0000,,thing. Just one is Latin and one is Greek.\NSo we're currently getting ready the plans
Dialogue: 0,0:08:34.10,0:08:37.95,Default,,0000,0000,0000,,to build Hyper-Kamiokande and we will\Nstart construction probably in the spring
Dialogue: 0,0:08:37.95,0:08:47.34,Default,,0000,0000,0000,,of 2020. Details of the Noble Prize are\Nstill to be determined. Now I said that 60
Dialogue: 0,0:08:47.34,0:08:52.63,Default,,0000,0000,0000,,billion neutrinos go through your\Nthumbnail every second. Of course Super-
Dialogue: 0,0:08:52.63,0:08:58.17,Default,,0000,0000,0000,,Kamiokande which is running right now is\Nmuch larger than your thumbnail. So
Dialogue: 0,0:08:58.17,0:09:03.63,Default,,0000,0000,0000,,there's not just 60 billion but 10000\Nbillion billion neutrinos passing through
Dialogue: 0,0:09:03.63,0:09:13.68,Default,,0000,0000,0000,,every day and only 10 or 15 of those get\Ndetected. So let's look at what this
Dialogue: 0,0:09:13.68,0:09:20.06,Default,,0000,0000,0000,,detection process looks like. Now this is\Nthe water inside Super-K. And there's a
Dialogue: 0,0:09:20.06,0:09:24.14,Default,,0000,0000,0000,,bunch of electrons in there but they'll\Nshow just one. And there's neutrinos
Dialogue: 0,0:09:24.14,0:09:31.94,Default,,0000,0000,0000,,flying through not just one, not just a\Nfew, but loads of them. And most of them
Dialogue: 0,0:09:31.94,0:09:36.52,Default,,0000,0000,0000,,go straight through without leaving a\Ntrace. But every once in a while we're
Dialogue: 0,0:09:36.52,0:09:41.45,Default,,0000,0000,0000,,lucky and one of those neutrinos will\Nactually hit the electron and give it a
Dialogue: 0,0:09:41.45,0:09:47.19,Default,,0000,0000,0000,,little kick. And that little kick you know\Nlike billiard balls basically and that
Dialogue: 0,0:09:47.19,0:09:55.17,Default,,0000,0000,0000,,little kick accelerates the electron to\Nfaster than the speed of light in water.
Dialogue: 0,0:09:55.17,0:09:59.87,Default,,0000,0000,0000,,Still slower than the speed of light in\Nvacuum which is the absolute cosmic tempo
Dialogue: 0,0:09:59.87,0:10:07.20,Default,,0000,0000,0000,,limit. But faster than the speed of light\Nin water. And then you get basically a
Dialogue: 0,0:10:07.20,0:10:12.92,Default,,0000,0000,0000,,sonic boom, but with light, which is this\Ncone of light. And let's just show the
Dialogue: 0,0:10:12.92,0:10:19.68,Default,,0000,0000,0000,,animation again. So you've got this cone\Nof light that hits the wall of the
Dialogue: 0,0:10:19.68,0:10:25.66,Default,,0000,0000,0000,,detector you see a little ring, this ring\Nof light. Well we've got very sensitive
Dialogue: 0,0:10:25.66,0:10:33.26,Default,,0000,0000,0000,,photo sensors all over the inside walls to\Ndetect this flash of light and from how
Dialogue: 0,0:10:33.26,0:10:39.76,Default,,0000,0000,0000,,bright it is we can tell the energy of the\Nneutrino. And we can also tell, you know
Dialogue: 0,0:10:39.76,0:10:43.55,Default,,0000,0000,0000,,just like was billiard balls, we can\Napproximately tell what directions a
Dialogue: 0,0:10:43.55,0:10:51.23,Default,,0000,0000,0000,,neutrino came from just based on in which\Ndirection it pushed the electron. So
Dialogue: 0,0:10:51.23,0:10:57.19,Default,,0000,0000,0000,,that's the basic idea how we detect\Nneutrinos from the sun. Now let's talk
Dialogue: 0,0:10:57.19,0:11:03.42,Default,,0000,0000,0000,,about what it's actually like to build one\Nof these detectors. So this is a drawing
Dialogue: 0,0:11:03.42,0:11:11.12,Default,,0000,0000,0000,,of Hyper-Kamiokande and you can see it's\N78 meters high, 74 meters in diameter and
Dialogue: 0,0:11:11.12,0:11:16.46,Default,,0000,0000,0000,,on the top left there is a truck for\Ncomparison. But maybe a better size
Dialogue: 0,0:11:16.46,0:11:22.20,Default,,0000,0000,0000,,comparison is to compare this to buildings\Nwhich you're familiar with. Like the
Dialogue: 0,0:11:22.20,0:11:28.88,Default,,0000,0000,0000,,entrance hall which you just came in\Nthrough this morning. Or the Statue of
Dialogue: 0,0:11:28.88,0:11:36.90,Default,,0000,0000,0000,,Liberty and it doesn't quite fit in there.\NThe arm still looks out. But you could
Dialogue: 0,0:11:36.90,0:11:41.94,Default,,0000,0000,0000,,drown the Statue of Liberty in this\Ndetector which nowadays is probably some
Dialogue: 0,0:11:41.94,0:11:51.06,Default,,0000,0000,0000,,sort of political metaphor. So this is the\Ngiant detector. And what's more we're
Dialogue: 0,0:11:51.06,0:11:57.31,Default,,0000,0000,0000,,building it inside the mountain about 650\Nmeters underground. So that all the rock
Dialogue: 0,0:11:57.31,0:12:02.28,Default,,0000,0000,0000,,on top will act as a kind of a natural\Nshield against all sorts of other
Dialogue: 0,0:12:02.28,0:12:06.56,Default,,0000,0000,0000,,particles, that are raining down on the\Natmosphere from outer space so that all
Dialogue: 0,0:12:06.56,0:12:12.64,Default,,0000,0000,0000,,other particles get stuck and only\NNeutrinos can make it through. Now of
Dialogue: 0,0:12:12.64,0:12:18.42,Default,,0000,0000,0000,,course to build such a huge cavern inside\Nthe mountain - that's something that we
Dialogue: 0,0:12:18.42,0:12:25.54,Default,,0000,0000,0000,,physicists can't do on our own. So we need\Nto talk to geologists who look at the rock
Dialogue: 0,0:12:25.54,0:12:31.64,Default,,0000,0000,0000,,quality and tell us, you know, what's a\Ngood place to build this cavern - where is
Dialogue: 0,0:12:31.64,0:12:37.58,Default,,0000,0000,0000,,the rock stable enough to do that. And to\Nfigure out the rock quality, they drill
Dialogue: 0,0:12:37.58,0:12:46.86,Default,,0000,0000,0000,,bore holes in what's actually called a\Nboring survey. {\i1}laughter{\i0} Now, during my
Dialogue: 0,0:12:46.86,0:12:51.51,Default,,0000,0000,0000,,years working on this experiment, I had to\Nlisten to several hours of talks on these
Dialogue: 0,0:12:51.51,0:12:58.30,Default,,0000,0000,0000,,geological surveys and I can tell you that\Nname is quite appropriate. {\i1}laughter{\i0}
Dialogue: 0,0:12:58.30,0:13:02.00,Default,,0000,0000,0000,,though of course, there's a reason I'm not\Na geologist, so, you know, take this with
Dialogue: 0,0:13:02.00,0:13:09.42,Default,,0000,0000,0000,,a grain of salt. But okay, let's say, you\Nknow, we talked to geologists, they told
Dialogue: 0,0:13:09.42,0:13:15.16,Default,,0000,0000,0000,,us where we can build our detector. The\Nnext step is: We need to actually excavate
Dialogue: 0,0:13:15.16,0:13:21.14,Default,,0000,0000,0000,,the cavern. And something to keep in mind\Nis that we are building this somewhere in
Dialogue: 0,0:13:21.14,0:13:26.40,Default,,0000,0000,0000,,the mountains of Japan, you know, pretty\Nfar away from any major city. So we have
Dialogue: 0,0:13:26.40,0:13:32.69,Default,,0000,0000,0000,,to think about stuff like lack of local\Ninfrastructure like what's the electricity
Dialogue: 0,0:13:32.69,0:13:40.61,Default,,0000,0000,0000,,supply like. Do we need to add the power\Nline. Or what are the local roads like.
Dialogue: 0,0:13:40.61,0:13:44.48,Default,,0000,0000,0000,,And do they have enough capacity for, you\Nknow, dozens of trucks every day to
Dialogue: 0,0:13:44.48,0:13:50.62,Default,,0000,0000,0000,,transport away the excavated rock. And, by\Nthe way, where do you store all that
Dialogue: 0,0:13:50.62,0:13:56.71,Default,,0000,0000,0000,,excavated rock? Because we will be moving\Nsomething like half a million cubic meters
Dialogue: 0,0:13:56.71,0:14:01.39,Default,,0000,0000,0000,,of rock. You can't just store that in your\Nbackyard. You need to find a place where
Dialogue: 0,0:14:01.39,0:14:08.05,Default,,0000,0000,0000,,all that fits. And, of course, if you've\Nlistened to or watch the Lord of the
Dialogue: 0,0:14:08.05,0:14:15.12,Default,,0000,0000,0000,,Rings, you'll know it's dangerous to dig\Ntoo deeply, to greedily. So we need a
Dialogue: 0,0:14:15.12,0:14:23.21,Default,,0000,0000,0000,,Balrog early warning system as well. But\Nokay let's say we've got all those and we
Dialogue: 0,0:14:23.21,0:14:31.30,Default,,0000,0000,0000,,managed to build a cavern, and now we need\Nto fill it. And as detector material we
Dialogue: 0,0:14:31.30,0:14:36.97,Default,,0000,0000,0000,,use water. Both because it's actually\Npretty good for detecting neutrinos, but
Dialogue: 0,0:14:36.97,0:14:42.13,Default,,0000,0000,0000,,also because it's cheap and there's lots\Nof it. So you can afford to build a
Dialogue: 0,0:14:42.13,0:14:49.69,Default,,0000,0000,0000,,detector of this size. A detector so big\Nthat that little dot there is a scuba
Dialogue: 0,0:14:49.69,0:14:59.46,Default,,0000,0000,0000,,diver. But even with water, you hit limits\Nof, you know, how much you can get. So to
Dialogue: 0,0:14:59.46,0:15:04.68,Default,,0000,0000,0000,,fill Hyper-Kamiokande you need about as\Nmuch water as 5000 people use in a year.
Dialogue: 0,0:15:04.68,0:15:13.86,Default,,0000,0000,0000,,And that's for drinking, for showering,\Nfor washing their car and so on. Now
Dialogue: 0,0:15:13.86,0:15:17.83,Default,,0000,0000,0000,,that's easy if you're near a big city. But\Nwe are not, we're somewhere in the
Dialogue: 0,0:15:17.83,0:15:23.56,Default,,0000,0000,0000,,mountains in Japan where the next biggest\Ntown has far fewer than 5000 people. So
Dialogue: 0,0:15:23.56,0:15:30.98,Default,,0000,0000,0000,,how do we get enough water to actually\Nfill our detector? And... we could use
Dialogue: 0,0:15:30.98,0:15:38.06,Default,,0000,0000,0000,,rivers nearby, we could use springs. We\Ncould wait for for the end of winter and
Dialogue: 0,0:15:38.06,0:15:43.46,Default,,0000,0000,0000,,for the snow in the mountains to melt and\Nuse that to fill our detector. But if you
Dialogue: 0,0:15:43.46,0:15:48.66,Default,,0000,0000,0000,,use melting snow to fill the detector, you\Ncan only fill it once a year. So, you
Dialogue: 0,0:15:48.66,0:15:54.95,Default,,0000,0000,0000,,know, even "where do you get the water" is\Nis a pretty... pretty important question
Dialogue: 0,0:15:54.95,0:16:03.78,Default,,0000,0000,0000,,that you need to solve. And then, we're\Nnot just using any water but we actually
Dialogue: 0,0:16:03.78,0:16:09.16,Default,,0000,0000,0000,,have, we will build our own water\Npurification system. So that we don't have
Dialogue: 0,0:16:09.16,0:16:15.96,Default,,0000,0000,0000,,any, you know, traces of radioactivity in\Nthere, any trace of dust and stuff in
Dialogue: 0,0:16:15.96,0:16:23.42,Default,,0000,0000,0000,,there. And let me let me just tell you\Njust how pure this water will be. So, this
Dialogue: 0,0:16:23.42,0:16:29.45,Default,,0000,0000,0000,,is my supervisor, who, when he was a PhD\Nstudent, worked in the detector on some
Dialogue: 0,0:16:29.45,0:16:35.61,Default,,0000,0000,0000,,maintenance work, so he was working on a\Nboat doing the work, and then at the end
Dialogue: 0,0:16:35.61,0:16:41.15,Default,,0000,0000,0000,,of his shift he leaned back on the boat,\Nand just the tip of his long hair fell
Dialogue: 0,0:16:41.15,0:16:48.02,Default,,0000,0000,0000,,into the water, which he didn't know just\Ndidn't think about too much until at the
Dialogue: 0,0:16:48.02,0:16:54.79,Default,,0000,0000,0000,,end of his shift. He went home, you know,\Nwent to bed, fell asleep, and then woke up
Dialogue: 0,0:16:54.79,0:17:00.98,Default,,0000,0000,0000,,in the middle of the night, with his whole\Nhead itching like mad. Now, what had
Dialogue: 0,0:17:00.98,0:17:06.57,Default,,0000,0000,0000,,happened there? The ultra pure water had\Nsucked all of the nutrients out the tip of
Dialogue: 0,0:17:06.57,0:17:12.18,Default,,0000,0000,0000,,his hair and then through osmosis over\Ntime those had sucked the nutrients out of
Dialogue: 0,0:17:12.18,0:17:30.66,Default,,0000,0000,0000,,the rest of his hair, and then his skin.\NSo that's how pure that water is. Now, I
Dialogue: 0,0:17:30.66,0:17:35.41,Default,,0000,0000,0000,,said "all over the inside walls". And here\Nis, kind of, a photo of the inside of the
Dialogue: 0,0:17:35.41,0:17:41.91,Default,,0000,0000,0000,,detector. And all these kind of golden\Nhemispheres, those are what we call
Dialogue: 0,0:17:41.91,0:17:48.85,Default,,0000,0000,0000,,Photomultiplier tubes, of PMTs for short.\NAnd those are, basically, giant very
Dialogue: 0,0:17:48.85,0:17:54.99,Default,,0000,0000,0000,,sensitive pixels. And we will have 40,000\Nof those lining the inside wall of the
Dialogue: 0,0:17:54.99,0:18:02.22,Default,,0000,0000,0000,,detector. Now, in smaller detectors, you\Ncould just have from each PMT one cable
Dialogue: 0,0:18:02.22,0:18:05.99,Default,,0000,0000,0000,,leading to the top of the detector and\Nthen have your computers there to analyze
Dialogue: 0,0:18:05.99,0:18:12.80,Default,,0000,0000,0000,,the signal. With a detector of this size,\Nyou just can't do that because you would
Dialogue: 0,0:18:12.80,0:18:21.56,Default,,0000,0000,0000,,need 40,000 cables some of which are over\N100 meters long. That wouldn't work. So we
Dialogue: 0,0:18:21.56,0:18:26.17,Default,,0000,0000,0000,,have to put some electronics in the water\Nto digitize the signal and combine signal
Dialogue: 0,0:18:26.17,0:18:33.94,Default,,0000,0000,0000,,from multiple PMTs into one, and then use\Njust a single cable, to bring it up
Dialogue: 0,0:18:33.94,0:18:41.07,Default,,0000,0000,0000,,to the top where we analyze the signal.\NBut that means we have to put electronics
Dialogue: 0,0:18:41.07,0:18:47.24,Default,,0000,0000,0000,,into the water, so that creates a whole\Nbunch of new problems. For example, we
Dialogue: 0,0:18:47.24,0:18:51.17,Default,,0000,0000,0000,,need these electronics to be watertight.\NAnd I'm not talking about the level of
Dialogue: 0,0:18:51.17,0:18:54.89,Default,,0000,0000,0000,,watertight as you'd expect from your\Nsmartwatch where it survives, you know,
Dialogue: 0,0:18:54.89,0:18:59.72,Default,,0000,0000,0000,,you standing under the shower for five\Nminutes. I'm talking below 60 metres of
Dialogue: 0,0:18:59.72,0:19:07.90,Default,,0000,0000,0000,,water for 20+ years. This electronics also\Nneed to be very low power, because we
Dialogue: 0,0:19:07.90,0:19:13.39,Default,,0000,0000,0000,,can't heet up the water too much.\NOtherwise these pixels, the
Dialogue: 0,0:19:13.39,0:19:21.70,Default,,0000,0000,0000,,Photomultiplier Tubes, would become noisy\Nand this would kill our signal. And then
Dialogue: 0,0:19:21.70,0:19:26.16,Default,,0000,0000,0000,,also, because we don't want one defective\Ncable to kill a whole section of the
Dialogue: 0,0:19:26.16,0:19:30.51,Default,,0000,0000,0000,,detector. We need to implement some sort\Nof mesh networking to introduce some
Dialogue: 0,0:19:30.51,0:19:37.66,Default,,0000,0000,0000,,redundancy. Now each of that by itself is\Nnot... not a heart problem. Each of these
Dialogue: 0,0:19:37.66,0:19:42.87,Default,,0000,0000,0000,,problems can be solved. It's just a lot of\Nadditional work you suddenly have to do,
Dialogue: 0,0:19:42.87,0:19:51.51,Default,,0000,0000,0000,,because your detectors is that huge. And\Nit gets even worse: This is what one of
Dialogue: 0,0:19:51.51,0:19:58.17,Default,,0000,0000,0000,,these PMTs looks like. It's about 50\Ncentimeters in diameter, and inside that
Dialogue: 0,0:19:58.17,0:20:06.76,Default,,0000,0000,0000,,glass bulb is a vacuum. So it's under a\Nlot of pressure. Plus we add 60 metres of
Dialogue: 0,0:20:06.76,0:20:12.37,Default,,0000,0000,0000,,water on top of it, which adds additional\Npressure. So you need to make absolutely
Dialogue: 0,0:20:12.37,0:20:16.83,Default,,0000,0000,0000,,sure when you're manufacturing those that\Nyou don't have any weak points in the
Dialogue: 0,0:20:16.83,0:20:25.64,Default,,0000,0000,0000,,glass. And they don't just have to\Nwithstand that water pressure, but there
Dialogue: 0,0:20:25.64,0:20:32.99,Default,,0000,0000,0000,,will probably be some PMTs that have some\Nweak points, some air bubbles or something
Dialogue: 0,0:20:32.99,0:20:40.49,Default,,0000,0000,0000,,in the glass. Some structural weakness.\NAnd the neighboring PMT don't only have to
Dialogue: 0,0:20:40.49,0:20:44.95,Default,,0000,0000,0000,,survive the normal water pressure. They\Nalso need to survive whether their
Dialogue: 0,0:20:44.95,0:20:51.10,Default,,0000,0000,0000,,neighboring PMT is imploding and sending\Nout a pressure wave. And that's not just a
Dialogue: 0,0:20:51.10,0:20:57.95,Default,,0000,0000,0000,,hypothetical - that actually happened, you\Nknow, 18 years ago. It's 17 years ago in
Dialogue: 0,0:20:57.95,0:21:05.12,Default,,0000,0000,0000,,Superkamiokande. And that, you know,\Nwithin seconds killed more than half of
Dialogue: 0,0:21:05.12,0:21:13.67,Default,,0000,0000,0000,,the PMTs we had in there and it took years\Nto restore the detector to full capacity.
Dialogue: 0,0:21:13.67,0:21:19.83,Default,,0000,0000,0000,,So, lots of problems to solve, and, you\Nknow, one group, one university can't
Dialogue: 0,0:21:19.83,0:21:24.54,Default,,0000,0000,0000,,solve all these on their own. So we've got\Nthis multinational collaboration with over
Dialogue: 0,0:21:24.54,0:21:29.92,Default,,0000,0000,0000,,300 people from 17 different countries\Nmarked in green here and across many
Dialogue: 0,0:21:29.92,0:21:36.85,Default,,0000,0000,0000,,different time zones. So right here right\Nnow, here it's about you know just before
Dialogue: 0,0:21:36.85,0:21:42.43,Default,,0000,0000,0000,,noon. In Japan people have already had\Ndinner and they're going to bed soon. In
Dialogue: 0,0:21:42.43,0:21:47.41,Default,,0000,0000,0000,,the U.S., people haven't even got up yet\Nin the morning. So good luck finding a
Dialogue: 0,0:21:47.41,0:21:57.54,Default,,0000,0000,0000,,time for phone meetings which works for\Nall of these people. So, that's kind of a
Dialogue: 0,0:21:57.54,0:22:01.72,Default,,0000,0000,0000,,glimpse behind the scenes of what it's\Nlike to work on this detector and to
Dialogue: 0,0:22:01.72,0:22:07.78,Default,,0000,0000,0000,,actually build it. But now I want to talk\Nabout what we use the detector for. And
Dialogue: 0,0:22:07.78,0:22:13.33,Default,,0000,0000,0000,,I've got two examples. But of course\Nthere's a whole bunch more that we do, I
Dialogue: 0,0:22:13.33,0:22:23.94,Default,,0000,0000,0000,,just don't have time to talk about it\Ntoday. So, first example: Why does the sun
Dialogue: 0,0:22:23.94,0:22:30.06,Default,,0000,0000,0000,,shine? That seems like such a simple\Nquestion, right? And yet it turns out it's
Dialogue: 0,0:22:30.06,0:22:36.33,Default,,0000,0000,0000,,really difficult to answer. So, in the\Ndays of the Industrial Revolution, when,
Dialogue: 0,0:22:36.33,0:22:41.48,Default,,0000,0000,0000,,you know, burning coal and steam power was\Nall the rage, people thought that, you
Dialogue: 0,0:22:41.48,0:22:48.12,Default,,0000,0000,0000,,know, maybe it's, you know, a giant ball\Nof burning coal. But when you when you do
Dialogue: 0,0:22:48.12,0:22:54.78,Default,,0000,0000,0000,,the math, it turns out that would burn for\Na few thousand years maybe. So that
Dialogue: 0,0:22:54.78,0:23:01.00,Default,,0000,0000,0000,,definitely doesn't work. A bit later,\Nphysicists suggested that maybe the sun is
Dialogue: 0,0:23:01.00,0:23:06.53,Default,,0000,0000,0000,,just slowly shrinking and shrinking and\Nit's that gravitational energy which is
Dialogue: 0,0:23:06.53,0:23:13.05,Default,,0000,0000,0000,,released as light. And that would give you\Na life time of a few million years. But
Dialogue: 0,0:23:13.05,0:23:17.07,Default,,0000,0000,0000,,then you've got, you know pesky geologists\Ncoming along and saying "no no, we've got
Dialogue: 0,0:23:17.07,0:23:21.83,Default,,0000,0000,0000,,these rock formations or, I don't know,\Nfossils maybe, for more than a few million
Dialogue: 0,0:23:21.83,0:23:28.31,Default,,0000,0000,0000,,years old on Earth. So the sun has to live\Nlonger than a few million years. And the
Dialogue: 0,0:23:28.31,0:23:33.75,Default,,0000,0000,0000,,arguments from the 19th century between\NLord Kelvin and the geologists back then
Dialogue: 0,0:23:33.75,0:23:41.40,Default,,0000,0000,0000,,are just amazing to read. If you find\Nthose somewhere. But, of course, nowadays
Dialogue: 0,0:23:41.40,0:23:49.25,Default,,0000,0000,0000,,we know that the answer is nuclear fusion.\NAnd here's, you know, a bunch of reactions
Dialogue: 0,0:23:49.25,0:23:54.79,Default,,0000,0000,0000,,which lead you the energy generation of\Nthe sun. But now the question is "how can
Dialogue: 0,0:23:54.79,0:24:02.72,Default,,0000,0000,0000,,we check that? How can we check that this\Nis actually what's going on?" And the
Dialogue: 0,0:24:02.72,0:24:08.57,Default,,0000,0000,0000,,answer is neutrinos, because many of these\Nreactions produce neutrinos, and we can
Dialogue: 0,0:24:08.57,0:24:16.31,Default,,0000,0000,0000,,detect them. So the one we typically\Ndetect in Super- and later Hyperkamiokande
Dialogue: 0,0:24:16.31,0:24:21.22,Default,,0000,0000,0000,,is the one on the bottom right here,\Ncalled "Bore and eight neutrinos" because
Dialogue: 0,0:24:21.22,0:24:28.93,Default,,0000,0000,0000,,those have the highest energy. So they are\Neasiest for us to detect. And the rate of
Dialogue: 0,0:24:28.93,0:24:35.56,Default,,0000,0000,0000,,various of these processes depends very\Nmuch on the temperature. So by measuring
Dialogue: 0,0:24:35.56,0:24:40.32,Default,,0000,0000,0000,,how many of these neutrinos we see, we can\Nmeasure the temperature inside the core of
Dialogue: 0,0:24:40.32,0:24:48.65,Default,,0000,0000,0000,,the sun. And we have done that, and we\Nknow that it's about 15.5 million Kelvin, plus or
Dialogue: 0,0:24:48.65,0:24:54.74,Default,,0000,0000,0000,,minus 1 percent. So we know the\Ntemperature in the core of the sun to less
Dialogue: 0,0:24:54.74,0:25:05.64,Default,,0000,0000,0000,,than 1 percent uncertainty. That's pretty\Namazing if you ask me. And, you know, I
Dialogue: 0,0:25:05.64,0:25:10.56,Default,,0000,0000,0000,,said that we could detect the directions\Nthe neutrinos were coming from. So we can
Dialogue: 0,0:25:10.56,0:25:16.70,Default,,0000,0000,0000,,actually take a picture of the sun with\Nneutrinos. Now this is a bit blurry and
Dialogue: 0,0:25:16.70,0:25:21.40,Default,,0000,0000,0000,,pixelated, not as nice as what you'd get\Nfrom a, you know, from the optical
Dialogue: 0,0:25:21.40,0:25:27.81,Default,,0000,0000,0000,,telescope. But this is still a completely\Ndifferent way of looking at the sun. And
Dialogue: 0,0:25:27.81,0:25:33.60,Default,,0000,0000,0000,,what this tells us is that this, you know,\Ngiant glowing orb in the sky. That's not
Dialogue: 0,0:25:33.60,0:25:45.90,Default,,0000,0000,0000,,some optical illusion but that actually\Nexists. Okay. So onto our next topic.
Dialogue: 0,0:25:45.90,0:25:54.28,Default,,0000,0000,0000,,Exploding stars or supernovae which is\Nwhat my own research is mostly about. So
Dialogue: 0,0:25:54.28,0:25:59.67,Default,,0000,0000,0000,,supernovae are these giant explosions\Nwhere one single star, like in this
Dialogue: 0,0:25:59.67,0:26:05.76,Default,,0000,0000,0000,,example here, can shine about as bright as\Na whole galaxy consisting of billions of
Dialogue: 0,0:26:05.76,0:26:15.06,Default,,0000,0000,0000,,stars. And the rule of thumb is this:\NHowever big you think supernovae are
Dialogue: 0,0:26:15.06,0:26:23.83,Default,,0000,0000,0000,,you're wrong. They're bigger than that.\NRandall Munroe as an XKCD fan had this
Dialogue: 0,0:26:23.83,0:26:30.29,Default,,0000,0000,0000,,excellent example of just how big\Nsupernovae are so he asks which of the
Dialogue: 0,0:26:30.29,0:26:33.98,Default,,0000,0000,0000,,following would be brighter in terms of\Nthe amount of energy delivered to your
Dialogue: 0,0:26:33.98,0:26:42.44,Default,,0000,0000,0000,,retina. Option 1: A supernova, seen from\Nas far away as the sun is from earth or
Dialogue: 0,0:26:42.44,0:26:49.92,Default,,0000,0000,0000,,Option 2: A hydrogen bomb pressed against\Nyour eyeball. So which of these would be
Dialogue: 0,0:26:49.92,0:27:00.28,Default,,0000,0000,0000,,brighter. What do you think? You remember\Nthe the rule of thumb we had earlier this
Dialogue: 0,0:27:00.28,0:27:08.77,Default,,0000,0000,0000,,supernova is bigger than that. In fact\Nit's a billion times bigger than that. So
Dialogue: 0,0:27:08.77,0:27:15.34,Default,,0000,0000,0000,,supernovae are some of the biggest bangs\Nsince the original big bang. They also
Dialogue: 0,0:27:15.34,0:27:19.99,Default,,0000,0000,0000,,leave a neutron star or a black hole which\Nare really interesting objects to study in
Dialogue: 0,0:27:19.99,0:27:26.24,Default,,0000,0000,0000,,their own right and the outgoing shockwave\Nalso leads to the creation of lots of new
Dialogue: 0,0:27:26.24,0:27:33.77,Default,,0000,0000,0000,,stars. But maybe most importantly\Nsupernovae are where many of the chemical
Dialogue: 0,0:27:33.77,0:27:40.78,Default,,0000,0000,0000,,elements around you come from. So whether\Nit's things like the oxygen in your lungs
Dialogue: 0,0:27:40.78,0:27:46.86,Default,,0000,0000,0000,,or the calcium in your bones or the\Nsilicon in your favorite computer chip.
Dialogue: 0,0:27:46.86,0:27:51.54,Default,,0000,0000,0000,,Life as we know it, and congress as we\Nknow it could not exist without
Dialogue: 0,0:27:51.54,0:28:01.57,Default,,0000,0000,0000,,supernovae. And yet we don't actually\Nunderstand how these explosions happen...
Dialogue: 0,0:28:01.57,0:28:18.89,Default,,0000,0000,0000,,well I have no idea what's happening....\Nlife as we know it could not exist without
Dialogue: 0,0:28:18.89,0:28:25.56,Default,,0000,0000,0000,,supernovae and yet we don't actually\Nunderstand how these explosions happen.
Dialogue: 0,0:28:25.56,0:28:31.38,Default,,0000,0000,0000,,And even observing them with telescopes\Ndoesn't really help us because telescopes
Dialogue: 0,0:28:31.38,0:28:37.06,Default,,0000,0000,0000,,can only ever see the surface of a star.\NThey can't look inside the core of the
Dialogue: 0,0:28:37.06,0:28:44.53,Default,,0000,0000,0000,,star where the explosion actually takes\Nplace. So that's why we need neutrinos.
Dialogue: 0,0:28:44.53,0:28:51.02,Default,,0000,0000,0000,,And we have tens of thousands of\Nsupernovae with optical telescopes, with
Dialogue: 0,0:28:51.02,0:28:58.71,Default,,0000,0000,0000,,neutrinos we've observed just one. This\None in February of 1987. And we've seen
Dialogue: 0,0:28:58.71,0:29:06.89,Default,,0000,0000,0000,,two dozen neutrinos which you see here on\Nthe right. That's what we know. So we know
Dialogue: 0,0:29:06.89,0:29:11.77,Default,,0000,0000,0000,,basically that there were many neutrinos\Nemitted during the first one second or so
Dialogue: 0,0:29:11.77,0:29:18.98,Default,,0000,0000,0000,,and then fewer and fewer for the next 10\Nseconds. We know that neutrinos make up
Dialogue: 0,0:29:18.98,0:29:25.99,Default,,0000,0000,0000,,most of the energy of the explosion of the\Nsupernova, with the actual energy of the
Dialogue: 0,0:29:25.99,0:29:32.39,Default,,0000,0000,0000,,explosion and the visible light making\Njust up a tiny fraction. We know that the
Dialogue: 0,0:29:32.39,0:29:42.45,Default,,0000,0000,0000,,neutrinos arrive a few hours before the\Nlight. And that's all, that's all we know.
Dialogue: 0,0:29:42.45,0:29:46.83,Default,,0000,0000,0000,,And still about these two dozen events,\Nthese two dozen neutrinos more than
Dialogue: 0,0:29:46.83,0:29:52.71,Default,,0000,0000,0000,,sixteen hundred papers are written. That's\Nmore than one paper a week for over 30
Dialogue: 0,0:29:52.71,0:29:59.73,Default,,0000,0000,0000,,years. So this gives you an idea of just\Nhow important this event was. And how
Dialogue: 0,0:29:59.73,0:30:03.77,Default,,0000,0000,0000,,creative physicists are. Or I guess, you\Ncould call it desperate.
Dialogue: 0,0:30:03.77,0:30:09.08,Default,,0000,0000,0000,,{\i1}Laughter{\i0}\NBut you know, I prefer creative. In fact
Dialogue: 0,0:30:09.08,0:30:14.74,Default,,0000,0000,0000,,this, you know, this one Supernova, we\Nobserved was such big deal, that 30 years
Dialogue: 0,0:30:14.74,0:30:22.69,Default,,0000,0000,0000,,later February of last year we had a\Nconference in Tokyo on supernova neutrinos
Dialogue: 0,0:30:22.69,0:30:30.70,Default,,0000,0000,0000,,and we had a 30th anniversary celebration.\NSo there we were about 40 or 50 physicists
Dialogue: 0,0:30:30.70,0:30:38.27,Default,,0000,0000,0000,,looking over the skyline of Tokyo having\Ndinner, there's the now leader of the
Dialogue: 0,0:30:38.27,0:30:43.68,Default,,0000,0000,0000,,Super-Kamiokande experiment who was a PhD\Nstudent back then when it happened, and in
Dialogue: 0,0:30:43.68,0:30:49.65,Default,,0000,0000,0000,,his hand he's holding the original data\Ntape with the events that he himself
Dialogue: 0,0:30:49.65,0:30:56.83,Default,,0000,0000,0000,,analyzed back then. So there we were, and\Nat one point that evening we actually
Dialogue: 0,0:30:56.83,0:31:04.42,Default,,0000,0000,0000,,started to sing Happy Birthday. So you\Nknow how it goes - happy birthday to you,
Dialogue: 0,0:31:04.42,0:31:11.78,Default,,0000,0000,0000,,happy birthday to you, happy birthday dear\Nsupernova 1987-A. You know it absolutely
Dialogue: 0,0:31:11.78,0:31:21.03,Default,,0000,0000,0000,,doesn't work, but it was still amazing. So\Nthat's all we know, and then there's what
Dialogue: 0,0:31:21.03,0:31:26.69,Default,,0000,0000,0000,,we think we know, and most of that comes\Nfrom computer simulations of supernovae.
Dialogue: 0,0:31:26.69,0:31:33.44,Default,,0000,0000,0000,,But the problem is, those are really\Nreally hard. You know it's one of these
Dialogue: 0,0:31:33.44,0:31:38.88,Default,,0000,0000,0000,,extremely rare situations where all four\Nfundamental forces: gravity,
Dialogue: 0,0:31:38.88,0:31:44.91,Default,,0000,0000,0000,,electromagnetism, and the weak, and the\Nstrong nuclear force, all play a role. You
Dialogue: 0,0:31:44.91,0:31:49.40,Default,,0000,0000,0000,,know normally, in particle physics you\Ndon't have to worry about gravity, and in
Dialogue: 0,0:31:49.40,0:31:53.90,Default,,0000,0000,0000,,pretty much all other areas of physics you\Nonly have to worry about gravity and
Dialogue: 0,0:31:53.90,0:31:59.62,Default,,0000,0000,0000,,electromagnetism. Here all four play a\Nrole. You've also got nonlinear
Dialogue: 0,0:31:59.62,0:32:05.17,Default,,0000,0000,0000,,hydrodynamics of the gas and plasma inside\Nthe star. You've got the matter moving
Dialogue: 0,0:32:05.17,0:32:09.62,Default,,0000,0000,0000,,relativistically at 10 or 20 percent of\Nthe speed of light and you've got extreme
Dialogue: 0,0:32:09.62,0:32:14.32,Default,,0000,0000,0000,,pressures and extreme temperatures that\Nare sometimes beyond what we can produce
Dialogue: 0,0:32:14.32,0:32:23.47,Default,,0000,0000,0000,,in the laboratory on earth. So that's why\Nthese simulations even in 2018 are still
Dialogue: 0,0:32:23.47,0:32:28.26,Default,,0000,0000,0000,,limited by the available computing power.\NSo we need to do a lot of approximations
Dialogue: 0,0:32:28.26,0:32:34.93,Default,,0000,0000,0000,,to actually get our code to run in a\Nreasonable time, but that gives you, some,
Dialogue: 0,0:32:34.93,0:32:41.43,Default,,0000,0000,0000,,that produces some problems, and in fact\Nthe week I started my PhD one of those
Dialogue: 0,0:32:41.43,0:32:46.21,Default,,0000,0000,0000,,groups doing the supernova simulations\Npublished a paper saying that there is a
Dialogue: 0,0:32:46.21,0:32:52.08,Default,,0000,0000,0000,,long list of numerical challenges and code\Nverification issues. Basically we're using
Dialogue: 0,0:32:52.08,0:32:57.89,Default,,0000,0000,0000,,this approximations and we don't know\Nexactly how much error they introduce, and
Dialogue: 0,0:32:57.89,0:33:03.39,Default,,0000,0000,0000,,the results of different groups are still\Ntoo far apart, and that's not because
Dialogue: 0,0:33:03.39,0:33:06.67,Default,,0000,0000,0000,,those people are dummies. Quite the\Nopposite they're some of the smartest
Dialogue: 0,0:33:06.67,0:33:14.80,Default,,0000,0000,0000,,people in the world. It's just that the\Nproblem is so damn hard. In fact, in many
Dialogue: 0,0:33:14.80,0:33:20.09,Default,,0000,0000,0000,,of these simulations the stars don't even\Nexplode on their own, and we don't know
Dialogue: 0,0:33:20.09,0:33:25.07,Default,,0000,0000,0000,,whether that means that some of these\Napproximations just introduce numerical
Dialogue: 0,0:33:25.07,0:33:31.39,Default,,0000,0000,0000,,errors which change the result, or whether\Nit means that there are some completely
Dialogue: 0,0:33:31.39,0:33:36.34,Default,,0000,0000,0000,,new physics happening in there which we\Ndon't know about, or whether that is
Dialogue: 0,0:33:36.34,0:33:44.15,Default,,0000,0000,0000,,actually realistic and some stars you know\Nin the universe don't explode but just
Dialogue: 0,0:33:44.15,0:33:52.73,Default,,0000,0000,0000,,implode silently into a blackhole. We\Ndon't know. We just don't know. So take
Dialogue: 0,0:33:52.73,0:34:02.28,Default,,0000,0000,0000,,any, you know, any results of the\Nsimulations with a grain of salt. That said
Dialogue: 0,0:34:02.28,0:34:09.03,Default,,0000,0000,0000,,here's our best guess for what happens. So\Nwe start out was a massive star that's at
Dialogue: 0,0:34:09.03,0:34:15.18,Default,,0000,0000,0000,,least eight times the mass of our sun, and\Nit starts fusing hydrogen to helium, and
Dialogue: 0,0:34:15.18,0:34:22.66,Default,,0000,0000,0000,,then on and on into heavier elements until\Nfinally it reaches iron, and at that point
Dialogue: 0,0:34:22.66,0:34:31.44,Default,,0000,0000,0000,,fusion stops because you can't gain energy\Nfrom fusing two iron nuclei. So there the
Dialogue: 0,0:34:31.44,0:34:37.38,Default,,0000,0000,0000,,iron just accretes in the core of the star\Nwhile in the outer layers - here in orange
Dialogue: 0,0:34:37.38,0:34:43.67,Default,,0000,0000,0000,,- nuclear fusion is still going on, but as\Nmore and more iron accretes and that core
Dialogue: 0,0:34:43.67,0:34:50.84,Default,,0000,0000,0000,,reaches about one-and-a-half solar masses\Nit can't hold its own weight anymore and
Dialogue: 0,0:34:50.84,0:34:55.82,Default,,0000,0000,0000,,it starts to collapse, and inside the core\Nin nuclear reactions you're starting to
Dialogue: 0,0:34:55.82,0:35:04.77,Default,,0000,0000,0000,,form neutrinos which I'm showing us ghost\Nemoji here. Now let's zoom in a bit. The
Dialogue: 0,0:35:04.77,0:35:13.28,Default,,0000,0000,0000,,core continues to collapse until at the\Ncenter it surpasses nuclear density, and
Dialogue: 0,0:35:13.28,0:35:21.67,Default,,0000,0000,0000,,at that point it's so dense that the\Nneutrinos are actually trapped in there.
Dialogue: 0,0:35:21.67,0:35:27.47,Default,,0000,0000,0000,,So even neutrinos which literally can go\Nthrough walls can not escape from there
Dialogue: 0,0:35:27.47,0:35:35.78,Default,,0000,0000,0000,,because matter is so dense, and the\Nincoming matter basically hits a wall
Dialogue: 0,0:35:35.78,0:35:39.69,Default,,0000,0000,0000,,because the matter in the center can't be\Ncompressed any further, so just hits the
Dialogue: 0,0:35:39.69,0:35:46.21,Default,,0000,0000,0000,,wall and bounces back. So from that\Ncollapse you suddenly get an outgoing
Dialogue: 0,0:35:46.21,0:35:51.30,Default,,0000,0000,0000,,shock wave, and in the wake of that\Nshockwave suddenly you get a whole burst
Dialogue: 0,0:35:51.30,0:35:58.65,Default,,0000,0000,0000,,of neutrinos which escape the star\Nquickly. Now that shockwave moves on and
Dialogue: 0,0:35:58.65,0:36:05.92,Default,,0000,0000,0000,,slows down and as it slows down the matter\Nfrom outer layer still falls in, and in
Dialogue: 0,0:36:05.92,0:36:13.39,Default,,0000,0000,0000,,this kind of collision region where\Nneutrinos in the center are still trapped
Dialogue: 0,0:36:13.39,0:36:18.66,Default,,0000,0000,0000,,in that collision region, neutrinos are,\Nyou know, being produced at a relatively
Dialogue: 0,0:36:18.66,0:36:25.14,Default,,0000,0000,0000,,steady rate and the shock wave has pretty\Nmuch stopped and just wavers back and
Dialogue: 0,0:36:25.14,0:36:32.53,Default,,0000,0000,0000,,forth, and we see some neutrino emission.\NNow after about half a second, maybe a
Dialogue: 0,0:36:32.53,0:36:37.59,Default,,0000,0000,0000,,second, neutrinos from the center are\Nslowly starting to escape. You know most
Dialogue: 0,0:36:37.59,0:36:44.08,Default,,0000,0000,0000,,of them are still trapped but some are\Nmaking their way outside and some of those
Dialogue: 0,0:36:44.08,0:36:48.81,Default,,0000,0000,0000,,actually manage to leave the star while\Nothers interact with matter in this
Dialogue: 0,0:36:48.81,0:36:54.41,Default,,0000,0000,0000,,shockwave layer and give that matter a\Nlittle energy transfer a little push and
Dialogue: 0,0:36:54.41,0:37:02.67,Default,,0000,0000,0000,,heat it back up. So the shock wave gets\Nrevived and the star actually explodes,
Dialogue: 0,0:37:02.67,0:37:09.52,Default,,0000,0000,0000,,and all of that took just one second, and\Nthen over the next 10 seconds or so the
Dialogue: 0,0:37:09.52,0:37:16.41,Default,,0000,0000,0000,,neutrinos remaining at the core slowly\Nmake their way outwards and then travel
Dialogue: 0,0:37:16.41,0:37:22.72,Default,,0000,0000,0000,,away at the speed of light hopefully to\NEarth to our detector. While that shock wave
Dialogue: 0,0:37:22.72,0:37:27.16,Default,,0000,0000,0000,,moves much slower than the speed of light,\Nyou know, slowly makes its way outwards
Dialogue: 0,0:37:27.16,0:37:32.100,Default,,0000,0000,0000,,and only a few hours later when that shock\Nwave reaches the surface of the star do we
Dialogue: 0,0:37:32.100,0:37:41.05,Default,,0000,0000,0000,,actually see something with telescopes.\NSo, remember earlier the neutrinos signal
Dialogue: 0,0:37:41.05,0:37:45.76,Default,,0000,0000,0000,,we saw was something like a bunch of\Nneutrinos in the first second and then
Dialogue: 0,0:37:45.76,0:37:53.76,Default,,0000,0000,0000,,fewer and fewer neutrinos for 10 seconds.\NNot a lot of detail but what we might see
Dialogue: 0,0:37:53.76,0:37:58.73,Default,,0000,0000,0000,,is something like this: a brief and\Nintense burst when the matter hits the
Dialogue: 0,0:37:58.73,0:38:03.68,Default,,0000,0000,0000,,wall and is thrown back in this first\Nshock wave, then as the shock wave
Dialogue: 0,0:38:03.68,0:38:08.69,Default,,0000,0000,0000,,stagnates we might see some wiggles\Ncorresponding to the shock wave, you know,
Dialogue: 0,0:38:08.69,0:38:17.27,Default,,0000,0000,0000,,sloshing around aimlessly until the shock\Nwave is revived. The explosion starts and
Dialogue: 0,0:38:17.27,0:38:22.08,Default,,0000,0000,0000,,then over the next 10 or so seconds we\Nwould see fewer and fewer neutrinos as a
Dialogue: 0,0:38:22.08,0:38:29.01,Default,,0000,0000,0000,,star cools down and as neutrinos escape.\NSo if we have good neutrino detectors we
Dialogue: 0,0:38:29.01,0:38:34.10,Default,,0000,0000,0000,,should be able to watch, you know,\Nmillisecond by millisecond what exactly
Dialogue: 0,0:38:34.10,0:38:43.43,Default,,0000,0000,0000,,happens inside the star. Now luckily we've\Ngot many more neutrino detectors by now.
Dialogue: 0,0:38:43.43,0:38:46.69,Default,,0000,0000,0000,,Probably the biggest one is the Super-\NKamiokande in the Mozumi Mine which would
Dialogue: 0,0:38:46.69,0:38:52.36,Default,,0000,0000,0000,,see about 4000 events from an average\Nsupernova in our Milky Way, and then we've
Dialogue: 0,0:38:52.36,0:38:58.07,Default,,0000,0000,0000,,got a bunch of other detectors which was\Ntypically you know hundreds of events, and
Dialogue: 0,0:38:58.07,0:39:01.58,Default,,0000,0000,0000,,some of these detectors are part of\Nsomething called the supernova early
Dialogue: 0,0:39:01.58,0:39:07.79,Default,,0000,0000,0000,,warning system or SNEWS, and snooze is\Nmeant to act as a wake up call to
Dialogue: 0,0:39:07.79,0:39:14.13,Default,,0000,0000,0000,,astronomers. So when when these detectors\Nobserve neutrinos which are probably from
Dialogue: 0,0:39:14.13,0:39:20.31,Default,,0000,0000,0000,,a supernova they will send out an alert to\Nastronomers to get their telescopes ready
Dialogue: 0,0:39:20.31,0:39:27.15,Default,,0000,0000,0000,,to be able to see that supernova from the\Nvery beginning and then of course just in
Dialogue: 0,0:39:27.15,0:39:31.77,Default,,0000,0000,0000,,the past few years we've also had\Ngravitation wave detectors like LIGO in
Dialogue: 0,0:39:31.77,0:39:40.01,Default,,0000,0000,0000,,the U.S, Virgo in Italy, and in just a few\Nyears we will get another one called KAGRA
Dialogue: 0,0:39:40.01,0:39:45.71,Default,,0000,0000,0000,,which is located in Japan actually inside\Nthe same mountain as Super-Kamiokande. So
Dialogue: 0,0:39:45.71,0:39:50.26,Default,,0000,0000,0000,,they're literally next door neighbors, and\Nthen we might get another detector in
Dialogue: 0,0:39:50.26,0:39:56.30,Default,,0000,0000,0000,,India, maybe one China in the future. So\Nthat's three completely different ways of
Dialogue: 0,0:39:56.30,0:40:05.20,Default,,0000,0000,0000,,looking at supernovae. So when we observe\Na supernova it will be headline news, and
Dialogue: 0,0:40:05.20,0:40:10.21,Default,,0000,0000,0000,,now you know what's behind those\Nheadlines. So I've introduced you to
Dialogue: 0,0:40:10.21,0:40:16.63,Default,,0000,0000,0000,,neutrinos, I've told you a bit about what\Nit's like to work on on such a detector
Dialogue: 0,0:40:16.63,0:40:22.48,Default,,0000,0000,0000,,and, you know the challenges of building a\Ndetector of this scale and I've showed you
Dialogue: 0,0:40:22.48,0:40:27.52,Default,,0000,0000,0000,,how with neutrinos we can observe things\Nbut we can't directly observe otherwise
Dialogue: 0,0:40:27.52,0:40:33.62,Default,,0000,0000,0000,,like the interior of exploding stars, and\Nwith that I want to thank you for your
Dialogue: 0,0:40:33.62,0:40:36.95,Default,,0000,0000,0000,,attention and please let me know if you\Nhave any questions.
Dialogue: 0,0:40:36.95,0:40:51.04,Default,,0000,0000,0000,,{\i1}applause{\i0}
Dialogue: 0,0:40:51.04,0:40:53.02,Default,,0000,0000,0000,,Herald: Thank you Jost, it was an amazing
Dialogue: 0,0:40:53.02,0:40:59.53,Default,,0000,0000,0000,,talk. We have plenty of time for questions\Nand there are two microphones. Microphone
Dialogue: 0,0:40:59.53,0:41:03.63,Default,,0000,0000,0000,,one is on the left side of the stage,\Nmicrophone two is in the middle so queue
Dialogue: 0,0:41:03.63,0:41:10.84,Default,,0000,0000,0000,,up and we're going to take some questions.\NFirst question from microphone two.
Dialogue: 0,0:41:10.84,0:41:17.41,Default,,0000,0000,0000,,Q: Yeah, thank you, I do have a question -\NI come from a mining area and I just
Dialogue: 0,0:41:17.41,0:41:24.45,Default,,0000,0000,0000,,looked up how deep other mines go and I'm\Nwondering why do you dig into useless rock
Dialogue: 0,0:41:24.45,0:41:30.73,Default,,0000,0000,0000,,if you can just go to some area where\Nthere are mines that are no longer used,
Dialogue: 0,0:41:30.73,0:41:37.06,Default,,0000,0000,0000,,my area they go as deep as 1,200 metres I\Nthink. I just looked up and was surprised
Dialogue: 0,0:41:37.06,0:41:41.29,Default,,0000,0000,0000,,that the deepest mine on Earth is almost\Nfour kilometres in South Africa - an
Dialogue: 0,0:41:41.29,0:41:46.84,Default,,0000,0000,0000,,active goldmine - so why don't you use\Nthose?
Dialogue: 0,0:41:46.84,0:41:52.06,Default,,0000,0000,0000,,A: So, part of why we're using that\Nparticular location is because we used it
Dialogue: 0,0:41:52.06,0:42:00.39,Default,,0000,0000,0000,,for Super-K and Kamiokande before, and the\Nmountain that Kamiokande was in actually
Dialogue: 0,0:42:00.39,0:42:07.76,Default,,0000,0000,0000,,is a mine. So we had some previous\Ninfrastructure there, and then there's I
Dialogue: 0,0:42:07.76,0:42:12.47,Default,,0000,0000,0000,,guess some tradeoff between the benefits\Nyou get from going deeper and deeper and
Dialogue: 0,0:42:12.47,0:42:19.67,Default,,0000,0000,0000,,the additional cost I think.\NHerald: Thank you, we have a question from
Dialogue: 0,0:42:19.67,0:42:24.65,Default,,0000,0000,0000,,the Internet, that's going to be narrated\Nby our wonderful Signal Angel.
Dialogue: 0,0:42:24.65,0:42:37.84,Default,,0000,0000,0000,,Jost: Hello Internet. So the question, I\Ndidn't understand then whole question, but
Dialogue: 0,0:42:37.84,0:42:42.52,Default,,0000,0000,0000,,something about earthquake. Okay.\NQ: Does the earthquake affect the
Dialogue: 0,0:42:42.52,0:42:49.97,Default,,0000,0000,0000,,detector.\NA: Well there's two parts of the answer:
Dialogue: 0,0:42:49.97,0:42:58.66,Default,,0000,0000,0000,,Part one I'm not a geologist. Part two I\Nthink the earthquakes are mostly centered
Dialogue: 0,0:42:58.66,0:43:06.44,Default,,0000,0000,0000,,in the cavern on the east coast of Japan\Nand we're about 200-300 kilometers away
Dialogue: 0,0:43:06.44,0:43:15.01,Default,,0000,0000,0000,,from there, so the region we're in is\Nrelatively stable, and in fact we've been
Dialogue: 0,0:43:15.01,0:43:22.95,Default,,0000,0000,0000,,running, since 1983 and we haven't had\Nproblems with earthquakes, and during the
Dialogue: 0,0:43:22.95,0:43:31.38,Default,,0000,0000,0000,,Fukushima earthquake our detector was\Nmostly fine but we've actually had, so in
Dialogue: 0,0:43:31.38,0:43:37.60,Default,,0000,0000,0000,,addition to what I was talking about we're\Nalso producing a beam of neutrinos at an
Dialogue: 0,0:43:37.60,0:43:43.18,Default,,0000,0000,0000,,accelerator which we shoot at the\Ndetector, and that accelerator is right at
Dialogue: 0,0:43:43.18,0:43:48.51,Default,,0000,0000,0000,,the east coast. So, the only damage from\Nthe Fukushima earthquake was to that
Dialogue: 0,0:43:48.51,0:43:57.38,Default,,0000,0000,0000,,accelerator, not to the detector itself. I\Nhope that answers your question.
Dialogue: 0,0:43:57.38,0:44:03.33,Default,,0000,0000,0000,,Herald: Next is from microphone two.\NQ: Hello, thanks for an interesting talk.
Dialogue: 0,0:44:03.33,0:44:10.09,Default,,0000,0000,0000,,Do you, or does science, have any theory\Nif the neutrinos who hit the electron are
Dialogue: 0,0:44:10.09,0:44:16.68,Default,,0000,0000,0000,,affected themselves from this hit, are\Nthey like directed in another direction or
Dialogue: 0,0:44:16.68,0:44:22.98,Default,,0000,0000,0000,,lose some sort of energy themselves or\Njust hit the electron and pass through.
Dialogue: 0,0:44:22.98,0:44:27.100,Default,,0000,0000,0000,,A: So, conservation of energy and of\Nmomentum still holds, so they would lose
Dialogue: 0,0:44:27.100,0:44:31.29,Default,,0000,0000,0000,,some energy as they give the electron a\Nlittle kick.
Dialogue: 0,0:44:31.29,0:44:34.85,Default,,0000,0000,0000,,OK. Thank you.\NHerald: Thank you, one more question from
Dialogue: 0,0:44:34.85,0:44:38.28,Default,,0000,0000,0000,,mic two.\NQ: Hello, thanks for your talk. My
Dialogue: 0,0:44:38.28,0:44:44.36,Default,,0000,0000,0000,,question is you said that the only\Nsupernova where we detected some neutrinos
Dialogue: 0,0:44:44.36,0:44:50.51,Default,,0000,0000,0000,,from is from the 80's. So what is so\Nspecial about that supernova that with all
Dialogue: 0,0:44:50.51,0:44:54.67,Default,,0000,0000,0000,,the new detectors built there was never\Nanother detection?
Dialogue: 0,0:44:54.67,0:45:00.15,Default,,0000,0000,0000,,A: So, the special thing about that one is\Nthat it was relatively close. So it was in
Dialogue: 0,0:45:00.15,0:45:05.94,Default,,0000,0000,0000,,the Large Magellanic Cloud about 150,000\Nlight years away which is, you know, on
Dialogue: 0,0:45:05.94,0:45:13.28,Default,,0000,0000,0000,,cosmic scales our next door neighbor,\Nwhereas other supernovae which we observe
Dialogue: 0,0:45:13.28,0:45:17.06,Default,,0000,0000,0000,,can be you know millions of light years\Naway. We can easily see them at that
Dialogue: 0,0:45:17.06,0:45:23.25,Default,,0000,0000,0000,,distance but we can't detect any\Nneutrinos, and we expect about between 1
Dialogue: 0,0:45:23.25,0:45:28.100,Default,,0000,0000,0000,,and 3 supernovae in our Milky Way per\Ncentury, so we're in this for the long
Dialogue: 0,0:45:28.100,0:45:32.25,Default,,0000,0000,0000,,term. Okay.
Dialogue: 0,0:45:32.25,0:45:36.04,Default,,0000,0000,0000,,Herald: Thank you, microphone two again\Nplease.
Dialogue: 0,0:45:36.04,0:45:43.63,Default,,0000,0000,0000,,Q: Hi, thanks for your talk. My question\Nis you said that changing the water once a
Dialogue: 0,0:45:43.63,0:45:50.17,Default,,0000,0000,0000,,year is not often enough, how often do you\Nchange the water?
Dialogue: 0,0:45:50.17,0:45:56.71,Default,,0000,0000,0000,,A: How often do we change the water in the\Ndetector? - Yes - So we completely drain
Dialogue: 0,0:45:56.71,0:46:05.79,Default,,0000,0000,0000,,and refill the detector only for repair\Nwork which, you know, happens every
Dialogue: 0,0:46:05.79,0:46:10.68,Default,,0000,0000,0000,,depending on what we want to do but\Ntypically every couple of years to, you
Dialogue: 0,0:46:10.68,0:46:17.52,Default,,0000,0000,0000,,know, 10 plus years and apart from that we\Nrecirculate the water all the time to
Dialogue: 0,0:46:17.52,0:46:22.48,Default,,0000,0000,0000,,purify it because there will always be\Nsome traces of radioactivity from the
Dialogue: 0,0:46:22.48,0:46:27.60,Default,,0000,0000,0000,,surrounding rock which make the way in the\Nwater over time.
Dialogue: 0,0:46:27.60,0:46:33.64,Default,,0000,0000,0000,,Mic 2: Thank you.\NHerald: Thank you, and that would be all,
Dialogue: 0,0:46:33.64,0:46:38.64,Default,,0000,0000,0000,,that was a wonderful start to the\NCongress, thank you Jost.
Dialogue: 0,0:46:38.64,0:46:41.40,Default,,0000,0000,0000,,{\i1}applause{\i0}
Dialogue: 0,0:46:41.40,0:46:46.60,Default,,0000,0000,0000,,{\i1}35c3 postroll music{\i0}
Dialogue: 0,0:46:46.60,0:47:03.00,Default,,0000,0000,0000,,subtitles created by c3subtitles.de\Nin the year 2019. Join, and help us!