Doctor Asks Physics Questions (ft @Medlife Crisis)

hi everybody this video is going to be a  little bit different because i'm here today   in london in the beautiful building of the royal  institution together with dr rohin francis who's   a cardiologist and he's also a youtuber so he  has his own channel which is called medlife   crisis. the plan is today that he'll be asking  me questions about physics and then i get to ask   him questions so there'll be a second part of  this video which you can watch on his channel rohin, this is the first time i'm talking to a  cardiologist who is not busy putting things on   my chest so first of all it's great to see you  well it's a privilege to to be here with you   sabine so i would just say go ahead and shoot  your questions at me okay so you've obviously   won a lot of fans with your kind of no-nonsense  explanations of physics and and um different   things so i'm gonna be pretty blunt here and i'm  gonna start by asking about dark matter uh you've   heard of dark matter i take it yes yeah good is  this just a fudge that physicists have made up   when their sums didn't work and are we just going  to see it overturned in years to come like we've   seen lots of theories in the past be disproven  i've heard physicists say, it's something that   they will say in their talk like we've just you  know given a name to it we have no idea what it is   we don't know what most of the maternity universe  is actually made of and i think what's happening   is they're trying to be funny but people don't  understand that they're just joking so i'm afraid   dark matter is a technical term so it's not just  stuff physicists use this word to mean something   very specific to begin with matter actually  means something so matter has a very particular   behavior when the universe expands usually  they're talking about some pressureless fluid   that has particular behavior under collapse  and and this this is all really important   it's something very different for example from  radiation or vacuum energy or scalar fields or   all other kinds of field so matter is really  a technical term and then also the word dark   actually means something means it  doesn't interact with light and and also   we know that it doesn't clump to itself or to  normal matter um so you see physicists don't just   invent something to make their sumps work out  they actually have a very specific model for it   which goes into the mass and so on and so  forth what's funny though is that i think   most people don't really know that  it's a fairly technical thing there was   a very interesting interview in the guardian  a couple of months ago with an epidemiologist   who was asked how is it that the covert death  rate in germany is so much lower than in the uk   and his idea was oh that's because the germans  have some type of immunological dark matter   so he clearly used the word just  to mean we have no idea what it is   but physicists actually mean  something very concrete with it   so some of the maps that i've seen of dark matter  sort of in the universe um i understand that it's   it doesn't interact with with light but is it is  it here is it in the room with us here or is it   is it something that's remote so if it exists it  should be here um so it will be going through us   without interacting without leaving a  trace i mean that's the problem right   they're building these big detectors and the  stuff just goes through if it exists right which   we don't know because it just goes through what  you see in these maps is that um they have some   observations for example gravitational lensing  so you see this distortion of the background of   the galaxy and galaxy clusters and you can use  this to calculate what the density distribution   of the dark matter must have been and so this is  how these maps come about but is there actually   some matter there um we we don't know so this is  just something which we infer from the data but   if you believe that this explanation for the  data is correct and yes it should be here and   people can estimate the density and the velocity  by which it should go through what they can't   estimate is how frequently it should interact  which is why you see this long series of   experiments with bigger and bigger detectors  and they still haven't seen anything yeah so   that kind of brings me to my next question about  detectors because it seems to me that every time   physicists build something and they  don't get the answer they want they go ah   we just haven't built it big enough and  the solution is always just a big something   build something bigger and i understand there's  now a plan to make a super large hadron collider   that's 10 times bigger or and then eventually  build one around the the equator of the earth and   out into into the solar system um so why is  the solution always just to just go bigger   because that's the easiest thing to do just  if you lack imagination you make it bigger   you get to test something that hasn't been  tested before but the underlying problem   is actually quite deep because if you look at the  history of physics or science in general it didn't   used to be the case for a long time if you look  at the history of say microscopes telescopes and   so on what happened was that they built one thing  and then they learned something from it so they   developed a better understanding of nature and  that helped them to develop new technologies which   improved the experiments which led to better  insights about nature and so on and so forth   so it was this virtuous cycle and at some point  it just broke so we we don't really have any new   technologies we're just you know squeezing out  the last drop from quantum mechanics basically   so you're saying that we're overdue some sort of  break in this cycle like if i use your telescope   analogy i guess you build bigger and bigger  telescopes but now actually there are a lot of   telescopes being built which are using different  technologies but you're saying particle colliders   we're waiting for a sort of change in the  technology is that right or well i would say   we should be waiting for a change in technology  because obviously if you just make things bigger   they get more expensive like for example  for this collider you would have to dig this   tunnel which is like 100 kilometers long and  that costs several costs several billions um so   size in and by itself eats up a lot of money  and the problem is that there have not been   any great technological changes that could have  shrunken things back into into a manageable   size but there's also like a deeper question  behind this which is what um john horgan has   been going on about in his book the end of  science like is there actually something   else to find or is this it like do we just  have to live with it and that's the best we   can do but surely that's not the case is it or  i mean i hear these claims that you know matter   that we understand is a tiny minority five  ten percent of the universe or something um   and this remainder the dark matter or plus  minus dark energy you know there is still a   lot yet to be understood so do you i mean do you  agree with horgan's statement that this is it or   no of course i don't agree and i think most  businesses don't uh agree with them but i think   it's not it's not quite as simple i mean there  there are some open questions for example dark   matter it's like we already talked about this but  also there's uh the quantization of gravity that's   the measurement problem in quantum mechanics  but for a long time people especially strength   theorists have propagated this idea that we're  really close to finding a theory of everything   which would be the last thing to ever be said  about the foundations of physics and um it's   a reasonable question to ask like if this theory  exists and if we find it will it actually be good   for something and i think most people who work  in this field don't expect it to be actually good   for something because it you know it uses energy  in such high ranges um that it's unclear what we   would ever be able to use it for right yeah i mean  i'll refrain from saying anything cheeky about   physics research i mean there's a lot that  doesn't seem that useful as you can probably   tell viewers i'm i'm here today to represent the  uneducated non-physicist asking dumb questions   so you mentioned sort of the problems with with  quantizing gravity and i understand part of the   issue of trying to achieve this um theory  of everything is marrying up quantum   theory with with gravity so what what actually to  someone like me a layman what actually is the the   problem with trying to do that well we don't  know how to do it okay simple as that so so we   do have ways mathematical methods um to make a  quantum theory out of a non-quantum theory and   people have applied those methods um to gravity,  einstein's theory of general relativity and   it turns out that it doesn't properly work  so you get a theory this way which is called   perturbatively quantized gravity and that's  fine as an approximation so it's believed to   be okay at low energies but it breaks down  at fairly high energies in the sense that   the mathematics just stops making sense so you  get probabilities larger than one or all kinds   of nonsense so that can't be the answer so this  normal method of quantization doesn't work and   then that's the question what do you do because  um we have an actual inconsistency between those   theories so if we just take general relativity  and quantum theory they don't work together   so there has to be a solution because nature knows  how to do it somehow but we don't know how nature   does it in the attempt of solving this problem  physicists have made up all kinds of theories   like string theories one of them loop quantum  gravity causal dynamical triangulation and so on   they're all mathematically fine i would say  more or less but the problem is that we have   absolutely no experimental evidence for any one  of them is that something we're going to get soon   i believe so yes um so but i have to say that  most physicists would probably not believe this   so to me it's a huge irony so i've been working  on how to experimentally test quantum gravity   for a decade or something and people will always  be like no no no way and um what's happened since   like in the past five to ten years or something  is that experimentalists have gotten on the case   and experimentalists are like they don't talk  they just do and so i think at some point just   come with the measurement and say okay so  we've measured it now please explain it   and then the theories will be you know oh my god  you know we never thought you'd be able to do it   and i mean it's not going to happen tomorrow  but maybe in 10 or 20 years and there would   certainly be a nobel prize for it yeah  so i i find it just ridiculous that   theorists aren't even they're not even  making predictions for the experiments changing tac slightly um how do we know there's  nothing smaller than a quark yeah a very good   question um so for starters particle  physicists don't really like to talk   about the size of particles because this is  all quantum and things and they're really just   fuzzy clouds and and so on but one can ask the  question without talking about size like could   it be that quarks are made of something else  like that they're not themselves fundamental  there are two problems with it. the one is  that it's theoretically hard to make work um   surprisingly and the other thing is that it's just  not compatible with experiment at least not so far because you haven't built a big enough collider the way that colliders work is that you slam  particles into each other with a very high   center of mass energy and because of quantum  things everything that can happen will happen   with a certain probability if the energy allows  it so if you have particles with a fairly small   mouse you'll produce them and this means that  you will detect the lightest particles the   easiest now what happens if you take a particle  like a quark of which you know the mouse and you   imagine it's made of other things then the masses  of the constituent particles have to be smaller   but then we'd already have seen them i understood  yeah okay so that doesn't work and then what you   can do is you can try to make it work the  same way it actually works for the proton   because the the proton is made of quarks but the quarks were actually discovered far later  than the proton so that seems to contradict what i   said earlier but the reason is that it  takes a lot of energy to pull these quarks   apart because the strong nuclear force is strong  as the name says and so you can do the same with   the quarks you can make them up of smaller  things that are strongly bound to each other   and there are theories for this so it's  called technicolor and the smaller things   are called preons and they've looked  for them at the lhc and didn't see it   so um at least the most straightforward theories  have just been ruled out but you know you can   always make more difficult theories and then  you can say well we need a bigger collider well one thing i did get from uh your  answer there is uh to just say if we   don't know because of quantum things i'm  going to take that phrase and the next time   a patient asks me something i don't know the  answer so it's just it's because of quantum things   what's your favorite particle clearly the neutrino  yeah so for one because neutrinos are a little   bit odd and a little bit weakly interacting so i  identify with this personally but there's also i   think they're our most promising evidence for new  physics in particle physics you know there's dark   matter they have an astrophysics cosmology but  in particle physics it's the neutrinos i actually   have a video coming up about this because there's  an anomaly in neutrino physics which um was   recently confirmed like in in 2018 but for reasons  that are entirely mysterious to me pretty much   no one paid any attention to it there's a pattern  in the oscillation of the neutrinos that just   can't be explained with the standard model so  we know that there has to be something else   and one of the maybe most exciting possibilities  is that it's actually also a signature for dark   matter well okay that's i didn't know that about  neutrinos don't get a lot of um attention i think   uh seeing as i know nothing about any of these  my favorite particle is from when i was at high   school and uh i learned the names of all the  quarks and i saw that one was called bottom   and i just felt very sorry and ever since then  i've had a soft spot for for bottom quark because   i just think what a name to be lumbered with it's  also sometimes called the oh well that's that's   uh that's a much nicer name i'm going to  call bottom the beauty quark from now on.   Sabine, can you magnet somebody to death? Are  you asking for a particular purpose? no comment. Yeah it's a good question it's not it's not  easy to answer um so to begin with there   are three different types of magnetism there's  ferromagnetism there's paramagnetism and there's   diamagnetism. so the one that we normally all know  about is just the ferromagnetism that's the thing   uh you know with the magnets that you  pin to the fridge and that kind of stuff   the other two are kind of responsive so if you if  you put something into a magnetic field then these   materials will respond to it and if you've seen  the footage of the levitating frog i think that   was diamagnetism so these materials  will be repelled by the magnetic field   so the the human body is not ferromagnetic no  matter what what you hear vaccines also don't   make you ferromagnetic you can't pin keys to  your face so you claim but there are various   parts of the human body various substances  that are either paramagnetic or diamagnetic   so what's going to happen if you put any kind of  organism in a really really strong magnetic field   as is that different parts of a cell or maybe  different chemical molecules will react slightly   differently and at some point i suspect and  i'm really just guessing it's going to cause   a problem because some chemical reactions  um you know won't work the way that they're   supposed to work and that's bad news yeah but  i mean even if if that doesn't kill you what's   going to happen eventually like if the magnetic  field is really really strong is that it will um   the energy levels of electrons um and then you  just fall apart i mean would you i assume you   might just heat up as well right is is that the  case in a super strong well if it's a static   field um i don't really see why there would be a  lot of energy transport but of course there's the   you know aesthetic magnetic field isn't really a  thing it's like an eternal black hole you know you   have to switch it on you have to get people in and  yeah you're probably right you know what probably   would kill you is if you get into the magnetic  field or if it switches on yeah but i mean in all   fairness you know if you you want to kill someone  it's much easier to do with an electric field   sure i mean i've got access to very  powerful mri scanners you see but that's   unrelated to why i'm asking but when i  have been inside a 7 tesla mri machine   and it's it's remarkable how you you do feel sort  of something happening like you can feel some   um nerve ending excitation you get these sort of  tingles uh which is noticeably different in a 3   or a 1.5 tesla mri um my phd research is all mri  based so this is maybe a slightly um odd question   but in a sort of commercial oven you can  get the temperature sort of 300 degrees   above room temperature without too much  problem so it's not that not not a lot   of work needed but only 300 degrees lower than  room temperature um is as low as you can go and   everything that we kind of know here on  earth is relatively speaking not that far   from absolute zero and then obviously go a huge  direction further up from there so my question   is how come all of life that we know here and and  sort of all these processes that occur on earth   are actually not that far off from absolute zero  how come absolute zero isn't isn't way way lower   yeah i guess i mean if you look at most of the  matter in the galaxy it'll be in stars and it'll   be tens of millions of degrees or something so  uh yeah i think you're right so it's a little   bit curious like why is it that everything we  know and like is at comparably low temperature   i mean ultimately it comes down to the constants  of nature but it's because at high temperature   it's very very difficult to form structures that  just fall apart immediately and it's only if you   get to fairly low temperatures that atoms will  stick together and you get interesting chemistry   and stuff starts to happen you know you get cells  organisms society culture or that kind of stuff it   needs to be at fairly low temperature slightly  more abstract or shall we say philosophical one   how do you personally think the universe is going  to to go honestly i don't think much about it   um fair enough i recently i i read a book  from uh lawrence krauss who's you know an   an astrophysicist cosmologist uh and then he had  this very funny quote where i thought it was funny   where he says he only makes predictions trillions  of years into the future because no one will be   around to check if he's right yeah and yeah i  think that's very spot on um how much should   you trust these predictions i think it's all  just speculations there is a very fundamental   problem to making predictions over so long time  scales because if there's any kind of effect   which is really really tiny on the time scales  that we have observations for so far it may still   kick in big time in the infinite future  because infinity is a really long time   there's just no way you can rule this out so  what's happening is basically that the error   on your prediction uh gets infinitely large  um and so i think all these speculations are   pretty much nonsense i mean you you can look at  them as a mathematical exercise we just take the   equations that we have so far and we run them  into the future and that will give us an answer   but don't take it seriously error rate approaching  infinities reminds me of my a-level maths   finally i i've i've uh i don't wanna give  the impression that i'm preoccupied with   with killing people here but how would you  actually die when you go into a black hole   realistically if you look at an actual black  hole like the ones that we actually see in the   centers of galaxies and so on they're  usually surrounded by really hot gas   so you know for practical purposes that would  probably kill you before you even fall into the   black hole yeah yeah but i mean we can think of  a mathematical black hole that just sits there in   empty space and then you fall in um so so the one  thing that's curious and which people sometimes   get confused about is that when you cross the  event horizon nothing actually happens it's not   like it is some kind of barrier but locally around  you there's just nothing it's it's empty space   and um exactly how strong the curvature is  like the space-time curvature at the horizon   depends on the size of the black  hole could actually be very small   but what happens is that once you're inside the  horizon uh you can't get back out or you you would   have to travel faster than the speed of light uh  to get out what's happening then is that you get   two different forces let's say you're falling in   a head first then the gravitational pull on your  head will be somewhat stronger than on your feet   so you'll get stretched and that'll get stronger  and stronger the closer you get to the singularity   so now if you're asking at exactly which point  do you die so i'm not sure you know eventually   you'll just be ripped into pieces yeah but  i would suspect that a long before this   it it becomes very difficult to pump around blood  and exactly when this would kill you you'd have   to ask a cardiologist ah well it's it's good to  be prepared for all eventualities you never know   when this might happen but i guess like lawrence  krauss's predictions we'll probably never find out   well sabine thank you so much for letting me ask  these daft questions and i hope they haven't been   too stupid but it's been a lot of fun listening  to your answers so thanks very much well i hope   you had fun too um listening to rohin's  question and my attempts to answer them   as i said there will be a second part to this  video where i get to ask him questions so you   don't want to miss this out so head over  to his channel and hear what he has to say   this video was sponsored by not vpn do you  also sometimes think you should be more careful   when you browse the 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Channel: Sabine Hossenfelder

Views: 84,005

Rating: 4.9650807 out of 5

Keywords: physics, medicine, doctor asks physics questions, dark matter, black holes, is dark matter here, how do you die in a black hole, are quarks made of something, how will the universe end, medlife crisis, rohin francis, hossenfelder, science without the gobbledygook, can you magnet someone to death, quantum physics

Id: bIT8_lS4vRY

Length: 26min 14sec (1574 seconds)

Published: Sat Sep 18 2021