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 internet especially when you're traveling not vpn makes this super easy not vpn is an app that you install on your phone or laptop and you use it to connect to one of their more than 5000 servers all over the world then you can browse the web from there this keeps 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thanks for watching don't forget to check out the second part of this video see you next week