An astrophysicist reacts to MOONFALL | Could a white dwarf fit inside the Moon?!

i mean the premise is you can't have anything  electronic so he destroys the guy's phone but he's   still got a torch in his hand?! That's powered by  batteries - that's electronic! Oh Jesus Christ.   Moonfall is Roland Emmerich's latest sci-fi  disaster movie and in it the Moon starts to   fall to Earth causing chaos and destruction. Even  in that one sentence there is so much to unpack   and I think this is why so many of you requested  that I watch and react to this film, to chat about   which bits are backed up by science and which bits  are firmly rooted in the fiction part of science   fiction. This is not a serious scientific review  it's just a bit of fun watching a sci-fi disaster   film but hopefully we'll all learn something along  the way. So without any further ado let's dive   into things and let's press play. but don't even  get me started on eclipses they're only possible   because the moon is exactly 400 times smaller than  the sun and exactly 400 times closer to the earth   anyone know how that happened i mean yeah it's  just coincidence right the moon didn't used to be   that distance from earth so the moon was actually  formed when another sort of proto planet in the   early days of the solar system collided with  earth and essentially was vaporized it put a load   of like junk in orbit around earth which slowly  coalesced and formed the moon much closer in to   earth and essentially what's been happening since  then is that the moon has been slowly moving away   from the earth all the time as the two essentially  exchange energy and and the earth essentially   slows down in the rate that it spins out that  impacts spun up the earth so a day would only   have been a couple of hours soon after the  impact happened and essentially as that spins   down the moon then gets further away so it's  complete coincidence that we happen to be around   when the moon is at roughly the right distance  to cause a full total solar eclipse of the sun   but we don't always get a full total solar eclipse  either because the moon's orbit isn't a perfect   circle it's sort of an oval shape so sometimes  it's closer to us and sometimes it's further away   so sometimes you actually get these eclipses where  you have this ring of the sun's light around the   outside as well so complete coincidence and if  this character here this you know samwell tally   from game of thrones character if he was you know  as into science as they've portrayed him so far   throughout the film he would know that right and  he wouldn't be so oddly sort of fixated like weird   conspiracy theorists that are on this idea of it  being 400 times closer but yet 400 times smaller   right he would know that it was a coincidence  the impact made the moon ring like a bell   it rang for hours and you know why because the damn moon is hollow well here's a sentence i didn't think i'd say  it today the moon is not hollow we know the   mass of the moon we know the size of the  moon and we know the density and we know   from that density that it cannot possibly hollow  we even left seismometers on the surface right to   detect moonquakes like earthquakes but on the moon  and we worked out the majority of the masses yeah   okay in the core of the moon but that's the same  way that the earth is set up as well the majority   of its mass is concentrated in the center in a  big iron core that's very very dense it's the fact   that the moon and the earth are actually made from  similar materials that we know that this giant   impact is what formed the moon because everything  then coalesced from the very same materials as   it was all thrown out in that big impact so  no the moon is not hollow look at the data   a natural body does not change its orbit overnight  yeah well i mean yeah he's right a natural body   does not change its orbit overnight unless  there's something catastrophic happen to it so   if you i mean if you did want to change the orbit  of the moon i mean not not you or me right but if   the universe didn't change the orbit of the moon  there's two ways that could possibly happen either   you could have an incredibly large impact or you  could have a very fast impact essentially both   those would give the moon enough energy at least  in the impact they would exchange enough energy to   change the moon's angle momentum changes energy in  order to change its orbit completely with a large   impact you're talking a body bigger than the moon  but all bodies bigger than the moon and the solar   system are already in orbit around either the sun  or jupiter or something like that right that's   they're never gonna also remove themselves from  those orbits in order to be able to impact with   the moon and then if you're thinking about well a  very fast impact that's also incredibly unlikely   because the things in the solar system will be  moving that fast to have such a huge amount of   energy when they impacted with the moon will have  already essentially left the solar system they   will have been completely unstable objects that  wouldn't have been able to get into a nice orbit   around the sun they would have been essentially  slingshotted out of the solar system to become   like rogue interstellar objects just you know  in the depths of space just completely isolated   you also could have an install object that would  enter the solar system the likes of umumua that   came through the solar system a couple of years  back but again like the odds of that actually   impacting with the moon and having enough velocity  to exchange enough energy to change the moon's   orbit to that degree are very very unlikely fun  fact though related to disaster movies this is the   way that we would change an asteroid's orbit if  there was one on a collision course with earth we   would essentially take something fairly heavy and  crash it into an asteroid at high speed in order   to exchange enough energy to change the asteroids  orbits they either you know took a little bit   longer to get to the earth in which case the earth  would be past where the impact was going to happen   or it would you know get to the earth a little  bit quicker in which case the earth would be a   little bit behind in its orbit again and it  would miss the earth and nasa is currently   testing that plan with the dark mission that's  set to arrive at an asteroid in september 2022 can someone tell me what the hell i'm looking  at the moon has entered an elliptical orbit   again moon is already on an elliptical orbit i  guess what they mean is that the ellipticity of   that orbit so sort of like how non-circular  how sort of elongated is is has gotten   more elongated i think is what they're probably  trying to say meaning it'll circle around this   three times before it reaches the roche limit at  17 000 kilometers okay so a couple of things um   they said it'll stick around them three times  before it hits the roach limit if the moon   for whatever reason was actually coming towards us  on its orbit it would take you know a lot longer   than three orbits for it to decay that amount  and actually reach the earth the roche limit   is a real thing in science the roche limit is  essentially if you've got two bodies so let's   say the earth and the moon and they get to a  certain distance away from each other which is   the roche limit that would be the point at which  the tidal forces on the smaller body the moon   would be so much stronger than the force of  gravity holding it together that the moon will   essentially get torn apart so what i mean by tidal  forces essentially is the difference in gravity   on one side of the moon to the other side of the  moon just because it's so much closer to the earth   that would be so much stronger over here than  this side that that is what it caused that sort of   sheer force to tear the moon apart and essentially  what would happen when it hit that roche limit   if it was coming in incredibly slowly obviously  like it would in reality if this was to happen   is that the moon would essentially become a  ring system and the earth would look more like   saturn than it you know it does in terms of  the earth and just the solid moon orbiting us   and the roche limit isn't like a set limit around  the earth that's the same for every single object   coming in it actually depends on the density  of both the earth and whatever other object   is on its way in as well that's why around saturn  you actually get moons orbiting within the rings   of saturn as well because you know they're still  held together by their own gravity whereas the   rings which are much less dense are torn apart by  the tidal forces much sooner than that what did he   actually say the did you say that the worst of it  was meaning it'll circle around this three times   before it reaches the roche limit at seventeen  thousand kilometers see he said seventeen   thousand kilometers that sounds a bit pretty  big for me we can actually work it out you know   we could there's an equation for the roche limit  let's let's work this out 12 seconds later okay   so the equation for the roche limit depends on  the radius of the moon the mass of the earth and   the mass of the moon because it really depends  on density but all those things that cancel out   so let's put in some numbers so the radius of  the moon is 1737.4 kilometers the mass of earth   is 5.972 times 10 to the 24 kilograms and the  mass of the moon is 7.342 times 10 to the 22   kilograms if you plug all those numbers in you  actually get 9484 kilometers which is around about   1.5 times the earth radius so 9484 not 17 000.  just saying probably should have done the maths so i think this must be the start of  sort of you know all of the chaos and   destruction that's going to happen because the  moon's uh getting ever closer so this will be   much higher tides than we're ever used to you know  coming further further in land tides caused by   tidal forces like i was talking about before right  the the pull of the moon makes it so that you have   a bulge in the earth's oceans pointing towards  the moon all the time right so that changes as   the moon orbits around us and changes its face  so when the moon is in its full moon phase it's   directly overhead at midnight that's when it's  pulling on the oceans and you get a high tide   at midnight but when it's in its half moon  phase it's either directly overhead at sunrise   if it's waning or sunset if it's waxing and so  therefore you only get the high tides at sunrise   and sunset and so when we look at this cliff  we've got a half moon and it's clearly not sunset   or sunrise it's clearly at moonrise this  whole picture just doesn't make sense   it's also worth pointing out here that like it  won't just be the oceans that'll experience tidal   forces as the moon gets ever closer and closer  to earth like you'll also get the actual very   crust of the earth affected by tidal forces in  the fact that you know that will also be pulled   slightly towards the moon as well then you'll  start to get more earthquakes more volcanic   eruptions as well as literally like the moon  uses the earth there's like a little squishy ball endeavor you have got a big ass gravity  wave coming your way you have to launch   now over did you say gravity wave so i think  what's going on here is that they said they were   going to launch when the moon was directly above  them because that would help them launch only on   two engines because they would be attracted more  to the moon's gravity and it would help them out   and so i think what's happening is that the  idea is like the moon is directly above them   and therefore the very oceans themselves are  being attracted to the moon up off the earth but   they're describing it as a gravity wave and that's  just complete nonsense right so a gravitational   wave is a wave that stretches and squashes space  itself it's sort of like the energy from a big   cataclysmic like explosion or merger something  incredibly incredibly heavy that then sends this   ripple out into space and what it does is cause  this change in distance between objects as this   wave passes through sort of in the way that we  would describe gravity under einstein's theory of   general relativity of being mass curves space and  time itself and if you remove that mass or make   it heavier or make it move in some way you will  send out these ripples out into space but i mean   the kind that you know for example ligo or virgo  detect these gravitational wave detectors that   detect the gravitational waves that come from  the merger of two black holes or a black hole   and a neutron star right they are waves that you  know are smaller than an atom itself right in   terms of the magnitude that they're detecting  so gravitational waves are a tiny tiny thing   as i said you would never ever describe this  as a gravity wave which doesn't make any sense like i feel like they're really hamming up  this whole like when the moon is like rising   or above you that's when like gravity  starts to get stronger and you start   to get pulled towards the moon but like if  the gravitational effect was that strong   like that would be happening like wherever the  moon was in the sky whether it was rising above   you setting or even like you know on the other  side of the planet you would be pulled with that   same force to the surface of the earth even when  the moon is on the other side of the planet right   especially if it was that strong as to pull  small children off the ground it starts to rise oh god that's a white dwarf i'm just sorry i'm still processing the fact  that there's a white dwarf inside the moon   oh i mean a white dwarf is what's gonna happen to  the sun when it runs out fuel and dies essentially   you know there's no hydrogen left to burn into  helium shed all of its outer layers into space to   become a red giant it'll leave behind this inner  helium core that would be incredibly incredibly   hot so it will be glowing and everything from  gamma rays and x-rays and all this harmful   radiation that you would not want to be that close  to and also you wouldn't even look at it you'd be   absolutely blinded by it as well you wouldn't be  like whoa a white dwarf you'd be like jesus christ   and white dwarfs are anywhere from like 10 of the  master sun up to 1.44 times the mass of so much   known as the chandrasekhar limit it's the maximum  mass you can actually have in a white dwarf   essentially if you add more material onto it at  that point it wouldn't be able to hold itself up   anymore and it would collapse under gravity down  into a neutron star and then a similar process   would happen to a neutron star and about three-ish  times the masses and it would become a black hole   so you've got something that's around about the  mass of the sun anyway and yeah okay white dwarfs   are incredibly dense they're around about you know  like like a percent or so of the sun's radius you   know in terms of that much mass but condensed into  that small of a space but i still think that'll be   small enough to fit inside the moon and the  thing is also like as as a white dwarf gets   heavier its radius gets smaller as well so to fit  it inside the moon it has to be an even heavier   white dwarf and i guess that would explain why  they were like oh our gravitational calculations   are all off because we haven't got the mass of  the moon right you always be able to measure   the mass of the moon the gravitational forces  the way we measure it it's through its effect   of gravity so we would always have been able to  get that mass and know that with the white dwarf   inside it but anyway i mean we could actually  work this out like we just did the rush limit   before because there is a relationship i think the  radius of a white dwarf is inversely proportional   to its mass to the power of a third i think  that's what what's up one minute 37 seconds later   okay yeah so i was right so the radius of a white  dog is inverse proportional to the mass to the   power of a third so okay let's just take a known  white dwarf so sirius the dog star for example is   a normal star with a white dwarf around it and so  because the two are obvious to each other we know   the masses quite well so let's use um sirius b as  our white dwarf to work out the proportionality to   so so looking this up so serious b once it  loads is how much of a mass is it so serious b   is 1.018 times the mass of sun in a radius of  0.084 times the radius of the sun okay so let's   figure this out okay so we want to know the  mass of a white dwarf that would fit inside   the moon's radius and i'm expecting it's not going  to so let's go with the entire moon radius rather   than what looked to be like a a small fraction of  it like here but that would mean that the radius   of the moon divided by the radius of serious b  would be equal to the mass of serious b divided by   the mass of our white dwarf inside of the moon  all to the power of a third and so if we rearrange   this with a mass of our white dwarf moon we get  that that'll be the radius of the moon divided by   the radius of series b cubed all times by the mass  of sirius b and so if you look at those numbers   we find that the mass of the white dwarf inside  the moon would have to be 38.77 times the mass of   the sun which is bigger than the chandrasekhar  limit right that maximum mass that is allowed   for a white dwarf so it's physically  impossible to have a white dwarf that would fit   inside the moon so i i guess roland emerick  just decided to ignore basic physics of   electron degeneracy pressure in the paly exclusion  principle for the sake of the plot here i knew it   the pile is the building blocks  of the universe no one look at me i might cry i love the fact that john  bradley is from manchester because   it makes him sound so much like brian  cox there it's ridiculous in the universe no no no no watch the hubble space telescope get destroyed  in so many sci-fi films like they did it in   gravity as well i don't want to keep watching  the whole space so let's go get destroyed please   the moon's enter the atmosphere over the north  alone yeah also like remember the rush limit   that they were talking about before how we  calculated it was like 9 000 kilometers away   from the center to the other was like 1.5 earth  radii the moon would break apart completely   and become rings would never actually enter  the earth's atmosphere remember that i mean   that really is the last of our problems we've  got some sort of weird like nano particle swarm   thing going on here anyway we're really in  like marvel territory now we saved the earth we should get started get started with what all right i think that's enough torch for one  i know i'm joking honestly if you love cheesy   disaster films you're gonna love this film  right in terms of the science there was a   little bit that they got right but that was far  outweighed by the amount of science they just   ignored for the sake of plot right this was the  sci-fi that was definitely firmly rooted in the   fiction side of things if there are any other tv  shows or films in the sci-fi genre that you want   me to react to as an astrophysicist let me know  down in the comments below or over on social media   i've also been thinking about like ranking recent  sci-fi films in terms of scientific accuracy so   let me know if that's something that you'd be  interested in seeing as well i'll be back next   week for my latest episode of night sky news where  we recap all the latest space news and what you   can see in the night sky in the next coming weeks  as well but until then everybody happy stargazing   before we get to the bloopers i just want to say  a big thank you to brilliant for sponsoring this   week's video brilliant is an interactive stem  learning website and app that helps you to learn   new concepts across topics in science maths and  computer science i've always found that i learn   best by doing and getting really stuck into a  topic and brilliant hands-on courses let you do   just that at your own pace in a really intuitive  and fun way now in the film moon 4 the alien   villain ended up being a corrupt artificial  intelligent nano swan but if you've always   been curious about machine learning and artificial  intelligence check out brilliant course on neural   networks with the real science on how we teach  machines to teach themselves neural networks   are a tool we also use in astrophysics to help  classify the reams of astronomical data we have   but they're applicable to so many problems so  it's a great knowledge base and skill set to have   so if that sounds like something you'd be  interested in head to brilliant.org forward slash   dr becky or you can click on the link in the video  description down below and sign up completely   for free plus the first 200 people that go to  that link will get 20 off an annual premium   subscription so thank you so much to brilliant for  sponsoring this video and now roll those bloopers thankfully our friends at spacex have a  propellant depot currently in orbit i love elon   right that's like the third reference to elon  musk or spacex that in this film am i like 50   minutes in like is it sponsored by spacex or  something or is this just to appease like all   of the elon musk fanboys that are watching  i got hungry and all bored i'm not sure ryan what's the plan save the moon save  earth in case he was right yeah save the   moon save earth do you think one of the  writers watched heroes during lockdown   save the cheerleader save the  world it's just too similar

Channel: Dr. Becky

Views: 249,154

Keywords: dr becky, doctor reacts, astrophysicist reacts, astrophysicist watches, science fiction, sci fi, syfy, astrophysics, physics, space, cosmos, female scientist, scientist, solar system, earth, accurate sci-fi, science, astronomer, armageddon, NASA, DART, impact, extinction level event, dinosaurs, deflection, Moon, moonfall, roland emerich, halle berry, patrick wilson, john bradley, samwell tarly, michael pena, charlie plummer, white dwarf, alien, artificial intelligence, machine learning

Id: aOWmVvto9EY

Length: 21min 46sec (1306 seconds)

Published: Thu Jun 16 2022