The NEW SCIENCE of Moon Formation

[@TheoriesofEverything]

Thanks Matt. It was an honor. Looking forward to speaking again.

[@jacobthompson6592]

I was surprised you mentioned the lunar seismometers. My grandfather helped build the radioisotope heater units for the seismometers that were installed during the Apollo 11 mission.

[@BaloneySansWits]

I worked at Marquardt, the company that made the R4d thrusters that one can see in fours on the sides of the Service and Lunar Excursion Modules

[@itzelpretzel]

Your grandfathers fingerprints (metaphorically, im sure it was all sterilized) were on the moon. Wow! Thats a beautiful legacy.

[@calebdunlap7566]

My fiancées great grandfather helped make the first US space boot

[@Skip6235]

I’m just trying to wrap my head around a column of molten rock several hundred thousand miles high raining down onto the surface of the planet in less than 24 hours. The sheer violence of such a thing is unimaginable.

[@krabkit]

noticeably less violent than the preceding impact

[@saturnexplorers]

Welcome to the universe

[@bottlekruiser]

smart people: violence is not a solution also smart people when asked how the moon came to be:

[@JoshWiniberg]

It's mind-blowing isn't it? And that's tame compared to many cosmological events.

[@tinygriffy]

I find that's peanuts compared to the next best Quasar out there..

[@subhanusaxena7199]

I hadn’t realised until I saw these videos that I should have played more attention to my fluid dynamics classes at college, as it seems central to many cosmological phenomena. Then I heard Leonard Susskind suggest that gravity is the hydrodynamics of entanglement, which blew my mind. Can we have a video on this please as I am really trying to get my head around what he meant. Thank you for these great videos

[@billbill6094]

This is by far the easiest to understand SpaceTime episode and most awesome topic yet. Imagine going back just shy of 54 years ago and telling someone not only are the moon and the Earth formed from the same two planets in the same orbit colliding, but in just _a single day_ there might have been _two_ moons, one even bigger. Absolutely mind blowing.

[@chriskennedy2846]

I agree, great topic. It goes to show there is plenty of fascinating science within our field of view that allows us to keep learning while being intrigued by the remaining mysteries yet to be solved. By contrast, we certainly don't need any more: black hole, worm hole, dark matter or dark energy videos for awhile. Great job. More science - please.

[@tehpw7574]

...and yet, there are idiots who publicly claim 'Teh World is flat'. :/ This theory, in how the moon was formed should be embraced at defacto-fact: Nothing else seems as accurate when it's visualized like it is in this video. Also, who is to say that electro-magnetism has much to say in the formation? Isn't that a after effect, not a cause (like gravity)? [Disclaimer, I'm a Gen-X Veteran Mechanic, not a scientist. WTF do I know about SCIENCE!?]

[@zes7215]

wrrg

[@Rydonittelo]

It's so sad that 30% of adults in the UK couldn't answer the question " What is bigger, the sun or the moon?" If you find this shocking as I did, ask people and you'll be astonished that some grown adults don't know the answer to this less than basic general knowledge question. Its mind blowing

[@Rydonittelo]

@Repent and believe in Jesus Christ The creature could not bear the wrong done to its creator, therefore the sun withdrew its rays so it would not behold the deeds of the wicked. Crystophusis ☀️🌤⛅🌥☁️🌫✝️

[@nellym46664]

It's crazy how such a random event possibly turned what may have remained a barren rock in space into the only known sanctuary for complex life in this universe. Pouring one out for Theia tonight.🙇‍♂

[@garmtpug]

I wouldn't assume we are the only place where complex life exists. There are many possibilities for life that don't necessarily have to be Earth-like. I'm a firm believer that life can arise in numerous conditions, as we have even seen on our planet. Various forms of life on Earth have been found in the most inhospitable places that we once assumed could not develop nor harbor any type of life forms. But life has been found in them! It does find a way! So, looking at that, it's easy to picture life forming in all kinds of planetary conditions throughout the Universe.

[@colterhikel9819]

Is life very robust and able to form in lots of adverse conditions, or is life fragile but able to adapt to harsh conditions after getting a foothold?

[@flintdavis2]

Or the process wasn’t “random “ but by design. Elementary my dear.

[@99names16]

Life is not robust. And it is not a force- it does not *have* to exist. I think we are far more lucky/special than we realize.

[@garmtpug]

@@99names16 Explain

[@firebladetenn6633]

It's always a good day when Spacetime uploads.

[@firebladetenn6633]

@sethevermanoff I didn't know I needed this today, but thanks.

[@crispymidget8531]

Indeed!

[@zes7215]

wrrg

[@harbirsingh7266]

18:00 "Some animals do have hands large enough to swim in a gas. They're called birds." This just blew my mind. How did I never think of that? Haha.

[@joansparky4439]

here is another one for you - we are living at the bottom of a gas ocean.

[@bazpearce9993]

@@joansparky4439 We are Crab people lol.

[@DriantX]

@@joansparky4439 And a gas ocean is living at the bottom of me. sorry

[@markzambelli]

And Penguins 'fly' through water

[@twistedtachyon5877]

No respect for bats smh

[@realzachfluke1]

This is my favorite episode to date. Beautifully done, Space Time team.

[@osmosisjones4912]

Here is the full clip : kzbin.info/www/bejne/f2i2aGeJra6dpJY

[@filonin2]

@@osmosisjones4912 So you're a bot now?

[@memofromessex]

Yeah, I understood 99% of that!

[@bazpearce9993]

Mine too.

[@TheScrubExpress]

Wild to think about such a big thing happening in...less than two days. In a universe where things usually happen over many thousands or millions of years, that's lightning quick.

[@edwardlazell3157]

There's an XKCD cartoon about how weird it is when something in astronomy occurs on a human scale, rather than being enormous/tiny or happening instantaneously/over billennia.

[@theexchipmunk]

@@edwardlazell3157 Do you have a link?

[@pizzainc.1465]

Billennia is a cool word, but it’s actually gigannum (or giga year). The real structure of million is milli- -on, not Mil- -lion. This is a common misconception, and it is ok in English (it’s already deformed), but not in Latin. Latin already has a structure, so you can’t make up words based on how you think they are assembled. The real word is: gig{a}- -{a}nn- -[suffix] Or gigannum

[@pizzainc.1465]

-MWAHAHAHAHHAHAAHAHA- **silence**

[@thezipcreator]

@@theexchipmunk it's xkcd #2707

[@ericstromquist9458]

I’ve always loved your show (having been a physics major long ago) but this episode is among the best. I’ve certainly heard of Theia and the collision hypothesis but your episode 1) systematically goes through the evidence to select the best scenario, and before watching I wasn’t aware that accretion at different radii from the sun had distinct isotopic signatures; and 2) highlights new research, showing the reference so you can go and download the paper to read. Absolutely excellent!

[@flaviusclaudius7510]

I love these n-body particle simulations. Best part of undergrad astro was getting to watch so many of them!

[@CaptainCuttlefish74]

I sent this to my grandmother I expect some of the more technical stuff will go over her head but she's expressed interest in stuff like this, and I figure this is one of the few Space Time videos she would have a good chance of understanding

[@Lupita311]

She won't understand it because she is a woman, or simply because she is a grandma, that the topic is too technical or is it that her small little brain can't understand the science but she'll be amused by the colorful pictures. Maybe it is me who doesn't get the joke in my tiny little brain.

[@CaptainCuttlefish74]

@@Lupita311 woah What is wrong with ypu

[@matteosposato9448]

@@Lupita311 wait wut?

[@The1oldfox]

@@Lupita311 easy girl

[@william41017]

So, what did your grandma say?

[@Kelly_Z]

Thank you so much for the captions in your videos! Yall cover such complicated topics that it's very useful to me to be able to listen and read what yall are saying so that I can absorb the information and keep following along, although usually by the skin of my teeth. Anyhow, thank you again, yall are awesome! I love learning about this kind of stuff

[@MofoMan2000]

One correction: Neptune's moon is Triton. Titan is one of Saturn's moons.

[@the_dark_one6052]

Beat me to it

[@LuisAldamiz]

It was not probably an actual error but rather his Australian accent.

[@donlevoneshabanov4437]

The subtitles say Triton but I don't hear the "r"

[@LuisAldamiz]

@@donlevoneshabanov4437 - It's Australian accent but BBC accent also lacks rhotics, it's a common (and confusing) feature in English language.

[@orsonzedd]

Same thing

[@dankuchar6821]

Thank you Matt and PBS FaceTime for all your hard work! It is appreciated. I wish this had been available when I was teaching physics.

[@nagualdesign]

PBS FaceTime! 🤭

[@spectator5709]

Could we take a moment and appreciate whoever makes the graphics for SpaceTime? You're a hero! 🙂 Thanks for all the good stuff! 💫📈🚀

[@ryans-7]

That clip of Theia getting larger and larger just before impact was terrifying. Kudos to the cgi folks for sure.

[@jus_sanguinis]

+1

[@dv2915]

The clumsy animation that appears at 11:06 was actually made by me, like, 20 years ago. I can't even remember what software (or hardware) I used to create it. Perhaps, a ZX Spectrum?

[@freddan6fly]

@@dv2915 For being 20 years back you did an excellent job with the limited resources of the time.

[@vblaas246]

Andrew Kornhaber is your principal hero.

[@Ricalloo]

I'd love to see a collision simulation in real time, that is at the speed it actually happened. I assume the ones we saw in this video were sped up by a lot.

[@N.M.E.]

yeah. You can assume the rotation speed of the earth after the collision should be close to 24h

[@genkibob]

If you have 2 or 3 days to sit and watch the video, sure.

[@doctorbeet3339]

@@N.M.E. Unfortunately not. With the presence of a water ocean, the tidal bulges which are displaced in the direction of Earth's rotation transfer angular momentum from the Earth to moon, increasing the diameter of it's orbit and slowing the Earth down in the process. See Tidal Acceleration on Wiki: "This geological record is consistent with these conditions 620 million years ago: the day was 21.9±0.4 hours"

[@Shadowkey392]

@@N.M.E. it would actually have been much faster.

[@N.M.E.]

@@doctorbeet3339 Interesting! Thanks for the correction. I guessed it would've been somewhat faster, but didn't know to what extent. Still somewhat in the ballpark though.

[@rlosable]

I've been wondering for a while: does the Thea event explain also why Earth has such a strong magnetic field (due to the larger iron core and additional energy/momentum imparted) and at least be part of the reason why Earth has such active plate tectonics? It would also mean a single explanation for many of the differences between Earth and its neighbors. If so, this single event would have played a huge role in creating the conditions for life to develop. And dialing "rare earth" up to 11 as a solution to the Fermi Paradox.

[@shoego]

Earth would probably be a dry dead rock without this impact. Possibly, most of our mantle would have cooled by now.

[@gobblinal]

I still posit that there's enough out there that we are not alone, but maybe we're reaching the limit of only one intelligent species per galaxy (or two if we're REALLY lucky, or more if galaxies collide?), so it just _feels_ really lonely.

[@matt2027]

Are Thea events actually rare? Do we really know enough about solar system formation to say for sure one way or the other?

[@gobblinal]

@@matt2027 At this moment, we do not. But, maybe with some of this hi-res modelling we might be able to get some idea of what it would take to happen. But seeing it "for real"? I have _no_ idea when that'll ever happen.

[@dankuchar6821]

Very possibly, yes!

[@bertoray5497]

Happy New Year Matt, and to all the fabulous crew at PBS Space Time. This content is actually consistent with what I envisioned the Internet tool would herald, lo, many moons ago.

[@scottslotterbeck3796]

Ha ha. Bad pun

[@xovvo3950]

18:06 Bats. You're thinking of bats. Bat wings are formed from membranous extensions from palm to fingertip between digits two through five. Bird hands are actually very small and have completely fused together into a structure called the carpometaparpus, tipped by greatly reduced digits II and III (digit I bearing the alula, anterior to the rest of the carpometacarpus). Birds just have very long feathers to form their flight surface!

[@anarchyantz1564]

Additionally Pterosaurs as well.

[@XKloosyvv]

Birds still "swim" though the air around us. Yes, bats do as well but Matt didn't say it was only birds. There's plenty of organisms capable of flight on earth.

[@Ezullof]

@@XKloosyvv Birds don't swim with their *hands* though, they use modified arms (with feathers). Which is the point that Xovvo is making. Similarly, flying insects also swim in the air, but not with hands.

[@XKloosyvv]

@@Ezullof quoting them.... "Bird hands are actually very small and have completely fused..." Birds have hands, but evolution has changed them dramatically. They still "swim" in the same concept as bats and insects.

[@JillianJolley]

Yes!!! I f***ing love people, like you @xovvo3950

[@NoMusiciansInMusicAnymore]

I absolutely love the sense of humour in this series, it more than makes up for my inability to understand half of the subject matter

[@ihsahnakerfeldt9280]

And his delivery is completely dry lol

[@wrylycoyote6940]

I finally have caught up on binge watching 7 years worth of PBS Spacetime, and can finally comment on a video. My brain feels heavy like a waterlogged sack of dirty laundry. I feel like I made it to the finish line even though the line keeps moving forward every 2 weeks (making it harder to catch-up). Ok, I admit I skipped some of the videos on aliens, because it's never aliens.

[@octavianova1300]

The possibility that the Gaia-Theia impact resulted in second, larger moon that then crashed back down into the earth definitely gets me thinking about the hypothesis that the LLSVPs are remnants of the giant impact. IDK how indicated such a connection is by this result, but on the surface at least it's an intriguing idea.

[@nagualdesign]

Don't confuse the Gaia hypothesis with the giant-impact hypothesis. Theia impacted the _proto-Earth._ Gaia developed millions of years later after considerable cooling.

[@ArawnOfAnnwn]

LLSVP?...

[@Neloish]

That is exactly what I was thinking, it could explain the gravitational anomalies.

[@Neloish]

@@ArawnOfAnnwn Large low-shear-velocity provinces

[@passintogracegoldenyearnin6310]

Jupiter's Red Spot could be an impact site. Apparently some hundreds of years ago it wasn't there, and it is slowly getting smaller. The mix of elements dredged up from below are also different from the typical outer layers. It could be the case that our planets have not cleared their orbital paths as much as we'd hoped.

[@panagiotisantonakas9603]

Mat I am hydrodynamic engineer/ astronomy lover and your video just made me wonder if we can make not only a Sim but a real hydro experiment.

[@ChemEDan]

Surface tension would probably be a big problem for experiments on a reasonable scale, same with trying to simulate self-gravitation. Maybe some sort of hybrid experiment could be developed e.g. many parallel hydro experiments used to simulate parts of the whole. Just need a mass-producible experimental apparatus that can generate the necessary Coriolis forces, and gravity could be approximated by earth's natural gravity and corrected for by scaling the resolution. So test volumes closer to proto earth would be physically smaller and visa versa, even though the apparatuses are all the same

[@T3sl4]

​@@ChemEDan It's interesting really, that gravity serves a very similar purpose as surface tension; the problem is, it's a much more diffuse force, whereas surface tension is, well, at the surface. Specifically, the internal pressure within a gravitationally bound body is proportional to depth, whereas with surface tension, the pressure is approximately equal, dropping suddenly to zero in the surface layer (which is probably a Debye scattering depth or something like that). So it's no accident that the simulation shows droplets, but the way they flow is very different.

[@boredgrass]

A happy new year, and fair winds and following seas for your channel!

[@ChefSalad]

There is an intermediate between solids and liquids, for some materials, specifically binary alloys. Sort of. For binary alloys, there are two temperatures involved in melting: the liquidus point, the temperature above which the material is fully molten, and the solidus point, the temperature below which the material is completely solid. For eutectic binary alloys, those temperatures are the same, but for non-eutectic alloys, the temperatures are different. Eutectic means that the melting point is as low as is goes and occurs when the solidus and liquidus temperatures are equal. (When you mix two materials together, the mixture will have a lower melting point than either component by themselves. At a certain ratio (the eutectic ratio), you get a minimum melting point.) The state between the solidus and liquidus temperatures (sometimes called the solidus phase) is a mixture of solid crystals suspended in liquid metal. It behaves kind of like a gel. It'll flow a bit, but also retain its basic shape. This is very important in soldering since, when using non-eutectic solders, moving the joint during the solidus phase will result in bad solder joints, since parts the workpiece can move without the solder flowing back in behind it. The effect is similar to a dry solder joint, but not quite the same and a bit harder to detect. This is why (near) eutectic solders are often preferred during hand-soldering. Eutectic solders go straight from liquid to solid as they cool, without any time between to harden.

[@AnderGdeT]

Amorphous polymers would also fit that criteria? They are solids with fixed forms, but can flow at higher temperatures while maintaing solid properties, don't really have a melting point but a "Glass Transition" point...

[@ChefSalad]

@@AnderGdeT not really the same thing. Similar though. With amorphous solids, the transition from liquid to solid is at a specific temperature, it's just that close to but below that temperature, the amorphous thing will be very, very flexible. This seems like flowing, but it's not really. With glass, you can get it really bendy, but to get two pieces to join, you need to get the joint just a bit hotter for the pieces to melt together. Even though they're soft, they won't flow together unless they're actually liquid at the joint. Or at least that's my understanding.

[@MrClickity]

TIL that Solidus Snake from Metal Gear Solid 2 got his name from an actual term and not just a word that Kojima made up because he thought it sounded cool.

[@rosemarymuthoni5853]

@@AnderGdeT how about non-Newtonian fluids?

[@dracoargentum9783]

As a quick follow-up question for soldering [new solderer here], if you NEED to move a non-eutectic solder, I take it you should heat the bend back up before bending?

[@brandtreppond2167]

That protoplanet soaring towards us was probably one of the scariest images I'll ever see

[@passintogracegoldenyearnin6310]

It's a great time for you to watch Moonfall then.

[@N.M.E.]

I shall suggest the Lars von Trier movie "Melancholia" (2011) with Kirsten Dunst then. (Although the visuals of the Planet are surely not the main thing this movie offers)

[@theexchipmunk]

@@N.M.E. Seconded. Good movie that one.

[@Rando_Shyte]

@@passintogracegoldenyearnin6310 You mean that steaming pile of garbage? No thanks.

[@nachoijp]

I never knew that two proto planets could form in the same orbit... I always thought that we were weirdly lucky to have a planet just hit earth, but this makes it a lot more credible

[@seb10wijngek]

Best episode so far, in my opinion. Very cool simulations, clear and concise info. Lots of fun!

[@brenorocha6687]

"[...] so, whatever." Seriously, seeing how you explain complex scientific concepts while using informal jargon and expressions is so pleasant. Specially because it doesn't feel forced or unnatural in any way.

[@franck3279]

He works as an university teacher to practice for those videos.

[@Flugmorph]

i liked that hidden schroedingers cat joke at the end there

[@MCsCreations]

Fascinating indeed. Moon's fast delivery!

[@davidthane9002]

About the metallic Hydrogen question: Metallic properties does not specifically mean "free moving electrons". The electrons in solids made up of covalent bonds (like diamond) are free moving as well. (some scientist argue that covalent and metal bonds in solids aren't really different anyway) The real catch is the electron's ability to have a change in "speed" (or "momentum") which leads to electrical conductivity. The main requirement are empty electronic energy states at the Fermi level. (i.e. the 'band' isn't completely filled and 'crosses' the Fermi level) . Which in turn leads to the simple picture of the "Valence-band" and "Conductorband" touching. (in contrast to the semi-conductor/isolator solids which show a band-gap. Incidentally solid hydrogen in its ground state has one band, (made from the 1s-electron orbitals) which is filled about 50%. So the Fermi-level and the half filled band directly intersect and the electrons have quire a few energy states available for change in impulse. And so it has the typical metallic properties of high electrical/thermal conductivity, metallic sheen (from absorbing and emitting light through the electrons) etc.

[@gobblinal]

As someone else points out, this could potentially add a few more parameters to the Drake equation. Is this what's needed in order to make a large enough magnetic field to protect a planet enough that life even has a chance to form, let alone multi-cellular and eventually "intelligence"? We've proven that our solar system is not unusual in that most stars appear to have planets, so that part of the equation is now a lot closer to 1 that might've previously been thought. But there's also the question of if inner rocky planets REQUIRE outer gas giants to keep space "clear"? And now we need multiple planets in the SAME orbit to collide and make a strong enough magnetic field to further protect the planet from the sun? Not to mention a moon big enough to make tides. So far most solar systems have only had gas giants or LARGE rocky planets so it's hard to determine where the little inner rocky planets are, so it's a while yet before we'll be able to determine if there's any systems with 1-orbit-2-planet systems. Is that dependent on age? Does it only happen in the first 0.1 billion years? So finding such an example is going to be very tricky. However, if there's one thing I know about the universe, nothing is unique. If it's happened once, it most definitely can happen again, so there is still hope for an Earth-2 out there, somewhere, potentially a LOT further away than originally supposed.

[@escapevelocity8092]

Have you considered that earth may have been in another star system originally? There's quite a bit of information to support this idea

[@gobblinal]

@@escapevelocity8092 Well, it WAS another star system originally. That's why we've got carbon and iron and all the other must-have atoms. We are second (at least?) generation star that went KABLOOEY and then when it's nebula cooled, we got our star and system. But if you are trying to suggest that the earth was a rogue planet that crashed into Theia and then stayed in orbit, that's an interesting suggestion. I'd like to see the models on that.

[@escapevelocity8092]

@gobblinal OK nice bit of sense you're talking, I'm suggesting nothing more ridiculous than this. Now, rogue planet idea, getting close indeed. I want you to imagine a petri dish with a chemical in it, we then introduce another reactive agent while looking through the microscope into the dish. To our eye, we see molecules smashing against molecules, creating new formations, charges being exchanged, looks like organised chaos no doubt, eventually a new order results. We are even aware of a world even smaller which isn't visible but we can measure its effects, atoms kicking out protons and exchanging electrons, all obeying physics which produces orbits out of attraction and repulsion. Is it such a stretch to conceive that what appears to us as a gigantic, chaotic clattering of heavenly bodies, actually lives within the intent of another form of consciousness, and thus planets are terra formed for purposes beyond our comprehension. Why should we sit at the top of the dominance hierarchy? If the universe is infinite then why would the energy apex end? Just because a species can't comprehend the next rung up, most prey die not knowing what predated on them...

[@escapevelocity8092]

@gobblinal we needn't prostrate ourselves at the feet of a deity to appreciate that maybe we are not the only 'self aware' consciousness in existence. Aren't we ourselves trying to 'seed' other planets right now, because we may destroy our own in the future. Its not hard to imagine that we are the way the universe can observe itself, and the physical expression of reality is a challenge. A separation into duality, separation always brings pain, and pain always brings growth.

[@milferdjones2573]

@@gobblinal Theia and Earth had to share the same building materials improbable for anything that originated outside of the Earth orbit.

[@whuzzzup]

It would be kinda neat to actually link your sources. Then I could actually use them for teaching more easily.

[@devinfaux6987]

I like to think that the immediate aftermath of an impact like this is the only sort of situation you would find and environment similar to the asteroid fields depicted in popular sci-fi like Star Wars. It wouldn't last for that long, but for just a little while you could lead TIE Fighters on a merry chase through it.

[@mutercim]

Not necessarily. You could lead your pursuers through something like Saturn's rings. Would be exactly the same, I imagine, as long as you stay in the thickest parts.

[@N.M.E.]

@@mutercim nah, as far as i know, the majority of particles in Saturns rings are far far smaller than your "usual asteroids"! More akin to dust and pebbles (largest particles are a few meters across)... aint no fun in flying through that. Also the denser rings are only about 5 - 100 m (max.) thick.

[@Yewbzee]

Damn, at last, I've managed to understand a full video on PBS. I'm off to celebrate with a bottle of wine or two.

[@8beef4u]

There's also one proposed theory that explains the "smoothness" of the Earth-facing side of the moon. It proports that a large satellite the size of Ceres collided with the moon, causing debris to rain down on the opposite side, explaining the smoothness of one side of the moon and also the disparity in crust thickness between the two sides. The new impact scenario could also help explain differences in the isotopes of potassium, phosphorus and rare-earth elements like tungsten-182 measured on the surfaces of Earth and the moon.

[@tracyh5751]

17:57 jokes like these really deserve to be made into youtube shorts. That kind of humor would really stand out in the sea of youtube shorts and could draw more people to your channel who might not have considered it otherwise.

[@ChocoboProduction]

So, what I gathered from the explanation on whether or not it's possible to swim in superfluids: You'd need a creature that is basically gigantic and almost completely wings/fins. Soooooo... giant manta rays? Sounds cool to me :D

[@passintogracegoldenyearnin6310]

DnD ahead of science with its space mantas and space turtles swimming through the ether.

[@TheIrf33]

Glad to see you uploading again. this channel is awesome

[@PeterGaunt]

More of this kind of stuff from time to time Matt!

[@RajeshYadav-to5zq]

Wassup homie

[@alexandrel4569]

Really love this episode that isn't as complicated as most of the time but EXTREMELY interesting

[@Eris123451]

I've just finished reading Lee Smolin's book The Trouble with Physics which pretty much explains the real extent to which physics is currently at something of an impasse; no Supersymmetry, no SU5, no real clue about the nature Dark Energy or Dark Matter and of course the by now well known problems with String Theory but especially that it's not a complete or testable. It's an interesting and not over demanding book one which I'd highly recommend.

[@zacharywong483]

Absolutely lovely video! Logical, understandable explanations paired with intriguing discussion! Great job, Space Time team!

[@HebaruSan]

7:23 - Triton, not Titan, right?

[@wingracer1614]

Correct

[@ashleydaniel1446]

Happy new year Dr o'dowd , can't wait for the videos you bring us

[@Nobody-df4is]

The Moon is so weird, it played an integral part in the evolution of life.

[@aalhard]

Hope your holiday was great. Thanks for coming back 😗

[@thomascaldwell184]

Damn I love PBS Space Time. Pretty much everything about it. Especially today the wry humor. (And/or humour for most of the rest of the English speaking world.)

[@bobmin1782]

That animation of the moon crashing into earth around 8:54 is spectacular. Thank you.

[@camicus-3249]

You're telling me Rome wasn't built in a day, but the whole entire Moon was?

[@scottdahneke1031]

Moon pun: "I'm Buzz Aldrin, second man on the moon. Neil before me."

[@baumgartnerwm]

After reading Azimov's Extraterrestial Civilizations on the Drake equation I wondered if the Earth's oversized Iron core was due to us steeling Theia's core. This is the first time I've seen that confirmed. The earth's powerful magnetic field is stronger because of the iron we stole from Theia. So many subtleties of that collision were essential to our existence.

[@Nobody-df4is]

It was donated. Not stolen.

[@ericeaton2386]

“Confirmed” is a little strong, but it certainly seems plausible!

[@zuthalsoraniz6764]

And having a large moon is probably also at least very helpful for developing complex life/technological civilisation. Both because it stabilises the axial tilt and thus the climate (Earth's tilt varies only by about two degrees on a 41000-year cycle, versus about 20 degrees over a 53000-Mars-year cycle on Mars), and because the tidal forms formed by the relatively strong tides such a large moon causes provide a good jumping-off point for life to make the transition from living in the oceans to living on land. Plus of course, a large moon will also deflect or intercept a lot of potential asteroid/comet impacts, which is again helpful for climate stability.

[@YouTubist666]

Maybe we should give a nod to Hartmann and Davis, the two scientists who suffered the ridicule of their short sighted, closed minded colleagues when they first put forth their theory, but who persevered with the best theory of how the moon formed.

[@scottgray4623]

Great video, like always! I'm just surprised that you didn't mention that the moon being tidally locked to the earth was a big part of the Theia hypothesis.

[@luudest]

Einstein just shows up everywhere.

[@HaloForgeUltra]

Ignore the bot. The video its sharing is just some stupid animal video. Here, I have an actual video of the moons formation conveniently ready, animated and 15 minutes long, with explanations. Or is it just a rickroll? You decide: kzbin.info/www/bejne/bITVpI2MmbpqapI

[@LordPhobos6502]

That was amazing, especially the ground view of Theia coming for a visit... Now we just need to convince Dr Who to take a trip back and get some footage... from a safe distance, of course.

[@peterkelley6344]

Should not be that hard as they are both from the BBC

[@thiagocastrodias2]

Wow, that was probably the best video about Moon Formation I've ever seen. Thank you!

[@franck3279]

Lets use a scale from moonfall to pbs spacetime in the future

[@captainsarahbee]

Great video to kick off the new year!

[@anarchyantz1564]

Happy New Orbital Revolution around our nearest celestial object! Fantastic visuals today, your team really hit the moon out of the orbit.

[@DrVictorVasconcelos]

It's not every day that we make a list of hypotheses for a natural phenomenon, and the winner hypothesis is the coolest one. Props to those involved.

[@WoAzMM]

A new PBS Space Time episode? The time must be tooth hurty (sorry Matt, hope it doesn't hurt and gets fixed soon!)

[@hugomzo]

I thought I was the only one to notice! I've seen so many episodes, it threw me off immediately

[@wk8219]

@@hugomzo It seemed to have happen just before the episode before this. Last episode only one person mentioned it but 8+ on this one. I dont see any reason mentioned. I hope he's ok.

[@Hermes_Agoraeus]

@@wk8219 My similar question from the last video didn't get upvoted, so I deleted it thinking I was mistaken--but here we are!

[@zwerko]

The response to the last question on cats being simultaneously solid and liquid is-chef's kiss!

[@NewMessage]

I dunno if I could gain that much weight in 24 hours.. but I'm willing to give it a go next Thanksgiving!

[@BattleBunny1979]

you might end up having your own moon if you do it well enough!

[@lexinwonderland5741]

Okay, the segue to the ad was hilarious, I'm actually impressed.

[@theGoogol]

"Reality is fake", said the photon.

[@Bassotronics]

‘Reality doesn’t exist” says the photon.

[@osmosisjones4912]

Color exist even if our brains don't pick them up

[@AceSpadeThePikachu]

Small correction: Neptune's large captured moon (probably from the Kuiper Belt.) is called "Triton," not "Titan." Titan is the largest moon of Saturn.

[@MichaelKire]

Never clicked a video so fast

[@theconstructortheorist3554]

same;-)

[@jakeuren8688]

We missed you! Hope you all had a great new year

[@Boomer08888]

Matt, did you chip a tooth? Hope you're alright!

[@AliAli-tj9pd]

Well explained and illustrated. Thanks for you & your efforts

[@1209-k3m]

Thanks for watching Tell Aɴᴅʀᴇɪ Jɪᴋʜ, you were referred by me he has something new to discuss with you easily get in touch with him 👆✍️

[@ramuk1933]

Wait... it couldn't have happened over months because the moon, and therefore months, didn't exist yet!

[@JillianJolley]

Tehehe

[@jimmyzhao2673]

People once walking on the Moon is sounding more and more like 'old man talk' you hear in a café.

[@JillianJolley]

Truths are uncovered only by removing layers of substance first

[@a51mj12]

Is his tooth chipped? If so, is it easily fixable...

[@tacobell2009]

6:25 Sometimes you just gotta eat out that moon.

[@markmuir7338]

My experimental observations on cat solid/liquid simultaneity: if I pick up my cat and hold him close to my chest, over the course of about 20-40s, my body heat will raise his temperature above the critical point and he begins to flow through my arms and land on the floor, where he rapidly regains his cool.

[@puncheex2]

I have been lead to believe that Theia was indeed accreting at L4 or L5. The kidney-bean-shaped orbit of an L4 or L5 object increases as the ratio of the masses of the smaller to the larger increases, which is exactly what the two accreting bodies would do. Eventually the orbit would become large enough that the Earth's gravity would overcome the L-point's in an excursion towards the Earth, leading to the collision.

[@stewartmartin7376]

It is quite amazing all these things that had to go right in order to get us

[@thewhitefang007]

The YET at 10:36 made me scream LFG as if this were a sporting event. I love science!

[@ravenwolf7128]

best episode ever--clear, to the point and what an awesome topic.

[@kin0cho]

Love this cross-genre episode, keep up the fantastic work 👏

[@adamthompson4072]

I remember seeing something a couple years ago that suggested we had 2 moons for a while after the formed but before they had cooled. It apparently explained why the the far side of the moon looks so different from the close side by saying the 2 moons had a very slow speed collision because one was chasing the other

[@WeBeGood06]

17:40 Unfortunately you are wrong, lacking a basic understanding behind the Physics of Thrust. Thrust is produced by a swimmer with his hands, it is Momentum Exchange, MV. If the density of the supercritical swimming pool is like water, the swimmer has lots of mass to push against. Each stroke grabbing a hand full of water and imparting velocity on it. Mass * Velocity. The lack of viscosity would reduce the swimmers drag, so he might swim fast with fewer strokes.

[@Dutch166462]

Bravo! Best spacetime video yet!

[@NiffirgkcaJ]

10:37 "Yet." This gave me goosebumps.

[@xiphosura413]

Have you guys heard of the synestia hypothesis? Would be cool to get a video on that, if there isn't already!

[@helloyes2288]

hah as you said "we can't smash worlds together to our heart's content" I mentally added "yet" - then you said it. Made me feel a personal connection separated as we are across... spacetime.

[@nightmareTomek]

I feel like the language of SpaceTime to communicate us all the exciting stuff changed a bit to better convey how certain scientists are with their findings and their theses, and I like it. It gives us a better understanding how much work has been done and how much there's still to explore. I know I'm quite nitpicky, but it's important to me and I like the more precise approach. Anyway, another very interesting video!

[@KCFreitag]

This series very much my flavor. The final explanation of critical cat temperature will warm me for years to come.

[@kbjerke]

LOVE the cat reference at the end. Great video, thank you!

[@hp127]

Wonderful explanations of procedures and the 'how do we know. Thanks

[@mrrolandlawrence]

i love the q&a section at the end. :)

[@giovannipescarmona3712]

This is the best content on the web. THANK YOU!

[@jimmystecher5214]

Every time I watch these episodes, it blows my mind. Wow.

[@sirgog]

0:51 - ouch. Pluto will always be a planet in my heart.

[@CannedMan]

Just for your information, Mr PBS Space Time: The plural of _mare_ is _maria_ (both of which are stressed out the first syllable (all the vowels are short)).

[@charlesjmouse]

Very interesting, and very well presented. Thank you. I wonder... if it might be found with sufficient simulation detail that there's an emergent property of such collisions that makes the formation of a moon over a wider range of starting conditions more likely? If there's one thing I dislike about the giant impact hypothesis it's the seeming improbability that might be improved if moons are 'built in'. Of course one could turn this question on it's head. What if this finding is no more than an emergent property of this level of detail in the simulation andit disappears when the resolution is cranked further? More simulations, more computing power!

[@garethdean6382]

Well we must also factor in that such impacts must have occurred throughout planetary formation, yet rocky planets do not all have moons. Which suggests that the formation of a moon cannot be guaranteed. Certainly with an L4/5 point object they become much more likely, since such an object will encounter a planet with the right low relative speed and shallow angle, while random impacts are much less likely to give rise to moons.

[@nicolaiveliki1409]

regarding your advertisement for learning languages: Schrödinger and Einstein both were quite proficient at speaking English, though at least for Einstein, a heavy Germanesque (he was Swiss) accent is documented. Einstein taught in the USA, Schrödinger in Ireland (yes, during and after WWII, which was much later than 1920, but English was well established as a language for Trade and Science)