True Color of The Moon, Capturing Sunspots, Constellation of Almost Hubbles | Q&A 253

Can we harvest energy from the Moon's temperature difference? Why don't we just launch multiple telescopes like Hubble? Why is the Moon grey? Why are sunspots black? Answering all these questions and more in this week's Q&A show!
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00:00 Start
00:27 [Andoria] Can we extract energy from Moon's temperature difference?
05:19 [Vulcan] Constellation of "Almost Hubbles"
08:40 [Risa] Why do sunspots look black?
10:26 [Aeturen] Will we still be 'alone' if we find life on Europa?
14:52 [Vendikar] Why do black holes shrink?
20:22 [Remus] What lifeforms can survive on Jovian moons?
25:01 [Janus] Why is the Moon grey?
26:44 [Cait] Why not build a very big spacecraft in orbit?
31:06 [Betazed] Will humans ever fly on solar sails?
33:09 [Cheleb] What does a lunar eclipse look like on the Moon?
35:03 [Nimbus] Will we ever see a Venus rover?
37:56 [Belos] Could Enceladus have life during the Sun's red giant phase?
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[@Anthrofuturism]

Wow I'm shocked and extremely honored to have been mentioned at the end, thank you so much!

[@TheSangson]

All that's missing is a link in the description. @Fraser Cain, maybe pin the comment or something, so we can use it to hop over^^

[@realzachfluke1]

VENDIKAR hands down. Whether that question was prepared for in advance or whether Fraser answered it on the spot is completely immaterial, because to my great satisfaction his answer _lands for me._ Talking about Unruh radiation had concepts clicking in my head that I never managed to take away from watching and rewatching the series of PBS Space Time videos that include the Unruh effect in the build up to grasp concepts like Hawking radiation, the black hole information paradox, and ultimately the holographic principle, which I had done multiple times in my life because I've loved Space Time since the start and enjoy watching it, but also because it always stuck out in my head that the Unruh effect and Unruh radiation were such memorable names to me, and yet I never found myself grasping and holding onto the explanations for them. So to put it succinctly my understanding of many ideas covered in PBS Space Time simply suffered because I was missing some foundational, building block concepts that ended up being way more vital than I imagined. I've heard the explanations for Hawking radiation many times before, and for several years I've been able to tell you that a black hole's size is directly proportional to the theoretical Hawking radiation it emits, with the smaller sizes evaporating quicker and appearing "hotter" than larger black holes. But when I heard that answer, it made me stop in my tracks wondering if what I'd heard was right, specifically because I understood it and hadn't in the past. I went back to the PBS videos on horizon radiation and Unruh radiation, and to my enormous gratitude, satisfaction and excitement, Fraser's answer led me to going back and successfully learning so many *wonderful concepts* that didn't stick before. Thank you to both the questioner and Fraser for that answer. I waited til the end of the show too so I'm very sure in my vote for this one.

[@frasercain]

That's fantastic, I'm really glad it helped you understand it.

[@nirbhay_raghav]

I just absolutely love listening to your Q&A. Seeing you answer questions looking straight into the camera it feels like you are talking to me! I know everybody does that but there is definitely something about your angle or something which makes it look so peaceful. The pace of your voice puts me to sleep often and I come back to complete the video!!

[@frasercain]

Hah, I use other KZbin videos to put me to sleep. I think that's my greatest service. :-)

[@KrystianChynal]

I love space news, and for me, this was probably the most informative (or at least eye opening) episode you've ever done. From the correction of the common misconception as to how black holes shrink, to the true color of the moon, to what a lunar eclipse on the moon would like you. Loved it!

[@user-li7ec3fg6h]

Very well said. It was also a particularly successful episode from my point of view.

[@BbjmL1]

Such a great presentation with awesome information. At a time when science and space videos are popular, it’s great to find a channel dedicated to current and accurate information without the hype and untruthful headlines/ clickbait crap that is now common among science channels. Thank you!!

[@bradley-eblesisor]

Vendikar. Your explanation is very illuminating. I was able to build a picture in my head thus I understand much more than I did previously.

[@realzachfluke1]

RIGHT?!? So much came together for me because of it. Great question, great answer.

[@Josh-ify]

Cheleb was a great question and answer!

[@aureaphilos]

ANDORIA: I've not heard this presented in any other programs, but it makes total sense. It also makes me wonder if in the future we could manufacture bricks of molten regolith to build shields or line structures on the moon?

[@sandromuscolino4956]

Only want to tell you your amazing enthusiasm comes out of your eyes! 💪🏻😊

[@frasercain]

Aww, thanks!

[@MrCoxmic]

Actually caught the live stream yesterday, thanks for answering my question.

[@revmsj]

With the Lunar Thermal Battery they could install a large array of parabolic mirrors to focus intensified sun light onto it in order to super heat it for the 2 Earth week day cycle before allowing it to release over the 2 week night cycle.

[@savagesarethebest7251]

Just imagine living on the moon with that sleep schedule! Insomnia would probably be common

[@PedroRafael]

Really cool to watch you go through the questions! I get to see questions that I never thought of, and have more knowledge. Really cool!

[@SpaceJimAstro]

Andoria's my pick! Love seeing this kind of enabling research for lunar exploration.

[@dennix01]

Thank you so much again Fraser.

[@BabyMakR]

Cheleb. That was a great question!!!

[@taeron6952]

Andoria. I always like to hear about super awesome technology, that already exist!

[@achecase]

And lots of sheep too..oh what's that? Oh, I thought you said Andorra.

[@v1jayanand]

Thank you

[@muleskinnerfilms6719]

Very good as always!!?

[@donporter8432]

Lots of good stuff here

[@toms-cubes-and-games]

Vendikar. Thanks, Fraser. Unfortunately, many people continue to repeat the virtual particles version of Hawking Radiation. Same with singularities are 'infinitely dense' and of 'zero size'.

[@NorthernChev]

Aeturen. I couldn’t type this fast enough. What a fantastic question.

[@hive_indicator318]

Risa, although I was tempted to go with the Enceladus one. Because those moons are so interesting

[@rogerdudra178]

I remember a song from Seattle called 'Compared to What' that reminded me of the sun.

[@rudykrutar3319]

2. Rudy Krutar 2023 May 13 Sat 23:00 1. The idea that time slows down in some circumstances is ludicrous. 2. Relativity with Fewer Tears becomes less silly when we cast it as clocks slow down in those circumstances. 3. Likewise yardsticks shrink in similar circumstances. 3. Also, the speed of causality is an awkward notion. 1. We should take the Causality Field to be c-squared at each point in space, 2. which is exactly 1 square füt per nsec per nsec in a vacuum, 1. where 1 füt = 29.9792458 cm 2. note 1 füt < 1 foot = 30.48 cm 3. so c = 1 füt/nsec wherever attenuation is negligible 4. in any inertial frame of reference 5. c-squared is constant but füt and nsec are not. 6. so füt shrinks as nsec stretches 3. less in a lens, and 0 square feet per nanosecond per nanosecond in a perfect mirror. 4. Huygens' Principle has all energy entering a tiny region of space quickly emitted in all directions uniformly. 1. Cellular Automata based on this notion show real physics such as evanescent waves at critical angles 2. and inflationary expansion of distances as gravity slows causality.

[@maciej5866]

[Cait] I've been wondering about a similar question for some time. We want to colonise the Moon. We are able to assemble spacecraft in space like the ISS. We could build a spacecraft, which could operate between orbits of Earth and Moon, with engines designed to operate in vacuum, not worrying about aerodynamics etc. We could launch rockets to the orbit, like we do constantly, refuel the spacecraft, put cargo inside and send it to the Moon colony. Isn't it better than constantly sending rockets with cargo to the Moon?

[@contraplano3157]

21:30 some bactérias use sulfor instead of oxygen. Other s use iron to produces energy

[@bbartky]

Cheleb. I’ve also wondered since I was a kid about what an eclipse would look like from the surface of the Moon.

[@mshepard2264]

I really like the moon temperature difference power generation. especially since the temperature differences are so huge. It should work great. andoria

[@Tara_Li]

Regarding the cloud of almost-Hubbles, there was Planetary Resources’ old ARKYD project. They had aimed at having thousands of mass produced smallsat telescopes for asteroid prospecting.

[@bucko4597]

one of the best shows ever. I like this site so much because this show is honest, it's fun to watch, and that's a rare combination. So a body with life, probably has water that is fluid for x-amount of time, and a gravity close to Mother Earth? In a perfect world, and contact has been made, how many years would it take to get caught up with the universe already used to technology? What would that even look like???

[@user-li7ec3fg6h]

Question: Astronomy: The further away objects on Earth are, the smaller they appear to us. What effect does this have on objects at astronomical distances? Do very distant objects appear much smaller to us than objects closer to us? Or are the angular dimensions negligible at such great distances because the angles are very small anyway? Thank you very much for your answers. The last Q&A show was another particularly good one, in my opinion. Thank you very much for your great work and your great channel.

[@gary3808]

Aeturen Another interesting program.

[@hatterson]

Regarding the first question, Matt Ferrell (Undecided) just did a video on current gen sand energy storage that was an interesting look at the technology. Obviously it's focused on earth based applications, and his recent video is focused on residential stuff, but it's an interesting look at the technology.

[@JamesCairney]

Janus It reminds me of F1 night races where the black track looks like a ribbon of light against the darkness of night. It's all relative.

[@MurraySciffer]

Thank you for the acknowledgement (as Muzz)

[@kolbyking2315]

Nimbus. I've been planning a KSP RSS Venus sample return for months, but I was away from the live show when this question was asked😭. In the game, it requires ~40 tons into LEO.

[@Chris.Davies]

There is only one possibility for a rover on the surface of Venus: we learn how to make the universe's highest temperature superconductor, so that a buoyant balloon-type probe, can sit at a temperature which is cold(ish) in the upper atmosphere. You would lower your rover to the surface using a graphene cable wrapped in superconductor. The rover would stay attached to the cable - with some slack, and the rover's systems would dump all the heat absorbed into the superconducting cable, which would be attached to a gigantic superconducting flag at the probe level. This would allow a nuclear-powered rover's important bits to stay at the ambient temperature of the upper atmosphere, because superconductors are... superconductors! But currently we have no way of joining or producing any room-temperature superconductors at all, and it is certain that when we build them, they will not be tolerant of 470 degrees C. We also have no idea how to produce a 70km long graphene cable with a breaking strain of thousands of tons, because a cable has to support its own weight, as well as the payload, plus a healthy safety margin. This is the sort of thing you might expect a fairly competent Type 1 civilisation to be able to seriously consider - but the expense would still be astronomical - no pun intended.

[@nerufer]

[Andoria] because I like Shran just as a sidenote on Nimbus: water-moons is great, however, the question for me is; would they be able to hold onto that water? Would you get an atmosphere and can it hold onto it?

[@zapfanzapfan]

Cheleb. I want to see that someday!

[@WingManFang1]

39:46 like Pandora from the James Cameron Movies for Avatar

[@ugiswrong]

Hi Fraser a question Could we use a lunastationary orbiting complementary satellite which would beam heat down to a point on the nighttime moon surface which could keep a rover warm during those 14-day evenings?

[@AriasThirdOfHisName]

Hi Fraser, you talked about the large telescopes being built like the ELT and the GMT and it struck me that I don't have a timeline feed of milestones around the development of these. Who is building them? Who are the associated companies and industries? What is the current step of development? Is this info out there and I'm unaware of it or is there simply not the appetite for constant updates such as you'd see around SpaceX development?

[@agapitosdovles9803]

Hi Fraser, could there be any stars trapped in the Lagrange points between the milky way and Nubecula Major (LMC)?

[@bbbenj]

Great video 😊 #SaveChandra

[@rogerdudra178]

Greetings from the BIG SKY

[@ConstantGeographer]

Dark Forest Hypothesis regarding alien life ;)

[@Chris.Davies]

FYI: Roy Kerr does not accept that Black Holes evaporate. I learned this during a Q&A with him after a Royal Society presentation.

[@JAGzilla-ur3lh]

Janus. The Moon being secretly black seems like such a basic, obvious fact I should have known, but I've somehow gone 35 years as a very casual astronomy nerd without knowing that, actually. Very weird. Totally logical, but mildly mind-blowing all the same.

[@Raz.C]

Hi Fraser In relation to that first question, are you familiar with Sterling Engines? They are powered by a heat differential. As long as one end is hot and the other is cold, those things will keep on turning. Would they be a good power source for a moon base? I mean, if you have a base, where people are living, you're going to need to keep it heated/ cooled. So there should be about a 200 degree kelvin temperature difference between the inside and outside of the base and this should be a permanent state of affairs (unless you don't like your astronauts). But as long as your heating/ cooling the inside of the base ANYWAY, then wouldn't it make sense to use a Sterling Engine to use that differential to generate power? I think you might have mentioned something many years ago now, about NASA looking into potential uses for Sterling Engines on the ISS. Do you know if they ever did? Cheers, mate.

[@rhoddryice5412]

Cheleb 33:09 Earth’s apparent diameter (2˚) is four times that of the Moon’s and as the moon is tidally locked I’d assume an eclipse would last for a couple of days(?) at the point of the eclipse. I’d love if you would expand your answer to this.

[@Level10Productions]

Thermal heat storage would be very in efficient and take up volumes of space. Seems a bit archaic to me. We need something efficient, like fusion.

[@Grungir2]

Question: Are there any plans for an electromagnetic acceleration system in space? Would make more sense than starshot in my mind. You can add rings and make the probe accelerate meters or thousands of km just by adding rings in your system, you can make them smaller or bigger etc. Is there a limit in terms of speed for such a system?

[@joeker1013]

A good KZbin channel that really gets into the nitty gritty details of Artemis and current space stuff is Phillip Sloss.

[@maciej5866]

I think there's more to the question about mini Hubble telescopes. With the constellation of Starlink satellites interfering with research already and other companies following their steps with their own constellations, time for on earth observatories is coming to an end. And when it comes to the money and resources, space telescopes could be built instead of those on earth. As you said, there's plenty of telescopes, so the parties which funded the telescopes could spend the same money on space telescopes instead.

[@AubriGryphon]

I believe what [Cait] was trying to ask was, why can't we just slap enough shielding on a spacecraft that the radiation load is comparable to flying in an airliner?

[@carlfollmer1767]

We don't know the layout of the Starship HLS interior, but isn't the pressurized, livable space in the same spot where the header tank currently sits? Can they move it to another part of the ship?

[@maybeezat114]

If your assumption about moon's gravel ture then moon's temperature must be balanced and not plummet to subzero temperatures in the luner night?

[@jduade]

Photons seem to be everywhere in space. Even when JWST or Hubble look at a patch of sky that looks empty they still find a myriad of galaxies whose photons are picked up by the Telescope. Since the photons have energy, albeit a teeny-tiny amount, could those photons be used as an energy source by a spacecraft while traveling through interstellar space?

[@brien9648]

What are some of the possible fixes do we have to address Lunar dust basically destroying everything it gets into?

[@davekohlenberg8902]

Would a concept of an igloo work for a habit on the moon? The regulith could be formed into an igloo with the walls being thick enough to store and heat the interior? The walls could be thick enough to provide heat even during shade times as well as provide protection from radiation.

[@IanBotwright]

Nimbus. Fraser thanks for all the hard work put in by the team and yourself.

[@WingManFang1]

You mentioned you’d wanna go to the moon to experience a Lunar Eclipse…..but no realistically you wouldn’t, because temperatures on the moon in the dark can drop low enough to cause frostbite or death “Allegedly,” now with that said if you could get a sufficiently safe way to heat a space suit for that temperature you could maybe make the trip. It’s not a 2 weeks of night thing, but still takes a few minutes longer than you’d wanna be in those cold temperatures.

[@disinclinedto-state9485]

Fraser, possible Fermi Paradox / SciFi story idea (original, but unlikely to be the first time it's been floated), what if life always finds a way to balance itself out to keep ecosystems functioning, and humans are the first to suffer a mutation that makes them wildly successful and move out of the food chain and dominate a planet. A particular cosmic ray hit the foetus of mitochondrial eve (or some earlier equivalent) and turned us into exploration/domination/exploitation machines the like of which is not yet seen in the visible universe. Also, I am tired and need coffee. Love your work. 😅

[@Akopalyze]

Question: How much usabel ice is expected to be found in the moons shadowed craters? How long could it possibly last when used for propellant production? I guess It needs to be done in order to expand into the solar system. I just find it funny how it's called "sustainable" when they talk about ISRU, yet all propellant will inevitably be thrown out into space until its all used up. Lets hope we'll have set up propellant farms elsewhere by then, right?

[@jamysmith7891]

Temperature on the Moon is like clockwork; Seems like a heating element of the right size, driven to the right depth of the natural ground should be able to maintain a constant temperature in a properly insulated habitat built over it with no special equipment

[@TomSnyder--theJaz]

Andoria

[@stefanandersson7519]

Very interesting to hear you explain the Unruh effect 👀 So, would that mean that everything with mass creates Unruh radiation around it? Would an immortal being ultimately evaporate just like a black hole?

[@frasercain]

In theory, everything releases Hawking radiation, just not very much with low mass and low gravity gradient.

[@l3zl13]

I'm not sure what kind of spaceship Tuesday Statzer had in mind when asking the question. I guess the spaceship in fiction that is closest to our current level of technology is something like the Hermes spacecraft from The Martian. I don't think it has any technology that we do not have currently at least in experimental phase so the only challenge is the actual manufacturing and the cost. On the other hand, without a ship of at least comparable level I don't think we should even attempt a manned Mars mission.

[@adamsutherland2593]

Question. Could a rocket engine be built with a vacuum sized nozzle but filled with something (heat tiles or similar) so that it starts as a sea level engine that insides slowly burn away qs it rises and becomes a vacuum engime, or woud it be the same a an areo spile engine and not worth the effort?

[@contraplano3157]

40:00 Júpiter can get mass from the red sun, and transforms to a brown Júpiter Star?

[@mshepard2264]

I probably have about 30 years left at the most so i really want a mission to the ice moons that samples to see if there are microbes on those moons. so if the mission doesn’t launch in the next 10 years the logistics are not going to work out. so aeturon also.

[@davidguy209]

I've seen the proposed design for the next iteration of the Mars helicopter. Its much bigger than Ingenuity. Wouldn't it be better to have a fleet of small helicopters, instead?

[@aelolul]

16:21 - Quick correction: unruh radiation has not been observed, or at least not unambiguously.

[@jaydonbooth4042]

The ISS is in fact a large spacecraft assembled in orbit, just not a spacecraft that can travel to other planets.

[@jensphiliphohmann1876]

08:41 The Sun spots aren't actually black, only _relatively_ dim _in comparison to_ the rest of Sun's photoshere which would blind you unless you dim it down so much that the Sun spots _appear_ black.

[@TheDarkFalcon]

Vendikar. 🤯

[@stooartbabay]

Question: instead of de-orbiting the ISS, could it be sent to orbit the moon and used as an emergency habitat for future moon missions?

[@bbartky]

No. It takes a lot of energy to move even small objects beyond low Earth orbit, let alone something the size of ISS.

[@stooartbabay]

@@bbartky but it’s possible?

[@GizzyDillespee]

ISS could be the centerpiece of a future lunar museum. Would it be worth it? It depends on what you needed to sacrifice, to accomplish something that's not useful for any practical purpose. Maybe if there was an experimental Earth to Moon rocket that needed testing, that would be a good project. How do you slow it down, at the moon, to privide for a gentle landing? Maybe a long slow trip is best? (Not suggesting they do it... but it IS possible)

[@Disasterina]

Andoria. Also, let’s say earth microbes hitch a ride on our landers and actually survive and propagate on another plantet or moon. How exactly will they effect it? Could bacteria change the atmosphere (or make an atmosphere) on one of these worlds?

[@davesilkstone6912]

Can we have a dive into the heat storage technology? I don't understand how the120 degrees Centigrade temperatre of the Lunar day can be stored in such a way that the regolith gets hot enough to melt, that seems counter to the laws of thermodynamics.

[@frasercain]

You have to concentrate it. Larger solar collectors heat up an element under the regolith.

[@JAGzilla-ur3lh]

Here's a question: Are there any plans to put a radio telescope in space? Would this provide any major advantage over ground-based radio observatories?

[@Hobbes746]

Not just plans, we’ve done that already. Just a small one for now (Spektr-R). The advantage comes when you place such an observatory far away from Earth to reduce radio interference from Earth.

[@gilbertozuniga8063]

The grey you see is the mouse eating the cheese moon

[@Chris.Davies]

26:33 - I think a better answer to the Grey Moon question is this: "Even very dark surfaces reflect some light, and a smooth surface reflects more than a jagged one. Sunlight is white (6500k) in colour, and when it reflects from a very dark surface, you see that white light. The sun's white light, reflected from the moon, looks mostly-white because there is so much of it, and it is reflecting from a colourless surface. If you look at a deep black piano, it looks black, but when a spotlight is pointed at it such that the spotlight is visible on the black surface, it looks white, and very bright. That is the exact same effect you are seeing when you see the sun reflected from the moon. It also helps to remember that the moon has no light of its own, and so it can only reflect light."

[@aaronperelmuter8433]

Actually, what you described about the piano is a phenomenon called specular reflection and by definition, it cannot occur over such a vast distance as per how you mentioned the moon would look. Furthermore, what relevance does the reflectivity of smooth versus rough surfaces have to do with how the moon looks? Averaging over vast distances, the moon would be quite rough and bumpy as there are SO many impact craters and the stuff thrown out from said craters and with no atmosphere to ever smooth any of it down, no air or water to wear away at the edges, there would be only a very small portion of the moon’s surface which would be smooth or even approaching being smooth. One last thing, daytime sunlight is actually much closer to a D50 spectrum, or a CCT of 5000K. Sunlight on a summer day, in a northerly direction, nearish to the equator is said to generally be about 5000-5500K. Today, my sunlight in Melbourne, Australia, at 4pm, 28/3/24, I just measured with a spectroradiometer, to be 5294K. I don’t think I can remember ever making a daytime sunlight measurement (I try to make my measurements between about 1230-330, or thereabouts) and the result being over 5800ish. The earlier in the day the measurement is taken, the higher the colour temp will be but 6500K is quite a blueish colour, as far as daylight is concerned. It’s very different from the colour temp of monitors and displays in general. In that case, 5000K is rather dingy and yellowish while 6500K seems generally quite neutral to blueish, depending on the screen, of course. Btw, I like the way you spelled grey and colour. It’s a pleasant relief to see there are still at least a couple of people besides me who still know how to spell. 😱😂

[@evenros]

When Webb or whatever telescope is looking "back in time", say at some of the earliest galaxies, are they looking in a specific direction? Wouldn't that make sense if the universe came from one point (big bang)? I can't wrap my head around the 3D layout of the universe and time...

[@Hobbes746]

No, they’re looking in all directions. ’13 billion years ago’ is a spherical shell all around us. This does induces headaches.

[@akers189]

Hey Fraser, which is worse for a rover, the heat of Venus or the cold of Mars. Is the dust on Venus as bad as the dust on Mars for a rover? Thanks, Jason

[@foxrings]

Andoria some of the more energy intensive activities on a moon colony are going to be thermal in nature. Smelting, metal forging, keeping humans and equipment warm during 14 day long lunar nights.

[@anthempt3edits]

Do we know how long the transition from hydrogen burning to helium burning takes for a sun like star? Like if a nearby star switched to helium tomorrow would we be able to watch it expand into a red giant, or would it be longer than a human lifetime?

[@davesilkstone6912]

The problem with Einsteins equivalency is time. At 1g acceleration an object would reach the speed of light in about 1 year, as objects cannot travel faster than light, if you are experiencing acceleration after one year you are in a gravitational field.

[@mattwuk]

Blackholes have to eventually shrink, imagine the temperature surrounding them is close to zero k, obviously there's equalisation constantly happening,

[@dustman96]

So what's the big picture of Hawking radiation and its impact on the evolution of the universe overall?

[@arthur_stephens]

Aeturen

[@igorscot4971]

Even if it was possible to get a rock sample from Venus would it be worth it? From what I understand Venus is very similar to Earth's chemical, so what new information could we gain?

[@darrellcherry9172]

Nimbus The escape from venus to orbit is extremely hard. The gravity is nearly the same as earth. The rotation is extremely slow (little or no velocity boost). A floating launch pad may not be high enough to see even 1 bar. It could be 5x or 10x (guessing here) for all we know. It's like lauching from underwater. The wind would be crazy even with "light" breezes. I think you over estimated our abilities.

[@alanmassoli5989]

Vulcan

[@tjmcguire9417]

Fraser. From another Frazer, thank you for your work. (same sept). Despite your excitement and great presentaion; would you consider doing more but shorter videos? I literally cannot do 41 or more minutes at a time. Just a thought from an old enquirer.

[@frasercain]

I'd just jump around and watch the questions that interest you. We put all the timecodes in the shownotes.

[@EnigmaDave]

Q: At a few moments after the big bang, once the fundamental forces split, and gravity became a thing, why wasn't everything pulled back into something like a black hole? Did the expansion of spacetime simply overcome the total effects of gravity that existed as matter started to form?

[@tonywells6990]

The universe was rapidly expanding (an expansion rate far far greater than it is today, after inflation) and the gravitational curvature of the universe was almost zero (the same density everywhere) so it could not collapse into a black hole. Cosmology models have moved on from a 'simple' expanding singularity proposed by Hawking and others, which suggested the initial conditions (such as the initial expansion rate) were just right to avoid the immediate collapse into a black hole.

[@EnigmaDave]

@@tonywells6990 Thank you!

[@DrDeuteron]

@@tonywells6990🤔Schwarzschild metric is on a static background. I don’t think it applies when the scale factor is significant. Somebody must have tried to solve it. I’d say if the radius divided by c is not much shorter than the time for the scale factor to double, then you need a whole new black hole solution, but idk.

[@tonywells6990]

@@DrDeuteronTo create a black hole you need density differences, in other words you need a lot of mass concentrated in one volume, but the density was almost the same everywhere. I think inflation solves everything.

[@Paulus8765]

28:35 Your AnthroFuturism guy cites a study that estimates a kg into low earth orbit will cost $100, not $5000. To the moon he estimates $500, not "a few million dollars".

[@Starman_67]

ANDORIA

[@AnthonyDD]

Hey Fraser, why aren’t there cameras on the moon pointed at the Earth? Wouldn’t there be some scientific value for watching the weather, auroras, or anything else from lunar orbit?

[@whoshotdk]

Don’t know about feasibility, but couldn’t we run a pipe from always-dark craters to lunar day lit areas? I think it’s called a Stirling engine, invented in 19th century.

[@doncarlodivargas5497]

Must not such a system pump, or transport something, typically a liquid from somewhere else to make this work, using up at least some of the energy such a solution would produce to the pumping action?

[@whoshotdk]

@@doncarlodivargas5497 Most definitely yes. Though you could say that about any system that converts energy from one form to another; energy loss is inevitable I think. I’ve actually no idea if a Stirling engine would be better than the system Fraser described, or even viable. It’s just something I heard about once and always thought it would be an interesting idea to try on the moon, or other extreme temperature places.

[@doncarlodivargas5497]

​@@whoshotdk - it would have been fun to know, guess the question should have been divided in two parts, first the technical part, if it could work, and then if it is a good idea, to me it sounds like a lot of (heavy?) parts, a complicated system and moving pistons, rods and bearings needing grease and maintenance etc, but i do not know

[@mrxmry3264]

funny, i just watched a video about using sand to store heat :-)