Daniel and Kelly’s Extraordinary UniverseDaniel and Kelly answer questions about binary star seasons, meat wasps and freefall.
How do some bees make meat honey? What are tapeworms up to in my tummy?
Can light escape from a black hole? What process produces coal?
Did Franklin hang that key from a kite? Why is dark chocolate better than white?
How do moles smell underwater? Why is the planet getting hotter?
How can humans live on Mars? What's the hold up with flying cars?
The current state of space law? The powerful mantis, shrimp claw?
Biology, physics, archaeology, forestry, really anything other than chemistry?
What diseases do you get from your cat? Well, we'll find the answers to all of that.
Whatever question keeps you up at night.
Daniel and Kelly's answer will make it right.
Welcome to another Listener Questions episode on Daniel and Kelly's Extraordinary Universe.
Hi.
I'm Daniel, I'm a particle physicist, and I've never read a poem on the podcast before.
Hi.
I'm Kelly Wiener Smith. And my husband just assumed that I'd be so bad at writing poems that when I read it out loud to my daughter, he left the room just so that he wouldn't be embarrassed. But you know what, I had fun.
I hope he's blushing somewhere. Whenever he's listening to this, he.
Might skip all of our Listener Questions episodes from here on out. But that's all right. I had a good time.
Well that's too bad, because those are my favorite episodes. I love hearing what people are wondering about, helping them unravel their confusion and getting to the topics that are really in people's minds. It's my favorite way to interact with our audience.
I love it as well, and I'm particularly excited about this Listener Questions episode. You know, one because my daughter's questions included and that's pretty cute. But two because we got a biology question for me that I was she is completely unaware of this group of species and they're so creepy and right up my alley and it was so much fun.
All right, Well, let's not waste any more time. Let's dig into it today. We have questions about seasons on Binary Star systems, about meat, wasp honey, and about how gravity actually works.
Let's do it.
So our first question is from Aida. She's ten years old and she lives in Virginia, and I think she knows Kelly pretty well.
Great place to live, I'll just throw that in there.
Here's Ada's question.
Hi. I'm Ada, I'm ten years old. I have a question for you. What would seasons be like if you were on a planet in a solar system that had two sons? Thank you?
All right? I like how she gets right to the point.
Yes, she's very succinct. I like that too.
Is she reading a book about life on a solar system with two sons? Or where do you think this question came from?
Gosh, you know, I'm sure it didn't come out of nowhere, but I don't know where she heard about solarsis with two suns. That sparkedness. Could have been science class at school.
Maybe she's writing a science fiction novel and she needs some science consultation.
That's right, Yes, and she reached out to the right person.
Yeh, she certainly did. So let's dig into it first. Let's remind ourselves why we have seasons on Earth, and then we can teleport ourselves mentally to a solar system with two stars and think about that one. So, on Earth, the reason we have seasons is because the Earth is tilted right. The Earth goes around the Sun, and there's a plane there where all the planets go around the Sun in the same plane, and the Earth also spins, but the axis that it spins on is not perfectly perpendicular to the plane of its orbit, so it's tilted a little bit. It like leans over. Now, the Earth is a sphere, so you know what is really leaning. It's still a sphere when it's tilted. But what's leaning is that axis of spin, that axis that controls the day night cycle. So what's closer to the Sun is the Northern hemisphere the spin lets you define a northern and the southern hemisphere, Then the Northern hemisphere is closer to the Sun during the summer, and the Southern hemisphere is further from the Sun during the Northern hemisphere summer and the Southern hemisphere's winter. It's not actually accurate to say that the Northern hemisphere is any closer to the Sun. Is just more exposed to the Sun because it's leaning that direction, got it?
And you know, I've got to admit that every once in a while, when I talk to like the few friends I have in Australia, I still forget that they're experiencing the opposite season that we are up here in North America. And we regularly have a disconnect.
Yeah, exactly. And so if we didn't have a tilt. For example, if the Earth's axis of rotation was perfectly perpendicular to the plane of its orbit, then you wouldn't have any seasons. You just always have I guess spring or fall. Right, the days would be the same length all year round. Going around the Sun wouldn't change your experience at all.
No seasons, totally boring, just like living in California. You knew where that was going halfway through the sentence.
Exactly, we'd all be happy all year long, right, it'd be amazing, so dull. And there are other tiny factors that also affect the weather and the seasons, things like the elliptical orbit, or the Earth doesn't orbit in a perfect circle around the Sun. It's an ellipse, which means sometimes it is closer to the Sun and sometimes it's further from the Sun. But this is a smaller factor than the tilt, which really dramatically changes how many hours of sunlight you get every day. The Earth is closest to the Sun in January and furthest from the Sun in July, so actually that counters the effect. It makes the summer slightly less severe and the winter's slightly less severe.
Is that why the year starts in January? Or did that have nothing to do with the calend No.
That's totally random. Yeah, Oka's totally right. And also the Earth tilt processes a little bit. It's not always in the same direction. It itself rotates a little bit, like a wobbly top. These are small factors, and that's affected by like the Jupiter and all sorts of other stuff. So mostly the Earth has seasons because it's tilted, So the northern hemisphere is getting more light and the southern hemisphere is getting less light during the northern hemisphere summer. All right, but that's a simple system, single planet going around a single star. So what about a binary star system in Ada's mind?
Can I back you up for a second? Are most planets tilted so like the Moon has a very little bit of a tilt. Is Earth weird having a twenty three point four degree tilt?
It's not weird to have a tilt like Urinus is tilted much more dramatically ninety seven degrees, basically totally on its side. Other planets are tilted more or less. The tilt we think comes from being hit. Like everything in the Solar System formed together from a big swirl. That's why everything is rotating in the same plane, and most of the planets are spinning in the same direction they move around the Sun, which is the same direction that the Sun is spinning itself. The whole Solar system is one big swirl, which then coalesces into a star and planets which all have the same swirl. But then you can get hit by something from outside the Solar system and it can knock you off axis a little bit. So we think that's probably the source of the Earth's tilt, and other planets tilt as well.
With all the stuff that's colliding, Would it be reasonable to expect that having no tilt would be rare because there's so many collisions that probably knock you off angle.
Yeah, As the Solar system forms, it's a little chaotic and things hit each other, so the average tilt is going to be zero, but it's unlikely for everything to have exactly zero tilt. Got it just the same with it, Like all the solar systems in the galaxy on average have zero tilt relative to the plane of the galaxy, but most of them are tilted relative to the plane of the galaxy. They're not all aligned with the actual rotation of the galaxy.
All right, So let's move on to systems with two sons.
All right. So system with two sons sound exotic, right, You're like, ooh wow, two sons, how cool, But the truth is that they're not actually that rare. Binary star systems are all over the galaxy. It's a significant fraction of the stars in our galaxy have a partner star. And the reason is that that big cloud of gas that collapses to give you a star usually it's part of a much bigger cloud. So stars are born together. Often you have two, three, four, five stars all born together, which begin a complicated swirl as they're forming. So you have these nurseries. We have a lot of star forming happening at the same time, and so stars are born with partners. And the reason we have a lot of binary star systems is that it's basically the most number of stars you can have in a system and have it be stable. Like you can have two things orbiting each other and have that be stable, like the Earth and the Sun or a star and another star. But you add a third object and it becomes chaotic, it becomes really complicated and unstable. So if you have three stars, for example, what's very likely to happen is one of them is going to get ejected and you're going to end up with a single star and then a pair of stars. So you have a lot of binary star systems out there, not very many trinary systems or quaternary systems, or not even know the descriptions for five or more stars.
So why is it more likely to get ejected than to get pulled into one of the other two stars and then just make like, I don't know, a big star, a big explosion.
Yeah, well that could happen also, but you know, stars are small compared to the distances between them, and so actual collisions are pretty unlikely, but they can spiral in and combine. That certainly does happen as well, But there's just many more outcomes where they get ejected, and just like in our Solar system, there's been chaos. We think probably there was another giant planet which got ejected from the Solar System because of the interaction between all the planets. So you have a lot of binary star systems out there, and then you have to think about the planets around those binary stars, and it becomes tricky already because now the planet is sort of like that third object. So you might wonder like, hey, isn't the planet just going to get ejected the way like a third star would get ejected, And the answer is yes, it's not easy to have planets around binary stars in a stable way. There's two ways to do it, and both of them basically make it look more like a binary star system. So one solution is you have the two stars near each other and the planet is far away, so it's sort of like, yeah, there are three objects there, but really it's sort of a nested set of binary systems. You have like the stars on one side and the planet that are orbiting each other, and then inside the sort of star system, you have two stars moving near each other. That's one situation, basically, like replace the Sun with two stars close to each other or closer to each other than to the planet. The other possible configuration is you have a star and a planet like the Earth and the Sun, and then you have another star that's much further away, so like put a star near Pluto or something much further from the Earth than the Sun and then it's far enough away that it's not unstable. Then you have like again a nested set of binary systems. You have three objects, but really it's like two objects acting as one and then in a binary system with the third object.
Okay, so then let's talk about seasons. In the first scen area, where you have two stars that are right next to each other, do they act like one just megastar when you sort of aggregate their effects.
Yeah, they act like one megastar. It's going to be very similar to as if you had one bigger star. It's going to be different and more dramatic in terms of like sunrise and sunset. Sunrise will be longer and sunset will be longer, and there'll be times when you have like one star above the horizon and one below, so you could have effects like you could have a sunrise where there's already a star in the sky, and then you have basically two sunsets, one more dramatic than the next. So that would be really cool, but it wouldn't really affect the seasons very much, right because the planet's relationship to the star is basically the same. If you have a tilt and you have an orbit that's going to determine your seasons. So in that situation where you have a planet around a binary star system where the stars are close to each other and further from the planet, the seasons are going to be very much like here on Earth.
I feel like it would be amazing to wake up to a sunrise with two stars in the horizon. That sounds really cool. But all right, So then our second scenario, you say, there's one sun that's kind of close to the planet and another sun that's super far out. Is it far enough out that it doesn't really impact climates and seasons anymore?
Unfortunately? Yeah, So the boring answer is for there to be a planet in this situation, that star has to be kind of far away. The closer you get it, the more dramatic and the impact on seasons and day night stuff, etc. But also the more unstable it is. Like, if you have the planet be the same distance from both stars, so it's like very dramatic, then that system is totally unstable and it's not gonna last for very long. So you got to push that second star kind of far away, which means really it's gonna be in the sky more like a bright star. Than a real sun and not really gonna affect your seasons. You're gonna have one totally dominant star and then a second star that's gonna sometimes make the night a little brighter or even the day a little brighter, but it's not gonna have that much effect. But you know, in a science fiction sort of inspiration, we can move that second star in as as much as possible and pretend that it does have some impact because there's some crazy dynamics that happen in that scenario.
Okay, let's go for it. What is that like super winter?
Yeah, exactly. If you think about the periods when you have sunlight, that really is what determines the seasons. Right in a single star, single planet system, it's the number of hours per day of sunlight you get that determine the seasons. And in the summer you're getting more sun. In the winter, you're getting less sun. Now put that second star around, say we have the second star, you know, in Mars orbit or something crazy, then you're going to be getting sunlight all sorts of weird configurations, like there can be parts of the year where each star is illuminating a different side of the planet. Put the planet between the two stars. Right, they're all in a line. You have star, planet Star, then every part of the surface is seeing a star. Right, It's like the whole world has noon at the same time, right, which would be crazy. So you have periods where the whole planet is seeing star, and then other scenarios where like in a line it goes star star planet where half of the planet is seeing both stars at the same time, and if they're both pretty close, that's gonna be superday. That's like super noon, right, and that's gonna be very intense, super duper hot. And also you'll get a weird effect there where potentially the stars eclipse each other. So like you know, we have solar eclipses and lunar eclipses, this would be like a stellar eclipse where one sun is behind the other sun briefly. That would be awesome.
Don't look at either.
But I actually looked up a simulator to try to figure out exactly what would happen through the year, and it depends crucially on the orbit of that second star. If that second star has a period of about a year, like the same as the planet's orbit, then you're gonna have a regular cycle. But you're gonna have times in the year where even at the equator you have no darkness, like you see one sun and the planet spins and you see the other sun. And so that's going to be very summary, right, because it's all about the hours of sunlight you get and other parts of the year where you're seeing both suns at the same time, so you're getting fewer hours of daylight, but they're more intense, they're brighter. So you're gonna have these really weird periods. I don't know how the plants would respond to that, or how you would evolve in that kind of.
Configuration circadian rhythms, mm hmm.
It's gonna be a total mess, but it would be regular, you know. And if, for example, the second star has a longer period, it takes longer to go around that first star and the planet, then its affects can slide through the year, right, It's not like every June we have double sun, every January we have one sun. It can slowly offset and that must really affect like the development of a civilization, you know, because we use the regular seasons, and the regular day night cycle really is a way to tell time. So either you have to have much more complex mathematics before you can even begin to use a calendar and develop it. Or maybe you get some art or quicker because the calendar is more complicated and it inspires more interesting mathematics. But the short answer is that the seasons are going to be intense and complicated, and it depends on a lot of the details, exactly how fast that second star goes around the first star.
I wonder if it would hinder the establishment of civilizations, because like being able to plan things like when you plant your crops seems really important. I wonder if we'd all be like wanderers because planning just isn't worth even trying, but really fun to think about it. You know, there's got to be a couple of sci fi novels in.
There, Yeah, exactly. And you know there's the famous book The three Body Problem, where they have essentially this question, except it's actually the four body problem because they have three stars and a planet. I don't know why they like couldn't figure out how to count to three. It's already complicated enough with two stars. You don't need a third star.
Yeah. Well, when Ada's done with her math homework, will have her listen to this explanation and hear what she had to say.
Maybe we should have her on in real time for a follow up. Let's do it, hi Ada, thanks very much for your question. I was curious what you thought about our answer and if you have any follow up questions.
I understood like what I heard when I listened to the podcast, m H. And I do have one follow up question.
Oh goodie, what is it?
So?
Was our sun in this our source system like part of a different source system and then was it ejected out or was it just not like that?
Yeah, that's a great question. Unfortunately we don't know the answer. Most stars are born with other stars nearby. There's like sibling stars sometimes two, three, five, seven, as part of a big nursery, and then they're separated, as you know, gravity lings them around. But we don't know the history of our star that far back, so probably it was born with other stars, but we don't actually know. Maybe one day we'll figure out some way to figure it out, but for now we don't know the answer. Thank you, thanks so much for your question.
All right, so now for something absolutely totally different, we have a fantastic question from listener James Palmer, and it is a question about meat bees otherwise known as vulture bees, which I had not heard of, but is absolutely right up my alley. So let's hear the question.
Hey, Kelly and Daniel, I have a burning desire to know everything about meat wasps. I just heard about them, and I feel like there's a lot to discuss here, Like apparently they are carnivorous and the eat on like flesh and like maybe it's rotting. Then they use that to make their honey and stuff like meat honey. Please tell me everything.
Meat honey, Daniel. You're dying to know about meat honey.
Right.
Well, you know, we have lots of different kinds of honey here in California, and often it's sold to us by promoting the kind of flowers that the bees visit, like ooh, this is lavender honey or wildflower honey, and you're supposed to imagine that you can taste the lavender as you're eating the honey. And so I'm wondering, now, meat bee honey, is it gonna taste like pepperoni or what's going on?
Oh gosh, you know, to be honest, I would never try it. But there's not a lot of honey that is meat honey. So there's a lot of bees that make something called honey, but there's only three species that do this meat honey thing exclusively. So I think maybe we should start with how honey is made. Yea, because I actually didn't understand this very well.
I have this naive understanding that like bee eat pollen and then do something internally and then vomit up honey. How wrong is that?
Yeah? I thought that too, Okay, totally, like almost one hundred percent. Okay, so that was my thought too. Okay, So let's start with the European honey bees as an example. Okay, So this is APIs Melfera, and what they do is they go out and they go to flowers, and the flowers produce both nectar, which is like sugar water, and pollen, which has a lot of protein. And so these fill two very different rolls for the bees. So they get their carbohydrates from the nectar, okay, and that's gonna become honey, and then the pollen is their protein source. And sometimes the pollen like gets in the honey. It almost sounds like it's accidental, but mostly the honey is from the nectar. Not from the pollen, but.
The bees also eat the pollen. I thought the pollen was incidental and going along for a ride, and it was part of the plants deal with the bees, Like you can eat the nectar, but then I'm gonna get the pollen all over you and you're gonna drop it on another flower and help us reproduce.
No, they eat it too. Oh no, they eat it and they feed it to like the baby bees, and so it's like a very important protein source. I didn't know that either. And actually there's four different kinds of bees. There's the honey bees, the orchid bees, the bumblebees, and the stingless bees. And they're all categorized by having what are called corbicula and these are like chunky thighs with like a way to like stick the pollen on there. And so like I saw a bee on one of our flowers the other day and I was like, what is this orange? Like it's like they've got bling on their hips. I know, as an ecologist, I should have been like mortified that I didn't know what this was already. But anyway, those are like four carrying pollen around so they can bring it back to the.
Hive, I see, And so do the plants get anything out of it? I thought bees were pollinators.
Yeah, I think some of it still like falls off and lands in the right place, so the pollination still happens. But the bees aren't moving the pollen around as a favor. It's more like incidental. So that's how nature. No one helps anyone out in nature unless they have to, all right.
So bees drink pollen and then they use that to make the honey. How do they actually make the honeyes that inside the bee? Or is that in one of their little hexagonal cooking vats.
Bees drink nectar. They don't drink the pollen.
Oh sorry, right, yes, okay.
That's okay. Or they sometimes drink a honeydew, which is this like sweet fluid produced by insects as like a way to attract organisms that like protect them from natural enemies. They collect it in this special organ where they collect all of this sugary water, and you know, they can use it a little bit for like their flight to get from place to place, but they're you know, trying to bring it back to the hive. So they fill up this organ and I think that something like half of their body weight can end up being this sugary water. But the sugary water is nowhere near concentrated enough to be honey. So what they do is they bring it back to the hive and they regurgitate it to bees whose job it is to try to get some of the water out and concentrate the sugars more. And so those bees they like start kind of partially regurgitating it and blowing these like bubbles that increase the surface area, so some of the water evaporates off it.
Didn't know that the physics of honey look at that, Yes, right, And.
I hadn't imagined that so much of honey involved vomit. But there you go, so much fun hanging out with biologists.
When I'm vomiting, I'm not busy also trying to concentrate it and evaporate it. So I have like gooey or vomit. I guess that's what a bee does.
I mean, you're not so great at multitasking. Too bad.
I'll work on that. I'll work on that. You know, good to have goals. Yeah, all right, So bees vomit up the nectar, and then other specialized bees help evaporate and concentrate it into honey. So that mean that honey is just nectar that's been concentrated down or is there some fermentation that also happens.
That's just one of the stages of evaporation that gets a little bit of the water out, and then when they store it in the combs, like the you know, honey combs, I'm under the impression that some more evaporation happens there. So bees produce a little bit of heat by like, you know, shaking their wings really fast. That also produces some airflow over the honeycombs, and that combination of heat and then air moving throughout the colony and then sort of back out of the hive, that finishes evaporating off the water until you get to a point where you've got enough concentrated sugar that you've got honey.
Wow. Fascinating.
Yeah, I didn't know any of that. That was awesome.
So then it makes sense that if I'm eating the honey from bees that visited lavender, it shit tastes like lavender because it really is like concentrated lavender nectar.
If lavender nectar smells like lavender, I don't know that it does. And I'm one of those people who has had honey from different places and been like, it's all honey to me. I don't have a delicate paletate.
Okay, So now tell us about meat wasps. Where do they get their supplies to make honey?
Okay?
So I'm terrified of this answer, by the way.
Yeah, all right. So the best honeymakers are the European honey bees, the best in terms of like producing honey that humans like, but a bunch of other kinds of bees they make similar honey, but often their honey is nowhere near as like concentrated with sugars. It's more watery. And there's a group of bees called the stingless bees, and now we're getting closer to the vulture bees. So the stingless bees they make honey, but their honey tends to be more watery, and instead of storing it in those combs, they make these little waxy pots, and it's harder to get it out of those waxy pots, and it's like more watered down when you do. So people did still keep these bees for sugary fluids, but as soon as honey bees came along, a lot of the stingless bees that do this more watered down, harder to get honey, they became less popular to culture. But so these stingless bees, they also get their nectar from flowers, but there's a group in the genus Trigona where they seem like they're less interested in flowers. So instead of going to flowers for nectar, they get their sugars from things like rotting fruits. They'll like take the sugars from that. And instead of getting pollen, they get their protein from dead animals, dead vertebrates in particular.
I see. So that's why they're called vulture bees, because vultures are scavengers. They don't kill anything. They eat already dead stuff. So these vulture bees will get their protein not from pollen, but from dead animals.
You're saying, that's right. And they'll get their sugar, which they used, you know, like make their honey stuff. They get that from things like writing fruit are free they find, Okay, So then the question is do they make meat honey? This is important and the answer I think is maybe.
Oh.
Really.
So there's only three species of these vulture bees, and they're all in the same genus, they're all closely related. It does turn out that there's a fair number of stingless bees that where like, if meat is left out, they'll go ahead and get some protein from it, but they're not required to get protein from it, so they're called facultatively necrophagic, which means they'll like eat dead stuff when they've got the chance, but they don't have to. But these vulture bees are obligately necrophagic, so they have to eat dead stuff. And currently they're really good at it, Like they've got ways to sort of attract other members to come so that they can like very quickly with these specialized mouth parts scrape a bunch of like rotting flesh. Oh my god, yeah, your face is like priceless.
It should be called nightmare bees. Yikes.
Yes, it's intense pretty metals. So then it's a little bit unclear what happens. So I found a nineteen eighty two paper that described what they were doing, and it said the bees masticate and consume flesh at the feeding site. They do not carry pieces of flesh to the nest, but appear to hydrolyze it with a secretion produced by either mandibular or salivary glands, which gives the feeding site a wet appearance. Side note iw.
That means they're slabbering right their slabberry and they have meat slabber.
They've got meat slabber, and their saliva is starting the process of breaking down the meat. That's what that means. And that says individual bees captured well feeding, then forced to expel the contents of their crop. So essentially they made these meat bees. Through up, we're carrying a slurry of flesh measuring between thirty seven and sixty five percent dissolved solids by volume.
So a slurry of flesh. Isn't that like a nine Inch Nails album title or something.
I feel like we have to get in touch with prent Resnor now and find some way to convey this to him.
Oh boy wow.
And so then the question is how do they store it when they get back. So I've read this paper from twenty twenty one and they were laying out some different hypotheses for what happens. It looks like that meat slurry gets stored in pots. Maybe it gets mixed with some of the sugary stuff they collect. I think at the end of the day, it's not really clear what they do how it's stored how long it's stored, but you probably could say they make something called meat honey, like they're taking that flesh slurry, they're storing it in these pots. It looks like it quote unquote matures for about two weeks into a paste that is also a little bit sugary. So they do appear to be making something like meat honey. Let's go for it. Looks like part of this process and if your wife we're here, maybe she'd be excited about this part. Part of it appears to involve the microbiome. So these vulture bees have microbiomes that include acidophilic bacteria, so bacteria that do really well in acidic environments. And you find similar categories of bacteria, they're not the exact same species, similar categories of bacteria in the guts of like vultures. So it seems like there's some kinds of bacteria that team up with organisms that eat dead flesh to sort of help process it and maybe also help make it safer, because bacteria that get to the flesh first start producing like toxins maybe to ward off these competitors, and these acid loving bacteria sort of help make it all happen, and your face is just priceless.
Right now, I'm so glad I don't eat breakfast because I'd be throwing it up into breakfast slurry right now, and some bees could come along and make breakfast.
Honey, meat honey, and so James, I have to thank you. I had never heard of these before. And let's go ahead and hear if you learned everything you wanted to know about meat honey, and.
If you're ever gonna eat honey again.
I think it's safe to say that you taught me everything I asked for and a lot more. So thanks ver so much for that, guys. I appreciate it.
All right. Our last question comes from Hans in the Netherlands who has a nephew in Perth, and they've been disagreeing about which direction the Earth is accelerating and how gravity actually works. Let's hear the question from Hans.
I have a question concerning freefall, as I understand it, when you're in freefall, you don't move it all. Instead, the Earth is ration to watch you. Now my question is this. I live in Howder, which is in the rest of the Netherlands. I have a nephew in Perth, Australia, which is roughly the opposite side of the earth. Well, we decided to jump out of an airplane on the same time, which way is the earth moving? Thank you very much for your answer.
All right, so you know, maybe first we should start with the disclaimer that you shouldn't do this unless you're a professional. Have you ever done sky jumping or have you ever jumped from a plane?
I one time did skydiving. Yes, I jumped from an airplane exactly one time. And I did it one time because I did my homework and I looked up how often people die skydiving, and it turns out it's very very rare to die the first time you jump, and it's very very rare to die after like ten jumps. But there's a danger zone between like two and nine jumps. And my understanding is that the first time you jump, you're very careful, you're freaked out, you check all the straps, you're like following all the safety videos, and when you survive that first time, you're like, oh, maybe it's not so dangerous. And then you get sloppy. And when you get sloppy and you're like feeling confident, that's the danger zone. Then and if you survive like nine or ten jumps, you become really good at it, and then you're back in the safe zone. So I did it once. I survived, and I'm never doing it again.
Wait, you controlled your own parachute and everything when you jumped.
I got to pull my parachute, but it was a tandem jump of strapped to another dude who was there to like make sure I did it right.
But yeah, when I did it, there was a dude on my back. Okay, I mean, did you ask the guy on your back is this your second to ninth jump? That's the guy you need to ask. I think that's right.
It might be his second and ninth jump that day. I think these guys go up all the time.
Yeah, yeah, I think so too.
But it was sort of terrifying because they told us, hey, you can change your mind at any moment. And the friend I went with, she was standing at the edge of the door ready to jump out, and she was like, yeah, no, I can't do it, and they're like, no, you're doing it. And she's like, you said I could change my mind, and they're like, we were lying. Nobody changes their mind, and then they pushed her out the door.
I had brought a boyfriend who you know didn't end up marrying, maybe not surprisingly after you hear this story for his birthday. Oh and he got to the door and he said, I don't want to do it. And the guy strapped to his back looked at me, and I said, and I pointed out, and the guy jumped. And you know, my boyfriend was happy afterwards that he did it, but he had also tried to back out at the last second.
So folks, when they tell you you can back out, don't believe them if you don't want to jump, and don't go up in the plane. Yeah, all right, but today we are not giving advice about ways to risk your life and get adrilline thrills. We're talking about understanding the fundamental nature of gravity, how does it work? And Hans, I think is responding to a conversation we had about gravity and freefall and who's really accelerating, in which an explanation I gave is that the Earth is accelerating up and out towards you. You're not falling towards the Earth. And so I think it's worthwhile to revisit that explanation a little bit and then unpack it in the context of Hans's question, All.
Right, let's go for it. So if you jump out of a plane, what does Newton say is happening?
Yeah, So, from a Newton point of view, if you're on the surface and you see somebody jump out of an airplane, you say, is a force of gravity and forces create acceleration. So gravity is accelerating you down towards the surface. And that's Newton's explanation. And from the point of view of the person on the surface, that makes perfect sense because you see somebody's velocity and they're accelerating because their velocity is changing, and so it looks perfectly like there's a force there and the person is accelerating. From the point of view of the jumper, right, they jump out of the airplane, they see the surface of the Earth rushing towards them. Right, they see Earth accelerating towards them. Now, velocity is perfectly relative, right, And so you might wonder, like, well, who's right, who is actually accelerating? And this is where Einstein comes in, because Einstein tells us that, like, velocity is relative, but acceleration is not. So let's unpack what that means for a moment like we say that distance is relative, like Kelly and I are three thousand miles from each other right now. And when we say distance is relative, we mean that you have to measure it relative to somewhere else. Like I can say I'm three thousand miles from Kelly. I can't just say I am three thousand miles. That doesn't have any meaning, right, I have to say what I'm three thousand miles away from. Velocity is also relative. I can say I have zero velocity right now relative to Kelly, but I don't have zero velocity relative to the Sun. And I don't have zero velocity relative to some particle that's speeding towards the Earth at almost the speed of light. In fact, I'm traveling at nearly the speed of light relative to that particle, right And so velocity is only defined relative to other stuff. And that's confusing because when somebody jumps out an airplane, you wonder, like, well, are they moving towards the Earth? Is the Earth moving towards them? Both of those are perfectly valid. Because velocity is relative, you can't say which one's actually moving. But now you get to acceleration. Acceleration is different. Acceleration is not relative. Velocity is relative. It's a property of a pair of objects, me and Kelly, and me and the Earth, me and the Sun. But acceleration is a property of an object. I can tell if I'm accelerating. You can tell if you're accelerating. How can you do that? Well, say, for example, you're in a truck and you have a bowling ball in the back of the truck. You can tell when somebody hits the brake on the truck. You can tell when somebody accelerates because the bowling ball in the back of the truck will respond. What happens if you hit the brakes, the bowling ball keeps going and will bang into the front of the truck bed. And if you accelerate, the bowling ball rolls backwards towards the back of the truck bed. So you can measure your acceleration yourself. You don't need to measure relative to the Sun or the Earth or your podcast co host or anything like that. So that means you can do something interesting. You can ask like, well, is the guy who jumped out of an airplane is he accelerating? Or is the guy on the ground on the Earth are they accelerating because both of them think the other one is accelerating. But Einstein says, no, you can actually just measure it and you can tell the answer.
And the answer is that the person who jumped is accelerating.
No, the answer is the person on the earth is accelerating. No, yes, absolutely. Imagine you jump out an airplane and you're holding a box with like a billiard ball in it. Right, what's going to happen to that ball? You feel like you're accelerating towards the surface of the Earth. But you look at the ball. The ball is not moving inside the box. The ball is going with you. It has exactly the same experience you do. Now somebody on the surface of the Earth, they have a ball in the box. That ball is pulled towards the surface of the Earth. That's measuring acceleration. Another way to do this is to have a scale. So you jump out of an airplane with a scale, and now you stand on the scale. Are you going to measure anything? No, because there's nothing pushing you onto the scale. Whereas if you put the scale in the surface of the Earth and you stand on it, you're going to measure your weight. Right, that weight is actually measuring your acceleration. Einstein says, what's happening there is the surface of the Earth and that scale are accelerating up and out right. So a scale is like an accelerometer. And so when you jump out of an airplane, you can measure that you're not accelerating. You're in free fall. There is no gravitational force on you, because there is no gravitational force on the surface of the Earth. What you're measuring is not the force of gravity. The weight doesn't measure the force of gravity. It measures the acceleration of the surface of the Earth up and out away from the center of the Earth.
That's counterintuitive, yeah, exactly, but it actually makes much more sense.
The way to think about forces and acceleration and gravity is to remember that there can be apparent forces like say, for example, you have a merry go round and somebody spins the merry go round. You feel this force pushing you off the merry go round, right, But there's no force there. There's nobody pushing on you. It feels like there's a force. There's an apparent force what we call in physics a pseudo force, because you're accelerating, because you're rotating creates this pseudo force. So some things in the universe can create these pseudo forces that make it seem like there's a force when there isn't really one. And that's what space does. That's what gravity is. Gravity isn't a force. It's just that space is bent in certain ways, and objects like to follow the curvature of that space. So, for example, near a huge mass, space is bent and objects like to follow the curvature of space, which brings them towards the center of that mass. You jump out of an airplane, space is curved there. Because you're near the Earth and your natural motion is towards the surface of the Earth, and you need acceleration. You need a force to prevent you from moving in free fall, to work against the motion of space and time. So I understand Hans's question. Hans is like, hold on, you're saying the Earth is accelerating. How can it be accelerating up in the Netherlands and up from Perth? Right, it seems like it's going in two directions. And that's because you're thinking about the Earth as a single sphere moving in one direction or moving in the other direction. Instead, imagine it as a sphere with variable radius. Gravity is trying to shrink the Earth down into a dot, and the structure of the Earth is pushing back up and out in every direction. So the answer is that it's accelera up and out in the Netherlands and up and out in Perth. Both are out away from the center. If there wasn't that acceleration, if the whole Earth was just a bunch of particles following the curvature of space time, it would collapse into a black hole. That's what gravity wants to do. It gathers stuff together because it bends space, and then the motion of those particles follows that bend space and things fall together. So Earth has to push up and out just to maintain the same distance from the center. So it's counterintuitive because now I'm saying you have to accelerate just to maintain a constant distance from the center of the Earth. That's very counterintuitive, but it's true because their natural motion is to fall in towards the center, and you have to accelerate, which means counter your motion relative to gravity, to avoid doing that. So, yeah, Hans, the Earth is accelerating up under you and up under your nephew in Perth.
Who does that make right? That's the important question.
Let's just all sit down over a night, play the meat honey and work it out.
Oh no, let's never do that. Let's never ever do that, or at least let's not be told that we're eating meat honey if that's what we're having.
All right. Well, I hope that cleared it up for Hans. Let's send him o answer and see if he's got some follow up questions.
Hi, Daniel and Katie, thank you very much for your answer. It was very enlightening. It still seemed somewhat counterintuitive to me, but I believe I can now understand what you mean, in particular the idea that you shouldn't see the Earth as a solid object, but as a constant moving against gravity to maintain the shape instantly. This reminds me of Alison Wonderland. You have to run to stay in place. I hope this makes any sense to you. Thank you very much again, Hans.
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