An Honest Dad Ranking

Summary

The Rest Is Science – "An Honest Dad Ranking"

Podcast: The Rest Is Science
Date: July 8, 2026
Hosts: Professor Hannah Fry (A), Michael Stevens (B, aka Vsauce)

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Episode Overview

This Field Notes episode is a whimsical and thoughtful detour into the scientific—and familial—side of objectivity, measurement, and honest self-assessment. Michael shares the story of his now-infamous "Number 1,093,750,012 Dad" mug and the comically serious methodology behind his less-than-glamorous dad ranking, courtesy of his daughter. The discussion playfully unpacks how we measure, compare, and rank things we care about—even when the metrics are delightfully subjective. The episode branches into deeper questions about fair assessment, parental expectations, and the ways our brains handle uncertainty and fear, all while answering inventive listener questions ranging from sailing physics to the cosmic oddity of solar eclipses.

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Key Discussion Points and Insights

Michael’s Infamous Dad Mug & Honest Rankings ([04:13]–[11:41])

• Setting: Michael joins from Rotorua, NZ (jokingly "Rotten Rua" due to its geothermal sulfuric smell). He recounts family travels and his daughter's hilarious reaction—"Who farted?"—upon entering the notoriously smelly region.
• The Mug: Michael showcases his custom mug:
  “Number 1,093,750,012 Dad—not number one dad.”
• Method:
  • Michael felt "number one dad" was too boastful. He wanted a mug that reflected a real, data-driven rank.
  • He asked his 6-year-old daughter to place his dad ranking on a worst-to-best scale. She marked him in the bottom half.
  • He measured her mark, converted the ratio to a number out of ~2 billion dads globally, and added a random “12” for pseudo-precision.

    “I took that ratio, compared it to the 2 billion dads who are alive today, and that's how I arrived at 1,093,750,012. Then I added 12 to make it look less like a round number, like I had more precision.” – Michael [07:05]

• Self-Reflection:
  • Michael’s daughter cites too little screen time & candy as main complaints.
  • Hannah suggests a broader, weighted ranking—consulting teachers, pediatricians, and maybe a multidisciplinary "jury."
  • Michael finds humility, noting some dads face more challenges or make greater sacrifices and should be ranked higher.

Quote

“I've always thought number one dad on coffee mugs… is kind of braggy. OK? Like I am not, I'm not the number one dad. …I think growing not just as a dad, but as a person is a great thing a parent gets to do.” – Michael [05:05]

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Data Science, Fairness, and Multi-Dimensional Dad Ranking ([09:55]–[11:41])

• Hannah proposes:
  • A fair, multidimensional ranking—“Let’s do a principal component analysis and then we’ll find out who the real best dad is based on everything.” [09:55]
• Mom Ranking Revelation:
  • Michael shares an uncensored image of his daughter’s rankings for both parents. His wife scored even lower.
  • Michael muses the mug's “sad, competitive” twist, but now it’s “an important piece of family history.”

Memorable Moment

“It's barely in the bottom quarter. She barely makes it 25% of the way along the line.” – Hannah [12:07]

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Are There More Fathers or Mothers? Global Tally Debate ([12:52]–[15:31])

• They discuss stats:
  • Are there more mothers or fathers in the world?
  • Prompted by polygamy vs. polyandry and biological constraints (e.g., one woman can have fewer children than one man, in theory).
• Hannah references sexual partner statistics and the paradoxes arising in reporting and measurement—unknowns, cultural biases, estimation errors.

Quote

“You must have a pairing...and yet the statistics for each group individually are not the same. So you get into paradox territory very easily there. I really like it.” – Hannah [17:59]

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The Coffee Mug’s True Function ([18:19]–[20:11])

• Is the mug good to drink from?
  • Michael drinks Coke Zero from it (“delicious”), not coffee (runs too hot, prefers cold caffeine).
  • The mug’s physicality, he says, elevates the experience—“just so sophisticated.”
• Hannah suggests:
  • Get his daughter to update the ranking yearly. Predicts his rank will climb as she appreciates the story's gesture.
• Michael’s joy:
  • The mug video is his daughter’s favorite; she “loves the one about this mug the most because it's telling a story about us.”
  • The mug’s “number 1” appearance from a distance makes it an icebreaker.

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Listener Mailbag: Science Questions & Experiments

(1) Can a Fan Power a Sailboat? ([22:28]–[28:40])

• Question from Eli (Sydney, age 11): What's the most efficient way to use a fan to power a sailboat?
• Discussion:
  • Sail can't distinguish wind source, but on-board fan fails due to Newton’s laws—force cancels out (see [23:05]–[24:14]).
  • Mythbusters Experiment:
    • Fan + sailboat did barely move, but only due to air reflecting off the sail generating a net force [25:11].
    • The effect is real, but inefficient ("mad but great").
  • Eli’s Method:
    • Put a huge fan on a separate boat, blow wind at sailboat. Works physically, but impractical—energy waste, must stay extremely close.
  • Conclusion:
    • “Economically unhinged, but my favorite category of invention.” – Hannah [28:05]

(2) Manhattanhenge and Future Eclipses ([28:44]–[34:28])

• Question: Will the next Manhattanhenge solar eclipse be total or annular?
• Background:
  • “Manhattanhenge”: When the sun aligns perfectly with NYC’s street grid.
  • Total solar eclipses require a rare alignment; the moon is moving away, so in 600 million years, total eclipses will cease.
• Calculation:
  • Next total solar eclipse over NYC: May 1, 2079—not the right “Manhattanhenge” date.
  • After that, possible future alignments will likely be annular (ring eclipse) only.
• Playful Suggestion:
  • “If we lifted up and rearranged the buildings, we could get a true ‘Manhattanhenge total eclipse’ for six minutes in 2079.” [33:35]

(3) Why Are We Scared Running Up Dark Stairs? ([34:28]–[41:25])

• Listener’s Fear: Running up dark stairs is scary, but not running down.
• Scientific/Evolutionary Reasoning:
  • Fear kicks in pre-consciously—triggered by uncertainty and lack of visual input.
  • Our “AIC” (anterior insular cortex) responds to uncertainty by invoking physical unease.
  • Evolution: Humans (like prey animals) have retained fear responses from periods of nocturnal vulnerability—e.g., lions attack during dark, moonless nights.
  • Direction of movement matters: ascending (facing darkness) vs. descending (retreating to safety); possible interplay with heart rate, orientation, and evolutionary biases.
• Personal Anecdotes:
  • Michael shares his recent experience in the New Zealand bush—walking alone with no moon, realizing how truly dark nights can be without artificial light.

    “When there's a full moon, you can read a book outside at night…it looks like you live on Pluto or something.” – Michael [40:33]

• Consensus:
  • The fear is "completely rational and normal."
  • “I think it…activates fear responses from your body in, like, at least three different ways that going down doesn’t.” – Michael [41:25]

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Notable Quotes & Memorable Moments

• On Ranking Himself:

  “I don't want to be called the number one dad…there are dads who’ve made sacrifices I haven’t. So that’s why I don’t want the title.” – Michael [08:55]

• On Data Science and Fairness:

  “Let's do a principal component analysis and find out who the real best dad is…” – Hannah [10:37]

• On the Mug’s Story:

  “She loves the one about this mug the most because it's telling a story about us.” – Michael [19:35]

• On Running Up Dark Stairs:

  “It activates fear responses from your body in at least three different ways that going down doesn't.” – Michael [41:25]

• On Cosmic Coincidence:

  “At the moment, the moon is perfectly aligned so that during a solar eclipse, it completely blocks the sun, which is one of the strange coincidences of the solar system.” – Hannah [31:45]

• On Fear of the Dark:

  “There's an ancient part of your brain called the AIC…when it feels a sense of uncertainty, it pulls blood from your gut, quickens your heart rate…so when you have that gut feeling, it is your AIC that is responsible for that horrible feeling of discomfort.” – Hannah [34:28]

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Timestamps for Important Segments

• [04:13] – Michael introduces the “1,093,750,012 Dad” mug and its origin
• [07:05] – Calculating the dad ranking with "precision"
• [09:55] – Hannah’s multidimensional dad metric proposal
• [12:07] – Wife’s ranking revealed
• [18:19] – Michael on drinking from the mug
• [22:28] – Listener Q1: Fan-powered sailboats
• [28:44] – Listener Q2: Manhattanhenge eclipse paradox
• [34:28] – Listener Q3: The fear of running up dark stairs
• [40:33] – The cosmic importance of true darkness and the moon
• [41:25] – Final reflections on fear and dark stairs

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Tone and Style

• Conversational, humorous, warm, and intellectually playful.
• Generous with self-deprecating anecdotes and parenthood humility.
• Genuinely curious, with a talent for turning playful stories into deep scientific inquiry.

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Summary

This episode balances mathematical whimsy and scientific honesty. It explores measurement—of parenthood, celestial wonders, and primal fear—with both mathematical rigor and heart. Michael’s dad mug is both an inside joke and a jumping-off point for examining how we assess ourselves and others, a thread that weaves through tales of self-effacing fatherhood, scientific paradoxes, and profound evolutionary instincts. The episode is peppered with listener questions that spark delightfully sprawling conversations, always bound by science’s sense of fun, fairness, and curiosity.

Transcript

[A]

Welcome to the Rest Is Science. I'm Hannah Fry.

[B]

And I am Michael Stevens.

[A]

And this is an episode of Field Notes, our weekly detour into objects and stories that we've gathered from across the globe. And sometimes just from the shelves in our homes. But this week, your object, Michael.

[B]

It's my object. And yes, it's from across the globe. This morning I am in Rotten Rua. This is a little inside joke. It's actually Rotorua, a town in New Zealand in the north island, in the Bay of Plenty. It's geothermally very active here.

[A]

Hold on, I want to get the joke. How do you, how do you, how do you spell it?

[B]

R O T O R U.

[A]

A Rotten Rua.

[B]

My aunt in law calls it Rotten Rua because it smells rotten. It is a very geothermally active area. It's like Yellowstone in America. As soon as you drive in, you smell all this sulfur. Let me make this very brief. We drove into here from Auckland. So where did we stop along the way? You guessed it, Hobbiton. And it was beautiful. There was a rainbow in the sky as we stood outside of Bilbo's door. It was incredible. It was so exciting. My daughter fell asleep as we finished the drive to Rotorua and the smell came into the car as we approached. And she wakes up and goes, who farted? And I said, no, no one farted.

[A]

The Earth farted.

[B]

The Earth farted. And by the way, this is where we're going to stay for another nine days. So enjoy.

[A]

Yeah, thank goodness. You'll adapt to it quickly.

[B]

You adapt to it very quickly. Like it took about half an hour before we were like, wait, did we leave? No, but I mean, and it doesn't cling to your clothes apparently. This episode is brought to you by Cancer Research uk.

[A]

Scientists have found that cancer risks usually increase with age and size. But some species defy the odds.

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For example, deep sea Greenland sharks, they can grow over 6 meters long, weigh more than a small car and yet live for up to 400 years.

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Now, understanding how Greenland sharks, cellular repair and immune systems seem to have managed to keep them cancer free for centuries, that could open up exciting research pathways,

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So by exploring the unexpected, Cancer Research UK scientists are uncovering new ways to tackle over 200 types of cancer. Their work has helped to double survival in the UK over the last 50 years and continues to save and improve lives around the world.

[B]

For more information about Cancer Research uk, their research and breakthroughs and how you can support them, visit CancerResearch UK. This episode is brought to you by Google Chrome. You think you know a browser, but Gemini and Chrome? That's new. It can help you with practically anything on the web, like restoring a vintage motorcycle from a 50 page restoration block. Or finally break down that long article you've had open for weeks. Gemini and Chrome is here for it, ready to make anything online make sense. There's no place like Chrome. Check responses set up required compatibility and availability various 18 are all batteries the same? That's like asking if all soccer players are the same. Take Messi, the most decorated player ever. Is there any other player who has achieved that? No, just him. Now take Duracell. Is there any other battery with powerboost ingredients inside? No, just Duracell. Remember, goats only trust goats because they're built different. And Messi only trusts Duracel. Anyway, speaking of my daughter, the object I want to show you today is the mug that I'm drinking out of. Did you see my short about this mug?

[A]

I did and I loved it. Tell us the story though.

[B]

I'll tell you the story and then I'm going to reveal a bit of the story I did not tell you on YouTube. Okay, this is the uncensored full story

[A]

for people who are listening rather than just watching. At the moment, Michael is holding a mug. It looks like it could hold a decent cup of coffee, I'll tell you that. And it says number 1,093,750,012 dad, not number one dad.

[B]

It's an honest ranking of myself. Now I would have ranked myself higher. I would have chosen like, I don't know, maybe top half a million.

[A]

How many dads are there?

[B]

Very good question. I had to look this up. Apparently there's an estimated 1.5 to 2 billion dads alive on earth right now.

[A]

So you're not even top 50%.

[B]

I'm not even in the top half. So I've always thought number one dad on coffee mugs or barbecue tools is kind of, it's kind of braggy. Okay? Like I am not, I'm not the number one dad. I'll admit that. You know, I, I, I aspire to number one. I forward to growing. I think growing not just as a dad, but as a person is a great thing a parent gets to do. Look, I want something also that it would just be funny if the mug ranked me for real. Or it tried to now. I would have put myself in, like, the top half million or so.

[A]

That's pretty braggy.

[B]

Is that still braggy? So I looked it up, and by looked it up, I mean I just Google searched it, and I looked at, like, a few links, and they all kind of said there might be one and a half, maybe 2 billion dads total alive right now on Earth. So that's your. That's your kind of bounds here, between 1 and 2 billion. Where do I fall?

[A]

Top million is like half of a thousandth of a percent.

[B]

I know that would be really high when you think about it. So I'm kind of happy that that didn't happen. What happened is I said, well, I got to ask my daughter now. She's six years old. And so what I did is I drew a line on a piece of paper, and I. Cause she. She. She understands, you know, On a scale of 1 to 10, where would you rank something? So I said, here. This is basically what that is. On a scale of the worst dad in the world to the best dad in the world, where would you put me? And she put me in the bottom half. And I didn't know what to do. I'm like, well, this is what she said. Now this has got to be how I rank myself on the mug, because it's what my daughter said. I can't. I can't ignore that. But I do wish I was higher. Now, what I then did is I measured where her mark on the line was, and I took that. That ratio and I compared it to the 2 billion dads who are alive today. And that's how I arrived at 1,093,000,750. But then I added 12 to make it look less like a round number. Like. Like I had more precision.

[A]

This was exactly where my next question was going. Because if you are. If you're at 1 billion, right, something's on the zone. You're measuring to nine significant figures.

[B]

I know.

[A]

What kind of laser electron microscope were you using to work out where she put her mark on this line? But now you've clarified it still, though, you're still measuring to what six significant figures were you?

[B]

Well, yeah. So, I mean, trying to remember exactly how I did this. I mean, 750. This is just a quarter. So did I really just. Was I really that specific? I must have been, because after I did the Math, I had 750,000 and a bunch of zeros. But, no, I wasn't counting how many atoms were on either side of her mark. Now, I love this. So. So she and my wife Then turned it into a custom mug. And I think it gives me something to aspire to, to be better. My daughter, I asked her why do you really think I'm in the bottom half? And she's not really happy with the amount of screen time. She's not happy with the amount of candy she's allowed to have.

[A]

I'm not sure if she would be the best person to assess how good a dad you are though. You know, for those exact reasons, I think that, that her opinion is biased. And actually I don't, I don't, I don't think you take her word for it. I think what you should do is you should go around to all the people who would be capable of making this assessment. So your wife, her school teachers, maybe a pediatrician, you know, all kinds of different exper. And then I think you should weight their responses accordingly, get a fair, proper metric.

[B]

I know. Rather than just asking a 6 year old who really doesn't, I think know yet all the different ways a dad can be. I should have empaneled a jury that would actually rank me in their experience or maybe, maybe I'll do that next year. But I think in some ways I also kind of think it's fair. Like I don't think I'm a bad dad. I don't think that I've had a lot of challenges. I'm lucky enough that I haven't had to make a lot of the same sacrifices that other dads have. So I'm happy for them to be ranked above me. Like, what makes you the number one dad? It can't just be that you're fun and like you've never had any kind of struggles. Like there are dads who've had a hard time and they've done much more heroic things and harder things. They've, they've made sacrifices that I haven't. Like, I just. So again, that's why I don't want to be called the number one dad.

[A]

My fundamental problem with this is that you're essentially, you're essentially ranking dads on one scale, right? Which is that, you know, you're, you're, I mean, you're, you're literally creating a ranking of them. And so you've got to weigh up all of these things simultaneously. I think that what we should do is we should have a multi dimensional dad ranking system, you know, because, and then I think that you can say I'm the 1 billion, what was it, 93,750,012 dad, according to this particular Metric in this particular dimension. I mean, look, let's take a proper data science approach for this. Let's do, let's, let's, let's, let's take all of the different variables, let's do a principal component analysis, and then we'll find out who the real best dad is based on everything.

[B]

And then we could do it to moms, which. This brings me to the secret part that I have not revealed yet. So we'll show on the screen the actual picture that my, my daughter drew ranking me on this line. Okay. So as you can see, it's in the bottom half. It's just, it's just a pencil line. And she made a little tick mark down a little bit low, in my opinion. That's what I showed in my video. But I'm going to send you, I'm going to, I'm going to message you, Hannah, the full image. I removed some of what was on that page just to avoid the distraction because a short can only be so long. Okay, so I have just sent Hannah the unredacted, uncensored ranking.

[A]

Is one of these for your wife? It is. Oh, lordy. Okay.

[B]

Yeah. Because of course, after I had my daughter rank me, my, my wife couldn't help but be like, okay, but what about me? So she drew a line and said, worst mom to best mom, where would you put me? And here's the results, listeners and viewers.

[A]

Okay. The only thing I can't tell is which one is which. But should I give you my guess? Because one of them has all the hallmarks of being written with a mechanical pencil.

[B]

Ah. Okay. Yes. And for those of you who are just listening, I'll just, I'll explain that. We're just looking at the back of, I think it's a, an envelope and like a ripped up envelope and it's got two horizontal lines with tick marks on them. One of them has a tick mark that's even closer to zero than the other.

[A]

Yeah. One of you did worse out of this than the other. Okay, I'm gonna guess that your wife did worse. She did. Yeah, she did. Oh, that was brutal. I mean, it's barely in the first, it's barely in the bottom quarter. You know, she barely makes it 25% of the way along the line.

[B]

Well, to be fair, I think my wife had suggested brushing my daughter's hair that morning, so that knocked her down a lot.

[A]

Absolutely fair.

[B]

Yeah. No, I felt terrible when she, when my daughter ranked my wife below me. I'm like, oh, no, this, this father's day gift is turning into the saddest, most competitive thing I never wanted it to be, but it's an important piece of family history. Now, this, this ranking, how many mothers are there?

[A]

Are there a similar number of mothers, or are there more mothers than fathers?

[B]

That is such a good question, and I did not come prepared with an answer. Well, I mean, let's just do a search. I'll do the exact same completely unrigorous search. All right, so soundvision.com statistics about mothers around the world. They say there are 2 billion mothers in the world. And 2 billion is about the same number I get when I look up. How many fathers are there? There's a Reddit thread from. They did the math and they put it at, whoa. This. This person calculated 1.06 billion moms. That's half as many as that other figure.

[A]

So I was gonna say, actually, if I would guess, I would guess it would be lower, right? Because there is a physical upper limit on the number of children that one woman can have. And so you get people like, you know, Elon Musk, right, who's got, like, unknown number of children, or Boris Johnson, unknown number of children with many different moms. So I would guess that the number of mums. Whereas I don't think you very often get it the other way around where someone has, like, 15 children. You know, where one woman has, like, 15 children.

[B]

Right? So the things we're considering are if a mother has multiple children with multiple men, then those kids all have just one moment. But they've. But there are a lot of dads that have been created in that scenario.

[A]

Agree, agree. The reverse is also true. However, there's less of an upper limit.

[B]

Right.

[A]

You see what I mean? And so I reckon the average number of kids per dad is higher slightly, possibly. Which means that the average number of dads or the number of dads should be lower. It's my guess, you guys, you're saying

[B]

the number of dads should be lower. Yeah. So the mom category is more competitive.

[A]

There's more in it. Look, this is my. I'm basing this on no evidence whatsoever, right? Just. Just having a story about Boris Johnson and Elon Musk in my mind.

[B]

Well, but I mean, this is. This is a part of, like, critical thinking. You know, let's figure out, like, how do we approach this, not having already consulted the experts? And. Yeah, so I don't know. My. My wife, her number might even be, like, what if her number was the same? Because even though she was lower, it was out of more moms. Wait, would that work?

[A]

Yes. Yes, it would.

[B]

Yeah.

[A]

No, wait, you'd be the other way around. Sorry, It'd be the other way around.

[B]

She would need to be higher to have the same rank. Yeah, right.

[A]

Oh, the thing that this reminds me of is there has been like really extensive research into the number of sexual partners that men and women have in heterosexual relationships. So it's a bit of a heteronormative story. But what's really interesting is that when it comes back, the average number of partners that men have is higher than the average number of partners of females. Okay. Which sort of doesn't make sense because in the same way as when you have children, you kind of have to have a matching. Right. So there were early suggestions which I think were basically founded in sexism, which said, okay, well, the reason why this still works is because most women have a smaller number of sexual partners than most men. But there are some women who have an extremely large number, and if they're not included in the sample, then that skews the average. And that's what's going on anyway. Turns out that's almost. Well, it's almost certainly not the case. Certainly not the reason why you see these differences in numbers. The first reason, actually, that you can get this real clue when you look at what the numbers actually are. If you look at a distribution of the numbers of sexual partners and women's has this, like, very neat distribution, sort of as you would expect. You know, you've got like sort of nice tails on either side of the distribution or on one side anyway, because it's sort of cut off at zero, isn't it? It can't have negative. Well, you can have negative encounters, certainly, but not.

[B]

You can.

[A]

But when you look at men's, right, you don't see that same pattern. Instead you see these really big peaks at numbers that are divisible by five, essentially. And there's two reasons for this. Two reasons for this. One is that women are more likely to say, this is like evidence. Back to stuff. Okay, this is not just sort of hearsay, although I am doing this from the top of my head, so please correct me in the comments if I've misremembered this. But women are more likely to say, okay, there was this person and then this person, and then count upwards, but like thinking of each individual person. Whereas guys are more likely to estimate and be like, wow, five a year for 10. You know what I mean? For this many years equals this. Yeah.

[B]

Oh, fascinating.

[A]

And also, women are because of sort of cultural expectations more likely to estimate downwards, whereas men are more likely to estimate upwards.

[B]

Right.

[A]

But anyway, I just, when you have, I find those kind of problems very, it's like weirdly, mathematically interesting where it's like, you know, there must be a pairing. Let's be a mum and a dad. And yet the statistics for each group individually are not the same. So you get into paradox territory very easily there. I really like it.

[B]

I like it too.

[A]

I've got the most important question though, about your mug. Does it taste good when you put coffee inside it? Because I think some mugs, coffee tastes better in some mugs than others.

[B]

I'll tell you, Coke Zero tastes delicious out of this mug. That's what's in here. I find I used to drink coffee all the time. Yeah, I drank so much because my dad did. He would brew up a whole pot of coffee just before bed. He thought it was really cool to that he, he could like drink coffee in bed and then still go to sleep. I got really into it today. I'm just too, I run too hot. Like, literally temperature wise, like a hot beverage just makes me too hot. So I drink cold, cold caffeine.

[A]

But does it taste good?

[B]

It tastes good. And there's something about the physicality of a mug. It's just like so sophisticated. It makes me think, it makes me savor. I can just do a little like, you know, I'll do a little slurp, little ASMR Here, go on. Oh, that sounds like coffee, but it's not.

[A]

Well, I think you should get your daughter to update her line every year. And I suspect that as she gets older and sees that you put that number on a mug in honor of her drawing, I strongly suspect that your, your number will increase.

[B]

I would, I would hope so. I hope, I hope I earn it though. But I will say that of all the, the shorts I've made, she loves the one about this mug the most because it's telling a story about us, you know, and so, yeah, maybe she'll, maybe she'll take it a little bit more seriously next year. I'd love to crack into the top billion at least. Like goodness. It is funny though, that being the number 1 billion, 93 million and so on, dad means that from an angle it almost looks like I have a number one dad mug. And then I can be like, psych, I didn't win the competition. I actually barely placed.

[A]

Okay, should we go for a break? And when we come back, we'll be answering some of Your questions. This episode is brought to you by Cancer Research uk. What if your immune system could learn to recognize cancer cells?

[B]

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[B]

For more information about Cancer Research uk, their research breakthroughs and how you can support them, visit cancerresearchuk.org restiscience this episode

[A]

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[B]

Okay, we are back. And first up, we've got a question to Hannah from Katherine and Eli. Here's the question. Hello. I'm writing on behalf of my son eli, who is 11 years old. He's a budding scientist and sailor in Sydney, Australia. He loves your show. He never misses an episode. Eli's question, what would be the most efficient way to use a fan to power the sail on a sailing boat? Eli's idea, put a huge industrial fan on a second boat which would motor next to the target boat. Thank you in advance, Catherine.

[A]

I absolutely love this. I love this question. This is my favorite bit of the week, by the way, when we get to answer this question, especially when they're like little ingenious ones like this. Because the thing is that the intuitive logic is there. Right. You know, like a sail can't distinguish between wind that's created by the sort of geophysics of the earth and wind that's created by a fan. And so if you stick a fan on a boat, it should sort of make sense that it would move the kind of traditional. I mean, Eli's not the first person to have had this idea. And the kind of traditional formulation of this is that you just put the fan on the same boat so you have it on the same deck. Just point it at the. Of the sale. And when people had, like, worked this through, they had come to the conclusion that it wouldn't work at all because of Newton's laws of motion. So every action has an equal and opposite reaction. So it would be like sort of trying to move by kind of pushing your hands together. You know, it sort of. It doesn't. It doesn't really work. Right.

[B]

Yeah, Right. The fan will blow onto the sail and push the sail forward, which will pull on the boat. But yet by pushing air forward, the fan gets pushed back and they're even. So the boat's getting pushed forward and back at the same. Doesn't go anywhere.

[A]

So it doesn't go anywhere. And that is definitely true. If you do small models of this, if you kind of build versions of it to see whether what happens on a car or whatever instead of necessarily on water, then it's absolutely true. Right. Like Newton's laws hold. It's all, you know, no laws of physics are broken and the boat doesn't move. However, Mythbusters, that amazing program with your friend Adam Savage, in fact, they did a version of this where they got this, like, massive swamp boat, which are generally driven by fans anyway, and they reversed the fan round and then had it blowing into a sail. And I mean, normally this boat. Right. When it doesn't have a sail there, can go at 20 miles an hour.

[B]

Right.

[A]

Can kind of zip along the water. But when they had the sail and the fan and it did move forward. It did, but only by about three miles an hour. So like a really, really small amount.

[B]

This is surprising. I'm surprised one because I've never seen this episode.

[A]

Uh huh.

[B]

Which is unusual.

[A]

Yeah.

[B]

And I expected something weird as soon as you started telling this story. I'm like, oh, it must work in some way. So why. What was the explanation for how they're able to blow themselves forward with a fan that's on board?

[A]

Okay. So there's arguments about this. Right. Like, if you want to see a couple of scientists get into a fight, ask them about aerodynamics in general, because it's really difficult to prove which force is the kind of dominant one one way or the other. You know, ask a pilot about the difference between Bernoulli and Newton, and they'll sort of descend into horror. But this is another one of those examples where basically people have got into massive fights about it. No one is perfectly sure, but I think. I think the most convincing argument is that the sail doesn't just absorb the air that's being blown towards it. It ends up reflecting some of that air backwards. And so in reflecting that air backwards, then the opposite reaction is that the sail moves forwards.

[B]

I see.

[A]

So that there's, like, an additional effect.

[B]

There's a net forward force on the boat because the reflected air doesn't then get reflected back and forth and back and forth. Eventually, it just leaves out the back.

[A]

Yeah.

[B]

Meaning the boat goes forward not as quickly as it would.

[A]

Not as quickly as it would. But I mean, in general. Okay. Like, in general, putting a fan on the same boat as a sail is like, it's not a good idea. Eli's version is. It's way smarter. Right? Way smarter, which is that he suggests that you put a fan on a boat behind and then blow the fan in, and then now Newton's not a problem. Right. You don't have to worry about equal and opposite reactions because the two things are physically separated from one another. This would totally work. Right. Only slight problem about it is that a jet of air, actually, it sort of falls apart really quickly. You know, it doesn't sort of keep its strength very quickly. It fans out, it sort of drags other air in, or the still air loses its speed and so on and so on. And so you would have to have the fan, like, absurdly close to the sail that it's blowing, and also it would have to go along with it. Right. So your. Your boat with the fan on, it would have to be propelled along and be, like, extremely close to the sail that it was following, at which point you've sort of got a boat that's already moving, and you may. You may as well just use a rope instead, you know? So, I mean, in terms of the laws of physics, it's perfectly legal. Economically. Unhinged, I think, is the. Is the best description of what he's come up with. But ultimately, that's my favorite category of invention, so fine by me.

[B]

It would look amazing, though, if I looked out on a lake And I saw a boat being blown by the fan in another boat. Yeah, I would. I would watch. I would love that. I'd love to see a race like that. Because, of course, yeah, it becomes, like, hilarious because the boat with the fan on it is going to have to be using much more energy to keep up because it's. Its fan is blowing it backwards. So it's got to work even harder to move forward and keep up with the boat it's pushing and all the

[A]

energy of the actual fan itself. Yeah, I mean, it's mad but great.

[B]

Mad but great. That should be one of the catchphrases of this podcast.

[A]

Absolutely.

[B]

Now, here's a question from Sever or Steve. Steve asks Michael. In about 600 million years, the total solar eclipse era will be over. The moon will have drifted far enough from Earth that we will only experience annual eclipses. This, of course, leaves us all wondering the same thing. Will the next manhattanhenge solar eclipse be total or annual? Okay, so I love this question because I didn't know. But I'm a huge fan of Manhattan Hinge. Manhattan Hinge is a phenomenon that was first described by Neil DeGrasse Tyson. It's based on Stonehenge in England, where these stones appear to be aligned with the sun for the solstices, the winter and summer solstice. And on those dates, the sun is like, it's lined up on certain stones, blah, blah, blah. The details don't matter. What matters is that any big monoliths could be assumed by future civilizations to also be aligned with the sun. So now, picture. Picture you are a future archeologist. It's the year 5000, and you've uncovered the ruins, these ancient ruins of New York City. And you notice that, of course, this was a celestially important religious site because four times a year, the city aligns with the sun. On May 28 and July 13, the sun sets exactly in between the buildings on either side of a block. And on December 5 and January 8, the sunrise happens perfectly in between the skyscrapers. So clearly that's why it was built the way it was.

[A]

That's cool. That's cool.

[B]

And Neil DeGrasse Tyson calls this the Manhattan solstice, the Manhattan Hinge. What Steve is asking us is, will the next solar eclipse that happens right in between the buildings on your left and right as you look down a New York block, will that be a full total solar eclipse? Because solar eclipses happen a lot. They happen a lot. They just don't happen right where you are on Earth. Very Often because the Earth is a big place. And he points out correctly, that total solar eclipses are not going to be around forever. The Moon is drifting away. In fact, the moon is drifting away at a very funny speed. And I calculated a funny way to keep this in mind. If every morning you woke up and you painted a layer of paint on the bottom of your shoe, and then you walked around, the next morning you woke up, painted another layer on top of that layer, you would be leaving Earth just as fast as the Moon is leaving Earth.

[A]

Feels like a deleted scene from Twits.

[B]

Yes, it's, it's, it's not fast, but. But the Moon is getting further and further away at the moment. The Moon is perfectly aligned so that during a solar eclipse, it completely blocks

[A]

the sun, which is one of the strange coincidences of the solar system that it should be 400 times smaller than the sun and yet also 400 times closer. I mean, it is a complete fluke that we get total solar eclipse.

[B]

We were born at just the right time to see such a phenomenal event as a total solar eclipse. But in 600 million years, sorry, there will be no more total solar eclipses. The moon will be too far to be large enough in angular diameter to completely block the sun. So will there be a total solar eclipse over Manhattan that is also aligned with Manhattan hinge before we lose the Moon? Well, at least before the moon is too far away to give us a beautiful total total solar eclipse. And the answer, I'm pretty sure, is no. The problem is that the, the next solar eclipse in New York city is in 2079, not that far from now, but it's going to be on May 1st.

[A]

Right. It needs to be on the correct date.

[B]

It needs to be on the correct day. So we need a lot of things to align. We need there to be a solar eclipse that is over Manhattan. It also needs to fall on one of these four days. May 28, July 13, December 5, January 8. It also has to be at sunrise or sunset. And those variables are not going to align in the next 600 million years. They probably will align at some point, but at that point, the eclipse will be annular, meaning you'll just see this ring of fire. You'll see the sun with the moon silhouetted in the middle of all of those three things.

[A]

The sun, the Moon, the Earth. I strongly suspect that the Manhattan grid will not, will not be around by the time there's the next one.

[B]

You know, I think you're right.

[A]

Is a bit ambitious. Ambitious.

[B]

I think Guess what? Here's talk about ambitious. We have time. The next total solar eclipse over New York City, 2079, on May 1. It's not too late to start moving all the buildings, okay? If we lifted them up, laid them down at a different angle, redid all the streets, we would be able to catch that 2079 total solar eclipse and have a total eclipse of the sun right in between the buildings. Wouldn't that be a really cool six minute payoff?

[A]

I think it's time we had something that brought us together, you know, I think it's time we had something to work for, something that everybody could get behind, something that was a sensible moonshot that everybody collectively around the world could celebrate. I don't see any problems with this. Get Mandani on the phone. Okay? Okay.

[B]

All right, I'm on it. Let's do it. Perfect. This is going to bring humanity together.

[A]

Okay, one last question. This is from Clayton. Clayton says it might just be my fiance and I, but we wondered, why do we get instinctually scared running up dark stairs? And why do you not feel the same running down dark stairs? Might be a silly question, but I can't get rid of the fear even if I try. Well, okay, I don't know if this is a silly question or a silly fear. I think that the thing about fear is that it happens at a level that's sort of beyond your conscious control. And so I think once you've decided that something is to be fearful of you, you kind of sort of. It's. It's a little bit out of your hands. One thing I will say about being scared of the dark is completely legitimate and makes a lot of sense. There's a number of different reasons for this. For one thing, you've got this loss of visual information, so your brain is having to make guesses about what's out there. We've spoken about this before on this podcast, but we are predisposed to absolutely despise uncertain, right? We really dislike it. It makes us feel extremely uncomfortable. There's like, a very ancient part of your brain called the aic. It's connected to all of your internal organs, right? So it's sort of like the monitoring system for your internal organs. And when it feels a sense of uncertainty, it essentially reacts by, like, pulling blood from your gut, by quickening your heart rate, and then reports those same physical sensations back to your brain as, like, something is not right. So when you're, like, in. When you have that gut feeling, it is your AIC that is is Responsible for horrible feeling of discomfort. And it's all happening sort of below the conscious level. The other thing about being scared of the jar, well, so there's all these lovely theories about how it's actually sort of founded in a kind of evolutionary history. So there's this really famous study where they were looking at this data of lion attacks on humans from Tanzania. And there'd been 500 attacks on people over a couple of decades. And basically the lions deliberately attack when the moon is really faint or below the horizon really. So when there is as little light as possible. And essentially the lions have worked out that they can exploit the differences. I mean worked out's a bit strong, sort of giving them agency that I don't think that necessarily is, is appropriate in this, in this particular context. But, but our eyesight is so weak when it's very dark and their eyesight is so much stronger, they have a massive advantage. I think that this is the idea generally that when we, we have this sort of biolog memory of when we were hunted, that same fear sort of presents itself when we're in the dark. So I think being scared of the dark actually is a completely rational and normal thing. The stairs thing though, stairs thing is interesting. Do you have this experience dark stairs?

[B]

Yes, of course. Like as a kid I remember being terrified when the lights were turned off in my grandparents basement while I was down there and I had to run up the stairs. There was this primal fear that something would be following me, chasing you up, going down into the dark. I just feel like there's something deep about which way you're facing that matters. If the darkness is behind you, you are one not able to see what's behind you. But you're also, you've got two vulnerabilities there. You're going up and you're also in the dark. If you're going down, you can retreat.

[A]

You know where you've come from.

[B]

I don't know if there is like maybe a fear of heights involved there or if just the act of going up the running up the stairs also gets your heart rate going just like fear does. I think there might be a bunch of modalities all mixing together to increase the physiological fear symptoms. It wasn't until literally last week that I realized how dark the night is with no moon. This is almost a bit of a religious experience. I've lived in places that had artificial light at night, everywhere. You know, maybe not always a lot, but enough that every night sort of felt the same. But I just came from Living off the grid on this island, the moon is such an important part of our environment. Like, of course, every fantasy novel set in medieval period talks about the moon all the time. Because when there's no moon at night, it is too dark. You can't see where you're gonna step next. But when there's a full moon, you can read a book outside at night. It was so beautiful.

[A]

Wow, that's amazing. I'm very jealous.

[B]

You gotta experience it. Because it was like nothing I'd ever felt before. And then, of course, every night is different. As the moon waxes and wanes, you feel each night is going to be different and the moon rises and sets at different times. So there'll be that moment in the night where the sun is down, but the moon isn't up yet and it's just pitch black. Here's another thing I learned about myself. I'm just like, not scared of the dark in the same way I used to be as a kid. I was walking through the bush to get back to our house in the middle of the night, Clear night, but no moon at all. And I turned off my flashlight to see if I could scare myself because I was all alone on this path in the middle of the bush. And I just sat there or I stood there in the dark and I just wasn't scared. I know I'm kind of bragging at the moment, but I just, I could not.

[A]

I couldn't. The number one billionth dad was okay in the dark. You go.

[B]

I'm just saying maybe I should tell my daughter this story could be impressive to her. I think it helped to know that I was in New Zealand. There were no venomous anything. I guess if I'd heard some twig

[A]

snapping, that would have been a bit scarier.

[B]

That would have been different. I probably would have just thought it was someone's dog, though.

[A]

That whole point about how connected the moon was to our history, you know, the whole idea of lunacy, right, that like, ah, yeah, people kind of go crazy at full moon. There's sort of something to it, but not, not in the sense that, you know, our, our mental state alters, but that actually when it was full moon, you know, people who liked doing things under the COVID of darkness had to change their behavior. You know, you would get more, more burglaries, you would get sort of more nefarious activity going on.

[B]

Yeah, of course, because the full moon is very bright. And again, if you live where people have street lights and external lights on their homes and all this Artificial light every night. Every night can feel very similar, and yet they are so different that, yes, when it's pitch dark at night, there's a new moon or it's overcast. You can't do anything outside if you don't have your own artificial light. But when there's a full moon and a clear sky, you can read a book. Your shadow is dark and crisp, and it looks like you live on Pluto or something. It's like it's daytime, but the sun's far away.

[A]

Amazing.

[B]

It's really. It's really amazing.

[A]

That's gonna be my next holiday attempt, is to go somewhere genuine dark sky place.

[B]

Do it.

[A]

Yeah, that sounds amazing. All right. Okay. I guess that brings us to the end of this episode. Just to wrap up the question here, Clayton, we don't know, but we agree that it's scary. I think that's sort of the ultimate conclusion that we can come to.

[B]

Yeah, Yeah. I think it. I think it. It activates fury responses from your body in, like, at least three different ways that going down doesn't.

[A]

Well, okay, as ever, you can send us in your questions to theresdo scienceoalhanger.com and we will be back for another main episode and then another episode of Field Notes next week.

[B]

Until next time, stay curious.

[A]

Bye.

[B]

Bye.