Episode Summary
Executive Summary: In this episode of The Rest is Science, hosts Michael Stevens and Hannah Fry explore the nature of gravity, from Newton's classical view to Einstein's revolutionary concept of curved spacetime. They discuss how gravity is a fundamental force that attracts objects with mass, its weakness compared to other forces, and the ongoing mysteries like dark matter and gravitons. The conversation includes experiments with fish in microgravity, the warping of time, and the possibility of extra dimensions, all while emphasizing that gravity remains one of the most profound puzzles in physics.
Main Topics: Explaining Gravity to an Alien: The hosts discuss how to describe gravity to an alien from a universe without it, focusing on the attraction between objects with mass and the concept of inertial vs. gravitational mass. Newton vs. Einstein: Two Views of Gravity: Comparison of Newton's force-based gravity with Einstein's general relativity, where gravity is the curvature of spacetime, explaining phenomena like Mercury's orbit and time dilation. Dark Matter and Unresolved Mysteries: The discovery of dark matter by Fritz Zwicky to explain galaxy rotation speeds, and the ongoing search for gravitons and understanding gravity at quantum scales. Gravity's Weakness and Extra Dimensions: Discussion of gravity's extreme weakness compared to other forces, and the hypothesis that it may leak into extra dimensions, explaining its feeble nature. Microgravity Experiments and Biological Effects: Experiments with fish and octopuses in space showing how organisms adapt to microgravity, and the importance of gravity for bone development in humans. Black Holes and Schwarzschild Radius: Explanation of black holes as regions where gravity is so strong that light cannot escape, with a demonstration using a tungsten sphere the size of Earth's Schwarzschild radius.
Key Arguments: Gravity is an attractive force between objects with mass, but it is extremely weak compared to other fundamental forces. Einstein's general relativity describes gravity as the curvature of spacetime, which explains phenomena like Mercury's orbit and time dilation near massive objects. Dark matter was proposed to explain why galaxies spin faster than expected based on visible matter alone. Gravity may be mediated by hypothetical particles called gravitons, but they have not been detected and would require a galaxy-sized particle accelerator. Extra dimensions could explain gravity's weakness if it leaks into those dimensions, but experiments at micron scales have not found deviations. The rubber sheet analogy for gravity is flawed because it relies on gravity itself to demonstrate the effect.
Data Points: Time difference between Boulder and Greenwich: 5.6 microseconds per year - Due to gravitational time dilation, time runs slower in Greenwich (lower altitude) than in Boulder (higher altitude). Gravitational acceleration in Boulder vs. Greenwich: 9.796 m/s² vs. 9.812 m/s² - Boulder's higher altitude results in slightly weaker gravity compared to Greenwich. Gravity's relative strength: 10^-38 times weaker than other nuclear forces - Gravity is incredibly weak compared to the strong nuclear force, electromagnetic force, and weak nuclear force. Earth's Schwarzschild radius: 8.87 mm - If Earth's mass were compressed into a black hole, its event horizon would be 8.87 mm in radius. Time for two baseballs to collide in space: 3 days - Two baseballs placed 1 meter apart in intergalactic space would slowly attract and touch after 3 days due to gravity.
Pivotal Quotes: "The gravitational influence of Pisces on you is less than the gravitational influence of the doctor who delivered you." — Michael Stevens: Explaining that nearby objects have a stronger gravitational pull than distant stars, debunking astrological claims. "If you take a piece of paper and you imagine that you have an ant living on this piece of paper... you can fold the piece of paper and make A and B combine in the same point, right? You can effectively create a wormhole that the ant didn't see coming." — Hannah Fry: Using Richard Feynman's analogy to explain how extra dimensions could allow for phenomena like wormholes. "If that was a black hole, its mass would be the same as the Earth. The entire Earth. You know, yeah, in the entire Earth, everything you've ever known or experienced." — Michael Stevens: Demonstrating the Schwarzschild radius of Earth with a tungsten sphere, illustrating the extreme density of black holes.
Implications: Understanding gravity is crucial for cosmology and quantum physics. The search for dark matter and gravitons could revolutionize our understanding of the universe. Practical applications include GPS corrections for time dilation and insights into the nature of spacetime.
From the Episode
It cannot overcome the air it would have to push out of the way, the friction between our butts and the seats, but yet we are attracted. In fact, when you're born, right, you've got some zodiac constellation that's like, I don't know, it's how does astrology work? Something, something, Pisces, right? Okay, so, okay, you're a Pisces if you're born in a particular time of the year, but yet the gravitational influence of Pisces on you. Is less than the gravitational influence of the doctor who delivered you on you. Because otherwise, birth ain't working. That's why, yeah, people are like, oh, so you're an Aquarius. And I'm like, no, I'm a schnitcookie. Because Dr. Schnitcookie was there influencing me physical level. Yeah. Not just the catchy, not just the physical touch, but the gravitational attraction to his mass. Right. It's been with me my whole life. Where is he now? Hey, now I want to be this alien again. And I want to say, all right, so I.
Earth and the sun. Yeah, it's where the analogies break down. The one that I do like, and I think this was Richard Feynman, was he was saying the reason why it's difficult for us to imagine additional dimensions. If you take a piece of paper and you imagine that you have an ant living on this piece of paper, and the ant is so small that it's effectively two-dimensional, right? It cannot conceive of up and down because even when it climbs up a wall, the curve between or the corner between the ground and the wall is so tiny that it's like it feels like it's just this continuous. Continuous surface. But if you take an ant on a piece of paper and you say, This is point A, this is point B, and you ask the ant what's the quickest way between these two points, the ant's going to say, oh, it's a straight line between the two, right? Which is like, yeah, great, well done, ant. But you could take that piece of paper, and because we have an additional dimension, we have three dimensions, whereas the ant only has two, you can fold the piece of paper and make A and B combine in the same point, right? You can effectively create a wormhole that the ant didn't see coming. And this is sort of a way to explain.
Thinking is something extremely dense. Yeah, we're talking about black holes. Black holes. So if this was a black hole, is this the size of the Earth if you squished it down to the density of a black hole? That's right. If that was a black hole, its mass would be the same as the Earth. The entire Earth. You know, yeah, in the entire Earth, everything you've ever known or experienced. Everything that's here, you don't throw any of it away, you just squish it down to that size. Then you'd be close enough to enough mass, you could never escape that. That is. Earth's Schwarzschild radius. If you did manage to create a black hole this size, let's maybe not use the matter of the Earth to leave us alone. I'd sort of, you know, prefer that everyone I've ever loved remained intact rather than compressed down into sort of infinite density. But let's say that you could manufacture a black hole this size, then experimentally, be way easier to find gravitons. Yes, it would. And then we might actually have an answer. And that's why I think someone should.
About The Rest is Science
Join mathematician Professor Hannah Fry and science creator Michael Stevens (Vsauce) as they dig into the weird scientific questions that often go unexplored. Welcome to The Rest Is Science, a show that sits in the fascinating space between what we think we know, and what we actually know. Why do we assume we understand things like time, randomness, or even gravity? Once you start questioning these familiar ideas, reality becomes astonishingly strange and completely fragile. Whether you're a lifelong science fan or just naturally curious, The Rest Is Science will change your perception of reality, and prove that the biggest questions are always the most fun.