The Rest Is Science – "We're All Being Pulled Together"

Podcast Hosts: Professor Hannah Fry and Michael Stevens (Vsauce)
Release Date: November 25, 2025

Overview

In this episode, Hannah Fry and Michael Stevens dive into the mysteries of gravity—a force so familiar and yet so deeply puzzling. They challenge everyday assumptions, explain how our understanding has evolved from Newton to Einstein (and beyond), and muse on what we still don’t know: from the elusive nature of dark matter to whether gravity has a quantum particle, and how extra dimensions might factor into the mix. With humor, rich analogies, and hands-on demos, they make the fundamental force that ties the universe together feel both astonishing and oddly personal.

Key Discussion Points and Insights

1. Experiencing Gravity—From Embarrassment to Wonder

• Michael opens by asking Hannah about the last time she fell over, setting the stage for a relatable entry point into a fundamental force.

  • [02:56] Hannah: “I think my limbs are longer than my brain expects them to be… I walked into a lamppost and then fell over backwards. And everyone in the queue saw me do it. That was not a good day.”
  • [03:23] Michael: “You’re a lucky duck, because that means you got to experience weightlessness on the way down.”

• Gravity’s omnipresence: Michael points out how we all constantly interact with gravity, but rarely ponder its true nature.

2. Explaining Gravity—Analogies for Aliens

• Alien thought experiment: How would you explain gravity to someone (or something) from a universe with none?

  • [04:48] Hannah: “In our universe, objects are attracted to each other… Without any interfering from outside, if you just have two objects near each other, they will come together. That’s it, really.”
  • Discussion of mass and mutual attraction: highlights that even two baseballs in deep space would eventually come together due to gravity—though it would take three days for them to do so.

• Misconceptions about gravity:

  • Astrology’s gravitational "influence" addressed:
    • [06:14] Michael: “The gravitational influence of Pisces on you is less than the gravitational influence of the doctor who delivered you.”

3. Mass, Motion, and Inertia

• Defining mass: Connection between gravitational mass (attraction) and inertial mass (resistance to acceleration). Are they really the same thing?

  • [07:19] Michael: “An object that's really hard to speed up and push around has a lot of inertia… But are... Is there still debate around whether they're the same thing?”
  • [08:04] Hannah: “I like to think that's sort of how I live my life... I don't like changing [motion].”

• Mutual attraction clarified: Whether dropping a pen or walking on the ground, both the object and the Earth are affected, but the difference is minuscule for the Earth.

  • [09:24] Michael: "If you dropped a pen from six feet up, it actually pulls the Earth up towards it. 9 trillionths the width of a proton."

4. Newton vs. Einstein—A Shift in Perspective

• Newtonian gravity: Described as a force causing mutual acceleration.

  • But puzzling: Newton’s model requires instantaneous action at a distance, which seemed problematic (e.g., what if the sun suddenly disappeared?).

• Einstein's general relativity:

  • Gravity is a curvature of spacetime, and gravity’s influence can only travel at the speed of light.
  • [13:19] Hannah: “Einstein has this great intuition that it's not just that objects are magically accelerating towards each other, but that spacetime itself has this curvature to it.”
  • Solved the mystery of Mercury’s weird orbit (the perihelion shift), famously matching observations with remarkable precision.
    • [14:25] Michael: “Level of precision… he said he was happy for days after he looked at those calculations… I found the missing piece to the puzzle.”

• Analogies for curved spacetime:

  • The "crumpled curtain" and the limitations of analogies like the stretched rubber sheet.
  • [21:53] Michael: “I've never really liked the rubber sheet analogy because it doesn't seem to do anything but just show what you already feel, which is that gravity makes things fall.”
  • Feynman’s ant-on-paper analogy helps imagine higher dimensions, but as [24:06] Michael admits: “You can also see how hard it is to jump up to where we live… How do I bend three dimensional space?”

5. Relativity and Time—Why Clocks Tick Differently

• Time dilation on Earth: Time moves at different rates at different altitudes due to differences in gravitational strength.

  • [16:44] Hannah: “The gravitational effect in Boulder is 9.796 meters per second. In Greenwich it’s 9.812. You are aging faster than me.”
  • [17:49] Michael: “If I could somehow look at your watch… I would notice that it was running behind. That's because you're closer to Earth's center of mass.”

• Experimental confirmation: Atomic clocks substantiate Einstein’s predictions—time really does run slower closer to massive bodies.

  • [17:58] Michael: “It's mind warping… but it's also experimentally confirmed.”

6. Life Without/With Gravity—Lessons from Space

• How organisms cope in microgravity:
  • Fish and octopus experiments on the ISS show Earth-born creatures struggle, while those born in space adapt better.
    • [19:48] Michael: “The octopuses that were born in space seemed like they were fine and then when they came back down they really struggled. They struggled on Earth.”
  • Human (and rat) infants would not develop properly in zero-G.

7. The Limits of Our Understanding—Dark Matter and Quantum Gravity

• Dark matter:

  • Introduced to account for strange galactic motions.

  • [28:35] Hannah: “There’s something going on with gravity here… these galaxies are spinning around so fast… they should be ripped apart... so maybe there’s all of this other stuff that we just can’t see… dark matter.”

  • We still don’t know what dark matter consists of, though it must be (weakly) present everywhere, including on Earth.

• Particle physics and gravity:

  • Other fundamental forces are mediated by particles (photon for electromagnetism, gluon for the strong nuclear force, etc.), but gravity’s "graviton" remains hypothetical and undetected.
  • [32:04] Hannah: "We don't know for sure... it might be that gravity is actually this emergent property like temperature or pressure… not this fundamental force."
  • Gravity is incredibly weak at the quantum scale—requiring implausibly huge accelerators to detect individual quanta.

8. Is Gravity "Leaky?" – Speculations on Extra Dimensions

• String theory and dimensions: If gravity feels weak, maybe it's because it “leaks” into hidden dimensions (from string theory).

  • [34:15] Hannah: “Maybe gravity exists inverted commas in different dimensions... Maybe we're in a space with 5 dimensions, 11 dimensions, 27 dimensions...”
  • Analogy: Ant on a tube—if you’re big, you think there’s just one way to go, but if you’re small, there are more directions/dimensions to explore.

• Gravity cannot be shielded or reflected: Unlike electromagnetism, gravity can't be blocked or mirrored—no “gravity shield” or “gravity mirror” exists.

9. Black Holes—Extreme Gravity

• Demonstration with tungsten cubes and spheres:

  • Michael brings a dense tungsten cube to appreciate pure mass.
  • [37:02] Michael: “It's a bit like a spiritual crystal for me. I can just hold it and meditate on gravitational attraction like that wants to be with the Earth…”

• What if Earth became a black hole?: The Earth’s Schwarzschild radius (the size it must be compressed to become a black hole) is just 8.87 millimeters (shown via a tungsten sphere).

  • [38:27] Michael: "If that was a black hole, its mass would be the same as the Earth."
  • Discussion of what would happen if such a black hole were created on Earth: "I don't think a black hole that size would be very dangerous... it would just fall right to the center of the Earth."
  • [39:25] Michael: "It would be explosive but it wouldn't eat up all the matter really quickly."

• Playful finale: Michael introduces a tongue-in-cheek "multi-fool" credit card with a hole the size of Earth's Schwarzschild radius—a humorous reminder of our planet’s continued safety.

Notable Quotes and Memorable Moments

• On gravity’s universality (Astrology joke):

  • Michael: "The gravitational influence of Pisces on you is less than the gravitational influence of the doctor who delivered you." [06:14]

• On the relativity of time:

  • Hannah: “What this means is that time travels slower in Greenwich than it does in Boulder... you are aging faster than me.” [16:50]

• On the challenge of explaining spacetime curvature:

  • Michael: “To leap from there to actually, maybe gravity is just a change in the shape of space. Time is really gigantic.” [14:45]

• On dark matter’s origins:

  • Hannah: “Let's just call it dark matter, add an extra term in our equations, everything's good, everyone can go home.” [29:47]

• On attempts to find the graviton:

  • Hannah: “You would need a particle accelerator that was basically on the scale of a galaxy.” [32:54]

• On higher dimensions:

  • Hannah: “I just don't think that your brain is capable. And that's not just you, Michael.” [25:17]

• On holding dense tungsten:

  • Michael: “It's a bit like a spiritual crystal for me. I can just hold it and meditate on gravitational attraction.” [36:45]

Important Segment Timestamps

| Topic/Quote | Timestamp | |---------------------------------------------------------------|-------------| | Hannah’s lamppost/weightless fall story | 02:56–03:23 | | Alien gravity explanation challenge | 04:00–05:32 | | Gravitational mass vs. inertial mass (and the bed analogy) | 07:07–08:28 | | Explanation of why a Newtonian view breaks down | 11:52–13:19 | | The Einstein breakthrough (Mercury’s orbit) | 13:19–14:25 | | Crumpling spacetime, time running differently on Earth | 15:29–17:23 | | Atomic clocks & gravitational time dilation | 17:58–18:38 | | Microgravity effects on life | 19:48–20:28 | | Dark matter and Fritz Zwicky | 28:35–30:01 | | Gravity at quantum scale, force particle speculation | 31:51–32:58 | | Gravity possibly leaking into extra dimensions | 34:15–35:12 | | Earth as a black hole (tungsten sphere demo) | 37:02–38:48 | | Episode wrap-up and "multi-fool" card | 40:00–41:03 |

Tone and Style

The episode is lively, playful, deeply curious, and occasionally self-deprecating. Hannah and Michael bounce between accessible analogies, deep questions, and witty banter, never shying away from saying "we just don’t know," and always eager to point out where reality is stranger—and more fragile—than it seems.

For science fans, teachers, the philosophically-inclined, or the simply curious, this episode expertly pulls listeners into gravity’s weirdest, wildest mysteries—reminding us that even the most familiar forces are anything but ordinary.