Speaker 1: Welcome to Bedtime Astronomy. Explore the wonders of the cosmos
Speaker 1: with our soothing Bedtime Astronomie podcast. Each episode offers a
Speaker 1: gentle journey through the stars, planets, and beyond, perfect for
Speaker 1: unwinding after a long day. Let's travel through the mysteries
Speaker 1: of the universe as you drift off into a peaceful
Speaker 1: slumber under the night sky.
Speaker 2: Look at the clock on your wall right now, or
Speaker 2: you know, check the time on your phone, or just
Speaker 2: glance at the watch on your wrist.
Speaker 3: Yeah, take us up and to really look at it.
Speaker 2: Because every single time that secondhand ticks forward or that
Speaker 2: digital number rolls over, well, it's lying.
Speaker 3: To you, completely lying, and it's it's funny because we
Speaker 3: all share this incredibly deep, almost unquestionable intuition about what
Speaker 3: those numbers mean.
Speaker 2: Right. We go through our entire lives operating on this
Speaker 2: assumption that time is a universal river, and you, me,
Speaker 2: the listener, we are all just floating in that exact
Speaker 2: same river, being carried downstream with the exact same speed exactly.
Speaker 3: I mean, the fundamental assumption of human existence is that
Speaker 3: a minute for you sitting right there, right now, is
Speaker 3: exactly the same as a minute for someone making coffee
Speaker 3: on the other side of the planet, or a minute
Speaker 3: for an astronaut orbiting the Earth.
Speaker 2: It's just a given.
Speaker 3: But that intuition is it's mathematically and observably wrong. The
Speaker 3: universal river of time is just a localized illusion.
Speaker 2: Wow. Okay, so this isn't some abstract, you know, philosophical wordplay.
Speaker 2: You are saying that our literal physical understanding of time,
Speaker 2: this masterclock we think is ticking away in the background
Speaker 2: of the universe, is just.
Speaker 3: Broken, completely shattered. Yeah. I mean the concept of a
Speaker 3: single steady master clock governing everything everywhere. It simply does
Speaker 3: not exist. Time is local, local, Yeah, it's malleable. It
Speaker 3: does not flow at the same rate for all observers.
Speaker 3: The actual fabric of time stretches and compresses, depending entirely
Speaker 3: on two things.
Speaker 2: Okay, what are they?
Speaker 3: How fast you're moving through space and how deep you're
Speaker 3: resting within a gravitational field.
Speaker 2: Okay, let's unpack this, because this means we are talking
Speaker 2: about the literal, structural source code of reality.
Speaker 3: Here, we really are.
Speaker 2: We're exploring how Albert Einstein realized the universe was playing
Speaker 2: this massive trick on us, and how this totally counterintuitive.
Speaker 2: Physics is secretly the engine running our modern world right now?
Speaker 3: Yeah, and why the whole concept of now, like this
Speaker 3: specific moment you and I are experiencing, might actually just
Speaker 3: be a psychological hallucination.
Speaker 2: Which is terrifying and fascinating because we are talking about cold, hard,
Speaker 2: miserable facts today.
Speaker 3: Absolutely, if you take two identical clocks, right, synchronize them
Speaker 3: perfectly so they tick in absolute unison, and then you
Speaker 3: just put them on different paths through space time, they
Speaker 3: will diverge, like they.
Speaker 2: Will physically show different times when you bring them back together.
Speaker 3: Yes, and neither clock is broken, neither has a mechanical flaw.
Speaker 3: They just traveled through different densities.
Speaker 2: Of time, different densities of time. That's such a wild phrase, eh,
Speaker 2: And this has been tested.
Speaker 3: Right, oh, tested and confirmed by experiment after experiment for
Speaker 3: over a century. And honestly, if we didn't mathematically correct
Speaker 3: for this warping of time every single second of the day,
Speaker 3: our twenty first century infrastructure would literally tear itself apart
Speaker 3: before lunchtime.
Speaker 2: Okay, So to really grasp why that clock on the
Speaker 2: wall is feeding us a localized fiction, we actually have
Speaker 2: to stop looking at time. Right, we have to look
Speaker 2: at light.
Speaker 3: Yeah, because to understand how time bends, you have to
Speaker 3: establish the one thing in the entire universe that refuses
Speaker 3: to bend, the speed of light exactly. So to trace
Speaker 3: that realization, we really need to go back to nineteen
Speaker 3: oh five, to the first of Albert Einstein's two big breakthroughs.
Speaker 2: Write his paper on special relativity.
Speaker 3: Yeah, at the time, physics was still living in the
Speaker 3: house Isaac Newton built. Newtonian physics assumes space is just
Speaker 3: an empty static stage and time is the unchangeable clock
Speaker 3: on the wall of that stage.
Speaker 2: Einstein basically took a sledgehammer to that.
Speaker 3: He really did. He looked at objects moving at constant velocities,
Speaker 3: and he built his entire theory on a single, uncompromising rule.
Speaker 3: The speed of light in a vacuum is exactly the
Speaker 3: same for all observers, no matter how fast the light
Speaker 3: source or the observer is moving.
Speaker 2: Okay, on the surface, if you don't know the physics,
Speaker 2: that sounds kind of mundane. Light goes fast, and it
Speaker 2: always goes the same amount of fast.
Speaker 3: Right, it doesn't sound revolutionary, But.
Speaker 2: Let's map that onto how everyday objects work, because that's
Speaker 2: where the absolute absurdity of Einstein's rule kicks him. Think
Speaker 2: about a highway. If I'm driving down the highway at
Speaker 2: sixteen miles an hour and another car passes me doing
Speaker 2: seventy my perspective from the driver's seat is that the
Speaker 2: passing car is only creeping ahead of me at ten
Speaker 2: miles an.
Speaker 3: Hour, exactly because velocities are additive and subtractive.
Speaker 2: Right. If I throw a baseball at one hundred miles
Speaker 2: an hour out the front of a train that's moving
Speaker 2: at one hundred miles an hour, someone standing on the
Speaker 2: platform sees that baseball traveling at two hundred miles an hour.
Speaker 2: That makes logical sense.
Speaker 3: To us, because the human brain relies on Galilean relativity,
Speaker 3: that simple addition of speeds. But light completely refuses to
Speaker 3: play by that rule.
Speaker 2: So how does light behave in that scenario.
Speaker 3: Well, imagine you're flying in a hyperadvanced spaceship at ninety
Speaker 3: nine percent of the speed of light.
Speaker 2: Okay, moving incredibly fast.
Speaker 3: Right, and you shine a flashlight at the front window.
Speaker 3: That beam of light does not travel at one hundred
Speaker 3: and ninety nine percent of the speed of light relative
Speaker 3: to someone watching.
Speaker 2: You, because there's a speed limit exactly.
Speaker 3: But it also doesn't just pull away from your ship
Speaker 3: at a mere one percent of the speed of light,
Speaker 3: which is what the highway logic would suggest, right.
Speaker 2: Seventy minus sixty is ten, so light speed minus ninety
Speaker 2: nine percent should be one percent.
Speaker 3: But it isn't. From your perspective inside the ship, that
Speaker 3: beam pulls away from you at exactly the full speed
Speaker 3: of light. Wait, and from the perspective of someone standing
Speaker 3: still on a planet watching you fly by, that exact
Speaker 3: same beam of light is also moving at exactly the
Speaker 3: speed of light.
Speaker 2: Okay, so this is the exact moment the universe backs
Speaker 2: us into a mathematical corner. You have two people moving
Speaker 2: at vastly different speeds, observing the exact same beam of light,
Speaker 2: and they both measure it moving at the exact same
Speaker 2: speed relatives to themselves.
Speaker 3: Yeah, which should be impossible.
Speaker 2: Right. To make that true, the universe has to cheat.
Speaker 2: It has to alter something else to keep the speed
Speaker 2: of light constant. Let's walk through the light clock thought experiment,
Speaker 2: because visualizing the geometry here is really what finally made
Speaker 2: this click for me.
Speaker 3: The light clock is perfect for this. It strips away
Speaker 3: all the mechanical complications, you know, gears and springs. Just
Speaker 3: imagine the simplest possible timekeeping device.
Speaker 2: Okay, I'm fixturing it.
Speaker 3: You have two highly polished mirrors facing each other, one
Speaker 3: mounted on the floor and one mounted on the ceiling
Speaker 3: directly above it, and a single pulse of light is
Speaker 3: trapped between them, just bouncing endlessly up and down.
Speaker 2: Got it. And we define one tick of this clock
Speaker 2: as the time it takes for the light pulse to
Speaker 2: leave the bottom mirror, hit the top mirror, and bounce.
Speaker 3: Back down exactly, up and down, tick, up and down.
Speaker 2: Tick. Okay. Now, let's take this light clock and mount
Speaker 2: it inside a transparent spaceship, and that spaceship is going
Speaker 2: to fly past me at a massive velocid, let's say,
Speaker 2: half the speed of light. I'm standing perfectly still on
Speaker 2: an asteroid watching the ship zoom by from left to right.
Speaker 3: So let's isolate the perspectives here, starting with the astronaut
Speaker 3: inside the spaceship. From their point of view, they're perfectly
Speaker 3: stationary inside their cabin. The floor is below them, the
Speaker 3: ceiling is above them. They watch the light clock, and
Speaker 3: they see the pulse of light traveling perfectly straight up
Speaker 3: and perfectly straight down, So.
Speaker 2: The distance the light travels for one tick is just
Speaker 2: twice the height of the cabin, right.
Speaker 3: Simple. But your perspective standing outside watching the ship fly
Speaker 3: past is entirely.
Speaker 2: Different because the ship is moving.
Speaker 3: Yes, when the light pulse leaves the bottom mirror, the
Speaker 3: ship is at let's say position A, But by the
Speaker 3: time the light travels up to hit the ceiling mirror,
Speaker 3: the entire ship has moved forward to position.
Speaker 2: B oh right. So from my vantage point outside, the
Speaker 2: light pulse didn't go straight up. It had to travel
Speaker 2: diagonally forward and upward to catch the moving ceiling.
Speaker 3: Mirror exactly, and the geometry continues on the return trip.
Speaker 3: By the time the light bounces off the ceiling and
Speaker 3: returns to the floor mirror, the ship has moved even
Speaker 3: further forward to position C, so the light has.
Speaker 2: To travel diagonally forward and downward.
Speaker 3: You got it. From your stationary perspective outside the ship,
Speaker 3: the light pulse isn't moving in a vertical line at all.
Speaker 3: It's tracing a zigzag pattern, a series of long diagonomal
Speaker 3: lines through space.
Speaker 2: And here's where the trap closes on us. Because basic
Speaker 2: pythagore and geometry tells us that a diagonal line connecting
Speaker 2: two horizontal points is always physically longer than a straight
Speaker 2: vertical line between them.
Speaker 3: It has to be so.
Speaker 2: The path the light took from my perspective outside the
Speaker 2: ship is a definitively longer distance than the path it
Speaker 2: took from the astronaut's perspective inside the ship.
Speaker 3: And this is where we apply einstein unbreakable rule. And
Speaker 3: the equation for speed is universally simple. Right. Speed equals
Speaker 3: distance divided by time. Right, we've established that the distance
Speaker 3: the light traveled from your perspective is greater than the
Speaker 3: distance it traveled from the astronaut's perspective, but the speed
Speaker 3: of the light cannot change. It must be identical for
Speaker 3: both of you.
Speaker 2: Right, So the distance is a larger number for me,
Speaker 2: and the speed is locked as a constant. The math
Speaker 2: physically forces the time to be a larger number. Two.
Speaker 2: The only way to balance the equation is if the
Speaker 2: time it took for the clock to tick was literally
Speaker 2: longer for me than it was for the astronaut.
Speaker 3: The inescapable mathematical reality is that the moving clock ticks
Speaker 3: more slowly than the stationary one from your perspective. Looking
Speaker 3: into that moving ship. Time itself is dragging. The physical
Speaker 3: progression of reality has slowed down to compensate for the
Speaker 3: longer distance the light had to travel just.
Speaker 2: To ensure the speed of light remains perfectly constant.
Speaker 3: Yes, this is special relativistic time dilation.
Speaker 2: You know. I always try to find the trick here
Speaker 2: to say, well, it's just an optical illusion. The light
Speaker 2: is just taking longer to reach my eyeballs because the
Speaker 2: ship is moving away. But that's not what's happening, is it.
Speaker 3: No, not at all. The actual biological aging of the astronaut,
Speaker 3: the decay of atoms in the ship's hull, the thoughts
Speaker 3: firing in the astronaut's brain, every single localized physical process
Speaker 3: is happening in slow motion relative to the rest of
Speaker 3: the universe.
Speaker 2: It's a genuine asymmetry in the fundamental rate at which
Speaker 2: reality unfolds. It's not an artifact of observation, right.
Speaker 3: Observers in different states of uniformation experience different intervals of
Speaker 3: time between the exact sam events.
Speaker 2: But the immediate counter argument anyone would have is, Okay,
Speaker 2: if motion slows down time, why don't I experience a
Speaker 2: time warp when I merge onto the interstate. Why don't
Speaker 2: my watch in my car's dashboard clock stay perfectly syncd Well.
Speaker 3: The physics is governed by a mathematical term called the
Speaker 3: Lorentz factor, and this factor dictates exactly how much time dilates,
Speaker 3: how much length contracts, and how much mass increases as
Speaker 3: an object's velocity approaches the speed of light.
Speaker 2: Okay, and the key.
Speaker 3: To understanding why our daily lives feel strictly Newtonian is
Speaker 3: the shape of that Lorentz curve. At the relatively sluggish
Speaker 3: speeds humans travel at, walking, driving a car, even launching
Speaker 3: a rocket into orbit, the velocity is such a tiny
Speaker 3: fraction of the speed of light that the Lorentz factor
Speaker 3: remains incredibly close to one.
Speaker 2: Meaning the time dilation multiplier is basically like one point
Speaker 2: zero zero zero zero zero zero zero one. It's so
Speaker 2: infinitesimally small that it completely falls beneath the threshold of
Speaker 2: human perception.
Speaker 3: Exactly to put a number on it, If you board
Speaker 3: a commercial jetliner and fly at a cruising speed of
Speaker 3: roughly one thousand kilometers per hour, you are absolutely experiencing
Speaker 3: special relativistic time dilation. I am yes, but the amount
Speaker 3: your local time slows down compared to someone on the
Speaker 3: ground is measured in a few nanoseconds per hour.
Speaker 2: A nanosecond being one billionth of a second.
Speaker 3: Right, So the biological difference is practically non existent to
Speaker 3: our senses.
Speaker 2: But the Lorenz factor isn't linear, is it. It's an asymptote.
Speaker 2: When we start pushing the velocity higher, the math stops
Speaker 2: being a rounding air and becomes violently dramatic. Let's say
Speaker 2: we finally invent a propulsion drive. They can push a
Speaker 2: spacecraft to ninety percent of the speed of light.
Speaker 3: At ninety percent of the speed of light, the Lorentz
Speaker 3: curve spikes sharply. Time for the crew on that ship
Speaker 3: would run at less than half the rate of a
Speaker 3: stationary observer on Earth.
Speaker 2: So for every hour that ticks by on the ship's.
Speaker 3: Clock, more than two hours pass for mission control back home.
Speaker 2: Wow, Let's push the engines to ninety nine percent of
Speaker 2: the speed of light.
Speaker 3: At ninety nine percent, the dilation becomes severe. Time on
Speaker 3: the ship runs at roughly one seventh the normal rate.
Speaker 3: If the crew spends a single year traveling at that speed,
Speaker 3: seven years will have evaporated on Earth.
Speaker 2: What about ninety nine point nine percent.
Speaker 3: The closer you shave the margin to the absolute speed limit,
Speaker 3: the more extreme the temporal distortion gets. At ninety nine
Speaker 3: point nine percent of the speed of light, time slows
Speaker 3: to about one twenty second of the stationary rate. The
Speaker 3: denominator in the Lorenz equation shrinks towards zero, which means
Speaker 3: the time dilation factor explodes toward infinity.
Speaker 2: And if we somehow breach the limit, if we hit
Speaker 2: exactly one hundred percent of the speed of light, if.
Speaker 3: An object with mass could somehow reach the exact speed
Speaker 3: of light, the mathematics dictate that time would stop entirely,
Speaker 3: just freeze. The internal clock of that object would freeze.
Speaker 3: I mean, think about a photon. A photon is a
Speaker 3: particle of light, so it naturally travels at the speed
Speaker 3: of light. It essentially experiences no time.
Speaker 2: Wait, really no time at all none.
Speaker 3: From a photon's perspective, the moment it is emitted from
Speaker 3: a star and the moment it strikes your retina millions
Speaker 3: of years later happens simultaneously.
Speaker 2: That is mind blowing.
Speaker 3: But for anything with mass, a human, a spaceship, even
Speaker 3: a single proton, reaching the speed of light is physically impossible.
Speaker 3: As the Lorentz factor approaches infinity, the energy required to
Speaker 3: accelerate the object also approaches infinity. The universe forbids mass
Speaker 3: from reaching the speed limit.
Speaker 2: This all sounds like a brilliant piece of chalkpord theoretical physics.
Speaker 2: But what blows my mind is that physicists didn't just
Speaker 2: lead this as a mathematical curiosity. They actually found ways
Speaker 2: to physically prove it. I mean, I know there was
Speaker 2: an experiment in the early nineteen seventies, the halfle keating experiment, Yes,
Speaker 2: a classic, where they supposedly put atomic clocks on commercial airplanes.
Speaker 2: But my first thought when I read about that was,
Speaker 2: how could a normal passenger plane flying at maybe six
Speaker 2: hundred miles an hour possibly go fast enough to measure
Speaker 2: in effect that requires the speed of light to become obvious.
Speaker 2: Weren't they just flying around the world on standard pan
Speaker 2: Am flights.
Speaker 3: Your right to be skeptical, because, as we established, passenger
Speaker 3: jets are crawling compared to the speed of light. The
Speaker 3: time dilation at those speeds is incredibly minuscule. But the
Speaker 3: brilliance of the hefel keating experiment wasn't in the speed
Speaker 3: of the planes.
Speaker 2: What was it?
Speaker 3: It was in the sheer, unfathomable precision of the instruments.
Speaker 3: In nineteen seventy one, Joseph Heffel and Richard Keating took
Speaker 3: four caesium beam atomic clocks. These are devices that measure
Speaker 3: time by counting the exact microwave resonances of caesium atoms.
Speaker 3: They're so precise they might lose or gain a single
Speaker 3: second over tens of millions of years.
Speaker 2: So they took these ultra sensitive instruments literally, bought them
Speaker 2: passenger tickets and strapped them into the seats of commercial airliners.
Speaker 3: Literally, they flew one set of clocks eastward around the
Speaker 3: world and another set westward around the world. And meanwhile
Speaker 3: they kept a reference set of identical atomic clocks, completely
Speaker 3: stationary at the United States Naval Observatory.
Speaker 2: Okay, so the goal was to see if the flying clocks,
Speaker 2: heavy experienced the velocity of the airplanes, would physically disagree
Speaker 2: with the stationary clocks when they got back. But why
Speaker 2: eastward and westward? Does the direction matter when you're just
Speaker 2: measuring speed?
Speaker 3: Oh, it matters immensely because the Earth itself is spinning
Speaker 3: the stationary clocks. The observatory are already moving because the
Speaker 3: surface of the Earth is rotating. Right when the plane
Speaker 3: flew eastward in the same direction as the Earth's rotation,
Speaker 3: it's velocity added to the rotational speed of the Earth.
Speaker 3: It was moving faster relative to the center of the
Speaker 3: Earth than the stationary clocks. Therefore, special relativity predicted the
Speaker 3: eastward clocks should run significantly slower and lose time.
Speaker 2: And the westward flight was flying against the rotation of
Speaker 2: the Earth, essentially subtracting from that rotational speed, so relative
Speaker 2: to the center of the Earth, the westward plane was
Speaker 2: actually moving slower than the stationary observatory on.
Speaker 3: The ground exactly. The mathematics predicted a very specific Chiny
Speaker 3: discrepancy for both journeys, and when Hafili and Keating brought
Speaker 3: the flying clocks back into the lab and compared the
Speaker 3: readouts to the reference clocks, the numbers did not match.
Speaker 3: The eastward clocks had lost time, the westward clocks had
Speaker 3: gained time. The physical time displayed on the instruments was
Speaker 3: fundamentally different, and the discrepancy perfectly matched the nanosecond calculations
Speaker 3: derived from Einstein's equations fifty years prior.
Speaker 2: They physically carried a slice of reality into a different
Speaker 2: temporal flow it'st deep there, and brought it back. That
Speaker 2: is profound, It's incredible. But there's another real world proof
Speaker 2: of special relativity that is even more dramatic because it
Speaker 2: doesn't require man made atomic clocks. Right. It happens naturally
Speaker 2: millions of times every single second right above our heads
Speaker 2: in the atmosphere. Uh the muons survival test.
Speaker 3: Ah. Yes, the behavior of muons is a continuous, naturally
Speaker 3: occurring demonstration of time dilation. Particle physicists rely on it daily.
Speaker 3: To understand it, we have to look at the upper
Speaker 3: limits of the Earth's atmosphere. Deep space is filled with
Speaker 3: high energy cosmic rays, mostly protons, traveling at immense speeds.
Speaker 3: When these cosmic rays slam into the molecules of oxygen
Speaker 3: and nitrogen in our upper atmosphere, the violent collision creates
Speaker 3: a shower of secondary sub atomic particles, and among these
Speaker 3: are particles called muons.
Speaker 2: So these muons are born high up in the atmosphere,
Speaker 2: maybe ten miles above the surface, and the momentum from
Speaker 2: the collision sends them hurtling downward toward the ground at
Speaker 2: velocities incredibly close to the speed of light.
Speaker 3: Correct, But the muon has a fatal flaw. It's a
Speaker 3: highly unstable particle. Once a muon is created, it has
Speaker 3: an incredibly short half life of roughly two point two microseconds.
Speaker 2: That's two point two millions of a second.
Speaker 3: Right after that microscypic flicker of time, it decays into
Speaker 3: an electron and a couple of neutrinos. It ceases to
Speaker 3: exist as a muon.
Speaker 2: Wait, let's look at the mat there. If a muon
Speaker 2: only lives for two millions of a second, it shouldn't
Speaker 2: be able to survive the trip to the ground, even
Speaker 2: if it's traveling at ninety nine point nine percent of
Speaker 2: the speed of light. The atmosphere is miles thick. Light
Speaker 2: itself takes significantly longer than two microseconds to travel ten
Speaker 2: miles it does. If time is a universal constant ticking
Speaker 2: away at the same rate for everything, every single muon
Speaker 2: ever created should die miles up in the sky. Yet
Speaker 2: we have detectors on the surface of the Earth and
Speaker 2: even deep underground in mines that are constantly being pinged
Speaker 2: by intact muons. How is that part possible?
Speaker 3: This is the exact paradox that makes time dilation an
Speaker 3: undeniable physical reality. If the universe operated on Newtonian time,
Speaker 3: the probability of a muon reaching the surface would be
Speaker 3: functionally zero. But we detect massive.
Speaker 2: Swarms of them, So how do they make it.
Speaker 3: To resolve the contradiction, you have to look at the
Speaker 3: journey from two completely different reference frames. Let's start from
Speaker 3: our perspective standing on the Earth next to our muon detector.
Speaker 2: Okay, from my perspective, I'm stationary, and the subatomic particle
Speaker 2: is rocketing toward me at ninety nine point nine percent
Speaker 2: of the speed of light. Because it's moving so incredibly
Speaker 2: fast relative to my frame of reference, the Lorenz factor
Speaker 2: is huge. Special relativity dictates that the muon's internal clock,
Speaker 2: the rate at which it experiences its own decay process,
Speaker 2: must be running exceptionally slowly.
Speaker 3: Exactly while the clocks in our laboratory are ticking away
Speaker 3: at a normal speed, the muon's biological clock, so to speak,
Speaker 3: is barely advancing. From our perspective, that fleeting two microsecond
Speaker 3: lifespan is violent.
Speaker 2: Stretched out, so it lives longer.
Speaker 3: Yes, it's dilated by a factor of perhaps fifty or sixty,
Speaker 3: depending on its exact speed. Because its time is running
Speaker 3: an extreme slow motion, it easily survives the ten mile
Speaker 3: journey down through the atmosphere before its internal clock finally
Speaker 3: reaches the two microsecond mark and it decays.
Speaker 2: That perfectly explains why we see them hit the ground.
Speaker 2: But the rule of relativity is that there's no preferred
Speaker 2: frame of reference, right what happens if we try to
Speaker 2: imagine this from the muon's point of view, Because in
Speaker 2: the Muon's frame of reference, it isn't moving at all.
Speaker 2: It was born, It's sitting completely stationary, and it's the
Speaker 2: Earth that is rushing up to hit it at ninety
Speaker 2: nine point nine percent of the speed of light.
Speaker 3: And that is a perfectly valid physical perspective. In the
Speaker 3: muon stationary frame, its internal clock is ticking normally. It
Speaker 3: does not experience time dilation from the moment it is created.
Speaker 3: It only has two microseconds to live, period.
Speaker 2: But if it only lives for two microseconds in its
Speaker 2: own reality, how does it physically cross ten miles of atmosphere?
Speaker 3: Four dies because of the necessary mirror image of time
Speaker 3: dilation length contraction length contraction, space and time are not
Speaker 3: separate entities. They are interwoven into a single four dimensional
Speaker 3: fabric called space time. When you move at relativistic speeds,
Speaker 3: time dilates, but the physical space along the direction of
Speaker 3: motion contracts. From the muon's perspective, the Earth is rushing
Speaker 3: toward it at near light speed. Therefore, the physical distance
Speaker 3: of the Earth's atmosphere is severely length contracted.
Speaker 2: So the ten miles of atmosphere literally shrinks.
Speaker 3: To the muon. The atmosphere is not ten miles thick,
Speaker 3: it is compressed down to a fraction of a mile.
Speaker 3: The physical distance it needs to cover is so incredibly
Speaker 3: short that even with a lifespan of only two microseconds,
Speaker 3: the Earth easily closes the distance before the muon decays.
Speaker 2: That is just phenomenal. If you ask the scientist on
Speaker 2: the ground, the muon survive because it's time stretched out.
Speaker 2: If you ask the muon, it survived because the physical
Speaker 2: distance of the universe shrank. Both observe is measured completely
Speaker 2: different times, in completely different distances, yet they arrive at
Speaker 2: the exact same physical event the muon hits the detector.
Speaker 3: Both realities are mathematically true. The undeniable physical fact is
Speaker 3: that the muons arrive at the ground, and that absolute
Speaker 3: fact could not happen without the elasticity of space time.
Speaker 2: Okay, so we've established the first mechanism, moving at high
Speaker 2: velocity warps time, but honestly, most of us aren't exactly
Speaker 2: traveling at near lightspeed on a Tuesday afternoon. However, the
Speaker 2: universe isn't done messing with our clocks. There is a second,
Speaker 2: entirely separate force that warps time, and it has absolutely
Speaker 2: nothing to do with velocity. It's happening right now, pulling
Speaker 2: time apart right beneath our feet.
Speaker 3: This brings us to nineteen fifteen, a full decade after
Speaker 3: special relativity, Einstein published his General Theory of relativity, which
Speaker 3: remains the current standard model of gravitation in modern physics.
Speaker 3: General relativity introduced a completely new mechanism for time dilation,
Speaker 3: the presence of.
Speaker 2: Mass gravitational time dilation. Every time gravity is brought up
Speaker 2: in documentaries, they always use the exact same analogy, the
Speaker 2: bowling ball sitting on a rubber trampoline creating a dip
Speaker 2: that makes smaller marbles roll toward it. But I have
Speaker 2: heard physicists actively grown when that analogy is brought up.
Speaker 2: Why is it flawed? And how should we actually visualize gravity.
Speaker 3: Physicists dislike the trampoline analogy because it uses gravity to
Speaker 3: explain gravity. The bowling ball pulls the rubber sheet down
Speaker 3: because of the Earth's gravity underneath it. It doesn't actually
Speaker 3: explain the mechanism of space time.
Speaker 2: Curvature that makes sense, So what's a better way to
Speaker 2: picture it?
Speaker 3: A much better way to visualize it is to imagine
Speaker 3: a three dimensional grid, like a massive block of translucent jelly,
Speaker 3: with perfectly straight grid lines drawn through it. If you
Speaker 3: inject a massive object like a star or a planet,
Speaker 3: into the center of that jelly, it pulls the surrounding
Speaker 3: grid lines inward toward itself. The grid lines bunch up
Speaker 3: and stretch around the mass.
Speaker 2: So gravity isn't a magical invisible tether pulling objects together.
Speaker 2: Objects are just trying to move in a straight line
Speaker 2: through the jelly, but because the gridlines themselves are curved
Speaker 2: toward the planet, following a straight path naturally leads them
Speaker 2: into a collision course with a massive object.
Speaker 3: Exactly what Newton perceived as a force pulling an apple
Speaker 3: from a tree. Einstein revealed to simply be the apple
Speaker 3: following the natural curve geometry of space time caused by
Speaker 3: the Earth's mass. But here's the critical leap. Space and
Speaker 3: time are a single fused fabric. You cannot warp the
Speaker 3: spatial grid lines without simultaneously warping the temple gridlines.
Speaker 2: So the presence of a massive object literally bends time
Speaker 2: just as it bends space.
Speaker 3: That is the core revelation of general relativity. Clocks that
Speaker 3: are deeper down in a gravitational potential, well meaning they
Speaker 3: are physically closer to the center of a massive object,
Speaker 3: will run more slowly than clocks that are further away
Speaker 3: from the mass. Gravity slows down time.
Speaker 2: The physical intuition behind velocity slowing down time made sense
Speaker 2: with the light clock geometry. But how did Einstein intuitively
Speaker 2: figure out that gravity slows down time? What was the
Speaker 2: thought process there?
Speaker 3: He used a thought experiment that he later referred to
Speaker 3: as his happiest thought. It led to the equivalence principle,
Speaker 3: the absolute cornersphone of general relativity. Einstein realized that the
Speaker 3: physical local experience of resting inside a gravitational field is
Speaker 3: utterly indistinguishable from the experience of being inside an accelerating
Speaker 3: reference frame.
Speaker 2: Let's break down the elevator thought experiment because this is brilliant.
Speaker 2: Imagine an astronaut sealed inside a box like an elevator
Speaker 2: car with absolute no windows. They cannot look outside to
Speaker 2: see where they are. Scenario one, the box is sitting
Speaker 2: stationary on the surface of the Earth. The astronaut feels
Speaker 2: their normal weight pressing down on their boots. If they
Speaker 2: take a pen out of their pocket and let go,
Speaker 2: it drops to the floor at an acceleration of nine
Speaker 2: point eight meters per second squared.
Speaker 3: Now consider scenario two. Take that exact same windowless box
Speaker 3: with the astronaut inside, and teleport it into deep interstellar space,
Speaker 3: light years away from any planets or stars. There's zero gravity.
Speaker 3: The astronaut is floating. But now attach a massive rocket
Speaker 3: thruster to the bottom of the box and fire it
Speaker 3: so that the box accelerates upward at precisely nine point
Speaker 3: eight meters per second squared.
Speaker 2: Because the floor is accelerating up to meet the astronaut
Speaker 2: at the exact same rate as Earth's gravity, the astronaut
Speaker 2: is pressed down into their boots with the exact same force.
Speaker 2: If they let go of the pen, the pen doesn't fall. Rather,
Speaker 2: the floor of the box accelerates up and smashes into
Speaker 2: the pen at nine point eight meters per second square
Speaker 2: exactly from the astronaut's perspective inside the sealed room, the
Speaker 2: physics look identically the same.
Speaker 3: The equivalence principle states that no local experiment the astronaut
Speaker 3: can perform inside that box will allow them to distinguish
Speaker 3: whether they are sitting on a planet experience in gravity,
Speaker 3: or floating in deep space experiencing constant acceleration. The two
Speaker 3: scenarios are completely physically equivalent.
Speaker 2: But how does equating gravity to a rocket engine prove
Speaker 2: that gravity bends time?
Speaker 3: Because if the two environments are truly equivalent, any physical
Speaker 3: phenomenon that occurs in the accelerating rocket must also logically
Speaker 3: occur in a gravitational field. Think about what happens to
Speaker 3: light in that accelerating elevator. Okay, Imagine a laser beam
Speaker 3: is fired horizontally from the left wall to the right
Speaker 3: wall in a stationary box. It travels in a perfectly
Speaker 3: straight horizontal line, But if the box is accelerating upward
Speaker 3: at a massive rate, by the time the light reaches
Speaker 3: the right wall, the wall has moved up.
Speaker 2: So the light being hits the right wall slightly lower
Speaker 2: than where it started on the left wall. From the
Speaker 2: astronaut's perspective, the light being didn't travel straight. It curved
Speaker 2: downward toward the floor exactly.
Speaker 3: Acceleration curves the path of light. Therefore, due to the
Speaker 3: equivalence principle, gravity must also curve the path of light.
Speaker 3: Now apply this logic to time. In the accelerating rocket.
Speaker 3: The floor of the box is constantly accelerating, essentially chasing
Speaker 3: the light signal sent from the ceiling. Because of the
Speaker 3: complex can image of acceleration, the back of the rocket
Speaker 3: behaves as though it is moving at a different relative velocity.
Speaker 2: Than the front, and we established earlier that different velocities
Speaker 2: mean different rates of time. So the acceleration forces the
Speaker 2: clock on the floor of the rocket to tick slower
Speaker 2: than the clock.
Speaker 3: On the ceiling, and the trap snaps shut again. If
Speaker 3: a clock at the bottom of an accelerating rocket runs
Speaker 3: slower than a clock at the top, and acceleration is
Speaker 3: indistinguishable from gravity, then a clock sitting lower down in
Speaker 3: a gravitational well must run slower than a clock sitting
Speaker 3: higher up, because.
Speaker 2: The bottom of the elevator is mathematically identical to being
Speaker 2: closer to the center of the Earth. This means gravitational
Speaker 2: time dilation isn't just happening near supermassive black holes or
Speaker 2: neutron stars. It's happening constantly right here on Earth.
Speaker 3: Oh. Absolutely.
Speaker 2: A clock sitting on the beach at sea level is
Speaker 2: physically ticking slower than an identical clock sitting in the
Speaker 2: cabin at the top of the rocky mountains.
Speaker 3: The gravitational poll is slightly weaker at the top of
Speaker 3: the mountain because the summit is further away from the
Speaker 3: dense center of the Earth's mass. Your higher up the
Speaker 3: gravitational potential. Well, therefore time flows slightly faster at altitude.
Speaker 2: Wait stop there. If time runs slower the closer you
Speaker 2: are to the Earth, that means right now, as I'm
Speaker 2: sitting in this chair, my feet are experiencing a stronger
Speaker 2: gravitational pull than my head, So my feet are physically
Speaker 2: aging slower than my brain.
Speaker 3: It sounds like the punchline to a physics joke, but
Speaker 3: it is a literal, unavoidable biological reality. Your head is
Speaker 3: roughly five or six feet further away from the center
Speaker 3: of the Earth than your feet are. The gravitational gingradient
Speaker 3: across your body means time is passing infinitesimally faster for
Speaker 3: your mind than it is for your toes.
Speaker 2: How does biological cohesion even work if my blood is
Speaker 2: pumping across different time zones.
Speaker 3: Because similar to the airplane speeds we talked about, the
Speaker 3: difference in gravity across six feet of human height is
Speaker 3: incredibly tiny. The time difference accumulated over an entire human
Speaker 3: life span would amount to a fraction of a microsecond.
Speaker 3: But the conceptual reality remains, your body is spanning a
Speaker 3: temporal gri.
Speaker 2: Radiant and just like the hefhil keating experiment, physicists couldn't
Speaker 2: resist measuring this. But they didn't go to Mount Everest.
Speaker 2: They measured the time difference across a distance so small
Speaker 2: at borders on the absurd.
Speaker 3: You're referring to the twenty ten experiment at the National
Speaker 3: Institute of Standards and Technology or NIST in Boulder, Colorado.
Speaker 2: Yeah, that's the one.
Speaker 3: By twenty ten, chronometry had evolved far beyond the caesium
Speaker 3: clocks of the nineteen seventies. NIST physicists were using optical
Speaker 3: aluminum ion clocks. These devices trap a single charged atom
Speaker 3: of aluminum using electromagnetic fields and measure the incredibly rapid
Speaker 3: oscillations of its energy state using ultraviolet lasers.
Speaker 2: A clock that relies on a single vibrating atom.
Speaker 3: They are so unthinkably precise that they would neither gain
Speaker 3: nor lose a single second over an estimated three point
Speaker 3: seven billion years.
Speaker 2: That's almost the age of the Earth exactly.
Speaker 3: They are sensitive enough to detect microscopic fluctuations in the
Speaker 3: fabric of space time itself. The physicists took two of
Speaker 3: these aluminum ion clocks, synchronize them, and placed them in
Speaker 3: the same laboratory, but they separated them in height.
Speaker 2: By how much like a few stories in a building, by.
Speaker 3: Thirty three centimeters roughly one foot.
Speaker 2: One foot a single step on a.
Speaker 3: Staircase, just a single step, and they monitored the ticking rates.
Speaker 3: The clock that was thirty three centimeters higher up ran
Speaker 3: demonstrably faster than the clock that was lower down. The
Speaker 3: results perfectly aligned with the equations of general relativity.
Speaker 2: The universe has a resolution so fine that it is
Speaker 2: actively keeping track of the gravitational time difference across the
Speaker 2: height of a coffee table.
Speaker 3: The structure of reality is incredibly sensitive. The curvature of
Speaker 3: the universe, dictates the rate of time at the macrostopic
Speaker 3: scale of galaxies and at the microscopic scale of your
Speaker 3: living room.
Speaker 2: It's so easy to listen to all of this aluminum
Speaker 2: ion clocks, fractions of a nanosecond variations across a footstool
Speaker 2: and file it away as microscopic trivia. It's a brilliant
Speaker 2: flex of experimental physics. But it feels completely disconnected from
Speaker 2: daily human life.
Speaker 3: But that is the ultimate illusion, right.
Speaker 2: The terrifying truth is that you, the listener, rely on
Speaker 2: this relativistic weirdness to navigate your day. If we ignored
Speaker 2: the fact that time bends and warps, our modern civilization
Speaker 2: would start to collapse within a few hours. Let's talk
Speaker 2: about the system that proves Einstein wright billions of times
Speaker 2: a day. The Global Positioning System.
Speaker 3: The GPS network is the ultimate, undeniable, practical application of
Speaker 3: relativistic physics. It's a constellation of at least twenty four
Speaker 3: satellites orbiting the Earth, providing continuous location data to military assets,
Speaker 3: commercial shipping, aviation, and of course, the phone in your pocket.
Speaker 2: Let's break down exactly how my phone knows I'm standing
Speaker 2: on a specific street corner. How does GPS actually work.
Speaker 3: It's a process called trilateration, and it is entirely dependent
Speaker 3: on ultra precise timing. Every GPS satellite is carrying multiple
Speaker 3: atomic clocks. These satellites are constantly broadcasting a radio signal
Speaker 3: down to Earth.
Speaker 2: Okay, and what's in the signal?
Speaker 3: The signal contains two vital pieces of information, the exact
Speaker 3: identity and location of the satellite in orbit and the
Speaker 3: precise time the signal was transmitted.
Speaker 2: So my phone's GPS receiver isn't transmitting anything, it's just
Speaker 2: listening for these signals raining down.
Speaker 3: From space exactly. Your phone picks up signals from at
Speaker 3: least four different satellites simultaneously. Radio waves travel at the
Speaker 3: speed of light, which is a known constant. When your
Speaker 3: phone receives a signal, it checks its own internal clock
Speaker 3: and compares it to the time stamp of when the
Speaker 3: signal left the satellite. The tiny delay the time it
Speaker 3: took the signal to travel from space to your pocket,
Speaker 3: allows the phone to calculate exactly how far away that
Speaker 3: specific satellite.
Speaker 2: Is because speed times time equals distance. If I know
Speaker 2: the signal took exactly a fraction of a second to
Speaker 2: reach me, and I know the speed of light. I
Speaker 2: know I'm sitting exactly on the edge of an imaginary
Speaker 2: sphere extending outward from that satellite precisely.
Speaker 3: One satellite tells you that you are somewhere on the
Speaker 3: surface of a massive sphere. Two satellites intersect to create
Speaker 3: a circle of possible locations. Three satellites intersect at exactly
Speaker 3: two points in space, and the fourth satellite eliminates one
Speaker 3: of those points, pinpointing your exact latitude, longitude, and altitude
Speaker 3: on the surface of the Earth.
Speaker 2: Because light travels incredibly fast roughly three hundred thousand kilometers
Speaker 2: per second, that time delay measurement has to be flawless.
Speaker 2: If the clock on the satellite and the clock on
Speaker 2: my phone are out of sync by even a microscopic
Speaker 2: fraction of a second, the distance calpulation will be wildly wrong.
Speaker 3: The synchronization must be maintained to an extraordinary, mind bending
Speaker 3: level of precision, and this is where the genius of
Speaker 3: Albert Einstein collides with modern engineering. The clocks on those
Speaker 3: satellites are orbiting the Earth, which means they are being
Speaker 3: subjected to both special and general relativity simultaneously, and the
Speaker 3: two theories are pulling time in opposite directions.
Speaker 2: This is the ultimate physics math problem. Okay, let's start
Speaker 2: with the motion special relativity.
Speaker 3: To maintain a stable orbit, GPS satellites travel at roughly
Speaker 3: fourteen thousand kilometer per hour relative to receivers on the ground.
Speaker 3: As we learn from the light clock, high velocity means
Speaker 3: slower time. Because they're moving so fast, special relativistic time
Speaker 3: dilation causes the satellite clocks to tick slower than clocks
Speaker 3: on the ground. The math calculates that they lose about
Speaker 3: seven microseconds seven millions of a second every single day.
Speaker 2: Okay, so special relativity is dragging the clocks backward by
Speaker 2: seven microseconds a day. But the satellites aren't just moving fast.
Speaker 2: They're very high up.
Speaker 3: They orbit at an altitude of approximately twenty thousand kilometers.
Speaker 3: At that extreme distance, they are significantly higher up the
Speaker 3: Earth's gravitational potential well than we are. The gravity they
Speaker 3: experience is roughly one quarter as strong as the gravity
Speaker 3: on the surface, and as we learn from the equivalence principle,
Speaker 3: weaker gravity means faster time.
Speaker 2: So general relativity is pushing the clocks.
Speaker 3: Forward, yes, because they reside in a weaker gravitational field.
Speaker 3: General relativistic time dilation causes the satellite clocks to run
Speaker 3: faster than clocks on the ground by approximately forty five
Speaker 3: microseconds per day.
Speaker 2: So we have a relativistic tug of war. Motion slows
Speaker 2: them down by seven microseconds. Gravity speeds them up by
Speaker 2: forty five microseconds.
Speaker 3: You combine the effects to find the net differential. The
Speaker 3: gravitational effect is stronger. The satellite clocks run fast by
Speaker 3: a net total of thirty eight microseconds per day relative
Speaker 3: to clocks resting on the surface of the.
Speaker 2: Earth thirty eight microseconds thirty eight millions of a second
Speaker 2: a day. Imagine being the project managers in the nineteen
Speaker 2: seventies trying to build this system. It'd be so tempting
Speaker 2: to look at that number and say Einstein's theories are
Speaker 2: a mathematical headache. Thirty eight millions of a second is
Speaker 2: a rounding error. Let's just assume Newtonian time is universal,
Speaker 2: ignore the relativity, and launch the satellites. What happens if
Speaker 2: we ignore the thirty eight microseconds.
Speaker 3: If the engineers had ignored that relativistic drift, the entire
Speaker 3: GPS network would be worse than useless. It would be
Speaker 3: catastrophically dangerous. Because the system calculates distance based on the
Speaker 3: speed of light, a timing error of a single microsecond
Speaker 3: translates to a distance error of roughly three hundred meters
Speaker 3: or about one thousand feet.
Speaker 2: Oh wow, one microsecond equals one thousand feet of error
Speaker 2: on the map.
Speaker 3: If you let an uncorrected error of thirty eight microseconds
Speaker 3: accumulate over a single day, the position calculations would drift
Speaker 3: by more than eleven kilometers per day.
Speaker 2: Eleven kilometers of error added every single day.
Speaker 3: Every day, within a matter of hours, your phone's GPS
Speaker 3: would place you blocks away from your actual location. By
Speaker 3: the end of the day, it would tell you to
Speaker 3: turn your car into a river, or insist that a
Speaker 3: commercial airliner was miles away from the runway was trying
Speaker 3: to land on. The banking system, which relies on GPS
Speaker 3: timestamps to synchronize global financial transactions, would desynchronize and fail.
Speaker 3: The power grid, which uses GPS to phase aligne alternating
Speaker 3: current across vast distances, could experience massive cascading blackouts.
Speaker 2: That is genuinely terrifying. Our modern infrastructure is entirely dependent
Speaker 2: on a network of space clocks that we literally had
Speaker 2: to program to ticket the wrong speed before we launched them,
Speaker 2: just so they would sync up with us once they
Speaker 2: hit the warping of orbit. We have built the curvature
Speaker 2: of space time into our everyday tools.
Speaker 3: Without a deep functional understanding of how both velocity and
Speaker 3: gravity warp the passage of time, the modern world as
Speaker 3: we know it would not function. It is the most
Speaker 3: consequential daily proof of relativity in existence.
Speaker 2: So we've conquered the microsecond scale. We've mastered the microscopic
Speaker 2: fractions of a second needed to keep our banking systems
Speaker 2: running and our digital maps accurate. But human ambition doesn't
Speaker 2: stop at low Earth orbit. What happens when we scale
Speaker 2: this up? What happens to human biology, human psychology, and
Speaker 2: human society when we push the math of relativity to
Speaker 2: the extremes of deep space travel.
Speaker 3: When we extrapolate these equations to the macro scale, we
Speaker 3: run into the most famous and historically the most fiercely
Speaker 3: debated thought experiment in all of relativistic physics, the twin paradox.
Speaker 2: I have struggled with the twin paradox for years, because
Speaker 2: because it feels like a logical trap that relativity sets
Speaker 2: for itself set the stage for us.
Speaker 3: The premise is simple. Imagine a pair of identical twins
Speaker 3: born on the exact same day. Let's call them the
Speaker 3: traveler and the home body. The traveler gets into a
Speaker 3: highly advanced spacecraft capable of interstellar travel. She fires up
Speaker 3: the engines and accelerates to a massive speed, say ninety
Speaker 3: percent of the speed of light. She travels to a
Speaker 3: distant star system, slows down to turn around, accelerates back
Speaker 3: to ninety percent of the speed of light, and eventually returns.
Speaker 2: To Earth and the home body twin.
Speaker 3: The homebody stays completely stationary on Earth, working at a desk,
Speaker 3: waiting for her sister to return from the voyage.
Speaker 2: Okay, applying what we know about special relativity and the
Speaker 2: Lorenz factor, the traveler is moving incredibly fast relative to
Speaker 2: the Earth. High velocity means time dilation, so the traveler's
Speaker 2: internal clock, the ticking of her watch, the beating of
Speaker 2: her heart, the cellular aging of her body is running
Speaker 2: significantly slower than the clocks on Earth.
Speaker 3: Correct. When the spacecraft finally lands back on Earth and
Speaker 3: the door open, the math dictates that significantly less time
Speaker 3: has passed for the traveler than for the homebody. The
Speaker 3: traveler steps out of the ship physically biologically younger than
Speaker 3: her identical twin who stayed behind.
Speaker 2: But here is where my brain rebels and where the
Speaker 2: paradox wears its head. Einstein's whole premise is that motion
Speaker 2: is relative. There's no absolute stationary background to the universe.
Speaker 2: If the traveler is sitting in her spaceship looking out
Speaker 2: the window, why couldn't she just claim that her ship
Speaker 2: is completely stationary And it's the Earth that fired invisible
Speaker 2: engines and rocketed away from her at ninety percent of
Speaker 2: the speed of light and then came flying back.
Speaker 3: That is the exact crux of the problem. It's a
Speaker 3: brilliant question, and it cause immense confusion in the early
Speaker 3: days of relativity, because if.
Speaker 2: The traveler thinks the Earth is the thing moving, then
Speaker 2: from her perspective, the Earth's time should be running slower.
Speaker 2: She should expect the homebody twin to be the younger one.
Speaker 2: Both twins have perfectly valid reasons to look at the
Speaker 2: other and say, you are the one moving, so your
Speaker 2: time is slower. But when the ship lands, they can't
Speaker 2: both be younger than each other. One of them actually
Speaker 2: steps out of the ship definitively younger. How is that
Speaker 2: not a phatological flaw in the theory.
Speaker 3: It appears to be a paradox, But the resolution lies
Speaker 3: in a critical physical asymmetry between their two journeys. The
Speaker 3: principle of relativity, the idea that you cannot determine who
Speaker 3: is really moving, only applies perfectly to inertial reference frames.
Speaker 3: An inertial frame is a perspective that is moving at
Speaker 3: a steady, constant velocity in a straight line with no acceleration.
Speaker 2: But the traveler didn't just move at a constant velocity forever.
Speaker 2: She had to turn around exactly.
Speaker 3: To leave Earth, the traveler had to ignite her engines
Speaker 3: and experience enormous acceleration forces pressing her into her seat.
Speaker 3: To stop at the distant star, she had to violently decelerate.
Speaker 3: To come back, she had to accelerate again, and to
Speaker 3: park the ship back on Earth, she had to decelerate
Speaker 3: one final time. The traveler physically felt the g forces
Speaker 3: of changing velocity, while.
Speaker 2: The home body twin just sat in a comfortable chair
Speaker 2: on Earth, never experiencing any massive g forces.
Speaker 3: The acceleration entirely breaks the symmetry between the two perspectives.
Speaker 3: The home body remained in the single inertial reference frame
Speaker 3: the entire time. The traveler, however, jumped between multiple different
Speaker 3: reference frames, the outbound frame, the turning around accelerating frame,
Speaker 3: and the inbound frame. The universe is fully aware of
Speaker 3: who accelerated, because acceleration is an absolute, physically measurable experience.
Speaker 3: Because of this asymmetry, the mathematical calculations yield an absolute result.
Speaker 3: The twin who underwent the acceleration and changed reference frames
Speaker 3: is unequivocally the one who ages less.
Speaker 2: So it is not a paradox at all. It's just
Speaker 2: a highly counterintuitive physical fact. If we ever build an
Speaker 2: engine capable of this, the traveling twin will return younger,
Speaker 2: and depending on the velocity. We aren't talking about microseconds anymore.
Speaker 2: We're talking about decades. Let's invent a hypothetical mission to
Speaker 2: truly grasp the deep space implications of this. Let's say
Speaker 2: we want to send a human crew to explore a
Speaker 2: star system that is four hundred light years away, and
Speaker 2: we've engineered a ship the can cruise at ninety nine
Speaker 2: percent of the speed of light.
Speaker 3: The math here shifts from physics to profound sociology. Let's
Speaker 3: look at the timeline from Earth's perspective. First, the star
Speaker 3: is four hundred light years away. The ship is traveling
Speaker 3: at just under the speed of light. Therefore, from the
Speaker 3: perspective of mission control on Earth, it's going to take
Speaker 3: the ship slightly more than four hundred years to reach
Speaker 3: the destination.
Speaker 2: Four centuries we launched the ship, and everyone involved in
Speaker 2: the launch dies of old age. Their great great grandchildren
Speaker 2: die of old age. Entire empires could rise and collapse.
Speaker 2: Technology will revolutionize completely. But what is the experience of
Speaker 2: the crew inside the ship?
Speaker 3: Inside the ship cruising at ninety nine percent at the
Speaker 3: speed of light, the Lorentz factor is roughly seven. The
Speaker 3: time dilation is immense for the crew. The journey does
Speaker 3: not drag on for four hundred years. From their biological
Speaker 3: and psychological perspective, only about fifty six years will elapse
Speaker 3: during the entire outbound transit.
Speaker 2: A young astronaut in their twenties boards the ship, and
Speaker 2: they arrive at the destination in their late seventies. They
Speaker 2: experience a single human lifetime, while the Earth experiences four
Speaker 2: centuries of.
Speaker 3: History, and consider the implications if they attempt to return.
Speaker 3: If they spend a few years exploring and then fly
Speaker 3: back to Earth at the same speed, another fifty six
Speaker 3: years will pass for them, but another four hundred years
Speaker 3: will pass on Earth.
Speaker 2: They will return having aged a little over a century,
Speaker 2: but they will step out of the airlock onto an
Speaker 2: Earth that is more than eight hundred years older than
Speaker 2: the one they left.
Speaker 3: They would return to a completely alien world. The language
Speaker 3: might be incomprehensible, the nations that launched them might no
Speaker 3: longer exist. Everyone they ever knew, loved, or read about
Speaker 3: would be ancient historical footnotes. Time dilation autolates at the
Speaker 3: absolute limits of human endurance. The same mathematical principles that
Speaker 3: make a smartphone map accurate today act as a one
Speaker 3: way time machine into the future. For interstellar travelers.
Speaker 2: It imposes a t tragic quarantine on the universe. You
Speaker 2: are physically allowed to travel among the stars, but the
Speaker 2: universe demands that you sacrifice your own timeline, your own era,
Speaker 2: to pay for the ticket. The isolation is profound.
Speaker 3: It is the ultimate boundary condition of human exploration, and
Speaker 3: we must remember this relativistic framework isn't just a quirky
Speaker 3: hurdle for future astronauts. It's already deeply embedded in the
Speaker 3: bedrock of modern physics. In quantum field theory, which governs
Speaker 3: the subatomic realm, particle physicists deal with extreme time dilation
Speaker 3: as a routine shore when they accelerate particles and colliders
Speaker 3: like cern, the particles are moving at fractions of a
Speaker 3: percent below the speed of light, their observed decay rates
Speaker 3: stretch out massively due to the Lorentz factor. The physicists
Speaker 3: have to manually correct for time dilation just to make
Speaker 3: their quantum equations balance. The theory is flawlessly robust, from
Speaker 3: the scale of the subatomic to the scale of the galactic.
Speaker 2: Okay, so we know the math is bulletproof. The GPS
Speaker 2: satellites prove the engineering works. Particle clisights prove the quantum
Speaker 2: mechanics work. The physical reality of time stretching and shrinking
Speaker 2: is undeniable. But this forces us into a very uncomfortable corner.
Speaker 2: If time runs at vastly different speeds depending on where
Speaker 2: you were sitting, how strong the gravity is, and how
Speaker 2: fast you're moving, what does that actually mean for the
Speaker 2: concept of now This is.
Speaker 3: Where we cross the border from rigid physics into the deepest,
Speaker 3: most unsettling realms of philosophy. Because relativity essentially assassinates our
Speaker 3: intuitive understanding of the present moment.
Speaker 2: We all walk around with this ingrained belief that there
Speaker 2: is a universal now. Like as I'm speaking these words,
Speaker 2: right at this exact second, of volcano is erupting on
Speaker 2: Jupiter's moonisle, and a star is going supernova in the
Speaker 2: Andromeda galaxy, and all of those events are happening in
Speaker 2: the exact same present slice of time that I'm currently experiencing.
Speaker 3: That is Newtonian time. It's the belief in a cosmic
Speaker 3: now that slices uniformly across the entire universe. But if
Speaker 3: time is relative, if the rate of clocks depends on
Speaker 3: motion and gravity, then the concept of a synchronized universal
Speaker 3: present cannot mathematically exist.
Speaker 2: Because two observers can completely disagree on the timeline of
Speaker 2: events exactly.
Speaker 3: Relativity introduces the concept of the relativity of simultaneity. Imagine
Speaker 3: you are floating in space and you see two distant
Speaker 3: stars explode at the exact same time. To you, those
Speaker 3: events are perfectly simultaneous, but another observer flying past. You
Speaker 3: in a spaceship at high velocity toward one star and
Speaker 3: away from the other, will see the light from the
Speaker 3: approaching star first to them. The explosions were not simultaneous.
Speaker 3: One clearly happened before the other, and because.
Speaker 2: There's no preferred reference frame, neither observer is wrong.
Speaker 3: Neither is wrong. If observers cannot agree on whether two
Speaker 3: events happened at the same time, then it is physically
Speaker 3: impossible to draw a single objective line across the universe
Speaker 3: and call it now. Your now is entirely local to
Speaker 3: your specific velocity and gravitational field.
Speaker 2: If the universal present doesn't exist, what replaces it? How
Speaker 2: do physicists vision ualize reality if it isn't a series
Speaker 2: of universal moments clicking forward.
Speaker 3: Many physicists are led by the equations of general relativity
Speaker 3: to a concept known as the block universe or eternalism.
Speaker 3: It requires abandoning the idea of time flowing entirely.
Speaker 2: Explain the block universe? How should I picture it?
Speaker 3: Imagine a massive solid block of transparent amber, But instead
Speaker 3: of just representing the three dimensions of space up, down, left, right, forward, backward,
Speaker 3: this block also contains time as a physical structural fourth dimension.
Speaker 3: In the block universe model, every single moment that has
Speaker 3: happened and every single moment that ever will happen, exists
Speaker 3: simultaneously within this eternal block.
Speaker 2: So the past hasn't vanished into nothingness and the future
Speaker 2: is in some blank, unwritten void. They're just physical locations
Speaker 2: within the block.
Speaker 3: Precisely, think about space. Just because you are sitting in
Speaker 3: London does not mean that Tokyo has ceased to exist
Speaker 3: or that New York hasn't been built yet. They all
Speaker 3: exist simultaneously. You just happen to be located at it
Speaker 3: specific coordinate. In the block universe, time works exactly the
Speaker 3: same way. The year nineteen twenty, the year you were born,
Speaker 3: the present moment you were listening to my voice, and
Speaker 3: the year thirty twenty all exists simultaneously, permanently etched into
Speaker 3: the fabric of four dimensional space time.
Speaker 2: There's a quote from the brilliant physicist term and while
Speaker 2: that always gives me chills when thinking about this, he wrote,
Speaker 2: the objective world simply is it does not happen.
Speaker 3: It does not happen. It is a profound summation in
Speaker 3: the block universe, the Big Bang, the construction of the pyramids,
Speaker 3: your entire life, and the eventual heat death of the
Speaker 3: universe are all just static structures embedded in the block.
Speaker 3: The flow of time, that visceral, unshakable feeling we all
Speaker 3: have of a moving present, of sliding relentlessly from the
Speaker 3: past into the open future might not be a physical
Speaker 3: property of the universe at all.
Speaker 2: Wait, if the universe is static, why do I feel
Speaker 2: like time is passing? Why do I remember yesterday but
Speaker 2: not tomorrow?
Speaker 3: The flow of time might simply be a subjective psychological illusion,
Speaker 3: a biological trick. Our brains evolve to process a static
Speaker 3: four dimensional reality one thin three dimensional slice at a time.
Speaker 3: Consciousness acts like a spotlight dragging slowly across the solid
Speaker 3: block of amber, illuminating one slice of space time and
Speaker 3: calling it now before moving to the next.
Speaker 2: That is a deeply unsettling conclusion, because if the block
Speaker 2: universe is real and the future is already sitting there
Speaker 2: in the amber, what happens to free will? If my
Speaker 2: choices tomorrow are already structurally embedded in the space time block,
Speaker 2: am I actually making choices? Or am I just a
Speaker 2: needle on a record player experiencing a song that has
Speaker 2: already been pressed into vinyl.
Speaker 3: You've hit on exactly why this is one of the
Speaker 3: most fiercely debated metaphysical topics in science. We must be clear,
Speaker 3: while the mathematics of relativity heavily imply the block universe,
Speaker 3: it is not universally accepted as the definitive truth of reality.
Speaker 3: There is significant pushback from both physicists and philosophers, so.
Speaker 2: The science doesn't mandate the exidential dread just yet. What
Speaker 2: is the counter argument on.
Speaker 3: Our question is whether the physics of relativity strictly dictates
Speaker 3: the metaphysics of existence. Proponents of eternalism argue that the
Speaker 3: relativity of simultaneity leaves no other logical option. If different
Speaker 3: observers have different nows that include events in another observer's
Speaker 3: past or future, all those events must be equally real.
Speaker 2: And the opponents the people who still believe time is
Speaker 2: actively slowing.
Speaker 3: They fall into camps like presentism or the growing block theory.
Speaker 3: They argue that the mathematical equations of relativity are just
Speaker 3: that mathematical models for calculating observations. They argue the math
Speaker 3: underdetermines the metaphysics. In their view, relativity is completely compatible
Speaker 3: with a dynamic universe where the present is an objectively
Speaker 3: real moving boundary that actively brings the future into existence.
Speaker 3: The fact that different observers measure that boundary differently due
Speaker 3: to light speed delays and reference frames doesn't mean the
Speaker 3: boundary itself is an illusion.
Speaker 2: So we have built a flawless mathematical apparatus that allows
Speaker 2: us to sink satellite networks to the microsecond and predict
Speaker 2: the exact decay rates of subatomic particles. But at the
Speaker 2: very bottom of the rabbit hole, the greatest minds in
Speaker 2: the world are still arguing about whether tomorrow has already
Speaker 2: happened exactly.
Speaker 3: It perfectly bridges the intense, rigorous technical precision of physics
Speaker 3: with the grandest, most unanswerable questions of philosophy. Equations can
Speaker 3: calculate the time dilation of a muon, but equations cannot
Speaker 3: definitively answer the nature of conscious experience or the existence
Speaker 3: of free will.
Speaker 2: To bring this massive journey all together, Albert Einstein looked
Speaker 2: at a universe that seemed chaotic and full of contradictions,
Speaker 2: like light refusing to behave like a throne baseball, and
Speaker 2: he brought an elegant, unbreakable mathematical order to it, but
Speaker 2: the price we had to pay for that mathematical order
Speaker 2: with the destruction of our common sense.
Speaker 3: He proved that the universe does not care about human intuition.
Speaker 3: It does not have a single master clock taking away
Speaker 3: in the background. As the science of time dilation proves
Speaker 3: with absolute tested certainty, the universe possesses exactly as many
Speaker 3: clocks as there are places, gravitational fields, and states of motion.
Speaker 3: Every single object, every planet, every rocket ship, every individual person,
Speaker 3: every single atom faithfully keeps its own unique time, and
Speaker 3: that time accelerates or drags, depending entirely on the curvature
Speaker 3: of space. Time it navigates.
Speaker 2: The universe keeps its own decentralized ledgers, and the math
Speaker 2: allows for two people to look at the exact same
Speaker 2: beam of light, experience a completely different flow of reality,
Speaker 2: biologically age at different rates, and both be one hundred
Speaker 2: percent perfectly correct in their measurements.
Speaker 3: Einstein himself once remarked that the most incomprehensible thing about
Speaker 3: the universe is that it is comprehensible. Time dilation embodies
Speaker 3: that paradox perfectly. It violently violates every ordinary assumption we
Speaker 3: possess about the universality of seconds, minutes, and years. Yet
Speaker 3: we can derive it from simple geometric principles, confirm it
Speaker 3: by flying atomic clocks around the globe, and apply it
Speaker 3: with astonishing engineering precision to a satellite network that guides
Speaker 3: us to the grocery store.
Speaker 2: The cosmos doesn't owe us a reality that makes sense
Speaker 2: to our primate brains. It operates on its own magnificent,
Speaker 2: warped logic.
Speaker 3: And the ultimate task of science is to follow the
Speaker 3: experimental evidence wherever it leads, even when it demands that
Speaker 3: we abandon the deepest, most comforting illusions we hold about reality.
Speaker 2: So as we wrap up, I want you to look
Speaker 2: back at the clock on your wall, the one we
Speaker 2: started this entire conversation with. It is still ticking, and
Speaker 2: it's keeping perfectly good, accurate time for you, right in
Speaker 2: the specific chair you're sitting in. But remember what it
Speaker 2: is actually doing. It is keeping its own local time.
Speaker 2: Nothing absolutely nowhere in the vastness of the cosmos is
Speaker 2: keeping universal time.
Speaker 3: Which leaves us with a truly mind expanding, somewhat haunting
Speaker 3: question to ponder. We discussed how the flow of time
Speaker 3: might simply be a psychological trick, a biological mechanism our
Speaker 3: brains evolve to navigate the static four dimensional block of
Speaker 3: space time. But try to imagine a perspective outside of that.
Speaker 2: Limitation, outside the human experience.
Speaker 3: Right, what would reality look like to a consciousness that
Speaker 3: wasn't bound by that evolutionary trick. If a hyper advanced
Speaker 3: artificial intelligence or some radically different, higher dimensional biological entity
Speaker 3: could somehow perceive all four dimensions of space time simultaneously,
Speaker 3: able to see the very beginning of your life and
Speaker 3: the absolute end of it in a single, unified, eternal glance,
Speaker 3: that's a huge thought. Would they even recognize us as living, conscious,
Speaker 3: thinking beings or would human lives just look to them
Speaker 3: like static, unchanging elongated shapes frizen forever in the solid
Speaker 3: amber of space time.
Speaker 4: The Days Das School