0:02 You are completely wrong about time. You
0:04 probably think you know what it is
0:05 because you look at a watch or you feel
0:07 yourself getting older. But that isn't
0:10 time. That's just a sensation, a
0:12 biological trick. Most people walk
0:14 around with this poetic idea in their
0:17 heads that time is a river. You imagine
0:19 it flows, sweeping you along from the
0:22 past through the present and into the
0:24 future. You think it moved. But here is
0:26 the problem with that beautiful image.
0:29 If time is a river, how fast does the
0:32 river flow? 1 second per second. That is
0:34 meaningless. That's like saying a table
0:36 is one table long. It tells you
0:38 absolutely nothing about the nature of
0:41 reality. The truth is much stranger,
0:44 much more mechanical and honestly a lot
0:46 less romantic than a flowing stream.
0:49 Time doesn't flow. Time doesn't push you
0:50 anywhere. And if you think you have a
0:53 good grip on how time works just because
0:55 you can count seconds in your head, you
0:58 are in for a very rude awakening. Let's
0:59 start with what goes on inside your
1:01 brain because that is where the
1:03 confusion begins. You think your
1:05 internal clock is a reliable instrument.
1:07 It isn't. It is a chaotic mess of
1:10 translation scheme. Consider a simple
1:12 experiment. Try to count to 60 seconds
1:15 in your head. Just sit there and count.
1:19 1 2 3. You think you are tracking time,
1:21 but what you are really doing is running
1:24 a very specific, very personal program.
1:26 Some of you, when you count, you hear a
1:28 voice in your head. You are literally
1:32 speaking to yourself, subvocalizing 1 2
1:34 3. If someone interrupts you and asks
1:37 you to speak, you lose your count. The
1:39 machine jams. But others, and this is
1:41 where it gets interesting, don't hear a
1:44 voice at all. They see images. They
1:46 might see a tape measure with numbers on
1:48 it clicking past like a ticker tape.
1:52 Clink, clink, clink. If you use that
1:54 visual tape measure system, you can
1:56 actually read a newspaper or check a
1:58 laundry list while you count time. You
2:00 can sort your socks, look at patterns in
2:02 the weaving, and still keep that mental
2:04 tape measure clicking perfectly. But the
2:06 person who counts with a voice, they
2:08 can't read a word without losing track
2:11 of the time. This tells us something
2:13 fundamental. What you experience as the
2:15 passage of time is just a mental
2:18 construct, a pattern matching game your
2:20 brain plays. It varies wildly from
2:23 person to person. It is not a universal
2:25 constant. It is a biological
2:27 hallucination. So when we talk about
2:29 physics, when we talk about the
2:31 universe, we have to throw your brain
2:33 out the window. We have to stop talking
2:36 about how it feels and start talking
2:38 about what it actually is. In
2:40 [clears throat] physics, we have to be
2:42 operational. That means we don't ask
2:45 what is the essence of time because that
2:47 is a question for philosophers who enjoy
2:50 arguing over coffee. We ask how do we
2:52 measure it and the answer is almost
2:54 disappointingly simple. Time is just a
2:57 way of ordering events. That's it. It is
2:59 a labeling system. Imagine you have a
3:01 deck of cards. You lay them out in a
3:03 row. You can say the jack is before the
3:06 queen and the king is after the queen.
3:09 The cards aren't moving. The table isn't
3:11 flowing. The order is just a structural
3:13 property of how the cards are arranged.
3:17 Time is the table. Events are the cards.
3:19 When we say time passes, we are just
3:21 reading the cards from left to right.
3:23 This brings us to the biggest mistake
3:26 everyone makes. You think time is a
3:28 container. You imagine the universe is a
3:31 big empty box and time is a clock on the
3:34 wall of that box ticking away even if
3:36 the box is empty. You think that if we
3:39 removed all the stars, all the planets,
3:41 all the atoms, and all the light, time
3:45 would keep ticking. Tick, tick, tick.
3:48 Wrong. This is the Newtonian view, and
3:50 it is dead. Time is not a background
3:53 stage. Time is a measure of change. If
3:55 absolutely nothing in the universe
3:58 changes, no atoms vibrate, no light
4:01 moves, no energy shifts, then time
4:04 stops. It ceases to have meaning. You
4:05 cannot define a second without a
4:08 physical process to mark it. A swinging
4:11 pendulum, a vibrating quartz crystal, a
4:14 seesium atom oscillating. Time is not
4:16 separate from the stuff in the universe.
4:18 Time is a property of the stuff. This is
4:20 where your intuition fights back. You
4:24 say, "Okay, but surely time acts on
4:26 things. Time makes me get older. Time
4:29 causes the milk to spoil." No, it
4:33 doesn't. This is a linguistic trap. Time
4:36 is not an agent. Time doesn't have
4:39 hands. It doesn't reach into the fridge
4:42 and sour your milk. Bacteria do that.
4:44 Chemical reactions do that. Entropy does
4:47 that. Time is just the bookkeeping
4:49 system we use to track the rate at which
4:52 those reactions happen. Saying time did
4:55 it is like saying inches built the
4:57 house. Inches didn't build anything.
4:59 Carpenters inches just tell you where
5:03 the walls are. Time is the ruler, not
5:05 the worker. Let's push this ruler
5:06 analogy further because this is where
5:09 things get really weird. If time is just
5:11 a ruler we use to measure the distance
5:13 between events, what happens if the
5:16 ruler itself is flexible? This isn't
5:18 science fiction. This is measurable
5:20 fact. We used to think that a second was
5:22 a second anywhere in the universe. If
5:24 you had a clock on Earth and a clock on
5:27 Mars, they would tick tock in perfect
5:30 unison. It feels obvious. It feels right
5:33 and it is completely false. The rate at
5:35 which clocks tick depends on where they
5:38 are and how fast they are moving. This
5:39 is not a mechanical failure of the
5:42 clock. It is a fundamental feature of
5:44 reality. Imagine you are driving a car
5:47 across a giant flat sheet of paper. You
5:49 can drive north or you can drive east.
5:52 If you drive purely north, you are
5:54 making maximum progress in the northward
5:56 direction. But if you turn the steering
5:59 wheel and start driving northeast, you
6:01 are sharing your speed. You are moving a
6:04 bit north and a bit east. You aren't
6:06 going north as fast as you were before
6:08 because you diverted some of that motion
6:12 to the east. Now replace north with time
6:15 and east with space. This is the essence
6:17 of relativity. You are always moving
6:19 through the universe at a constant
6:22 speed. But that motion is shared between
6:24 space and time. If you sit perfectly
6:27 still in your chair, you are dedicating
6:29 all your motion to moving through time.
6:31 You are traveling into the future at
6:35 maximum speed, 1 second per second. But
6:37 the moment you stand up and walk or get
6:40 in a rocket and fly, you are diverting
6:42 some of that motion into space. You are
6:44 moving through space, which means you
6:48 must mathematically must move slower
6:51 through time. Your clock slows down.
6:53 Your aging slows down. You aren't
6:55 breaking the machine. You are just
6:57 changing direction on the map. If you
6:59 could move at the speed of light, which
7:01 is the maximum speed limit of the
7:04 universe, you would be using 100% of
7:06 your motion for space. You would have
7:09 zero motion left for time. For a photon
7:12 of light, time does not pass. It is born
7:15 and absorbed in the same instant of its
7:17 own perspective. The universe is frozen.
7:20 Now, you might be thinking, "Well, I
7:22 don't feel my watch slowing down when I
7:25 run for the bus." Of course not. You are
7:28 too slow. You are a biological snail.
7:30 The effects are tiny at human speeds,
7:33 but they are real. We have to program
7:35 satellites with this math. Lightites are
7:37 moving fast. So, their time is different
7:39 from your time. We literally have to
7:42 adjust their clock motion. There is
7:44 another aspect of time that tricks us.
7:46 And it comes back to that counting socks
7:48 problem. The idea of pattern
7:51 recognition. We perceive time as having
7:54 a direction, an arrow. Past is fixed,
7:57 future is open. You can remember
7:58 breakfast, but you can't remember
8:01 dinner. Why? If physics equations work
8:04 forwards and backwards, and most of them
8:07 do, why can't we remember the future? If
8:09 you film a planet orbiting a star and
8:11 play it backward, it looks perfectly
8:14 fine. It obeys all the laws of gravity.
8:16 But if you film an egg falling on the
8:18 floor and breaking and then play it
8:21 backward, everyone knows it's fake. The
8:24 yellow yolk doesn't leap off the floor,
8:26 assemble itself into a ball, and seal
8:29 itself inside a shell. Here's the
8:31 secret. This isn't about time itself.
8:34 It's about probability. It's about
8:37 disorder. It is much, much easier to
8:39 break an egg than to build one. There
8:41 are a billion ways for an egg to be
8:44 broken. Scattered here, splattered
8:47 there, shell in three pieces, shell in a
8:49 thousand pieces. But there is only one
8:52 specific arrangement where the egg is
8:55 whole. So as things move and interact,
8:57 they naturally stumble from the
9:00 organized state, few options, to the
9:02 disorganized state, many options. We
9:05 call this entropy. And this is the only
9:08 reason you feel an arrow of time. You
9:10 are watching the universe shuffle the
9:12 deck of cards. You started with a
9:15 perfectly ordered deck and every second
9:17 that ticks by is just the universe
9:19 shuffling it a bit more. You can't
9:22 unshuffle the deck just by hoping. This
9:24 means that your sensation of time
9:27 flowing is actually just your brain
9:29 registering the increase of messiness in
9:31 the universe. You are a disorder
9:33 detector. When you distinguish the past
9:35 from the future, you are really just
9:38 distinguishing less messy from more
9:40 messy. If the universe were in a state
9:43 of maximum mess, maximum entropy, where
9:45 everything was evenly spread out and
9:48 nothing interesting was happening, your
9:50 brain wouldn't be able to tell the past
9:52 from the future. There would be no egg
9:54 to break. There would be no memory to
9:57 form. In a thermal equilibrium universe,
10:00 the arrow of time vanishes. So, let's go
10:02 back to those people counting in their
10:05 heads. The ones seeing the tape measure
10:07 versus the ones hearing the voice. They
10:09 are both struggling to impose a rigid
10:12 linear structure on a universe that is
10:14 actually much more flexible. We build
10:17 these mental models, these counting
10:20 machines because we need to survive. We
10:22 need to know when the tiger is coming or
10:24 when the harvest is ready. We evolved to
10:27 track duration, but we did not evolve to
10:30 understand the dimension of time. Our
10:32 brains are efficient, not accurate. We
10:34 focus on the now because that is where
10:38 we live. But in physics, now is a very
10:40 slippery concept. If you and I are
10:43 standing next to each other, our now is
10:45 effectively the same. But if you are on
10:48 a planet a million light years away and
10:50 you start walking away from me, your
10:52 definition of now slices through the
10:55 universe at a different angle than mine.
10:57 What you consider to be happening right
11:00 now might be in my future. What I
11:02 consider right now might be in your
11:05 past. There is no universal now that
11:06 covers the whole universe like a
11:09 blanket. The universe is a block of
11:11 events, a four-dimensional loaf of
11:14 bread. And how you slice that loaf
11:17 depends on how fast you are moving. This
11:20 is hard to grasp. It feels wrong. It
11:21 feels like I'm telling you that up is
11:24 down. But that is because you are trying
11:26 to translate the high-level language of
11:28 the universe into the low-level language
11:30 of your biology. You are trying to count
11:33 socks when you should be measuring light
11:35 beam. When you try to force the universe
11:37 to fit your intuition, you get
11:40 confusion. You get paradoxes. But when
11:42 you let go of what you think time is,
11:44 when you stop trying to count it like a
11:46 pile of laundry and start measuring it
11:49 like a dimension of space, suddenly the
11:51 equations work. Suddenly the universe
11:54 makes sense. We are not done because
11:56 even if we accept that time is a
11:58 dimension and that it stretches and
12:00 squashes with speed, there is a much
12:02 deeper question lurking at the bottom of
12:05 the well. We talked about measuring time
12:07 and we talked about the arrow of
12:09 disorder, but we haven't talked about
12:11 the beginning. If time is a measure of
12:13 change, what happens when you run the
12:16 movie backward all the way to the first
12:18 frame? If the universe is expanding and
12:21 we wind it back, it gets smaller and
12:24 smaller, hotter and hotter. Eventually,
12:26 you hit a point where the laws of
12:28 physics themselves start to melt. You
12:31 see, all our clocks, our atoms, our
12:34 planets, our light beams, they exist
12:36 inside the universe. But if the universe
12:38 itself was born in a moment we call the
12:41 big bang, does it make sense to ask what
12:43 happened before that? This is the
12:45 ultimate test of your new definition of
12:48 time. If time is just a way of ordering
12:50 events inside the universe, then asking
12:53 what happened before the universe might
12:55 be as nonsensical as asking what is
12:58 north of the North Pole. It sounds like
13:00 a valid question grammatically, but
13:03 geometrically it is gibberish. There is
13:05 no north of the North Pole. There may be
13:08 no time before time began. And yet we
13:11 still have that nagging feeling, that
13:15 internal counter, that voice counting 1
13:18 2 3. We desperately want the universe to
13:20 have a backstory. We want a timeline
13:23 that stretches back forever. It is hard
13:25 to accept that the tape measure might
13:27 just start, that the counting machine
13:30 had an on switch. This creates a
13:32 friction between our psychology and our
13:35 cosmology. We are finite beings trying
13:38 to comprehend the infinite using tools
13:40 made of meat and electricity. It is a
13:43 wonder we understand anything at all.
13:45 Consider the patterns again. The person
13:47 who sees the tape measure in their head
13:49 can count while reading because they are
13:52 using different circuits. Visual versus
13:55 verbal. Physics is the same. Classical
13:57 mechanics was the verbal counting. It
13:59 worked for day-to-day stuff. Relativity
14:02 is the visual tape measure. It allows us
14:04 to process complex patterns that the old
14:07 way couldn't handle. We are constantly
14:09 upgrading our mental software to match
14:12 the hardware of reality. And the upgrade
14:14 process is painful. It requires
14:16 discarding ideas we love like the river
14:19 of time. But here is the beautiful part.
14:21 Even though your intuition is wrong,
14:23 even though your internal clock is a
14:26 biological hack, and even though time is
14:29 a flexible, relative, bendy dimension
14:31 rather than a strict metronome, it still
14:33 works for you. You can still boil an egg
14:36 usually. You can still meet a friend for
14:38 coffee at 2 p.m. The weirdness of
14:41 relativity is hidden under the hood. You
14:42 don't need to understand the combustion
14:45 engine to drive the car, and you don't
14:47 need to understand space-time metrics to
14:49 live your life. But isn't it better to
14:51 know? Isn't it better to know that the
14:53 engine is there? This brings us back to
14:55 that strange experiment with the
14:56 counting. Remember the difference
14:58 between the person who hears numbers and
15:01 the person who sees them? This is not
15:03 just a party trick. It reveals a
15:05 terrifying gap in how we understand the
15:07 universe. When two people talk to each
15:10 other about something complex like time
15:13 or relativity or love, they think they
15:15 are speaking the same language. They
15:18 nod. They agree. They say, "I
15:20 understand." But what is really
15:22 happening? You are running a massive
15:24 invisible translation scheme. You take
15:26 the words I say and convert them into
15:29 your private internal imagery, which
15:31 might be completely different from mine.
15:34 I say 1 minute and I see a clock face.
15:37 You hear a voice saying 60 seconds. We
15:38 arrive at the same answer, so we think
15:41 we agree, but the machinery inside is
15:44 totally alien. This matters for physics
15:46 because it exposes the fragility of
15:48 common sense. Common sense is just the
15:50 collection of prejudices you acquired by
15:53 age 18. It is built on your specific
15:55 internal imagery. If your mental image
15:58 of time is a tape with numbers on it,
16:00 you will struggle to understand how time
16:02 can bend. If your mental image is a
16:04 voice counting, you will struggle to
16:07 understand how time can be spatial. When
16:09 we try to teach you about the quantum
16:11 vacuum or the curvature of spacetime, we
16:14 aren't just giving you new facts. We are
16:16 asking you to delete your operating
16:18 system. We are asking you to throw away
16:20 the tape measure and silence the voice.
16:23 And that is why it feels so hard. That
16:25 is why your brain rejects it. You aren't
16:27 just learning. You are translating
16:29 against the grain of your own biology.
16:31 So let's try to break that biology one
16:33 more time. We talked about how time
16:36 slows down when you move. But there is a
16:37 consequence of that which is even more
16:40 disturbing. It destroys the concept of
16:43 simultaneity. Imagine you have two very
16:46 long poles miles apart. You decide to
16:48 flash a light on top of both poles at
16:51 the exact same instant. Now you see them
16:54 flash together. Simple. But now imagine
16:57 a spaceship flying past you at half the
16:59 speed of light. To the person in the
17:01 spaceship, those flashes do not happen
17:04 at the same time. They will measure
17:06 absolutely correctly using perfect
17:09 instruments that one pole flashed before
17:12 the other. Who is right? You or the
17:14 spaceship? You are both right. This is
17:17 the part that breaks the human brain. We
17:19 are obsessed with the idea of a
17:22 universal now. We think that right now
17:24 something is happening on Mars. But
17:27 right now is not a physical reality. It
17:29 is a coordinate choice. If you change
17:32 your speed, you slice the loaf of
17:34 spaceime at a different angle. You
17:36 literally change what events are
17:38 considered simultaneous. This means
17:41 there is no universal master clock
17:43 ticking in the background of the cosmo.
17:45 There is no God's eyee view where
17:47 everything happens in a neat sequence.
17:49 The order of events can actually flip
17:52 depending on how you move. Cause and
17:54 effect usually stay safe, but the timing
17:58 the timing is up for grabs. If now is
18:00 relative and time is just a dimension
18:02 like space, this leads to a conclusion
18:05 that makes the river of time look like a
18:08 nursery rhyme, we call it the block. If
18:11 time is a dimension, then the past, the
18:13 present, and the future all exist
18:16 simultaneously. Think of a movie reel.
18:18 You watch the movie frame by frame, so
18:21 it feels like a story unfolding. But if
18:23 you hold the reel in your hand, the end
18:25 of the movie exists at the same time as
18:28 the beginning. The frames are all there,
18:30 frozen and plastic. The only thing
18:32 moving is the light of the projector. In
18:35 this analogy, your consciousness is the
18:37 light. The events of your life, your
18:39 birth, your breakfast this morning, your
18:42 death, they are all just frames on the
18:45 real. They already exist. They always
18:47 have. This is why physicists sometimes
18:50 say the flow of time is an illusion. We
18:53 don't mean it's fake. We mean it's a
18:55 perspective trick. The dinosaur that
18:59 died 66 million years ago is not gone in
19:01 the sense of being erased from reality.
19:03 It is just at a different coordinate
19:05 down the road in the time dimension.
19:07 Just because New York is far away from
19:10 you doesn't mean New York ceases to
19:13 exist. It's just elsewhere. The past is
19:16 just elsewhere in time. The future is
19:18 elsewhere in the other direction. The
19:21 structure is static. The experience is
19:23 dynamic. Now you might ask, if the
19:26 future already exists, do I have free
19:28 will? That is the wrong question. That
19:30 is a philosopher's question. The
19:33 physicist's question is, does the system
19:35 allow for predictability? And the answer
19:38 is messy. Remember the egg breaking?
19:40 That's entropy. The future is the
19:43 direction of more mess. Even if the
19:45 block is static, the patterns inside the
19:48 block follow rules. You can't just jump
19:49 to the end of the movie because the
19:51 frames between here and there are the
19:54 necessary steps to build that future.
19:56 You are the process. You are not a
19:58 passenger riding through time. You are
20:02 the chemical reaction that is time. You
20:04 are the shuffling of the deck. Let's go
20:06 back to the counting experiment one last
20:08 time because there is a hidden lesson
20:10 there about capability. The person who
20:12 could visualize the tape measure could
20:14 do something the voice counter couldn't.
20:16 He could read and count at the same
20:19 time. He had a parallel processing power
20:21 because his internal imagery was
20:23 different. Physics gives you that power.
20:25 When you stop translating the universe
20:28 into rivers and flows and start seeing
20:31 it as geometry, as math, as structure,
20:34 you gain a superpower. You can see how
20:37 black holes stop time. You can see how
20:39 gravity is just the bending of the map.
20:41 You stop being a victim of the illusion
20:44 and start becoming a reader of the map.
20:46 And yet, we must be humble. We talked
20:49 about how we store information. Vessel
20:51 functions, exponentials, electric
20:54 fields. We learn these fancy terms. We
20:57 write down these symbols and we think we
20:59 have captured reality. But remember, the
21:02 guy next to you might be storing that
21:04 same vessel function using a completely
21:06 different mental image. He might see a
21:08 vibrating drum head while you see a
21:11 squiggly line. We are all just blind
21:13 people touching an elephant, describing
21:16 it to each other in languages we barely
21:19 understand. The math work that is always
21:21 always a translation. We found that
21:24 simple counting to a minute is
21:26 susceptible to all kinds of external
21:28 factors and internal methods. If our
21:30 sense of a mere 60 seconds is that
21:33 unstable, imagine how unstable our sense
21:37 of eternity or beginning. We ask how did
21:39 the universe begin? And we expect a
21:42 story like once upon a time. But the
21:44 universe doesn't work in story. It works
21:47 in states. It works in field. It works
21:49 in ways that might not even have a
21:52 before. We are trying to count the socks
21:54 of the universe. But the universe isn't
21:56 wearing socks. It's weaving the fabric
22:00 itself. So what is time? Time is the
22:02 thing that stops everything from
22:04 happening at once. Time is the heat
22:07 death of the universe waiting to happen.
22:09 Time is the curvature of space caused by
22:12 matter. But most importantly, time is
22:15 the mirror. It reflects the limitations
22:17 of your own brain. When you look at a
22:20 clock, you aren't seeing time. You are
22:22 seeing a machine designed to comfort
22:24 you. You are seeing a regulator for your
22:28 society. Real time, physical time, is a
22:31 wild untamed beast that moves at
22:33 different speeds, stops near black
22:36 holes, and might not even flow at all.
22:38 If this makes your head hurt, good. That
22:41 means the translation scheme is breaking
22:43 down. That means you are starting to see
22:46 the cracks in the wall of common sense.
22:49 Don't be afraid of the confusion. In
22:52 science, confusion is not a dead end. It
22:54 is the starting line. It means you are
22:57 about to discard a comfortable lie for a
22:59 difficult truth. Time is not what you
23:02 think it is. It is so much more. And the
23:05 fact that we little biological machines
23:08 made of stardust and anxiety can figure
