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So, we all know that there is nothing faster than light in the universe. In just one second, light can circle the earth 7 times. It's quite quick, like a flash and it's gone. One spit, and you would think that at this speed, the entire cosmos should be at our fingertips almost instantly. But no, light takes over 8 minutes just to reach us from the sun, which for some reason seems insanely slow. And it takes more than four years for light to reach us from the nearest star, Proxima Centauri. And then there's our own galaxy. It takes light about 100,000 years just to cross the Milky Way. And remember, the Milky Way is just one galaxy among hundreds of billions in the visible universe,
perhaps as many as 2 trillion if some estimates based on Hubble's data are accurate. And here we begin to understand: light is not slow. Obviously not. It's the fastest thing in the universe. But on the scale of the entire cosmos, or even our own little solar system, even the fastest thing in the world starts to seem painfully slow. Not because the light has failed us, but because the universe is so absurdly vast that the human mind is simply not designed to comprehend such distances. It just doesn't fit in my head. But saying that the universe is huge doesn't explain anything to our brain. A million kilometers or a billion, it seems, are almost the same. In our imagination, they simply merge into one blurry spot. A
bunch of kilometers somewhere very, very far away. Either way, your brain just thinks it's too much. So instead of just throwing bigger and bigger numbers at you, let's turn these absurd cosmic distances into something we can understand with our minds. Time spent waiting for a response to a message. Let's say you decide to chat with someone on the moon. You're sending a signal, but wait, let's clarify something quickly. Before we go any further, sound does not travel in empty space. You probably already know. Less with that. No air, no sound. That's why we communicate using radio waves. And radio waves are light. Of course, invisible light, but essentially the same.
Electromagnetic waves. In a vacuum, they move at the same speed. So, the signal's journey to the moon takes about 1.3 seconds one way. This means that in a normal conversation, there will be this weird, little delay where you'll constantly be interrupting and talking to each other at the same time, like you're on some crappy video call. It's annoying, yes, but it's still human. This is still a conversation. Next Mars. The one- way signal takes anywhere from three to 22 minutes, depending on where Earth and Mars are in their orbits. That means you will have to wait for a response from 6 hours to 44 minutes. At this point, it's not really a conversation anymore. You simply exchange voice messages. When the planets are
close together, you send a voice message, then sit awkwardly, fidgeting with your fingers, scrolling through your mail, taking a sip of coffee, and waiting. When they're further apart, you go to work out, maybe turn on some new cool videos, rethink some of your terrible decisions, and then come back for the answer. Now let's take a look at Voyager 1. It's the most distant spacecraft we've ever sent into space. We launched it in 1977. And ever since then he's been flying, or drifting, or running away, call it what you will. Further and further away from us. It has already crossed the heliosphere, the protective bubble of the sun, and entered interstellar space. And just sending him a command and then waiting for confirmation that he actually heard us
takes almost two days. At such a distance, real-time communication is not just difficult, it's dead. OK. Now about the stars. Our closest stellar neighbor after the Sun is Proxima Centauri. It takes about 4.24 years for the signal to get there. And this is where we will finally need this great cosmic yardstick. Light year. A light year is not time. This is the distance that light travels in one year, almost 9.5 trillion km. Proxima is more than four such light years away. So, let's say you send a message there when your baby is born. By the time the answer comes, this kid will already be in third grade. He will be 8 years old. And by the time he responds next, he'll be
running off on dates, getting scolded for coming home late, and wondering where to start. But this is only the nearest star in fact. neighboring house. What if we want to write to someone in the center of the Milky Way? The distance is about 26,000 light years. You send a message today and the response comes 52,000 years later. While you wait for the notification signal, the entire known history of mankind will have time to repeat itself several times in a row. That's right. Ping. But the Milky Way is still just our local space region. Let's look at our next-door neighbor, the Andromeda galaxy. It is located at a distance of about 2.5 million light years. Now imagine that right now, today, we receive a response from Andromeda to a message
that was sent in the past. This would mean that our usual hello, how are you, must have left Earth about 5 million years ago, before the genus Homo even existed. Homo. Besides, people didn't just not exist back then, we weren't even close to it. The hominins that roamed Africa were so ancient that they looked much more like chimpanzees than anything remotely like us. Here is an illustration. And that's where the madness lies. On the cosmic map, the Milky Way and Andromeda are essentially neighbors, although not close in any human sense. There is a cosmic chasm between them, but
by the standards of galaxies, it is practically next door. And here's the thing. Even here, communication ceases to be communication. And you don't text a friend in a neighboring city. You are sending a message so far into the future that the person who receives the reply will not just be older. It will be a completely different species, living in a completely different world, provided that by then there will be anyone left at all to check their email. Some of you are probably thinking, "Okay." We realized, on the scale of the universe, even light, the fastest thing we know of, is actually very, very slow. But let's lower our expectations.
Can we at least reach the nearest star in a reasonable amount of time? I mean, we have some idea of how big a light year really is. But how long will it take us to travel at least one light year? Let's start with the absolute record holder, the fastest man-made object in history, the Parker Solar Probe. We launched it back in 2018 with the mission to touch the Sun. And he literally does it. It flies through the sun's outer atmosphere, the corona. But that's a story for another time. So, Parker reaches an insane 191 km/sku. That's 688,000 km/h. Half. Fast enough to orbit the Earth in about 3/5 minutes. Sounds absolutely cool. But there is one huge nuance. Parker doesn't have some kind of miracle runner who can accelerate
him to that speed when the call comes. Initially, a good rocket was supposed to launch him into space. Then seven flybys of Venus gradually pulled its orbit closer and closer to the Sun. And once it gets close enough, the Sun's gravity turns it all into a mad dive downward, accelerating the umbrella to the aforementioned superspeed. This speed is real, but it is the speed of falling towards the sun as it moves away. Again, solar gravity takes a significant portion of this velocity back. If we want to fly away, we need to fight gravity, not fall into it. That's exactly what Voyager 1 is doing. It's hurtling into deep space at a speed of about 17 km/s.
And unlike Parker's peak speed near the Sun, this is Voyager's actual outward speed, achieved by its launch vehicle and gravity maneuvers near Jupiter and Saturn. This is what ultimately gave Voyager a good jolt, throwing it beyond the planets and into interstellar space. So moving at that speed only to cover one single light year. Voyager will take 18,000 years. The funny thing is that even if we flew that one light year for 18,000, we would still be hanging out in our own backyard somewhere within the Orta skyscrapers right on the edge. But technically still within our solar system. We wouldn't even have crossed Zaporizhzhia yet. So what if we wanted to get to the nearest star, Proxima Centauri? Something
moving at the speed of Voyager would drag its ass there for about 75,000 years. This means that almost 3,000 generations would have changed on Earth after launch. Just think about it, you're sending an expedition, and the one who actually gets there will be your great-great-great- grandfather. Well, you get the idea. Your grandson with the prefix pra added about 3,000 times. The obvious answer. So what's the problem? Let's just build a bigger rocket, load it with enough fuel, and fly faster. But here we are faced with what engineers call the tyranny of the rocket equation. And that is what tyranny is. You can't argue with mathematics. And don't care about our
ambitions. To fly faster, you need to burn fuel, but fuel has mass. To disperse that extra fuel, it takes even more fuel, and to pull that fuel that pulls fuel, it takes even more fuel. And all this mess is described by the so-called Tsiolkovsky equation, which I will now display on the screen. But let's skip the complicated math. The point is simple. Each additional bit of speed causes the rocket's required launch mass to swell faster and faster. At some point, you will hardly be able to see the ship itself next to this mountain of fuel. A tiny little boat. Big, loud, giant gas tank. And that's just for acceleration. If you just want to speed past Proxima Centauri like space racers. Perfectly. You don't
slow down. Congratulations. You've just seen it for about 12 seconds, but if you really want to get there, stop, look around, take a few pictures, maybe put a little flag that says, "Yay! We did it," then now you have a second problem. In space, there is no asphalt for your tires to grip, and no air to open a parachute. You are in a vacuum. Nothing will stop you for free. To stop at a nearby star, about halfway to it, you would have to turn the ship backwards and fire the engines in the opposite direction. This means that you will have to carry the fuel for braking from the very beginning, making the ship much heavier. Because of this, you will need extra fuel. Technically reactive mass, but not the essence. To disperse brake fuel, remember?
And to disperse this extra fuel, you need, guess what? That's right, even more fuel. And now the rocket equation is n't just annoying, it shows you its nose or some other body part and laughs. Now add space dust to the list. Interstellar space is almost empty, but almost is the key word here. At 20% of the speed of light, even tiny particles hit like bullets at hyperspeed. They literally shoot through your shield, rip off materials, and gradually reduce the bottom of the ship to dust. And if you collide with something large, say a grain of sand, the collision will be catastrophic. To spot something so small in advance as it approaches you at 60,000 km/h would be, to put it mildly, a terrifying nightmare. So, the ship will need a
massive protective shield. And even a relatively thin shield on such a huge ship can weigh, well, let's say, a whole bunch of tons, which, again, you have to accelerate and decelerate, and then the cycle repeats. more mass, more fuel, even more mass, and so on. Okay, you could say that chemical rockets are a thing of the past, primitive old-school 20th century technology. Someday we will invent hyperdrives like in Star Wars, or Warprockets like in Star Trek, or build mass relays like in Mass Effect. Even though in that universe they were built by an ancient race of killing machines. But it doesn't matter, somehow we'll break the system. Okay, let's imagine that we've solved all the engineering problems. We threw chemical fuel in
the trash, invented some insanely powerful sci-fi energy source. figured out how to accelerate, brake, protect the ship, keep everyone alive, and make the whole thing actually work. Will this help? Well, obviously, it would help a lot, but to be honest, it wouldn't. This still won't solve the real problem, because the deepest barrier isn't hidden in the rocket blueprints, it's built into spacetime itself. So why does this speed limit even exist? The phrase "nothing can move faster than light" sounds as if light is the absolute champion of the universe, and everyone else simply can't keep up with it. But in reality, this is not the case at all. This speed limit is not a personal best. The constant goes
much deeper. It is built into the very fabric of space-time, and light travels at such speed in a vacuum simply because photons have zero rest mass. To understand how this all works, let's use a simple mental model. It is clear that this is an inaccurate scientific description, but it does explain the relationship between speed in space and proper time. I mean the time on your own watch. They are interconnected. Imagine that any light with mass has a certain limit to its motion, and it can divide this motion between space and time. Let's say you are walking across an endless empty field.
Your speed is absolutely constant. You can't go faster or slower. If you are going straight north, 100% of your speed goes to moving north. But the moment you turn slightly east, your northward movement slows down. And the total speed doesn't change, it's just split between the two directions. Now replace north with time and east with space. This fixed speed is the constant C. The speed limit of the universe. When you are sitting on the couch and not moving, your speed in space relative to the room is zero. This means that 100% of your speed goes towards moving through time. You age as fast as possible, but as soon as you get up and go to the kitchen, some of your speed goes into moving through space. This
means that less of your movement is left to move through time. Your clock starts ticking a little slower compared to the clock left on the couch. Does this mean that if you run all the time, you will age more slowly? Well, technically yes. You do age more slowly, but our human speeds are so insignificant compared to the cosmic limit that you only save billionths of a second. Everything changes if you accelerate a spacecraft to 99% of the speed of light. For travelers, I am one year old, while on Earth, I am about seven years old. It's just geometry. You only have 100% of your speed to divide between these two directions. Choose where you want to fly: into space or into the future. So, anything that has mass must
divide its motion between space and time. Photons, on the other hand, have no rest mass, and that changes everything. So in a vacuum, they simply have no choice. All their movement must go through space. This means that they have absolutely nothing left to move through time. Think about it. Speaking in the language of the theory of relativity, while a photon is flying, its own time simply does not pass. Not one second, not one trillionth of a second, nothing. For us, millions of years can pass between the emission of a photon on the surface of some distant star and its absorption on your retina. But the proper time along this trajectory is zero. Okay, that's what the masses do. But what happens
if we do break physics and fly faster than this limit. The constant C is not just the speed of light, it is the speed of cause and effect. The highest speed at which any signal, influence, or change can propagate through the universe. A boundary can be drawn around each event, showing how far its impact can reach. One second is one light second, one year is one light year. In normal space, this would look like an expanding sphere, but in spacetime. When we plot it on a graph like this, this expanding boundary forms what's called a light cone. Everything that is inside,
everything that maintains a cause-and-effect relationship with this event. It sounds complicated, but it really only means one thing. One thing can affect another. One event can cause the next: and everything that is outside is completely devoid of this connection. This event will no longer be able to affect him in any way. To connect them with light, a signal, or literally anything, you would have to exceed C, which is the speed of light. Traveling faster than light would mean somehow going beyond this cone. And in special relativity, there is no single privileged frame of reference that is always correct. Different
observers differ in their opinions about which distant events occur simultaneously. So for some of them, your arrival on another planet from Earth would occur before your departure. You would have been there before you left. If you sent a similar signal faster than light, say a message in the form of a question from this planet back, the answer could arrive before the question was even asked. This is why you can't break physics. If you exceed the speed of light, you don't hit a physical wall, you hit logic. Think of the limit on the speed of light as a built-in protection for the universe against causal paradoxes, essentially, against the catastrophes of the collision of cause and effect. And there's another barrier even before that. For
anything that has a lot of rest, a ship, a person, a wormwood, anything. The closer you push it to the speed of light, the more and more energy it needs to continue its own acceleration. And as you approach si, or the speed of light, the energy required doesn't just become large, it increases infinitely, unceasingly. Therefore, reaching the speed of light would require infinite energy. And that doesn't mean a lot of energy, no more than we can currently produce. Infinite energy is the universe's polite way of saying, "No, you can't do that." What were you thinking about anyway? It is this speed limit that turns the terrifying scale of space into a real problem. The constant C is not some
artificial limitation. This is a fundamental property of space-time that prevents cause and effect from switching places. A light year is not just a unit of distance. This is a hard limit on how far any of our influence can spread in a single year. But combine this rule with cosmic distances, and our isolation becomes obvious. The gaps between worlds are so huge that what is common now no longer works as we would like. At such distances, there is no real conversation, no quick answer, no wait, I'll be right there. There is only distance and time. And that strict speed limit that keeps everything at a distance. And yet there is one comedic thing about all of this. We sit on a tiny planet, unable to change any of these rules. But somehow
we figured them out. We have even mapped these boundaries from the scale of one light year to the most distant galaxies from which light can still reach us. By some miracle, we, confused little monkeys on a tiny pebble in the middle of boundless space, were able to comprehend this. And I personally believe that one day we will find a clever way to get around these rules, because simply put, we are just amazing.
