Astrum Space - The Speed of Light Reveals Something Strange About the Universe

Episode Date: July 15, 2026

What would happen if you travelled near the ultimate speed limit of the universe? Spoiler: strange things start happening to space and time. This Astrum compilation explores the speed of light. Find out what the speed limit really means in 4D space, why it exists at all, and the strange ways light behaves when we’re not looking. ▀▀▀▀▀▀Astrum's newsletter has launched! Want to know what's happening in space? Sign up here: ⁠https://astrumspace.kit.com⁠A huge thanks to our Patreons who help make these videos possible. Sign-up here: ⁠https://bit.ly/4aiJZNF

Why does reality have a speed limit? It is common knowledge that the speed of light is the fastest that anyone can go, but why does this cap on causality exist? And why is it exactly 299,792,458 meters per second? Why not more? Why not less? If you're like me, you've wondered about these strange properties of light, but recently, I think I might have found an answer.

and it lies in hyperbolic geometry. And the more I've considered it, the more it's blown my mind. I'm Alex McColgan and you're watching Astrom. Join with me today for the third part in our series on the unseen world and bring together what we have learned so far to try to answer some of the biggest questions about why our universe is the way it is. Before we begin, I should mention that this is a continuation of a

model that has been developed in collaboration between me and my brother, which we began in this video about 4D space, and continued exploring in this video about the shape of our universe. If you haven't watched those videos yet, I would highly recommend you check them out, as we will be blending both concepts together in this video. Check the links in the description or the top right if you need a refresher. With that out the way, let's talk a little bit about light. There is an interesting observation we can make about light. From an external perspective, it appears as if light is travelling at 299,792 meters per second. This is true no matter what perspective you look at it from, whether you are at standstill,

whether you are moving towards it or away from it. It always looks as if it is travelling at this speed. However, there is a single, interesting exception to this rule which had always puzzled me, the photon's perspective. Einstein has proven that for an object travelling at light speed, time would slow down so much that it would be at zero. If you were to suddenly start travelling at the speed of light towards Jupiter, you would notice zero time passing, but would observe that you have travelled 679 million kilometres. And there would probably die of the lack of air, the punishing G forces and the friction

burn along the way. But what happens if we try to calculate your speed using these figures? Well, speed is distance over time, so 679 million divided by zero equals... If you tried plugging this into your calculator, you would quickly run into an error here. calculators do not like dividing by zero. This is because the smaller the denominator becomes on a fraction, the larger the total number becomes. If you reduce the value of the denominator all the way down to zero, the only way this can work is if your total answer becomes infinity. If you travel for zero time over any distance greater than zero, you have just traveled at infinite speed. So from

From light's perspective, it is travelling infinitely fast, not at 299,792,458 meters per second. Let's call that C from now on. So why is it that everyone else detects light travelling at sea, but light thinks it's going infinitely fast? What I'm about to share is one possible theory. It's going to involve a 4D hyperbolic space. That's quite a mouthful, so let's take our time exploring this space. so we know what we're talking about.

To quickly recap on the rules of a 4D space, let's imagine that all of 3D reality has been compressed into a single flat line travelling horizontally across space. This leaves us free to make everything up or down in this space into the future or the past. To put it another way, the x-axis represents moving through space and the y-axis represents moving through time. This is how we can get the extra dimension, our fourth D. Here in 4D space, time is simply another direction we can go in. Hyperbolic might sound a little intimidating too, but simply put, all it means is that the lines diverge away from one another, always. This has the effect of warping space in a way our brains don't really process well, but essentially means there's

more and more space the further out you go, but exponentially so. Other than that, traveling through this space obeys the same rules that traveling through 3D space uses in terms of the physics rules involved. Objects that start moving must be acted upon by another force or they will continue moving at the same rate. Objects at rest remain at rest. Conservation of momentum is maintained. Now, let's imagine for whatever reason there was some big expansion event in the past that sent us all moving in the upwards direction. A big bang, if you will. I wonder where one of those might have come from. But this expansion was not simply in space, but in time too. It's a 4D explosion. We are now in motion, moving solely up at the top

of this expanding bubble. For now, we are not moving anywhere in space. We are simply moving forwards in time. We travel consistently, and will continue to travel consistently until we are acted upon by another object or force. But as we are new, and there is nothing but empty space above us, we are going to go up infinitely. There's nothing up there to bump into. Now, let's imagine for a second that we decide we no longer want to go straight up. Let's try to change direction.

In physics, any change of direction is a form of acceleration. This may not make much sense intuitively, but it becomes easier to understand if we split our vector into two components, our velocity in the X direction and our velocity in the Y direction. It then becomes easy to see that changing our direction comes about by decelerating with one of our values and accelerating with the other. We don't have to change both values, though. Let's just give ourselves a little impetus in the X direction.

Obviously, the more we are pushed, the faster we are going to travel, and the more our total vector begins to lean towards a perfect horizontal line. The size of our vector increases. However, let's say that we want to go faster. In fact, we want to go so fast that we are no longer traveling in the Y direction and are only moving in the X direction, or space. Is there any amount of push we can get in the X direction that will make it so that we are actually going completely horizontally? No. You could increase the distance in x by a larger

and larger amount, but as long as Y has some value, you'll never actually get that vector perfectly going across space. The only way you could get your vector in the time direction to slow down is if you pushed against something that's ahead of you, or pulled on something behind you. But if everything near you is in the same second you are in, there's nothing to push against. You can only push each other left or right. Nothing is ahead or behind. Interestingly, with only this available to you, your vector can trend closer and closer to flat, but it never actually reaches it. And increasing your speed produces diminishing returns on how much flatter you can get your vector. You have a limit. You would essentially

need to go infinite speed to approximate a flat line, and to go infinite speed you would need need infinite energy, difficult to get your hands on. Of course, this is where the idea diverges from reality. There's nothing here so far that imposes a speed limit on our model. You should easily be able to go faster than the usual light speed limit. With infinite energy, you could go 3 billion meters per second, or 3 trillion. But in the real universe, we don't see that. Everything normally seems to be capped at sea.

There is a similar trend where the more energy you put in, the less additional speed you get, but that occurs at close to light speed, not infinite speed. So our 4D model seems to have failed. But this is not regular 4D space. This is a hyperbolic 4D space. Let's observe what happens when you try to travel at near infinite speeds when the lines start to bend. Here you have zoomed along at a speed that's as fast as infinite as you can imagine.

Speed is a tricky little concept here, but let's say that from your perspective you covered a distance of 400 million meters in a second. So faster than the speed of light. What happens? Well, you hit this little curve line over here. Although it is bent to be almost a C shape, if you follow the line down, you'll see that it is a timeline, not a space line. And because it is a hyperbolic space, there is more here than meets the eye.

Let's jump over to that point and see where we ended up. Although in our movement vector, by our origin we only traveled one square high, by our end destination we have ended up at a point multiple squares high. By taking a journey sideways and by only experiencing a second to forward momentum through time ourselves, we have ended up many seconds into the future. We have taken a shortcut into the future. This is what we observe in the real world. Objects that move at great speed seem to suddenly experience reduced time.

They believe only a few seconds have passed, but far more time can occur to an external observer. And suddenly it really throws off our maths. Because how does an external observer record our speed? If we started at an origin point of zero, but ended at an origin point that's 10 seconds into the future, they have to say that we have travelled 400 million meters. in 10 seconds for a speed of 40 million meters per second, far below the speed of light, no matter what we thought we were doing. Which is kind of like what light seems to be experiencing.

And the faster you push yourself in the X direction, the more you encounter the warping effects of hyperbolic geometry, and the more it keeps pulling you back towards the speed limit cap of the universe, it will never let you exceed it. This explains why there is a cap to the universe. even light, which, as far as it is concerned, does travel infinitely quickly, would be able to overcome it, provided the base we were resting on was ever so slightly curved. As soon as the photon slid onto the plane that was space, it would get swept up in the curvature of this hyperbolic 4D space. It would trace the limit of it true, but it would get caught in it. And then,

from our perspective, it would start to look as if we were simply moving uniformly at a speed of of sea. After all, we would see it leave, and then we would time how long it would take to arrive at its destination. It doesn't matter for us that it believed it had arrived there instantaneously by taking a shortcut through time. We would just record it as having arrived after some time had passed. So there you have it. Why is there a speed limit for our universe? Perhaps because space is curved and our 40 space is hyperbolic. At least, so claims this theory. It is, it must be stressed, just a theory.

It's possible that smarter people than me in the comments will explain why this is wrong. However, it does neatly explain to me why time dilation happens, and why reality has a speed limit, which I find quite appealing. In fairness, perhaps the only way to test it would be to try to go faster than the speed of light, and we have never gotten close to that speed. The fastest a human has ever gone is 11,083 miener. meters per second, when NASA astronauts returned in a spaceship from the moon, it would require incredible amounts of energy to travel sea from our perspective.

If it is true though, it would provide firm evidence that our universe really was hyperbolic in nature, and sadly quash any hope of us travelling backwards in time at any point, so sorry time travel fans. But at least we can console ourselves that although we probably can't travel to the past, Traveling through shortcuts to the future is definitely within the realms of possibility. How would the universe change if you approach the speed of light? What would everything around you look like? How would space and time act?

The answer is, a lot different from what you are currently used to. To travel the speed of light isn't actually possible for anything other than massless particles, like photons. It would require infinite energy. to get something with mass to that speed. The energy required exponentially goes up the closer you get. But there are instances of matter coming close. We've observed some particles travelling 99% of the speed of light.

Now for you and me, we have no hope of ever approaching these speeds. But if you did manage it, what happens to space and time from your perspective would be very noticeable. Let's ease you into this, as it's going to be a bit of a bit of. bit tricky to wrap your head around. We will simulate going from standing to traveling almost the speed of light. This is a fun little game called A Slower Speed of Light, released by MIT, demonstrating what would happen if the speed of light got progressively slower, eventually to walking speed. At first, my character looks around and sees the world normally.

But as I start to pick up these orbs, instead of speeding me up, the game slows the speed of light down to simulate what it would look like if we were travelling extremely fast over vast distances. As the speed of light slows, what becomes apparent to you? The first thing I notice is that the colours start to change. This is because of something called the relativistic Doppler effect. You see, when you look around and you see colour on objects, this is because light is reaching your eyes at specific wavelengths.

Longest wavelengths you can see are reds. The shortest wavelengths are violets. Beyond the range of our site are the infrared and ultraviolet. But when you are going very fast, because of the Doppler effect, some of the wavelengths that were in the infrared and ultraviolet now shift to wavelengths you can detect. Suddenly things that were invisible to us before become visible, like heat in infrared and fluorescent substances in ultraviolet. The faster you travel, the larger your visible range now becomes.

Light does travel in waves, but it is also a stream of particles called photons. As you head into the flow of particles at speed, the more particles will hit your eye, making everything ahead of you brighter. On the other hand, if you look behind you as you travel forwards, everything will get darker because less photons are reaching you. This is known as the search light effect. What else do you start to notice? You may notice that we seem to be gradually speeding up, but actually our speed always stays

the same throughout the game. We are just walking like we were at the beginning. This is the result of special relativity, namely time dilation. One of the laws of the universe is that the speed of light is a constant, however space and time are not, and can be warped. So, when you are moving, two things change, your time and your distances relative to stationary observers. Let me explain.

Time goes slower for an object that goes faster. This has been proven. If you have two clocks, one stationary and the other in rapid motion, say on a rocket, the times on each will go out of sync. This is why the times on satellites in orbit around Earth need to be occasionally adjusted, Or they'd go out of sync with Earth-based clocks. Not by much, a few milliseconds per year, but they would add up eventually. The faster you go, the more time dilation happens, until should you hit the speed of light,

the rate of time reaches zero. This means photons, or light particles travelling the speed of light, are unaffected by the passage of time. But let's go back to how time dilation affects us in the game. Removing the lighting effects will help us see this a lot more clearly. Now remember, throughout the game, our walking speed stays the same. It's the speed of light that slows down as we collect more orbs. And yet, it seems that we move a lot faster towards the end of the game than at the beginning.

What is happening here is that our time is going slower than everything around us. As a result, it's like the distances of space are shorter, meaning we get somewhere quicker from our perspective. In practice, this means that if we traveled in a vehicle that approaches the speed of light, we travel for one year at that speed, it all seems normal for us, but ten years have passed for people on Earth. Should you actually be able to travel the speed of light, you could get anywhere in the universe instantaneously from your perspective, but on Earth, however far in light years your journey

takes you, will equal the equivalent amount of years from their perspective. So do you want to go 40 light years away and can travel the speed of light? You get there instantaneously from your perspective, but for people on Earth, you show up there 40 years later. Again though, in practice, light speed travel is impossible for anything made of matter. The last effect is a weird one. It's like our field of view changes. This is from the effects of the aberration of light and the Lorentz transformation.

Light takes time to reach our eyes, and when we see anything, we are seeing that object in the past. Even now, you are watching this video with a tiny, tiny, tiny time delay, as light takes time to leave your screen and reach your eyes. As we move in the game, that object we are seeing isn't where we think it is anymore. You may have thought as you've been watching this video that I must be useless at computer games because I keep crashing into walls and missing orbs. But this effect means that I'm not standing where I think I am, because the more orbs

I have, the slower light is travelling, so I actually need to start turning a little ahead of what I'm used to, which is difficult to comprehend while navigating. like playing with lag. This effect also means that I can see much more of my surroundings in one go. This animation helps show why. The light source is moving relative to me as I move forward. But because the beam of light takes time to reach me, I see where it was relative to me in the past. When there is a lot to see around me, it's as if my field of view increases the faster I travel, as I'm suddenly seeing all these objects as they were relative to me in the past. Light, space, and time get more complicated still, but I won't delve into it

in this episode. All I can say is that I'm glad light appears almost instantaneous for us. This game was a bit of a thought experiment to see what the world would be like if light was slow, but it hasn't even gone into the other really problematic scenarios, like Earth traveling around the sun at the speed it does, how all our electronics would be affected, and other major issues. In the opposite vein, us being able to approach the speed of light would be beneficial for travelling large distances in short times. However, time is passing normally for people on Earth, meaning travelling anywhere in the universe and coming back again could be possible for you, but Earth would look a lot different on your return, with years,

decades, millennia, or more having passed, depending on how far you went. On your journey, due to the various effects, outside your ship everything would look warped, your field of view would be greater, a greater range of light wavelengths become visible, and in front of you would be much, much brighter. So, there we have it, how your universe would change if you approach the speed of light. What is time? In this channel, we've talked a lot about time. As black holes warp space around them, we've learned that time slows down. We've discovered the time-influencing effects of gravity, and even how the James Webb telescope can peer through time to the distant past by taking advantage of the fixed speed of light. All this makes sense so far, but what actually is

time. You can't taste it, touch it, or feel it. Yet time has an unstoppable influence on us, and is pushing us forward whether we like it or not. Doesn't something that impacts everything we do deserve some additional understanding? I'm Alex McColgan and you're watching Astrom. And while this is an area that scientists have many theories about, I'd like to share with you today one model that might help you understand this mysterious concept that is ticking all around us. By the end of this video, we are going to have a possible explanation for why time slows down as velocity increases, and why shapes warp when undergoing velocities close to the speed of light. This video is a collaboration with my brother, based on Recognize Scientific Theory,

where we have taken scientific concepts and combined them into something you may not have seen before. But before we get to that, we have to begin with one foundational idea. Time is actually another dimension. Now, before you double check that you haven't logged into some sci-fi channel by mistake, let's discuss what I mean by dimensions. While in popular culture, different dimensions are often described as parallel worlds that are very similar to ours, yet subtly different, In this context, when we talk of different dimensions, we are referring to the dimensions of space,

as in three-dimensional space, or 3D space, which may be far more familiar to you. This is by no means trivial, though. 3D space is all around you, it is the around you, and is very relevant to our topic. Let's begin by making sure we understand the 3Ds, and the relationships between them before we add the 4th D. Broadly speaking, 3D or 3-dimensional space simply refers to space that can be measured in three different perpendicular directions. The perpendicular nature of these dimensions is important, but we'll get to that later. Three-dimensional space is usually described as having height, width, and depth, and they all have 90-degree angles between them. Simply put,

Objects like us that exist in 3D space can move left and right, up and down, and forwards and backwards. We are comfortable with this kind of space. Using this as our basis, it becomes much easier to imagine what we mean by 2D space and even 1D space. To move from one space to another, all we need to do is remove or add an extra dimension of measurement or movement that must be a 90 degree angle from all previously existing angles. So, 2D objects move in a plane that's bounded by the X and Y directions, or the X and Z directions, or the Y and Z directions, but not all three at once. 1D objects can only move either along X or Y or Z.

Imagine a person who lived in such a 1D world. Their whole existence would be found either moving one way or the other. All of reality would exist either to the left or to the right of them, and would appear as a singular dot. They could not move or see in any of the other directions, and probably could not even comprehend such directions as even existing. Photons whizzing by them would only be visible if they entered the singular line that was a 1D person's whole area of existence. Now, adding extra directions of movement is what's needed to move things up from 1D to 2D to 3D. So, in theory, we can predict what we need to do if we were to jump to 40. However, here we hit a snag.

While it's easy to draw a line that's perfectly perpendicular to a single other line, or to draw another line on top of those lines that is perpendicular to the two previous lines, how would we draw a fourth line that's perpendicular to all three? Surely such a thing is impossible. Well, within 3D space, such a thing is impossible. The best we can do is draw approximations. For instance, it's possible to draw an approximation of a 3D shape on 2D paper by doing something like this.

These lines are all two-dimensional, but we look at this and our brain recognizes that this is a picture of a 3D shape. So in the same way, we could probably do something similar to what a 4D object might look like using just 3D lines. Mathematicians have attempted to do this, although their results tend to be a little little confusing. Although this is mathematically sound as a basis for a 4D object, I personally don't find my understanding a 4D space deepened by looking at it, so I won't focus on it in this video. There is some evidence, however, that a fourth direction exists, and we are moving

along it right now. That fourth direction, or dimension, is time. Einstein predicted this connection when he links space and time into one unified space-time in its theories of relativity. According to him, time and space are two parts of the same thing. To me, this connects with 4D space very nicely. Just as there is no real difference between the Z and the X or Y directions, so two would there not be any difference between time and space if time is just another direction, albeit one that we can't see. And time is important.

Without time, our 3D space wouldn't move. It would perpetually be in one state because it's time that allows us to move about in it. But why can't we see it? Why can't we look in the direction of time? To explain this, let's look at the difference between the different dimensional spaces. We best notice this when we consider what 2D objects might look like if they were to move around in 3D space. This is where we start to delve into the model.

Let's begin by visualizing a standard 3D space, but because we want to eventually see all of space and time in one model, let's cheat a little. Let's compress all of 3D reality as we know it into a flat, two-dimensional place. In this plane, let's make that our XY plane, which we will label space, which frees up the Z dimension for time. In this model, all 3D people are now just 2D. A 2D person could exist and live their lives in the place marked space at the bottom of our chart. However, by moving them up on the chart at a constant rate, they are also moving through time. Let's for ease and convenience say that the top of our diagram is the future, while the bottom is the past. So the higher up our 2D person goes in this diagram, the older they get.

As we don't seem to have a whole lot of control over our ability to travel through time, let's imagine for a second that our 2D person travels upwards at a constant rate, as if there is some consistent force or wind at play pushing them upwards towards the future. Sadly, we cannot slow down time for ourselves, simply through willpower, no matter how much we might want to do so. However, it is misleading to say that we can't change it at all. The faster we travel in space, the slower we travel in time. This is one of the guiding principles of Einstein's relativity.

This model can express this idea through the power of vectors. As our 2D person tries to move to their left or to their right, their vector of travel changes. While travelling at a fixed rate, like a sail on a ship catching a breeze, we can only go as fast as the wind takes us, so the vector coming out from their front must always remain the same. To travel the fastest through time, our 2D person must orient his vector completely in the future direction, or upwards. However, if they are to travel any amount in either direction to their sides, they can only do so by pointing their vector away from their direction of travel. They have motion in the X direction now, but they have done so by reducing their motion

in the Z direction. They are moving through space, but at the cost of moving a little slower through time. Taking this to its furthest extreme, our individual has completely flipped on their side, now only has motion in the direction of x and none in the direction of z. They have velocity in space, but not time. So I suppose this implies our vector is the speed of causality, or the speed of light. If this is the speed we're talking about, then moving at low speeds through space would not have any noticeable difference in our speed through time. We'd have to go really fast before we started to notice anything. The vector still mostly points upwards.

An interesting result of this model is that, from the 2D man's perspective, nothing has really changed. He has his own view of what reality is. For him, the vector coming out of his chest, is still time. The dimensions of the plane he's lying flat on is his space. To him, it's the rest of the universe that's gone a little weird, but he himself is perfectly normal. However, once he reorients himself, it is clear that the rest of the universe has moved on without him. This is clearer if we add a second 2D person. Initially, both of our individuals do not move in space. All of their vector is pointing in the direction of time. Nothing that strange seems to happen so far. However, if our stick man on the right turns and vectors at near

the speed of light for a bit, then reorients himself, while the second 2D man on the left just stays where he is, it becomes clear that our 2D men have not moved at the same rate through time. Assuming that our two-stick men can somehow still see each other, let's imagine that they somehow project an image of themselves onto the other person's space plane, they immediately noticed that there is a difference in age. The one who traveled at the speed of light did not advance so quickly through time as the other, who remains stationary, and so is younger. But why do we find this model so compelling? Well, it is because of what those projections would look like during changes in direction.

From the point of view of the first stickman, initially the projection of their friend seems fairly normal. However, as they start travelling very quickly in space and their vector oriented in a direction away from time, a 2D shape reveals its inherent flatness. And from a face-on perspective, it goes from this to this. The speedily travelling stickman appears to flatten, with an effect that's more pronounced the fire.

faster they go, and the flattening takes place in the direction of their travel. The stickman who remains stationary might wonder at the strange change that is occurring to their friend, never comprehending that it represents a reorientation of a 2D figure in 3D space. Now, what captures my imagination about this is that this same thing happens in real life. According to Einstein's theories of relativity, objects traveling at great speeds in 3D space would appear from an external observer to flatten in the direction of their travel. This squishing effect happens exactly in line with this model, and is to do with time dilation.

However, from the person whose travelling's perspective, they do not flatten, but it is the rest of the universe that warps. I talk about this in greater depth in another video of mine, where we can see the effects of spatial warping in a computer model. From their perspective, everything would stretch at the edges of their vision, while their destination would seem further away, which is again what this model would predict. The only difference is that in this model we're just exploring a 2D object stretching. So the stretch is only in one direction, while in real life it's 3D, which means it stretches in two directions instead. But that is what you might expect, as you turn away from our conventional three dimensions and start orienting yourself away

from time. But if this is correct, so what? Why does it matter? If time is truly a direction, then it deepens our understanding of the universe. It also raises more questions. What is the force that pushes us ever forward in time? Why does it seem that we can never move against it? Although in this model, there is no reason why a vector could not point downwards, in real life that doesn't seem to ever happen. This model also answers the question of, if time is a direction, what is our shape in time? Does part of us protrude into the past or into the future? According to this model, that does not happen. We are flat pancakes in the fourth dimension, pennies that look round when you look at us head on, but revealing our thinness when we turn away

from you. That's a strange thought, but it may just be true. This might explain why we are unable to see through time. We just don't extend enough in that direction for it to be visible. Your form might be quite different than you first thought. Of course, this model is just a theory of ours, although we have tried to base it on scientific observations and conventional theory. But what do you think? Does this model help you make sense of time as a fourth dimension? Please leave your ideas in the comments below on the nature of time and what it might actually be instead. I hope to explore more strange concepts like this in a new series called The Unseen World, where I want to explore the shape of reality around us.

While it's normally invisible to us, the shape and dimensions of the universe can explain why things are the way they are, and I'm excited to explore it with you, if you are interested in it. Let me know. Light is so much stranger than you might think. Sure, it may seem simple enough, traveling around the universe, delivering energy from one place to another. It helps us see. It provides life to plants, and thus to our planet generally. It has a reputation for being very fast. And yet, for a source of energy that has become synonymous with greater understanding, light is surprisingly difficult to understand.

Light helps us see other things better, sure, but when scientists tried to look at light itself, it was surprisingly difficult. No, I don't mean that they started staring into any lamps. Please don't do that at home. But experiments in the last 200 years or so have proven that what light appears to be and what light is are actually two different things. For one simple reason,

annoyingly enough, light behaves differently when you're not looking at it compared to when you are. What is the true nature of light? Why is it behaving strangely when we're not looking? And what does it say about how the universe really works? I'm Alex McCulligan and you're watching Astrum, and in today's video it's time we try and find out. Let's shed some light on light. Let's begin with the basics. What is light?

In the early 1700s, Isaac Newton theorized that light was made up of tiny little particles that he called corpuscles. But in 1801, nearly 100 years later, a man named Thomas Young discovered that light must actually be more wave-like than particle-like. He proved this, using an important method known as the double slit experiment. He set up a source of light and shone it threw two narrow slits onto a board. Young noticed that rather than getting two bands of light on the other side of the slits, a strange striped pattern was forming. This was known as an interference pattern

and was incontrovertible proof that light had been traveling as a wave. Why? Let's talk about waves for a moment. When waves travel, they oscillate up and down. But when two waves try to oscillate the same point in space at the same time, you get something known as interference. Imagine you had a bathtub with a rubber duck sitting on the surface. Two waves reach the duck at once.

One wave tries to raise the duck up, at the exact same time the other wave tries to drop it down. What happens? Provided the waves are of the same magnitude and are perfectly outer phase, they will cancel each other out and the duck would not move at all. This is called destructive interference. Similarly, if the waves both tried to raise the duck up at the same time, the duck would be raised twice as high. This is known as constructive interference. Because waves tend to expand in a circle, two waves next to each other will start to both

constructively and destructively interfere with each other. Here are two waves in water. See these lines? These calmer patches are where the waves are cancelling each other out. This is the effect we see with light travelling through the two slits. As the light from, one slit propagates, it cancels out the other wave of light at certain points, creating the interference pattern that Young noticed on the board. So the mystery was solved. Light was a wave and not a particle. Except there is more to this experiment than meets the eye. Let's fast forward another 100 years to 1905. Scientists around this time had become puzzled by something known as the photoelectric effect. It turned out that when you shone,

a light on a metal surface, electron-like particles were coming off it. This was deduced to be because electrons in the metal were getting knocked off it by the increased energy the light was imparting. Imagine it like a fruit on a tree. If you pull the fruit off the tree, you need to use a certain amount of energy. Once the energy is greater than the strength of the fruit's connection to the branch, the fruit pops off. This was happening with the light and the electrons. Once the energy, the light hit an electron and gave it enough energy to pass the threshold, it broke free from the metal. However, what surprised scientists was that if you increased the intensity of the light, they had expected the electrons to be knocked away faster. If you pulled the fruit off the tree

harder, it would come off faster. More energy equals more departing kinetic energy. However, this did not appear to be the case. Instead, increasing the frequency of the frequency of the of the light increased the velocity of the departing electrons. The intensity of the light didn't affect the departing electrons velocity at all, but did affect the quantity of electrons being emitted. It was a bit of a puzzler. Albert Einstein was the man who solved the puzzle. He deduced that light must be travelling in little packets of energy, so sending more of them, increasing the frequency was the only way to increase the energy going to the electrons. He called these packets photons, and later earned a Nobel Prize for his work.

Light, it seemed, was more like a particle again. Or both a wave and a particle at once? Of course, even this is not the full picture. To be honest, we aren't completely sure about the full picture even now. Instead, we have more results that are contradictory. Let's go back to the double-slit experiment. Armed with the knowledge of photons, physicists once again took a look at the double slit experiment. Experimental techniques had improved in the last 100 years, and it was now possible to emit a single photon of light at a time. So the double slit experiment was done again. This time, only a single photon would be sent through the slit onto a detector on the far side. When this was done, the detector registered the arrival

of the photon at just a single point. So, light was behaving like a particle again. But then, why had it interfered with itself in the previous version of the experiment? Scientists had an idea. They sent through multiple photons one at the time and plotted the result on the detector. And this is where the result became really strange. Once again, the detector started seeing the photons arriving at single points, one at a time. But bafflingly, the arriving photons started creating a pattern. It was the interference pattern, the proof that light behaved like a wave.

But strangely enough, this was only occurring when a single photon was going through at a time. Somehow, the single photon, which was leaving the detector like a particle and was arriving at its destination as a particle, was apparently in some way traveling through both slits at once, enough to then interfere with itself on the other side like a wave. If light was just a particle, then when it went through the slits, you wouldn't see this pattern. You would only see two blobs of light, one for particles that went through the slit and one for particles that went through the other one. And yet, here was the interference pattern with its multiple lines of light disproving that. Scientists tried to pin light down. They set up the

the experiment, but this time with two more detectors at the slit, so that scientists could observe whether it was indeed passing through both at the same time. It didn't. But at the same time, it stopped creating an interference pattern on the furthermost detector. And from this, scientists began to realize something. Light cared about being observed. To be clear, it didn't matter whether it was observed by a human eye. or a machine. The moment light was interacted with in some way by any particle, which is the only

way we can detect light, there's no other way to observe it, it started behaving differently than if it hadn't been detected at all. It was if light was snapping into focus any time the universe asked it the question of where exactly it was. When without the scrutiny, it appeared to relax into something a little more nebulous. Bizarrely enough, this is a seems to imply that light actually is more like a wave of probability rather than any discrete particle or wave. Any time it was asked where it was, it confidently provided a definitive answer. It was at this point on the detector.

It was not at any other point. But with no one checking up on it, light seems to be travelling in all directions at once, in accordance with certain probabilities. If you ran the experiment multiple times, you could quantify those probabilities, discovering that it was more likely to be on the bands of the interference pattern and less likely to be in the gaps. But any time a single photon of light was asked, it gave an answer that was 100% concrete. This is highlighted through something known as the Three Polarizer Paradox.

Consider for a moment a pair of polarizing sunglasses. Obviously, these reduce the amount of light that can pass through them, usually by about 50%, depending on the type of lens and the wavelength of light. They work by being formed of thin chains of molecules that run lengthways across the lens. Any light that oscillates in the same orientation as this lens gets absorbed. Any that is perpendicular to the chains can pass through without trouble. The interesting case occurs when a single photon is passed through an orientation that's diagonal to the lens. In this case, you don't get half a photon going through. Apparently,

you can't just absorb part of the oscillation that is parallel to the lines and let through the other part that is perpendicular. Instead, the photon snaps into either the one orientation or the other. It either is completely absorbed or passes through entirely, but now with a new perpendicular polarization to match what it would have to have had to have been able to pass through easily. How do we know that the photon wasn't this orientation all along? Because of what happens when you start adding more lenses. When you place a second lens behind the first, you can block out the light entirely, provided the two polarizations are perpendicular to each other. Let's say we rotate the second lens 90 degrees compared to the first one. Any light that gets through the first

lens has a 0% chance of getting through the second, like trying to post a letter through a chain-linked fence. As a result, we see only black. But add a third lens and place it at a 45-degree angle between the other two, and bizarrely light starts making it through all three lenses again. This may seem counterintuitive. How does adding more blockages increase the amount of light that makes it through. But this result actually rules out the possibility that the light has a fixed orientation. It must be snapping into focus at each new lens, rolling a quantum dice each time to see if it was the right orientation all along or not. If it makes it through the first lens, a 50% chance, it only did so because it was oriented perfectly perpendicular to the lens's

polarization, which means once it reaches the second, it's coming at it from a polarization that's diagonal. So once again, there's a 50-50 chance that it makes it through. It rolls a quantum dice again, and once again has a 50-50 chance of proceeding. If it gets through this hurdle too, then it again snaps to the new orientation, as if it were that new orientation all along, which it obviously wasn't, which means that now it's polarized diagonally relative to the third lens, meaning that it now has a final 50% chance of getting through. Of course, some photons do not make it through all three of these probabilistic gauntlets, only about 12.5% of them make it, but that's more than 0%, which is what was happening previously

when you only had two lenses. Light likes to behave in discrete quantum. quantities. It is quantum. It seemingly snaps to a discrete value when observed. And honestly, we don't really know why. If you think about a wave, there is no reason why you couldn't simply have half a wave. You could half it again and again an infinite number of times and still have an answer that makes mathematical sense. And yet, it seems that down on a low enough quantum scale, you can't half light past a certain point. you can't have half a photon, or even one and a half photons. And if you try to do so, the photon instead snaps to one or the other nearest integer,

based on probabilities, but only when it's asked. Otherwise, it's quite content to exist probabilistically, interfering with itself like a wave as it travels along, before jumping to an answer when later asked exactly where it is. What is going on here? This is still being theorized about. The closest comparison we have to it is something known as harmonics, where on a bounded string, only a certain number of waves can exist.

On a guitar string, you can have one wave or two or more, but never a number that isn't a whole number. It seems that light works in the same way. Perhaps something pinches the beginnings and the end of the path light travels down, although what this might be and what mechanisms drive it are unknown as of now. Fundamentally, though, perhaps the craziest thing about all of this is that this isn't just about light.

Although we've focused on light behaving like a wave and behaving probabilistically, all particles of matter do the same. Light is just another form of energy, and energy and matter are linked. Particles of matter, atoms and even complex molecules, have been shown to have wavelengths. Electrons are just as quantifiable, and just as driven by probabilities as photons are. We are apparently all driven by probability if you scale things down small enough. So what is everything truly made of? What makes up energy and matter that causes it to behave in the way it does?

What is going on under the hood of reality? Why is the universe behaving different when looked at compared to? to when not? And what does it imply to think that even you are on some level probabilistic? What this all means is anyone's guess. The person who figures it out will be the Einstein of our time. But for now, all we can say is that when it comes to reality, it seems the universe is playing dice. You and the world around you might be a lot less certain than you might have thought. worse, but over astronomical distances it's really quite slow.

R.S. Puppis is a variable star tucked into a nebula, and being a variable star means it pulsates in brightness over time, in this case 41 days. And incredibly, because light is so slow over these vast distances, you can watch the light move through the surrounding nebula in what is called a light echo. Every time the star peaks and dips in brightness, you'll see a new crest of light move away from the star through the nebula. This is a real Hubble time lapse taken over several weeks. This is not CGI. You may have noticed this video didn't have any sponsors, and that's because it was brought to you by our Astronauts on Patreon. Consider joining our Patreon to keep these

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