Have you, like me, ever looked out your window,
and wondered why the universe was the way it was? As you watched clouds float by, or stars twinkle
in the night sky, did you stop to consider why we live in a universe that looks quite
the way it does? “All great truths are simple in final analysis,
and easily understood; if they are not, they are not great truths.” So said Napolean Hill in his book “The Law
of Success”, and when it comes to the universe, I believe that he is right. There have been many complicated mathematical
formulas over the years that have attempted to map out the universe, but when great breakthroughs
have happened and our understanding of the universe has been advanced, it has often been
through equations and explanations that are incredibly simple. F=ma. E=mc2. These are succinct enough to be explained
in just a few lines of text, or a few algebraic characters. But more than just the clouds; what are the
great truths that underpin the universe itself? What is time? Why does the universe look the way it does
– constantly expanding in all directions, from everywhere? Why does light have a speed limit? I’m Alex McColgan, and you’re watching
Astrum. And if you have ever wondered these same sorts
of questions, perhaps the models in this video that I’ve developed with my brother might
help explain the answers. Ultimately, a great truth must be simple. The ideas here likely still need development. But I believe that they explain the subject
in a simple enough manner that they might just be the starting point we need to find
the truth. To begin with, let’s start with a fundamental
question. What is time? On 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. This all may make 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? Thanks to this first model, 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 model is based on recognised 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 on to 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 3 D’s, and the relationships between them before we add a fourth D. Broadly speaking,
3D or three-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° 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. Here, we might need something that looks like
this, except with little 90° markers between them. Maybe have a little ball moving around in
this space: 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 at
a 90° angle from all previously existing angles. So, 2D objects can 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 3 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 or 3D. So, in theory, we can predict what we need
to do if we were to jump up to 4D. 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 both
of those lines that is perpendicular to the two previous lines: How would we draw a 4th
line that’s perpendicular to all 3? 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 2 dimensional,
but we look at this and our brain recognises that this is a picture of a 3D shape. So in the same way, we can probably do something
similar to guess 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 confusing. Although this is mathematically sound as a
basis for a 4D object, I personally don’t find my understanding of 4D space deepened
by looking at it. So, I won’t focus on it in this video. There is some evidence, however, that a 4th
direction exists, and that we are moving through it right now. That fourth direction, or dimension, is time. Einstein predicted this connection when he
linked space and time into one unified “space-time” in his 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 direction and the x or y directions, so too 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 visualising 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, 2 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 also are 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 him 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 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 flipped completely on their side and 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 introduce 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 stickman on the right turns
and vectors at near the speed of light for a bit and then reorients himself, while the
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 stickmen can still somehow
see each other (let’s imagine that they somehow project an image of themselves onto
the other’s “space” plane), they’d immediately notice that there is a difference
in age. The one who travelled at the speed of light
did not advance so quickly through time as the other who remained 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 seemed to be fairly normal. However, as they started travelling very quickly
in “space”, and their vector oriented in a direction away from “time”, a 2D
shape reveals its inherent flatness. 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 faster they go, with the flattening taking place in the direction of
their travel. The stickman who remained 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 travelling 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 spacial 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 in only one direction, while
in real life it’s 3D, which means it stretches in 2 directions instead. But that is what you might expect, as you
turn away from our conventional 3 dimensions, and start orienting yourself away from time. But if this is correct, so what? Why does this 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 this 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 4th 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 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
at first thought. It’s useful to consider the existence of
other dimensions beyond the 3 that we see, but there are other edges and frontiers in
the universe that pose further questions. For one, does space ever end? Is the universe inescapable? If we were to conquer the limitations of light
speed and were to travel to space’s furthest edge, what might we find? Just more space? Infinite planets and planetary systems? Or would we somehow come back to where we
started? Amazingly, according to scientists, all of
these are possible, but which one is correct comes down to the nature of that unseen world
all around us. We need to understand the shape of space. And to do that, we need to begin by talking
about infinity. You likely are already familiar with infinity. In maths, it is the concept of a number so
large, it cannot possibly be beaten. Of course, no such number exists – for any
number you can name, I could come up with a number that is at least 1 larger than it. But in a way, that’s sort of the point. In infinity, there is always another number. And when it comes to our universe, we have
so far discovered no edges. There may always be another star or planet. An infinite universe is a little mind-boggling
for us. We live in a very finite world, with edges
and endings. So, the idea that there might be literally
infinite more planets out there is a little bewildering. However, as we develop more and more powerful
telescopes and push back the darkness further and further at the edges of what we can observe
in our universe, all we are finding is that even the darkest patches of the night sky
are turning out to be brimming with stars. So increasingly, an infinite universe might
be something we are forced to contemplate. But that is not to say that just because the
universe is infinite, there are not a finite number of things in it. That may sound a little counterintuitive but
let me show you what I mean. Believe it or not, there are different kinds
of infinity when it comes to our universe. Three possible scenarios could be true: a
flat universe, a spherical one, or a hyperbolic universe. Allow me to explain. In a flat universe, if we were to form a grid
to broadly represent reality, everything would seem fairly standard. All the lines would either be parallel to
each other, or perpendicular. An infinite universe of this variety would
simply extend outwards in all directions forever and ever. This is a little boring, so I won’t spend
too much time on it. However, this is a lot like what we perceive
the universe to be. For the most part, all lines of direction
appear straight to us. We can distinctly see the planets and stars
around us, and we notice no real curving or warping. However, this is not the only way that the
lines can be drawn. Consider for a moment a black hole. You may immediately notice the strange rings
that appear to run around its equator, as well as across the top of it and along the
bottom. This is something of an illusion. There are no rings across the top or bottom
of this black hole. What you are seeing is the equatorial ring
that’s on the other side of the black hole. However, due to the powerful gravity of the
black hole, the light that is hitting it is not bouncing off upwards or downwards into
space. Instead, the rays are curving towards us,
as the black hole’s gravity pulls them in. You are seeing the top and the bottom of that
ring at the same time. Light being bent by gravity… what do I mean by that? Actually, this is an excellent example of
our second kind of universe. In a flat universe, all the lines that make
up reality are fairly straight. But what if we were to come up with a rule
– all the lines must instead curve towards each other? There is only one way such a universe could
be drawn, and that is in a sphere. Consider trying to draw two parallel lines
on a sphere. You might start off well, but would quicky
realise that your task is impossible. All lines would converge towards each other,
intersecting at least twice, as they return back to where they started. What would a universe that was based on these
kinds of lines look like? Essentially, rather than going in the straight
line you thought you were going in, you actually would be travelling in a massive curve. It’s a little bit like those computer games
where you travel off one end of the screen only to reappear from the other side. In a spherical universe, you could try to
travel infinitely, but ultimately, you would only end up arriving back to where you started. With a powerful enough telescope, and if light
were to travel a whole lot faster all of a sudden, it would be possible to look at the
back of your own head. This kind of universe contains a finite amount
of things, but it appears infinite just because you’d keep bumping into the same things
infinite times. Thanks to objects like black holes and powerful
stars, we do indeed have evidence that our reality sometimes is a curved, spherical one
– at least near large bodies of mass. The inside of a black hole’s event horizon
is this kind of infinite space – no matter what path you take, you can never get out
of it. However, let’s consider our last example
– the hyperbolic universe. This one is the hardest to visualise, but
the idea is simple. Instead of having all lines remain parallel
or move towards each other, every line must move away. From everything. Drawing this is inherently tricky, because
everything keeps getting wider exponentially. The only way you can do that is to either
buckle your nice flat disk until it becomes something like this: Or warp what you are
seeing like this: All of the objects in this image are squares. However, they are squares that are obeying
our rule that all their lines must be diverging away from each other. This leads to the very strange situation where
you can have 5 squares all meeting up at a corner, instead of the usual 3 that is possible
in normal 2D space. All right, this seems a little confusing. What does it mean if space is hyperbolic? Well, let’s consider what it is we are curving
around. You might have noticed when we talked about
our spherical shape that there must be something we were curving around. That direction of curvature is in regards
to time. Imagine if you will a series of timelines:
We go a little more in depth with the interplay between space and time in my last video, which
I would really recommend you check out. But for now, just remember for this model
that objects in time move forward along their timelines in the direction of “up”, or
the future. If they move left or right, they are moving
through “space”, getting closer to each other. If we introduce a large mass into this model,
it warps the timelines: Now, if you were a small object travelling along one of those
arrows that got too close to the mass, suddenly your path of travel no longer goes directly
up towards the future, it pulls you left or right towards the mass. There are reasons for this, but the essential
thing to recognise here is that now, your “straight” path towards the future pulls
you in towards the planet, so you’ll have to accelerate away from it just to stay on
a straight path. In a nutshell, you are experiencing gravitational
pull. Even the planet is effected by this – the
atoms on either side of it are squeezed towards the centre of mass, as if it were being forced
down a narrow tube by giant, invisible hands. Let’s get back to Hyperbolic space. In this model, the opposite thing is happening. All lines are moving away from each other. We could represent this by curving space and
letting our timelines be straight: which is nice because it captures the idea that from
your perspective, your time is always ticking forward normally. But let’s warp this slightly so that it’s
space that is flat. It’s all a matter of perspective, after
all: Here, parallel lines are also impossible. But this time, rather than converging, all
parallel lines diverge more and more. Everything moves further and further apart… Hmm, why does that sound familiar? It is because that is what the universe is
doing. This is not noticeable within a galaxy, where
there is enough mass and gravity to keep everything together. However, from what we can see of the universe
as a whole, every galaxy is moving away from every other galaxy. Scientists try to explain that with dark energy. But maybe all that is happening is that the
universe is just naturally hyperbolic in its shape? So what would that mean if the universe really
was hyperbolic? Well, for starters, it would mean that the
universe was really infinite. The flat space we looked at was infinite – for
each light year you travelled out, you’d discover another light year’s worth of space. However, with hyperbolic space, you’d discover
more than another light year’s worth of space. It’s like opening infinite doors, except
inside each door are two new ones. The possibilities would be far more endless,
far more infinite, than in just regular flat-space models. But also, it means that, given enough time,
the rest of the universe would drift away from us until our galaxy was all that was
left… Scientists have looked out across the universe,
however, and have not noticed this hyperbolic space in action. In fact, things all look pretty flat. So perhaps flat space is the correct answer. Yet, this still leaves room to me for hyperbolic
space to be the default. After all, if matter is curving space towards
it, and the universe appears flat, it would make sense that the universe was curved in
the inverse, at least to some degree. Perhaps all three models are true: Perhaps
the universe is by default hyperbolic, but mass brings it together in such a way that
it perfectly offsets the inverse curves of the universe to the point where everything
appears flat? There certainly seems to be some evidence
that this is the case. But it’s very difficult to know for sure. Which model do you think is correct? Or maybe you feel that we do not live in an
infinite universe at all? Please leave a comment down below to tell
me what you think! But for now, just remember – the unseen
world might be a lot more influential on our universe than we are currently aware of. There is one last question that’s always
puzzled me about the universe, but one that thanks to our last two models we are now equipped
to answer. 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 m/s? 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. 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 299,792,458 m/s. 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
299,792,458 m/s. 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 0. If you were to suddenly start travelling at
the speed of light towards Jupiter, you would notice 0 time passing, but would observe that
you have travelled 679million km. And then would promptly 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, S=D/T. So, 679million/0=… 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 0 time over any distance
greater than zero, you have just travelled at infinite speed. So from light’s perspective, it is travelling
infinitely fast, not at 299,792,458 m/s (let’s call it “c”). So why is it that everyone else detects light
travelling at “c”, but light thinks it is going infinitely fast? What I am about to share is one possible theory. It’s going to incorporate the 4D space we
talked about when considering the nature of time, as well as the hyperbolic universal
geometry we discussed for the shape of space models. Both models were important building blocks
that we can now build upon in a single 4D hyperbolic geometry. This may sound intimidating, but it’s the
same as the 4D space we worked in before. Let’s compress all of 3D space down into
a single 2D plane; this leaves us the final dimension free to be made into the “time”
direction we looked at earlier. For the hyperbolic element, all it means is
that in our space, all 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, travelling through this space
obeys the same rules that travelling 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 that 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, lets say that we want to go faster. In fact, we want to go so fast that we are
no longer travelling 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 will 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 hit a limit. You would essentially need to go infinite
speed to approximate a flat line – and to go infinite speed, you would need infinite
energy. Difficult to get your hands on. Of course, that is where this 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 299,792,458 m/s speed limit. With infinite energy, you could go 3 billion
m/s, or 3 trillion. But in the real universe, we don’t see that. Everything normally seems to be capped at
299,792,458 m/s. 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 a 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 manage. “Speed” is a little tricky a concept here,
but let’s say that from your perspective, you covered a distance of 400,000,000m in
a second. So, faster than the speed of light. What happens? Well, you hit this little curved line over
here. Although it is bent to be almost a “c”
shape, if you follow the line down you will see that it is a time line, not a space line. And because it is hyperbolic space, there
is more here that 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 travelled 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
of 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 speeds 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 0, but
ended at an origin point that’s X seconds in the future, they have to say that we travelled
400,000,000m in 10 seconds, for a speed of 40,000,000m/s. 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 speed cap to
the universe. Not 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 above 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 it were simply moving uniformly at a speed of c. 299,792,458 m/s. 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 4D
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 to me why this is wrong, and it doesn’t entirely account
for the role of gravity in distorting this 4D space. However, it does neatly highlight why light
physically can’t travel faster than it does – the faster it moves, the more serious
the drag placed upon it by the hyperbolic geometry it encounters, which I find quite
appealing. In fairness, it would be intriguing to see
if from our perspective we could travel faster than the speed of light. This model claims it is allowable, but we
have never even gotten close to this speed, so it would be difficult to test it. The fastest a human has ever gone is 11,083
m/s, when NASA astronauts returned in a spaceship from the moon. It would require incredible amounts of energy
to travel 299,792,458 m/s, 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 for 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, travelling through shortcuts to the
future is definitely within the realms of possibility. So, there you have it. The universe is a strange place, filled with
features that we can’t entirely account for with our intuition. However, with the right models everything
becomes a little easier to conceptualise. Time and space are no longer quite so mysterious. Of course, as time goes on we will likely
encounter new strange phenomena that will force us to reconsider our models, but in
so doing we get nearer and nearer to what really is going on. Through theorising and developing our theories
based on new information, we will one day create a model that accounts for everything. Until then, hopefully the models we’ve discussed
today have given you some things to think about. It's incredible to me that although much of
the universe around us cannot be directly seen, it’s possible to explore it. But that is the beauty of the unseen world. Although we cannot see it, we can detect its
influence on our day to day lives. It shapes the motion of our day, as we pass
from the present into the future. It lays out cause and effect happening one
after the other, but never the effect happening before the cause. It bounds the universe, and gives us the scope
of what we have to work with. The reasons for this happening are sometimes
mysterious and baffling, but our logic allows us to catch glimpses of the truth that underpins
it. It just takes us stopping occasionally and
asking the most important question of all: Why?
