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.
I'm Alex Mccoan, and you're watching
Astramm. 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
is being 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
traveling 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 traveling at this
speed. However, there is a single
interesting exception to this rule which
had always puzzled me. The photons
perspective.
Einstein has proven that for an object
traveling at light speed, time would
slow down so much that it would be at
zero. If you were to suddenly start
traveling at the speed of light towards
Jupiter, you would notice zero time
passing, but would observe that you have
traveled 679 million km
and then 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 /
0 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
light's perspective, it is traveling
infinitely fast, not at 299,792,458
m/s.
Let's call that C from now on.
So why is it that everyone else detects
light traveling at C, 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 traveling 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 yaxis
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 [music] 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 [music] explosion.
We are now in motion, moving solely up
at the top of this expanding [music]
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
[music] 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 [music]
that we decide we no longer want to go
straight up. Let's try to change
direction.
In [music] physics, any change of
direction is a form of acceleration.
This may not make much sense
intuitively, but it becomes [music]
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
[music] 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 [music] impetus in the x
direction. Obviously the more we are
pushed the faster we are going to travel
and the more [music] our total vector
begins to lean towards a perfect
horizontal line. the size of our vector
[music] increases.
However, let's say that we want to go
faster. In fact, we [music] 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 [music] we can get in
the x direction that will make it so
that we are actually going completely
horizontally? No. You can increase the
distance in X by a larger and larger
amount, but as long as Y [music] 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, [music]
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 [music] 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, 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 m/s or 3 trillion. But in the
real universe, we don't see [music]
that. Everything normally seems to be
capped at C.
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
[music] our 4D model seems to have
failed. But this is not regular 4D
space. This [music] 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 [music]
from your perspective you covered a
distance of 400 million m 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 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 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 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 traveled 400
million m in 10 seconds for a speed of
40 million m/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 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 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 C.
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
that 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 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
m/s. 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 traveling 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 traveling 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 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 traveling extremely
fast over vast distances.
As the speed of light slows, what
becomes apparent to you?
The first thing I notice is that the
colors start to change. This is because
of something called the relativistic
Doppler effect.
You see, when you look around and you
see color on objects, this is because
light is reaching your eyes at specific
wavelengths.
The longest wavelengths you can see are
reds. The shortest wavelengths are
violets.
Beyond the range of our sight 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
traveling 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 1 year at that speed. It all seems
normal for us.
But 10 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 speeded 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 Lorent 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
traveling. So, I actually need to start
turning a little ahead of what I'm used
to, which is difficult to comprehend
while navigating. It's 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 traveling large
distances in short times. However, time
is passing normally for people on Earth,
meaning traveling 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 approached 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 Mccoan and you're watching
Astramm. 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 recognized
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 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 [music] 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° 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 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 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 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 fourth
direction exists and we are moving along
it right now. That fourth direction or
dimension is time. Einstein predicted
this connection when he linked space and
time into one unified spaceime 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 zed 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 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 marks 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 traveling 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 and now
only has motion in the direction of x
and none in the direction of zed. 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 stickmen 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 notice 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 friends seems fairly normal.
However, as they start traveling 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 traveling stickman appears
to flatten with an effect that's more
pronounced the faster they go. and the
flattening takes place in the direction
of their travel. The stickman who
remains stationary might wonder 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
traveling'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 headon, 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 Mccoan and you're watching
Astramm. 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
corpuscals.
But in 1801, nearly 100 years later, a
man named Thomas Young discovered that
light must actually be more wavelike
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 through 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 [music] was
forming.
This was known as an interference
pattern [music] 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 [music] 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. [music] 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 out of 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 canceling each other out.
This is the effect we see with light
traveling 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 [music]
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 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 pull 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 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 traveling 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 a 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 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 seems to imply
that light actually is more like a wave
of probability rather than any discrete
particle or wave. Anytime 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 traveling 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 anytime 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°
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
chainl fence. As a result, we see only
black. But add a third lens and place it
at a 45° 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
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
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
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.
Light may seem instantaneous to us, but
over astronomical distances, it's really
quite slow. RS Papus 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.
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