Stay tuned until the end of the video for more about that.

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 Astrum, 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 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 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 3-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. 3-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 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 recognises 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 spacetime 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 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 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, 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 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 re-orients himself, it is clear that the rest 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 re-orients 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 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 stick man, 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 stick man 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 stick man who remained stationary might wonder at the strange change that is occurring to their friend, never comprehending that it represents a re-orientation of a 2D figure in 3D space.

Now what captures my imagination about this is that this same 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 who's 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 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!

I'm very pleased to finally show you something that's been in the works for a while.

I've been working together with Stuart McPherson and the Don Hanson Foundation to produce a book.

It has already been sent to thousands of schools around the world to hopefully help school children develop a love for space, and now they are available to you too!

The focus of this 160 page book is the solar system, and contains thousands of facts about the different celestial bodies found there.

And what I actually love most about the book is the print quality combined with the images.

Somehow these images just look so good when printed out compared to seeing them on a computer screen.

I spent hours finding the very best images to include, and I'm very proud of the finished product.

The initial sale is a limited edition of only 175 books, so it's really fast.

And they will include a signed card from me and a serial showing your unique number.

I really expect these to go fast, so don't delay and check my store link below!

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