In the previous part of this series,I used an analogy to show why we can't see into the fourth dimension.I also promised it would get interesting.

So to the primary question: What is the fourth dimension?
Many people have said that the fourth dimension is Time,but that would be a partial truth.It would be more accurate to refer to it as Spacetime.Then again you'll ask: What is Spacetime?

Spacetime is a concept in physics that refers to any mathematical model that combines space and time into a single interwoven continuum.

Are you lost? Don't be...

We understand the concept of 3D.Think of 4D as 3D+1D.The 3 spatial dimensions of length,width and depth combined with the temporal dimension of time.

If you want to meet a friend somewhere,you'd give him co-ordinates.You'd say "Meet me in the conference hall of the Sheraton at 4B,Unity close,Ikeja."
But to increase your odds of meeting your friend,you'll add "At 5:30pm".
Do you see my logic?The concept of space and time are not mutually exclusive.

Keep Up....

Sheikwonder:
In the previous part of this series,I used an analogy to show why we can't see into the fourth dimension.I also promised it would get interesting.

So to the primary question: What is the fourth dimension?
Many people have said that the fourth dimension is Time,but that would be a partial truth.It would be more accurate to refer to it as Spacetime.Then again you'll ask: What is Spacetime?

Spacetime is a concept in physics that refers to any mathematical model that combines space and time into a single interwoven continuum.

Are you lost? Don't be...

We understand the concept of 3D.Think of 4D as 3D+1D.The 3 spatial dimensions of length,width and depth combined with the temporal dimension of time.

If you want to meet a friend somewhere,you'd give him co-ordinates.You'd say "Meet me in the conference hall of the Sheraton at 4B,Unity close,Ikeja."
But to increase your odds of meeting your friend,you'll add "At 5:30pm".
Do you see my logic?The concept of space and time are not mutually exclusive.

Keep Up....

so we see in 2d and the brain interpretes it as the closest estimates to the real 3d image we saw. I read this some where. Explain.

paranorman:

so we see in 2d and the brain interpretes it as the closest estimates to the real 3d image we saw. I read this some where. Explain.

I will summarily say this.

The human retina is 2D.We should therefore only see in 2D,which we do.If you saw in 3D it would mean that if you look at me you should see not only my face,but the back of my head as well!

Much of what you see when you look at 3D objects is a function of various factors.One is the presence of a pair of eyes.If you close one eye and focus on an object,it tends to shift position than when you observe with 2 eyes.The extra eye provides detail.This phenomenon is known as binocular disparity.

Another is depth perception.One eye perceives depth differently than two.As a result images fed on your retina are sent to the brain which tries to balance out the conflicting images your two eyes see by providing depth...

There's more,please hold on...

The angle between our eyes helps to gauge the distance of objects.For example we can fairly judge distances when people approach us from afar.

Shadows help too.You can obviously tell that an object is 3D by looking at it's 2D shadow.The shadow of a 2D object would be 1D,i.e a line.By extension,a 4D object would have a 3D shadow and so on.

Inference is also another way we perceive 3D.We can easily infer that an object is 3D by changing our view of objects,by shifting positions etc. So even though you may not see all sides of a box on a table,by changing positions,lifting the box,you can tell that the box is 3D.Also by repeated observation,your brain automatically infers an object's dimension.

Occlusion,Geometric Perspective,Shading etc. are other ways by which the brain interpretes images.

Note: No one method works in isolation,the brain combines different options to get results.Also,extra eyes don't mean we'll see higher dimensions,it only provides added detail like those mentioned above.