[henrikschroder]

Again, there's a huge difference between 4D space and 3D spacetime. Both are 4-dimensional mathematical spaces, but the visualization is completely different.

"Time is the fourth dimension" is the single most damaging sentence for your understanding of time and space.

To have an n-dimensional spacetime where time is not the nth dimension makes no sense.

[cianestro]

1) Although videos are visual aids by definition, it wasn't suggesting that a human could visualize any dimension except the 1st, 2nd, and 3rd I believe; this is why mathematicians must use numerical expressions (iterated for the nth time on HN) because human cognition is inextricably tied to interpreting perceptual data within the 3D Cartesian plane. 2) It is a youtube video. 3) Node (n-2) of this one was merely suggesting rather matter-of-factly that confusion is a weak conjecture. 4) I really don't disagree on node (n-1) because any spatial dimension can be parametrized possibly dispelling the "4th" part. I'm assuming your beef is that time breaks down in 5D (or 4D depending on who's counting) because it ceases to move in one direction? 5) If the former is true, Poe's Law still holds, and no matter what, I plea the 5th on further comment of this submission other than god forbid an innocent observe this video and enter into the nth dimension with an error margin of +-D. ;)

[bad_user]

> "Time is the fourth dimension" is the single most damaging sentence for your understanding of time and space.

The video didn't expand on the person living in a 2D space example ... if such of thing would be possible, he would be able to explain the presence of a third dimension using time (going so far as to consider time as being the third dimension).

[henrikschroder]

he would be able to explain the presence of a third dimension using time

NO! Absolutely not! 2D spacetime does not look like 3D space at all!

In 3D space, I can take a 2D angle bracket, flip it in the third dimension, and get its mirror image. This will seem like magic to 2D creatures. In 2D spacetime, I can do no such thing. No matter how long I wait (i.e. move in the third time dimension), the angle bracket won't transform into its mirror image.

In 4D space, I can take a 3D right-hand glove, flip it in the fourth dimension, and get a left-hand glove. This will seem like magic to 3D creatures. In 3D spacetime I can do no such thing. No matter how long I wait, a right-hand glove will never transform into a left-hand glove.

Do you understand?

Do you see how adding time to n-dimensional space does absolutely nothing to explain n+1 space?

[rbanffy]

That's because dimensions are not ordered. There is no first dimension, or second, or third. For a flatlander, time is what he perceives as a third dimension. Depth may be a fourth dimension. If you wanted to do the same trick to you, you would have to flip yourself in a non-time higher dimensional space. I think any dimensional space would do.

But it's early in the morning and I haven't had breakfast. Talk to you when my brain joins me.

To perceive time as a dimension is useful because it helps you realize you actually perceive four dimensions the same way a flatlander perceives three.

[henrikschroder]

To perceive time as a dimension is useful

If you want to do space-time calculations, yes.

because it helps you realize you actually perceive four dimensions the same way a flatlander perceives three

Absolutely not. We perceive time as time and space as space. The concept of spacetime does not help us understand or visualize higher dimensional spaces at all. It only confuses the issue, which is exactly the original complaint against the video this whole discussion is about.

Edit: One more example: Can you visualize the difference between a 3D cube moving in time, and a 4D cube moving in the 4th dimension? If you project the 4D cube down to 3D, it will look like a double cube that twists itself inside and out, but the 3D cube moving in time will just look like a 3D cube. Spacetime does not help you understanding 4D space.