Hacker News Reader

Comment by RevRal | Hacker News Reader

I've seen that video a few times over the years, and it has always struck me as... how do I say it... not correct. Something in there just seems wrong. I do like some of the ideas in there, though.

Hopefully someone here can elaborate because it's been on my mind since I first saw it.

View on HN

Well, I'm no physicist, but I agree - it's bogus. The problem, I think, is that it assumes that time is the fourth dimension. Instead it should be the last dimension. So if you're talking about 6-space, then time should be the 7th dimension. If you always call time the fourth dimension, then you get these wacky results where in 5-space and up you can see and exist in all time simultaneously.

This is the problem with calling time a dimension. It's useful, but it makes it natural to talk moving forwards and backwards in time. Error.

The root of the problem is that most people can't see the difference between 4D space and 3D spacetime.

3D spacetime behaves mathematically exactly the same as 4D space, it is a construct to make it easier to analyze and do physics calculations of 3D objects over time, by setting time as the 4th dimension, thereby giving every object a position in time as well.

But the visualization is completely different, and the things you can do are completely different. If I have a 3D left-hand glove in a 4D space, I can "turn" it in the 4th dimension and end up with a right-hand glove. But if I have the same glove in spacetime, it doesn't matter how much I wait around (i.e. move in the 4th dimension), my left-hand glove will never turn into a right-hand glove.

There were a couple of things that I noticed that I don't think are correct. I thought it was fine up through the first 3, more or less. One issue that kind of bugged me was that it seemed to imply that spaces cannot be curved. The video I think would suggest that the surface of a sphere is 3-dimensional when it's actually only 2. Calling infinity a point in the seventh dimension also bugged me.

Overall, it seems like the creator of it knew a little bit of math, and probably some physics, and extrapolated from there. More probable though is that their only knowledge of the subject came from philosophy, or epistemology.

Overall, it seems like the creator of it knew a little bit of math, and probably some physics, philosophy, or epistemology. More probable though is that their only knowledge of the subject came from late night sessions passing the bong, listening to Floyd.

There, fixed that for you.

Reply on news.ycombinator.com