4 ms·

Do I know more physics than you? Problynot. But he’s my attempt to explain how I understood the article: We experience a universe with 3 spatial dimensions, if

Do I know more physics than you? Problynot. But he’s my attempt to explain how I understood the article: We experience a universe with 3 spatial dimensions, if we imagine an axis through space, there are two other axes orthogonal to the first axis and to each other, that an object can move on any of the axes independently, without moving in any of the others. We can’t add a fourth axis, there is no fourth line we can choose along which an object can move without also moving in at least one other dimension - or at least that is our experience. We also know from seeing 2d shadows of 3D objects, that a higher dimensional object can be projected into lower dimensions. We can twist an object and see changes in a shadow that make perfect sense if we know the shadow is a 2d projection of a rotating 3D object. There are features of our universe that make sense if we think about the universe as a 3D shadow of a higher dimension system. So what does that mean? Are higher dimensional models a nice math trick, or do the models work because they describe the true higher dimensional nature of the universe, that we experience as a lower dimensional projection. Ok time to pass the baton who can take this deeper.

lgl 6y ago
Good answer, a 4th dimension and the shadow projection analogy is brilliantly exemplified by Carl Sagan in this popular video: https://www.youtube.com/watch?v=UnURElCzGc0 https://www.youtube.com/watch?v=UnURElCzGc0
- travisjungroth 6y ago
  I think it's also the most important analogy, more than things like a 2D being meeting a 3D being. The goal of these physics models is to better explain the world. It's a hint that a model is better when it simplifies things (not that the model itself is necessarily simple). Think of the crazy things astronomers drew to explain the paths of the planets in the sky with the Earth in the center and circular orbits. But what if the Sun is in the center and the orbits are ellipses? Things are way easier. Same thing happens if you look at the projection of a cube. It looks like chaos. But if you are aware of a third dimension, it all makes a lot of sense.
m12k 6y ago
I think it helps build an intuition of how higher dimensions can help us explain physics, if instead of a shadow, you think of projection as a cross-section, like the ones you see in brain scans, where you only see one "layer" of the brain at a time. Objects that are moved into the plane of the scanner (so they intersect the plane) will essentially "pop into existence" from the perspective of someone looking only at that cross-section - and then that cross-section morphs and changes shape as the object is moved so different parts of it intersect the scanner. What if the same thing is happening when elementary particles pop into existence and later annihilate, that we're seeing the cross-section of a higher-dimensional object as it intersects our 3 dimensions? What if matter and antimatter are like the outer edges of such a cross-section, appearing in a single point as the object touches our plane, moving apart as the bulk of the object passes through our plane, and then finally coming together in a single point before disappearing (annihilation), as the object stops intersecting our plane?
moehm 6y ago
> There are features of our universe that make sense if we think about the universe as a 3D shadow of a higher dimension system. Which one would this be?
- monkeycantype 6y ago
 fair call, I was trying to make it clear that my comments were 'how is understood the article and vid' and not my Wolfram/Weinstein 'physics is wrong I'm going to fix it' manifesto. So let me try improve that line: <strike>There are features of our universe that make sense if we think about the</strike> Kaluza-Klein theory proposed that electromagnetism could be modelled using an additional closed fourth dimension. Kerner generalised this approach to model gravity, time, electromagnetism and the strong and week forces using a total of 11 dimensions. I have understood these models as describing our experience of the universe as a 3D <strike>shadow</strike> projection of a higher dimension system. Kaluza-Klein was the exact point at which I lost interest in pursuing university physics, so the sentence is marks the point at which the ship of my knowledge hits the rocks. I loved first year physics, but in my second year at university a tutor convinced that physicists now worked exclusively on string theory, which he explained beginning with Kaluza-Klein theory. What he described reminded me of Copernican epicycles, and I felt so little enthusiasm for it, and was deeply disappointed after having loved first year physics and it was the end of my imagining I might be a physicist. Much later I discovered he was suicidally depressed the dry bloodless descriptions he gave were him trying to hang on and keep himself together while describing a subject he had come to hate.
 - moehm 5y ago
 Thank you for answering.

lgl 6y ago

Good answer, a 4th dimension and the shadow projection analogy is brilliantly exemplified by Carl Sagan in this popular video: https://www.youtube.com/watch?v=UnURElCzGc0 https://www.youtube.com/watch?v=UnURElCzGc0

travisjungroth 6y ago
I think it's also the most important analogy, more than things like a 2D being meeting a 3D being. The goal of these physics models is to better explain the world. It's a hint that a model is better when it simplifies things (not that the model itself is necessarily simple). Think of the crazy things astronomers drew to explain the paths of the planets in the sky with the Earth in the center and circular orbits. But what if the Sun is in the center and the orbits are ellipses? Things are way easier. Same thing happens if you look at the projection of a cube. It looks like chaos. But if you are aware of a third dimension, it all makes a lot of sense.

m12k 6y ago

I think it helps build an intuition of how higher dimensions can help us explain physics, if instead of a shadow, you think of projection as a cross-section, like the ones you see in brain scans, where you only see one "layer" of the brain at a time. Objects that are moved into the plane of the scanner (so they intersect the plane) will essentially "pop into existence" from the perspective of someone looking only at that cross-section - and then that cross-section morphs and changes shape as the object is moved so different parts of it intersect the scanner. What if the same thing is happening when elementary particles pop into existence and later annihilate, that we're seeing the cross-section of a higher-dimensional object as it intersects our 3 dimensions? What if matter and antimatter are like the outer edges of such a cross-section, appearing in a single point as the object touches our plane, moving apart as the bulk of the object passes through our plane, and then finally coming together in a single point before disappearing (annihilation), as the object stops intersecting our plane?

moehm 6y ago

> There are features of our universe that make sense if we think about the universe as a 3D shadow of a higher dimension system. Which one would this be?

monkeycantype 6y ago
fair call, I was trying to make it clear that my comments were 'how is understood the article and vid' and not my Wolfram/Weinstein 'physics is wrong I'm going to fix it' manifesto. So let me try improve that line: <strike>There are features of our universe that make sense if we think about the</strike> Kaluza-Klein theory proposed that electromagnetism could be modelled using an additional closed fourth dimension. Kerner generalised this approach to model gravity, time, electromagnetism and the strong and week forces using a total of 11 dimensions. I have understood these models as describing our experience of the universe as a 3D <strike>shadow</strike> projection of a higher dimension system. Kaluza-Klein was the exact point at which I lost interest in pursuing university physics, so the sentence is marks the point at which the ship of my knowledge hits the rocks. I loved first year physics, but in my second year at university a tutor convinced that physicists now worked exclusively on string theory, which he explained beginning with Kaluza-Klein theory. What he described reminded me of Copernican epicycles, and I felt so little enthusiasm for it, and was deeply disappointed after having loved first year physics and it was the end of my imagining I might be a physicist. Much later I discovered he was suicidally depressed the dry bloodless descriptions he gave were him trying to hang on and keep himself together while describing a subject he had come to hate.
- moehm 5y ago
 Thank you for answering.