What does the universe expand into? Do we expand with it?
The expansion of the universe is the increase in distance between any two given gravitationally unbound parts of the observable universe with time. It is an intrinsic expansion whereby the scale of space itself changes. The universe does not expand « into » anything and does not require space to exist « outside » it. Technically, neither space nor objects in space move. Instead it is the metric governing the size and geometry of spacetime itself that changes in scale. As the spatial part of the universe’s spacetime metric increases in scale, objects move apart from one another at ever-increasing speeds. To any observer in the universe, it appears that all of space is expanding while all but the nearest galaxies recede at speeds that are proportional to their distance from the observer – at great enough distances the speeds exceed even the speed of light.
Learn more : https://en.wikipedia.org/wiki/Expansion_of_the_universe
Could it be that the universe does not expand but we shrink instead? What does it mean that the universe expands anyway? And if it does, what does it expand into? In this video I tell you what you need to know about Albert Einstein’s General Relativity to make sense of all this.
Correction to the illustration at 3 mins 31 seconds: It should just have been « smaller than 2 Pi R », not « R smaller than 2 Pi R » (which is correct, but makes no sense). Sorry about that!
Correction to what I say at 6 mins 40 seconds: It’s been brought to my attention that in 1992 it was proved one needs in general only 8 dimensions, not 10, see https://en.wikipedia.org/wiki/Whitney…