Question

Some scientists (especially string theorists) have suggested there are higher dimensions. Why would higher dimensions need to exist in their models?

If the universe does expand forever, how do you account for conservation of energy (i.e. energy at the beginning equals energy at the end)? There is much debate about this question. Support you answer with a reliable source.

Answer 1

1. These higher dimensions in different theories are required to make the theories more mathematically consistent and formulate it in a better way.
2. The conservation of energy holds in expanding universe due to the presence of Dark Matter/Dark Energy whose density appears constant even when the universe is expanding. This gives the extra positive energy which is balanced by the negative energy produced by gravitational sources, and it is depended on the rate of expansion. As the universe expands the dark energy also increases and the negative energy also increases. Thus keeping the energy constant in the universe.