Because we see no voids no matter how far away we look it is claimed that space bends back upon itself so that there are no edges. This implies that there must be some other dimension for it to bend into. General relativity also requires an extra dimension where space is supposedly distorted by the presence of mass.

String theory, which is currently popular, is also not content with just the three observable spatial dimensions but instead postulates that there are at least 10 dimensions.

No spatial dimensions other than three we are all familiar with have ever been detected and neither can they be.

If we take a cube we can define every point within that cube with just three coordinates from whatever point on its frame we choose. There is no limit to how small a piece of space can be defined and therefore it is totally illogical to suggest that extra dimensions could be rolled up into spaces smaller than we can detect especially when there is a theory that can explain everything without resorting to such trickery.

FET is able to explain every known phenomenon using only the three normal dimensions of space and a separate time dimension. It does so without having to introduce forces that act as if by magic, space that bends back upon itself, or have temperatures, pressures and energy densities that go far beyond what we can experience here upon the Earth.