... Gravity denies extra dimentions continues

 

The Hierarchy problem questions this immense difference of the strength between different fundamental forces of nature. Why does gravity so much weaker than the other forces?  This is against the Grand Unified theory assumptions.

 

In Brane-universe conjecture, there are other dimensions and branes. String theorists assume that although gravity is equal to other forces, but because it gets diluted in other dimensions, what we observe is the very feeble strength in comparison.

Of course, the force decline is related to the size of extra dimensions as well. Nevertheless, one would expect that the force of gravity gets diluted much greater than what inverse square law dictates. At least, such a gravity decline should reveal itself in astronomical calculations. So far, cosmological observations confirm the Newton’s inverse square law. No further decline has been observed.

 

As it mentioned before, string theorists believe that gravity penetrates inside the extra dimensions as well. Claims that the extra dimensions are Planck distance small therefore the effect is negligible, cannot be sound for the reason that there are countless extensions of these extra dimensions along the way. So we should be able to measure the soaking effect in the gravity or magnetic force. This effect is not detected.

In 1988, the gravity law could be tested down to 1mm with the then current probes. This led Nima Arkani-Hamed, Savas Dimopolous, and Gia Devali to speculate that “in the brane-world scenario, extra dimensions could be as large as 1mm” ⁶⁹

So it was assumed that in scales less than 1mm, the inverse square law will break down. Currently, the gravity has been tested down to one tenth of the millimeter and inverse square law still holds.

Branes in string theory are assumed to be multidimensional and sometimes very large space-like entities. If they have existed the dilution of the forces should have certainly been detectable everywhere. None of these effects have been observed.

 

Flat Universe

 

In addition, string theorists have assumed that the main dimensions (four dimensions in Minkowski's space) are circular in big scale (spherical universe). So they speculated that at the time of Big Bang all dimensions evolved from a point. As the universe expanded, space opened up and created circular dimensions. So the observable dimensions are supposedly circular. They further assumed that if this is the case, so maybe there exist other dimensions, which did not open up. These guess work might offer some solutions so string theorists could avoid zeros. However, Brian Greene questions: “What if the spatial dimensions are not circular in shape? Do these remarkable conclusions about minimal spatial extent in string theory still hold? No one knows for sure.”¹

 

However, recently cosmological constant was announced as small but a non-zero factor. A non-zero cosmological constant favors an almost flat universe.

The Cosmological Constant is a factor that was first introduced by Albert Einstein. It wee supposed to act against the gravity and prevents the collapse of the universe. There is controversy about the origin and the nature of this constant. In fact, Recently it is shown that its effect surpasses the gravitational force of existing bodies in the universe and according to current believes it is creating the force for accelerating expansion of the universe.

If the universe is flat, we may conclude that spatial dimensions are linear and not circular. Therefore, the base of the assumption of wrapped extra dimension is trembling.