Hyperspace poses something of a dilemma for modern physics. On one hand it is very useful for explaining how the Universe is constructed at the very smallest level, and it even provides a useful concept for explaining what came “before” the beginning of time. On the other hand, hyper-dimensional space is incompatible with a Universe of matter as we know it.

The following Economist article describes an exception to this model that helps explain why gravity is such a weak force relative to the amount of matter in the Cosmos. In the Einsteinian view of the Universe, gravity is a warping in the geometry of space-time caused by the presence of matter. The Hyper-dimensional Theory of Gravity in the article that follows posits that most of the gravitational effect of matter is exerted towards warping hyper-dimensional space.

The changing positions of the galaxies, stars and planets would be driving the spatial turmoil in hyperspace through the warping effects of hyper-dimensional gravity — bringing the different geometries of an unknown number of hyper-dimensions perpetually into conflict with one another. This perpetual, twisting dance of hyperspatial geometries would explain the Universe’s enormous hidden store of virtual energy. Even the feeble effects of gravitational warping on 3-D space-time is enough to move whole galaxies and compress stars far enough to force nuclear fusion.

A Matter of Gravity

Newton discovered it. Einstein complicated it. But nobody really understands the force of gravity. Part of the explanation may be that it is not really all here

Not many people think that a small magnet is performing a remarkable feat when it grabs a nail off a table. Nima Arkani-Hamed, on the other hand, does. The nail, he points out, has the entire mass of the earth tugging down on it through gravity, but this still cannot overcome the force of the magnet. Why is gravity so miserably weak?

This is a question that has puzzled physicists for decades. But two recent papers in Physical Review Letters, by Lisa Randall of Princeton University and Raman Sundrum of Stanford University, suggest an answer. They build on an idea proposed earlier this year by Dr Arkani-Hamed, who works at the University of California, Berkeley, and two of his colleagues: Savas Dimopoulos of Stanford, and Gia Dvali, of New York University. Together, all these physicists believe that the reason gravity is such a weak force in the universe is that it does not actually spend much of its time here.

Hide and Seek

In the traditional way of looking at things, gravity is one of four fundamental forces that hold the universe together. The other three are the strong nuclear force, which binds the particles in atomic nuclei; the weak nuclear force, which is responsible for some sorts of radioactive decay; and electromagnetism.

All three of these other forces are much more powerful than gravity. But it was not always so. Most physicists believe that, at the time of the Big Bang, when the universe began, all four forces were symmetrical, and thus of equal strength. According to this idea, the different sorts of sub-atomic particle in the early universe were also symmetrical with each other.

Dr Arkani-Hamed describes these highly constrained starting conditions as requiring the universe to be like a pencil balancing on its point-possible in theory, but wildly improbable in practice. He likens previous attempts to explain the so-called hierarchy problem (why gravity is so much weaker than the other three forces) to the creation of a hand designed to hold the pencil up.

Instead, he and his collaborators propose a different explanation. Rather than circumventing the hierarchy problem, they propose to abolish it entirely. In their view, the problem does not exist. The weakness of gravity is an illusion. It actually remains just as strong as it ever was, but not all of its strength is exercised in the perceptible universe. Rather-and in contrast to the other three forces-gravity frequently operates in two or more extra dimensions beyond the commonplace four (the three of distance, plus time). And the longer it spends in these other dimensions, the weaker are its effects in the dimensions inhabited by people.

A consequence of string theory is that with the addition of an 11^th dimension the universe can be divided into so-called membranes. These are regions with fewer dimensions than the space surrounding them. (A familiar analogy might be with a wall, which is a two-dimensional thing in an otherwise three-dimensional room.)

Electromagnetism, and also the strong and weak nuclear forces, are confined to their membranes, and thus to this universe. That is because the ends of the strings of which they are composed tend to “stick” to the membrane in question. But gravitational strings have no sticky ends and can wander freely off into Dr Arkani-Hamed’s extra dimensions, where they have no effect on matter stuck to the membranes of the observable universe. That is why gravity appears to be so weak.

NARRATOR: Randall had been fascinated by an apparently inexplicable phenomenon: the weakness of gravity.

NIMA ARKANI-HAMED (Harvard University): Gravity certainly does not look weak in everyday life. It’s responsible for keeping our feet on the ground and keeping Earth spinning around the Sun and so on, but actually gravity is incredibly weak compared to the, to the other forces. This is easy to appreciate if you take an ordinary refrigerator magnet and stick it on top of a metal pin. We all know this fridge magnet will actually pick that pin up off the table, so that sort of dramatically illustrates how feeble gravity is compared even to the magnetic force of a tiny fridge magnet.

NARRATOR: When M Theory emerged, Randall and her colleagues wondered if it might provide the explanation. Could gravity be leaking from our Universe into the empty space of the eleventh dimensions?

NIMA ARKANI-HAMED: Gravity might only appear to be weak even though it’s fundamentally just as strong as everything else because it dilutes its strength out in all these extra dimensions that we can’t see.