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There are many theories that attempt to explain what we observed in our three dimensional environment in terms of higher dimensions.  However they all suffer from the same problem in that the existence of those higher dimensions are primarily based on abstract on mathematical models.  The reason is because we as three dimensional beings are only able to observe objects in the three-dimensional environments we occupy.  Therefore we must rely on mathematics to guide us in understanding how their existence influences what we observe in our world.

Many feel the most promising is called string theory, which attempts to define all of the observed properties of our universe in as many as ten dimensions.
However, as is pointed out on page 51 of Lee Smolin book “The Trouble with Physics” all attempts at unifying physics through extra dimensions suffer from the same problem.  There are a few solutions that lead to the world we observe but there are many which do not.  One has to set the initial conditions, which are found by observing our world to determine which solutions define what we observe.  The use of this circular methodology means its validity is not based on its theoretical structure but on its flexibility.

In other words its validity is not based on connecting the observed properties of our environment to it but the randomly picking which the ones do the best job.

Einstein’s theories are very different in that they make specific predictions based on the existence of a single space-time environment that if found not to occur would invalidate it.

For example his theory tells us that light should bend as it passes by a massive object.

If this was not observed his theory would have to be discarded.

However 1919 Arthur Eddington lead an expedition to photograph the Total Eclipse of the Sun. The photographs revealed stars whose light had passed near sun had been bent exactly as Einstein had predicted. The experiment was repeated in 1922 with another eclipse with the same confirmation.

Additionally in past century since he proposed his theory there has not been any observations of our macroscopic universe that disagree with any of its predictions.

Even so this does not mean that we should assume that our universe is physically made up of four dimensional space-time because as with all multidimensional theories when Einstein derived the geometric properties of a space-time universe in terms of the constant velocity of light he also define another one with identical properties in terms of four *spatial* dimensions.

In other words by defining the geometric properties of space-time in terms of the constant velocity of light he provided a qualitative and quantitative means of redefining its time related properties in terms of only four *spatial* dimensions.

As was mentioned earlier the fact that light bends as it passes by massive objects doers not mean our universe is made up of four dimensional space-time because the symmetry of equations used to make that prediction also predicts one made up of only four *spatial* dimensions will do the same.

Therefore the fact that light bends as it passes by a mass cannot be used to eliminate that possibility.

However there is a experiment very similar to the one Arthur Eddington preformed that would resolve this ambiguity.

Einstein’s Theory of General Relativity tells that objects that create gravitational field cause time to “move” slower.  However due to the symmetry of his equations one could also say that time slowing down results in the formation of a gravitational field.  Therefore one must assume that a gravitational field must always be attractive because observations indicate that time only moves in one direction forward.

However the fact that one can use Einstein’s equations to qualitatively and quantitatively redefine the energy he associated with gravity in terms of four *spatial* dimensions is one bases for assuming as was done in the article “Defining energy?” Nov 27, 2007 that it can be derived in terms of a spatial displacement in a “surface” of a three-dimensional space manifold with respect to a fourth *spatial* dimension as well as one in a space-time dimension.

However unlike time which is observed to only move in one direction forward observations tell us that we can move in spatially in two directions up down backwards and forwards.

Therefore if the universe was made up of four *spatial* dimensions there should exist a form of mass that posses a negative gravitational potential.

One candidate for such a mass is antimatter.  We know from observations that in it posses an opposite electrical charge than its matter counterpart.  Therefore it is logical to assume that it posses a gravitational field that is oppositely directed from that of matter.

An experiment has be proposed that could determine if this is indeed true.

As describe in the New Scientist article “Antimatter mysteries 3: Does antimatter fall up?” Apr 29, 2009, it involves using uncharged particles to prevent electromagnetic forces from drowning out gravitational effects.  It will first build highly unstable pairings of electrons and positrons, known as positronium, then excite them with lasers to prevent them annihilating too quickly.  Clouds of antiprotons will rip these pairs apart, stealing their positrons to create neutral antihydrogen atoms.

Pulses of these anti-atoms shot horizontally through two grids of slits will create a fine pattern of impact and shadow on a detector screen.  By measuring how the position of this pattern is displaced, the strength – and direction – of the gravitational force on antimatter can be measured.

In other words there is an experiment that could determine if our universe is physically composed of four dimensional space time or four *spatial* dimensions because as was mentioned earlier a universe physically composed of four dimensional space-time cannot support a negative gravitational potential while one made up of four spatial dimensions can.

Yet if found to be true it does not mean that Einstein’s theories are invalid because his theories and predictions were based on pure mathematics and as mentioned earlier a universe consisting of four dimensional space-time and four spatial dimensional are mathematically are equivalent in every respect.  

However it would require us to rethink our understanding of the physical geometry of our universe and the causality of gravitational forces.

Later Jeff

Copyright 2015 Jeffrey O’Callaghan

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