4. Describing the Behaviour of a 4 + 1 Dimensional Wave: The Need for Observables and Complex Functions
In this Section, continuing the study of the behaviour of a 4 +1 dimensional wave in our framework, we will direct our efforts toward describing how a 3 + 1 dimensional observer can model the behaviour of a quantity that changes in reference to the 5th dimension.
In order to do that and in accordance with
Section 2, we turn our attention on a specific point in 4D space
= (
). If the 4th dimension is treated as space, then at any such point the amplitude A of the 4th dimensional wave (not to be confused with the wave’s angular frequency in the 5th dimension which we also expressed as
above) will oscillate in the 5th dimension with frequency f
= ω
/2π.
Figure 2.
How the Amplitude of a 4-dimensional wave changes in the 5th dimansion (Max Amplitude = 1, T´ = period of the wave in the 5th dimansion) for a specific point in 4D space = ().
Figure 2.
How the Amplitude of a 4-dimensional wave changes in the 5th dimansion (Max Amplitude = 1, T´ = period of the wave in the 5th dimansion) for a specific point in 4D space = ().
This means that for a specific point in space and for a specific moment in time, as a 3D observer perceives it, a 4 - dimensional wave would seem to possess many values of A which cannot be known in advance since the observer doesn’t have access to the 5th dimension.
From the very first moment we try to mathematically model a dynamic spacetime, in the sense that we explained above, problems start to arise. More specifically, is it possible for a 3D observer to describe changes that happen in the same moment in time (4th dimension), like the Amplitude oscillation mentioned above?
In order to answer this question and start giving our dynamic spacetime a mathematical foundation, we once again turn to the 3 - dimensional wave of the form given in (1) and we ask a different question which may give us some insight into our problem. Can we model some aspects of the interactions and interferences of 3 dimensional waves without the need of time, only by using space?
Not surprisingly the answer is yes. If these waves all travel with the same speed (
) and all obey the equation:
= f
λ, then we can make predictions about the Amplitude of the wave on a specific point in space in correlation with its Amplitude on another point in space and also make predictions about interference patterns if we know the geometry of the sources and the relative phases of the waves [
2]. This is where complex numbers come into play. For example, in a single wave if we measure the Amplitude (A
1) of the wave in one point in space we can know the amplitude (A
2) of another point at distance dx from the first point by multiplying it with a phase factor in the form:
Also, in the case of the double slit experiment for light, we know that the Amplitude of the interference pattern for any point on the screen is analogous to
+
, where
,
the distances of the slits from the point measured on the screen and
[
2,
9].
Figure 5.
The double slit experiment and how it creates constructive and destructive interferences which have to do with the geometry of the experimental setup.
Figure 5.
The double slit experiment and how it creates constructive and destructive interferences which have to do with the geometry of the experimental setup.
If there was an observer oblivious to the concept of our time (4th dimension) in any point of the screen of the double slit experiment, it would seem to him that the Amplitude of the wave can take many possible values. The only way any conclusion or correlation about the wave and its behavior can arise is with the use of complex numbers. Still some information is lost to the observer (like the exact value of the Amplitude because it oscillates with time, which the observer can’t measure or understand) but at least a great portion of the total information of the system would be accessible (for example if there is a constructive or destructive interference like in the double slit experiment for light).
Taking that into account, the observer who can’t understand and measure time would have to make use of complex functions and associate them with observables which the observer can measure and understand such as wavelength λ or energy (if the energy of a wave is proportional to its frequency which is the case for electromagnetic radiation – photons and free fundamental particles). Also, such waves can not be entirely described only by spatial functions (for example ). Using the complex plane gives us a necessary extra degree of freedom, essential for our correlations.
Complex numbers are also essential for quantum mechanics. Experiments have shown that it is impossible to predict experimental results with real-number quantum theory. Also, the use of complex numbers is apparent in the fact that we can’t derive both Planck-Einstein and deBroglie relations (E=hf and p=h/λ) in quantum mechanics without their use.
A 3D wave is oscillating both in space and in time. For two different points (x
1, y
1, z
1, t
1) and (x
2, y
2, z
2, t
2), making precise correlations about the Amplitude in different times is impossible without any information about the time separation t
2-t
1. Analogous to this, if we (the 3D observer) wanted to describe a 4+1 dimensional wave and model its behaviour, the only way we could achieve this would be through the use of complex numbers, using them for correlations together with quantities measurable in the 3D plane (observables) such as distance, time separation or energy. This is where the connection with quantum mechanics in our framework starts to arise, since in quantum mechanics there is also a need for operators (which are measurable quantities) in order to determine the evolution of the quantum state and its expectation values, in reference with the values this quantum state possesses in a different point in space or in time [
4,
5].
Finally, we will try to give the most basic form of an equation in our framework by attempting to model a pure 4 +1 dimensional wave of a Scalar Field (Φ), which does not interact with lower dimensional disturbances of itself or any other field and propagates in a harmonic way. The magnitude of its rate of transmition is taken to be equal to the magnitude of the speed of light. For this wave the 5th dimension is acting as time and the 4th dimension (our time dimension) is acting as another spatial dimension. We are interested in modelling this wave in a way that makes sense to us, the 3 + 1 dimensional observer, following the same rules we imposed on the previous Sections.
This equation would take the form:
The following apply:
- -
The wave is 4 + 1 dimensional which means that time for this wave is the 5th dimension
- -
For this wave our time (the 4th dimension) is behaving as a spatial dimension. For this reason, our time dimension will be included in the spatial derivative terms
- -
Since we are modelling the wave’s behaviour in the reference frame of a 3 + 1 dimensional observer, all quantities and relations must apply to that reference frame.
Taking all these into account our equation should have the form:
(where
is the wave’s angular frequency in the 5th dimension)
The second spatial derivative terms will now include 3-dimensional time (4th dimension) and we will again make use of the Minkowski metric (metric tensor for flat spacetime) because we want the results to have a physical meaning to us the 3 + 1 dimensional observer. This means that the spatial derivative terms will take the form [
6]:
Combining (10), (11) and (12) we get:
which is equal to the Klein – Gordon equation if we consider that:
The same result for as the one we derived earlier!
This is very promising since the mass term we derived by alternative means in
Section 2 is identical to the mass related component in the Klein – Gordon and Dirac equations [
7,
8]:
Also, in QFT the mass term is recognized as a term in the Lagrangian that is quadratic in the field and has the form
for some
(
∝ m the mass of the particle) [
7,
8]. Since we can not exactly model the behaviour of 4+1 dimensional waves as we showed in this Section and need to make correlations with observables, such a term would make sense to appear in any attempt of the 3D observer to model the possible interactions and of those waves with themselves and other lower dimensional waves.