Unification
As it is said in the previous sub-chapter, there are 4 fundamental
forces acting in our Universe: gravity, strong nuclear, weak nuclear and electromagnetic.
One of the challenges which physicists have faced during the recent years has
precisely been to unify these forces in one single primordial force, in an epoch in which
the Universe was ruled by the high energies.
Cooling and Symmetry Break-Up
It is thought that the division of the initial force into 4 distinct
forces (what is called the symmetry break-up) was due to the cooling of the
Universe. Stephen Hawking compares this symmetry break-up to the one that occurs
when a ball swings around a roulette at a high speed. When the roulette slows
down, the ball tends to fall in one of its 37 holes, which may represent 37
different states in which the ball can exist. Therefore, one may say that, in
the beginning, 4 balls were swinging around the "Universe" roulette
showing similar behaviours and moving at identical velocities. When the
"Universe" roulette slowed down (lost energy), the 4 balls ended up
falling in 4 holes of the roulette, each one with its own particular
characteristics.
The Electroweak Force
The electromagnetic and the weak nuclear forces were the first ones that theoreticians
achieved to unify. The messenger particle of the electromagnetic force (the
photon) has an infinite range of action, in opposition to the messenger
particles of the weak nuclear force (W+, W- and Z0,
commonly known as intermediate bosons) which are weakened in space due to their
large masses. For that reason, they lose intensity just after crossing a very
short distance.
But it's presumed that the field responsible for the weakening of the
intermediate bosons (called the field of Higgs) vanishes under high-energy
conditions. This way, such a high-energy environment provokes the disappearance
of the distinctions that set apart the weak nuclear force from the
electromagnetic force, which are merged into an unified force - the electroweak
force. The intermediate bosons were observed for the first time in 1983, under
the high energies generated at the CERN (Centre Européen de Recherche
Nucléaire), in Geneva. It was then proven the unification between these two
forces.
Bird-eye view of the CERN
in Geneva, where in 1983 was proven the existence of the electroweak force
The GUT Force
Following this achievement, scientists looked for reaching the
unification between the electroweak and the strong nuclear forces, into the
so-called GUT (Grand Unified Theory). The strong nuclear force is the most
powerful of the 4 mentioned forces but has a short range of action, as the weak
nuclear force.
Some experiences in big particle accelerators (like the CERN) indicate
that the strong nuclear force is weakened under high-energy conditions, so then
the quarks (particles that are joined by this force) and the gluons (messenger
particles of the mentioned force) behave themselves almost as free particles.
On the other hand, both the electromagnetic force and the weak nuclear force
become more powerful under such high energies.
Therefore, there must be a determined energy level, a very high one,
where elecroweak forces (weak nuclear + electromagnetic) and the strong nuclear
force have the same intensity and, thus, assume themselves as being different
aspects of a single force. The GUT also predicts that the quarks and electrons were essentially different aspects of the same
particles in the primordial Universe, so then another
unification is obtained.
The Ultimate Unification
To finish, we miss unification between the gravity
and the GUT force, which shall be achieved at even higher
energies. The first step for attaining this purpose is to combine the general
relativity (which describes the gravity and is deterministic) with the
principle of uncertainty of the quantum theory (which describes the other 3
forces). That reconciliation is eased by the conception of a particle that,
similarly to the other bosons, obeys to that principle
and is the responsible for the transportation of the gravity force - the graviton.
Superparticle with Multiple Personality
The graviton is a particle with a spin of 2, contrasting with the other
bosons, which have a spin of 1. Therefore, for unifying gravity (spin of 2)
with GUT force (spin of 1), it's necessary to conceive a theory proposing that
particles with different spins may be seen as different aspects of a single
super-particle. This way, not only the gravity and the GUT force are unified,
but also is achieved an unification between the fermions (with fractional spins) and the bosons (gravity and GUT, with
whole numbered spins).
Superstrings
One theory that quite successfully explains a Universe where the
symmetry is actually certified is the superstrings theory which is not,
nevertheless, experimentally proved. According to this theory, the particles
are not infinitely tiny dots in space, but rather unidimensional entities
(similar to lines) which may be closed strings (as rings) or open strings (as
segments). This way, the story of each particle (its evolution across the time
dimension) is represented by a bidimensional surface which may take the shape
of a ribbon, in the case of the open strings, or the shape of a tube, in the
case of the closed strings. Two particles that are attracted or repelled by one
force (gravity, electromagnetic of nuclear) may so be seen as two
strings united by a third string, which represents the messenger of the force.
At the points where the 3rd string touches the other two, the behaviour of
these ones is affected by the intervention of the force.
The several particles can be described as string vibrations. The vibrations
of the open strings (which have sizes comparable to the Planck's extent - 10-32 mm - below which any observation
becomes impossible) generate bosons with spin of 1. The open strings can become
closed strings, but in that case they generate different particles, as the
gravitons (bosons with a spin of 2).
Closed string (MoonRunner
Design UK)
The 10 Dimensions Universe
The superstring theory predicts that the Universe originally existed in
10 dimensions. But at 10 dimensions the Universe should be unstable, because it
existed in a state of false vacuum, different from the inferior state of
energy. The analogy that can be made is the water retained by a dam: apparently
it exists in a state of low energy (because it's relaxed), but its truly
inferior state of energy would only be achieved if the water could surpass the
dam for freely flow heading the sea. As it is unstable at 10 dimensions, the
Universe was probably partitioned in two - one with 4 dimensions (ours) and another with 6 dimensions. It was
eventually that violent split that gave birth to the Big Bang, according to the
physicist Michio Kaku. The 6 dimensional universe would have been, meanwhile,
contracted to an astonishingly small size, several quadrillions inferior to
that of an atomic nucleus.
Stephen Hawking defends, on the other hand, that in primordial times,
all the dimensions should be very folded. Let's imagine a hair (thread-shaped):
it actually contains 3 dimensions: height, largeness and length. Nevertheless,
as it is seen by us, it looks like an unidimensional line, stripped from any
largeness or length, since the measures of both assume very little values
(almost unobservable), opposing to measures of its height, which can reach
several centimetres. Therefore, for some reason, 4 dimensions (the time dimension and the 3 space dimensions) would
have been unfolded, while the other 6 would have been kept folded as before.
It's possible that there are universes where more than 4 dimensions were
unfolded or universes where more dimensions were kept folded. Is it possible
the existence of life in such universes?
The 5th Dimension
How is it possible to imagine a universe with 5 dimensions (4 space
dimensions and 1 time dimension)? To be able to establish a comparison between
our Universe and one 5 dimensional universe, let's imagine that someone living
in a 3 dimensional universe (2 space dimensions and 1 time dimension) would
face the existence of a universe like ours.
The 3 dimensional universe would be comparable to an enormous flat sheet
(bidimensional) where the events would occur along a time dimension (as in our
universe). Let's imagine that a ball crosses the flat sheet: an observer would
see it not as a sphere, but as a circle that would arise from nothing, it would
expand and contract again until it would finally disappear. In a 4 dimensional universe, a cube can be represented on a paper sheet
as a large square (the front side), containing a smaller square (the back
side), where each apex of the large square is linked to an apex of the smaller
square by an edge. It is perfectly possible for us to visualize all the sides
of the cube (turning it around), in the same way as it is possible for us to
see the entire representation of the cube, even if the edges are opaque. To one
creature living in a 3-dimensional universe that's not possible. Unless that
creature breaks the edges of the exterior square, it will never be able to see
the interior (smaller) square, or in other words, the representation of the
4-dimensional universe cube.
Therefore, by analogy, the representation of a cube existing in a
5-dimensional universe shall be given to us by a cube inside another cube. If
the sides of the exterior cube are opaque, it's obvious that we'll never be
able to see the interior cube, unless we break it. Even more difficult is to
imagine a universe that is also endowed with 5 dimensions, but where there are
2 time dimensions and 3 dimensions. Or are there universes where the dimensions
assume forms other than space or time?
3 dimensional cube, its 2
dimensional representation, a 3 dimensional representation of a 4 dimensional
cube
Searching
for the Last Theory
Should this be the ultimate theory about reality? Possibly not. And is
there any unified theory about reality? There are 3 possible answers to this
question:
- There is a complete unified theory;
- There isn't any fundamental theory, but
an infinite succession of theories that describe reality with an
increasing precision;
- There isn't any theory about reality: the
phenomena can only be predicted in a certain scale, beyond which they
occur aleatorily and arbitrarily.
An even more metaphysical question is: Why did cosmos make such an
effort for existing? Is the unified theory so imperative that originates its
own existence?
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