Going into the sixth year of the new millennium
physicists are consistently getting closer to discovering a theory
of everything, known as String
Theory. The question as to how the
universe works has perplexed some of the greatest minds in human
existence, and thus far all have failed to come up with a comprehensive,
water tight answer. The principal reason is that in order to do
so physicists must construct a framework that transcends unimaginable
scales of size, time and dimension.
The universe is a place of extremes. On a
larger scale it is dominated by huge clusters of stars bound together
by gravity. Our galaxy, the milky way, is just one of countless
millions. Like stars galaxies themselves bond to form clusters and
super clusters which extend out far into the observable universe.
On a small scale it is another realm entirely, composed of atoms
and sub atomic particles (electrons, protons and quarks) glued together
by strong and weak electro magnetic forces.
Amongst the greatest achievements of Albert
Einstein was his ability to fathom the working of the universe on
a grand scale. In 1905 Einstein published his 'special theory
of relativity', the crux of which was a new way of perceiving space
and time. Einstein announced that space and time are not separate
(as was previously believed), but rather are woven
together–they are one and the same. He called this 'spacetime.'
Put simply special relativity binds together
not three but four dimensions, three for space (forward–backward,
up–down and left–right) and the fourth being time. We move through
all of these dimensions everyday of our lives. Einstein proposed
that whichever of these dimensions we are moving through, the sum
total of the velocities of all of them must always be equal to the
speed of light. In this sense space and time are similar dimensions
and we can think of the objects speed through time in a similar manner
as its speed through space. As you move around here on earth you
do so through the three dimensions of space, but only at a fraction
of the speed of light. But remember your speed through all four
dimensions must always equate to the speed of light. To compensate
for your pathetically slow speed on earth you move through time
at quite a jog, relatively speaking. In fact almost all of your
speed is given over to your movement through time.
Of course Einstein's theory provokes an intriguing
paradox. If you were traveling through space close to the speed
of light you would no longer be traveling so fast through the dimension
of time because you are already fulfilling the rule of light speed
travel. Special relativity states that when traveling at velocities
very close to the speed of light the time dimension element of the
sum equation becomes smaller. Hence the faster you travel through
space, the slower time passes as seen from a stationary observer
(for whom time passes more quickly). hen traveling through space
at the speed of light the passage through the time dimension is
zero–time stops completely. Therefore as photons (of which light
is composed) travel at the speed of light, time does not exist for
them, they are as young as the day they were created (big bang?)
billions of years ago.
The reason as to why we find the implications
of this theory so difficult is because we live in an incredibly
slow world, one that blocks out the true mechanics of spacetime.
Special relativity is therefore a theory that requires us to look
at the universe in a way that we are not accustomed. However in
doing so it reveals the true nature of space and time, and in doing
so dismantling Newton's 'clockwork universe' in which time and space
are separate entities.
GENERAL RELATIVITY AND
WARPED SPACE
Einstein's keen perception and ultimate understanding
of relative motion and time led him to formulate his elegant special
theory of relativity. Yet it threw up a further conflict, clashing
again with the work of Isaac Newton–this time Newton's sacrosanct
theory of gravity. Newton correctly theorised that a body exerts
a gravitational pull on another body with a force determined by
two properties–the mass of their bodies and the distance apart.
Newton then surmised that if you were to change one parameter for
one body, the other body would instantly feel a change in the way
its tugged: the pull of gravity would instantly change. But special
relativity states that nothing can travel faster than the speed
of light.....
E
= mc2
In this equation E represents an infinite
amount of energy, which is needed to accelerate mass (m) to the
speed of light (c).
Based on special relativity where nothing
can travel faster than the speed of light, including the effect
of gravity, it follows that if the sun were to suddenly disappear
earth would not be affected by the loss of the suns gravitational
pull. However as Newton's understanding of gravity implied, the
loss of the sun would be felt a little after eight minutes–the time
it takes light to travel the 93 million miles between the two bodies.
This conflict led Einstein to the formulation of his general theory
of relativity. With general relativity Einstein once again
revolutionised the understanding of space and time. He showed through
mathematics that space is warped by mass–the greater the mass the
greater the warping of space. I would use the analogy of placing
a bowling ball on the surface of a trampoline, which will dent its
surface, and so the mass of the sun (or any other mass) dents the
fabric of spacetime. The earth orbits the sun as it is trapped on
the limb of the warped space, mass dictates how space is warped,
the manifestation of this warping is the force we call gravity.
Furthermore since space and time are interwoven, warping space warps
time.
THE QUANTUM WORLD
Put simply quantum theory describes the workings
of the universe at the tiniest level. If we were to shrink down
to the atomic and sub atomic world it is very different from the
world we experience. The essence of quantum theory (also known as
quantum mechanics) is that matter at sub atomic levels takes on
a Jeckyll and Hyde personality, having both wave and particle properties.
WHAT IS LIGHT?
The idea of this theory stems from a series
of discoveries made during the late 19th and early 20th century.
In 1905 Einstein solved a riddle that had perplexed the German scientist
Max Planck. Planck deduced that atoms could absorb or emit energy,
in the form of electromagnetic radiation (as in light or infra red
heat energy) but only in discrete packets. Planck surmised that
such an observation was a consequence of the ability of atoms to
emit energy only in separate chunks. Then Einstein proved that electromagnetic
waves, such as light, are themselves composed of discrete packets
of energy, or 'quanta.' Later the quanta were named 'photons.' If
you turn on a light bulb or an electric fire billions upon billions
of photons stream out each second to illuminate or heat a room.
Einstein had these ideas whilst he was trying to explain an observation
called the photoelectric effect. Not only did he shows that light
came in photons, but he also came up with the notion that light
waves can actually act as if they were light particles.
The photoelectric effect happens when light
bombards the surface of a metal, and electrons are ejected from
the metal, only when light of a minimum frequency (or energy) is
used. Above that frequency increasing the intensity of light increases
the number of electrons that are ejected. Hitherto light had been
thought of as light waves that bend on hitting a solid surface.
But it is easier to imagine that a particle rather than a wave could
dislodge an electron from an atom by colliding with it. Once the
critical minimum energy or frequency of light is exceeded, the energy
content of each photon is enough to cause one metal atom to lose
one electron. Below the critical energy no single photon has enough
energy to dislodge an electron from an atom, but above it more photons
will dislodge more electrons. The governing idea of Einstein's photoelectric
effect is that light sometimes has the properties of a wave and
sometimes has the properties of a particle...a phenomenon known
as wave–particle duality.
WHAT IS MATTER?
In 1923 a French prince (de Broglie) used
Einstein's special theory of relativity to reason that since energy,
which is propagated through wave motion, and mass (matter) are interchangeable
through Einstein's equation, then matter too must display wave–particle
duality. If light can be considered to have both wave and particle
properties, then why doesn't matter behave in the same way? His
assumptions were vindicated a few years later by scientists who
demonstrated that electrons, minuscule particles of matter, also
behaved like waves. The particles themselves were considered to
be point particles, in effect having no spatial extent. This is
an important factor when considering the validity of string theory.
Essentially all matter has wave like characteristics,
not just electrons. What is important is that this occurs at the
smallest sub atomic level, and that all matter has wave like properties,
including the particles that make up your computer. Yet there is
another twist in the quantum world, one that lies at the heart of
quantum mechanics, 'the uncertainty principle.'
WAVES, PARTICLES AND UNCERTAINTY
The uncertainty principle was
developed in the 1920s by Werner Heisenberg, and is a result of
matter having wave–particle duality. The premise is this–think of
a particle of matter, such as an electron. It is a tiny point of
matter, and has a position in space. However the electron also has
wave properties, and so it is moving, and you can measure where
it is and where it is going. But....the two measurements are
in direct conflict, if the electron is moving it doesn't have a
stable position. Waves do not have a position in the same
sense as particles, they only have a direction and momentum
since all mass that moves carries a momentum force.
This shows that mathematically
you cannot know both the position and momentum of an electron at
the same time. The uncertainty principle states that electrons,
and all other point particles, cant be described as being in such
a place at such a time with such a momentum. You can measure say
the momentum of a particle but not its position. In fact the more
precisely you know property, the less sure you can be of the other.
Okay so I hear you say that you would be able to know the position
of a moving car at an instant in time with a fairly high degree
of accuracy. However in the tiny world of quantum mechanics this
becomes more difficult as the numbers get smaller. You may be looking
at your computer thinking 'I know exactly where my computer is'
but on a sub atomic level it is impossible to know instantaneously
the velocity and position of any of the electrons that are part
of the atoms in the material from which your computer is made.
BRINGING IT ALL TOGETHER
Einstein's general theory of
relativity (built upon his earlier formulation, special theory of
relativity) is a theoretical framework that describes the universe
on a large scale–the interaction between stars, galaxies and clusters
of galaxies, space and time.
Quantum theory provides a theoretical
framework for understanding the universe on atomic and sub atomic
scale. Both general relativity and quantum theory have been vindicated
through years of thorough experimentation, but there does remain
a problem.....the two theories are incompatible!!!
Effectively general relativity
breaks down at a sub atomic level and uncertainty dominates. Not
only is the position of particles unpredictable, so is the whole
fabric of space time. The perfect geometric shape of spacetime degrades
into a chaotic unpredicted foaming mass at the quantum level. whilst
the two theories explain the macro and micro universe beautifully,
it seems that the two will not join. This has represented the key
conflict between 20th century physicists, but a result to provide
a link between the two has been sought and found.........in the
guise of String
Theory.
