M-Theory

Let us imagine a goldfish, in a curved goldfish bowl.

Gazing out the goldfish, would have a distorted view of reality.

Our view outside the bowl, would be different.

For example, an object moving in a straight line,

would be observed by the goldfish, to move along a curved path.

If the goldfish formulated a theory,

it would be true from its frame of reference.

Is it possible that we are inside a giant goldfish bowl,

and have our vision distorted, by an enormous lens?

Our ancestors had a different perception of reality.

CE stands for current era, and is the modern equivalent of AD.

Ptolemy who lived around 150 CE, was a famous scientist of his time.

He formulated the theory of the universe.

In his theory, the earth was stationery, and was situated at the centre of the universe.

The Sun, the planets, and the stars, orbit the Earth.

This was the perception, of learned people, and the common man,

for more than 14 centuries.

This was their perception, of reality for more than, 1400 years.

This view had a strong grounding.

Everybody knew that the Earth, was not moving under their feet.

So, it was quite obvious, to them that the Earth was stationary.

In 1543 CE, a scientist named Copernicus,

proposed a radical different model of the universe.

In this model, the sun was at rest,

and the Earth and other planets orbited it, in a circular fashion.

The idea faced tremendous resistance from the people, and the church.

Galileo who developed on the copernican model,

was put on trial, and found guilty of heresy,

and confined to house arrest, for the rest of his life.

Only in 1992, the church finally acknowledged,

that it had been wrong, to condemn Galileo.

When belief systems are strong, it is very difficult to accept a new idea.

Specially so, if it is radically different.

We need a very open mind, to appreciate a new model of the universe,

that is emerging.

It is broadly called as M-theory.

There is no picture, or theory independent concept of reality.

We need to adapt a view called, Model dependent realism.

A physical theory, is a model, and a set of rules,

that connect the elements of the model to observations.

This provides a frame work, to interpret modern science.

What is reality?

In classical science, if all human beings,

observe the properties of a object,

and if they are consistently same,regardless of the observer,

it is considered as reality.

Modern science requires a different perspective.

Here the observer and the observed object, are intimately related.

In quantum physics, a particle has neither a definite position,

and a definite velocity, unless and until,

these values are measured by an observer.

We need to be aware, that our observations, are analogous,

to that of the goldfish, in a curved bowl.

Many scientific theories that had proven successful,

have been later replaced by other successful theories,

based on a wholly new concepts of reality.

According to model-dependent realism,

it is not relevant whether a model is real.

It is only relevant whether a model agrees with observation.

One can use which ever model is more convenient,

in a given situation.

We need to be aware, that our perception,

is shaped by a kind of lens,

the interpretative structure, of our human brains.

For example, when we see something, the eyes sends a series of signals,

which the brain interprets, and builds a mental picture, of what we see.

What we "see", is an interpretation of the data.

The brain is very good at model building.

If people are fitted with glasses, which changes the images,

to be upside down, their brains after a time, change the model,

so that they see the right way up.

If the glasses are removed, they see the world, upside down, till they adapt.

We cannot see sub atomic particles.

We need to depend on a model, to understand these particles.

We cannot see electrons, but we know they exist.

We extensively use gadgets, where electricity, or electrons are moving around.

We cannot see something called, Quarks.

Protons and neutrons are made of quarks.

The binding force between quarks, increases with separation.

Isolated free quarks cannot exist in nature.

In protons and neutrons, they exist in groups of three.

In pi meson, they exist as pairs, of a quark, and an anti-quark.

Quarks behave as if they are attached by a rubber band .

Quarks are not observable particles.

It helps to build a model.

According to model-dependent realism, quarks exist.

This model agrees with our scientific observations,

and is able to make more and more accurate predictions.

This model is able to explain the beginning of the universe,

and the beginning of time, 13.7 billion years ago.

It is called, in a lighter vein, as a big bang model.

A model is a good model, if it :

1. Is elegant.

2. Contains few arbitrary or adjustable elements.

3. Agrees with and explains all existing observations.

4. Makes detailed predictions about future observations.

Early scientists like Aristotle, proposed models of the world.

He proposed that the world, is comprised of, four basic elements:

Earth, Air, Fire, and Water.

Since then our understanding of the universe, has dramatically evolved.

To quote Einstein, a model should be as simple as possible,

but not simpler.

When observations no longer agrees with the model,

it is time to look for a newer model,

which can explain the new observations.

One example, of a old model, is the idea of a static universe.

Till the 1920's, scientists believed that the universe was static.

In 1929, Hubble observed that the universe was expanding.

He did not directly observe the universe expanding.

He observed the light emitted by galaxies.

The light carries a characteristic signature or spectrum.

This spectrum changes by a known amount,

if the galaxy is moving relative to us.

Scientist now accept a model of an expanding universe.

There are many examples, where models have evolved.

Newton thought that light comprised of small particles called corpuscles.

This model explains very well, many properties of light.

Newton himself observed, what is called as Newton's rings.

This is caused by a phenomenon called interference.

This could not be explained by the corpuscle theory.

Light needs to behave like a wave, to explain interference.

When the waves are out of phase, they cause interference.

The concept that an object could be described as a particle,

or as a wave, is known as wave/particle duality.

Scientists now accept that light behaves as both particle and wave.

Situations in which different theories, accurately describe,

the same phenomena, is consistent with model-dependent realism.

Each theory can explain certain properties, and would be as valid as another.

There seems to be no single theory, that can describe every aspect of the universe.

There seems to be a network of theories.

We call this M-theory.

Each theory in the M-theory network, is good at describing phenomena,

within a certain range.

When the ranges overlap, the various theories in the network agree.

In this case, we can say they are part of the same theory.

No single theory of the M-theory network, can explain every aspect of the universe.

This is acceptable in model-dependent realism.

Quantum theory is a fundamental principle,

for a modern view of nature.

The approach to quantum theory is called alternative histories.

In this view, the universe does not have a single existaence or history.

Every possible version of the universe exists simultaneously.

This is called as quantum superposition.

This theory has passed every experimental test, to which it is subjected.

We will now review the wave behaviour of light.

Newton observed this phenomena and it is called as Newton's rings.

A lens is placed on a flat reflecting surface.

It is illuminated by a single colour light.

If we look down from above, we will see a series of light and dark rings,

centred on where the lens touches the surface.

The light and dark rings are caused by a phenomenon called interference.

A wave consists of a series of crests and troughs.

When the waves collide:

If the crests and troughs happen to correspond, they reinforce each other.

This results in a larger wave.

This is called constructive interference.

Here the waves are said to be "in phase".

If the crest of one wave, coincides with the trough of another wave,

the waves will cancel each other.

Here the waves are set to be "out of phase".

This results in destructive interference.

In Newton's rings, the light from the lens, collides with the reflected light,

from the reflecting plate.

The bright rings that we see are caused by constructive interference, of these waves.

The dark rings that we see are caused by destructive interference, of these waves.

Scientists did an equivalent experiment using buckyballs.

Buckyballs are 60 carbon atoms molecules.

They were made famous by the architect Buckminster Fuller,

who designed buildings, based on the structure of this molecule.

They were called geodesic domes.

The carbon buckyballs that architects used, were atomic sized molecules.

Scientists fired these balls to a barrier, with 2 slits in them.

Beyond the barrier, the scientists situated, the equivalent of a screen,

to detect the emergent molecules.

If the molecules behave like particles, a certain pattern,

can be expected on the screen, when both the slits are open.

When one or the other slit is closed, a different pattern,

can be expected on the screen.

But the scientists observed surprisingly different results.

When both the slots were open,

some areas on the screen, received more molecules,

and some other areas, received no molecules.

This is very similar to the interference pattern of light,

passing through two slots.

The areas where more molecules were received,

correspond to the bright areas,

and the areas where no molecules were received,

correspond to the dark areas.

In the history of science ordinary experience,

and intuition were the basis of theoretical explanation.

As technology evolved, it expanded the range of phenomena,

we could observe.

We began to discover, that nature behaves in ways,

that were less and less in line, with our everyday experience, and intuition.

The Buckyball experiment is typical of the type of phenomena,

that cannot be explained by classical science.

It can be explained by what is called as quantum physics.

Quantum physics was developed recently.

Quantum physics provided a frame work for understanding,

on how nature operates on atomic and sub atomic scales.

It is a completely different conceptual scheme.

In this concept an object's position path, and even its past,

and future, are not precisely determined.

Quantum theories of forces such as gravity, all the electromagnetic force,

are built into that frame work.

Though the component objects of everyday life, obey quantum physics,

Newton's law still holds good for larger composite objects,

that are a part of everyday life.

This may sound strange.

But there are other instances, in which a large assemblage,

appears to behave in a different way, than its individual components.

The behaviour of a single neuron, does not explain the behaviour of the brain.

The behaviour of a system, cannot be explained,

by the behaviour of its individual components.

Scientist now agree that quantum physics applies to atomic and subatomic levels,

and Newton's laws are a good approximation for macroscopic behaviour.

Quantum physics is a new model of reality,

that gives us a picture of the universe.

It is a picture, in which many concepts of our intuitive understanding of reality,

no longer have meaning.

Scientists have observed the quantum nature of electrons,

and particles in the atomic and subatomic scale.

In general the larger the object, the less apparent and robust,

are the quantum effects.

The wave/particle duality of light is well accepted.

That matter particles, behave like waves, surprised everyone.

The particles of light are called as photons.

Even a one watt bulb, emits a billion billion photons, every second.

Scientists have succeeded in creating an extremely small beam of light.

It is so small, that it consists of single photons.

These photons can be detected individually.

The dual slit experiment was carried out with this ultra thin beam of light.

The photons were fired at the barrier, one photon at a time,

with a few seconds interval between each photon.

The same interference pattern, was exhibited in this experiment.

Scientists were startled.

The wave nature of light, is not just the behaviour of a beam of light,

but the behaviour of individual photons.

Another main tenet of quantum physics, is the uncertainty principle,

formulated by Heisenberg.

It tells us the limit of our ability to simultaneously measure certain data.

For example, the position and velocity of a particle.

The more precisely we measure speed, the less precisely we can measure position.

The more precisely we measure position, the less precisely we can measure speed.

There is a scientific way to state this principle.

If we multiply the uncertainty in the position of a particle,

by the uncertainty of its momentum, the result can never be smaller than a fixed quantity.

This fixed quantity is called as Planck's constant, which is a extremely small value.

It has a value of 6 divided by 10,000,000,000,000,000,000,000,000,000,000,000.

It can also be expressed as,

4.136 multiplied by 10 to the power of minus 15 electron volts per second.

The units of measurements are meters, kilograms, and seconds.

If you are measuring macroscopic objects like a football,

the values of mass, position and velocity will still be very very accurate.

But in the same unit the mass of an electron,

is 000,000,000,000,000,000,000,000,000,001 kilogram.

It can also be expressed as,

9.1 multiplied by 10 to the power of minus 31 kg.

If we measure the position of the electron, we cannot measure the speed of the electron,

more precisely than plus or minus thousand kilometers per second.

This obviously is not very precise.

According to quantum physics the outcomes of physical processes,

cannot be predicted with certainty.

This is because they are not determined by certainty.

Nature does not dictate the outcome of any process.

It allows a number of different eventualities,

each with a certain likelihood of being realised.

Quantum physics leads us to accept, a new form of determinism.

Given an current state, the laws of nature determine the probabilities,

of various futures and past.

Despite the probabilistic nature, we can still test quantum theories.

In the double slit experiment, according to quantum physics,

each particle has some probability of being found,

anywhere in the universe.

The probability of finding the electron within the double slit experiment is very high.

Yet there exists a minuscule probability, that it exists in another galaxy.

We need to digest this reality.

The probability in quantum physics, is different from probabilities in classical physics,

which we experience in every day life.

A skilled player aims darts, to hit a bull's eye in the dart board.

In this classical case, the probability of the dart, landing near the bull's eye is greater,

and keeps diminishing, as we move away from the bull's eye.

This results in a probability pattern.

This pattern results because, the conditions of launch, is incomplete.

The player releases the dart, with certain parameters like, angle, spin, velocity, etc.

If we precisely know all these parameters, we can determine the outcome,

with a great deal of precision.

In this classical case, our use of probability, to predict the outcome,

only reflects our ignorance of the parameters involved.

Probabilities in quantum theory are different.

They reflect a fundamental randomness in nature.

The quantum model contradicts, our intuitive concept of reality.

If we find this difficult to grasp, we can take comfort in the fact,

that even great scientists like Einstein and Feynman experienced similar difficulty.

However, quantum theory today has been tested and proved.

In the quantum model, of the double split experiment,

the particle is said to have no definite position,

during the time it is between the starting and ending point.

Feynman had a remarkable insight for its behaviour.

He said that the particles take every possible path connecting the points.

They take all these paths simultaneously.

This he asserted, is what makes quantum physics, different from classical physics.

Feynman formulated a mathematical expression for this.

It is called Feynman's sum over histories.

M-Theory is not a concrete theory.

It is still evolving, and we will continue the discussion.