lawyer

Thu Feb 09 2006 at 16:01:26

Physicists will tell you that the laws of physics aim to describe the world around us so that mathematicians and other physicists can understand what is going on. Physicists, for better or worse, tend not to talk in terms of hosts of golden daffodils fluttering and dancing in the breeze. Instead they use shorthand phrases like, "force is equivalent to the product of mass and acceleration .” Or more likely, perhaps, "F equal M-A.”

Describing the world of physical laws

So when a physicist says the laws of physics describe the world around us, it's true, but only up to a point. The description afforded by these laws is extremely limited. The laws of physics describe a bare minimalist world, devoid of irrelevant detail and populated with a panoply of simplifying assumptions.

The laws of physics do not cover love or life. The laws of physics steadfastly avoid truth, beauty and charm. Physicists have adoped these words to describe the undescribable properties of their fundamental particles, but the world of physics is only beautiful in the sense that the equations underlying those laws are simple, symmetrical and elegant.

The reason for this extremely specialised approach to describing the world is that, for a physicist, a simple, universally applicable law is far more attractive than a complicated one, or one that applies only to a limited range of phenomena.

For a physicist, the simplest, most elegant laws are those which apply in many different situations and circumstances, describing a whole range of seemingly different phenomena. One law to rule them all and in the model to bind them

You can change the laws of physics

One of the most famous of the multifarious laws of physics is the law of conservation of mass. It says that mass can be neither created nor destroyed. At first sight, this seems like a bit of a no-brainer .

Common sense or not, it's useful in all sorts of ways. One of the most famous —to scientists — examples of the use and development of this law was when Antoine Lavoisier began the the journey of changing medievel alchemy into modern chemistry. Back in the 1780s, Lavoisier was weighing all the ingredients to an experiment, reacting them together, and then —very accurately —weighing the resulting solids, gases, smoke and other materials. The total weight after the reaction was always exactly the same as the total weight before the reaction. Conservation of mass.

Lavoisier, incidentally was chief tax collector of Paris in the days leading up to the Revolution. He died on the guillotine in 1794, despised and hated by the leaders of the revolution. Eighteen months after being executed, he was exonerated and praised by the same revolutionaries.

It is said that, knowing he was about to be guillotined, Lavoisier arranged an experiment with an accomplice in which he would attempt to continue blinking after head was severed. The accomplice was to note the number of blinks, and use it to estimate the survival of consciousness after decapitation. A scientist to the very end.

Despite what Scotty might say Conservation of mass is one of those laws that has changed.

Around a century ago, Albert Einstein derived one of the best-known equations of modern physics: E = m c 2 . While this equation rolls off the tongue quite easily, the meaning is sometimes lost.

It means mass can be converted to energy and vice versa. So in certain types of process — nuclear reactions. for example — if you measure the ingredients and the results, there will be a difference in mass. It's usually pretty small, but nevertheless, it is there. This small change in mass is accompanied by a large change in energy.

E = m c 2 means the energy-equivalent of any amount of mass is the amount of mass multiplied by the square of the speed of light. Light goes pretty fast, so the speed is a big number: 300 million or so. Multiplied by itself.

The atomic bomb dropped on Hiroshima in 1945 had a yield of 20 kilotons, which is equivalent to 9 x 1013 joules. Using E = m c 2. we can work out how much mass was converted into energy in that conflagration. 0.1g, or a short strand of wire.

Up until 1905 or so, the world's top scientists all believed that the law of conservation of mass was one of those universal and absolute laws of physics.

But now we know better. Einstein helped us realise that mass —to a physicist —is just a special form of energy. The law of conservation of mass became a variant of the more universal law of conservation of energy. In the phycisists' eyes, the law of conservation of energy became more elegant and more useful, as it subsumed the law of conservation of mass.

Note the sterility of the physicists' view. Mass is just energy. No matter if the mass is a rose, or a daffodil. No matter if the mass is a person, or a work of art. The amount of energy in 0.1g of a man is the same as the amount of energy in 0.1g of over-cooked cabbage, or 0.1g of fissile isotopes. Whatever, it is still enough to destroy a city and strike fear into the heart of all who bear witness.

The law of conservation of mass is still useful. It still helps us to understand the world around us. In a few special cases we have to adapt that law and take account of the fact that sometimes, mass can switch into energy and vice versa. But we have the tools that tell us how to account for the change in total mass.

The introduction of relativity did not really change anything in the world of physics. Instead, the old Newtonian rules were adapted so that they could deal with speeds approaching the speed of light. The old rules still apply to almost everything in the real, physical world. Only when speeds get silly do we need to correct our answers for relativistic effects.

While relativistic speeds are the best known of the changes and adaptations of the so-called laws of physics, there has been a steady evolution in many areas. Back in 1850 or so, we thought magnetism and electricity were different things. With James Clerk Maxwell's equations, published in 1873. scientists realised that they were simply different manifestations of the same thing.

That was not the end though. In 1970s scientists managed to show that the weak nuclear force was part of the same family as electricity and magnetism. It's now called the electroweak force .

This intellectual process of bringing electricity, magnetism and the weak nuclear force together into one electroweak theory is identical to the process of bringing conservation of mass and mass-energy equivalence together under the law of conservation of energy. Bringing two or three laws together and forming one single more powerful and more generalised law from them is one of the prime driving forces of physics, and it is how we get to such powerful, such useful laws as conservation of energy, the laws of thermodynamics and the laws of motion.

And still, this process of combining different laws has not stopped. One of the great prizes of 21st century physics is to combine the electroweak force with the strong nuclear force and with gravity. It's certainly more intellectually challenging than combining electricity and magnetism, but it is no different in concept.

So the laws of physics don't change, they just get more refined with time.

The laws of physics come from many experiments performed by different people in different places over many years. They tend to go in two or three phases. The first phase is simply gathering data.

Neolithic shamans would spend years noting the position of planets and stars so that they could tell their tribes when to celebrate midwinter, or that the fiery disc of the life-giving sun would be eaten by the night-time monster from the underworld. Data gathering.

As more and more data accumulates, the theoreticians get to work to try and make sense of it all. Eventually one of them proposes a model or theory of what is going on.

The model has a number of components. First, is a mechanism for how the thing works. (large heavenly bodies orbiting around each other) Second is a formula or mathematical model that makes sense of the data and allows the modern-day shaman to infer the results from a set of observations. In the most successful models, this formula or equation becomes a new law of physics. The third part of the model is a set of experiments that can test the predictive power of the model.

Sometimes these models aim to describe a small, limited part of the real world. Robert Hooke worked out how a few things stretch and predicted how other things should stretch when he formulated Hooke's Law. Hubble did it with his estimate for how fast the galaxies are retreating from one another. Thousands upon countless thousands of other scientists did the same thing, each in their small, specialised area of interest.

Other times a really clever scientist brings together three or four or more of these limited mathematical models and refines them into something much more general and much more powerful.

The really famous scientists all fall into this latter category: Newton did this with his Principia. Einstein did it with special and general relativity. Maxwell did it with his equations of electricity and magnetism.

These great leaps forward tend to revolve around a formulation of an important, fundamental laws of physics: Newton's laws of motion ; the laws of thermodynamics ; Relativity .

These are the heavyweights in the physicists' arsenal. These are the things Scottie was talking about when the dilithium crystals were burning out as the Klingons were swarming around the near-earth space of Uranus .

Changing these heavyweights is always going to be near-impossible because they are so general and so powerful that they have been tested and found to be reliable in million — billions — of instances. If you want to change these laws, then you have to find a model and an equation that fits all the historical examples, as well as any future example. Not impossible — as Einstein showed with the development of special relativity. but seriously difficult to do.

The third key step in the beatification of a law of physics is when hundreds of scientists all around the world try to break the theory. They think of experiments that would test the theory to its limit, and then carry them out to see if the theory can still predict the outcome at the extreme edges of human ingenuity. If the theory survives this test — a process that can last for centuries — it is promoted to the status of a Law of physics.

Throw a ball up in the air at some speed and at some angle, and the laws of motion will tell you where that ball will land. Add some more complicated mathematics to take account of wind resistance, viscosity, bouyancy, the curvature of the earth, the rotation of the Earth and other factors, and the sums will predict to the nearest millimetre exactly where the ball will land, no matter how hard or how high the ball is thrown.

The laws of physics can be used to predict how a tropical storm will move across the Ocean, or explain how a bumblebee flies. They can be used to build a telescope to see the furthest planet, or a diffraction grating to view the crystal structure of DNA

Some might argue that a scientist who blindly trusts the laws of physics is no better than a zealot who blindly follows the tenets of a dogmatic religious cult. And it is true that some fundamentalist scientists choose to place their faith just as blindly in the laws of physics as their fundamentalist brethren do in the religious sphere.

The more enlightened, however, point to a crucial difference between a law of physics and a truth revealed in the Holy text.

The first test of a law of physics is that it explains how things work, and provides a theoretical and mathematical model for understanding that phenomenon.

My friend the Devil's Advocate will argue that the truth revealed in his sacred book offers a more believable explanation of the universe than your fanciful notion of gravity. You claim that everything in the universe influences every other thing, yet you propose no mechanism for this. There is no evidence for gravitational waves. still less for gravitons. You cannot even come up with a coherent theory of how gravity works. Five hundred years since Newton realised apples fall from trees and you still cannot offer me a better reason that God made it so. You dare to suggest that as more lumps of rock agglomerate together, they pull ever more forcibly on the surrounding chunks of rock? How, exactly?

My friend says that God pulls on the stars and the planets and God's will keeps them in motion. Simple, elegant and sublime. Forget your ill-thought-out, over-complicated notion of a mysterious and ill-defined gravitational force that somehow acts over billions of kilometers.

The second — and most crucial — test of a law of physics is that the mathematical model expressed in the law can predict the outcome of an experiment. And even more convincingly, the Law can point the way to new insights. Insights that are completely new to human imagination.

Although the theory of gravity, remain incomplete, the law of gravity offers a quantitative way to explain why the moon orbits the earth at the distance and speed that it does. Expressed mathematically, the law of gravity (g = G M₁ M₂ / r2 ) allows us to predict how the planets orbit around the sun, and say with some accuracy, how fast they orbit and what happens to the satellites that orbit around the planet.

Add in a few more laws worked out by Johannes Kepler and other astronomers and we can predict that there are a couple of stable points in the orbit where a small object can sit undisturbed for millions of years.

Sure enough, when we use our telescopes — constructed according to the laws of optics — to view the Earth-Sun Lagrangian points, we see lumps of rock just sitting there, stable in a gravitational well.

The theory gives us insights that we never before knew were possible. And today, we have put a satellite in one of the stable Lagrangian points, in a stable orbit far remote from the earth, to study the sun and other extraterrestrial phenomena. Gathering data for the next generation of theoreticians to develop their models and theories.

It is this ability to predict the result of an action and create new knowledge that sets the laws of physics apart from revealed truths such as those found in the Bible.