'Laws" have all kinds of implications. They're onerous if they represent seemingly arbitrary restrictions. They're unfair if not equally applied. They're an imposition if enforced by a capricious authority.
On the other hand, laws are comforting. They provide frameworks to build upon. They represent predictability. They exhibit order where chaos seems to reign.
Science identifies universal laws of nature, or simply natural laws. These laws are concerned with regularities in the physical world. Typically the models scientists build to represent classes of regularities are what we call laws.
What does the notion of natural laws imply? Usually they address fundamental phenomena. They characterize what is left when obscuring superficialities are stripped away. They account for why events play out in predictable ways even when their details suggest they are unrelated.
If there are laws looming in observed regularities, they exist regardless of where or when the regularities occur. Laws are not here today and gone tomorrow. Neither are they good in one corner of the universe and not in another; hence the moniker universal.
In many respects, physics is the granddad of the sciences. Physics textbooks discuss a wide range of phenomena, but, they are all built on a surprisingly small number of principles. Physicists strive to describe more happenings with fewer, unifying laws.
Laws don't have a lot to say about solo events. Some events that seem to occur once may simply recur on a very long timeline. The orbit of Haley's Comet is no different in its gravitational interaction with the Sun than the orbit of other objects trapped by the Sun's gravitational field.
However, it is likely to be seen only once in a lifetime. It simply spends most of its 75 year orbital period very far from the Sun and isn't visible. Odd or irregular events may simply appear to be so because of our limited perspective.
One of Newton's great insights was the law of gravitation. It accounts for the behavior of an apple falling from a tree in the same way it accounts for the Moon orbiting the Earth! These seem like dissimilar occurrences, but he showed they have the same phenomenological underpinnings.
The classical Newtonian laws of motion apply to all objects. Other than the masses of objects and how far apart they are from each other, the specific details of an object are of no consequence.
It became evident in later investigations that Newton's gravitational model was not universal. It failed to account for some observations of far-off stars and galaxies.
Once relativistic effects were taken into account, we had a truly universal law of gravity. As is often the case, Newton's law was not wrong; his theory was simply a special case of a more all encompassing law.
The laws of thermodynamics are also universal. How we discuss the temperature, heat or entropy of an object is the same no matter what other properties the object has. Be it a hot air balloon or the atmosphere of a gas planet like Jupiter, the fundamental thermodynamic processes governing each are the same.
It is truly gratifying to discover that the validity of many physical laws is based on something as simple as the properties of physical space. This is the case for conservation laws in physics. This was proven in 1915 by a little known and greatly underappreciated female mathematician, Emmy Noether.
Is the outcome of an experiment or event different if it takes place in one location verses another? Does it matter that an experiment or event happens now, or later, or in the past? Is it important if an experiment or event has one orientation or if it is rotated about an axis?
Noether proved that if outcomes are not dependent on time, place or orientation important quantities are conserved. Conservation of momentum is the consequence of the symmetry of space. The result of an experiment is the same no matter where in space it is preformed.
Furthermore, energy conservation is the consequence of time symmetry; experimental results are not dependent on when it is preformed. And, angular momentum is conserved in an event whatever its orientation in space.
So simple, yet so elegant! These are the most basic natural laws. Insofar as space, time and spatial orientation are symmetric, they give rise to universal conservation laws.
So powerful is this insight, it has been generalized to many applications. Behind nearly every discussion of fundamental physical processes is an attempt to reveal symmetry or violation of symmetry.
Natural laws are not onerous since they are not arbitrary. Being universal, they are not imposed unequally. They are discoverable, in large part, because they don't change. They don't turn on and off for unfathomable reasons.
They are in fact comforting. They give those who are patient and disciplined enough to seek them out a foundation upon which to construct order out of what might seem chaos.
Steve Luckstead is a medical physicist in the radiation oncology department at St. Mary Medical Center. He can be reached at firstname.lastname@example.org.