Last year, I wrote a series of articles on the four fundamental forces of nature, highlighting the fine-tuning of each force as a necessary feature of our universe to support life as we know it. In addition to this complete suite of forces, the physical nature of things is governed by other principles that comprise essential characteristics of our universe. These principles are the conservation laws of nature. Without them, life could not exist.
Laws of nature such as the conservation of energy, momentum, and electric charge appear so fundamental to “the way things are” that they may not show up on a Top 10 list of parameters finely tuned for life. However, without the law of conservation of angular momentum, we would be faced with disastrous effects at all levels. Planetary orbits would be unstable, with planets freely spiraling into the sun or soaring off into interstellar space. At the atomic level, electron orbits around a nucleus would not remain stable, disrupting even the ground state existence of atoms.
It’s beyond the purpose of this article to suggest a numerical value for how finely tuned the conservation laws of this universe are. However, some postulated multiverse models allow for completely different laws of physics in “possible” universes, and it’s acknowledged that many of these divergent universes would fail the anthropic principle, having laws of physics incompatible with life.
A Game of Billiards
What gives rise to the fundamental laws of conservation we’ve come to know and depend upon in our universe? In the history of science, observations of how things work gave early empirical knowledge of conservation of momentum and energy. For example, physicist Ethan Siegel describes the pre-20th century understanding of the principle of conservation of mechanical energy:
There was no fundamental reason known that would necessarily imply that energy was conserved; it was only observed that if you accounted for all the different forms of energy properly, that there was no way to either create or destroy it, only to convert it from one form to another.
Beyond the anthropic necessity of the conservation properties of nature, as a physics professor, I can attest that these laws comprise a useful basis for facilitating the solution of many typical physics problems. Without the principles of conservation of momentum and energy, physics students would be hard pressed to solve for something as simple as the resulting motion in a game of billiards from knowing just the initial conditions of a cue ball striking another ball.
Matter and Radiation
More importantly, conservation laws figured prominently in historic physics experiments in the early 1900s that helped form the basis for our modern understanding of matter and radiation. Two examples are the (Ernest) Rutherford scattering experiment, leading to knowledge of the nuclear model of the atom, and the (Arthur Holly) Compton effect which was significant in validating the photonic (or “particle-like”) nature of electromagnetic radiation.
The predicted experimental results for these phenomena could only be calculated by using the conservation of energy and momentum. And of course, these principles also guided the actual behavior of the experimental results, providing a match with the theoretical predictions.
A Remarkable Discovery
In the early 20th century, a remarkable discovery came to light that showed a foundational basis for the conservation laws of physics.
In 1918, the brilliant mathematician Emmy Noether made a groundbreaking discovery that revealed a deep connection between symmetry and conservation.
Fundamental examples of these connections include:
- Spatial translation symmetry: If a physical system is invariant under arbitrary shifts in space then Noether’s theorem tells us that momentum is conserved along physical trajectories in phase space. In other words, momentum is a constant of motion.
- Time translation symmetry: If the laws of physics do not depend on the specific time at which an experiment begins, then there is a corresponding conserved quantity, which is nothing else than energy.
- Rotational symmetry: If the dynamics of a system remain unchanged under continuous rotations, then angular momentum is conserved during its evolution.
Ethan Siegel comments on the depth of intuition and meaning brought to light by Emmy Noether (1882-1935; she is pictured at the top) in her theorem,
Beyond the fact that symmetries exist, there’s an incredible connection between symmetries and conserved quantities, and it’s one of the deepest physical insights to come out of all of physics history.
The Anthropic Design
In our attempt to appreciate the anthropic design involved in the physical conservation laws of the universe, does Noether’s theoretical insight lead to a dismissal of their significance? Not at all. The connection between conservation laws and symmetries merely elevates the mystery to a higher level.
We can now state that without the symmetries present in our universe, its physical properties would not be conducive for life. But the types and prevalence of symmetries in the physical properties of our universe also require a “just right” balance for us to be here. Siegel points out,
The temptation to make nature more symmetric is one we must beware of, as our Universe is fundamentally asymmetric in a number of important fashions.
For example, certain types of particle decay processes exhibit unusual asymmetries, in that,
The “mirror image” version of reality is fundamentally different from the reality that we observe.
Neutrinos are lightweight fundamental particles that move at nearly the speed of light. They possess a property called spin, in that they have angular momentum, somewhat like the Earth’s angular momentum as it spins on its own axis. Here’s the asymmetry, though — every neutrino only moves in the direction its “south pole” is pointing! Physicists call this property “left-handedness.” The anti-neutrino, however, only ever moves in the direction its “north pole” is pointing (right-handedness).
This unique handedness of each type of neutrino is different from all the other fundamental particles of the same broad class as neutrinos (“fermions”), which can exhibit either handedness.
This leads to the question: Where are all the right-handed neutrinos and the left-handed antineutrinos? It remains a mystery…
Matter Over Antimatter
Another example of an essential asymmetry in our universe that’s absolutely necessary for life’s existence is the prevalence of matter over antimatter. In every experiment, when energy converts to matter, the outcome is always a balanced ratio of matter to antimatter particles. Modern cosmology maintains that high energy photons in the early universe, mere fractions of a second after the Big Bang, formed into particle-antiparticle pairs of fundamental particles.
If the ratio of particles to antiparticles in the early universe had been perfectly symmetric, they would have all annihilated each other, leaving us with a universe of energic photons, devoid of matter, and very uncongenial for life! The theoretical explanation for why this didn’t happen is unclear, but the evidence points to a slight asymmetry that favors the production of particle matter versus antiparticle matter, to the tune of one extra particle for every billion antiparticles.
Despite the understanding afforded us in Noether’s theorem of the fundamental importance of symmetries that yield essential conservation laws, the existence of unexpected asymmetries in some physical properties of the universe is also required for life. Perhaps the universe could be described as contrived, quixotic, or inscrutable, or we could say it’s extremely carefully designed to attain the delicate balance that allows for life. In reality, if it looks designed, it is.