Photosynthesis Reveals Quantum Design
Imagine riding a “bicycle” with pedals attached to sled runner in place of wheels. It just wouldn’t work! Wheels allow even the most rudimentary bicycle to move across the ground in spite of all the other inefficiencies, like friction. In a system that provides the bulk of the energy used by life, biological organisms exhibit a design far more elegant than the wheel. To achieve a global diversity of life-forms, poor wheel design can be tolerated; but a non-fine-tuned photosynthetic process cannot.
All scientists agree on one essential characteristic of life; namely, that it must harvest energy from its environment to perform biological functions. The Sun provides the ultimate energy source for virtually all multicellular and most single-celled organisms. Photosynthetic organisms “absorb” the light energy from the Sun and convert it into chemical energy stored in carbohydrates. These carbohydrates are utilized by the photosynthetic organisms or by other life that eats the photosynthetic organisms.
Overall, photosynthesis is an “inefficient” process. Typical plants convert one to four percent of the incident sunlight into stored carbohydrates (the best crop, sugar cane, reaches seven to eight percent efficiency). However, one key step of photosynthesis operates so efficiently, it makes the process work despite limitations.
As a photon (the smallest unit of light) from the Sun interacts with the light-harvesting proteins in a photosynthetic organism’s cells, an electron absorbs the photon’s energy which then frees the electron to move around the cell. This electron must move to a reaction center and deposit the energy for use in making the carbohydrate before the environment within the cell drains the energy. If the electron moved through the cell according to the rules of classical physics, a significant fraction of its energy might be lost before conversion. However, the latest research reveals that electron motions exhibit remarkable quantum properties that transport the energy from the light-harvesting proteins to the reaction centers with extraordinary efficiency.
According to classical physics, objects follow welldefined trajectories that are precisely specified at all times. On the other hand, quantum physics allows a particle to be in a combination of positions at any given time (know as a superposition of states) and to follow simultaneously multiple paths to the same
Two different teams of scientists have documented how these bizarre quantum physics effects play a critical role in moving the light energy through the cell. One team studied marine algae and found evidence that the electronic energy is coherently shared by regions of the proteins (those involved in photosynthesis) separated by a few billionths of a meter.1 While a small distance in everyday experience, the sharing clearly indicates the presence of quantum processes. This quantum sharing means that the light energy absorbed in one location can be chemically harvested in another location with better than 95 percent efficiency.
The other team ran detailed computer simulations of the molecular components involved in harvesting the sunlight. The simulations revealed coherent quantum correlations similar to those found in the marine algae.2
Scientists studying these quantum effects typically have to look at simple systems (only a few particles)
cooled to low temperatures (a few degrees above absolute zero). Yet the two discoveries confirm the operation of these quantum effects in large, chemically complex proteins at much higher temperatures.
These findings show design in two different ways. First, if the light-harvesting machinery in the cells did not operate with such high efficiency, the entire photosynthetic process would likely grind to a halt. Such a stoppage would severely curtail Earth’s ability to support a teeming, diverse biosphere. While certain organisms derive energy from thermal processes in Earth’s interior, this heat reservoir contains much less usable energy than the continual bath of energy received from the Sun.
Second, our study of how biological organisms utilize quantum processes to convert light into energy could lead to better human-made machines for the same purpose. For example, scientists and engineers could utilize this knowledge to build faster and more powerful computers.
Without the highly efficient transport of converted light energy, the prime energy supply of life on Earth disappears. By understanding how this transport works, scientists gain inspiration to build better devices than before. The quest to understand photosynthesis has buttressed two legs of the cumulative case for God’s design of Earth and the life it contains.
- Elisabetta Collini et al., “Coherently Wired Light-harvesting in Photosynthetic Marine Algae at Ambient Temperature,” Nature 463 (February 4, 2010): 644–47.
- Darius Abramavicius and Shaul Mukamel, “Quantum Oscillatory Exciton Migration in Photosynthetic Reaction Centers,” Journal of Chemical Physics 133 (August 14, 2010): 064510.