The best way to understand something–such as life–is to build it yourself. That’s why, determined to understand the way groups move, a team of New York University physicists set out to create particles that could imitate the way flocks of birds, schools of fish and even colonies of bacteria organize and move together.
What they ended up with, described in Science magazine yesterday, were two-dimensional “living crystals” that form, break, explode and re-form themselves elsewhere.
The researchers developed self-propelled particles that would turn on in response to blue light. When the light is on, the randomly swimming particles collide and cluster. A chemical reaction set off by the light causes the particles to crystalize. When the light turns off, the particles stop and split apart.
The crystals have metabolism and mobility, two of the general requirements for classifying something as life, according to Paul Chaikin, one of the paper’s authors, but they lack the ability to reproduce. By one count, there are a total of seven requirements that an organism should exhibit to be considered life.
“Here we show that with a simple, synthetic active system, we can reproduce some features of living systems,” lead author Jeremie Palacci told Wired. “I do not think this makes our systems alive, but it stresses the fact that the limit between the two is somewhat arbitrary.”
Palacci and Chaikin are now working on a particle that has a metabolism and can self-replicate, but lacks mobility. …
… Scientific evidence suggests that life began on Earth approximately 3.5 billion years ago. The mechanism by which life emerged is unknown although many hypotheses have been formulated. Since then, life has evolved into a wide variety of forms, which biologists have classified into a hierarchy of taxa. Life can survive and thrive in a wide range of conditions. The meaning of life—its significance, origin, purpose, and ultimate fate—is a central concept and question in philosophy and religion. Both philosophy and religion have offered interpretations as to how life relates to existence and consciousness, and on related issues such as life stance, purpose, conception of a god or gods, a soul or an afterlife. Different cultures throughout history have had widely varying approaches to these issues.
Though the existence of life is only confirmed on Earth, many scientists believe extraterrestrial life is not only plausible, but probable. Other planets and moons in the Solar System have been examined for evidence of having once supported simple life, and projects such as SETI have attempted to detect transmissions from possible alien civilizations. According to the panspermia hypothesis, life on Earth may have originated from meteorites that spread organic molecules or simple life that first evolved elsewhere. …
- Homeostasis: Regulation of the internal environment to maintain a constant state; for example, electrolyte concentration or sweating to reduce temperature.
- Organization: Being structurally composed of one or more cells — the basic units of life.
- Metabolism: Transformation of energy by converting chemicals and energy into cellular components (anabolism) and decomposing organic matter (catabolism). Living things require energy to maintain internal organization (homeostasis) and to produce the other phenomena associated with life.
- Growth: Maintenance of a higher rate of anabolism than catabolism. A growing organism increases in size in all of its parts, rather than simply accumulating matter.
- Adaptation: The ability to change over time in response to the environment. This ability is fundamental to the process of evolution and is determined by the organism’s heredity, diet, and external factors.
- Response to stimuli: A response can take many forms, from the contraction of a unicellular organism to external chemicals, to complex reactions involving all the senses of multicellular organisms. A response is often expressed by motion; for example, the leaves of a plant turning toward the sun (phototropism), and chemotaxis.
- Reproduction: The ability to produce new individual organisms, either asexually from a single parent organism, or sexually from two parent organisms.