Anthropic Principle:
The idea that the fundamental constants of physics and chemistry are just right (or “fine-tuned”) to allow the universe and life as we know it to exist, and indeed that the universe is only as it is because we are here to observe it. Thus, we find ourselves in the kind of universe, and on the kind of planet, where conditions are ripe for our form of life.
Antimatter:
A large accumulation of antiparticles - antiprotons, antineutronsand positrons (antielectrons) - which have opposite properties to normal particles (e.g. electrical charge), and which can come together to make antiatoms. When matter and antimatter meet, they self-destruct in a burst of high-energy photons or gamma rays. The laws of physics seem to predict a pretty much 50/50 mix of matter and antimatter, despite the observable universeapparently consisting almost entirely of matter, known as the “baryon asymmetry problem”.
Atom:
The basic building block of all normal matter, consisting of anucleus (which is itself composed of positively-charged protonsand zero-charged neutrons) orbited by a cloud of negatively-charged electrons, so that the positive charge is exactly balanced by the negative charge and the atom as a whole is electrically neutral. Atoms range from about 32 to about 225 picometres in size (a picometre is a trillionth of a metre). A typical human hair is about 1 million carbon atoms in width.
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