01:750:109 Chapter Notes - Chapter 13.1: Superstring Theory, Strong Interaction, Planck Units
The Big Bang Theory
●The scientific theory that describes what the universe was like early in time is called the Big
Bang theory
○Idea that all we see today, from Earth to the cosmic horizon, began as an incredibly hot
and dense collection of matter and radiation
What were conditions like in the early universe?
●Observations demonstrate that the universe is expanding and cooling with time, implying that it
must have been hotter and denser in the past
Particle Creation and Annihilation
●The universe was so hot during the first few seconds after the Big Bang that photons could
transform themselves into matter, and vice versa, in accordance w Einstein's formula E=mc^2
●Reactions that create and destroy matter are more relatively rare in the universe but physicists
can reproduce many such reactions w particle accelerators such as the Large Hadron Collider
○Electron-antielectron pair
■When two photons collide with a total energy greater than twice the
mass-energy of an electron (the electron's mass times c^2), they can create two
brand-new particles: a neg charged electron and its pos charged twin, the
antielectron (aka a positron
)
Fundamental Forces
●Everything that happens in the universe is governed by 4 distinct forces:
○Gravity
■Glue that holds planets, stars, and galaxies together
○Electromagnetic force
■Depends on the electrical charge of a particle and not its mass is much stronger
than gravity
■Dominant force btwn particles in atoms and molecules, responsible for all
chemical and biological reactions
■Lose out to gravity on large scales
○Strong force
■Binds atomic nuclei together
○Weak force
■Crucial role in nuclear reactions such as fusion and fission
■Only force besides gravity that affects weakly interacting particles such as
neutrinos
●Strong and weak force operate only over extremely short distances making them imp within
atomic nuclei but not on large scales
Document Summary
The scientific theory that describes what the universe was like early in time is called the big. Idea that all we see today, from earth to the cosmic horizon, began as an incredibly hot and dense collection of matter and radiation. Observations demonstrate that the universe is expanding and cooling with time, implying that it must have been hotter and denser in the past. The universe was so hot during the first few seconds after the big bang that photons could transform themselves into matter, and vice versa, in accordance w einstein"s formula e=mc^2. Reactions that create and destroy matter are more relatively rare in the universe but physicists can reproduce many such reactions w particle accelerators such as the large hadron collider. Everything that happens in the universe is governed by 4 distinct forces: Glue that holds planets, stars, and galaxies together. Depends on the electrical charge of a particle and not its mass is much stronger than gravity.
