THE UNIVERSE

• Universe the sum of all space, matter, and energy that exist, that have existed in the past, and that will exist in the future.

• You are part of the universe, as is Earth and everything on it.
• We see the universe now as it was in the past.

• It takes time for light to travel in space.

• The farther away an object is, the older the light that we receive from that object.

• Most of the universe is empty space

• Space is a vacuum with no air and no air pressure.
• The universe is expanding.

• Observations of spectral lines from other galaxies indicated that they were moving away from us

• Red shift an apparent shift toward longer wavelengths of light caused when a luminous object moves away from the observer
• Blue shift an apparent shift toward shorter wavelengths of light caused when a luminous object moves toward the observer
• Expansion implies that the universe was once smaller.

• Long ago, the entire universe might have been contained in an extremely small space.

• All of the matter in the universe appears to expand rapidly outward, like a gigantic explosion

• Scientists call this hypothetical explosion the big bang.
• Did the universe start with a big bang?

• Scientists have proposed several different theories to explain the expansion of the universe.

• The most complete and widely accepted theory is the big bang theory.

• Big bang theory the theory that all matter and energy in the universe was compressed into an extremely small volume that 10 to 20 billion years ago exploded and began expanding in all directions
• Cosmic background radiation supports the big bang theory.

• Cosmic background radiation is a steady but very dim signal from all over the sky in the form of radiation at microwave wavelengths.

• Many scientists believe that the microwaves are dim remnants of the radiation produced during the big bang.
• Radiation dominated the early universe.

• According to the big bang theory, expansion cooled the universe enough for matter such as protons, neutrons, and electrons to form.

• Processes in stars lead to bigger atoms.

• Once hydrogen atoms formed, stars and galaxies began to form, too.
• All elements other than hydrogen and helium form in stars.
• The future of the universe is uncertain.

• The universe is expanding, but the combined gravity of all the mass in the universe is also pulling the universe inward.
• The competition between these forces leaves three possibilities:

1. The universe will keep expanding forever

2. The expansion of the universe will gradually slow down, and the universe will approach a limit in size.

3. The universe will stop expanding and start to fall back in on itself

• The fate of the universe depends on mass.

• If there is not enough mass, the gravitational pull will be too small to stop the expansion.
• If there is just the right amount of mass, the expansion will continually slow down, but will never stop completely.
• If there is too much mass, gravity will eventually overcome expansion and the universe will contract.
• New technology helps scientists test theories.

• Powerful telescopes and other sensitive equipment help scientists study the universe.

• Scientists make observations to test theories and develop new explanations.
• There is a debate about dark matter.

• There is more matter in the universe than what is visible.

• Scientists call this dark matter.

• Dark matter may be planets, black holes, or brown dwarfs (starlike objects that lack enough mass to begin fusion.)
• Scientists use mathematics to build better models.

• Theories can be expressed in mathematical form.

• Mathematical models can be used to help test theories that are not easily observed.