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11 Cards in this Set

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Olber's paradox

-He questioned why the sky was dark at night




-If the Universe were static, infinite, eternal and uniformly filled with stars the sky would be uniformly bright like the surface of a star.




-its not because the Universe is not infinitely old, or that the look-back time is not greater than the age of the observable Universe

The doppler shift

Hubble's observations have shown that the recession velocity of a galaxy is proportional to its distance

Hubble's Law

-The larger the distance between two galaxies the faster they recede from each other



-Uniform expansion means there's no center to it.

cosmic background radiation (CBR)
-The Big Bang theory predicts that the hot gas left over from the time of creation of the Universe should be observable as a leftover background radiation coming from all directions

-Can be seen in the infared

Big Bang Theory

-The Universe was dominated by radiation over the first million years and matter was opaque as a result.



-After 1 million years the Universe became cool enough for neutral atoms to form. The gas became transparent for radiation. This is called the recombination phase. ~The universe was 3000K at this time



-After recombination, the Universe became matter dominated and first galaxies were formed out of gas condensations

How long it took to make elements after the Big bang

-10^-5 sec after the Big Bang, density was comparable to that of an atomic nucleus and Photons produced particles of matter and antimatter which annihilated and became photons again.



- In the first 4 secs, protons, neutrons and electrons were made



-At the end of 3 mins., H and He were produced



-In 30 min., the Universe expanded and cooled enough, so that all nuclear reactions stopped.

Geometry of space



It is a curved space that is finite but has no bounds.

The evolution of the universe is governed by...

- a struggle between the momentum of expansion and the pull (or push!) of gravity.



-The strength of gravity depends on the density and pressure of the matter in the universe. But the pressure of matter is low so it's fate is really governed by just density.

Big chill/Big freeze

-If the density of the Universe is less than the critical density, it will expand forever. There wouldn't be enough gravitational pull to stop it.



-it is known as the big chill/freeze b/c the Universe will slowly cool as it expands until eventually it is unable to sustain any life.

Big Crunch

-If the density of the Universe is greater than the critical density, then gravity will eventually win and it will collapse back on itself

Dark energy's role in fate of the universe

the Universe is actually accelerating or speeding up,because of the existence this form of matter with a strong negative pressure.This will cause it to expand forever.