Cosmology is the study of the structure and evolution of the universe.

In this section, we'll study the size of space, going out to the most distant

objects astronomers can measure with the largest telescopes.

With large telescopes, we look out in space and

also back in time because light does not travel with infinite speed.

300,000 kilometers per second means that the nearest galaxies

are seen as they were a few million years ago.

The most distant galaxies are seen as they were billions of years ago.

We've managed with the largest telescopes to look back within 5%

of the age of the universe now measured to be 13.7 billion years.

The contents of the universe are still enigmatic.

Cuz 95% of the universe is dark energy and

dark matter, both still poorly understood in a physical sense.

The rest of the matter, normal stars and normal galaxies is 5%.

Cosmology is based on the Big Bang model.

The idea that the universe had a hot dense beginning.

The Big Bang model is well supported by a web of evidence, primarily the expansion

of the universe observed through the recession velocity of galaxies.

The microwaves left over from creation which is an imprint of the radiation left

over in the universe seen when it was only 400,000 years old.

Also, we can only explain the large amount of helium in the universe from

nucleus synthesis occurring in the first three minutes when the universe itself was

as hot as the center of a star.

Finally, we have good evidence from large telescopes that the universe was not

always the same.

Galaxies were smaller and bluer in the past, and have been assembled from smaller

pieces and we can observe this process occurring over billions of years.

The critical piece of evidence supporting the Big Bang is the microwave background.

Now observed in exquisite detail with the WMAP satellite.

More speculative additions to the Big Bang model such as the inflation scenario

are on the edge of being tested by microwave observations.

This would take us back to the first time fractions of a second after the Big Bang.

Current ideas of the future of the universe are based on the omnipresence

of dark energy causing an accelerated expansion.

In all likelihood, the universe will continue to grow larger and

more diffuse, forever.

At the frontiers of the Big Bang theory is the idea of the multiverse.

It's a conventional part of the Big Bang theory that physical space, all there is,

is larger than the observable space we can see with our telescopes.

But the Big Bang theory also involves the idea of quantum genesis or

perhaps there were other parallel space times, unobservable by us, but

exist contemporaneously with our universe.

This speculative idea may be on the edge of being tested by future observations.

The subject of cosmology addresses the biggest questions there are in astronomy.

Why are we here, how did we get here, and where did it all come from?

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Cosmology introduction video