there was a singularity, what made it expand
i so confused
No one knows the answer to this question. It is an open area of research. The relatively new field of Quantum Cosmology tries to answer such questions.
Think of the entire age of the universe to-date as a calendar year. So the first day of creation was January 1. It is immediately obvious that expansion did not begin right on January 1st; it actually began two weeks before, during baking and cookie season, and following right through the holidays. January 1st is simply the first day the universe measured itself on the weigh scale in an ultimately doomed attempt to live up to its New Year's Resolution of dropping twenty-five pounds in order to fit in the bikini this summer that it bought last summer that was two sizes too small but was going to diet in-to.
A singularity is a breakdown in a theory. A place where some model blows up and stops being applicable. Typically singularities get fixed by modifying the model---this has happened with other theories in other branches of physics. At present there is no reason to believe that a singularity occurred. As Einstein-Online says, most cosmologists would be quite surprised if there turned out to have been one.
However "what made it expand?" is a very good question. Whatever was there at the start of expansion, why did it begin expanding?
Nick is right! No one knows. There are theories (in the new field of Quantum Cosmology) which give answers. But they have not yet been tested.
Here are the papers in QC written since 2005.
There are 362 papers that appeared in the four years 2006-2009 alone. That is about 90 papers per year.
If you look at the first 50 papers listed, that is, at the most often cited ones, they are almost all using bounce models where there is no singularity but rather there is a prior contraction, and quantum effects kick in at very high density making gravity repel strongly instead of attract. So the whole things begins expanding.
Quantum gravity as these researchers have formulated it, has a natural brief inflation episode.
For a further discussion of how Quantum Cosmology (with the bounce feature) relates to inflation you could look at Ashtekar's recent paper:
So the answer to your question is that nobody knows but they have several interesting ideas, and the field is called QC, and they are working on it pretty hard.
And currently one of the areas of QC getting a lot of attention is how to test the models.
There is an international workshop on that coming up this year in Stockholm.
Here is a sample paper addressing the QC testing problem, if you are curious. It talks about "footprints" of QC to look for in the temperature map of the cosmic microwave background. Observable features of the CMB.
not answer i was hoping for because its a shame we have yet to know why
i will have to look at all of those papers hopefully the vocabulary will not be so difficult for me
excuse my english i learning
And this is one of the more exciting developments in that we are now getting so much data out of cosmological observations that "what happened before the big bang" is something that is becoming an observational question rather than a philosophical one.
The basic idea is that with observations of the cosmic microwave background we are seeing very detailed ripples, and we are getting to the point that people think that they might be able to use details about these sorts of ripples to work out how the process of the big bang worked.
Not really a shame.. All things were unknown to us at some point. It seems like quantum cosmology is a very exciting and expanding area of research. And for the scientist that finally answers that question, almost certainly a nobel prize awaits them. So I look at it that way, that if there are no questions left to answer than we wouldn't need new scientists.
Expansion was a shot in the dark by Alan Guth to address problems like homogenity and thermalization of the universe. It works well and is still widely accepted to this day. It is what is called an effective theory - it appears to work but has no underlying physics that explains why it works.
I think you mean inflation (not expansion).
Expanding universe models were written down by Willem de Sitter in 1917 and by Alex Friedman around 1922.
Simple expansion has the underlying physics of Einstein's 1915 General Relativity.
Alan Guth didn't come along with the scalar-field inflation idea until around 1980.
Bingo. http://en.wikipedia.org/wiki/Inflation_(cosmology)" [Broken]is the simple separation of matter.
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