1.2 – The Universe had a Beginning
I. The Development of the Universe
A. Two Competing theories
1) Steady State Theory
- Up until the 1920s, Einstein and most other physicists believed that the universe had always
existed in a “steady state” – that the universe has always been here, neither expanding nor
contracting. It looks basically the same going backward in time and forward in time.
2) Expanding Universe Theory
- The evidence for an expanding universe was first observed by Edwin Hubble, Albert
Einstein, and Georges Lemaître, a Belgian physics professor, astronomer and Catholic priest.
- In 1927, Lemaître showed Einstein a mathematical solution to the field equations in
Einstein’s theory of General Relativity that described not a static universe, but an expanding
universe. Lemaître called his theory the “hypothesis of the primeval atom”
- Einstein was initially unwilling to accept Lemaître’s theory, because it challenged all of his assumptions about
how the universe worked. He agreed that the math was correct, but didn’t agree with the conclusion & wanted to
see observational evidence supporting the theory that the universe was actually expanding, not in a steady-state.
B. Observations
1) Motion of Distant Galaxies
- In 1929, Edwin Hubble concluded almost a decade of observations of distant galaxies.
- Observations by Edwin Hubble (and others) of light from distant galaxies showed that
- Light from distant galaxies is “red-shifted”  They are moving away from us.
- Galaxies that are further away are moving away faster!
Ex. Measuring motion of sound & light sources
- We can detect the motion of a sound source (e.g. a horn) using the Doppler Effect.
It will have a higher pitch when moving towards us
It will have a lower pitch when moving away from us
(waves bunch together)
(waves stretched out)
- We can detect the motion of a light source (e.g. a galaxy) by measuring the Red Shift.
Light becomes higher frequency when moving towards us (blue shift)
Light becomes lower frequency when moving away from us (red shift)
- Hubble discovered that distant galaxies are all moving away from our galaxy. This confirmed Lemaître’s theory.
2) Hubble’s Law (1929)
- The greater the distance between any two galaxies, the greater their relative speed of
separation.
- In 1931, Einstein paid a visit to Hubble at Mount Wilson Observatory in Los Angeles county
in California, Hubble showed Albert Einstein observations that supported the expanding
universe model, convincing him that the universe is expanding and thus had a beginning.
- Einstein “renounced his own static cosmology and endorsed the expanding universe model.
His support was enough for The New York Times to embrace the mavericks, running an
article with the headline ‘Lemaître Suggests One, Single, Great Atom, Embracing All
Energy, Started The Universe.’” (http://www.nytimes.com/2005/01/02/opinion/02singh.html?_r=0)
“This is the most beautiful and satisfactory explanation of creation to which I have ever
listened.” (Albert Einstein in response to Lemaître’s theory at a series of seminars in California in January
1933, as quoted in http://catholiceducation.org/articles/science/sc0022.html)
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C. Big Bang Theory
Ex. Balloon Analogy
- Let’s imagine a ballon. Pretend that the surface of the balloon is like space in the universe back in time, when
the universe was smaller. We’ll draw some dots on the surface of the balloon to represent different galaxies in
the universe. Now watch the dots on the balloon as we blow the balloon up. The dots all move apart from each
other. That’s exactly what Hubble showed Einstein: all distant galaxies are moving away from us, like the dots
on the expanding balloon.
- Now imagine reversing time to look into the past. What would we see? All the dots would get closer and closer
to each other. And it would end just like the deflated balloon, with everything contracting into an infinitely
dense and hot beginning. We can only go back so far, it hits a wall, a beginning that physicists call a
“singularity” where all the laws of physics break down as things get infinitely dense and hot and close together.
- This shows that at the beginning of the Universe everything was together.
And that the Universe likely had a beginning.
D. You can’t get something from Nothing
- If the universe had a beginning, then once upon a time it wasn’t there, not even the laws of
physics. Essentially there was nothing and the universe
- If there is nothing, truly nothing, no time, no vacuum, no space and no energy, something can’t
just appear from it. Something else must already be there to create it or it couldn’t exist.
- Even the vacuum of space is still something. There’s still time in a vacuum, the quantum field
exists. So, the vacuum is still something. “Nothing” here means truly nothing, no time, no
vacuum, no space and no energy.
- “If the universe had a beginning, then something else had to start it. The universe started, and we
know that no thing can come from true nothing. If it started, something started it.
III. Multiverses & Bouncing Universes
Most scientists agree that the Big Bang is the most likely explanation for how the universe began, that
the Big Bang was the beginning of our universe. But some theorize that there could be other kinds of
universes: oscillating universes, or even multiverses.
A. Oscillating Universe
1) In an oscillating or bouncing universe the expansion of the universe slows down and reverses.
This eventually leads to a Big Crunch and then another Big Bang, repeating over and over.
2) But this theory has several fatal problems:
- Every bounce there would be more entropy (disorder) in the universe, so if the universe has
been around for an infinite number of bounces, there would be no stars, no life.
- We have evidence that the expansion of the universe is speeding up, not slowing down!
This means that we will not end up with a Big Crunch, leading to another Big Bang.
B. Multiverse
- Problem: A multiverse that is expandingwould require an ultimate beginning based on the BordeVilenkin-Guth Theorem (BVG Theorem). According to the BVG theorem, a multiverse
connected to our universe would ultimately need a beginning
- The BVG Theorem demonstrated that in a universe that has a positive expansion, “inflation alone is not
sufficient to provide a complete description of the Universe, and some new physics is necessary in order to
determine the correct conditions at the boundary.” (Arvind Borde, Alan H. Guth, Alexander Vilenkin,
“Inflationary spacetimes are not past-complete,” v2, 2003, http://arxiv.org/abs/gr-qc/0110012)
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