Main Question or Discussion Point
I'm writing an essay for a contest and I'm about half way done. I want to know how accurate my information is. It should be self explanatory as we are supposed to write it for the general non-physics person who might have no clue about the subject. The asterisks are places where I'll have to insert a footnote to briefly explain the concept, similarly to the way I explained the Doppler effect.
Thanks for reading.
After this I will start talking about dark matter/energy.The accelerating expansion of the universe
Until the last century it was widely believed that the universe was fixed and unchanging. Even Einstein himself accepted the favored model of a static universe at some point. Forced to manipulate his equations to account for what he assumed to be the unchanging radius of the universe, Einstein became furious with his erratic calculations; little did he know that his own theory of relativity had predicted one of the greatest discoveries of cosmology decades before it was confirmed.
At one time or another, you might have heard that the universe is expanding. Indeed in 1929 Edwin Hubble, by studying distant galaxies, noted that the light omitted by the vast majority of them tended to shift towards the red end of the light spectrum. Because of the Doppler effect this indicates that the source of light is moving away from the observer. (It is also because of this Doppler effect that a police car's siren sounds higher in pitch as it approaches you, and lower in pitch as it drives away.) In other words, the clusters of galaxies he observed were not simply hovering at some fixed point in space, but rather flying towards the opposite direction. Although not the first to make these observations, Hubble is credited with analyzing the motion of galaxies in every direction relative to the Earth and arriving at the undeniable conclusion that everything is moving away from us. Think of an empty balloon and on it's surface imagine dots representing some galaxies; as you fill up the balloon and watch it expand, the space between the dots grow uniformly larger and larger, regardless of which dot you chose as your point of view.* As often is the case in science, this discovery brought along more questions than answers.
So it was agreed upon that the universe is evidently expanding, but where to? In recent years, scientists had entertained the idea of a cyclic universe. Such universe's mass density* would be just enough so that its own gravity would eventually halt the expansion and cause all matter to collapse back into itself at one single infinitely dense pinpoint, called a singularity. Appropriately named, this hypothetical Big Crunch is imagined to be able to spark another Big Bang, and the cycle of creation and destruction would continue indefinitely. In his most recent publication, The Grand Design, professor and theoretical physicist Stephen Hawking argues that, because of the laws of gravity, the universe can and does create and recreate itself in a never ending cycle. This is an attractive and even comforting scenario: it pushes back the need to complete the puzzle with a beginning and an end, the before and the after. And for the hopeful, the possibility of endless new universes is a charming thought.
Much to Hawking's dismay, however, the 2011 Nobel prize winners, through observations of distant supernovae at the edge of the observable universe some 13 billion light years away, have gathered information that seem to contradict the popular idea of a self-birthing universe: instead of slowing down as was imagined, the galaxies are actually accelerating away at ever increasing rates.
The evidence presented by them seem to point at another somewhat bleaker fate of our universe – the Big Freeze. As the name suggests, if nothing stops the expansion, eventually all the stars will have exhausted all the finite amount of fuel available and temperatures would no longer be adequate to sustain work and motion. But there's plenty of time for scientists to change their minds – according to this model, the last remnants of the universe are not due to evaporate until another 10100 years (that is the number 1 followed by 100 zeros). Worse things could happen to you before then.
Thanks for reading.