Part I: The Big Bang Theory
What the Standard Big Bang Theory does Not Predict or Explain
In the previous post I outlined the basics of the big bang theory. As things stand, there remain a few issues which have not been addressed, and are taken as principles or ‘as given’. There are still many major mysteries of the state and origin of the universe, however for the purpose of this series, I will focus on three.
Paradox 1: the homogeneity and isotropy of the universe
The dictionary defines homogeneity and isotropy as follows:
Homogeneous: Of the same kind of nature; consisting of similar parts, or of elements of the like nature
Isotropic: Having the same properties in all directions.
And these are the properties that the universe seem to exhibit. Namely, regardless of which direction you observe the properties of the universe, it appears the same. The standard Big Bang theory as described in the previous part offers no explanation to this phenomena.
Paradox 2: the age of the universe
To get an estimate on how old the universe is, cosmologists use a combination of astronomical observations and theory. One way of doing this is by observing distant clusters of galaxies, then plugging in the theory about how these clusters evolve, one then gets an estimate on the age of universe. The estimate is repeated with other structures, so the observers seems pretty sure of the estimate 13.7 billion years.
So far things are looking pretty consistent, we can estimate the age of the universe using theories of how galaxies and stars evolve, and also from the expansion of the universe. Since, if our understanding of the Big Bang and the expansion of the universe is correct we should be able to figure how long it has been doing so.
We hit a pretty big snag though when asking the question “how big was the universe when light ceased to be trapped by electrons?”. The answer naturally is “much smaller than it is today”, which is fine, except for one thing, it was not small enough to explain the why the universe was homogeneous and isotropic.
I’ll explain, remember that the universe is expanding, so when we look up into the night sky, two points in the sky that are today very far apart, would have been very close together in the past. Remember that the universe is homogeneous, now I am going to try an analogy (and am rather naff at them) take a water tank with a divider down the middle, pour water into one side and sit back. The system is now in-homogeneous, one side has water the other does not. How do you get water from one side to the other (each side has an individual lid and they are sealed), obviously remove the divider, now water flows into the second chamber and we have a homogeneous system! What did you do? You allowed the two chambers to communicate (exchange water and air), the divder was blocking information (water and air).
In the universe, distance is the barrier to exchanging information (in this case light), since light can only travel a certain distance in a certain time. So back to our problem, about 310,000 years after the big bang, the universe was quite big so a point in that universe could not have communicated with all other points. On top of that, rewinding 300,000 years, using known theories, the universe still wasn’t small enough, and a point still could not communicate with all the points in the universe!
So the question is: how did the universe end up homogeneous if one half of it didnt know what the other was planning? Coincidence?
Paradox 3: the origin of large scale structure (aka galaxies and galaxy clusters)
Phew, that last effect I find the hardest to explain, this one is relatively simpler (she says). In the Big Bang theory one needs an original ‘mass’ in the various places in the universe where we see galaxies and stuff today, this local fluctuation in the uniform mass of the universe will then attract more matter towards it and grow and grow till the galaxies and stuff appear. The Big Bang theory just ‘assumes’ it exists.
Told you it was simple 🙂
Now what we need is an explanation, a phenomena, an IDEA! We want this idea to explain how the universe is so uniform, why it is uniform, and how come we end up with these ‘mass fluctuation’! An we do, it’s called ‘Inflation’…
Part III: a neat solution, Inflation