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Wednesday 18 January 2017

Observable Universe - two Titanics

We are fascinated at the vastness of the observable universe. If we wish to apply a model of the universe using smaller entities from our regular life, it can give us a simpler perspective to the size of the cosmos we perceive.

Let us take our sun and equate it to the nucleus of a Hydrogen atom - yes, a proton. If we take the diameter of the sun to be the diameter of the nucleus of the atom, then the electron orbiting the sun is actually at 20 times the distance of Pluto! Rather, Pluto is orbiting the nucleus at 1/20th of the distance of the first electron at the highest energy level (1s orbital). Earth is much closer - just 1/1000th of the distance the electron would be held at!

Now, how does the currently perceivable limits of the universe scale when the sun is the size of the proton? With simple, back of the envelope calculations, we can find that the approximate size that humans can observe with current instruments is about twice the length of the Titanic. Yes, that is about it. Approximately 535 metres in each direction - so the entire observable universe from end-to-end would be a bit more than a kilometer.

Where do we fit in, in this model? We are obviously the size of a minute dot in this Hydrogen atom. Each person would be the size of a dot 3 billionths of the size of that nucleus, orbiting at a distance of 215 times the size of the nucleus. The earth is approx 1/100th the size of this nucleus (approximately 109 per Wikipedia article on Sun).

What is the size of the Milky Way in that case? The milky way will fit into a small ball-bearing - yes, approximately 2 mm diameter on the elongated side of the spiral galaxy. That is, it is a spiral between 1.1mm - 2mm in size.

That is all? That is it? Yes, that is the limits of our abilities, science and scientific instruments we have constructed till date.

Here is a tid-bit: How many molecules of gaseous Hydrogen will fit into that Milky way galaxy in this comparison? If we would like to compare the number of hydrogen atoms in 1.1mm to 2mm size Milky way, with the number of stars that are estimated to exist in this galaxy, we have about 250,000 hydrogen atoms for each star in the galaxy. This shows how sparsely Milky way is populated by stars, compared to standard 1 atomospheric pressure Hydrogen atoms (solar systems) in similar scale.

Open question that we will discuss later: Is there a possibility that the universe is much larger? Yes, it is very much possible. One has to read up on Cosmic microwave radiation to look for one example of unexplained uniformity from currently observed lumped galaxies and vast empty space.

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