Diameter of the Universe: Unknown…

Seeing is believing, my old teacher used to tell me, and that is the base of all modern Science.The problem is, when it comes to the infinitely big, Physics itself prevents us from seeing most of what is. Remains only the observable Universe…

Let’s remember a few fundamentals.

1/ it all physically started at a single point, in a massive explosion: the Big Bang

2/ since then, the Universe has been continually expanding

3/ at a macro scale, the universe is homogenous and uniform (at “micro” scale, of course, there are gas clouds, stars, black holes, etc…)

4/ nothing can go faster than the speed of light

These are well established facts, and seem straight forward, but it has an interesting consequence: we don’t (can’t) know for sure the current size of the Universe!

Let’s take the item (4) – nothing can go faster than the speed of light. Since we estimate the Big Bang to occur some 94 billion years ago, and Light “takes time” to travel distances, what we “know” – or what we can see – is not more than 94 billion light-years away. The light of any object (or event) further did not come to us yet, so we cannot see it.

And then, since the universe is homogeneous, we can see the same way in very directions – the Universe we know is then a bubble… of 94 billion light-years radius! (well, plus 1 light-year every passing year)

That seems big for us, but a mere 2% of the estimated total size (if it is actually finite…)

But that is still not even the condition of the Universe NOW – or at the current time – but merely the condition at that time. The current situation may be very different, but we will know only when light finally reaches to us… in 94 billion years…

So, the further you look, the older the things? Well, older from us, but actually younger in time (whatever relative meaning Einstein put on it)…

It’s like looking at a person at different locations: at the other side of the street – grandpa – at the end of the field – in his 40’s – at the top of the hill – toddler – of the mountains – not even born… So, the further you look, the closer from the origin of time (scientifically speaking) you can look: the Big Bang

So each time you look at something you always have to convert Distance = Time = Age, to know what you are actually looking at.

But as if this was not mind blowing already, due to the expansion of the Universe, things may move from each other, in every direction, and can even have a different sequence from us, now that we see their lights, than billions of years ago.

We are back to Socrates: “The only true wisdom is knowing you know nothing”

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