My daughter wants to know....

[Alex K]

She's 14 and in advanced and accelerated classes in 8th grade, with one class being Advanced honors algebra One.

And she wanted to clarify that using logic and reason does make sense.

And she's still going on about explosions not creating life. She gave an example of "if this house exploded, would it create life? The answer is no, it wouldn't."

I can't win.

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Ultimately, we don't know where the energy of the big bang came from or if it even had to come from anywhere. But - it wasn't an explosion, it was more like akin to a vessel of hot water expanding and cooling, and in the course of that, the water condenses and complexice crystals and snow flakes form.  The cooling atoms fused together to form more and more complex matter.

I read this to her. Her question is:

How do we have any proof that this happened?

- We can observe the light that comes from distant nebulae and galaxies and it tells us which kinds of chemical elements they are made of. You can compare that to the numbers you get from the assumption that they were formed in a super hot universe that expanded and cooled quickly, and what you get is that the kinds of elements we observe in space follow the expected pattern - lots and lots of hydrogen which is the simplest, less Helium and Helium3, less Lithium. The pattern matches just to what you'd expect from basic nuclear physics if everything had been made in the crucible of a hot expanding universe. Only with Lithium the numbers are a bit high, though exactly in the right ball park, but that can be accounted for by some physical process. All other elements are super rare and only found to be created by stars - why would we only observe only those chemical elements in space which can be made in a hot big bang, and in the right proportions, and basically nothing else?

- The cosmic microwave radiation that we receive from all directions has the most perfect spectral shape of anything you'd find in nature, and it cannot originate from some recent astrophysical process due to its uniformity and spectrum. It does however perfectly match with what you'd expect if the universe had been a homogeneous hot soup that suddenly cooled below 3000 centigrade 14 billion years ago. The small fluctuations we observe in this microwave radiation can be translated to differences in density of this hot soup 14 billion years ago, and they match neatly with the structures we now observe in how galaxies are distributed in space - so you get a coherent picture how these differences in density would.develop to.amass galaxies and clusters of them.

to be continued...

Edit: And of course the most obvious evidence - the universe is of course expanding!