How can we know what happened in the past

I am fascinated by some of the search terms that are used to get people clicking on my blog here.  This one really caught my eye.  As I thought about it, I realized that this is critically important.  So here’s the question

How can we visualize events that happened millions and, in many cases, billions of years ago?

There’s a lot of detail here.  And this is a critical exercise.  I often hear from creationists and ID supporters that we can’t know what has happened in the past.  Of course, if we use that logic, then no crime can ever be decided by a judge or jury because it happened in the past.

So how do we know what happened? 

Uniformitarianism

This is the principle that the exact same natural laws operating now have always operated in the exact same way.  This is a pretty big assumption.  But if we don’t have this assumption, then we can’t really ever be confident in anything.  Without this principle, we might wake up tomorrow and find that hydrocarbons don’t burn.  That would be bad.

But how can we know that this is the case?  Is this really an assumption?

No, it’s not.  We can actually see things that happened millions and even billions of years ago and compare them to what’s happening now.  In fact, this point is critical to the book I’m reading, A Universe from Nothing.  We can look at stars.  We have one right next door.  We can see how physics and chemistry operate in this star.  We can measure the type of light absorbed by the hydrogen.  We can see how light bends around it.

We can also see this happening in stars that are millions and billions of light years away.  We see the exact same absorption lines in stars billions of light years away.  We see the exact same gravitational effects in super clusters of galaxies.

We know that this occurred in the past because light travels at a finite speed and that speed is fixed.  There are some notions that the speed of light is variable, but there is nothing that has been shown experimentally… or even (as far as I am aware) that any notions could be tested.  However, there is a significant body of work that supports a constant measure of the speed of light (and the fine structure constant, and a bunch of other fundamental values within the universe).

So, if everything happening 12 billion years ago happened in exactly the same manner that it is happening now, then nothing has changed.  The same physical rules of the universe apply at all times.

That’s good because, now we can use processes like radioactive dating, tree-rings, ice-cores, geologic samples, astronomy, etc to tell us what happened a long time ago.

P.S. I started writing this about a week ago, then work kicked in.  It was intended to be much longer, but my train of thought has been derailed on the tracks of work.  Sorry.  This will probably have to be a multi-part topic

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