Can you ever prove that something never happens? Sometimes. Pretty much.

I often like to say on this blog, and elsewhere, “Nothing is absolutely certain.” That’s why science, our best means of understanding reality, is never 100% certain about anything.

That remaining bit of uncertainty, which could be as small as .0001%, or even less, allows for the possibility of error in any and all scientific theories. Which permits science to progress by replacing old flawed knowledge with new less-flawed knowledge.

Since nothing is absolutely certain, obviously this applies to medical knowledge. Today I read a Reuters story in our local newspaper, “CDC site adopts anti-vaccine views.” Here’s a PDF file of the story if that link doesn’t work for you.
US CDC adopts Kennedy’s anti-vaccine views on recast website | Reuters

Some excerpts show the philosophical aspect of this issue.

The U.S. Centers for Disease Control and Prevention recast the vaccine safety section of its website on Wednesday to align with the view of Health Secretary Robert F. Kennedy Jr. that childhood vaccines cause autism, countering decades of science showing them to be safe.

The U.S. public health agency’s website was changed to say, “The claim ‘vaccines do not cause autism’ is not an evidence-based claim because studies have not ruled out the possibility that infant vaccines cause autism.”

…The CDC’s website previously said “studies have shown there is no link between receiving vaccines and developing autism spectrum disorder.”

The World Health Organization and other health agencies around the world have repeatedly said evidence shows vaccines do not cause autism and referred back to earlier statements when asked about the CDC website change on Thursday.

…Scientists took issue with statements on the website that studies have not ruled out the possibility that infant vaccines cause autism, arguing that it is “exploiting a quirk of logic.”

“You can’t prove something never happens,” Jake Scott, a professor at Stanford Medical School, wrote on Substack. “Scientists can’t prove vaccines never cause autism because proving a universal negative is logically impossible.”

I wasn’t familiar with the term “universal negative,” so I Googled can you ever prove a universal negative? The AI overview began with a summary statement:

Yes, you can prove a universal negative by demonstrating a logical contradiction or by limiting the scope to a well-defined and exhaustively searchable area. For example, proving there are no “married bachelors” is a universal negative, as the concept is self-contradictory. However, proving that something does not exist over an entire, undefined universe is often impossible. 

So Scott seems partly right and partly wrong. Looking at one of Google’s top search results, “Of Course You Can Prove a Negative,” revealed two things. One, I’m not really interested in abstruse academic philosophical arguments. Two, the author of the essay, Ben Burgis, seems to agree with the Google AI summary, though I didn’t read the essay closely enough to be sure of this.

In short, whether a negative statement like “vaccines don’t cause autism” can be proven depends on various factors, including how certain you want to be that the negative statement is true. As I thought about this in a much less philosophical fashion, I came up with these ideas.

The AI summary said, “proving that something does not exist over an entire, undefined universe is often impossible.” Our universe is the most universal thing there is. So this helps explain why the religious claim, God created the universe, is so difficult, if not impossible, to disprove by claiming, God did not create the universe.

How can you prove that negative statement? a religious believer will ask. The way I see it, no one can supply that proof. My common sense reason is that so far as we know, there has only been one creation of our universe. Religions say God is responsible for that creation. Scientists say it was the big bang. But they don’t know what caused the big bang, so that leaves open the possibility of God being the cause.

Maybe this is what Google AI meant by an “undefined” universe of something, in this case the universe itself. It is undefined because what, if anything, came before the creation of the universe currently is an unanswerable question,, and may always be unanswerable — in part because science says time came into being at the moment of the big bang along with space, so “what came before” is a question wrapped in an enigma.

The more instances we have of something happening, the more likely we can assign a cause to it. A one-time universe creation doesn’t allow for this. However, cases of autism are continually being created. That allows medical scientists to study the possible causes of autism through sophisticated research buttressed by solid statistical methods.

This enabled Peter Hotez, M.D., a doctor I follow on X, to write a book called Vaccines Did Not Cause Rachel’s Autism: My Journey as a Vaccine Scientist, Pediatrician, and Autism Dad. This is the Amazon description:

This fits with everything I’ve heard and read about whether vaccines cause autism. They don’t. That’s a conspiracy theory, not reality. So while nothing is absolutely certain, it is hugely more likely that vaccines don’t cause autism than that they do. Negative assertions can indeed be proven. Just not with 100% certainty.

By the way, I’m virtually completely certain that God didn’t create the universe. There’s no way I can prove this. It just makes much more sense to me than the theistic belief that God did create the universe — which also can’t be proven and makes much less sense.