Today is #PhilosophyFriday !

Today I want to talk about a very meta question:

How do you know that what you know is true?

We all have some intuitive idea of the difference between opinions and facts.

We know there are some things we believe in, but others might disagree, and still be right.

And then there are some things that are simply impossible to object to.

These last, we call them "facts", objective statements about the world that are simply, undeniably, true.

Or are they? How can we be sure, like, sure-sure? And would we be able to recognize if they weren't?

Let say I want to convince you that some idea I have about reality is true. Let's call that idea a "hypothesis".

For example: "there is an attraction force between Earth and everything else".

How can I convince you?

A possible way is trying to make some predictions from that hypothesis, and see if those predictions hold.

For example, if such a force exists, then I can lift a small rock with my hand, let it loose, and it should fall downwards, right?

So we make the experiment, and indeed, the rock fell! Is that proof that my hypothesis is true?

Well, it could be, but there are lots of other explanations that might produce the same evidence.

For example, rocks, in particular, could be attracted to Earth, not everything. So, in order to convince you I would have to drop *everything* and see that it falls? You see the problem with that...

A sufficiently complex hypothesis can never be fully proven by evidence.

Now, let's suppose I make a prediction, and it fails.

For example: If the Earth is flat, and I shoot a sufficiently powerful laser at a big mirror, say, 100 KMs away, without obstacles (e.g., at the sea surface), I should see the reflection.

( Go ahead, give it a shot)

A failed prediction automatically renders a hypothesis false.

Maybe not completely false, but at least you have to go back to the drawing board, and change something in the hypothesis that produces predictions that are more compatible with observations.

This is, at its core, the Scientific Method.

It's not about proving that you're right. It's about trying very hard to prove that your wrong, and consistently fail to do so.

To this end, we ask any scientific hypothesis to be *falsifiable*: If it is false, there should be a way to prove it.

No hypothesis is ever proven right. At most, it remains consistent with observations for a very long time, which makes it increasingly likely to be accurate.

Any currently accepted hypothesis is likely wrong, and we'll find an experiment that falsifies it. And then, from its ashes, we'll come up with a better, more realistic hypothesis.

This is the purpose of Science, to build an incrementally better understanding of reality.

What happens with unfalsifiable hypotheses?

For example, if I say we are living inside a simulated universe run by some God-like intelligence that creates on-demand the expected effects of any observation, how can you prove me wrong?

These types of hypotheses, at the very least, are useless as a means to achieve a better understanding of reality.

They can also be harmful, by giving us a false expectation that we have figured it all out.

Keep in mind though, that several important questions fall in this category:

- what is the meaning of life?
- can the universe be completely understood?
- is there a correct moral system?
- ...

For some fundamental questions, Science cannot help.

This doesn't mean that these questions are less important, though.

But it does mean that, whatever answer you have, just keep in mind that you cannot objectively convince me that you're right. At most, you can persuade me that I like your answer better than mine.

So next time you're trying to convince someone of something, ask yourself:

If that belief of mine were false, how could I prove it to myself without any doubt?

If you cannot answer that, then maybe you are not having an objective discussion. And maybe that's what you want.