I pick up a stone.
I hold it in my hand, my palm over the stone, my fingers curled underneath.
I let go.
The stone falls.
Why?
This one-word question takes us to the heart of what physics is.
And, perhaps more importantly, what physics isn’t.
Infinite regress
I like being asked questions about Wolfram Physics.
When I try to answer them, though, I often find myself trapped in an infinite regress.
To address a question about Wolfram Physics, I might first need to address another, more fundamental question, about physics.
And to address that question, I might first need to address another, more fundamental question, than might be more philosophy than physics.
Today, I’m going to go to one of those deep questions that need to be asked, if not answered, before I can begin to address many of the questions I’ve been asked about Wolfram Physics.
What is physics?
Naming ≠ explaining
Let’s go back to the stone.
Why does it fall when I let go?
Suppose I told you that the stone falls because of obexiston.
Obexiston, that sounds kinda scientific, right?
Still, you might be dissatisfied with that answer.
I haven’t explained why the stone falls.
All I’ve done is named the phenomenon of falling.
Obexiston! Mystery solved!
Not very satisfying.
And yet, when 6-year-old children ask why a dropped stone falls to the ground, I bet most parents say that it’s because of gravity.
Gravity, that sounds kinda scientific, right?
Still, as a 6-year-old child, you might be dissatisfied with that answer.
On its own, the word “gravity” has no more explanatory power than the word “obexiston”.
Naming a phenomenon is not the same as explaining it.
We’re going to have to do better than that.
Describing ≠ explaining
Suppose I told you that the stone falls because it’s earth-like, and the natural movement of all earth-like things is down, to the natural place of all earth-like things, below all water-like, air-like and fire-like things, at the centre of the universe.
This is what Aristotle might have said.
No disrespect to Aristotle, but you might be dissatisfied with this answer, too.
Nonetheless, it is progress. Aristotle’s physics tells you, for example, that not everything falls. A stone may fall, but fire rises. Air, if trapped in water, also rises, in bubbles, until it reaches its natural place above the water.
Still it doesn’t tell you why a stone falls.
Saying that earth-like things fall because their natural movement is down is kinda circular. It’s like saying that earth-like things go down because earth-like things go down.
Describing a phenomenon is not the same as explaining it.
Quantifying ≠ explaining
Suppose I told you that I can predict the rate at which a stone falls.
I might predict that 1 second after I drop the stone, it’ll be falling at 22 miles per hour, and 2 seconds after I drop it, it’ll be falling at 44 miles per hour.
Assuming it doesn’t hit the ground first, of course.
I might also predict that 1 second after I drop the stone, it will have fallen 16 feet, and 2 seconds after I drop it, it will have fallen 64 feet.
So if I didn’t want it to hit the ground before reaching 44 miles per hour, I’d need to drop it from a height of at least 64 feet. The top of the Leaning Tower of Pisa, at 183 feet and 3 inches on it’s lower-leaning side, would do nicely.
These are the kinds of predictions Galileo might have made.
Now we’re really getting somewhere.
We’re not merely giving the phenomenon of falling a name, we’re giving it numbers, too.
Numbers that we can check against reality.
Galileo might not have dropped stones from the top of the Leaning Tower of Pisa, but he did measure the rates at which balls rolled down ramps. He surmised, correctly, that stones falling and balls rolling is the same phenomenon, subject to the same calculations.
So now we know the precise speeds and distances the stone might fall.
We still don’t know why the stone falls.
Quantifying a phenomenon is not the same as explaining it.
Elucidating ≠ explaining
Everything changed with Newton.
He proposed that there’s a force, called gravity, that attracts anything with weight to anything else with weight.
He proved that the force that attracts a stone to the Earth is the same as the force that attracts the Earth to the Sun.
This was unexpected.
Indeed, until Newton, it was unimaginable.
A stone falling to the ground and the Earth orbiting the Sun are the same phenomenon?
Preposterous.
And yet, Newton’s calculus showed that it was true.
Everything changed... and nothing changed.
Newton gave us a more general framework for describing the fall of the stone and more accurate equations for quantifying the fall of the stone.
But did he give us an explanation?
Sure, when 6-year-old children ask why a dropped stone falls to the ground, we can now say more than just that it’s because of gravity. We can say that gravity is a force that attracts anything with weight to anything else with weight. We even have an equation that quantifies how the force varies with the masses of those things and the distance between them.
But we haven’t answered the question of why the stone falls.
We’ve shifted the question. Instead of asking why the stone falls, we can now ask a more sophisticated question: why are weighty things attracted to other weighty things?
But just because the question is more sophisticated, it doesn’t mean that we’re any closer to an answer.
Newton’s laws of gravity and motion gave us a more lucid account of the universe, but elucidating a phenomenon is not the same as explaining it.
Elucidating ≠ explaining (reprise)
Everything changed again with Einstein.
According to Einstein, it’s not that there’s a force that attracts weighty things to other weighty things, it’s that space-time itself is curved by weighty things.
He suggested that everything, whether weighty or weightless, simply follows the shortest possible path through curved space-time.
This was unexpected.
Indeed, until Einstein, it was unimaginable.
Space-time is curved? Even things without any weight – things like light – follow a curved path?
Preposterous.
And yet, experiments to measure the curving of starlight around the sun showed that it was true.
Again, everything changed... and nothing changed.
Einstein gave us an even more general framework for describing the fall of the stone and even more accurate equations for quantifying the fall of the stone.
But we still haven’t answered the question of why the stone falls, we’ve just shifted the question again, to the more sophisticated question: why is space-time curved by weighty things?
Einstein’s theories of relativity gave us a more lucid account of the universe, but once again, elucidating a phenomenon is not the same as explaining it.
Physics never gets there
Aristotle, Galileo, Newton and Einstein gave us ever more satisfying accounts of how the universe works.
Always, however, these accounts address the how, not the why.
Physics seeks answers to the question of how the universe works, not the question of why it works the way it does.
I’m not knocking physics here. Giving ever more satisfying answers to the question of how the universe works is no small thing.
And I’m not ruling out the possibility that physics might one day give an answer that’s so satisfying that we realize that it’s also an answer to the question of why the universe works the way it does.
But I think that’s unlikely.
My guess is that physics will never get there.
Discovering the how of the universe? That’s what physics is.
Discovering the why? That doesn’t seem to be what physics is.
I’m not sure that the question of why the universe works the way it does, or, indeed, why the universe exists at all, is meaningful.
I can’t imagine what an answer to that question would even look like.
Still, if the history of physics teaches us anything, it’s that we should never rule something out just because it’s unimaginable.
What does all this have to do with Wolfram Physics?
Some of the questions I’ve been asked about Wolfram Physics address the why, not the how.
These are the questions I like the most.
Please keep asking them!
And...
Please forgive me if I respond by admitting that I can’t imagine what an answer to your question would even look like, and referring you back to this article about what physics is, and what physics isn’t.