I was talking to someone the other day who explained to me that the laws of physics as we understand them are not necessarily ‘rules’ that things on a really tiny scale obey, and the calculations we use to talk about physics on a scale that’s relevant to humans are more like estimations of what will *most probably* happen as a result. This also means there’s no such thing as a perfect circle or a perfect sphere I think? Could someone ELI5?
In: Physics
Physics works differently at different scales due to the principles of quantum mechanics at small scales (atoms and subatomic particles) and general relativity at large scales (cosmological and massive objects). These theories describe phenomena that deviate from classical physics, leading to distinct behaviors in the microscopic and macroscopic worlds.
Let me choose an example you are familiar with. On a one-meter, surface tension does not matter very much. Yet at the scale of 1mm, surface tension (with water) is dominant. So, bugs can walk on water, and you can get beautiful drops of water on pine needles.
The laws of physics aren’t different, but when calculating the force on an insect foot on a lake, surface tension is important compared to mg. Less so with a human foot.
Physics is trying to translate what we observe into a mathematical language.
The goal is to keep the math as simple as possible. To do that, we limit the scale. When you throw a baseball in the air, it comes down. Simple math. If you throw a feather in the air, it comes down and there’s air resistance. Slightly more complex math. If you launch a rocket into orbit… even more complex math.
Overall, we’re trying to keep the math as simple as possible while still getting meaningful answers for whatever system we’re observing at that time.
At present, we’re still working out “Grand Unification” that will bring all the different scales together.
Physics itself does *not* work differently at different scales. Objects of all sizes from ants to galaxies are made of the same tiny particles like molecules, atoms, electrons and quarks. they follow the same rules, and interact through the same waves like microwaves, visible light, and X-rays.
However physics *appears* to work differently when we focus on a certain scale and try to tell a simple story. For example a basketball bouncing on the floor, or a chemical reaction, or a rocket taking off, or a star exploding into a supernova. For each of these, going back to the behavior of elementary particles to try and piece the whole story together would be way too complicated. But at each scale, we’ve often been able to come up with a few simpler rules that do the job. We don’t care about what happens to atoms in the basketball or molecules in a glass of water, so we can make the story much simpler.
It’s a bit like a historian talking about an army marched against another army, instead of talking about how a particular grain of sand ended up in the pocket of soldier #13546834. At some point we decide that the details don’t matter.
I’d argue it doesn’t really. It’s the same on all scales.
It’s just at larger scales we can make simpler approximations and still get accurate results. So why go through all the work?
It’s like how one person clapping creates a rythmic periodic sound. But as you add more and more it turns into a steady roar. At some point you can just treat it as one single sound rather than a combination of lots of smaller ones.
The actual mechanics of the origin of the sound are the same. But you don’t have to be that detailed in modeling the sound anymore. You can say it’s a single source with a specific intensity and disperses by the inverse square law.
Also, physics doesn’t have rules
We observe the universe, find patterns, and then mathematically model those patterns
Stuff like the effects of gravity are super well understood and we can be extremely confident those patterns will continue ro hold true. We can’t be 100% certain, but pretty close
However, any day, we can find exceptions that throw out everything we think we know. As we get better tools and can observe more things, we can see more and more patterns which may go against patterns we were already familiar with
Physics doesn’t work differently at different scales. What does work differently are some of the approximations we make do describe physics. There’s no scientifically accepted formula to describe a macroscopic process that works perfectly in 100% of cases.
You can apply Newton’s law of gravitation to calculate the orbit of a satellite, but the larger the orbiting body is, the less accurate they’ll become. At some point you need to switch to relativistic gravity because by then the Newtonian model is too far off to be useful at all.
It’s all a product of the way we explore the world and conduct science. We started describing the things we could see with our naked eye, and only then moved down smaller and smaller, into the atomic and then quantum scales. That’s not how the universe works, though, everything that happens is a product of quantum processes at the tiniest scale (and who knows, maybe one day we’ll realise it goes even smaller). It’s like looking at a cup of water and trying to come up with math to describe how it responds to outside forces. Yes, you can get pretty close, but you’ll never get a fully accurate model unless you’re going down to the smallest level and simulating everything that each little particle does. It’s those countless interactions that add up to produce the effects we see at our scale.
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Because some of physics is related to volume, some to area and some to distance. So if you scale something 100 times you have 100x distance, 10 000x area and 1 000 000x volume.
Or rather some values are squared and cubed and some not.
For example we have two balls touching each other. Now let’s scale them 10 times. 1000x more mass. 100x (r^2) less gravity force due to distance but 1000×1000 more gravity force due to mass. So 10000x bigger force is acting on a 1000x more massive object. That changes the behaviour a little
If you shoot a fly at a truck. The we can ignore the fly in the calculation of the truck velocity.
If you shoot a fly at another fly. You need to know the size and weight, and perhaps air pressure and humidity data, friction, compression of the body data, to properly calculate where the fly will end up after a collision.
If the fly is blasting through an electron cloud … does it even interact with the fly?
At each level. More detail is required. So our full understanding of everything isn’t clear enough for us to have 1 calculation for everything
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