Questions About Physics: Perspectives from Macro & Quantum Levels

[ƒ(x)]

I don't know enough physics to answer these questions myselfs. For all I know, they might be foolish.

Is there a branch of physics that takes perspective into account. I use that word in its most basic sense. To an observer on the quantum level, might everything appear to work according to the rules of normal physics? Similarly, to another observer on a macro level, might the planets and galaxies behave according to the rules of quantum physics?

 

[JaredJames]

Surely it's macro to macro, micro to micro.

 

[ƒ(x)]

Surely it's macro to macro, micro to micro.

It was just a thought. That's why I used the word "perspective" though

 

[JaredJames]

Macro concepts of things like gravity don't apply on a microscopic scale. So if you were 'at' that scale it wouldn't apply to you.

I'm sure someone more knowledgeable can go deeper into this with you.

 

[ƒ(x)]

Macro concepts of things like gravity don't apply on a microscopic scale. So if you were 'at' that scale it wouldn't apply to you.

I understand. I was more thinking along the lines of that there were different forces to go to different scales, and that to someone not from our scale, gravity might appear completely different (like quantum forces, perhaps?) and be defined by different equations.

 

[micromass]

I understand. I was more thinking along the lines of that there were different forces to go to different scales, and that to someone not from our scale, gravity might appear completely different (like quantum forces, perhaps?) and be defined by different equations.

It's a view of the universe that I particularly like myself. It would be quite beautiful if it were true. But I fear that it might be to naive for current physics. Anyways, we'll never know, since we will never be able to witness the universe on macro or micro scale...

 

[SamirS]

I don't know enough physics to answer these questions myselfs. For all I know, they might be foolish.

Is there a branch of physics that takes perspective into account. I use that word in its most basic sense. To an observer on the quantum level, might everything appear to work according to the rules of normal physics? Similarly, to another observer on a macro level, might the planets and galaxies behave according to the rules of quantum physics?

I'm not sure if I understand you correctly but there are certainly many parts of physics that take "perspective" into account. Take aerodynamics - for small flying insects, air "feels" very different, more like a liquid than a gas.

Brownian motion isn't a visibly dominating observation in our daily lives (you don't see parts of your desk moving into random directions); it's certainly different for bacteria.

Outside of that, I don't see the point of "perspective". It's probably fun to think about actually "seeing" (whatever that means on this level) quantum tunneling effects in a science-fiction way, but as a serious thought, I don't see how it could make sense.

 

[Jimmy Snyder]

Similarly, to another observer on a macro level, might the planets and galaxies behave according to the rules of quantum physics?

Presumably, planets and galaxies do behave according to the Rules of Quantum Mechanics. Even at that scale, energy of orbits is quantized. However, the quantum of action is the same for planets as it is for atoms, approx $$6.63 x 10^{-34}$$Js. While this amount can have a significant effect on an atom, it is undetectable for a planet.

 

[Mike Pemulis]

I don't know enough physics to answer these questions myselfs. For all I know, they might be foolish.

Is there a branch of physics that takes perspective into account. I use that word in its most basic sense. To an observer on the quantum level, might everything appear to work according to the rules of normal physics? Similarly, to another observer on a macro level, might the planets and galaxies behave according to the rules of quantum physics?

According to everything we know, the answer no -- scale is absolute. Atoms are not small solar systems; galaxies are not large molecules. I can see the attraction of a theory where the universe is "turtles all the way down" but to my mind the real world is much more beautiful. The fact that the same theory can describe the world accurately over a giant range of scales, but also tell us why specific systems behave differently on different scales is, to me, nothing short of breathtaking. A few examples,

1. Warm-blooded animals on Earth cannot be smaller than a certain size. This is because warm-blooded animals must keep their body temperatures above the ambient temperature to live, and most of the time the environment is colder than the inside of the animal. The amount of heat energy contained in an animal at a certain temperature is roughly proportional to its volume, which goes roughly as its (length)³. The rate at which body heat radiates away is proportional to its surface area, which goes roughly as its (length)². So as an animal shrinks, the amount of heat contained inside it goes down much more quickly than the rate at which which it radiates heat to the environment; a mouse looses a larger fraction of its body heat per second than an elephant. To keep its body temperature up, then, a small animal must eat much more food than a large animal relative to its size. A mouse eats its body weight every day, and that's about the limit for warm-blooded animals. Animals like insects are much smaller than mice, but they are all cold-blooded. (If you've ever seen the movie Honey, I shrunk the kids, all this implies that the kids would actually freeze to death!)

2. There is a similar argument for upper limits on animals' size. Bone strength is proportional to the cross-sectional area of the bones, which goes roughly as (length)², and again, volume goes as (length)³. So if you keep an animal the same but simply scale it up, its bones get weaker relative to its body mass. Elephants aren't the biggest animals possible; some dinosaurs got a lot bigger, and some animals bigger than elephants existed in more recent times before early humans killed them off, as hunting technology advanced faster than evolution. But fantasy animals like Godzilla and King Kong would just collapse under their own weight. At the other end of the scale, insects are much stronger relative to their mass than large animals. You may have heard than ants can lift fifty times their own weight, and if you could do the same you could life a schoolbus or something. But it's exactly because they are so small that ants have such large relative strength. If you scaled them up, they would be as weak as larger animals.

3. Now to more basic physics. The atom with the smallest nucleus is Hydrogen-1, which is just a proton. The proton is the smallest nuclear particle; you can't make a nucleus smaller than a proton. Now protons and neutrons are attracted to each other by the strong nuclear force, so larger elements are readily created by fusion in stars. But the nuclear force is mediated by a massive particle called a pion. A proton or neutron in one part of the nucleus emits a pion, which is absorbed by another proton or neutron, and this interaction communicates an attractive force. But pions are massive particles, which according to the rules of quantum field theory means that they only live for a short amount of time. Pions are so massive that most of the time they decay in the time it takes to cross a large atomic nucleus, which means that the nuclear attraction gets very weak with distance. Meanwhile, protons also repel electrically because they are all positively charged. The particle that carries the electric force, the photon, is massless, so it can travel forever, unlike the pion. All this means that, for small nuclei, the strong nuclear attraction wins over the electrical repulsion, but at larger distances electrical repulsion wins. And so atomic nuclei have a certain size range, which is unavoidable -- you cannot make a bigger nucleus by putting more nuclei together, because that large nucleus would immediately decay.

4. Speaking of stars, there is a reason they are the size they are. Stars are powered by fusion, which cannot occur unless atoms are squeezed very close together. The force that squeezes the atoms together in stars is gravity. So you need a lot of mass in order to generate the forces necessary. The sun is large enough to sustain fusion, but a smaller clump of gas, like planet Jupiter, isn't. So the sun shines and Jupiter doesn't, purely because the sun is bigger. You might ask if there is an upper limit, and it seems that the upper limit is just how much gas is available. In the early universe, stars were much more massive, but massive stars burn hotter and faster, and so die quicker. In the modern universe, the surviving stars are much smaller because there is not as much available hydrogen left to burn anymore. In fact, the rate of star formation in the universe has already peaked -- today on average, more stars are dying than are being created.

There are countless more examples. I have only talked about size scales, but of course there is scale-dependent behavior in energy, speed, mass, time, temperature, and any other measurement we can think of. It is remarkable that the more we discover laws that apply to all scales, the more we can see that the actual behavior at different scales varies widely, precisely because the laws are universal.

I hope that wasn't too verbose. I've had the above essay bouncing around in my head for a while, and it seemed like a good answer to your question. I may not have understood your question though -- is that what you were asking?

 

[ƒ(x)]

I hope that wasn't too verbose. I've had the above essay bouncing around in my head for a while, and it seemed like a good answer to your question. I may not have understood your question though -- is that what you were asking?

Almost but not quite. I was thinking more along the lines of what micromass said. I was more thinking something like this...
Let's say you're on our scale, basic objects move, more or less, according to Newton's laws. But, if you zoom out by..say...twenty magnitudes or something, would everything still look like it's working according to those laws. Or would it look different...like say quantum physics.

 

[Mike Pemulis]

Okay, I think I understand a little better. Answer is still no -- scale is absolute. A super-large observer might have trouble seeing things on our scale, but if he could, he'd see the same behavior we do.

I'm having a hard time imagining how it could be any different, to be honest. I throw a ball to you, and it follows Newton's laws as it flies. A super-giant physicist watches the same event. Surely he sees the same thing?

 

[khemist]

Maybe you mean that someone who is able to perceive more or less dimensions than we do would see something else?

 

[ƒ(x)]

Mike, that's what I was wondering.

Khemist, not really. I'm not well versed in physics (only had high school physics), but I wasn't thinking along the lines of different dimensions.