Why don't we see quantum weirdness in everyday world?

[tarekatpf]

PS: Or any documentary?

 

[phinds]

Thank you very much. Can you suggest any book for general readers that explains how random particles could together form objects that apparently follow Newtonian-mechanics? I can't visualize particles jumbling around coming together to make something that's as stable ( motion-wise ) as a planet.

Hm ... not clear why you are puzzled by this. Newtonian Gravity is quite enough to cause planets and suns to form and to keep them in stable orbits. NASA has long been sending spacecraft to the moon and Mars without even thinking about GR. I'm not sure if the missions to the outer planets have to use GR or not, but if they do I would expect the corrects from Newtonian gravity to be small.

 

[analogdesign]

Thank you very much. Can you suggest any book for general readers that explains how random particles could together form objects that apparently follow Newtonian-mechanics? I can't visualize particles jumbling around coming together to make something that's as stable ( motion-wise ) as a planet.

You don't need quantum physics to understand this principle. For example think of a river. Even in classical terms a river is a vast collection of water molecules. The water molecules have thermal energy so they are vibrating and can travel every which way. However, because of the closeness of other molecules the overall flow of trillions of water molecules is regular and predictable.

Also, consider the air in the room where you are sitting. Each molecule in the air has thermal energy and different molecules are flying in all different directions. Why doesn't sometimes all the air go into the corner of the room so you can't breathe? There is nothing fundamental why this couldn't happen. It is just that, after you work out the probabilities, the odds of it happening are extremely, extremely low. It would take many times the age of the universe for such a thing to happen. It is very close to impossible. So it is with your tennis ball. The mass *is* changing slightly (in theory) but the changes are so small they could not be detected by any means we have today. So in practice, the mass is constant.

Also, consider this. Imagine that one of the electrons in the tennis ball is able to appear a measurable, macro distance from the tennis ball. Because the wavefunction decreases exponentially, this would be an almost unbelievably low probability of occurring but it could happen. But, for you to notice anything strange about the tennis ball, a large number of these unbelievably low probabilities would be multiplied. The odds of that are so small they are in practice zero.

So it's all probability. The odds of the kind of macro behavior of a tennis ball actually happening are so small it would almost require observing an infinite time. That's why people don't see them.

Does it make sense now why a planet can be stable? All the quantum weirdness tends to average out and the overall system is stable.

A great book written a low time ago about this type of thing is "one, two, three, infinity" by the great physicist George Gammow. It is a very popular book and you could get it at a library most likely. I loved the book and you may like it too.

 

[Simon Bridge]

Thank you very much. I needed that. I don't like things that are absolutely unpredictable. I mean who wants to live in a world in which everything happens by a 50/50 chance?

Since there are usually more than two ways that something could go, the odds of a particular thing happening would actually be a lot less than 50:50 were everything totally random.

Here - "totally random" would mean a "flat" probability distribution.
It would be like having to roll a million-sided dice each morning to see what the day may bring.
You've noticed that the world does not work like that - so you are puzzled when scientists keep going on about randomness.

I think this is core to your question.
You need to get a feel for probabilities before continuing.

So, I want to know how much can you predict about something?

Like everything in life it depends.
The field of study that answers that question is applied math: probability and statistics.
It is a big field, you need to find books about that to suit your education level.
A good primer, though, is John Allen Paulos' Innumeracy - which I believe you can still get on Amazon.
Don't be put of the title.

I read somewhere it's possible to predict accurately around 90% of times the motion of an electron. Is that true?

I'm afraid the statement to far too vague to comment on.
Chances are the person you heard it from was just making numbers up.

Richard Feyman regularly stated that the methods of quantum electrodynamics could predict behavior of certain kinds for electrons and photons to something like 10 decimal places of accuracy ... that is a LOT more accurate that 90%.

How much can you predict about something as small as maybe an atom or subatomic particle? Is it different for larger things? What does predictability depend on?

It depends on how much of something you have, and what you need to know.
The position of a baseball only needs to be known well enough to catch it ... it is easy to predict it's position to within the size of a catchers mitt so catchers rarely miss.

You can use your experience of cards and dice to get other examples.
The main take-away lesson here is that probabilties are not all equal.

So does the universe strictly follow the laws of classical mechanics?

The "laws" of classical mechanics are only followed on average.
The question should really be "how strictly does the universe strictly follow the laws of classical mechanics?"
The short answer is "very".
Slightly longer: it depends.

We would describe how strictly something sticks close to an average course by telling you the distribution about that course ... but to understand that, you need to learn about probabilities.

I want to understand how the universe has come to such a state.

Lots of us do ... it's a popular obsession.
Nobody does yet though there are a lot of very shrewed ideas of how such a state, may have come about given certain assumptions.
Meantime, the quest for understanding is fascinating.

We know it's just a product of the big bang. Now, in the earliest moments, the universe had no matter. Then came matter and antimatter, but matter slightly more. I suppose all the matter particles were still behaving weirdly then: here and there at the same time. Then how did the universe get a stable form?

You are right - this is a new topic ... start a new thread.
However - I doubt the answers will do you a lot of good while you are still new to how probabilities behave.

If things keep switching between places, how come something as big as a planet or star can form?

Because the places they keep switching between are almost all inside the planet or star ... usually inside an atom.

Is the universe becoming more of less predictable? Does gravity alter predictability of particles?

The answers need you to know something of probability math so you can explain what you mean by "predictable" ... i.e. the entropy law says that the amount of chaos in a closed system increases (or stays the same). If we associate more chaos with less predictability, then, very loosely, this would mean that the Universe cannot get more predictable and is likely getting less. OTOH: that is a prediction that gets more certain over time... is that an increase or a decrease in predictability?

That's a rhetorical question btw.
What I want you to notice is how much of your confusion comes from being imprecise in your language. A lot of learning about science involves learning to be careful with language.


Summary:
1. not all probabilities are equal - you need to read up on probabilities.
2. much confusion is avoided by careful language

 

[tarekatpf]

Hm ... not clear why you are puzzled by this. Newtonian Gravity is quite enough to cause planets and suns to form and to keep them in stable orbits. NASA has long been sending spacecraft to the moon and Mars without even thinking about GR. I'm not sure if the missions to the outer planets have to use GR or not, but if they do I would expect the corrects from Newtonian gravity to be small.

No, no, no, I have no doubts about Newtonian mechanics, because they're not counter-intuitive. Unlike quantum mechanics, it has, at least apparently, cause-effect relationship between events. But quantum mechanics -- how order originates from disorder -- keeps bugging me.

 

[ZapperZ]

No, no, no, I have no doubts about Newtonian mechanics, because they're not counter-intuitive. Unlike quantum mechanics, it has, at least apparently, cause-effect relationship between events. But quantum mechanics -- how order originates from disorder -- keeps bugging me.

Please make sure we continue to discuss physics and NOT personal tastes. If this discussion degenerates into simply a matter of personal preferences, then it is no longer physics and this thread is done.

Zz.

 

[tarekatpf]

You don't need quantum physics to understand this principle. For example think of a river. Even in classical terms a river is a vast collection of water molecules. The water molecules have thermal energy so they are vibrating and can travel every which way. However, because of the closeness of other molecules the overall flow of trillions of water molecules is regular and predictable.

Thank you very much. But the flow of a river can be explained easily, at least how I understand it. I could be wrong, but isn't water pouring down from mountains and falls into a channel pushes all the water molecules in a river towards the sea? Maybe all individual molecules are moving in random directions, but the flow from the mountain is always downhill. And since the channel from the mountain up to the sea is packed with water molecules, any additional molecules will be pushing other molecules towards the sea. Isn't that how a river flows?

Also, consider the air in the room where you are sitting. Each molecule in the air has thermal energy and different molecules are flying in all different directions. Why doesn't sometimes all the air go into the corner of the room so you can't breathe?

That's true, and that's my point. Random movements of any number of molecules remain random. They never form something stable, like a ball of air molecules. How did such stable stuff like stars, galaxies and planets could originate from molecules/ atoms that are apparently hopping around? Maybe as Simon Bridge said, I need to understand the mathematics of probability first. I need some time, but I hope I can get back to it soon ( I have exams for next two months, so can't for now. )

Because the wavefunction decreases exponentially,

Thank you very much. That's something I didn't know.

Does it make sense now why a planet can be stable? All the quantum weirdness tends to average out and the overall system is stable.

No, sorry, despite your sincere efforts ( and that of other members who tried to help me in this post ) I couldn't get it. I can't visualize order arising from chaos. Maybe I need to think about it more.

Thank you very much about your recommendation on the Gammow book. I do have that book in my computer. ( Off the topic, I have thousands of ebooks on my computer. Almost on any subject. If anybody needs a catalogue, please let me know through a private message. )

 

[tarekatpf]

You need to get a feel for probabilities before continuing.

Yes, I think so too.

A good primer, though, is John Allen Paulos' Innumeracy - which I believe you can still get on Amazon.

Thank you very much. I will start reading it once my exams are over ( that is not before March. )

It depends on how much of something you have, and what you need to know.

Say, I have an electron and there is wall with 10000 holes each 1 cm apart. I am 10 mitre away from the wall and at a right angle on the middle point of the wall. I throw the electron straight towards the hole in front of me. Now, what are the chances that the electron will go through, say, the number 189 hole from the left in the wall?

We would describe how strictly something sticks close to an average course by telling you the distribution about that course ... but to understand that, you need to learn about probabilities.

Yes, thank you. I'll try.

Because the places they keep switching between are almost all inside the planet or star ... usually inside an atom.

Thanks. The idea that matters keep switching places usually between a long distance ( say a mm ) makes me kind of grow a disliking for the universe.

the entropy law says that the amount of chaos in a closed system increases (or stays the same).

But that's what troubles me to think. As the second law of thermodynamics says, the universe is going from relatively ordered state to a disordered state. How could order arise from a chaos which the early universe has been?

What I want you to notice is how much of your confusion comes from being imprecise in your language. A lot of learning about science involves learning to be careful with language.

Thank you for your suggestion. I don't have a proper understanding of this whole thing, so my thoughts are in a disordered state as well. I need to have clearer conception on this quantum thing first, maybe.

Thanks a lot again for helping so much.

 

[tarekatpf]

Please make sure we continue to discuss physics and NOT personal tastes. If this discussion degenerates into simply a matter of personal preferences, then it is no longer physics and this thread is done.

Zz.

Sorry, I couldn't articulate my thoughts properly. What I meant is I can't visualize, despite best efforts from several members of the Physics Forums in this thread, how quantum mechanics makes transition to Newtonian mechanics. Maybe I need to know more about both, and probability first.

 

[ZapperZ]

Sorry, I couldn't articulate my thoughts properly. What I meant is I can't visualize, despite best efforts from several members of the Physics Forums in this thread, how quantum mechanics makes transition to Newtonian mechanics. Maybe I need to know more about both, and probability first.

Actually, if you want my opinion, based on what I've read of your posts, you have a more general issue with understanding how something that can behave randomly at the single-particle level can actually have a well-defined collective behavior. In other words, you don't have a grasp of not quantum mechanics, but rather, statistical mechanics in general.

Zz.

 

[tarekatpf]

Actually, if you want my opinion, based on what I've read of your posts, you have a more general issue with understanding how something that can behave randomly at the single-particle level can actually have a well-defined collective behavior. In other words, you don't have a grasp of not quantum mechanics, but rather, statistical mechanics in general.

Zz.

Your observation is correct. I didn't know what statistical mechanics is ( I googled it after I read your post ), but you are spot on the fact that I don't understand "how something that can behave randomly at the single-particle level can actually have a well-defined collective behavior".

 

[Simon Bridge]

Your observation is correct. I didn't know what statistical mechanics is ( I googled it after I read your post ), but you are spot on the fact that I don't understand "how something that can behave randomly at the single-particle level can actually have a well-defined collective behavior".

The word "random" is a common everyday term without a very tight definition ... when we need to make a distinction, we usually call the small-scale behavior of particles "statistical" rather than random.

You would be quite happy with the idea that adult human males are about a certain height where you live - despite the fact that the height of individuals varies randomly. Even though people's height is random, you don't get just any old height.

It seems there is a predictability in spite of the randomness.

In fact - the predictability is because of the randomness ...
... a graph showing number of people with a particular height against the height shows a rough bell-shape: it is humped up around the average height and trails off exponentially the further the height is from that.

In fact, if you graph the number of occurrences vs the thing occurring for anything that has a large number of random factors contributing to it, you get a similar shape to the graph.
i.e. a ral simple example: you roll 3 dice and add the values - do this a 100 times, and plot the number of times a particular total appears against the total, then you get a similar bell-shaped graph.

Do you have trouble understanding how this happens?

...which is where a study of probability and statistics will help you.
Like I said - the amount you need for the understanding you seek is not that hard, and does not take all that long to get.



From there, the usual path takes you through ideal-gas thermodynamics to classical statistical mechanics and quantum mechanics. But you need a grounding in probability and statistics.
Bon apetit.

 

[tarekatpf]

The word "random" is a common everyday term without a very tight definition ... when we need to make a distinction, we usually call the small-scale behavior of particles "statistical" rather than random.

You would be quite happy with the idea that adult human males are about a certain height where you live - despite the fact that the height of individuals varies randomly. Even though people's height is random, you don't get just any old height.

It seems there is a predictability in spite of the randomness.

In fact - the predictability is because of the randomness ...
... a graph showing number of people with a particular height against the height shows a rough bell-shape: it is humped up around the average height and trails off exponentially the further the height is from that.

In fact, if you graph the number of occurrences vs the thing occurring for anything that has a large number of random factors contributing to it, you get a similar shape to the graph.
i.e. a ral simple example: you roll 3 dice and add the values - do this a 100 times, and plot the number of times a particular total appears against the total, then you get a similar bell-shaped graph.

Do you have trouble understanding how this happens?

...which is where a study of probability and statistics will help you.
Like I said - the amount you need for the understanding you seek is not that hard, and does not take all that long to get.



From there, the usual path takes you through ideal-gas thermodynamics to classical statistical mechanics and quantum mechanics. But you need a grounding in probability and statistics.
Bon apetit.

Sorry about being late to reply. Am dead busy with exams.

Thanks a lot, again. Hopefully I'll get back with some understanding of these things once my exams are over.

 

[Simon Bridge]

Good luck - hopefully you won't need it :)

 

[MightyKaykoher]

I think ( but may be wrong ) quantum mechanics allows for practically anything to happen. As I said I could be wrong. The probability of something like an entire apple disapearing would be maybe 10^(-10^100) % per (year)??. I wouldn't count on it happening in your lifetime with you there to witness it either. I have pondered on this same topic. If you could calculate the probability of a single atom vanishing I could give a better statistic... (Wonder what the probability of the Earth dissapearing is)


But in this same sense (which I am completely unsure of ) if their in an infinite amount of time the apple will eventually dissapear. Because infinite time times 1/10^(10^100) is like... Infinite? Yeah in an infinite amount of time practically everything is possible??Is this true?

 

[phinds]

in an infinite amount of time practically everything is possible??Is this true?

No. Things that are not physically possible are not physically possible. Quantum weirdness IS physically possible, though, so theoretically lots of strange things can happen if you wait long enough but personally, I'm not going to wait around for them.

 

[lightlamb]

disappearing into thin air

Since, we and everything else in our real world are made up of electrons, protons, and electrons, protons, and atoms show quantum weirdness, why don't we ever see such things to happen in real world? Such as, why don't we see part of an apple suddenly disappearing into thin air? Why do classical mechanics never fail to predict motion of things bigger than atoms?

Quantum physics is based on unpredictability. Image that you are watching an archer shoot an arrow and you don't know if your going to see the beginning, or end. You will randomly appear after he/she already shoots the arrow. Quantum physics can only be measured during a single point in time and space. We only perceive the present because that is the rule of our dimension.

 

[maajdl]

It is precisely the fact that quantum weirdness isn't seen everyday, that makes it weird.

 

[Simon Bridge]

It is precisely the fact that quantum weirdness isn't seen everyday, that makes it weird.

You mean in the trivial sense that everydayness is, by definition, the opposite of weird?
So rephrase the question to this definition: how come the uncommon effects of QM are not more apparent on everyday scales?

Quantum physics is based on unpredictability.

... not exactly.
Is it not rather based on varying levels of predictability?

But even if we accept that - the question under consideration is how things get to be as predictable as they are despite this underlying unpredictability.

Image that you are watching an archer shoot an arrow and you don't know if your going to see the beginning, or end. You will randomly appear after he/she already shoots the arrow.

Then you know you cannot see the beginning but you may see the end.

[Grammar Nazi says: After he/she shoots the arrow or after he/she has already shot the arrow?]

Quantum physics can only be measured during a single point in time and space.

Quantum physics cannot be measured at all - any more than mathematics or an idea can be measured.
You measure physical properties.
Measurement in QM seldom happens at exactly one point at one time... our equipment is neither zero dimensional nor instant.

I know this seems pedantic but one of the banes of the science world is when people go out of their way to play-up the weird mystery of science by using unclear terms.

I think ( but may be wrong ) quantum mechanics allows for practically anything to happen.

You are wrong ;)

Time alone cannot make a purely statistical event certain, no matter how likely it is, unless it started out with a probability of 1. But you are thinking in terms of "infinite" time. It is not clear that the Universe has an infinite amount of time to play around with - we certainly don't. "Everything is possible with infinite time" makes a trite aphorism but it is otherwise useless.

What we usually care about, is some sort of functional infinity - like the length of time before the research grant can no longer be reliably renewed. We try to propose physics which has a chance of being verified in this sort of time frame.

The apple vanishing due to quantum uncertainty in the position of each of it's components is something that cannot happen because of the quantum mechanics of the apple. Its like each bit is keeping track of the other bits through the EM interaction - so the bits don't get to wander off. You also won't get it to exhibit wave-like properties in bulk. Fire it at narrow enough slits and you get to demonstrate it's sauce-like properties instead.

Have the three of you actually read the preceding thread at all?

 

[bhobba]

Maybe I need to know more about both, and probability first.

I would look into something called the Central Limit Theorem:
http://en.wikipedia.org/wiki/Central_limit_theorem

As the size n increases the variance of the mean (which is a measure of the spread) decreases, so that for very large collections the behavior approaches that of the average (mean is just a fancy word for average).

Right now unless you have studied probability it likely doesn't make a lot of sense. But as you learn more, what is going on will be clearer. For now just keep in mind that there are powerful theorems at work that explain this sort of stuff.

Thanks
Bill

 

[bhobba]

Yeah in an infinite amount of time practically everything is possible??Is this true?

Well there are some things that by the nature of things are impossible such as gravity suddenly reversing or the fine stricture constant suddenly changing - as far as we can tell at this juncture anyway - who knows what future research may bring.

However it is possible, for example, that all the molecules in the room will move in the same direction and accumulate at one side. If you wait long enough in principle it will likely happen and for an infinite amount of time its a dead cert. But this is just one of the weird properties of infinity. Since infinity is simply a concept useful in certain situations, and doesn't actually exist, its simply a weird property it has - like the very definition of infinity - that it can be put in a 1-1 correspondence with a proper subset. No object out there is like that. It's simply a conceptualization - good for getting a handle on some things mathematically - but beyond that - not really of much value.

Thanks
Bill

 

[lightlamb]

Then you know you cannot see the beginning but you may see the end.

[Grammar Nazi says: After he/she shoots the arrow or after he/she has already shot the arrow?]

You are correct.

 

[DevilsAvocado]

That's true, and that's my point. Random movements of any number of molecules remain random. They never form something stable, like a ball of air molecules.

Never? Wanna bet?

Air is a little bit too "opaque" to discuss, since it's a mixture of gases, so let's just focus on oxygen; all matter is composed of atoms which, to form molecules, uses chemical bonds:

https://www.youtube.com/watch?v=_M9khs87xQ8
(Will phinds like this one? ;)

Matter exists in four states: solid, liquid, gas and plasma.

Oxygen condenses at −183 °C and becomes liquid:

https://www.youtube.com/watch?v=7NXfyCezUFk

So, how can we make a ball of this stuff?? That’s easy, just use the Leidenfrost effect:

https://www.youtube.com/watch?v=57gUKxpcT_g

As you see, as a liquid its (para)magnetic properties become visible, and this can only be fully understood via QM properties of spin = quantum weirdness in everyday world!

How did such stable stuff like stars, galaxies and planets could originate from molecules/ atoms that are apparently hopping around?

This is obvious, isn't it? It looks like you maybe are a little bit 'confused' about the four fundamental forces of physics:

https://www.youtube.com/watch?v=gGC2Zz9fO0k

Thanks. The idea that matters keep switching places usually between a long distance ( say a mm ) makes me kind of grow a disliking for the universe.

Nooo, never dislike the whole universe, you're an integrated part of it!

You must understand that in QM there's a "wave–particle duality", and the electrons you want to throw in the wall must – before they are measured – be treated as a wave, or better, as a wave packet:

As you see, this is not a localized point/particle but a spread out wave, which can interact with itself and the environment. There are different interpretations on what this wave really is, if it exist or not, if it's 'just' a mathematical representation, etc. Anyhow, it all works beautifully and perfectly well in practice, when doing experiments and construction electronic gadgets, computers, etc.

Hopefully this documentary could help you get the basics:

Nova - Fabric of the cosmos: Quantum leap - hosted by Brian Greene

https://www.youtube.com/watch?v=4Z8Ma2YT8vY
http://www.youtube.com/watch?v=4Z8Ma2YT8vY&hd=1

 

[Dale]

This thread has run its course.