Quantum physics.

I've just started reading what seems a very well written book for someone with little knowledge on the subject. 'How to teach quantum physics to your dog'. Bit of light reading to go along with the 'Introduction to Radiation Protection' book :o
 
Maths lots and lots of maths.

And not the easy maths, you knwo the maths that just has numbers and the + - / * = symbols, not even that more complicated maths you do later that has letters in too. No this is that breeze block to the balls maths where there's letter symbols and all manner of things that aren't even on your keyboard, symbols you've never seen before in your life. That kind of maths.


So to sum up quantum physics is the mental equivalent of a breeze block to the testicles.
 
I'm coming to the end of my second year in maths/physics with a quantum exam coming up soon, and I've got a loooong way to go before I feel confident in saying I understand the stuff.

Basically though, everything in the universe is quantised (hence the name), distance, position, momentum, energy, charge, etc.. This means that individual particles can only fall into discrete quantum states, the simplest version of this would be electron shells in an hydrogen atom. The electron can only take certain energy and momentum values, leading it to only exist orbiting at a discrete distance from the proton.

The two other majorly mind boggling things are wave-particle duality and the uncertainty principle. Wave particle duality stats that everything is both a wave and a particle, and will behave as one or the other simultaneously, sort of.

The uncertainty principle says that for certain values, the more precisely you know one, the less precisely you know the other. For instance you are allowed to know the total angular momentum of a particle at the same time as one component of the angular momentum ( taken as the z component) at the same time. But knowing both the x and y components a the same time is forbidden. Momentum and position have a similar relationship.


One of the principles of quantum mechanics is that as the quantum numbers are scaled up, the way particles behave becomes much more normal until it fits a classical model of physics. Think of a digital sound signal looking like an analogue wave at low resolution.

These three things more or less govern most quantum interactions as far as I'm aware. Lots more things are massively confusing if your not used to pure mathematics (such as the order of addition effecting the result mention somewhere earlier). I'd explain more, but I should get back to revision :(
 
Sherbs said:

Gives quite a good insight. Watch Parts 1,2,3 and 4.

Also don't worry about mavity, even Physicists don't know what mavity is. (Well not fully anyway)
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Regarding the string being infinitely long point (I've only seen halfway through part 2 thus far, so it might be a stupid question), surely at some point you'd reach the atomic level, at which point the length is lost as it is almost entirely empty space? If you say you stop before you get to the atomic level, thus avoiding the problem of dealing with the empty space, then surely there is a limit on how long you can say the string is?

EDIT Oh wait, nvm, pressed play and they just dealt with it (well, stated it and didn't deal with it so much as acknowledge and ignore it)
 
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Ksanti said:
Regarding the string being infinitely long point (I've only seen halfway through part 2 thus far, so it might be a stupid question), surely at some point you'd reach the atomic level, at which point the length is lost as it is almost entirely empty space? If you say you stop before you get to the atomic level, thus avoiding the problem of dealing with the empty space, then surely there is a limit on how long you can say the string is?
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You will be able to get far past the atomic size level. Look up the "Planck length", might help you a bit. :)
 
DAnDan said:
You will be able to get far past the atomic size level. Look up the "Planck length", might help you a bit. :)
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After a brief bit of research, I'm not sure "help" is the right word xD
EDIT: Actually, if the planck length is just a unit of length, then it doesn't really change my point. I wasn't talking about the limitations of measuring being down to a scale of atoms, but saying that within an atom, you have mostly empty space. The only constant is the nucleus, and that isn't connected to anything except empty space, i.e. there is no border constant through the piece of string, i.e. it has no length, just the circumference of all the nuclei in its atoms?
 
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Kristoph said:
Bit of light reading to go along with the 'Introduction to Radiation Protection' book :o
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That's my line of work that! Anything to do with radiation, then I'm your man.

With regards to quantum physics, is that cat still in the box and if so, is it alive or dead?
 
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Just like to take the opportunity to thank BetaNumeric for his contributions to the forums so far. First noticed him/her in the 6÷2(1+2) thread making fools of the absolutists and a few other highly involved and educated posts have followed - it's such a refreshing change to have someone who knows what the hell they're talking about in discussions like this, especially in a field in which I hold a personal interest.

My question: Electrons exist not as points in space but as probability density distributions across their apparent orbits, such that rather than an electron orbiting a nucleus along a fixed path, at any one time it has a varying probability of existing at certain points around that boundary. However, the sum of the probabilities is not necessarily 1 - putting it in the simplest possible terms, if we consider only three points to the 'orbit', the electron has a 70% chance of being at point A, 25% chance of being at point B and 15% chance of being at point C, simultaneously. I may have garbled it little bit, but this is how I recollect it being explained to me by a lecturer.

Edit: Right, in the form of a question. Errr... what if.... that thing I said?
 
Deadbeat said:
Just like to take the opportunity to thank BetaNumeric for his contributions to the forums so far. First noticed him/her in the 6÷2(1+2) thread making fools of the absolutists and a few other highly involved and educated posts have followed - it's such a refreshing change to have someone who knows what the hell they're talking about in discussions like this, especially in a field in which I hold a personal interest.

My question: Electrons exist not as points in space but as probability density distributions across their apparent orbits, such that rather than an electron orbiting a nucleus along a fixed path, at any one time it has a varying probability of existing at certain points around that boundary. However, the sum of the probabilities is not necessarily 1 - putting it in the simplest possible terms, if we consider only three points to the 'orbit', the electron has a 70% chance of being at point A, 25% chance of being at point B and 15% chance of being at point C, simultaneously. I may have garbled it little bit, but this is how I recollect it being explained to me by a lecturer.

Edit: Right, in the form of a question. Errr... what if.... that thing I said?
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The way we model it is not as it being a % chance of it being at a specific place, but a 95% chance of it being within its relevant orbital (be it s,p,d or f). If that's what you're asking?
 
Deadbeat said:
My question: Electrons exist not as points in space but as probability density distributions across their apparent orbits, such that rather than an electron orbiting a nucleus along a fixed path, at any one time it has a varying probability of existing at certain points around that boundary. However, the sum of the probabilities is not necessarily 1 - putting it in the simplest possible terms, if we consider only three points to the 'orbit', the electron has a 70% chance of being at point A, 25% chance of being at point B and 15% chance of being at point C, simultaneously. I may have garbled it little bit, but this is how I recollect it being explained to me by a lecturer.

Edit: Right, in the form of a question. Errr... what if.... that thing I said?
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I think what you mean that you get an equation for an electron being something like:
psi(x,y) = n ( 0.5psi_(1,1)(x,y) + 0.25psi_(3,1)(x,y) - 0.25psi_(2,2) + 0.75psi_(1,2)(x,y) )

where the psi_(l,ml)(x,y) correspond to the various values of angular momentum it can take.
The co-efficients add up to equal n(0.5 + 0.25 - 0.25 + 0.75) = 1.25n but this doesn't mean the total probability is greater than one.
We choose n so that n^2 * (0.5^2 + 2*(0.25^2) + 0.75^2) = 1 Then the square of the coefficent psi_(l,ml)(xy) is the probability of the electron being in that state. So in this case the probability of the electron being in a quantum state with quantum numbers = 1 would be 0.25n^2



Not too sure if this is what you asked however
 
physichull said:
That's my line of work that! Anything to do with radiation, then I'm your man.

With regards to quantum physics, is that cat still in the box and if so, is it alive or dead?
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Ahh interesting :) where do you work?

I'm a science technician at an Energy Skill centre working with some ex Magnox guys who are now running NVQ courses in rad protection etc.

I've got myself onto the Award For Nuclear Industry Awareness course and trying to build on my knowledge by reading the book. Interesting stuff, although some of the maths takes a bit of reading (neutron flux calculations etc) but I think that's more than I need to know at this point.
 
Quantum physics is something we will understand a lot better when we can finally figure out how to use more then 10% of our brain lol! so basically a long ******* time! haha!
 
Westie said:
Quantum physics is something we will understand a lot better when we can finally figure out how to use more then 10% of our brain lol! so basically a long ******* time! haha!
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Except that 10% brain usage is a myth. We use all of it. Just not at the same time.
 
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