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Quantum Mechanics

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KaraCleary
874918.  Tue Jan 03, 2012 8:43 am Reply with quote

I've just found out that I could walk through walls according to quantum mechanics, which is strange because I'm sure I can't. Flying seems an equally unlikely event, and yet I am assured the probability, although small, is definitely not zero.

I would be interested to hear from someone what the actual probability is in percentage terms and why it exists at all. Walls are verrrry solid!

This may well be an extremely silly question...

 
Jenny
875023.  Tue Jan 03, 2012 12:23 pm Reply with quote

The silliest-sounding questions are sometimes the most interesting, so I look forward to somebody with a better grasp of quantum physics than me explaining why you can't walk through walls!

 
aTao
875150.  Tue Jan 03, 2012 6:31 pm Reply with quote

Brain Cox recently presented a televised lecture from the Royal Institution, in which he showed the result of the relevant calculation for the probability that the diamond would spontaneously move to Jonathan Ross's pocket.
The duration in which such an event had more than 50-50 chance of happening came out a 3*10^29 seconds. Thats considerably many times older then the universe, its possible but no particularly probable.

 
KaraCleary
875402.  Wed Jan 04, 2012 4:45 pm Reply with quote

So if I stand in front of the wall long enough, I'll go through it. Excellent! Now to extend my life-span by several billion years.

That's not at all the only QM question I have. Observation results in linear collapse of wavefunction and subsequently affects outcomes in the microscopic world, yes? So then, when Einstein asked Bohr if he was expected to believe the moon wasn't there when he wasn't looking, Bohr replied: 'can you prove to me otherwise?'.

What about tides? I believe they still occur when we aren't staring at the moon. Does that count as observation?

The gravitational pull of the moon has affected climatic conditions favourably - we would live in a world with a far more hostile environment without the Moon.


Who wants to discuss the two slit experiment?

 
orablu
875405.  Wed Jan 04, 2012 4:51 pm Reply with quote

well, in that case, you'd have to look away from the moon, at the sea.
but if there isn't any sea to observe, can you prove to me that there are tides?

 
CB27
875424.  Wed Jan 04, 2012 5:35 pm Reply with quote

I think this is going into the realm of Schrodinger's cat :)

 
dr.bob
875524.  Thu Jan 05, 2012 5:08 am Reply with quote

KaraCleary wrote:
What about tides? I believe they still occur when we aren't staring at the moon. Does that count as observation?


Arguably, though something else could be producing the tides. You could argue that the tides prove that there's something out there, but not necessarily the Moon.

However, this kind of logic veers swiftly away from Physics and more into Philosophy, which I find a singularly unhelpful thing to pursue. Before you know it, we'll be talking about Russell's teapot.

KaraCleary wrote:
Who wants to discuss the two slit experiment?


What would you like to discuss about it?

 
KaraCleary
875600.  Thu Jan 05, 2012 1:00 pm Reply with quote

The fact that it exists! Conscious little particles? Are there multiple theories to explain what COULD be happening? So far I've heard none, just wondered whether there were any ideas... Wave/particle duality is a mind-boggling concept at the best of times!


Quote:
well, in that case, you'd have to look away from the moon, at the sea.
but if there isn't any sea to observe, can you prove to me that there are tides?


The axial tilt of the earth is steadied by the moon, hence why without it we would live in a verrrry different environment.

Quote:
You could argue that the tides prove that there's something out there, but not necessarily the Moon.


I believe scientists are certain it is the combination of sun and moon that influence tides, since they increase when the two are aligned. Without the moon there would certainly be a measurable difference in both timing and extent of difference in water levels.


I think Russell's teapot is arguably a force for good in the world!

 
dr.bob
875742.  Fri Jan 06, 2012 5:17 am Reply with quote

KaraCleary wrote:
The fact that it exists! Conscious little particles? Are there multiple theories to explain what COULD be happening? So far I've heard none, just wondered whether there were any ideas...


I think that just proves that either we really don't understand what's actually going on there, or what is going on there is so outside of our sphere of experience that it's impossible to describe in terms that we understand.

KaraCleary wrote:
Wave/particle duality is a mind-boggling concept at the best of times!


A case in point. I can't remember who said it, but many years ago I heard the following description of wave/particle duality:

Imagine trying to describe a lion to someone who'd never seen one before. You might choose to say that it was the colour of honey, and that it made a noise like a motorbike. However, by saying those things, you're not actually saying that the lion is made of honey, or that it's actually a motorbike. You're simply describing something outside of someone's experience in terms that they can understand. Likewise, subatomic particles are probably not waves or particles. They're something else, but something that we have no experience of so the only way we can describe them is by using terms that we understand, like "wave" and "particle", but which aren't actually accurate descriptions.

 
PDR
875760.  Fri Jan 06, 2012 6:34 am Reply with quote

KaraCleary wrote:
So if I stand in front of the wall long enough, I'll go through it. Excellent! Now to extend my life-span by several billion years.

That's not at all the only QM question I have. Observation results in linear collapse of wavefunction and subsequently affects outcomes in the microscopic world, yes? So then, when Einstein asked Bohr if he was expected to believe the moon wasn't there when he wasn't looking, Bohr replied: 'can you prove to me otherwise?'.

What about tides? I believe they still occur when we aren't staring at the moon. Does that count as observation?

The gravitational pull of the moon has affected climatic conditions favourably - we would live in a world with a far more hostile environment without the Moon.


I believe you are missing the point of the Einstein/Bohr discussion. Einstein was asking if Bohr expected him to believe that the moon was still there when there was no longer any observable evidence of its presence at all (ie it is the same question as Schroedy's moggie). He *wasn't* asking about alternative ways of detecting the moon other than staring at it.

PDR

 
PDR
875762.  Fri Jan 06, 2012 6:35 am Reply with quote

dr.bob wrote:
Imagine trying to describe a lion to someone who'd never seen one before. You might choose to say that it was the colour of honey, and that it made a noise like a motorbike. However, by saying those things, you're not actually saying that the lion is made of honey, or that it's actually a motorbike. You're simply describing something outside of someone's experience in terms that they can understand. Likewise, subatomic particles are probably not waves or particles. They're something else, but something that we have no experience of so the only way we can describe them is by using terms that we understand, like "wave" and "particle", but which aren't actually accurate descriptions.


Bob, that's absolutely brilliant! May I steal it for future use?

PDR

 
dr.bob
875808.  Fri Jan 06, 2012 9:01 am Reply with quote

Please do. I stole it off someone, and I can't even remember who, so it would be churlish of me to keep it to myself now :)

 
KaraCleary
875837.  Fri Jan 06, 2012 10:53 am Reply with quote

Quote:
I believe you are missing the point of the Einstein/Bohr discussion. Einstein was asking if Bohr expected him to believe that the moon was still there when there was no longer any observable evidence of its presence at all (ie it is the same question as Schroedy's moggie). He *wasn't* asking about alternative ways of detecting the moon other than staring at it.


I am well aware of what was meant. I am asking these questions more or less to find out if there is a defined parameters for what constitutes observation. I suspect not...

 
dr.bob
875840.  Fri Jan 06, 2012 10:59 am Reply with quote

I really don't like the "waveform collapse by observation" idea. To me it's a bit too close to the pointless philosophical wanking over whether or not a tree makes a noise when it shits in the woods (or something).

 
PDR
875845.  Fri Jan 06, 2012 11:06 am Reply with quote

I guess I'm with you Bob - I don't agree with the Boss Man (jumping jack) that a "sound" only exists when it is heard.

PDR

 

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