The Secrets of Quantum Physics
Discussion
Heads up science folks - BBC4 21:00 tonight
http://www.bbc.co.uk/programmes/b04tr9x9
Einstein's Nightmare
The Secrets of Quantum PhysicsEpisode 1 of 2
Professor Jim Al-Khalili traces the story of arguably the most important, accurate and yet perplexing scientific theory ever - quantum physics.
The story starts at the beginning of the 20th century with scientists trying to better understand how light bulbs work. This simple question led them deep into the hidden workings of matter, into the sub-atomic building blocks of the world around us. Here they discovered phenomena unlike any encountered before - a realm where things can be in many places at once, where chance and probability call the shots and where reality appears to only truly exist when we observe it.
Albert Einstein hated the idea that nature, at its most fundamental level, is governed by chance. Jim reveals how, in the 1930s, Einstein thought he'd found a fatal flaw in quantum physics because it implies that sub-atomic particles can communicate faster than light in defiance of the theory of relativity.
For thirty years his ideas were ignored. Then in the 1960s a brilliant scientist from Northern Ireland called John Bell showed there was a way to test if Einstein was right and quantum mechanics was actually mistaken. In a laboratory in Oxford, Jim repeats this critical experiment - does reality really exist or do we conjure it into existence by the act of observation.
The results are shocking!
http://www.bbc.co.uk/programmes/b04tr9x9
Einstein's Nightmare
The Secrets of Quantum PhysicsEpisode 1 of 2
Professor Jim Al-Khalili traces the story of arguably the most important, accurate and yet perplexing scientific theory ever - quantum physics.
The story starts at the beginning of the 20th century with scientists trying to better understand how light bulbs work. This simple question led them deep into the hidden workings of matter, into the sub-atomic building blocks of the world around us. Here they discovered phenomena unlike any encountered before - a realm where things can be in many places at once, where chance and probability call the shots and where reality appears to only truly exist when we observe it.
Albert Einstein hated the idea that nature, at its most fundamental level, is governed by chance. Jim reveals how, in the 1930s, Einstein thought he'd found a fatal flaw in quantum physics because it implies that sub-atomic particles can communicate faster than light in defiance of the theory of relativity.
For thirty years his ideas were ignored. Then in the 1960s a brilliant scientist from Northern Ireland called John Bell showed there was a way to test if Einstein was right and quantum mechanics was actually mistaken. In a laboratory in Oxford, Jim repeats this critical experiment - does reality really exist or do we conjure it into existence by the act of observation.
The results are shocking!
Edited by MartG on Tuesday 9th December 17:15
Going to watch it again until I do.I watched it too, twice. Liked it very much but totally puzzled. I admit to being ignorant of much of Physics but entertained by the arguments. Strikes me as guesswork being supported by establishment figures running after bandwagons. Alternative theories, and that's all they are, divide 'camps' and provoke discussion. No bad thing, but the eminence of the prophet has no bearing on the sleight of hand of card tricks. That demonstration was in every issue of Magic Tricks for Kids. Doesn't do the cause much good I'm afraid. Can't wait for the next one though.
AA999 said:
It is truly fascinating.
I think that finding the level at which the microscopic world turns in to the quantum world would be a clue as to what is going on, or at least what fundamentally is 'changing' between the two different scales of dimension.
There may not be a defined cutoff point - merely a sliding scale whereby as objects become smaller, quantum effects increase or become more apparent. The double slit experiment for example has been performed on increasingly larger molecules.I think that finding the level at which the microscopic world turns in to the quantum world would be a clue as to what is going on, or at least what fundamentally is 'changing' between the two different scales of dimension.
http://arstechnica.com/science/2012/03/quantum-int...
I watched it again this evening. Still more than a little confused by the proof against Einstein's explanation. It still seems to me that they are testing on a basis of an untested theory. Or rather, the theory is proved by the results of this test.
I was happy with the gloves explanation.
I can hold the idea that nothing is predictable if we go into enough detail, but reality not actually being real strikes me as being a bit of an explanation looking for a problem.
Perhaps it will all become clear after the subsequent programme. But then I think the most predictable outcome in the universe will be that it won't.
So perhaps it might.
I was happy with the gloves explanation.
I can hold the idea that nothing is predictable if we go into enough detail, but reality not actually being real strikes me as being a bit of an explanation looking for a problem.
Perhaps it will all become clear after the subsequent programme. But then I think the most predictable outcome in the universe will be that it won't.
So perhaps it might.
Derek Smith said:
I was happy with the gloves explanation.
Me too 
The idea that two particles created at the same time, being then moved to opposite sides of the universe with all that vast distance between them, can then send information to each other instantaneously, to me sounds like there is a mis-understanding of the mechanism at play, or a further set of yet to be discovered tricks being played by nature with the observations. (Like Einstein said - its information being sent faster than light speed).
But the thing is, is that this mechanism has been tested and observed countless times, and the best minds on the planet are still yet to produce a better explanation than the one in play already.
Moonhawk said:
There may not be a defined cutoff point - merely a sliding scale whereby as objects become smaller, quantum effects increase or become more apparent. The double slit experiment for example has been performed on increasingly larger molecules.
http://arstechnica.com/science/2012/03/quantum-int...
Yes, I remember reading something about that last year or so. http://arstechnica.com/science/2012/03/quantum-int...
My knowledge on the subject is limited, although growing via sheer curiosity, but in my mind there must be some region of scale whereby things go from particle nature in to wave-like nature. Like you say its probably a 'sliding scale' of things, but I'm wondering if the sliding scale is a narrow-band or whether its 'linear' or 'exponential' etc.
I think I remember reading something about CERN operating at larger energies next year in that they hope to find observed evidence of higher dimensions, maybe this may shed some light on what is happening?
I caught up with the programme last night. I was very interested in the experiment done towards the end of the programme, showing that perhaps Niels Bohr was "correct" in stating nothing is pre-determined, in contrast to that suggested by Albert Einstein.
Not a great deal was said about the experimental equipment, but I would like to know more and understand more. Can anyone enlighten me as to what was happening in the experiment, and what was being altered between runs and if the result really is correct?
Not a great deal was said about the experimental equipment, but I would like to know more and understand more. Can anyone enlighten me as to what was happening in the experiment, and what was being altered between runs and if the result really is correct?
thatdude said:
I caught up with the programme last night. I was very interested in the experiment done towards the end of the programme, showing that perhaps Niels Bohr was "correct" in stating nothing is pre-determined, in contrast to that suggested by Albert Einstein.
Not a great deal was said about the experimental equipment, but I would like to know more and understand more. Can anyone enlighten me as to what was happening in the experiment, and what was being altered between runs and if the result really is correct?
How one tests is the difficult bit of course. I have to say that I struggled with the logic (or is that a dirty word in quantum physics?) of the tests.Not a great deal was said about the experimental equipment, but I would like to know more and understand more. Can anyone enlighten me as to what was happening in the experiment, and what was being altered between runs and if the result really is correct?
There was a bit in a couple of national newspapers, and also on Sky News, about a university which had concluded that women were half again as likely to drive attentively as men.
I'd just written an article about accident rates broken down by gender and per mile women, age for age except over the age of 65, were more likely, by a factor of 2 at certain ages, to have more accidents per mile driven. (Lots of arguments as to why this is, not for this thread.) The results of the research were sent to me via lots of emails with the demand to EXPLAIN THAT!!!!!!!!!!!!!!!
So I contacted the uni but got no joy. I contacted a journalist who got me the research.
An undergraduate had, for her thesis, decided to discover whether there was a difference in alertness when driving between men and women. The measurement used by the woman was to stand on a bridge over a road and record the number of men and women who drove with the hands at the 10 - 2 position.
It is all down to the method of testing. Before you assess the results, assess the way to them.
thatdude said:
I caught up with the programme last night. I was very interested in the experiment done towards the end of the programme, showing that perhaps Niels Bohr was "correct" in stating nothing is pre-determined, in contrast to that suggested by Albert Einstein.
Not a great deal was said about the experimental equipment, but I would like to know more and understand more. Can anyone enlighten me as to what was happening in the experiment, and what was being altered between runs and if the result really is correct?
It wasn't really explained in the program. But from what I understand the experiment sends two particles out, which have a specific relationship analogous to a pair of gloves, in that once you have measured an attribute of one of the pair this implies what it must be for the other.Not a great deal was said about the experimental equipment, but I would like to know more and understand more. Can anyone enlighten me as to what was happening in the experiment, and what was being altered between runs and if the result really is correct?
So you decide what to look for, check a particle, then check the other one so quickly as to rule out any communication between the two.
If you get a 'left' particle accompanied by a 'right' about half the time, then the particles are preselected and your observations are having no effect.
If you get a 'left' more than half the time, some of which are accompanied by another 'left' then this implies your observations are affecting the first particle you look at but not the other.
Or what actually happened in the experiments. You get a 'left' most of the time and each one is accompanied by a 'right'. This implies that one particle is neither left nor right until you check it, but once you check it this somehow instantly affects the other, 'spooky action at a distance' involving faster than light communication which Einstein didn't like. Or alternatively, and this wasn't mentioned in the program, there is one universe where the particle you look at is a 'left' and the other a 'right' and one where they are the other way about. By looking and identifying a 'left' you are not affecting the experiment but locking yourself into the universe where your particle is a 'left' and the other is a 'right', therefore ensuring you find a 'right' when you look at the other particle.
What jarred with me was that when the program talked about the slit experiment and the interference pattern, it was in terms of the 'possibility' of the particle going through the other slot being what caused the interference. But the interference isn't possible or potential interference, it's actual real visible interference. So to say that the thing that causes it is merely a possibility of something stretches semantics beyond breaking point. Something is clearly going through the other slot, we just don't know what.
Hmm, not sure what bearing this has, however a point did occur to me.
A source is generating discrete photons or electrons and these are being detected after passing through a pair of slits. If we try to detect which slit the particle travels through the wave superposition does not occur.
Does this also apply if we even try to detect the emission of a particle prior to the slits, to put it another way do we only see particles that reach the detector at the far end? Are all of the emitted particles actually being detected or are some lost, can we even tell?
A source is generating discrete photons or electrons and these are being detected after passing through a pair of slits. If we try to detect which slit the particle travels through the wave superposition does not occur.
Does this also apply if we even try to detect the emission of a particle prior to the slits, to put it another way do we only see particles that reach the detector at the far end? Are all of the emitted particles actually being detected or are some lost, can we even tell?
thatdude said:
I caught up with the programme last night. I was very interested in the experiment done towards the end of the programme, showing that perhaps Niels Bohr was "correct" in stating nothing is pre-determined, in contrast to that suggested by Albert Einstein.
Not a great deal was said about the experimental equipment, but I would like to know more and understand more. Can anyone enlighten me as to what was happening in the experiment, and what was being altered between runs and if the result really is correct?
This page describes the experiment:Not a great deal was said about the experimental equipment, but I would like to know more and understand more. Can anyone enlighten me as to what was happening in the experiment, and what was being altered between runs and if the result really is correct?
http://en.wikipedia.org/wiki/Bell_test_experiments
The property being tested was the polarisation angle which is why the presenter was twizzling the filters between each run.
steveT350C said:
I get confused by the logic of an experiment that uses what is, more or less, an analogy. We have the theory that these particles are wave-like because they exhibit the same results as waves unless observed, in which case . . .
Can we only judge these particles against their similarities to other particles or should we just accept that they behave differently, and go by the results?
If a globule of oil behaves in one way, that does not, surely, have anything to do with something totally unconnected with it.
I can appreciate the frustration of an experimental scientist when confronted by something which is, it seems, unmeasurable. How about getting a different ruler?
I was talking to a scientist for an article on petro-chemicals. After the chat, and the, unfortunately fulfilled, promise of sending me the data we had discussed, I mentioned another article I was struggling with on BHP and torque. I was trying to find a way of making it intelligible not only for the readers, but for me.
He said the problem was that the 'ruler' did not give me useful information. He asked me what I wanted to know and I said how fast the car would accelerate and what its top speed was. He then asked if a bhp reading would answer this.
I got his point.
I started the BHP/torque article with two paragraphs on measurement and the editor deleted them. He said it was pointless him paying for 2500 words on a subject I told everyone was pointless.
It seems to me that if we have something we can't effectively describe then we might be making assumptions and measuring the wrong thing.
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