The Secrets of Quantum Physics BBC4

[french frank]

The problem with all this is that the coin analogy isn't very good

I was handling duff goods, then. I thought that a bit of imagination might make some sense of it, given the unreal world of QM (sound of one hand clapping?). Yes, passports work, except that people or 'intelligences' are more susceptible to jiggery pokery than particles.

I hope Paul Dirac comes into next week's programme. He went to primary school just up the road. Same as Cary Grant. And my father. What are the odds of that, then?

[Gordon]

....It occurred to me that awareness of the different colour of heated metals precedes the light bulb by several thousand years of metallurgy.

Of course any blacksmith from the last several thousand years could tell you that a hotter metal is less red/yellow that a cooler one but what did any of them do about it except use the light to sense the right time to work the metal. The light bulb was just a means of illustrating the problem; it wasn't that the invention of the bulb itself suddenly revealed it but the fact that electricity was being used to cause the bulb to light up, more electricity whiter light. The connection between electricity - more voltage, more energy in the electrons, more ease of release of higher energy photons hence whiter light. No blacksmith made that connection.

This light bulb demonstration although intended for the UVC was also indicative of the photoelectric effect but he used the spark gap instead. The sparks also emit radio waves predicted in 1864 by Clark-Maxwell and discovered in sparks by Hertz in 1888. He could have used the idea of the behaviour of metals to describe the photoelectric effect, avoiding the use of sparks. Telegraphists in the early part of the 19th century used Selenium as part of the circuit to tune up their apparatus. Selenium is a light sensitive metal whose resistance varies if you shine light on it and behaves just like the spark did in being selective about the wavelength of the light. Perhaps a spark is more exciting to a television audience.

I googled "Helium the three body problem" which is I think a reference to the mechanics of any 3-body problem compared to the relative simplicity of the hydrogen atom, whose emission lines were a factor in the acceptance of Planck's ideas.

Certainly Planck's quantum idea explained why atoms have the emission and absorption spectra that they do and this helped to demonstrate that the sun was made of Hydrogen and Helium.

My experience of the "three body problem" was in mechanics where 3 massive bodies in common rotation around each other is hard to describe mathematically. How does that relate to Hydrogen atoms and Helium? I googled the phrase and did not find much. However there is a quantum 3 body preoblem which is easier to solve than the mechanics one. Because there is only 1 negative electron and two positive protons [the 3 bodies] - the latter repelling each other but each attracting the electron - the forces are disposed differently and because quantum rules dictate the properties of the bodies [unlike massive uncharged ones] the problem is not the same.

One thing though, completely wrong, was the shadow of his hand, NOT diffraction ( he said "bending") of the light waves as they pass your hand, that only applies if the shadow-casting object is of similar wavelength to light e.g. an eyelash. The fuzziness of the shadow is because the sun is not a point source of light but a disc. Compare the hard-edged shadows of spotlights in a theatre with the softer-edged shadows of floodlights.

Yes that explanation was less than convincing. The fuzziness of the shadow was in most part the umbra/penumbra feature of a sun which is not a point source as you say. However, a degree of diffraction will always occur when light [or any EM wave such radio] passes over a solid body but does so most markedly when the object has fine sharp edges [not a rounded fuzzy surface] and when the radius of the edge is comparable to the wavelength. Light wavelengths are measured in hundreds of nanometres eg Red is about 700 nM [a billionth of a mter] and Blue about 400 nM. A human hair diameter is about 50,000 nM, 100 times larger than blu-ish light. True diffraction wasn't happening.to any significant degree. It did help that his hands were a short distance from the wall, the closer they were the sharper the shadow boundary.

[Gordon]

I was handling duff goods, then. I thought that a bit of imagination might make some sense of it, given the unreal world of QM (sound of one hand clapping?). Yes, passports work, except that people or 'intelligences' are more susceptible to jiggery pokery than particles.

I hope Paul Dirac comes into next week's programme. He went to primary school just up the road. Same as Cary Grant. And my father. What are the odds of that, then?

Not a matter of odds FF just entanglement, they knew what to do all the time!! I bet your dad parted his hair on the right BUT Dirac did so on the left!! Always. Must have a look at a Cary Grant film to see which way he parts his hair [the right].

[Gordon]

With this brief exposure to some science on the tele, next year is 2015 and no doubt Magna Carta and Waterloo will feature in the schedules as will the continuing story of WW1.

What about Einstein's General Relativity published in 1915? Just as important and influential in many ways as those other events in history.

[french frank]

Right, leaving the analogies behind since they don't prove anything anyway - they just illustrate what would be happening if the theory is correct (as RT found out with his spinning coins): what about Bell's equation and the way it was solved:

What, exactly, were the figures measuring? And what is the difference between positive and negative results (as aeolium mentioned above)? Normally, if you add figures which include a negative, you subtract it. In JaK's example it seems to have been both treated as a negative AND subtracted, making it positive.

If I were adding 0.56, 0.82, -0.59 and 0.56, I would make it 1.35 - less than 2; JaK made it 2.53 - more than 2.

So I assume it's something to do with what is being measured? (Sorry, I'm not a mathematician Don't bother, if it's too complicated to explain ).

[Gordon]

Right, leaving the analogies behind since they don't prove anything anyway - they just illustrate what would be happening if the theory is correct (as RT found out with his spinning coins): what about Bell's equation and the way it was solved:

What, exactly, were the figures measuring? And what is the difference between positive and negative results (as aeolium mentioned above)? Normally, if you add figures which include a negative, you subtract it. In JaK's example it seems to have been both treated as a negative AND subtracted, making it positive.

If I were adding 0.56, 0.82, -0.59 and 0.56, I would make it 1.35 - less than 2; JaK made it 2.53 - more than 2.

So I assume it's something to do with what is being measured? (Sorry, I'm not a mathematician Don't bother, if it's too complicated to explain ).

If you look at the board on which JaK was writing down the results of his laser experiment there were 4 terms that needed to add up to less than or equal to 2 [the equation is derived from Bell's]. The third term was itself negative ie you SUBTRACT that term's value from the sum of the other three.

If that term had been positive then you surely would subtract it. But the experiment produced a negative number [your -0.59] and so, with the term being SUBTRACTED from the total of the 3 positive terms; mathematically a subtraction of a negative number is ADDITION so it does add up to more than 2.

So: SUM = 0.56 + 0.82 -(-0.59) + 0.56 = 0.56 + 0.82 + 0.59 + 0.56 = 2.53. You ADDED them all directly without changing the signs correctly.

What was being measured? The property that was being measured was the polarisation of the photons from a laser source. The crystal he described splits the laser beam into two with opposite polarisations and these two beams are taken to 2 detectors that respond only to those opposite polarisations, one to each. The equipment set ups just changed the rotations of the polarisations of the 2 beams to produce different conditions of the particles when they reached the detectors.

Those results that the detectors reported were an accumulation of a large number of particles [photons, ie light] being passed through the equipment expressed as the correlation among those many measures, ie to what degree do the 2 detectors observe all those oppositely polarised particle pairs behaving in the same way in each experimental run. The equipment used 4 different set ups of the detectors, each set up measuring a different alignment of the particles corresponding to the 4 terms of the equation. Correlations, like probabilities, are always less than 1.

Polarisation is a property of light and radio waves - look at the TV aerials around your home and most will be horizontally aligned and point the same direction [probably south to Mendip transmitter where you are] but there may be some that point somewhere else and will be aligned vertically. That's because some transmitters send the wave to you "vertically" polarised and others "horizontally" polarised. It has to do with isolating the transmissions from each other to avoid mutual interference. The horizontal aerial can't "see" the vertical signal and vice versa.

The detectors in this experiment would be the same as the aerials; one detector sees one polarisation but not the other and vice versa. All those particles that are sufficienty aligned with a given detector will pass and be counted, all others will not. By changing the polarisations en route [the set ups] in each experimental run the detectors will see different counts.

[french frank]

If that term had been positive then you surely would subtract it. But the experiment produced a negative number [your -0.59] and so, with the term being SUBTRACTED from the total of the 3 positive terms; mathematically a subtraction of a negative number is ADDITION so it does add up to more than 2.

So: SUM = 0.56 + 0.82 -(-0.59) + 0.56 = 0.56 + 0.82 + 0.59 + 0.56 = 2.53. You ADDED them all directly without changing the signs correctly.

Sorry, I'm afraid the explanation simply restates the precise point that puzzled me: I was ADDING four numbers together, so there was no case of subtracting a negative number (which would of course have become positive) whereas if you ADD a negative number it's a straightforward subtraction in most calculations. That was the point that troubled me. To me it just looks like subtracting it twice. I think I'm not mathematically advanced enough to understand that .

[Gordon]

Sorry, I'm afraid the explanation simply restates the precise point that puzzled me: I was ADDING four numbers together, so there was no case of subtracting a negative number (which would of course have become positive) whereas if you ADD a negative number it's a straightforward subtraction in most calculations. That was the point that troubled me. To me it just looks like subtracting it twice. I think I'm not mathematically advanced enough to understand that .

HMM!! Perhaps just following the rules and not trying to involve intuition would help!! We all do it from time to time.

Try thinking about the + and - signs not as Subtraction or Addition but as operators telling you what to do. A negative followed by a negative cancels?

The double negative is clear enough in text and common speech isn't it? EG "I don't disagree", it resolves to "agree" but we use it in speech because we seem to want extra logical states to escape FULL agreement/disagreement whilst not then taking the obvious opposite state of DISAGREE/AGREE. That is the states are: FULL AGREE, Don't Disagree, Neutral [neither one or the other], Don't Agree, FULL AGREE. In the trade this is called Soft Decisions!!

[french frank]

You've lost me somewhere

If you have to ADD four numbers together, a + b+ c+ d, where a=1, b=2, c=-3 and d=4, you would say the answer was 10 and I'd say it was 4? I presume, in that case, you'd 'agree' that it was 4?

(Did you mean FULL DISAGREE at the end, or are you flummoxing me again!?)

[Gordon]

You've lost me somewhere

If you have to ADD four numbers together, a + b+ c+ d, where a=1, b=2, c=-3 and d=4, you would say the answer was 10 and I'd say it was 4? I presume, in that case, you'd 'agree' that it was 4?

Ignoring signs the sum of numbers makes 10, yes. However the correct answer is 4.

(Did you mean FULL DISAGREE at the end, or are you flummoxing me again!?)

Mea culpa!!! I should have said FULL DISAGREE in the last one!! Well spotted. No, I wasn't trying to flummox, just being lax. Would I do that to you?

[french frank]

No, I wasn't trying to flummox, just being lax. Would I do that to you?

I think you have been doing that right royally!

[clive heath]

On a bank statement 1,2, and 4 would be credits. money paid in, and 3 would be a debit, money paid out. Balance?

[ferneyhoughgeliebte]

If you look at the board on which JaK was writing down the results of his laser experiment there were 4 terms that needed to add up to less than or equal to 2 [the equation is derived from Bell's]. The third term was itself negative ie you SUBTRACT that term's value from the sum of the other three.

If that term had been positive then you surely would subtract it. But the experiment produced a negative number [your -0.59] and so, with the term being SUBTRACTED from the total of the 3 positive terms; mathematically a subtraction of a negative number is ADDITION so it does add up to more than 2.

I've read this section about seventeen times, Gordon, but I can't follow why (when a negative number results) we no longer add it (in other words, subtract it because it's a negative) but suddenly have to subtract a subtraction (in other words, add it as if the result hadn't been a negative in the first place) . Why do we "surely" subtract a positive when we've been told we should be adding the four bits up?

[ferneyhoughgeliebte]

SUM = 0.56 + 0.82 - (-0.59) + 0.56 = 0.56 + 0.82 + 0.59 + 0.56 = 2.53.

In other words, where has this extra minus sign suddenly come from? Why isn't it a plus sign like all the others?

[french frank]

In other words, where has this extra minus sign suddenly come from? Why isn't it a plus sign like all the others?

I didn't like to pursue that point ....