Big Questions in Science

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http://www.upscale.utoronto.ca/PVB/Harrison/SternGerlach/SternGerlach.html

Stern-Gerlach experiment

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Superpositions of electrons:

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Radiatioactive decay is random. Same true for photon emission by atom:

unpredictable.

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Traveling wave Frequency (and velocity) well-defined

Position ill-defined

Wave pulse Position well-defined

Frequency (and velocity) ill-defined

Planck’s constant:

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Planck’s constant:

The larger the object, the smaller the uncertainty.

For large objects, probabilities are sharply peaked.

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Big Questions in Science, fall 2012. SdH, AUC

Quantum physics seem to have bearing on music as well. Anyone who's ever played in a blues band will confirm that, while you know where the drummer is (in the pub), there's no way of knowing what time he will show up for rehearsal (or sound check, or whatever). This is known in quantum mechanics as Heisenberg's Uncertainty Principle : "The more precisely the POSITION is determined, the less precisely the MOMENTUM is known".

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• First bank transfer encoded via quantum crypto for entangled photons

• Information via glass fiber cable from Vienna City Hall to Bank Austria Creditanstalt branch office “Schottengasse”

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“God does not play dice”

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Determinism: “I would always be able to keep my

deterministic faith for fundamental phenomena” (Lorentz)

Causality Can compute, but what does it mean? “If I am not

satisfied with current state of problem it is because I do not understand yet physical meaning of its solution. What Heisenberg has said is mathematically unexceptionable, but the point in question is that of physical interpretation” (Schrödinger).

“Anschaulichkeit”: “The way Dirac has formulated

Schrödinger’s theory [leads to] a more advanced renunciation of Anschaulichkeit, a fact very characteristic of symbolic methods in quantum theory” (Bohr).

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• No influences faster than light. • Particle must have velocity

before measurement. • Violation of • Quantum mechanics is

incomplete.

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Einstein:

There is no faster-than-light interaction in this experiment.

Experimental set-up defines the meaning of ‘velocity’.

Change in position: from ‘to measure is to interact’ to ‘measurement context’.

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Faster-than-light interaction is not needed. We only have correlations.

Entanglement: particles correlated and system behaves as a whole rather than sum of parts.

Bell’s theorem (‘64): If velocities defined before measured, this implies certain inequality. QM violates this: experiment confirms quantum mechanics (Aspect ‘82).

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• First bank transfer encoded via quantum crypto for entangled photons

• Information via glass fiber cable from Vienna City Hall to Bank Austria Creditanstalt branch office “Schottengasse”

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Record: 144 km in La Palma, Tenerife

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Share a randomly generated key

110100010 110100010

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Can be used for secure communication. Eavesdropper destroys correlations.

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Photons:

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Interference means change No possible ‘unvisible’ eavesdropper Applications:

Banking

Confident information

Collaboration fundamental research with industry (and government).

Key feature: entanglement (“spooky action at a distance”)

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Counter-intuitive aspects: “If you are not confused by quantum physics then you

haven’t really understood it.” (Niels Bohr) “I think I can safely say that nobody understands

quantum mechanics.” (Richard Feynman). After WWII: “Shut up and calculate”. Imposed by increasing numbers of students: “Such

classroom numbers, Berkeley’s department chair exclaimed to his dean, were ‘a disgrace and should not be tolerated at any respectable university’… The larger the class, the less time spent talking through the big issues.” (David Kaiser)

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Complementarity: waves and particles Interference, superpositions Heisenberg’s uncertainty principle

Probability No determinism Applications: cryptography, quantum computing

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Modern science

Time and relativity

Radiation and QM

Atoms, forces

Our cosmic origins

Classical physics

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Outline (or summarize in a diagram) EPR’s line of argument against quantum mechanics.

What where they contending?

Describe the experiment in a few lines.

What were the key concepts and what do they mean?

What assumptions did they make?

How did they arrive at their conclusion?

Can you reformulate the paradox in terms of spin?

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Download from BB: “Transgressing the Boundaries”. Skim through the paper. Have a quick look at the

introduction and first section. Questions: 1. What is, according to the introduction, the relation

between physics and power? 2. What is the announced aim of the paper? 3. Do the sections have any particular structure

(argumentative, logical, etc.)? 4. Are any of the suggested arguments convincing? 5. What, in your opinion, is the author trying to argue?

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