Quantum Implications 07262011

Gary Stilwell The Implications of Quantum Physics Uncertainty and Entanglement

Quantum Physics is the physics of the microscopic world - that of the elementary components of reality. Quantum Physics

Why Quantum Physics? At the turn of the last century all appeared well with physics. We had: Newton's laws of mechanics (force and motion) Thermodynamics (heat) Electromagnetism (light) These three broad areas seemed to explain the real world. And, everyone now knew that matter was made of atoms and light was made of waves . Then, things began to fall apart.

Why Quantum Physics? - cont. In 1900, Lord Kelvin gave a lecture at the Royal Institution in which he acknowledged that there were "two dark clouds " on the horizon of classical physics: In what medium did light wave? the ether? Why did "black body" thermal (heat) radiation not behave as it should? where was the predicted ultraviolet radiation, since waves should carry any amount of energy? The physics of the time could not address these problems!

Why Quantum Physics? - cont. Max Plank, working on the black body problem, wondered why the "ultraviolet catastrophe" did not happen, since a wave can carry any amount of energy. He was forced to hypothesize that light must behave as a discrete particle. Each particle is so small that it cannot carry an unlimited amount of energy, thus avoiding the catastrophe. His hypothesis "solved" the problem - but how, since light had been proven to be a wave? The " dark clouds " were the forerunners of Quantum Physics

We Have a Light Dilemma Newton (1600s) had said that light was particles Christian Hygens (1600s) had proposed waves *Thomas Young (1800) had proved it to be waves by the famous two-slit experiment Max Plank solved the black body problem by claiming it to be a particle Albert Einstein (1905) explained the photoelectric effect by showing light to be a particle So, what is it? It's a Particle !??

*Young's 1800 Two Slit Experiment Light source 1 first slit 2 second slit

Two-Slit Experiment - Interference Patterns -- Prove Light is a Wave Only waves can d o this! Try it with rocks in water Light source Two-slits Light and Dark Interference Pattern Diffraction - bending around corners

Two Slit Experiment - dim the light so only one photon at a time goes thru a slit Even at one photon present at a time , the interference pattern will still build up. Somehow, while in flight, each photon seems to 'know' about both slits !!! Close one slit and the interference pattern will not develop. does it look like a particle or a wave? light source

It's a Wave When light passes through both slits the resulting waves interfere with each other This is the same interference pattern we see with water waves If the light passes through only one slit, then there is no interference pattern

It's a Wave - John Wheeler's 'delayed decision experiment' What if I choose to close one slit AFTER the photon is in-flight? Detection of a photon even after passing through a double slit would be sufficient to change the outcome of the experiment and the behavior of the photon. Therefore, if the observers know which slit it goes through, the photon will seem to respond even to our delayed choice instantly and retroactively and behave as a particle, rather than as a wave. can a change in the present affect the photon's decision in the past as to behave as a particle or a wave??? Quantum measurements interject our consciousness into the arena of the so-called objective world . Violates causality? No, if you are willing to give up on the idea that there is a fixed and independent material world even when we are not looking at it!

It's a Particle (like a ball) If we look at the light with a photon detector, then we see a particle - if we don't try to detect it, it acts like a wave This is true even if the light passes through one or two slits We can demonstrate the wave or particle properties of light by changing the type and location of our measuring device We get what we are looking for!

Actually, It's Both The light 'knows' when to behave as a wave or when to behave as a particle -- depending on what is looked for!! [looking (measuring) destroys the interference pattern by collapsing the wave function *] Does it really depend on we the observer? Conscious choice shapes manifest reality! Light will never show both properties simultaneously This is the famous wave-particle duality of the Copenhagen Interpretation where Bohr's principle of complementarity says that the wave and particle aspects complement each other *represents quantum probability waves

It Gets Worse - Matter is Also Both Light (a photon) is energy , so we might buy in to this duality thing But matter ? How does a bowling ball show wave and particle aspects? Electrons fired at a two-slit experiment show exactly the same kind of schizophrenic behavior as light So a matter particle can be viewed as a wave - just like a photon particle can be viewed as a wave This will explain a "weird" implication in the atomic model ---

The Bohr Atom in 1913 (Solar System Model) Bohr used quantum mechanics to show why the atom was stable Classical physics said that the electron should spiral into the nucleus Why didn't it??? Energy comes in discrete amounts (quanta) - until the electron gains or loses enough energy, it will stay in its orbit - then JUMP to another!

Bohr Atomic Model This model allowed only discrete orbits Electrons radiate or absorb light waves only when jumping from one orbit to another This jumping became known as the quantum leap - going from one orbit to the next without going though the intermediate space between orbits HOW? God of the gaps? photon photon

The Electron (A Particle) is Also a Wave! This concept explained why Bohr's atom model worked Only a whole number of waves can fit around the atomic nucleus -- NO partials allowed. This is explained by quantum physics! No need for God of the gaps. deBroglie discovered that matter was a wave Quantum Leap Solved

Quantum Weirdness Now, it really gets weird! Superposition - could be here, could be there Uncertainty - can't know both position and velocity (momentum) Effect on the Macro World -- Schrodinger's Cat Entanglement - quantum wholeness and non-locality

Probability Wave Function Since the position can be spread out - the photon is at all positions - known as superposition .

Superposition - could be here, could be there Which slit did the electron or photon go through? Both! Until we actually detect the electron, it is in a superposition state, neither here nor there , but with a probability of being found here and a probability of being found there. The wave amplitude squared gives the probability. Reality consists of two kinds - actual and potential. A quantum entity exists in multiple possibilities of realities known as superpositions. Upon detection (by a measurement) the superposition state ceases to exist and the wave function is said to collapse . Therefore the observer and the observed are inextricably intertwined!

Heisenberg's Uncertainty Principle Quantization means that we cannot observe the universe without affecting it. We observe by shining light on the subject. If the subject is an electron, the light will bounce off and change its speed and direction. Therefore we can't get precise momentum ( p=V x M) Lower the energy of the light to reduce the bounce and now the longer wavelength (lower energy) can't pinpoint the electron's position ( x ). If you make velocity measure more precise, you lose information about position - and vice versa! The Uncertainty is REAL - the particle does not have a position or momentum until measured - until then, it is a wave. [Same applies to TIME and ENERGY ]

The Indeterminant Universe D x D p > h uncertainty in position times uncertainty in momentum > plank's constant (see next slide) Remember Newton's Deterministic Clockwork Universe? Homer's Fates? The Greek and Roman Stoics? Similarly - St. Paul and Calvin's Predestination? A MAJOR Implication of QP -- Determinism is gone with Quantum Physics!!

Other Implications - so far The Uncertainty Principle's Implications: An electron in an atom exists in a standing wave in a small space, therefore its momentum is very uncertain. A particle can never have zero energy - minimum is called zero-point energy There is no perfect vacuum - empty space is full of zero-point energy This energy demands that there be spontaneous appearance of particles out of "empty space" [ quantum fluctuations ] These particles are called virtual particles They trade energy for time ---- D e D t > h --------------- Planck's Constant = 6.63 x 10 -34 kilograms per square meter per second A thrown baseball - we could know position & momentum to 16 decimal places

Einstein thought that hidden variables, associated with the entangled particles, gave them deterministic rules. He was convinced that there must be physically real things that cannot be described by QM He used entanglement to argue that QM had to be incomplete Einstein said "QM is incomplete"

Einstein and Bohr - Einstein did not like the uncertainty (indeterminism) of QM - "God doesn't play dice" The EPR Experiment - Tried to disprove Uncertainty Einstein, Podolsky, and Rosen claimed that: entanglement + locality hidden variables Bell's Theorem - Faster than light? Aspect's Experiment - All is One? Entanglement - Quantum Wholeness and Non-locality

EPR, Bell, Aspect Einstein argued for determinism against Bohr. Devised EPR [variations done on spin ] experiment to refute " spooky-actions-at-a-distance " and Uncertainty. A B C D Measurement Detector Entangled Particle At Time At time D, Bob measures position At time D Alice measures momentum and then knows position is exactly opposite Bob's - therefore knows both with no UNCERTAINTY.

Spooky action at a distance is a fact! A diagram of the preceding experiment using electron spin - if D1 is spin UP, we know that D2 must be spin DOWN Looks good. Why not? Emission Detection 1 Detection 2

Remember that until measured, they have no particle attributes. If 2 particles are in an entangled state, neither particle has a definite quantum state of its own. 2 entangled particles are regarded as a single system - not 2 systems If we measure particle 1, particle 2 gains a definite state at once even if they are far apart. -- but not due to hidden variables! Bohr said "not so"

Bell's Theorem and Aspect's Experiments Bell (1964) showed mathematically that quantum theory predicts different measurements than classical physics would on the EPR - type experiments. Local hidden variables* are incompatible with QM Any hidden variables must reside in a world outside of space-time Gave two choices: give up determinism (hidden variables), or allow instantaneous influence over distances (non-locality) Aspect (1982) confirmed quantum indeterminacy and non-locality** by experiment. ------------------ *Einstein thought there must be hidden variables, behind the scene, that control the particles and determine their trajectories - he was wrong. **Non-locallity means that there is an instantaneous influence or communication without any exchange of signals through space-time - confirmed Locality says that all interactions among objects occur via fields or signals that propogate through space-time obeying the speed limit of light - only true in classical reality

Quantum Connectedness Implication: The Universe is somehow connected A particle here does affect a particle there even if they are miles (or light years !!) apart What connects them?? An electromagnetic signal (light)? no, Relativity Hidden Variables? no, proved to not exist by Bell and Aspect Non-local instantaneous message? yes, proved by Bell and Aspect but HOW? Something transcendant to time and space??

Implications We've seen several implications already. These follow from the experiments: - Whatever reality is, it must be non-local that transcends local space-time . - The experiments indicate the existence of an invisible non-local reality . - If waves, spread out over vast distances, instantly collapse when measured, the influence of our measurement is not traveling locally . - The world is not determined by initial conditions, once and for all, and every event of measurement is potentially creative and may open new possibilities . - Before these experiments, one could still argue that a local signal between the particles, unbeknownst to us, was mediating the influence, which was thereby strictly obeying material realism.

Implications - cont. - It is your observation that collapses the wave function of one of two correlated particles in the experiment, forcing it to take on a certain state [spin, position, momentum, polarization]. - The wave function of the correlated particle also collapses immediately . We will now cross over to the twilight zone into the realm of philosophy!

- A consciousness that can collapse the wave function of a particle at a distance instantly must itself be non-local . What does that say about consciousness? - Instead of non-locality being a property mediated by superluminal signals, or hidden variables, one could posit that consciousness operates in some substratum of the world which lies beyond the world of phenomena. Are we sure that material realism is correct? What if the basic stuff of the universe is consciousness? Implications - cont.

QT Defies Common Sense and Understanding "If you are not confused by Quantum Physics then you haven't really understood it" Niels Bohr "Common sense is the deposit of prejudice laid down in the mind before the age of 18" Albert Einstein

END Discussion? Some slides follow for optional discussion

The Photoelectric Effect Einstein to the rescue again: In 1905 he explained that light is not a wave with the energy spread out, but rather a concentrated particle-like 'bundle' of energy - photons A photon hits an atom and can knock an electron out For high energy photons, the ejection occurs at once For low energy photons, an electron will not be ejected counter intuitively, color matters, intensity does not We have now described the quantum and the quantum jump

Schrodinger's Cat Example Can superposition affect the our macro world? The cat experiment asked that question. Cat in box with radioactive atom with 50% random probability of decaying in the next hour. If it decays, a Geiger counter clicks and releases poison. After an hour is the cat dead or alive? According to Copenhagen - the entire box and contents are in a state of superposition until we look in the box. The cat is both dead and alive!!

QT - Probability of Decay 1 - Two Nuclei 2 - One Decays Spontaneously 13 N 13 N

Quantum Weirdness - The Double Slit Experiment - wave interference

Quantum Tunneling Tunneling accounts for radioactivity - a spontaneous emission of a particle from a nucleus Classical Physics Quantum Physics

Bell's Theorem and Aspect's Experiments Bell (1964) showed mathematically that quantum theory predicts different measurements than classical physics would on the EPR - type experiments. Local hidden variables* are incompatible with QM Any hidden variables must reside in a world outside of space-time Aspect (1982) confirmed quantum indeterminacy and non-locality** by experiment. *Einstein thought there must be hidden variables, behind the scene, that control the particles and determine their trajectories - he was wrong. **Non-locallity means that there is an instantaneous influence or communication without any exchange of signals through space-time - confirmed Locality says that all interactions among objects occur via fields or signals that propogate through space-time obeying the speed limit of light - only true in classical reality

Spooky action at a distance is a fact! A diagram of the preceding experiment using electron spin - if D1 is spin UP, we know that D2 must be spin DOWN Remember that until measured, they have no particle attributes.

Quantum Implications 07262011

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Quantum Implications 07262011