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 slit2 second slit

Two-Slit Experiment - Interference Patterns -- Prove Light is a Wave

Only wavescan do this!

Try it with rocksin water

Light source

Two-slits

Light and Dark InterferencePattern

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.

lightsource

does it look like a particleor a wave?

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 discreteorbits

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 numberof waves can fitaround the atomicnucleus -- NO partials allowed.

This is explained by quantum physics!

No need for God of the gaps.

deBrogliediscovered 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

DxDp > 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 ---- DeDt > 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

MeasurementDetector

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 onceeven 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

Various Interpretations of QM

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 DecaysSpontaneously

13N 13N

Picture of Schrodinger's Cat

Quantum Weirdness - The Double Slit Experiment - wave interference

Quantum Tunneling

Classical Physics

Quantum Physics

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

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.

The Bohr Atom

Interpretation

Copenhagen interpretation

de Broglie-Bohm theory

von Neumann interpretation

Many-worlds interpretation

Deterministic?

NO

Yes

NO

Yes

Hidden variables?

NO

YES

NO

No

Local?

NO

No

No

Yes

Abox

Bradioactive element

CGeiger counter

Dbreaker

Epoison

Fcat

G & Hobservers