Quantum borders.pdf

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Borders of quantum physicsHenrik Ekerfelt, 2011-05-13

I. INTRODUCTION

The sometimes irrational behavior of quantum systems is considered complex and non-

intuitive. They lack reference in our day-to-day life making them hard to grasp. For many of

us quantum physics is regarded as a non-applicable mathematical theory. While at the same

time, physicists claim that quantum physics is the best tool we have to describe reality. No

other theory can make such exact predictions, but what are the limits? Plancks constant, a

reoccurring figure in most quantum equations, is so small that when one tries to describe

macroscopic objects the quantum effects would be insignificant. Even bacteria remain

unaffected, but what happens if one looks inside the living organisms? Zooming in to a levelwhere the basic process of life is performed, one will be looking at the nanometer scale. Here

quantum phenomena are expected to be directly influential. It is widely debated how much

quantum laws have had a part in the development and the processes of life. While some

scientist claim that there is no advanced underlying quantum mechanism in life, others even

go as far and hypothesize that life itself could be a quantum phenomenon. But what can we

say with certainty so far and what can we expect? In this paper I will discuss the borders

between quantum and classical physics.

II. BORDERLAND

A. Quantum phenomena

When speaking of quantum physics there

are several phenomena involved, and it

remains questionable if all of them end

at the same experimental values.

1. Quantum tunneling

There is a chance for particles to tunnel

through barriers that would be impossibleto cross in the classic world. This

phenomenon is responsible for alpha-decay

and also occurs in everyday electronic

devices to name a few applications.

2. Particle-wave duality

A phenomenon in which all matter can be

described both as a wave and as a particle.

3. Discreteness of quantum measurements

Nature seems to have a finite number ofenergy levels in which a particle can exist.

4. Quantum entanglement

States that if two particles are entangled

one of them cantbe described without the

other. This is the basis of e.g. quantum

encryption and teleportation.

5. The Pauli principle

No two fermions can have the samequantum numbers.

6. Quantum randomness

As of now there is no method to predict the

exact outcome of an experiment. The only

possibility is to calculate the different

probabilities.

B. Experimental environment

When observing the quantum phenomenain an experiment setting scientists most


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likely will use an ultrahigh vacuum and

ultralow temperature which renders an

environment where the quantum effects are

dominant. This makes it possible to

measure the effects. However, one of the

problems is that it leaves the question how

much the quantum phenomena affect the

macroscopic world unanswered e.g. the

process in a living cell. (Arndt [2])

In nature the thermal disturbance makes it

hard to observe the coherence. Interaction

with other particles leads to entanglement,

resulting in collapsed wave function thus

making it hard to define any exact borderfor the phenomena. (Arndt [2])

1. The double slit

It has been more than 200 years since

Young first conducted his famous double

slit experiment (see Fig. 1) proving light

had wave properties, or in his case, that

light was some kind of wave. Since then,

modern physics has been developed at an

increasing speed.

Figure 1. The double slit experiment setup1

.

In the early years of the twentieth century,

Albert Einstein, Niels Bohr, de Broglie,

Erwin Schrdinger and Paul Dirac amongst

others received the Nobel prize in physics

for their contributions to theoretical atomic

physics. They had all contributed to the

theory of quantum mechanics and its

widespread phenomena. In 1929 the first

1http://upload.wikimedia.org/wikipedia/

commons/4/4c/Ebohr1.svg

slit experiments were setup with electrons,

by Davisson and Germer (Davisson [4]),

showing that they, just like light, also

embodies wave characteristics like de

Broglie had predicted.

During the following 70 years, the same

experiment was setup with neutrons, atoms

and dimers, all showing the same expected

results. But how complex can molecules

get before the wave-function collapses?

Theory and experiments shows that if any

information about the particles path is

obtained, the wave function collapses.

In 1999 this experiment was successfully

conducted with fullerenes, a spherical

carbon molecule shaped almost like a

football(see Fig. 2). The fullerene has a

diameter of almost 1 nm which makes it at

least a 100 000 bigger than a neutron. A

comparison between the experimental

results and theory tells us that the

molecule acts as a single heavy particle.

Another interesting aspect is the hightemperature in the molecules during the

experiment, which shows that the thermal

energy does not affect the superposition of

de-Broglie-waves (Arndt [1]).

Figure 2.The structure2.

2

Michael Strck (2006),http://upload.wikimedia.org/wikipedia/commons/4/

41/C60a.png
http://upload.wikimedia.org/wikipedia/http://upload.wikimedia.org/wikipedia/http://upload.wikimedia.org/wikipedia/http://upload.wikimedia.org/wikipedia/


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C. Biology

Studying the borders of quantum

phenomena are especially interesting in

molecular biology since this is where life,

and all its mystery, begins. It is important

to mention that today the scientific society

just has begun exploring this school of

science. There are a lot of hypotheses and

much remains to be scientifically proven or

disregarded. For example some scientists

claim that our consciousness and mind are

too complex to be described by classical

physics.

In a biological environment, quantumtunneling was first shown to appear in

1956 (Marcus [3]). Since then it has been

shown to be a part of the famous

photosynthesis process (Blackenship [5])

and it also plays a part in electron transport

along DNA (Winkler [6]). More recently,

protons have been experimentally proven

to tunnel (Cha [7]). By replacing hydrogen

cores with deuterium (hydrogen with an

extra neutron) cores, it can be shown that

tunneling is part of some processes since

tunneling depends on the mass of the

object. It has also been suggested that

small molecules, consisting of a few atoms

only, possibly could tunnel but this theory

still lacks supports from experiments

(Arndt [2]).

Another widely discussed topic is quantumtunneling being a part of our sense of

smell. The functions of the receptors are

well defined by classic laws but some

questions remain, e.g. how mankind are

able to distinguish particles with similar

size and characteristics, like OH and SH

(Turin [8]).

Entanglement has recently been shown to

persist in macroscopic thermal states(Markham [9]) and can be traced in the

thermodynamic variables. Despite the fact

that there is a large loss of information

compared to single atomic measurements it

remains a very interesting discovery since

it shows that entanglement influences the

thermal state.

1.Photosynthesis

This widely known process that converts

carbon dioxide into sugars by absorbing

light is one of the basic facts about life, yet

the specifics remain to be discovered.

There are different kinds of photosynthesis

on earth but common for all is that they

absorb sunlight and turn it into chemicallybound energy. As evolution has developed

this process over millions of years, it might

not be very surprising that it serves as a

role model for todays scientist when they

try to create solar cells (Blankenship [10]).

The more we study this process the more

we learn that it involves more complex

processes than we imagined. For example

theres long ranged excitation transfer,hydrolysis (water is turned into hydrogen),

proton transport, redox-reactions

(molecules have their oxidations number

changed) and phosphorylation (a process

that activates or deactivates enzymes).

Some of these may actually require

coherence, tunneling or entanglement to be

described fully. Worth mentioning is that

all of these processes are extremely fast,measuring just a few femtoseconds

(Brixner [11]).

First, in photosynthesis a photon is

absorbed by a pigment molecule. Then the

energy is used to excite an electron which

begins a very complex chain of energy

transportation. All resulting in chemical

potentials. Studies show that this transport

is much optimized. A quick process is vitalsince any kind of delay most probably


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would result in thermal instead of chemical

energy (van Grondelle [12]).

Attempts to explain this with classical

physics fail to explain the speed efficiency

of the transport. Delocalization and

coherent excitation between the pigment

proteins has been suggested as the most

likely explanation (Arndt [2]). Coherence,

lasting for as long as a few hundred

femtoseconds over the width of several

nanometers, has been observed in

laboratories (Collini [13]).

What part does the constructive/destructive

interference play?

In fact this process is so efficient that it has

been considered that quantum information

processing is used, could some kind of

quantum algorithm provide the information

on the fastest route? (Engel [14]) Another

suggestion is quantum random walks,

where the positions of the random walker

would be a superposition of positions(Mohseni [15]).

2. Evolution

In 1988 John Cairns wrote an article on the

spontaneity of mutations. He suggests that

mutations might not be entirely random.

Supporting his suggestion is an experiment

which shows that starving bacteria have a

higher mutation rate than those fed. This

indicates that there might be somethingtriggering evolution (Cairns [16]).

In the book Darwins black box, the

biochemist Michael J Bethe mentions

irreducible complexity. Here he claims that

there are some things that are too complex

to have evolved e.g. the human eye and the

bacteria flagella. He states that if just one

part is removed they will be useless. The

existence of simpler eyes e.g. light

sensitive cells makes this statement

questionable. (McFadden [17])

However he also mentions the chemical

processes surrounding ATP (An energy

transporter in the living cell). To the best

of our knowledge, the only way to make

ATP is from another molecule called

AMP, which requires a thirteen step

process each involving a specific enzyme.

If one step is skipped it will be entirely

useless. This is a problem for todays

evolutionary biologists. How could this

have evolved? Some suggests that it

happened backwards, AMP could haveexisted in the primordial soup and when it

ran out there was first a one step process to

create it, and then two steps, etc.

(McFadden [17]))

McFadden on the other hand said this is

highly unlikely since nothing supports the

fact that AMP would have existed in

sufficient amounts. Instead he suggests

quantum physics has a big role to play inevolution (McFadden [17]).

3. Mystery of life

The biggest mystery of life is the question

about how it all started, how did life really

begin? The smallest self-replicating

molecule found by scientists contains 32

amino acids. Assuming that, even though

its highly unlikely, the amino acids only

could bind with other amino acids in the

primordial soup, there would be

possible proteins. This fact would suggest

that occurrence of life is very unlikely

(McFadden [17]).

Taking into account that it seems as if life

sprung into existence as soon as it was

possible (when earth cooled down and

primordial soups existed) this doesntmake sense. Indicating that there should be


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something with the beginning of life that is

yet to be discovered (McFadden [17]).

III. DISCUSSION

I expect that sooner rather than later,

quantum physics will be a widely accepted

part in the process of life. To what extent it

influences is hard to tell, but personally I

find it hard to believe that quantum physics

wouldnt play a vital part. Today our

knowledge of its part is limited to just a

few molecules, but is it possible that there

could be a bigger picture here as well? One

could interpret the facts McFadden discussin his book as if the bigger picture actually

exists. Still the whole idea is still on the

hypothesis stage with few experiments

supporting it.

Maybe this topic will be one of the most

investigated topics in the twenty-first

century, who knows what will be found?

IV. CONCLUSION

The subject seems to have an increasing

popularity throughout the scientific

society. There are a lot of hypotheses on

the subject, some more believable than

others. Too few are tested, or could be

tested, experimentally yet. In the following

100 years, we may expect the picture of

what life is will change.


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3.Marcus, RA (1956). Theory of oxidation-reduction reactions involving

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4. Davisson, C.J. Germer, L.H. The scattering of

electron by a single crystal of nickel. Nature 119,

558-560 (1927).

5. Blankenship, RE (1989). Special issue -

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