MOTION MOUNTAIN

the story of the brain 247
Challenge 249 ny
Challenge 250 s
Ref. 221
Obviously every record is an object. But under which conditions does an object qualifyasarecord?Asignaturecanbetherecordoftheagreementonacommercialtransaction.Asinglesmalldotofinkisnotarecord,becauseitcouldhave
appeared by mistake,
for example by an accidental blot. In contrast, it is improbable that ink should fall on
paper exactly in the shape of a signature. (The simple signatures of physicians are obviously
exceptions.) Simply speaking, a record is any object, which, in order to be copied,
has to be forged. More precisely, a record is an object or a situation that cannot arise nor
disappear by mistake or by chance. Our personal memories, be they images or voices,
have the same property; we can usually trust them, because they are so detailed that they
cannot have arisen by chance or by uncontrolled processes in our brain.
Can we estimate the probability for a record to appear or disappear by chance? Yes, we
can. Every record is made of a characteristic numberNof small entities, for example the
number of the possible ink dots on paper, the number of iron crystals in a cassette tape,
the electrons in a bit of computer memory, the silver iodide grains in a photographicnegative,
etc. The chance disturbances in any memory are due to internal fluctuations, also
called noise. Noise makes the record unreadable; it can be dirt on a signature, thermal
magnetization changes in iron crystals, electromagnetic noise inside a solid statememory,etc.Noiseisfoundinallclassifiers,sinceitisinherentinallinteractionsandthusin
all informationprocessing.
Itisageneralpropertythatinternalfluctuationsduetonoisedecreasewhenthesize,
i.e.,thenumberofcomponentsoftherecordisincreased.Infact,theprobabilityp mis for
amisreadingormiswritingofarecordchangesas
p mis ∼1/√N , (93)
whereNisthenumberofparticlesorsubsystemsusedforstoringit.Thisrelationappears
because,forlargenumbers,theso-callednormaldistributionisagoodapproximationof
almostanyprocess.Inparticular,thewidthofthenormaldistribution,whichdetermines
theprobability ofrecorderrors,growslessrapidly thanitsintegral whenthenumber of
entitiesisincreased;forlargenumbers,suchstatementsbecomemoreandmoreprecise.
Weconcludethatanygoodrecordmustbemadefromalargenumberofentities.The
largerthenumber,thelesssensitive the memory is to fluctuations. Now, a system of large
size with small fluctuations is called a (physical) bath. Only baths make memories possible.Inotherwords,every
record contains a bath. We conclude that anyobservation of a
system is the interaction of that system with a bath.This connection will be used several
times in the following, in particular in quantum theory. When a record is produced by
a machine, the ‘observation’ is usually called a(generalized)measurement. Are you able
to specify the bath in the case of a person looking at a landscape?
learns within a fewsecondsto avoidsimilar situations forthe restofits life.Incontrast,learning atschool
cantake many months forasimpleidea.Itfacteverybodycan influencetheeaseandspeedoflearning; by
mentally attaching images, voices, emotions, fantasies or memories to a topic or situation, one can speed
uplearning andreducelearning effortconsiderably.
Research hasshownthatintheamygdala, whereemotions andmemoryare combined,theenzymecalcineurinandthegeneregulator
Zif268areimportant fortraumaticmemory: lowcalcineurin levelsleadto
increasedexpression of the gene regulator and to longer-lasting traumatic memory, high levelsreduce the
traumaticeffect.
Motion Mountain – The Adventure of Physics copyright © Christoph Schiller June 1990–November 2015 free pdf file available at www.motionmountain.net