BBC Focus - 09.2019

Q&A

NYELEWIS-DAVIES

WHATDOESTHEWORLD

LOOKLIKEOUTSIDE OF

OUR BRAINS?

Yourquestionhasechoesofthe

AmericanphilosopherThomas

Nagel’sclassicpaper“Whatis it like

tobea bat?”– a creaturethatis

abletonavigateusingecholocation

(bybouncingsoundsothe

environment).Nagelwrotethatwe

canneverstepoutsideofourown

brainandtakethebat’sperspective

ontheworldbecausewelacktheir

sensoryequipment.Likewise,one

couldarguethatwecannever

know what the world ‘looks like’

freefromourbrainsbecausewecan

onlyperceiveobjectivereality

throughtheveilofoursenses,such

asviawavelengthsoflighthiingour

retina,orodorousmolecules

stimulatingnervecellsinournose.

Wecan’tevenevertrulyknowif

theworldlooksthesamefromthe

perspectiveofanotherhumanbrain.

Forinstance,thecolourthatI label

‘red’maysubjectivelylookdierent

toyouthanit doestome.

Weknowasa maeroffactthat

thereareaspectsofphysicalreality

thatwecannotdetectourselves–

suchasradiowaves,ultravioletlight

(detectablebybirdsandbees,among

othercreatures)andhigh-pitched

ultrasound(usedbybats).Andof

course,therearelikelymanyother

aspectsofrealitynotyetdetectable

byanycreatureorourmost

advancedtechnology– a possibility

thatfuelstheimaginationofscience

fictionwritersandmysticsalike.

Butwhileourtakeontheworldis

restrictedbythelimitationsofour

ownneurologicalsystems,it would

bea mistaketounderplaytheir

potential.Forstarters,wehaveway

morethanfivesenses(amongthe

otherarebalance,hungerand

proprioception– thesenseofwhere

ourbodyis inspace).What’smore,

recentresearchsuggeststhatit may

bepossibleforustolearna formof

echolocation,bymakingclickswith

ourmouths.Indeed,someblind

peoplecanalreadydothis,usingthe

echoestopiecetogethertheir

environment as a bat would. CJ

MARTINOGILVIE,NORWICH

WHEREDO

SMELLS GO?

Smells‘disappear’whenthe

aromamoleculesdispersein

theairtoa concentration

belowyourdetection

threshold.Yournoseis more

sensitivetosomecompounds

thanothers:theeggysmellof

hydrogensulphideis

detectableatconcentrations

oftwopartsperbillion,while

nailvarnishremover

(acetone)needstobe50,000

timesmoreconcentrated

beforeyoucansmellit.Some

aromamoleculesmayalso

chemicallyreactinthe

airtoforma dierent

compoundthatyou are less

sensitiveto.LV

JULIUSCENTIK,PIEANY,SLOVAKIA

WHYDOESTHECLINKING

SOUNDGODOWN IN

PITCHWHENI STIR

SUGAR INTO MY COFFEE?

Whenaddingsugarintocoee– oranyhotdrink– the

‘clink’ofthespoonstrikingthemug’ssidesbecomes

lowerinpitch.Theexplanationis surprisinglysubtle,

andliesintheeectofthesugarontheliquid.The

roughsurfaceofthesugargranulestrapsmoleculesof

airdissolvedintheliquid,creatingtinybubbles.These

maketheliquidinthemugmore‘squashable’– the

technicaltermis ‘compressible’– allowingit tomop

upmoreoftheenergyinthesoundwavescreatedby

thespoon,whichinturnmakesthemtravelmore

slowlythroughtheliquid.Asthespeedofthesound

wavesinthemugis proportionaltotheirfrequency,

thereducedspeedlowerstheir frequency, which we

hear as a drop in pitch.RM