Brian Greene: The Elegant Universe.
(1) Super-strings.

Super-strings, hiden dimensions, and the quest for the ultimat Theory.

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Leter y spels ryd for reed or read and partys for parties.
Leter w spels swn for soon. )

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Finit strings remov infinitys.

Greene's award-wining siens bwk ( publish'd in 1999 ) introduses us to relativity and quantum mekaniks by imajining familiar komparisons with ther basik ideas. String theory maks jeneral relativity and quantum theory kompatibl, if it is korekt. We dont no this yet bekaus the supos'd strings, that replas point elementary partikls, ar on far tu smal a skail ( the Planck skail ) to be rych'd by experiment, requiring the kind of enerjys to be found swn after the emerjens of the univers in the big bang.

As Greene puts it, fysisists wil hav to mak the big bang itself do, as a kosmik akselerator experiment, and mesur its results, in the laboratory of the univers.

In such extrym senarios, as the big bang, or blak hols, the konditions for the larj skail fysiks of jeneral relativity and smal skails of quantum mekaniks kom together. Jeneral relativity predikted a singularity or infinitly dens point and infinit kurvatur at the orijin of the univers, or within a blak hol. This breks down the law of spas-tIm being jeometrikly kurv'd with gravitational mas.

Quantum theory apyr'd to ofer a way out of this impas with Heisenberg's unsertainty prinsipl. A foton that throws lIt on an elektron nyds a short wav-lenth to determin its position akuratly. But shorter wav-lenths hav hIer enerjy and giv the elektron a kik that kreats an unsertainty in its momentum. A longer wav-lenth disturbs les its momentum but is a les presis observation of position. It's not just a question of disturbing the momentum of a partikl the mor akuratly it is mesur'd for position, and vice versa.

Empty spas is ryly a sything mas of enerjy eruptions, viw'd on a suficiently smal skail. Tho, over-al, a vakuum has zero enerjy. The unsertainty relation alows enerjy to be borow'd in invers proportion to the tIm taken. The mor enerjetik a partikl and anti-partikl kreation, the quiker they must anihilat ych other, thus preserving the spirit of the konservation law of mas-enerjy, within Heisenberg's terms.

At the inkredibly smal Planck lenth, to konfIn a partikl, in so narow a rejon, is to kreat ( literaly ) masiv unsertainty. Konsequently, the kurvatur of the spas and tIm dimensions wil lws ther kontinuity and bekom tu groteskly distorted to be myningful as left or rIt etc. Jeneral relativity is inaplikabl to the so-kal'd 'quantum foum'. A kombIn'd theory of quantum gravity is thus frustrated.

Akording to the string theorists, the kaus of this difikulty is the trytment of elementary partikls as infinitly smal points of no dimension. Such points wud be smal enuf to proub the quantum foum, below the Planck lenth. Supos that elementary partikls ar uon dimensional 'strings', so to spyk, of about Planck lenth. Then they wil be tu 'big' to proub the quantum foum, just as uon's finger is tu insensitiv to fyl the iregularitys of a granit surfas.

Mor exaktly, a Feynmann diagram, of partikl inter-aktions, has a nw interpretation, owing to special relativity, if re-drawn in terms of lwp'd strings, rather than point partikls. Hw-ever observ'd the infinitesimal point partikls wud agry on ther positions at a point of inter-aktion. But for the finit-sIz'd lwps, koming together to form a diferent lwp and therfor a diferent partikl, deskrIb'd by a diferent vibration patern, diferent observers wud disagry wen and wer the inter-aktion twk plas. For, in special relativity, observers in relativ motion yus spas and tIm ko-ordinat systems that disagry wen 'now' is.

The inter-aktion lokation is smyr'd out along the observational indefinitnes, so the fors of the partikl nyd no longer be tryted as of infinit strenth at an infinitesimal point. Finit strings produs wel-behav'd finit ansers du to the bluring over of the sub-Planck skail with its quantum foum.
Nor wud it avail uon to pump mor enerjy, and therfor frequensy, into a string, to giv it a shorter wav-lenth, mor probing of an objekt's position, as is don with fotons. The string is myrly magnify'd in sIz, rather than bekoming a magnifyer.

A kombIn'd theory of quantum gravity bekoms posibl, after al.

String resonanses as 'elementary' partikls.

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A basik valu of string theory is that al the suposedly elementary partikls may be taken as varius vibrational paterns, or resonanses, of a singl lwp of Planck lenth 'string'. ( To giv an idea of this mesur, if an atom was expanded to the sIz of the nown univers, the Planck lenth wud skersly rych the hIt of an averaj try. )

Mater is mayd up of over a hundred or so atoms, depending on how many protons and nutrons they kontain in ther nuklei, until ther number maks them tu unstabl to hold together. Ther elektrik charjes ar nutralis'd by a kloud of elektrons, with oposit elektrik charjes. This akounts for the fakt that the elektro-magnetik fors dos not normaly prevail over the extrymly fybl, but pyurly atraktiv, gravitational fors, that holds the galaxys together, the planets to the sun and things to the planets.

The elektrons ar elementary partikls. They ar mysteriusly asociated, in inter-aktions, with nutrinos, a skersly inter-akting partikl, tu lIt for any mas, it may poses, to be mesur'd as yet. ( After-nout, 2002: the nutrino has byn found to poses a smal mas. ) The protons and nutrons ar mayd of kombinations of thry sub-atomik partikls kal'd quarks. ( They kan also pair to form 'mesons'. ) Quarks ar held together by eit posibl gluons, as the naim sujests.

For som presently unnown reson, the elektron, nutrino and a pair of quarks kom in tw further sets of mor masiv and efemeral versions of themselvs.

Partikls klasify into fors partikls and mater partikls. Ther ar 4 nown forses of natur. The gluons ar the inter-aktiv or fors partikls for the 'strong fors' that holds the nukleus of an atom together but dos not extend beyond it.

A relativly 'wyk fors' is responsibl for radio-aktiv dekay of the nukleus. It has its own thry inter-aktiv partikls, wich hav byn kompar'd to 'hevy' fotons, in the elektro-wyk theory that unIts the elektro-magnetik fors with the wyk fors. The fotons ar the kariers or inter-aktiv or 'mesenjer' partikls of the elektro-magnetik fors.
Al the partikls hav anti-partikls, wich ar the saim but of oposit charj. Nutral partikls, lIk the foton, ar ther own anti-partikl.

If mater partikls ar hit with hIer enerjys, they produs mor masiv versions of themselvs, wich quikly dekay into ther basik versions. Thys ar kal'd resonans partikls, hundreds of wich hav byn found. The naim is by analojy with pluking a string to put mor enerjy into it, produsing hIer resonanses.
In fakt string theory, du to the extrym tension of strings, predikts an infinit number of hIer resonanses, just as ther kan be an infinit number of wav-lenths and korespondingly hIer frequensys and the hIer enerjys that go with them.

A vibrating string has mor enerjy with mor and, therfor, shorter wav-lenths lIk chopy sys insted of jentl rolers. Also, ther's mor enerjy if the 'sys' ar hIer, that is if ther krests and trofs mark hIer amplituds. Special relativity translats enerjy into mas. So, the mas of an elementary partikl kan be understood in terms of the vibration patern of a string.

Ther is a hypothesis'd fors-karying partikl for gravitational mas, kal'd the graviton. Jeneral relativity predikted gravitational wavs, tu fybl to detekt by present devIses.
An erly sukses of string theory of partikls as resonanses was to predikt the propertys of the graviton. It was also kalkulated that 'the strenth of the fors transmited by the propos'd graviton patern of string vibration is inversly proportional to the string's tension.' Sins gravity is so fybl, the tension work'd out at 10, to the power of 39, tons ( the Planck tension : enuf perhaps to work the univers up into a lIt swet )!

Not surprisingly, this tension kontrakts a string lwp down to the afor-mention'd Planck lenth. The enerjy, for such stif strings, must be extrymly hI for them to vibrat at al: on the Planck mas skail.

Greene says, supos diferent pepl wer only entrusted with uon diskryt monetary denomination, koresponding to enerjy being quantis'd or permited only at sertain diskryt levels ( as, in the Bohr atom, elektron orbits ar quantis'd ). Thys pepl ar only alow'd to pay in houl number multipls of thys denominations, as nyrly as posibl, up to the kost of a purchas ( being let off, in so far as ther denomination may not fuly ad up to the ful prIs ).

LIkwIs, strings hav a minimum enerjy denomination proportional to the string's tension, itself proportional to the number of krests and trofs in a vibration patern, hws enerjy is a houl number multipl, determin'd by its amplitud, of this quantis'd enerjy minimum. The typikal mas-equivalent of som vibrating lwp is 1, 2, 3,... tIms the Planck mas.

This is about the mas of a grain of dust, masivly beyond the mases of elementary partikls. DespIt the tension of strings, quantum unsertainty ensurs som vibration, wich is asociated with a negativ enerjy that kan kansel out the string's Planck enerjy, manifested in the lowest, or uon tIms Planck enerjy, vibration levels. This kan produs the tIny mases of elementary partikls, tho not typikly.
Thes kanselations work'd perfektly for the vibration patern hypothesis'd as the graviton, wich is just as wel, bekaus the graviton, akin to the foton, as a fors karier, is rekon'd to hav zero mas.
( String patern theory kan also be related to natur's other thry fors-karying partikls. )


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String theory is expekted to inkorporat the prinsipl of super-symetry. For the laws of natur to be truly jeneral, they must aplI in al maner of sirkumstanses. It shud not mater wen or wer an event hapens, from wat angl, or in wat motion. The law shud stil be observ'd to hold.
Laws that respekt thys konditions ar said to exhibit sertain symetrys, such as thru translations in spas and tIm.

Special relativity is symetrik with respekt to observers in relativ motion, hw kan al equaly klaim they ar at rest, relativ to any motion betwyn themselvs and other observers. Jeneral relativity gos further, as akselerating observers ar, in efekt, at rest in a gravitational fyld. This enforses a symetry that ensurs equality of al points of viw.

The other thry forses ar also requir'd to enfors other mor abstrakt 'gaij' symetrys. How-ever, ther was uon further symetry to do with spas, tIm and motion, naimly spin. This is rather as the erth rotats, as wel as revolvs. Elementary point partikls wud not sym to hav a myningful spin. But the magnetik propertys of elektrons, for instans, show'd that in a quantum sens they had. Only, this spin did not vary lIk the skater puling in her arms to spin faster.

The partikl spin is a fix'd quantity that gos to defIn its natur. Its quantum mekanikal rait is spin uon-haf for al mater partikls and spin uon for thry of the fors kariers. The graviton wud hav spin tw. String theory aktualy demands a vibration patern that koresponds to a masles spin-tw partikl.

It turns out that spin invoks an other symetry prinsipl of natur: 'super-symetry'. Brian Greene says no mor about it than: 'supersymmetry can be associated with a change in observational vantage point in a "quantum-mechanical extension of space and time".'

Wat-ever that myns, it implI'd that partikls must kom in pairs with spins difering by uon haf. This wud naturaly partner the mater and fors partikls. Unfortunatly, the standard model, that unifys thry of the for forses ( lyving out gravity ), match'd non of the existing partikls. Insted of efektivly halving the number of partikls, super-symetry dubl'd them, by positing a komplyt nw set of partners.

How-ever, super-symetry pairings of bosons ( with houl number spins ) and fermions ( with haf-number spins ) giv kanseling kontributions to partikl inter-aktions that the standard model can other-wIs only mak ad-up by extrym fIn tuning of its kalkulations.

The thry non-gravitational forses, tho of greitly disparat strenth, aparently diverj'd at an erly staij of the big bang's evolution. The quantum flux of virtual partikls wer found to wyken the intrinsik fors of an elektrikly charj'd partikl they surounded, until aproch at very klos distans. The oposit situation held for the strong fors and to a leser extent the wyk fors, so that at very short distans not greitly abov the Planck lenth, the thry forses' strenths konverj.
But, it was found that extra quantum fluktuations provided by super-symetrik partikls wud mak the konverjens perfekt.

In the super-symetrik version of string theory, it emerj'd that the boson and fermion paterns of vibration kaim in pairs.

Richard Lung.

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Hiden dimensions: part 2.

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