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dly anyone really understood it；including heisenberg himself （鈥渋 do not even know what a matrix is ；鈥潯eisenberg despairedto a friend at one point）； but it did seem to solve certain problems that schr？dinger鈥檚 wavesfailed to explain。 the upshot is that physics had two theories； based on conflicting premises；that produced the same results。 it was an impossible situation。
finally； in 1926； heisenberg came up with a celebrated promise； producing a newdiscipline that came to be known as quantum mechanics。 at the heart of it was heisenberg鈥檚uncertainty principle； which states that the electron is a particle but a particle that can bedescribed in terms of waves。 the uncertainty around which the theory is built is that we canknow the path an electron takes as it moves through a space or we can know where it is at agiven instant； but we cannot know both。
3any attempt to measure one will unavoidably3there is a little uncertainty about the use of the word uncertainty in regard to heisenbergs principle。 michaelfrayn； in an afterword to his play copenhagen； notes that several words in german…unsicherheit； unscharfe；unbestimmtheit…have been used by various translators； but that none quite equates to the english uncertainty。
frayn suggests that indeterminacy would be a better word for the principle and indeterminability would be betterstill。
disturb the other。 this isn鈥檛 a matter of simply needing more precise instruments； it is animmutable property of the universe。
what this means in practice is that you can never predict where an electron will be at anygiven moment。 you can only list its probability of being there。 in a sense； as dennis overbyehas put it； an electron doesn鈥檛 exist until it is observed。 or； put slightly differently； until it isobserved an electron must be regarded as being 鈥渁t once everywhere and nowhere。鈥�
if this seems confusing； you may take some fort in knowing that it was confusing tophysicists； too。 overbye notes： 鈥渂ohr once mented that a person who wasn鈥檛 outraged onfirst hearing about quantum theory didn鈥檛 understand what had been said。鈥潯eisenberg； whenasked how one could envision an atom； replied： 鈥渄on鈥檛 try。鈥�
so the atom turned out to be quite unlike the image that most people had created。 theelectron doesn鈥檛 fly around the nucleus like a planet around its sun； but instead takes on themore amorphous aspect of a cloud。 the 鈥渟hell鈥潯f an atom isn鈥檛 some hard shiny casing； asillustrations sometimes encourage us to suppose； but simply the outermost of these fuzzyelectron clouds。 the cloud itself is essentially just a zone of statistical probability marking thearea beyond which the electron only very seldom strays。 thus an atom； if you could see it；would look more like a very fuzzy tennis ball than a hard…edged metallic sphere （but not muchlike either or； indeed； like anything you鈥檝e ever seen； we are； after all； dealing here with aworld very different from the one we see around us）。
it seemed as if there was no end of strangeness。 for the first time； as james trefil has put it；scientists had encountered 鈥渁n area of the universe that our brains just aren鈥檛 wired tounderstand。鈥潯r as feynman expressed it； 鈥渢hings on a small scale behave nothing like thingson a large scale。鈥潯s physicists delved deeper； they realized they had found a world where notonly could electrons jump from one orbit to another without traveling across any interveningspace； but matter could pop into existence from nothing at all鈥斺�減rovided；鈥潯n the words ofalan lightman of mit； 鈥渋t disappears again with sufficient haste。鈥�
perhaps the most arresting of quantum improbabilities is the idea； arising from wolfgangpauli鈥檚 exclusion principle of 1925； that the subatomic particles in certain pairs； even whenseparated by the most considerable distances； can each instantly 鈥渒now鈥潯hat the other isdoing。 particles have a quality known as spin and； according to quantum theory； the momentyou determine the spin of one particle； its sister particle； no matter how distant away； willimmediately begin spinning in the opposite direction and at the same rate。
it is as if； in the words of the science writer lawrence joseph； you had two identical poolballs； one in ohio and the other in fiji； and the instant you sent one spinning the other wouldimmediately spin in a contrary direction at precisely the same speed。 remarkably； thephenomenon was proved in 1997 when physicists at the university of geneva sent photonsseven miles in opposite directions and demonstrated that interfering with one provoked aninstantaneous response in the other。
things reached such a pitch that at one conference bohr remarked of a new theory that thequestion was not whether it was crazy； but whether it was crazy enough。 to illustrate thenonintuitive nature of the quantum world； schr？dinger offered a famous thought experimentin which a hypothetical cat was placed in a box with one atom of a radioactive substanceattached to a vial of hydrocyanic acid。 if the particle degraded within an hour； it would triggera mechanism that would break the vial and poison the cat。 if not； the cat would live。 but we could not know which was the case； so there was no choice； scientifically； but to regard thecat as 100 percent alive and 100 percent dead at the same time。 this means； as stephenhawking has observed with a touch of understandable excitement； that one cannot 鈥減redictfuture events exactly if one cannot even measure the present state of the universe precisely！鈥�
because of its oddities； many physicists disliked quantum theory； or at least certain aspectsof it； and none more so than einstein。 this was more than a little ironic since it was he； in hisannus mirabilis of 1905； who had so persuasively explained how photons of light couldsometimes behave like particles and sometimes like waves鈥攖he notion at the very heart of thenew physics。 鈥渜uantum theory is very worthy of regard；鈥潯e observed politely； but he reallydidn鈥檛 like it。 鈥済od doesn鈥檛 play dice；鈥潯e said。
4einstein couldn鈥檛 bear the notion that god could create a universe in which some thingswere forever unknowable。 moreover； the idea of action at a distance鈥攖hat one particle couldinstantaneously influence another trillions of miles away鈥攚as a stark violation of the specialtheory of relativity。 this expressly decreed that nothing could outrace the speed of light andyet here were physicists insisting that； somehow； at the subatomic level； information could。
（no one； incidentally； has ever explained how the particles achieve this feat。 scientists havedealt with this problem； according to the physicist yakir aharanov； 鈥渂y not thinking aboutit。鈥潱゛bove all； there was the problem that quantum physics introduced a level of untidiness thathadn鈥檛 previously existed。 suddenly you needed two sets of laws to explain the behavior ofthe universe鈥攓uantum theory for the world of the very small and relativity for the largeruniverse beyond。 the gravity of relativity theory was brilliant at explaining why planetsorbited suns or why galaxies tended to cluster； but turned out to have no influence at all at theparticle level。 to explain what kept atoms together； other forces were needed； and in the1930s two were discovered： the strong nuclear force and weak nuclear force。 the strong forcebinds atoms together； it鈥檚 what allows protons to bed down together in the nucleus。 the weakforce engages in more miscellaneous tasks； mostly to do with controlling the rates of certainsorts of radioactive decay。
the weak nuclear force； despite its name； is ten billion billion billion times stronger thangravity； and the strong nuclear force is more powerful still鈥攙astly so； in fact鈥攂ut theirinfluence extends to only the tiniest distances。 the grip of the strong force reaches out only toabout 1/100；000 of the diameter of an atom。 that鈥檚 why the nuclei of atoms are so pactedand dense and why elements with big； crowded nuclei tend to be so unstable： the strong forcejust can鈥檛 hold on to all the protons。
the upshot of all this is that physics ended up with two bodies of laws鈥攐ne for the worldof the very small； one for the universe at large鈥攍eading quite separate lives。 einstein dislikedthat； too。 he devoted the rest of his life to searching for a way to tie up these loose ends byfinding a grand unified theory； and always failed。 from time to time he thought he had it； butit always unraveled on him in the end。 as time passed he became increasingly marginalizedand even a little pitied。 almost without exception； wrote snow； 鈥渉is colleagues thought； andstill think； that he wasted the second half of his life。鈥�
4or at least that is how it is nearly always rendered。 the actual quote was： 鈥渋t seems hard to sneak a look atgod鈥檚 cards。 but that he plays dice and uses 鈥榯elepathic鈥櫋ethods。 。 。 is something that i cannot believe for asingle moment。鈥�
elsewhere； however； real progress was being made。 by the mid…1940s scientists hadreached a point where they understood the atom at an extremely profound level鈥攁s they alltoo effectively demonstrated in august 1945 by exploding a pair of atomic bombs over japan。
by this point physicists could be