▁he ▁developed ▁the ▁approach ▁to ▁quantum ▁field ▁theory ▁that ▁is ▁described ▁in ▁the ▁first ▁chap ters ▁of ▁his ▁book ▁The ▁Quant um ▁Theory ▁of ▁Field s ▁and ▁started ▁to ▁write ▁his ▁text book ▁Gra v itation ▁and ▁Cos m ology . ▁▁ ▁In ▁ 1 9 6 6 , ▁Wein berg ▁left ▁Ber keley ▁and ▁accepted ▁a ▁lect urer ▁position ▁at ▁Harvard . ▁In ▁ 1 9 6 7 ▁he ▁was ▁a ▁visit ing ▁professor ▁at ▁M IT . ▁It ▁was ▁in ▁that ▁year ▁at ▁M IT ▁that ▁Wein berg ▁proposed ▁his ▁model ▁of ▁un ification ▁of ▁elect romagnet ism ▁and ▁of ▁nuclear ▁weak ▁forces ▁( such ▁as ▁those ▁involved ▁in ▁beta - dec ay ▁and ▁ka on - dec ay ), ▁with ▁the ▁masses ▁of ▁the ▁force - car riers ▁of ▁the ▁weak ▁part ▁of ▁the ▁interaction ▁being ▁explained ▁by ▁sp ont aneous ▁symmetry ▁breaking . ▁One ▁of ▁its ▁fundamental ▁aspects ▁was ▁the ▁prediction ▁of ▁the ▁existence ▁of ▁the ▁H ig gs ▁bos on . ▁ ▁Wein berg ' s ▁model , ▁now ▁known ▁as ▁the ▁electro weak ▁un ification ▁theory , ▁had ▁the ▁same ▁symmetry ▁structure ▁as ▁that ▁proposed ▁by ▁Gl ash ow ▁in ▁ 1 9 6 1 : ▁hence ▁both ▁models ▁included ▁the ▁then - unknown ▁weak ▁interaction ▁mechanism ▁between ▁le pt ons , ▁known ▁as ▁neutral ▁current ▁and ▁medi ated ▁by ▁the ▁Z ▁bos on . ▁The ▁ 1 9 7 3 ▁experimental ▁discovery ▁of ▁weak ▁neutral ▁curr ents ▁( medi ated ▁by ▁this ▁Z ▁bos on )