I.: Chn khng, trong vt l c in, l khng gian khng cha vt cht. h vy chn khng c th tch khc khng v khi lng bng khng. Do khng c vt cht bn trong, chn khng l ni khng c p sut. Mt s l thuyt lng t cho rng khi nim chn khng theo ngha c in khng tn ti, do vi phm nguyn l bt nh. Chn khng, theo cc l thuyt ny, lun c s dao ng khi lng (v do nng lng) nh. iu ny ngha l, mt thi im no , lun c th xut hin mt cch ngu nhin cc ht c nng lng dng v mt thi im khc ht ny bin mt. Cc ht ngu nhin xut hin trong chn khng to ra mt p sut gi l p sut lng t chn khng. Cc th nghim o c p sut ny s gip khng nh chnh xc ca cc l thuyt lng t v chn khng. Trong thc t, khng c ni no trong v tr quan st c tn ti chn khng hon ho nh l thuyt. Cc th nghim v cc ng dng thc t c th to ra cc khng gian cha t vt cht v c p sut thp. Nhng khng gian ny cng hay c gi l "chn khng" trong k thut. h vy, chn khng c hiu l khong khng-thi gian c th c mt vt cht thp hoc rt thp. Lu , khi nim thp v rt thp y c hiu mt cch tng i... L Trng thi chn khng c hiu l trng thi c p sut nh hn p sut kh quyn trung nh chun, v c chia thnh: 1. Chn khng thp (p>100Pa) 2. Chn khng trung b.nh (100Pa>p>0.1Pa) 3. Chn khng cao (0.1Pa>p>10-5Pa) 4. Chn khng siu cao (p