{"product_id":"1420-mhz-plate-042-physics-poster","title":"1420 MHz – Plate 042 Physics Poster","description":"\u003cp\u003ePlate 42 speaks for itself: \u003cem\u003e“The note the whole galaxy hums.”\u003c\/em\u003e\u003c\/p\u003e\u003ch3\u003eThe Physics\u003c\/h3\u003e\u003cp\u003eNeutral hydrogen's electron and proton spins can flip from parallel to antiparallel, emitting a 21 cm radio photon. The flip is very rare per atom, but the galaxy holds so much hydrogen that the line maps its spiral arms.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eλ = c \/ ν\u003c\/strong\u003e\u003c\/p\u003e\u003cul\u003e\n\u003cli\u003eλ: wavelength ≈ 0.211 m\u003c\/li\u003e\n\u003cli\u003ec: speed of light, m s⁻¹\u003c\/li\u003e\n\u003cli\u003eν: frequency 1420.405751768 MHz, Hz\u003c\/li\u003e\n\u003c\/ul\u003e\u003cp\u003eEwen \u0026amp; Purcell, 25 March 1951. Colours symbolic; radio is invisible.\u003c\/p\u003e\u003cp\u003e\u003cem\u003eHonest caveat:\u003c\/em\u003e 'Hum' is a metaphor: the line is a radio signal at 1.42 GHz, not sound, and nothing in the galaxy is audible.\u003c\/p\u003e\u003ch3\u003eSources\u003c\/h3\u003e\u003cul\u003e\u003cli\u003eH. I. Ewen, E. M. Purcell, Nature 168, 356 (1951).\u003c\/li\u003e\u003c\/ul\u003e\u003ch3\u003eOn the poster\u003c\/h3\u003e\u003cp\u003ePlate 042, “1420 MHz”: the pixel-art plate with its slogan “The note the whole galaxy hums.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.\u003c\/p\u003e","brand":"Printify","offers":[{"title":"9'' x 12\" (Vertical) \/ Matte","offer_id":50961927831655,"sku":"20728839117747007184","price":19.99,"currency_code":"USD","in_stock":true},{"title":"9'' x 12\" (Vertical) \/ Fine Art","offer_id":50961927864423,"sku":"30112272394047004672","price":29.99,"currency_code":"USD","in_stock":true},{"title":"9'' x 12\" (Vertical) \/ Semi Glossy","offer_id":50961927897191,"sku":"15791822828224984807","price":19.99,"currency_code":"USD","in_stock":true},{"title":"18″ x 24″ (Vertical) \/ Fine Art","offer_id":50961927929959,"sku":"12911323112469066416","price":44.99,"currency_code":"USD","in_stock":true},{"title":"18″ x 24″ (Vertical) \/ Semi Glossy","offer_id":50961927962727,"sku":"81542611443726607766","price":29.99,"currency_code":"USD","in_stock":true},{"title":"18″ x 24″ (Vertical) \/ Matte","offer_id":50961927995495,"sku":"25612930670834039539","price":29.99,"currency_code":"USD","in_stock":true},{"title":"36'' x 48\" (Vertical) \/ Matte","offer_id":50961928028263,"sku":"21560774806213329794","price":69.99,"currency_code":"USD","in_stock":true},{"title":"36'' x 48\" (Vertical) \/ Fine Art","offer_id":50961928061031,"sku":"18863005944654156068","price":119.99,"currency_code":"USD","in_stock":true},{"title":"36'' x 48\" (Vertical) \/ Semi Glossy","offer_id":50961928093799,"sku":"24623178957789668334","price":69.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0596\/8746\/9159\/files\/18275316606066757706_2048.jpg?v=1793633913","url":"https:\/\/pixelatedphysics.com\/sv\/products\/1420-mhz-plate-042-physics-poster","provider":"Pixelated Physics","version":"1.0","type":"link"}