CINXE.COM

<!DOCTYPE html><html lang="en-US"><head><title>Just a moment...</title><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=Edge"><meta name="robots" content="noindex,nofollow"><meta name="viewport" content="width=device-width,initial-scale=1"><style>*{box-sizing:border-box;margin:0;padding:0}html{line-height:1.15;-webkit-text-size-adjust:100%;color:#313131;font-family:system-ui,-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Helvetica Neue,Arial,Noto Sans,sans-serif,Apple Color Emoji,Segoe UI Emoji,Segoe UI Symbol,Noto Color Emoji}body{display:flex;flex-direction:column;height:100vh;min-height:100vh}.main-content{margin:8rem auto;max-width:60rem;padding-left:1.5rem}@media (width <= 720px){.main-content{margin-top:4rem}}.h2{font-size:1.5rem;font-weight:500;line-height:2.25rem}@media (width <= 720px){.h2{font-size:1.25rem;line-height:1.5rem}}#challenge-error-text{background-image:url(data:image/svg+xml;base64,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);background-repeat:no-repeat;background-size:contain;padding-left:34px}@media (prefers-color-scheme:dark){body{background-color:#222;color:#d9d9d9}}</style><meta http-equiv="refresh" content="390"></head><body class="no-js"><div class="main-wrapper" role="main"><div class="main-content"><noscript><div class="h2"><span id="challenge-error-text">Enable JavaScript and cookies to continue</span></div></noscript></div></div><script>(function(){window._cf_chl_opt={cvId: '3',cZone: "academy.newscientist.com",cType: 'managed',cRay: '8e932596591687a5',cH: 'jaQ37WwwM0AfWlU8kuXHb.omUEpPt48gjpzCgPgBU68-1732721293-1.2.1.1-0aDl_ih8cP6qzpbIrTxUjQRLs2d45kpN2H4gJsyXZyiZdL7DWQGCX8Ct2fVQpaFS',cUPMDTk: "\/?__cf_chl_tk=No6RG8PuuIr_LrE.yZXI0lfalgJCeoc21py6A60fWVc-1732721293-1.0.1.1-jA51GoJdv.XIbB2ymeYa2OT.aNwQNWHtjPA3qRN.sOg",cFPWv: 'b',cITimeS: '1732721293',cTTimeMs: '1000',cMTimeMs: '390000',cTplC: 0,cTplV: 5,cTplB: 'cf',cK: "",fa: "\/?__cf_chl_f_tk=No6RG8PuuIr_LrE.yZXI0lfalgJCeoc21py6A60fWVc-1732721293-1.0.1.1-jA51GoJdv.XIbB2ymeYa2OT.aNwQNWHtjPA3qRN.sOg",md: "oE4W_hYMSN0.mtuImocu00o8fU4Ce.rTzvfHd.TMdO4-1732721293-1.2.1.1-PziLOyenqoSZU71G3xnzgry8Yy5g0YAczsu5QqUxS91YZCEmu6ayfUjBBDCeNrcC3LgehjnZE6Z3zR9IhWaZSDvFpTrUXkUgDnQTKGyiOvE25Ok7Q0yc5VeRiSVXPWvWryvHsUVjNvU6gwDZfDvSEI.Ysbav5zymgpEegD16F2S_yGAsz.NcIIaKIHUiJt4mvHsQVmrQcAXoLWWPoyVmXIslOZPXJhLtk5cpSR3ZYrLg8snecujGDdyfLQCRik6.mtHO3CUvwmKaL108hdOd7DRbZLLTA7kbvxtnEnKPDKQU.r8ImTKaK7Te84np8ygm1l.MHOB4_ME4XhUzQMx_0ByKmGzbvhRvBx8BKxPT9qFOxGocR5Ww0aPSVbdhHILjYGFkHijjyq983cwN_CaEEuaMvN.pkuUOUHHohxQhPXuN6QjAe24GFSAtHmKIQ2MWoIGCaKKsMqSTte2Tf94Bu11O9mJcB4_axt90sb415rfxjqkw0HpaK1XKuBSXmOlKZaDP_uA5x1X8VXsZDp1Bcdh98UAKDkoAAkKe8fP6rWxGaw3QSGyCjU.1lmydHZyNB1e57dURp._2EkL3g.KioH1FSxObIFGvIZXZOF6XXqZ_WxW2KLjsFvGLJWGw6.7IJ9QYcIn1x8axGjYlx5nv27tKFcbOkfFx0hwinhmLnb5RjMxA0bKiUR8vtomNaNsbetDfBz_lnWNbPkpPgDhNlZbRWJ4Mg9VjjKJcPdy7PSgxDJNoieemkat4RTOS_A1wUzAc3rkK19XsoblKbRKhNkB.wNV7QH_wIdor9PMVw2bf7iGwkuZM5fX74vubcMhU6qSeW_TGCJpYXVKIw55HUcrT.4jjGdL.zLCs88dAkujKt1Du9kYGTpbVP4g9C4b3sUYhYfbnw5fDNScyTnjKw3qGprWM.gO98DYfSp.v1jGeF0X8WzNP9t5W.TM26XrDwH8_PHLN4aYaAv.kbuB7TCgGaBehK.75bDhtdaT9Mf2DVoDdjDSbcF2A7qNUffrJF00ZOcaxSbiuuAWbztOYcjIVVhPHA5T3cEPq8QVUID.1FO5.x4g1Xl4uTb.23Q6c0D_dAwlTgFDyILZG2WXrhRdr0AHQFB.immJgdxseaY4utl2KFadMp6Bh1L6qlaRmUEK_6WGHEH4PA2an5ABTLknOfHQEHvWE8zCpA2eZofi6moHPi4quz93Kgjhk9.1hzdvtScd9LbPaI5XUb4Ur09k9rpytr6hNC6hitVqVwCjZlMTUAWLyqCz26p0Lk37d5f9ly08WEWY0uv2PuyIy4VhwtsuDas1U6w8dT7Jk1hQFJosPUOPVuBLa5GMDqbDppC_1L8aILjCMf4XO.UXMaPr2nUFGl5MlbiEwG1LPbnXGqAmTmoDrZPkrbpmdhayQQ8US2Upx7Ru9BoXRFOW8H__h0Ep5J3e.22DzTg3NRyfgd0Bn3nouOPWu_fRLf3ahcDYiJO_1NOYLyPpHvbDPVI8zxuQSXs7wCdEGacy6P15lYpbGGYjG0we1z48UefZrTds9MJ4ByFgZMQqF9uw8f_Tn4PVCGdnqeTvtJjUmIxEUXP_gI6niVh_hniRLA15QJPmmznL5c1YQ09vveOWzsSfXPFOrVlsvBUBQhLQyLG5xTa23i1x_TBNixqptxMUgriWAjX8DyHMtf272zDQSo7YYlFQE3cEKkWBAAbEKa04j7YpAktqSNVxw1NtF5SMf92c9JzSdB92.sIw8_GKF5hB4viopQxDoz3EFQBEEMnLR5T9rj6Oexlrvs2oTeg7MQxtjGIaLzgIcCYg_L2Mz0hotQEGHyIc5V7sAAEWO.II3hISmlxEAKpoYw6GBHpAHiKwYHYfWvg_lPi9svNOYGDpq9itFrHxjmlEPjTVW_9D7s0JzJ_hZBCqVWzATiQfpPziP.fHgneFmdvz4a2r4W1xZJdsF9toVpn.6.obrdm_Co2xmOioyyEQTBGRjspEFBG13G0c4m.JGcDc0f5533QFrmugFBOETE.XpLAex9LrGejWnDv2wN0ZTbuWdyrRWhtMXHfxPqverCoVBVz_N8Rer1p6_Z.186cgvfb2KSk3Cv.uG5Ft6jDEwhteP6jbDS6miqI9S6XeLl3NWB0yi8Ok0Y0x5a7GZQE1sEMNVywQJaR64Em1NlHcg5jYAdc.3UFyTRt_47NrkdzO0bL7W8BNcerPTydv9ioCC8OXv3pDQ_MQmeK0gYDps4nCQlvOTQIsS9LljqNTs475EyJJzLFpfkqpo1bgPc_L64aFjoaNtlBw8mvfIxQMifzukAKwXE0oVHTKKgj2d0xfyXGUaqjXEaEamsG4IMcjU44l2u8Lyqp7uf2ZDyruz80CAEFCl5.Wt6zMUPL2V9_78nfxxGE49pLxBd0XP4tUoqSiDddn_SWVXELmkt9QHAXsq66ifNaJHzQpuCXvGyslBmUMtspqwZR9tMdou6nuxOD_.gIlTQZVYDhQMzQaqPoLhDrrdctatEf_FN9db9zxJ20TpUbq5fKWdb5MWyLHIKz0nXjJZTuseHdaVSqSfJXEO6I4sU_ecgqYEKiKPv.14vuhFD2eYH.gnnasKohVXa5QJ9cbyDgEIFmTBnwSmdvlW1U.S1YAjFxA0cEZtPzPFeFifgWoYppWC3EVIY0Nk1GAErz.KL8z6Tq__gA7icyn9WgduG16UkQUOaAOqBPGJ7gVYhWSVsHk2TQmD1TBnvzFCiGeNs59vQfzHOeYPzf5OgI9oTsN5ATMMnWMZtx0ZhEbY3cr7SHN2isVtqDcJ.4O_.hxCMoJdAPKCRQ4Lxt3fEIf_DoeAi2DhYTDnwk3zIgmYC7QsbLUr9X1KBJwb5ZRsUBL4kY5VzmnTPAY4NejyM2Czv3L9yNC_jPL7rg.u04CE_A",mdrd: "aeEOuGMWQudcO9wt_A5CwEaOuh7yNTm_kOA35beshJA-1732721293-1.2.1.1-mXgnw5Y88_9i_VRxmA0zJDKOE9YQpzVUaPR2T0AVTCpZC6WrY_xk0gWI5swXA2jmxqAOVrDkvhSJ_DZzyvslV4xis.s8kWq8KFoKwkikRCmhGzSqUc2m9gVa_bn9eIguU983lo0RX_jlX4wOrivTwuKMyjYd0o8TVZYEdA2ZsKlDAw2Mq7ZM.SFdOLlaC7oYMkT8.QUWiFf0vYQ794zC7GVRQiqzsfq6ZQssgt0j8gnbDOAUSEw9NBZ_NgvUYiTY6Og3BrKr8iiCI.PdxOAF4KCKy4iDW1Wnz897XqGOCNVGd18J5U9IThphaRB5oZ.__TjwS5cjrcUYq6pLlH6xJLr3dUE7CoWklVssGAXQKgBSOaIECmHw1S9pmHB72J4xaC.dYDXe1G0leSD6kpbP020pGS2HzYqe7mswTfaYfDJ8v11S1qpXg0IfV.PYpd9E96k5n3OUmY4HUEatYgBD7JT.jbcv4p2V6ZOFHTKUoy7ogzNozJoIMKVLn.Oupto4O8m8dCPC2i9qG4EHOscmCUaM3cpI4AwJoqqXl6yTTJjvp76MDG1byhmXR4DQs8j7H5Tn19krah4xZpapQg3IMUWJrSFv.uEFsET_clxStfZeqSiI4osSxK9elir6fqn9KHMfie2crkfLn8DCJzipGR9zzc6T7mP7uq_lNv4uQ9o0DU.9nNGj1bm79aUBvDPk_Rcd6VkduDN1PU8hpaaA6dvhlcYj_ffQdVDam4JLYV8ofCn77L7jQfsD5sHbGJoVtIpfK5fKaTU4YbTT55loYyBq4.ay8EYJLotY4DQhE1UZx0qCWHqvm1PEgwQMMWBfLT_Ac5QJXG66e0nVKguhz4HmNf9aycocY4E3ZRRxBfnQvi9gWvt6p9uoWiNUfp9EI7U4_qUx7is_2iacpuTDv_GWi5YK8WHT9OwMZZ59Ai4FbVPG1MbW8UPM7bXA.wnX6oqDUzOZZO0KgLEP7aXc4u.31soWSBk1vDwAvtlCslNjHRbtArrD59_4mV86qpndRXm9UoGvEc13CnpKFW0ejOHvQLbvncA9FRyKaudDxAVjTTV6G58oK7rPJFe1QuyxN2AdIw_8ZdEHOk.SejD1GZN52HZqkhMigWQDbvcJRUneWTDJmcvYrCcri4mMTbTXHj_IfjuF0k9N_9mJBWezLOKgVYaFK9IKlbrxwLL3ZEjA5WlVHajqaRbU_9lK7fNc_oG03CGrl5KSKISYI_HBkTdzRw7taoGom63aFSbQUzUb92_5XPx7lVwlRKCSWXsIKHuUNULj.tIz8k11hSoOxCiB0zEvH1RRzRacubsny8EVef2aK3xExpFzlaOBuBkB7SAL9PDjkDQMIILWMP68WyNWYwZKdi6kcxLNvGSlF5VANbd543cL2lW5x5M2SNnThbHSgHdgWBDEmSRV2pJ4zVN6JRZqJozWBzZeiGyQDbJViX7doDkC_GHmugXQja0lObpdbSzPGDMIH7rIaC5iTHKdWJ5fhFknAKtGmbGv4H9TutLfXnempD0ZiISZJIM8g5H.ScMCew3D7oe9V6aNI_Lmg1rChwjjkczePkFf3ToMQj3JapHyH_881dMb9q1QjnYgdeAaDenslJe7q2ZFCutwM_wknBJ2LSqObZ2uWsoh57eZ6jmgNVEN7PI3.kEpFT_v62JvBvGA.ThHETcHYls5VQU5.ACyRSMFR0T_b60INrvto1WwN8yNQtQdr1Xews_FL.cZPq.B.VVkJcEdvDfRepkxm7Rg_xi3I.fglr4qoQ5F3Jl8AkVI7LkZnEIz8sGcT9SlikeFx671MABDiBGA4z2crwovbn0jizruNFXdqNPynvAC8QJrKt0JOQ7.R4OvD8FU2GCbRphZA21ZrLAvX.eq1v6JGJcAaAnuY2khtxY6jpcD_Bc_xS8VyAdkDwgod8mWHaKV7ZwU3nQxVHoClZ74.YnTpQGeR4Q7YywMjxUOfac_hj9VC0J6EDEwU1ytvxP.rSnkMmI9foHDZA"};var cpo = document.createElement('script');cpo.src = '/cdn-cgi/challenge-platform/h/b/orchestrate/chl_page/v1?ray=8e932596591687a5';window._cf_chl_opt.cOgUHash = location.hash === '' && location.href.indexOf('#') !== -1 ? '#' : location.hash;window._cf_chl_opt.cOgUQuery = location.search === '' && location.href.slice(0, location.href.length - window._cf_chl_opt.cOgUHash.length).indexOf('?') !== -1 ? '?' : location.search;if (window.history && window.history.replaceState) {var ogU = location.pathname + window._cf_chl_opt.cOgUQuery + window._cf_chl_opt.cOgUHash;history.replaceState(null, null, "\/?__cf_chl_rt_tk=No6RG8PuuIr_LrE.yZXI0lfalgJCeoc21py6A60fWVc-1732721293-1.0.1.1-jA51GoJdv.XIbB2ymeYa2OT.aNwQNWHtjPA3qRN.sOg" + window._cf_chl_opt.cOgUHash);cpo.onload = function() {history.replaceState(null, null, ogU);}}document.getElementsByTagName('head')[0].appendChild(cpo);}());</script></body></html>