Astronomija

Kako vemo, da je vakuum brez snovi?

Kako vemo, da je vakuum brez snovi?


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Vakuum je stanje brez delcev snovi (od tod tudi ime) in brez fotonov.

Ne razumem, kako najdemo del vesolja, kjer ni nobene snovi? Kako je to mogoče?


To je le definicija vakuuma.

Vakuum je prostor, iz katerega je odstranjeno vse, za kar vemo, da ga je mogoče odstraniti. V njej je še vedno temna energija ter Higgsovo polje in geometrija vesolja in časa, ker se, kolikor lahko ugotovimo, teh ne moremo znebiti. Če se motimo in lahko odstranimo še več, potem kar imenujemo vakuum, je pravzaprav lažni vakuum.


Navajate napačno in morda napačno berete

"Vakuum je prostor brez snovi". To je definicija na vrhu strani. Nato še ugotavlja, da resnični vakuumi ne obstajajo, toda vesolje je zelo dober približek vakuuma, saj ima le nekaj delcev vodika na kubični meter v medgalatnem prostoru.

Kasneje obravnava "kvantni elektro-dinamični vakuum" (stanje brez delcev in fotonov). Takoj ugotavlja, da "tega stanja ni mogoče eksperimentalno doseči." Nemogoče je doseči popoln vakuum in tudi če bi lahko odstranili vse delce, ne bi mogli izključiti vseh fotonov. Gre za teoretično konstrukcijo, pri kateri je povprečna vrednost elektromagnetnega polja enaka nič, vendar obstajajo lokalna naključna nihanja, ki se kažejo kot navidezni delci.

Napačno ste citirali wikipedijo in stavka niste prebrali v kontekstu.


Kaj pomeni "vakuum", je odvisno od tega, koga vprašate:

Če vprašate splošnega relativista, vam bodo rekli, da je območje prostora-časa vakuum, če je desna stran enačb Einsteinovega polja nič. To pomeni ne glede na snov ali sevanje in je zato eksperimentalno nemogoče. Vendar ima to prednost, da obstajajo številne znane rešitve enačb polja za vakuume (na primer Schwarzschildova rešitev, ki opisuje vakuum, ki obdaja sferično simetrično nenapolnjeno nerotirajočo maso). Zdi se, da resnični prostori, v katerih ni veliko snovi ali energije, približujejo te rešitve.

Če vprašate kvantno mehaniko, vam bodo rekli, da je vakuum najnižje energijsko stanje med različnimi polji, ki prežemajo prostor in čas. V tem stanju še vedno obstaja nekaj možnosti opazovanja delca, ki izhaja iz pravil kvantne mehanike.

Če vprašate strokovnjaka za dinamiko tekočin, vam bo povedal, da je vakuum območje z dovolj majhno gostoto plina, da je povprečna prosta pot delcev plina (povprečna razdalja, ki jo prevozijo, preden se udarijo) primerljiva z velikostjo regije. Na tej točki se preneha obnašati kot plin z natančno določenim tlakom in temperaturo in tako naprej in se je začel obnašati kot kup posameznih delcev.

Če vprašate nekatere inženirje, je vakuum karkoli pod tlakom, ki je bistveno pod okolico (tako težka industrijska vakuumska oprema tlaka ne zniža zelo nizko, je pa dovolj za sesanje zraka).

Če vprašate raketnega inženirja, bodo verjetno označili tisto, kar je zunaj njihove rakete, ko bo približno 100 km (morda manj), podtlak.

in tako naprej. Zlate definicije ni.


Kako vemo, da je vakuum brez snovi? - astronomija

Moje vprašanje: Kako sonde (kot je Voyager 1) krmarijo po vesolju, pasu asteroidov in okoli planetov, ne da bi pri čemer trčile?

Zavedam se, da je prostor ogromen, toda s hitrostjo, ki jo ima vse, in z zaostankom v komunikaciji, kako se je mogoče izogniti kamnu (kakršna koli velikost bi bila katastrofalna)? Predvidevam, da je večina vseh kamnin preveč temna in hladna, da bi bila vidna. Ali sonde za vodenje uporabljajo radar? Če je odgovor pritrdilen, kateri vir energije se uporablja, ki ne odteka?

Vse vesoljske sonde brez posadke so usmerjene od tal. Kot pravite, je v vesolju veliko prostora in ni videti, da bi bilo na cesti kakšna neravnina. Zelo natančno spremljamo položaj in hitrost vesoljskega plovila in glede na te lahko zelo natančno napovemo, kam gre, zato nalet na velike predmete ni problem. Na splošno je pot vesoljskega plovila načrtovana že leta vnaprej, zato je "krmiljenje" le stvar, da se ji ukaže, naj opravi ustrezne rakete ob pravem času, in izvede majhne prilagoditve. In pravzaprav se v misijah, ki jih opravljajo ljudje, zgodi popolnoma enako, le da namesto da bi ukazal, da to stori vgrajeni računalnik, le lepo vprašate pilota.

Asteroidom lahko sledimo do velikosti približno 50 km in predmete do 1 cm v nizki zemeljski orbiti. Seveda so manjše, neopazne kamnine številčnejše. Vendar so tudi v pasu asteroidov razpršeni na tako velikem območju, da je verjetnost trka s skalo, ki je dovolj velika, da konča misijo, zelo, zelo majhna in jo moramo preprosto sprejeti kot eno od tveganj vesoljski polet.

Vesoljska plovila pogosto prizadenejo mikrometeoriti do velikosti zrnca peska. Nekaj ​​takšnih zadetkov se šteje za običajno obrabo. Drug pogost vir težav so zadetki kozmičnih žarkov, ki so visokoenergijsko sevanje. To lahko povzroči majhne napake v vgrajeni programski opremi ali redkeje poškoduje elektroniko.

Vendar pa mora biti najpogostejši razlog za izgubo misije okvara komponente ali človeška napaka. Vesoljska plovila se izgubijo, ko njihovi motorji eksplodirajo (na primer CONTOUR, ki po načrtovanem izgorevanju ni poklical domov in je bil kasneje najden vzdolž načrtovane orbite - v treh kosih), ko jim ljudje pošljejo napačne ukaze (kot Mars Observer, kjer JPL je menil, da jim podizvajalec opeče metrične enote in jih dejansko pošilja v imperialnih enotah ali kadar odpove ključni sistem (na primer sistem za pristanek na Mars Polar Observer ali slaba napeljava v rezervoarjih za kisik na Apollo 13 ). Vesoljske misije so izjemno zapletene in misijo lahko obsodi majhna napaka katerega koli kritičnega sistema, bodisi v zasnovi bodisi zaradi poškodb med izstrelitvijo ali izpostavljenosti ekstremnim temperaturam in mora sesati vesoljska plovila.

Vesoljska plovila pogosto odpovejo, ne da bi navedli, kaj je šlo narobe. Prenehajo radijsko oddajati nazaj na Zemljo. Ali je prišlo do težave s programsko opremo? Je vesoljni žarek pohabil računalnik? Je kritičen del strojne opreme odpovedal? Ali ga je udaril meteorit?

Tveganje lahko izračunamo na podlagi zadetkov meteorita in je precej nizko. Človeške napake in inženirske napake pa so veliko bolj nepredvidljive.

Stran je bila nazadnje posodobljena 25. junija 2015.

O avtorju

Britt Scharringhausen

Britt preučuje Saturnove obroče. Leta 2006 je doktorirala na Cornellu in je zdaj profesorica na Beloit College v Wisconsonu.


Vakuum je prostor, popolnoma brez snovi

Presenetilo me je vprašanje. Kako resno je bilo. Po tem, kako resen je bil lastnik. Pogovarjal sem se za službo v prodajalni krofov, zato sem vedel, da me bodo vprašali o mojih delovnih izkušnjah s krofi - s pripravo hrane in postrežbo na splošno. Sem se pa pripravil na preprostejša vprašanja. Teden dni pred razgovorom za službo sem hodil po majhnih krogih po svoji majhni sobi v pol poti in vadil.

—Čokoladna krema je moja najljubša.

—Ponavadi s kavo, dobro pa tudi z mlekom. Nikoli pa s sodo. Ne razumem ljudi, ki menijo, da sta Pepsi ali Coca-Cola dobra s krofi.

—Krofov še nikoli nisem delal, toda z mamico sem odraščala v peki in prodaji kruha in piškotov. Tako je dodatno zaslužila, da nam je kupila šolska oblačila in pripomočke in podobne stvari.

—Dve leti sem bil kuhar na IHOP. Pri Dennyju približno šest mesecev pred tem. Ko sem bil otrok, sem si v moji rezervaciji pripravil hamburgerje v kavarni Tribal.

—Ni alergičen na nič, zato lahko jem ali pripravim kakršen koli krof.

- Nisem kuhala, ko sem bila v zaporu. Pral sem posodo. Moja kazen je bila le osemnajst mesecev. Dela za kuhanje so dajali fantom, ki se resno ukvarjajo. Želeli so kontinuiteto v kuhinji.

Neprekinjenost ni bila beseda, ki bi jo uporabil na običajnem. Toda to je beseda, ki jo je uporabil zapor. In takoj mi je bil všeč njen zvok. Con-ti-nu-i-ty. Torej je bila beseda, ki sem jo imel v možganih za kasnejšo uporabo. Ko bi lahko koga navdušil s svojim besediščem. Sem pameten fant - vsaj nadpovprečno - vendar obstaja nekaj besed, zaradi katerih lahko kdo zveni pametnejši. Vendar moraš biti previden. Nekateri se počutijo užaljene, če uporabite besedo, ki je ne razumejo. In če nekoga užališ v zaporu ali po moji rezervaciji, boš morda moral nekoga udariti po obrazu in v zameno dobiti po obrazu. Nisem bil naravni borec. Nisem se rodil, da bi delal pesti. Toda ponekod ste prisiljeni biti pugilist.

Pugilizem je ena mojih najljubših besed. Je pa zapletena beseda, ki ni primerna za vsakdanji pogovor. In zagotovo ni besede, ki bi jo uporabili na razgovoru za službo, razen če se morda prijavljate za službo v boksarski telovadnici. Kadar se želite zaposliti, morate uporabiti prave besede. In našel bi besedo kot kontinuiteta bi mi lahko pomagal dobiti tisto krofno. Ne vem, zakaj, toda zdelo se mi je krof in kontinuiteta sta bili dve besedi, ki sta šli skupaj.

"Hej," je rekel lastnik krofne. "Vprašal sem, ali si krof."

Bil je majhen fant, visok komaj pet metrov, in tehtal je morda kakšnih trideset dolarjev, a roke so bile ogromne. Niso ustrezali njegovemu telesu. Niti blizu. Bila je risanka. Kot da je bil stripovski zlikovec z imenom Veliki prsti. Nagnil se je čez pisalno mizo in trdo gledal name. Želel je odgovor.

"Ne vem, ali sem človek s krofi," sem rekel. "Sploh ne vem, kaj je krof."

Lastnik se je naslonil na stol.

Moja poklicna svetovalka v ameriškem indijanskem centru Jana me je naučila, kako zrcaliti ljudi. Rekla je, da ustvarja podzavestna čustvena povezava. Tako sem jo dvajset minut vadil v zrcaljenju med pretvarjenim intervjujem. Potem sem jo vprašal na zmenek. Rekla je ne. Nekaterih čustvenih povezav, mislim, ni mogoče zrcaliti. Jana je bila Lakota. Eden tistih Indijancev, ki so lovili bivole. In ubil Custerja. Prihajala je iz slavnega plemena. Prihajam iz plemena, za katero noben belci še niso slišali. Tudi večina Indijcev ni nikoli slišala za moje pleme. Torej bi bil jaz z Lakoto kot avtomehanik iz Idaha, ki bi hodil z odvetnikom v Seattlu. Verjetno se takšna romanca zgodi, vendar ne prav pogosto.

Upal sem, da mi bo zrcaljenje lastnika prodajalne krofov uspelo bolje kot zrcaljenje, kot je to storila Lakota. Navsezadnje sem plačo potreboval veliko bolj, kot da bi me poljubil.

"Torej, John," mi je rekel lastnik. "Ali želite uganiti, kaj je krof?"

Zdelo se mi je kot trik vprašanje. Če bi me policaj vprašal kaj takega, bi zahteval odvetnika in potem hudiča utihnil. Položil bi obraz na mizo in ostal tam, dokler se moj javni zagovornik ni zlezel. Toda ta razgovor za službo je bil le 49-odstotni zaslišanje, zato sem vedel, da mu moram odgovoriti.

"Ne maram ugibati stvari," sem rekel.

Lastnik je prikimal z glavo. Mislim, da mu je bil moj odgovor všeč. Zdelo se mi je, da sem morda resnično poskusil dobiti to službo. Že od izhoda iz zapora me je zavrnilo šestindvajset drugih krajev.

"Ne dovolite, da vas to demoralizira, John," je karierni svetovalec Lakota rekel o mojem maratonu ne, ne, ne, ne.

"Demoraliziraj," bi rekel. "Dobra beseda."

Lastnik prodajalne krofov se je dvignil, se sprehodil okoli svoje mize in se postavil poleg mene. Sedel sem, vendar sem bil vseeno višji od njega.

"Tip je včeraj prišel v želji po tej službi," je dejal. »Vprašal sem ga, ali je krof. Veste, kaj je rekel? "

"Ta tip me je pogledal v oči," je dejal lastnik. "In je prisegel bil je krof. «

"Nisi mu verjel," sem rekel.

Lastnik se je zasmejal in ploskal z rokami.

"Pameten si," je rekel. "Saj vidiš stvari."

"Včasih je bolje kot ne."

Malo sem se tresla. In potenje. Vaši lastni živci se včasih počutijo, kot da neredijo proti vaši krvi.

"Veste kaj še?" je vprašal.

Skoraj sem jokala. Skoraj. Ker lahko sreča poškodovan.

"Hvala," sem rekel. "Trudil se bom."

Odprl je visoko omarico, prijel predpasnik z obešalnika in mi ga dal. Vstal sem in si ga zavozlal okoli vratu in pasu. Počutil sem se bolje kot v pol leta življenja.

"Hej," sem rekel. "Kaj je krof?"

"Hudiča, če vem," je rekel lastnik. "To je sranje vprašanje, ki sem si ga izmislil včeraj."

Lastnik se je imenoval Wes Walden. Trgovina se je imenovala Superstar Donuts. Bilo je na Maple Street. Ja, trgovina s krofi na Maple Streetu. Wes je dejal, da tega nikoli ni spoznal, dokler mu ga stranka ni opozorila.

"Samo naključje," je dejal Wes. "Tako sem približno dve sekundi pomislil, da bi ime spremenil v Coincidental Donuts."

Wes je imel trgovino skoraj petindvajset let. In to ni bila samo trgovina. Tudi tovarna krofov je bila. V kraju smo izdelali in prodali štirideset sort krofov. In stranke so na treh mizah in šestih stolih uživale v svojih priljubljenih. Krofe pa smo spekli tudi na debelo in jih dostavili v petdeset lokalnih restavracij, kavarn, majhnih trgovin in trgovin.

Vsak dan je približno dva tisoč ljudi mislilo, da Superstar naredi precej dobre krofe. Bilo je majhno podjetje, tako kot milijon drugih malih podjetij. Ampak to so bili krofi. Vsi imajo radi krofe. Torej je trgovina s krofi, kot je Superstar, ljubljena. In ker smo krofe naredili, so bili zaposleni v Superstarju ljubljeni. Redne stranke so se hitro naučile in uporabile moje ime. Neverjetno, kako to deluje.

Howard je bil glavni pek. Wendy je vodila knjige. Darren in Sarah sta bila pomočnika peka. Eddie in Julio sta vozila tovorna vozila. Wes Walden je bil seveda zadolžen za vse in zdelo se je, da so vsi odgovorni zame. Ampak to je bilo v redu. Zaslužil sem samo minimalno plačo, toda vsak denar se vam zdi bogat, ko začnete od nič.

Naredil sem vse, kar je bilo treba. Izpolnil sem vrzeli. Pred odpiranjem, med delovnim časom in po zaprtju sem trgovino pekel, vodil blagajno, razbijal mize in čistil trgovino. Štirideset ur na teden se je običajno spremenilo v petinpetdeset ali petinpetdeset. Toda Wes mi ni plačal dvojnega ali celo časa in pol za nadure in mi ni plačal za vsako dodatno uro, ko sem delal. Nisem pa stavkal glede tega ali zagrozil, da bom ustanovil zvezo. Wes mi je skrajšal morda trideset ali štirideset dolarjev na teden. Toda ugotovil sem, da je to cena, ki sem jo moral plačati, ker sem bil nekdanji prevarant. Moral sem ga sprejeti.

Toda kratkotrajnost ni bila najslabši del službe. Niti približno ni bil najslabši del. Veste, moral sem se zbuditi vsak dan ob 2:00 zjutraj, da sem se tuširal, obril in vozil z avtobusom, da bi začel delati ob 3:00 zjutraj. Če ste kdaj delali na pokopališki izmeni, potem veste, kako čudno in rahlo odklopljeno se počutite. Kot da si tujec, ki živi na planetu, ki je od Zemlje oddaljen le pet centimetrov. Še huje pa je, da se zbudite ob dveh zjutraj. Po tednu dni tega sploh nimaš občutka, da imaš telo. Postaneš dežna kaplja, ki se valja po oknu. Postaneš veter, ki ropota prometno signalizacijo. Postanete stalen radijski signal, kjer je vsaka četrta beseda jasna.

Torej, ja, začutil sem neresnično ki delajo krofovske ure. A vseeno sem bila hvaležna za to resnično službo.

Služba je bila metla in smetnjak, vreča za smeti in smetnjak. In to je bilo sredstvo za čiščenje brisač in vedra ter tal. In to je bila WC ščetka in belilo. In to so bili umazani krožniki in skodelice, vilice, žlice in noži ter umivalnik, poln milnice, tako vroč, da sem izgubil tri nohte. In to so bili sladkor in jajca ter javor in moka ter olje za kuhanje in čokoladna omaka ter kokosovi posip ter smetana in cimet. In to je bilo ozvezdje opeklin in ureznin na mojih rokah.

Verjetno ste že videli krofe, ki jih izdelujejo v Krispy Kreme. Verjetno ste jih že videli, kako so se valjali po tekočem traku, vsi gladki, čisti in sveži. Imeli smo tudi tekoči trak, vendar je bil to starina. Poimenovali smo ga Eden, ker smo se spraševali, ali je bil na tem stroju narejen prvi krof.

In ta stroj je imel toliko kotičkov in rež, rež in vijakov ter vijakov in verig ter valjev in podložk ter kovine in plastike ter obročev in cevi, da sem ga vsak večer očistil vsaj štiri ure. To nalogo sem opravil povsem sam. S krpami in vedrom vode sem drgnil in drgnil in drgnil.

Edina oseba, ki je ostala v trgovini.

In moji zglobi so bili deset kilometrov izkopane makadamske ceste.

To čiščenje je predstavljalo večino mojih nadur. Torej, ja, nekaj tega krvavega dela je ostalo neplačano. In ko sem končal s čiščenjem, sem nastavil alarmni sistem, zaprl trgovino in ujel avtobus nazaj do pol poti in zaspal ob dveh ali treh popoldan, spal enajst ali dvanajst ur in se nato zbudil gor in ponovite.

Po treh tednih v Superstarju me je Wes Walden vprašal, ali se želim izučiti za dostavljavca. Bil sem presenečen. Navsezadnje sem bil nov uslužbenec in sem bil nekdanji obsojenec. Torej sta obstajala dva dobra razloga, zakaj se je zdelo prezgodaj za napredovanje.

"Kaj pa Eddie in Julio?" Vprašal sem.

"Eddie bo še vedno glavni voznik," je dejal Wes. »Toda Julio želi zmanjšati svoje ure tukaj, ker gre za polni delovni čas na drugo službo. In ima novega otroka. Tudi sam želi biti malo bolj doma. "

Nimam pojma, kako ljudje, ki delajo na minimalnih plačah, preživljajo svoje družine. Predvidevam, da so kot alkimisti, ki enajst dolarjev na uro spremenijo v polne hladilnike.

"V redu," sem rekel. »Vozil bom. Dokler bo z Eddiem in Juliom kul, bom poskusil. Nimam pa več vozniškega dovoljenja. Sploh ne vem, ali dovolijo bivšim vojakom, da dobijo vozniško dovoljenje. "

"Zakaj ne raziščeš," je rekel Wes. "Dobite licenco in Eddie vas bo naučil zgodnje dostave."

Izkazalo se je, da država hoče nekdanji kontra, da si po izstopu iz zapora prislužijo ali podaljšajo vozniško dovoljenje.

"Izboljšuje zaposljivost nekdanjih con," je dejala Jana Lakota.

"Sem že zaposlen," sem rekel.

"Potem ste boljši zaposleni," je dejala.

Jana me je odpeljala do pisarne DMV. Za podaljšanje licence mi niti ni bilo treba opravljati papirnatega ali vozniškega izpita. Pravkar sem naredil očesni test, da sem dokazal, da vidim, nato pa sem dobil nazaj licenco.

Naslednje jutro sem se povzpel na sovoznikov sedež dostavnika. V sončnih očalih me je Eddie pogledal in rekel, da v kombiju ne smem kaditi.

"Mislil sem, da vsi kadijo v zaporu," je dejal.

"To je bilo v nasprotju s pravili, kjer sem bil," sem rekel. »A to ni bilo pomembno. Nikoli nisem bil kadilec. «

"Huh," je rekel, kot da sem razkril nekaj pomembnega.

"In kaj si naredil?" Je vprašal Eddie. "Kdaj si bil notri?"

Pogosto so me spraševali o času, ki sem ga preživel za rešetkami. Predvsem moški. Bili so obsedeni s posilstvom v zaporu. In nestrpno so mi povedali, kako si nikoli ne bodo dovolili, da bi jih posilili. Prisegli so, da bodo umrli v boju. Neznanci v avtobusu bi mi povedali svoje natančno načrtovane strategije za premagovanje zapornikov.

Mislim, da vsak človek verjame, da bi postal zaporniški gladiator. Toda skoraj vsak človek se popolnoma moti sam.

"Kaj ste storili, da ste prišli tja?" Je vprašal Eddie. Vodila sem njegov testosteron. Še en civilist, ki se poskuša pokazati kot zločinec.

"Kaj si naredil?" Je spet vprašal Eddie.

Vedela sem, kaj Eddie želi vedeti, vendar sem ga igrala.

"Preden sem prišel sem delal v nekaj restavracijah," sem rekel.

"Ne," je rekel. "Zakaj ste šli v zapor?"

"Ubil sem dostavljavca," sem rekel.

Eddie se ni smejal. Tako tudi nisem.

"Ne misliš resno, kajne?" je vprašal.

"Pravzaprav," sem rekel, "oropal sem Starbucks."

"Vau," je rekel. »Še nikoli nisem slišal, da bi se to zgodilo. Koliko ste ukradli? Ste pravkar vstopili s pištolo, kot da je banka? "

"Oropal sem privoz," sem rekel. "In jahal sem konja."

Eddie mi je za trenutek verjel, nato pa me je pokvaril.

"Daj no, kreten," je rekel. "Povej mi, kaj si naredil."

"To se vas ne tiče," sem rekel. "In predvidevam, da ste Wesa vprašali o meni. In tudi ni mislil, da se to vas tiče. "

"Karkoli, John," je rekel, prižgal kombi in ob 4.30 zjutraj umaknil na ulico, ki je bila prazna.

Ne vem, zakaj sva se z Edijem nenadoma odločila, da se ne bova marala. Pred tem dnevom se še nismo toliko pogovarjali. In govorili smo samo o poslu. Nekaj ​​časa smo se vozili v tišini. In potem se je zdelo, da je Eddie v redu, če je ves čas govoril.

"V redu," je rekel. »Na tej prvi tekmi imamo samo dvanajst postankov. Mislil sem, da bi te začel enostavno. Temu pravimo zgodnji zgodaj. Potem gremo nazaj na redno-zgodnje. Vsako mesto na tej vožnji vzame različno količino krofov, vendar jih sešteje dvainsedemdeset ducatov. "

"Osemsto štiriinšestdeset krofov," sem rekel, ko sem v glavi hitro opravil matematiko.

Presenečen me je Eddie pogledal.

Namišljeni naslov: EX-CON DODA HITRO.

Drugi namišljeni naslov: AROGANTNI INDIJANEC SARU SVOJEM SODELOVALCU.

"Prva postaja je Al's Grocery," je dejal. "Dobijo tri ducate."

"V redu," sem rekel, nato pa vzel svoj mali zvezek in zapisal nekaj podrobnosti.

"Kaj delaš?" Je vprašal Eddie.

"Želim se prepričati, da sem ga natančno dobil," sem rekel.

"Nisem vedel, da morate genije iz matematike zapisovati."

"Nisem genij," sem rekel in poskušal igrati mir zdaj.

"Karkoli," je rekel že tretjič. »Približno mesec dni sem rabil, da sem se naučil vseh poti. Verjetno vam bo vzelo več časa. "

In tako smo dostavili osemsto in šestinšestdeset krofov v različnih količinah v Al's Groce Store, tri različne kavarne Ferch, dve restavraciji na obeh straneh postaje Greyhound, malo kavarno na postaji Amtrak, restavracijo v Sacred Srčna bolnišnica, jedilnica upokojenske skupnosti na južnem hribu in triindvajset ur hitrih martov.

Hitro smo delali. Vzelo nam je manj kot devetdeset minut.

Zapisala sem vse ustrezne naslove, imena in številke. Mislil sem, da si bom vse zapomnil, potem ko sem trikrat pretekel pot. Ali morda štirikrat, saj so bili moji možgani tako zamaknjeni že zgodaj zjutraj. Ampak ne bo šlo vse tako zapleteno. Zakaj se je torej Eddie zdel zapleten? Me je samo sral? Ali pa se je boril z učenjem stvari? V resnici ni bilo pomembno. Midva sva hotela samo opravljati svoje delo.

"Koliko časa je trajalo, da se navadiš na te ure?" Eddija sem vprašal, ko smo se vrnili v Superstar, da prevzame naslednji tovor.

"Tu delam pet let," je dejal. "In tega še vedno nisem vajen."

"Prekleto," sem rekel potrt zaradi izčrpanosti, ki me je čakala, a tudi vesel, da mi je Eddie povedal resnično dejstvo o sebi. Tako sem se odločil, da bom tudi resničen.

"Hej," sem rekel, "žal mi je, da sem bil prej kreten."

"V redu je," je rekel. »To je služba. Vsi se kdaj pa kdaj trkamo. «

"Kul," sem rekel. "In, hej, v zapor sem šel, ker sem v Lockerju ukradel čevlje."

"To je vse? Ste šli v zapor zaradi kraje v trgovini? "

»No, okrog polnoči sem vdrl v Foot Locker in ukradel petdeset parov Nikeov. In blagajna. In eden tistih posterjev LeBrona Jamesa. "

Ker je bil to zločin stoletja.

Nazaj v trgovini se je Wes Walden nasmehnil in ploskal ter nas pozdravil nazaj.

"Kako je šlo?" je vprašal Eddieja. "Lahko John reši pot?"

Eddie je okleval, preden je spregovoril. In potem je šel mesojed.

"Žal mi je, da to rečem," je rekel Eddie. »Toda John ima težave s podrobnostmi. Stvari si zapisuje, a vseeno pozablja na stvari. Tudi v majhnem teku. «

Moj prvi instinkt je bil, da Eddija udarim v njegova lažna usta. V zaporu ali po moji rezervaciji bi vam zlepili zobe, ker bi tako lagali.

Bil pa sem nekdanji prevarant, ki je delal na minimalni plači. Če bi koga udaril, bi končal nazaj v zaporu. Odslužil sem polno kazen in nisem bil pogojno pogojen. Toda vsak nekdanji za vedno je neuradno pogojno. Spoznal sem, da bom vedno podrejen pravični in nepravični sodbi. In tudi spoznal sem, da Eddieju ne morem nasprotovati. Leta je delal v Superstarju. Imel je delovno dobo in si zaslužil zaupanje. Bil sem novi, neznani dejavnik, ujeti tat.

"John," je rekel Wes. "Zakaj mi niste povedali, da imate težave s spominom?"

V vsem svojem življenju nisem nikoli želel narediti ničesar več, kot sem hotel kričati celoten seznam imen, naslovov, količin in lastnosti te dostavne poti. Lahko bi kričal barve oblačil skoraj vseh na poti. Lahko bi vam povedal, kakšno pijačo je kuhala barista pri Ferch Coffee on Division, ko smo ji dostavili krofe. In v redu, vseh teh podrobnosti se ne bi popolnoma spomnil, a vseeno bi izkazal impresivno količino odpoklica za otroka, ki je nekoč oropal prekleto omarico Foot.

Pogledal sem Eddieja in pričakoval, da bom videl smehljaj. Toda zdel je resnično zaskrbljen zame. Ta tip je bil igralec. Hladnokrven psihiac. Hladneje kot polovica fantov v zaporu.

Bil sem navdušen. Mislim, da ni bil knjižno pameten. Obstajajo pa tudi drugi načini, kako biti pameten.

Eddie je zmagal v igri. Nisem se zavedal, da igrava. In potem sem spoznal, da se me boji. Razumel sem. Bil sem nekdanji prevarant, zato me je bilo naravno strah, a edino, kar sem napadel, so bila zadnja vrata trgovine s čevlji. Prav tako sem spoznal, da se je Eddie bal, da bom prevzel njegovo službo dostave. In v redu, to ni bilo veliko dela, ampak je bilo njegovo službo. In hotel bi končati vsako grožnjo svojemu denarju, svojemu delu, svoji identiteti.

Poznal sem ljudi v zaporu, ki so umorili zaradi pet dolarjev dolgov. Tako sem razumel, da Eddie ščiti svoje sranje.

"Prihajam iz indijanskega plemena, iz rezervata in iz zapora," mi je rekla Jana Lakota. "Zaradi tega ste del treh častnih kultur."

"Kaj je kultura časti?" Sem vprašal.

"To pomeni, da ste kulturno dolžni braniti svoj ugled," je dejala. "In glede na vaše okoliščine pomeni, da ga boste zagovarjali na kakršen koli potreben način."

Tako da mislim, da se je Eddie odzval na neki bojevniški vzgib.

Ali pa je bil le maščevalni pič.

Moja edina možnost je bila predaja. Ampak nisem hotel priznati učne težave. Moral sem na nek majhen način zaščititi svojo čast. Zato sem moral skrbno izbirati besede. Moral sem povedati resnico, ne da bi povedal resnico.

"Ne morem opraviti poti," sem rekel Wesu. "Ampak vseeno si želim svojo službo."

"Služba je še vedno tvoja," je dejal. »Moram pa priznati, da sem razočaran. Upal sem nate. "

Jaz tudi, Mislil sem, a nisem rekel.

Moja mati je umrla zaradi raka, ko sem bil v zaporu. Povedala mi je, da je bila med zadnjim obiskom pri meni. Oče me ni nikoli obiskal. Če mislite, da so Indijanci bolj zvesti drug drugemu, ker smo Indijanci, potem ste idiot. V zadnjem tednu v zaporu mi je oče po telefonu rekel, da tatu ne bo pustil živeti v njegovi hiši. Tako se nisem mogel vrniti v rezervacijo.

Ste že kdaj pojedli krof, posut s sramom? Imajo še slabši okus, kot bi si lahko predstavljali.

Nadaljeval sem z delom v Superstaru. Toda pri svojem delu sem se počutil le malo bolje kot takrat, ko sem pomival posodo v zaporniški kuhinji.

Zdelo se mi je, da je vse moje življenje minimalno.

Potem, tri tedne po tem, ko me je Eddie privil, ko sem drgnil tekočino za krofe, sem dobil epifanijo. Mogoče prva epifanija v mojem življenju. In zagotovo najpomembnejši, ki sem ga kdajkoli imel.

Spoznal sem, da lahko tekoči trak očistim veliko hitreje in temeljiteje, če Superstar kupi brizgalno pištolo za vrtno cev in štirideset-galonski mokro-suhi prodajni sesalnik. Z vodo bi lahko prebrskal vse kotičke in v nekaj minutah namesto ur posrkal vso umazano vodo.

In potem sem spoznal, da če bom omenil svojo epifanijo Wesu Waldenu, bom izgubil službo. Vsaj moja redna zaposlitev bi postala honorarna. Za Superstar Donuts bi bil enako pomemben kot nov vakuum.

In potem sem bil prepričan, da je moral Wes v nekem trenutku v preteklosti tudi spoznati, da bo škatla s štirideset litrov revolucionarno. To je velika beseda za stroj, ki bi morda stal sto dolarjev. Ampak mislim, da je bila prava beseda. Ta vakuum bi bil čaroben kot časovni stroj.

Toda ves čas sem mislil, da je moral Wes razmišljati o nakupu sesalnika. Ni bil neumen. Moral je vedeti, da mu bo vakuum prihranil čas in denar. Potem sem se vprašal, ali Wes raje počne stvari po starem in počasi. Ali pa so mu bili bolj všeč ljudje - tudi nekdanji -, kot pa stroji. Torej, ja, morda sem bil Wesu všeč. Prevaril me je zaradi denarja in verjel, da ne zmorem dostavne poti z dvanajst postanki, vendar me je vseeno zaposlil in mi plačal dovolj denarja, da sem nadaljeval svoje majhno življenje.

To se sliši protislovno, vem, toda poznal sem zapornika, ki je starejšim zapornikom privoščil odvečno arašidovo maslo in žele sendviče, čeprav je ustrahoval vsakega drugega zapornika, ki ga je celo pogledal.

Ljudje so polni več nasprotij kot kosti.

Tisti dan, potem ko sem končal s čiščenjem tekočega traku, sem se prijavil v računalnik podjetja, poiskal najboljšo sliko štirideset-galonskega sesalnika in ga natisnil na navaden papir. Bila je zamegljena slika, vendar bi delovala. To sliko vakuuma sem posnel na tekoči trak. In na to sem napisal tudi opombo: »Dragi gospod Walden, ta stroj za krofe je čist. Lahko pa bi bilo čistejše. "

Potem sem se z avtobusom pripeljal domov, spal šestnajst ur, se zbudil in odpeljal do Indijskega centra.

"Jana," sem rekel tistemu na pol svetniku Lakoti. "Potrebujem novo službo."

Vedela je vse zgodbe, ki so bile kdaj povedane. Tako me ni vprašala, kaj se je zgodilo s staro službo. Nasmehnila se je, se nagnila k meni in rekla: "V redu, potem gre za novo iskanje."


Fiziki pravijo, da so manipulirali s "čistim ničemer" in opazovali padavine

Po kvantni mehaniki vakuum sploh ni prazen. Pravzaprav je napolnjen s kvantno energijo in delci, ki za trenutek utripajo in izstopajo - čudni signali, znani kot kvantna nihanja.

Že desetletja obstajajo le posredni dokazi o teh nihanjih, toda leta 2015 so raziskovalci trdili, da so teoretična nihanja zaznali neposredno. In zdaj ista ekipa pravi, da so šli še korak dlje, saj so manipulirali s samim vakuumom in v praznini zaznali spremembe teh čudnih signalov.

Tu vstopamo na ozemlje fizike na visoki ravni, toda v tem poskusu je resnično pomembno, da so raziskovalci, če bodo ti rezultati potrjeni, morda le odklenili način opazovanja, sondiranja in preizkušanja kvantne sfere, ne da bi pri tem posegali v to.

To je pomembno, ker je ena največjih težav s kvantno mehaniko - in našim razumevanjem le-te - ta, da vsakič, ko izmerimo in opazujemo kvantni sistem, ga uničimo, kar pa ne sluti dobro, ko želimo razdražiti, kaj se v resnici dogaja on in the quantum world.

This is where the quantum vacuum comes into it.

First of all, let's think of a vacuum in a classical way - as space entirely devoid of matter, with the lowest possible energy. There are no particles there, and nothing to interfere with pure physics.

But a byproduct of one of the most fundamental principles in quantum mechanics, Heisenberg's uncertainty principle, states that there's a limit to how much we can know about quantum particles, and as a result, a vacuum isn't empty, it's actually buzzing with its own strange energy, and filled with particle-antiparticle pairs that appear and disappear randomly.

These are more like 'virtual' particles than physical matter, so ordinarily you can't detect them. But although they're invisible, like most things in the quantum world, they subtly influence the real world.

These quantum fluctuations produce randomly fluctuating electric fields that can affect electrons, which is how scientists first indirectly demonstrated their presence back in the 1940s.

For decades, that was all we had to go on.

Then, in 2015, a team led by Alfred Leitenstorfer from the University of Konstanz in Germany claimed they'd directly detected these fluctuations, by observing their influence on a light wave. The results were published in Science.

To do this, they fired a super short laser pulse - lasting only a few femtoseconds, which is a millionth of a billionth of a second - into a vacuum, and were able to see subtle changes in the polarisation of the light. They said these changes were caused directly by the quantum fluctuations.

It's a claim that's still being debated, but the researchers have now taken their experiment to the next level by 'squeezing' the vacuum, and say they've been able to observe the strange changes in the quantum fluctuations as a result.

This isn't just further evidence of the existence of these quantum fluctuations - it also suggests that they've come up with a way to observe experiments in the quantum world without messing up the results, which is something that would ordinarily destroy the quantum state.

"We can analyse quantum states without changing them in the first approximation," said Leitenstorfer.

Usually when you're looking for the effects of quantum fluctuations on a single light particle, you'd have to detect that light particle, or amplify it, in order to see the effect. And this would remove the 'quantum signature' left on that photon, which is similar to what the team did in the 2015 experiment.

This time, instead of looking at the changes in quantum fluctuations by absorbing and amplifying photons of light, the team studied light on the time domain.

That sounds weird, but in a vacuum, space and time behave in the same way, so it's possible to examine one to learn more about the other.

Doing this, the team saw that when they 'squeezed' the vacuum, it worked kind of like squeezing a balloon, and redistributed the strange quantum fluctuations within it.

At some points, the fluctuations became way louder than the background 'noise' of an unsqueezed vacuum, and in some parts, they were quieter.

Leitenstorfer compares this to a traffic jam - when there's a bottleneck that cars build up behind, in front of that point, the density of cars will decrease again.

The same thing happens in a vacuum, to a certain extent - as the vacuum gets squeezed in one place, the distribution of the quantum fluctuations changes, and they can speed up or slow down as a result.

That effect can be measured on the time domain, which you can see below charted out on space-time. The bump in the middle is the 'squeeze' in the vacuum:

As you can see, as a result of the squeeze, there are some blips in the fluctuations.

But something else weird happens too, the fluctuations in some places appear to drop below the background noise level, which is lower than the ground state of empty space, something the scientists call an "astonishing phenomenon".

"As the new measurement technique neither has to absorb the photons to be measured nor amplify them, it is possible to directly detect the electromagnetic background noise of the vacuum and thus also the controlled deviations from this ground state, created by the researchers," explains a press release.

The team is now testing just how accurate their technique is, and how much they can learn from it.

Even though the results so far are impressive, there's still a chance the team might have only achieved a so-called weak measurement - a type of measurement that doesn't disturb the quantum state, but doesn't actually tell researchers very much about a quantum system.

If they can learn more using this technique, they want to continue to use it to probe the 'quantum state of light', which is the invisible behaviour of light at the quantum level that we're only just beginning to understand.

Further verification is needed to replicate the team's findings and show that their experiment really works. But it's a pretty cool first step.


So the weight of the mercury in the tube pushes the mercury out into the jar, and Volume devoid of matter just appears? Can you do this with a tube of water as well? and if vacuum forms in the top of the tube would that make water boil because vacuum exerts no pressure on water (thus lowering the boiling point?)

The space above is not pure vacuum. The space above is filled with mercury vapor at the equilibrium vapor pressure corresponding to the temperature of the liquid mercury. If you did the same thing with water, the space above would be filled with water vapor at the equilibrium vapor pressure corresponding to the temperature of the liquid water. The vapors in these spaces result from the evaporation of a tiny amount of the liquid. Since the vapors are in equilibrium with the liquids, the liquids can't boil.


Ask Ethan: Does The Aether Exist?

Both photons and gravitational waves propagate at the speed of light through the vacuum of empty . [+] space itself. Despite the fact that it isn't intuitive, there's no evidence that there's a physical medium, or aether, required for these entities to travel through.

NASA/SONOMA STATE UNIVERSITY/AURORE SIMONNET

All throughout the Universe, different types of signals propagate. Some of them, like sound waves, require a medium to travel through. Others, like light or gravitational waves, are perfectly content to traverse the vacuum of space, seemingly defying the need for a medium altogether. Irrespective of how they do it, all of these signals can be detected from the effects they induce when they eventually arrive at their destination. But is it really possible for waves to travel through the vacuum of space itself, without any medium at all to propagate through? That's what Wade Campbell wants to know, asking:

Back in the late 1800s, an "aether" was proposed as the medium that light travels through. We now don't believe that is the case. What is the evidence and/or proof that no aether exists?

It's an easy assumption to make, but a difficult assertion to disprove. Here's the story.

Whether through a medium, like mechanical waves, or in vacuum, like electromagnetic and . [+] gravitational waves, every ripple that propagates has a propagation speed. In no cases is the propagation speed infinite, and in theory, the speed at which gravitational ripples propagate should be the same as the maximum speed in the Universe: the speed of light.

Back in the earliest days of science ⁠— before Newton, going back hundreds or even thousands of years ⁠— we only had large-scale, macroscopic phenomena to investigate. The waves we observed came in many different varieties, including:

  • the ripples that wind caused in clothes on a clothesline or on a ship's sails,
  • water waves on the sea, ocean, or lake,
  • the waves that propagated through the ground during an earthquake,

In the case of all of these waves, matter is involved. That matter provides a medium for these waves to travel through, and as the medium either compresses-and-rarifies in the direction of propagation (a longitudinal wave) or oscillates perpendicular to the direction of propagation (a transverse wave), the signal is transported from one location to another.

This diagram, dating back to Thomas Young's work in the early 1800s, is one of the oldest pictures . [+] that demonstrate both constructive and destructive interference as arising from wave sources originating at two points: A and B. This is a physically identical setup to a double slit experiment, even though it applies just as well to water waves propagated through a tank.

Wikimedia Commons user Sakurambo

As we began to investigate waves more carefully, a third type began to emerge. In addition to longitudinal and transverse waves, a type of wave where each of the particles involved underwent motion in a circular path ⁠— a surface wave ⁠— was discovered. The rippling characteristics of water, which were previously thought to be either longitudinal or transverse waves exclusively, were shown to also contain this surface wave component.

All three of these types of wave are examples of mechanical waves, which is where some type of energy is transported from one location to another through a material, matter-based medium. A wave that travels through a spring, a slinky, water, the Earth, a string, or even the air, all require an impetus for creating some initial displacement from equilibrium, and then the wave carries that energy through a medium towards its destination.

A series of particles moving along circular paths can appear to create a macroscopic illusion of . [+] valovi. Similarly, individual water molecules that move in a particular pattern can produce macroscopic water waves, and the gravitational waves we see are likely made out of individual quantum particles that compose them: gravitons.

Dave Whyte of Bees & Bombs

It makes sense, then, that as we discovered new types of waves, we'd assume they had similar properties to the classes of waves we already knew about. Even before Newton, the aether was the name given to the void of space, where the planets and other celestial objects resided. Tycho Brahe's famous 1588 work, De Mundi Aetherei Recentioribus Phaenomenis, literally translates as "On Recent Phenomena in the Aethereal World."

The aether, it was assumed, was the medium inherent to space that all objects, from comets to planets to starlight itself, traveled through. Whether light was a wave or a corpuscle, though, was a point of contention for many centuries. Newton claimed it was a corpuscle, which Christiaan Huygens, his contemporary, claimed it was a wave. The issue wasn't decided until the 19th century, where experiments with light unambiguously revealed its wave-like nature. (With modern quantum physics, we now know it behaves like a particle also, but its wave-like nature cannot be denied.)

The results of an experiment, showcased using laser light around a spherical object, with the actual . [+] optical data. Note the extraordinary validation of Fresnel's theory's prediction: that a bright, central spot would appear in the shadow cast by the sphere, verifying the absurd prediction of the wave theory of light.

Thomas Bauer at Wellesley

This was further borne out as we began to understand the nature of electricity and magnetism. Experiments that accelerated charged particles not only showed that they were affected by magnetic fields, but that when you bent a charged particle with a magnetic field, it radiated light. Theoretical developments showed that light itself was an electromagnetic wave that propagated at a finite, large, but calculable velocity, today known as c, the speed of light in a vacuum.

If light was an electromagnetic wave, and all waves required a medium to travel through, and — as all the heavenly bodies traveled through the medium of space — then surely that medium itself, the aether, was the medium that light traveled through. The biggest question remaining, then, was to determine what properties the aether itself possessed.

In Descartes' vision of gravity, there was an aether permeating space, and only the displacement of . [+] matter through it could explain gravitation. This did not lead to an accurate formulation of gravity that matched with observations.

René Descartes: Prinzipien der Philosophie, Teil 3

One of the most important points about what the aether couldn't be was figured out by Maxwell himself, who was the first to derive the electromagnetic nature of light waves. In an 1874 letter to Lewis Campbell, he wrote:

It may also be worth knowing that the aether cannot be molecular. If it were, it would be a gas, and a pint of it would have the same properties as regards heat, etc., as a pint of air, except that it would not be so heavy.

In other words, whatever the aether was — or more accurately, whatever it was that electromagnetic waves propagated through — it could not have many of the traditional properties that other, matter-based media possessed. It could not be composed of individual particles. It could not contain heat. It could not transfer energy through it. In fact, just about the only thing left that the aether was allowed to do was serve as a background medium through which things like light were permitted to travel.

If you split light into two perpendicular components and bring them back together, they will produce . [+] an interference pattern. If there's a medium that light is traveling through, the interference pattern should depend on how your apparatus is oriented relative to that motion.

Wikimedia commons user Stigmatella aurantiaca

All of this led to the most important experiment for detecting the aether: the Michelson-Morley experiment. If aether really were a medium for light to travel through, then the Earth should be passing through the aether as it rotated on its axis and revolved around the Sun. Even though we only revolve at a speed of around 30 km/s, that's a substantial fraction (about 0.01%) of the speed of light.

With a sensitive enough interferometer, if light were a wave traveling through this medium, we should detect a shift in light's interference pattern dependent on the angle the interferometer made with our direction of motion. Michelson alone tried to measure this effect in 1881, but his results were inconclusive. 6 years later, with Morley, they reached sensitivities that were just 1/40th the magnitude of the expected signal. Their experiment, however, yielded a null result there was no evidence for the aether at all.

The Michelson interferometer (top) showed a negligible shift in light patterns (bottom, solid) as . [+] compared with what was expected if Galilean relativity were true (bottom, dotted). The speed of light was the same no matter which direction the interferometer was oriented, including with, perpendicular to, or against the Earth's motion through space.

Albert A. Michelson (1881) A. A. Michelson and E. Morley (1887)

Aether enthusiasts contorted themselves in knots attempting to explain this null result.

  • Perhaps the aether was being dragged by objects traveling through space, such as the Earth, and that's why a null result was obtained.
  • Perhaps there is a stationary, motionless aether, and as objects moved through it, they experienced length contraction and time dilation, explaining the null result.
  • And maybe, just possibly, the same aether that light traveled through, whatever it was, allowed for the propagation of Newton's gravitational force as well.

All of these possibilities, despite their arbitrary constants and parameters, were seriously considered right up until Einstein's relativity came along. Once the realization came about that the laws of physics should be, and in fact were, the same for all observers in all frames of reference, the idea of an "absolute frame of reference," which the aether absolutely was, was no longer necessary or tenable.

If you allow light to come from outside your environment to inside, you can gain information about . [+] the relative velocities and accelerations of the two reference frames. The fact that the laws of physics, the speed of light, and every other observable is independent of your reference frame is strong evidence against the need for an aether.

Nick Strobel at www.astronomynotes.com

What all of this means is that the laws of physics don't require the existence of an aether they work just fine without one. Today, with our modern understanding of not just Special Relativity but also General Relativity — which incorporates gravitation — we recognize that both electromagnetic waves and gravitational waves don't require any sort of medium to travel through at all. The vacuum of space, devoid of any material entity, is enough all on its own.

This doesn't mean, however, that we've disproven the existence of the aether. All we've proven, and indeed all we're capable of proving, is that if there is an aether, it has no properties that are detectable by any experiment we're capable of performing. It doesn't affect the motion of light or gravitational waves through it, not under any physical circumstances, which is equivalent to stating that everything we observe is consistent with it's non-existence.

Visualization of a quantum field theory calculation showing virtual particles in the quantum vacuum. . [+] (Specifically, for the strong interactions.) Even in empty space, this vacuum energy is non-zero, and what appears to be the 'ground state' in one region of curved space will look different from the perspective of an observer where the spatial curvature differs. As long as quantum fields are present, this vacuum energy (or a cosmological constant) must be present, too.

If something has no observable, measurable effects on our Universe in any way, shape or form, even in principle, we consider that "thing" to be physically non-existent. But the fact that there's nothing pointing to the existence of the aether doesn't mean we fully understand what empty space, or the quantum vacuum, actually is. In fact, there are a whole slew of unanswered, open questions about exactly that topic plaguing the field today.

Why does empty space still have a non-zero amount of energy — dark energy, or a cosmological constant — intrinsic to it? If space is discrete at some level, does that imply a preferred frame of reference, where that discrete "size" is maximized under the rules of relativity? Can light or gravitational waves exist without space to travel through, and does that mean there is some type of propagation medium, after all?

As Carl Sagan famously said, "absence of evidence is not evidence of absence." We have no proof that the aether exists, but can never prove the negative: that no aether exists. All we can demonstrate, and have demonstrated, is that if the aether exists, it has no properties that affect the matter and radiation that we do observe.


Ask Ethan: How Can We See 46.1 Billion Light-Years Away In A 13.8 Billion Year Old Universe?

After the Big Bang, the Universe was almost perfectly uniform, and full of matter, energy and . [+] radiation in a rapidly expanding state. As time goes on, the Universe not only forms elements, atoms, and clumps and clusters together that lead to stars and galaxies, but expands and cools the entire time. The Universe continues to expand even today, growing at a rate of 6.5 light-years in all directions per year as time goes on.

If there's one thing we've experimentally determined to be a constant in the Universe, it's the speed of light in a vacuum, c. No matter where, when, or in which direction light travels, it moves at 299,792,458 meters-per-second, traveling a distance of 1 light-year (about 9 trillion km) every year. It's been 13.8 billion years since the Big Bang, which might lead you to expect that the farthest objects we can possibly see are 13.8 billion light-years away. But not only isn't that true, the farthest distance we can see is more than three times as remote: 46.1 billion light-years. How can we see so far away? That's what Anton Scheepers and Jere Singleton want to know, asking:

If the age of the universe is 13.8 billion years, how can we detect any signal that is more than 13.8 billion light-years away?

It's a good question, and one that you need a little bit of physics to answer.

We often visualize space as a 3D grid, even though this is a frame-dependent oversimplification when . [+] we consider the concept of spacetime. In reality, spacetime is curved by the presence of matter-and-energy, and distances are not fixed but rather can evolve as the Universe expands or contracts.

We can start by imagining a Universe where the most distant objects we could see really were 13.8 billion light-years away. For that to be the case, you'd have to have a Universe where:

  • objects remained at the same, fixed distance from one another over time,
  • where the fabric of space remained static and neither expanded nor contracted over time,
  • and where light propagated through the Universe in a straight line between any two points, never being diverted or affected by the effects of matter, energy, spatial curvature, or anything else.

If you imagine your Universe to be a three-dimensional grid — with an x, y, in z axis — where space itself is fixed and unchanging, this would actually be possible. Objects would emit light in the distant past, that light would travel through the Universe until it arrived at our eyes, and we'd receive it the same number of "years" later as the number of "light-years" the light traveled.

In a static, unchanging Universe, all objects would emit light in all directions, and that light . [+] would propagate through the Universe at the speed of light. After a time of 13.8 billion years had passed, the maximum amount of distance that the light could have traveled would be 13.8 billion light-years.

Andrew Z. Colvin of Wikimedia Commons

Unfortunately for us, all three of those assumptions are incorrect. For starters, objects don't remain at a constant, fixed distance from one another, but rather are free to move through the space that they occupy. The mutual gravitational effects of all the massive and energy-containing objects in the Universe cause them to move around and accelerate, clumping masses together into structures like galaxies and clusters of galaxies, while other regions become devoid of matter.

These forces can get extremely complex, kicking stars and gas out of galaxies, creating ultra-fast hypervelocity objects, and creating all sorts of accelerations. The light that we perceive will be redshifted or blueshifted dependent on our relative velocity to the object we're observing, and the light-travel time won't necessarily be the same as the actual present-day distance between any two objects.

A light-emitting object moving relative to an observer will have the light that it emits appear . [+] shifted dependent on the location of an observer. Someone on the left will see the source moving away from it, and hence the light will be redshifted someone to the right of the source will see it blueshifted, or shifted to higher frequencies, as the source moves towards it.

Wikimedia Commons user TxAlien

This last point is very important, because even in a Universe where space is static, fixed, and unchanging, objects could still move through it. We can even imagine an extreme case: an object that was located 13.8 billion light-years away some 13.8 billion years ago, but was moving away from us at a velocity very close to the speed of light.

That light will still propagate towards us at the speed of light, traversing 13.8 billion light-years in a timespan of 13.8 billion years. But when that light arrives at the present day, the object can be up to twice as far away: up to 27.6 billion light-years away if it moved away from us arbitrarily close to the speed of light. Even if the fabric of space didn't change over time, there are plenty of objects we can see today that could be farther away than 13.8 billion light-years.

The only catch is that their light could travel for 13.8 billion light-years at most how the objects move after emitting that light is irrelevant.

Light, in a vacuum, always appears to move at the same speed, the speed of light, regardless of the . [+] observer's velocity. If a distant object emitted light and then moved quickly away from us, it could be just about as far away today as double the light-travel distance.

But the fabric of space isn't constant, either. This was the big revelation of Einstein that led him to formulate the General theory of Relativity: that neither space nor time were static or fixed, but instead formed a fabric known as spacetime, whose properties were dependent on the matter and energy present within the Universe.

If you were to take a Universe that was, on average, filled relatively evenly with some form of matter or energy — irrespective of whether it were normal matter, dark matter, photons, neutrinos, gravitational waves, black holes, dark energy, cosmic strings, or any combination thereof — you would find that the fabric of space itself is unstable: it cannot remain static and unchanging. Instead, it must either expand or contract the great cosmic distances between objects must change over time.

First noted by Vesto Slipher back in 1917, some of the objects we observe show the spectral . [+] signatures of absorption or emission of particular atoms, ions, or molecules, but with a systematic shift towards either the red or blue end of the light spectrum. When combined with the distance measurements of Hubble, this data gave rise to the initial idea of the expanding Universe: the farther away a galaxy is, the greater its light is redshifted.

Vesto Slipher, (1917): Proc. Amer. Phil. Soc., 56, 403

Beginning in the 1910s and 1920s, observations began to confirm this picture. We discovered that the spiral and elliptical nebulae in the sky were galaxies beyond our own we measured the distance to them we discovered that the farther away they were, the greater their light was redshifted.

In the context of Einstein's General Relativity, this led to a surefire conclusion: the Universe was expanding.

This is even more profound than people typically realize. The fabric of space itself does not remain constant over time, but rather expands, pushing objects that aren't gravitationally bound together apart from one another. It's as if individual galaxies and groups/clusters of galaxies were raisins embedded in a sea of invisible (space-like) dough, and that as the dough leavened, the raisins were pushed apart. The space between these objects expands, and that causes individual objects to appear to recede from one another.

The 'raisin bread' model of the expanding Universe, where relative distances increase as the space . [+] (dough) expands. The farther away any two raisin are from one another, the greater the observed redshift will be by time the light is received. The redshift-distance relation predicted by the expanding Universe is borne out in observations, and has been consistent with what's been known all the way back since the 1920s.

This has enormous implications for the meaning behind our observations. When we observe a distant object, we don't just see the light that it emitted, nor do we merely see the light shifted by the relative velocity of the source and the observer. Instead, we see how the expanding Universe has affected that light from the cumulative effects of the expanding space that occurred at every point along its journey.

If we want to probe the absolute limits of how far back we're able to see, we'd look for light that was emitted as close to 13.8 billion years ago as possible, that was just arriving at our eyes today. We'd calculate, based on the light we see now:

  • how much time the light has been traveling for,
  • how the Universe has expanded between then and now,
  • what all the different forms of energy present in the Universe must be to account for it,
  • and how far away the object must be today, given everything we know about the expanding Universe.

This simplified animation shows how light redshifts and how distances between unbound objects change . [+] over time in the expanding Universe. Note that the objects start off closer than the amount of time it takes light to travel between them, the light redshifts due to the expansion of space, and the two galaxies wind up much farther apart than the light-travel path taken by the photon exchanged between them.

We haven't just done this for a handful of objects at this point, but for literally millions of them, ranging in distance from our own cosmic backyard out to objects more than 30 billion light-years away.

How can the objects be more than 30 billion light-years away, you ask?

It's because the space between any two points — like us and the object we're observing — expands with time. The farthest object we've ever seen has had its light travel towards us for 13.4 billion years we're seeing it as it was just 407 million years after the Big Bang, or 3% of the Universe's present age. The light we observe is redshifted by about a factor of 12, as the observed light's wavelength is 1210% as long as it was compared to when it was emitted. And after that 13.4 billion year journey, that object is now some 32.1 billion light-years away, consistent with an expanding Universe.

The most distant galaxy ever discovered in the known Universe, GN-z11, has its light come to us from . [+] 13.4 billion years ago: when the Universe was only 3% its current age: 407 million years old. The distance from this galaxy to us, taking the expanding Universe into account, is an incredible 32.1 billion light-years.

NASA, ESA, and G. Bacon (STScI)

Based on the full suite of observations we've taken — measuring not just redshifts and distances of objects but also the leftover glow from the Big Bang (the cosmic microwave background), the clustering of galaxies and features in the large-scale structure of the Universe, gravitational lenses, colliding clusters of galaxies, the abundances of the light elements created before any stars were formed, etc. — we can determine what the Universe is made of, and in what ratios.

The distance/redshift relation, including the most distant objects of all, seen from their type Ia . [+] supernovae. The data strongly favors an accelerating Universe. Note how these lines are all different from one another, as they correspond to Universes made of different ingredients.

Ned Wright, based on the latest data from Betoule et al.

Today, our best estimates are that we live in a Universe made up of:

  • 0.01% radiation in the form of photons,
  • 0.1% neutrinos, which have a small but non-zero mass,
  • 4.9% normal matter, made of protons, neutrons and electrons,
  • 27% dark matter,
  • and 68% dark energy.

This fits all the data we have, and leads to a unique expansion history dating from the moment of the Big Bang. From this, we can extract one unique value for the size of the visible Universe: 46.1 billion light-years in all directions.

The size of our visible Universe (yellow), along with the amount we can reach (magenta). The limit . [+] of the visible Universe is 46.1 billion light-years, as that's the limit of how far away an object that emitted light that would just be reaching us today would be after expanding away from us for 13.8 billion years.

E. Siegel, based on work by Wikimedia Commons users Azcolvin 429 and Frédéric MICHEL

If the limit of what we could see in a 13.8 billion year old Universe were truly 13.8 billion light-years, it would be extraordinary evidence that both General Relativity was wrong and that objects could not move from one location to a more distant location in the Universe over time. The observational evidence overwhelming indicates that objects do move, that General Relativity is correct, and that the Universe is expanding and dominated by a mix of dark matter and dark energy.

When you take the full suite of what's known into account, we discover a Universe that began with a hot Big Bang some 13.8 billion years ago, has been expanding ever since, and whose most distant light can come to us from an object presently located 46.1 billion light-years away. The space between ourselves and the distant, unbound objects we observe continues to expand at a rate of 6.5 light-years per year at the most distant cosmic frontier. As time goes on, the distant reaches of the Universe will further recede from our grasp.


Physicists Discover an Unexpected Force Acting on Nanoparticles in a Vacuum

Researchers have discovered a new and unexpected force that acts on nanoparticles in a vacuum, allowing them to be pushed around by pure 'nothingness'.

Of course, quantum physics is beginning to make it clear that 'nothingness', as we like to think of it, doesn't actually exist - even vacuums are filled with tiny electromagnetic fluctuations. This new research is further proof that we're only beginning to understand the strange forces that are at work at the smallest level of the material world, by showing how nothingness can drive lateral motion.

So how can a vacuum carry force? One of the first things we learn in classical physics is that in a perfect vacuum - a place entirely devoid of matter - friction can't exist, because empty space can't exert a force on objects travelling through it.

But, in recent years, quantum physicists have shown that vacuums are actually filled by tiny electromagnetic fluctuations that can interfere with the activity of photons - particles of light - and produce a measurable force on objects.

This is called the Casimir effect, and it was first predicted by physicists back in 1948. Now, the new study has shown that this effect is even more powerful than they imagined.

Why does that matter? This Casimir effect might only be measurable on the quantum scale, but as we start engineering smaller and smaller technology, it's becoming clear that these quantum effects can greatly influence the overall products.

"These studies are important because we are developing nanotechnologies where we're getting into distances and sizes that are so small that these types of forces can dominate everything else," said lead researcher Alejandro Manjavacas from the University of New Mexico in the US.

"We know these Casimir forces exist, so, what we're trying to do is figure out the overall impact they have [on] very small particles."

To figure out how else Casimir forces could impact nanoparticles, the team looked at what happened with nanoparticles rotating near a flat surface in a vacuum.

What they found was that the Casimir effect could actually push those nanoparticles laterally - even if they weren't touching the surface.

That's a little strange, but imagine it like this - you have a tiny sphere rotating over a surface that's constantly being bombarded with photons. While the photons slow down the rotation of the sphere, they also cause the sphere to move in a lateral direction.

University of New Mexico

In the classical physics world, friction would be needed between the sphere and the surface to achieve this lateral motion, but the quantum world doesn't follow the same results, and so it can be pushed across a surface even when it's not touching it.

"The nanoparticle experiences a lateral force as if it were in contact with the surface, even though is actually separated from it," said Manjavacas.

"It's a strange reaction but one that may prove to have significant impact for engineers."

All of this might sound a little obscure, but it could play an important role in figuring out how to develop smaller and smaller technology, as well as devices such as quantum computers.

Intriguingly, the researchers show that they could control the direction of the force by changing the distance between the particle and the surface, which could one day come in handy for engineers and researchers who are constantly looking for better ways to manipulate matter on the nano-scale.

The findings now need to be replicated and verified by other teams. But the fact that we now have evidence of an intriguing new force that could be used to direct nanoparticles within 'nothingness' is pretty exciting - and suggests we're one step closer to understanding the weird forces at work in the quantum world.


Vacuum

Defined strictly in scientific terms, a vacuum is any space that has all of its matter removed. It is impossible to create a perfect vacuum in a laboratory on Earth because not every single atom can be removed. Even the so-called vacuum of outer space is not a true (perfect) vacuum because even it contains tiny amounts of gas spread over vast volumes of space. However, in everyday terminology, a vacuum is described as any volume of space where pressure is less than standard sea-level pressure — that is, atmospheric pressure of 29.92 in [760 millimeters]) of mercury (or, one atmosphere [1 atm]).

Thus, vacuum is a term that describes conditions where the pressure is lower than that of the atmosphere. A sealed container is said to be under vacuum in this case whereas it is pressurized when the pressure is higher than atmosphere. In a vacuum, it becomes necessary to define pressure microscopically. This means that the pressure, or force per unit area, is determined by the number of collisions between the atoms or molecules present and the walls of the container.

The first experiments involving vacuum date back to 1644 when Italian physicist Evangelista Torricelli (1608 – 1647) worked with columns of mercury, leading to the first barometer (a device for measuring pressure). The famous experiment of German scientist and inventor Otto von Guericke (1602 – 1686) in 1654 demonstrated the astounding force of vacuum when he evacuated the volume formed by a pair of joined hemispheres and attached each end to a team of horses that were unable to pull the hemispheres apart.

In order to create a vacuum, some kind of pump is needed. Simple mechanical pumps create a pressure difference, or suction force, which can be sufficient to pump water, for example. The most common use of pressure difference, the vacuum cleaner, is simply a chamber and hose, which are continuously evacuated by a fan (but the pressure difference created is far from a vacuum). Sophisticated vacuum pumps must be sealed to prevent air from leaking back into the pumping volume too quickly. These pumps increase in complexity, as better vacuums are needed. Pumps can generally be grouped into two categories: dynamic pumps, using mechanical or turbo-molecular action, and static pumps, using electrical ionization or low temperature (cryogenic) condensation.

Vacuum is important for research and industry, especially for manufacturing. Many industrial processes require vacuum either to be efficient or to be possible at all. Vacuum can be used for the prevention of chemical reactions, such as clotting in blood plasma or the removal of water in the process of freeze drying. Vacuum is also necessary for the prevention of particle collisions with background gas, in a television picture tube for example. For the fabrication of integrated electronics, it is very important to avoid impurities on a microscopic scale. It is only with excellent vacuum that such conditions can be obtained.


VACUUM

VACUUM [1] [2] [3] [4] is a set of normative guidance principles for achieving training and test dataset quality for structured datasets in data science and machine learning. The garbage-in, garbage out principle motivates a solution to the problem of data quality but does not offer a specific solution. Unlike the majority of the ad-hoc data quality assessment metrics often used by practitioners [5] VACUUM specifies qualitative principles for data quality management and serves as a basis for defining more detailed quantitative metrics of data quality. [6]

VACUUM is an acronym that stands for:

  1. ^"VACUUM". www.enterprisedb.com . Retrieved 2021-04-27 .
  2. ^
  3. Jim Nasby (2015), All the Dirt on VACUUM, PGCon - PostgreSQL Conference for Users and Developers, Andrea Ross , retrieved 2021-04-27
  4. ^
  5. "The Internals of PostgreSQL : Chapter 6 Vacuum Processing". www.interdb.jp . Retrieved 2021-04-27 .
  6. ^
  7. "An Overview of VACUUM Processing in PostgreSQL". Severalnines. 2019-11-22 . Retrieved 2021-04-27 .
  8. ^
  9. Pipino, Leo L. Lee, Yang W. Wang, Richard Y. (2002-04-01). "Data quality assessment". Communications of the ACM. 45 (4): 211–218. doi:10.1145/505248.506010. ISSN0001-0782.
  10. ^
  11. Wang, R.Y. Storey, V.C. Firth, C.P. (August 1995). "A framework for analysis of data quality research". IEEE Transactions on Knowledge and Data Engineering. 7 (4): 623–640. doi:10.1109/69.404034.

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