Sterrekunde

Is daar voorspellings oor die verspreiding van materie aan die einde van die tyd?

Is daar voorspellings oor die verspreiding van materie aan die einde van die tyd?


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Is daar teoretiese voorspellings of 'opgevoede bespiegelinge' deur kosmoloë oor hoe materie in die toekoms op baie, baie ver tye versprei sal word?

Dit sal byvoorbeeld saak maak:

  • agglutineer tot 'n groot koue bal?
  • verdun oor die heelal in klein stukkies?
  • groot trosse trosse hier en daar?
  • iets anders?

Die huidige moontlikhede is:

  • Die Groot Vries
  • Die Groot Rip
  • The Big Crunch
  • Die groot weiering
  • Die Groot Slurp

Met ons huidige onvolledige begrip van donker energie, kan ons egter nie met sekerheid sê nie.

Gebaseer op TV-dokumentêre programme oor kosmologie, blyk dit dat 'n kombinasie van die Big Freeze en Big Rip die huidige gunstelinge is - altans onder wetenskapskommunikators.

The Big Freeze is: Alles sal koud word, die swart gate verloor energie deur Hawking-bestraling, en uiteindelik sal daar totale entropie / geen inligting wees nie.

Die Big Rip is: Alles sal uitmekaar geruk word deur donker energie. Geen protone of neutrone meer nie (ek is egter nie seker oor elektrone en kwarks nie).

The Big Crunch is: Alles word een swart gat.

Die Big Bounce is: nadat een swart gat geword het, is daar nog 'n oerknal.

The Big Slurp: Die heelal eindig 'vroeg' met vakuumverval wat 'n krag uitoefen wat veroorsaak dat alle materie net ophou om materie te wees, deur die universele konstantes te verander. So 'n einde sal versprei teen die ligspoed, dus sal ons dit nie sien kom nie (aangesien geen inligting vinniger as die ligspoed kan beweeg nie).


Die basiese antwoord op u vraag is "ja vir al die bogenoemde, in verskillende tydperke".

As ons die ooreenstemming gebruik $ Lambda $Die CDM-model, met die kosmologiese konstante konstant, sal die heelal vir ewig met 'n versnelde tempo uitbrei. Die eerste groot effek hiervan is dat swaartekraggebonde trosse materie soos sterrestelsels op al hoe groter afstande geskei sal word (maar dit word self nie merkbaar verander nie). Die huidige kosmiese web van sterrestelsels en leemtes disintegreer in klein geskeide druppeltjies oor die volgende paar honderd miljard jaar.

Binne hierdie 'eilandallee' is plaaslike gravitasie-interaksies geneig om sterrestelsels met mekaar te laat saamsmelt en uiteindelik 'n enkele groot elliptiese sterrestelsel te word.

Oor lang tyd (ongeveer $10^{20}$ jare) naby ontmoetings tussen sterre lei daartoe dat sommige sterre uit die sterrestelsel in die buitenste duisternis geslinger word, en die ander nader aan die sentrale swart gat. Uiteindelik verminder dit die sterrestelsels tot groot swart gate en verspreide sterre. Die verspreide sterre koel af tot lae temperature.

As protonverval plaasvind, dan êrens verder $10^{33}$ jare of so verdamp die verspreide sterre stil en stadig in elementêre deeltjies. Daar word verwag dat die swart gate ook verdamp, en daarna $ sim 10 ^ {99} $ jare of so sal die enigste ding wat oorbly, afsonderlike stabiele elementêre deeltjies wees - elektrone, positrone, neutrino's, fotone, miskien 'n stabiele donker materie. As gevolg van die uitbreiding sal elke deeltjie alleen in sy sigbare heelal wees.

'N Goeie oorsig is Adams en Laughlin se "The Five Ages of the Universe" (of hul referaat, vir meer besonderhede).


Waarom Ray Kurzweil & # 39s voorspellings 86% van die tyd reg is

Dit is weer die tyd van die jaar wanneer tegnokundiges weer asemloos alles vertel van die tegnologie- en innovasietendense wat in 2013 groot sal wees. Dit is wonderlik, maar baie van hierdie voorspellings sal teen die einde van Maart hopeloos verkeerd wees. Daarom is dit so fassinerend dat Ray Kurzweil, een van die voorste denkers wat die toekoms van tegnologie betref, al amper twee dekades so sterk rekord het in die voorspelling van tegnologie. Trouens, van die 147 voorspellings wat Kurzweil sedert die negentigerjare gemaak het, het 115 daarvan korrek geblyk, en nog 12 het 'in wese korrek' geblyk te wees (met 'n jaar of twee), wat sy voorspellings gegee het 'n pragtige 86% akkuraatheidskoers. So hoe doen hy dit?

Die feit is dat Ray 'n stelsel het en die stelsel word die wet van versnelde opbrengste genoem. In sy nuwe boek How to Create a Mind: The Secret of Human Thought Revealed wys Kurzweil daarop dat "elke fundamentele maatstaf van inligtingstegnologie voorspelbare en eksponensiële trajekte volg." Die bekendste van hierdie trajekte was natuurlik die prys / prestasie-pad van rekenaarkrag oor meer as 100 jaar. Danksy paradigmas soos Moore's Law, wat die rekenaarkrag verminder tot 'n probleem met hoeveel transistors u op 'n skyfie kan stamp, kan iemand intuïtief verstaan ​​waarom rekenaars mettertyd eksponensieel vinniger en goedkoper word.

Die ander bekende eksponensiële groeikurwe in ons leeftyd is die groot hoeveelheid digitale inligting wat op die internet beskikbaar is. Kurzweil teken dit gewoonlik as 'bits per sekonde wat op die internet gestuur word'. Dit beteken dat die hoeveelheid inligting op die internet ongeveer elke 1,25 jaar verdubbel. Daarom is "Big Data" deesdae so 'n modewoord - daar word toenemend erkenning verloor dat ons al die inligting wat ons op die internet lewer, verloor, van Facebook-statusopdaterings tot YouTube-video's, tot snaakse memeboodskappe op Tumblr. Oor net 'n dekade sal ons meer inhoud skep as wat daar duisende jare bestaan ​​het in die mensdom se vorige ervaring.

En dit is nie net die rekenaarkrag of die groei van die internet nie. Hoofstuk tien in Kurzweil se nuutste boek How to Create a Mind bevat 15 ander kaarte wat hierdie eksponensiële groeikurwes by die werk toon. Sodra enige tegnologie 'n inligtingstegnologie word, word dit onderhewig aan die Wet op Versnelde Opbrengste. Oorweeg byvoorbeeld biogeneeskunde. Noudat die menslike genoom vertaal word in 'n digitale lewenskode van 1's en 0's wat deur rekenaars verwerk kan word, is dit ook 'n inligtingstegnologie, en dit beteken dat dit ook onderhewig is aan die Wet op Versnelde Opbrengste. As u kyk na die koste om 'n menslike grootte genoom te volgorde, het die koste omstreeks 2001 eksponensieel begin daal en in ongeveer 2007 van die genomiese krans afgeval - ongeveer dieselfde tyd wat Craig Venter se genoomprojek opgestyg het.

Soos Ray opmerk in How to Create a Mind, is die rede waarom tipiese kenners en voorspellers dit jaarliks ​​jaar verkeerd maak, dat die menslike verstand ontwikkel het om lineêr te dink, nie eksponensieel nie. Ons beskou 40 stappe as 'n lineêre vordering: die een stap na die ander, van 1 tot 40. As Ray egter aan 40 stappe dink, beskou hy dit eksponensieel as 2 ^ 40, en dit is 1 triljoen. Trouens, tydens 'n onlangse toespraak wat Kurzweil op TEDx Silicon Alley in Manhattan gehou het, het hy genoem wat die '1% dwaling' genoem kan word. As die meeste mense hoor dat slegs 1% van die probleem opgelos is, gee hulle gewoonlik op en neem aan dat dit nog jare sal duur totdat dit opgelos is. Ray dink egter eksponensieel. Vanuit sy perspektief, as u 1% van die probleem opgelos het, beteken dit dat u nie 1/100 van die pad daarheen is nie (dws 99 klein liniêre stappe om te gaan), dit beteken dat u nog net enkele eksponensiële stappe is weg. Daarom is Ray se nuutste projek - reverse engineering van die menslike brein - so opwindend. Nadat ons net 1% van die menslike brein omgekeer het, beteken dit dat ons net 'n paar tree van die skep van 'n sintetiese korteks af is - die wêreld se beste algoritmiese patroonherkenningsmasjien.

Waarop kan ons dus reken vir 2013? Dink soos Ray, en gebruik die wet van versnelde opbrengste tot u voordeel. Bepaal die omvang van die probleem waarmee u te make het, bereken die rekenaarkrag wat nodig is om dit te bereik, en werk dan agteruit om by 'n geskatte tydlyn uit te kom. Met behulp van hierdie eenvoudige benadering kon Ray voorspel dat 'n tegnologie vir kunsmatige intelligensie soos Deep Blue in 1998 'n grootmeester van die skaak sou kon verslaan. Hy het met 'n grootmeester gesels en agtergekom dat 'n AI-masjien 100 000 moontlike raadsposisies sou moes herken by te eniger tyd, en dat dit die rou rekenaars moet hê om alle moontlike kombinasies van hierdie 100 000 bordposisies telkens weer te verknies. Sodra die vereiste rekenaarkrag moontlik was (danksy die wet van Moore), was dit tyd om na die volgende uitdaging oor te gaan - om 'n gevaar te word! kampioen. Nou, met die oorwinning van Watson, is dit tyd om voort te gaan na die volgende uitdaging - om die wêreld se beste dokter te word.

Die baie opwindende kenmerk van die wet van versnelde opbrengste is dat dit implisiet veronderstel dat een eksponensiële tegnologie bo-op die volgende eksponensiële tegnologie voortbou. Iets soos 3D-drukwerk is 'n voorbeeld van een eksponensiële tegnologie wat bo-op 'n ander eksponensiële tegnologie gebou word. In werklikheid kan 3D-drukwerk die beste eksponensiële tegnologie vir die komende 12 maande blyk te wees, soveel so dat Chris Anderson van WIRED sy reputasie daarop inset. Watter ander gebiede kan dus volgende jaar ryp wees vir verrassende deurbrake as gevolg van eksponensiële spronge in rekenaarkrag? As u die tipe voorspeller is wat dit geniet om die dobbelsteen in Vegas te gooi, is dit 'n spel waar die kans in u guns gestapel word, en u het 'n kans van 86% om die huis te klop.


Die begin van astrologie

Astrologie het ongeveer twee en 'n half millennia gelede in Babilonië begin. Die Babiloniërs het geglo dat die planete en hul bewegings die lot van konings en nasies beïnvloed het, en gebruik hul kennis van sterrekunde om hul heersers te lei. Toe die Babiloniese kultuur deur die Grieke opgeneem is, het astrologie geleidelik die hele Westerse wêreld beïnvloed en uiteindelik ook na Asië versprei.

Teen die 2de eeu vC het die Grieke die astrologie gedemokratiseer deur die idee te ontwikkel dat die planete elke individu beïnvloed. Hulle het veral geglo dat die konfigurasie van die son, maan en planete op die oomblik van geboorte 'n persoon se persoonlikheid en welvaart beïnvloed - 'n leerstelling genoem geboorte-astrologie. Natalse astrologie het 400 jaar later sy hoogtepunt bereik met Ptolemeus. Net so bekend vir sy astrologie as vir sy sterrekunde, het Ptolemeus die Tetrabiblos, 'n verhandeling oor astrologie wat die & # 8220bybel & # 8221 van die onderwerp bly. Dit is in wese hierdie antieke godsdiens, ouer as die Christendom of die Islam, wat steeds deur die hedendaagse sterrekykers beoefen word.


Donker materie selfinteraksies en kleinskaalse struktuur

Sean Tulin, Hai-Bo Yu, in Fisikaverslae, 2018

2.2 Diversiteitsprobleem

In Λ CDM produseer hiërargiese struktuurvorming self-soortgelyke halo's wat goed beskryf word deur NFW-profiele. Aangesien die halo-parameters (bv. Ρ s en r s) sterk gekorreleer is, is daar slegs een parameter wat 'n halo spesifiseer. As die maksimum sirkelsnelheid Vmax (of enige ander halo-parameter) byvoorbeeld vasgestel is, word die halo-digtheidsprofiel volledig bepaal in alle radiusse, insluitend die binneste digtheid (tot by die verstrooiing). Aan die ander kant vertoon die innerlike rotasiekurwes van waargenome sterrestelsels aansienlike diversiteit. Sterrestelsels met dieselfde Vmax kan 'n beduidende variasie in hul sentrale digthede hê. Enige meganisme om die kern-cusp-kwessie te verklaar, moet ook hierdie skynbare diversiteit akkommodeer.

Ter illustrasie van hierdie kwessie, het Kuzio de Naray et al. [68] het sewe LSB-sterrestelsels toegerus met vier verskillende halo-modelle, met inbegrip van byvoorbeeld 'n pseudo-termiese profiel ρ dm (r) = ρ 0 (1 + r 2 ∕ r c 2) - 1. Fig. 5 (links) toon die sentrale DM-digtheid ρ 0 - afgelei deur die binneste helling van V circ (r) - versus V max vir hierdie sterrestelsels. Binne die steekproef is daar geen duidelike korrelasie tussen die binneste (ρ 0) en die buitenste (V max) dele van die stralekrans nie. Verder kan die verspreiding in ρ 0 groot wees vir sterrestelsels met soortgelyke Vmax, tot 'n faktor van O (10) wanneer Vmax ∼ 80 km ∕ s. Die resultaat is onafhanklik van die keuse van 'n halo-model en massa-tot-lig-verhouding.

In plaas daarvan om by 'n spesifieke halo-profiel aan te pas, het Oman et al. [67] het die diversiteit van rotasiekurwes meer direk geparametreer deur V circ (2 kpc) teenoor V max te vergelyk, wat onderskeidelik die binne- en die buitenste halos voorstel. Fig. 5 (regs) toon die verspreiding in hierdie snelhede vir waargenome sterrestelsels (blou punte) in vergelyking met die korrelasie wat verwag word van slegs CDM-halo's (soliede lyn) en CDM-halo's met barione (rooi band). Vir V max binne 50 - 300 km ∕ s is die verspreiding in V circ (2 kpc) 'n faktor van 3 vir 'n gegewe V max. Wanneer V max ∼ 70 km ∕ s byvoorbeeld is, voorspel CDM (slegs) V circ (2 kpc) ∼ 50 km ∕ s (soliede lyn), maar waargenome sterrestelsels strek van V circ (2 kpc) ∼ 20 tot 70 km ∕ s. Sterrestelsels aan die lae kant van hierdie reeks ly onder die probleem met massa-tekorte wat hierbo bespreek is. Vir hierdie uitskieters sal die vergelyking vererger deur die bydrae tot die baroniese bydrae te vererger. Aan die ander kant kan sterrestelsels aan die boonste punt van hierdie reeks ooreenstem met CDM-voorspellings sodra die bydrae tot die baronon ingesluit is [67]. Die verspreiding in die baryonverdeling speel egter 'n minder belangrike rol in die opwekking van die verspreiding in V sirkel (2 kpc) vir CDM-halo's, aangesien die ingeslote DM-massa in die skoot geneig is om te heers oor die baryonmassa.

Fig. 5. Links: Afgeleide sentrale kerndigtheid ρ 0 as 'n funksie van die maksimum waargeneemde rotasiesnelheid van sewe sterrestelsels met 'n lae oppervlak-helderheid. Elke simbool verteenwoordig 'n ander model vir die gevormde DM-halo-digtheidsprofiel. Vir 'n gegewe model is ρ 0 nie 'n konstante vir 'n vaste V max nie. Die klein grys simbole dui die resultate aan as 'n ster-massa-lig-verhouding nie-nul aanvaar word. Herdruk vanaf Verw. [68]. Regs: Die totale (gemiddelde) rotasiesnelheid gemeet teen 2 kpc teenoor die maksimum rotasiesnelheid vir waargenome sterrestelsels. Soliede swart lyn dui op CDM-voorspelling wat verwag word vir NFW-hale van gemiddelde konsentrasie. Dik rooi lyn toon die gemiddelde verband wat voorspel word in die kosmologiese hidrodinamiese simulasies [67], en die gekleurde areas toon die standaardafwyking. Gegewens saamgestel in [67].


26 Junie: Dark Matter: Nie soos die Luminiferous Ether nie

Beskrywing: Dark Matter is die geheimsinnige stof wat die grootste deel van die sterrestelsels en sterrestelsels uitmaak. Ons kan dit nie direk sien nie, ons sien dit net indirek as gevolg van die swaartekrag-effekte van sy teenwoordigheid op die sterre en die gas rondom dit, of op die lig wat daar naby gaan. Omdat dit so ontwykend is, wil baie mense instinktief die bewyse daarvoor verwerp. Inderdaad, dit word soms vergelyk met die gloeiende eter, 'n teorie uit die draai van die twintigste eeu wat uitgevind is om 'n skynbare verskil tussen Newton se meganika en ons teorie van elektromagnetisme te verklaar. Die gloeiende eter bestaan ​​nie, en die teenstrydighede is verklaar deur die bekendstelling van Einstein & # 8217s Special Relativity. Dark Matter is egter nie soos die ligter eter nie, en dit is nie net daar nie, want ons neem aan dat dit is, en omdat ons dit nodig het om verskille te verklaar. Ons het eerder direkte en positiewe bewyse dat dit bestaan.

Bio: Rob Knop het in 1997 'n PhD in Fisika aan Caltech behaal. Daarna werk hy saam met die Supernova Cosmology Project en was hy deel van die ontdekking dat die uitbreiding van die heelal versnel. Na ses jaar as assistent-professor aan die Vanderbilt Universiteit, het hy twee jaar in die rekenaarbedryf gewerk. Hierdie semester gaan hy fisika onderrig aan die Belmont Universiteit in Nashville, en volgende jaar sal hy by die nuwe kollege Quest Unviersity in British Columbia aansluit. Hy hou gereelde sterrekundepraatjies in Second Life in samewerking met die Meta-Instituut vir Berekeningssterrekunde.

Vandag se borg: & # 8220Tussen die tuiskoms van Hayabusa vanaf Itokawa en die Rosetta-vlieg van die asteroïde Lutetia, 13 Junie tot 10 Julie 2010, word hierdie episode van 365 Days of Astronomy anoniem geborg en gewy aan die nagedagtenis van Annie Cameron, ontwerper van die Tryphena Sun Wheel, Great Barrier Island, Nieu-Seeland, 'n projek wat nog moet begin. ”

Donker saak: nie soos die ligter eter nie

Ek is dr. Rob Knop. Die komende herfs sluit ek aan by die fakulteit van die Quest University in Squamish, British Columbia, waar ek fisika en verwante vakke gaan onderrig.

Donker materie. Dit is die geheimsinnige middel wat die grootste deel van sterrestelsels en sterrestelsels uitmaak. Ons kan dit nie direk sien nie. Dit straal nie lig uit nie, dus kan ons dit nie waarneem terwyl ons sterre waarneem nie. Dit absorbeer nie lig nie, dus kan ons dit nie eens waarneem soos ons stofwolke waarneem wat die lig van agtergrondsterre en newels blokkeer nie. Ons kan dit slegs indirek sien as gevolg van die swaartekrag-effekte van sy teenwoordigheid op die sterre en die gas rondom dit, of op die lig wat daar naby gaan. Omdat dit so ontwykend is, wil baie mense instinktief die bewyse daarvoor verwerp. & # 8220Astronome is besig om 'n sprokiesstof uit te vind om probleme in hul data te verklaar, & # 8221 sê hulle. & # 8220Hulle moet iets uitvind wat ons nie eens in beginsel kan sien om hul waarnemings by hul teorieë te pas nie. Waarom moet ons dit glo? & # 8221 Dit is 'n regverdige vraag, maar die waarheid is dat die bewyse vir Dark Matter vandag rotsvas is.

Dikwels, as ek openbare toesprake oor Dark Matter lewer, sal iemand dit vergelyk met die helder eter. Die implikasie van hierdie stelling is dat Dark Matter iets is wat ons uitgevind het, iets wat nie regtig is nie, om iets te verduidelik wat ons nie verstaan ​​nie. Trouens, Dark Matter is glad nie soos die ligter eter nie. Maar om u hiervan te oortuig, moet ek u eers vertel wat die ligter eter is.

Teen die einde van die 19de eeu het ons 'n volledige teorie van klassieke elektromagnetisme ontwikkel, opgesom in Maxwell & # 8217s Vergelykings. Hierdie teorie het beskryf hoe magnetiese en elektriese velde interaksie gehad het, en hoe dit met elektriese ladings en elektriese strome saamgewerk het. 'N Eenvoudige manipulasie van hierdie vergelykings voorspel die bestaan ​​van elektromagnetiese golwe, of lig & # 8211 lig is net 'n elektromagnetiese golf. Die vergelykings dui aan dat hierdie golwe teen 'n sekere snelheid, die ligspoed, beweeg. Die probleem is dat dit & # 8217; s nie duidelik uit die vergelykings wat die spoed is relatief tot.

Destyds het al die ander golwe waarmee fisici vertroud was, relatief tot 'n medium beweeg. Golwe op die oppervlak van die water beweeg relatief tot die water. Klankgolwe is drukgolwe in die lug wat relatief tot die lug beweeg. As daar wind in een rigting is, beweeg klankgolwe vinniger in daardie rigting as in die teenoorgestelde rigting, want hulle beweeg deur die lug. As die lug self beweeg, dra dit die klankgolwe saam. Met elektromagnetiese golwe was dit egter nie duidelik wat die golwe gewaai het nie. Wat was die medium waarin hierdie golwe bestaan ​​het? Om hierdie vraag te beantwoord, het fisici die ligter eter veronderstel. Dit was 'n medium wat deur die heelal deurgedring het, en dit was die medium wat gedink word dat liggolwe waai, net soos die oppervlak van die oseaan die medium is wat watergolwe waai.

Die ligter etherhipotese het toetsbare voorspellings gelewer. Spesifiek, as daar 'n medium in die heelal was waarteen die lig beweeg, sou ons ons eie beweging ten opsigte van die medium kon opspoor deur die snelheid van die lig in verskillende rigtings te vergelyk. As ons deur die eter beweeg, sal dit dieselfde wees as daar 'n eter & # 8220wind & # 8221 oor en deur die aarde waai. Die ligspoed in die rigting van hierdie wind sou vinniger wees as in ander rigtings. Dit is natuurlik heeltemal moontlik dat die aarde op die oomblik dat ons hierdie eksperiment gedoen het, rus sou hê ten opsigte van die eter, in welke geval die lig dieselfde spoed in alle rigtings sou hê. 'N Beter eksperiment sou wees om die spoed van lig in verskillende rigtings op verskillende tye gedurende die jaar te vergelyk. Soos die aarde om die son wentel, beweeg dit op verskillende tye gedurende die jaar in verskillende rigtings. As sodanig, as die aarde op 'n keer net in rus was met betrekking tot die eter, sou dit nie drie of ses maande later wees nie.

En so het fisici hierdie eksperiment uitgevoer, die beroemde Michaelson-Morley-eksperiment. Hierdie eksperiment het getoon dat lig in alle rigtings met dieselfde snelheid beweeg, ongeag wanneer u gedurende die jaar metings gedoen het. Dit was 'n eksperiment wat die voorspelling van die ligter eterhipotese weerspreek het. Ons moderne siening is nou die siening wat verskaf word deur Einstein & # 8217s Special Relativity, dat die snelheid van die lig in alle verwysingsraamwerke dieselfde is, en dat daar geen spesifieke medium is wat gewaai word nie, en dat liggolwe relatief tot beweeg. Die waai van lig is die waai van die elektromagnetiese velde self, en die feit dat elke waarnemer dieselfde snelheid vir hulle meet, het heelwat interessante gevolge.

Die ligter eter word aan die asblik van die geskiedenis oorgelaat. Dit was 'n onsigbare middel wat uitgevind is om dinge te verduidelik wat ons nie in ons fisika kon verstaan ​​nie. Die meganika van Newton het voorgestel dat u slegs 'n spoed kan spesifiseer as dit relatief tot 'n spesifieke verwysingsraamwerk is, en daarom het ons die eter uitgevind om die ding te wees waarmee hierdie spoed relatief was. Maar die eter bestaan ​​nie regtig nie, en die werklike antwoord is dat die meganika van Newton onvolledig is en deur Relativiteit aangepas moet word.

Laat ons terugkom na Dark Matter. Sterrekundiges weet sedert die middel van die twintigste eeu dat daar fout is met die dinamika van sterrestelsels en sterrestelsels. U kan die massa van 'n sterrestelsel skat deur al die & # 8220luminous & # 8221 materie op te meet, dit wil sê al die materie wat ons met teleskope kan opspoor. Dit sluit al die sterre en gas en stof in. Lichtstowwe hoef nie te gloei nie, want sterre kan ons ook atoomwaterstofgas met radioteleskope opspoor en byvoorbeeld geïoniseerde plasma met X-straalteleskope. As ons al die ligmassa in 'n sterrestelsel meet, kan ons uitvind hoe sterk swaartekrag in 'n sterrestelsel is. Ons kan ook meet hoe vinnig die sterre en gas in 'n sterrestelsel beweeg, of hoe vinnig individuele sterrestelsels binne 'n groep sterrestelsels beweeg. Die gevolg is dat dinge te vinnig beweeg vir hoeveel swaartekrag daar is! Hulle beweeg so vinnig dat sterrestelsels nie bymekaar gehou moet word nie, maar moet uitmekaar val. Sterrestelsels moet almal ongebonde wees, en die sterrestelsels moet almal uit die trosse vlieg. Tog neem ons sterrestelsels oral oor en waarneem ons sterrestelselshope oral, en dit is dus blykbaar stabiele voorwerpe.

Hierdie teenstrydigheid het gelei tot die hipotese van donker materie. As daar nie genoeg swaartekrag van die massa is wat ons kan sien om sterrestelsels bymekaar te hou nie, moet daar meer massa wees as wat ons kan sien. Daar was baie voorgestelde vorms van hierdie donker materie, maar die meeste daarvan kan as MACHO's en WIMP's saamgevat word. Nee, ek maak dit nie op nie, dit is regtig wat hulle genoem word. MACHO's, of & # 8220massiewe kompakte halo-voorwerpe & # 8221, is voorgestelde bruin dwerge, swart gate, baie dowwe sterre of ander stergrootte voorwerpe wat nie genoeg lig uitstraal om in ons begroting van massiewe voorwerpe ingesluit te word nie. Indirekte soektogte na MACHO's in ons eie sterrestelsel het getoon dat daar eenvoudig nie genoeg van hierdie onderliggende voorwerpe is om die nodige ontbrekende massa op te stel om sterrestelsels bymekaar te hou nie, dus is ons oor met WIMP's, of & # 8220swakly interacting massive deeltjies & # 8221 .

WIMP's is deeltjies soortgelyk aan neutrino's, wat massa het, maar wat nie via die elektromagnetiese krag interaksie het nie. As sodanig straal hulle nooit lig uit nie. Hulle sal dwarsdeur planete en sterre beweeg asof daar niks is nie. Hulle vorm 'n soort gas wat sterrestelsels deurdring en omring. Ons verstaan ​​vandag dat iets soos 90 persent van die massa sterrestelsels en sterrestelsels uit hierdie Dark Matter-deeltjies bestaan.

Maar hou vas, jy sê. U het net 'n eksotiese nuwe vorm van materie uitgevind, 'n vorm van materie wat ons nooit op aarde waargeneem het nie, ondanks al ons hoë energie deeltjiesversnellers, wat ons nie direk kan sien nie, as gevolg van 'n boekhoudfout tussen hoeveel swaartekrag u dink sterrestelsels het, en hoe vinnig sien jy dinge gaan. U mag vra, maak u nie dieselfde fout as wat met die ligter eter gemaak is nie?

Die antwoord is nee. In die eerste plek was die ligter eter nie 'n fout nie. Dit was 'n hipotese, 'n redelike hipotese, wat toetsbare voorspellings gemaak het. Hierdie voorspellings is getoets, en is nie geverifieer nie, dus weet ons dat die ligter eter nie werklik was nie. Dark Matter is anders. Die hipotese van 'n eksotiese donker saak wat nie bestaan ​​uit normale protone, neutrone en elektrone nie, maak ook toetsbare voorspellings. Hierdie voorspellings is getoets en is geverifieer. Dark Matter is eg.

Die oudste bewys van donker materie is die boekhoudfout tussen die snelhede van sterre in sterrestelsels en die hoeveelheid ligmassa. Dit kan ook verklaar word deur te sê dat ons nie regtig verstaan ​​hoe swaartekrag op die weegskaal van sterrestelsels werk nie, en dat hierdie boekhoudfout ons wys op 'n dieper en beter teorie van swaartekrag. Dark Matter maak egter ander voorspellings. Berekeninge van kernfusie in die vroeë heelal vertel ons byvoorbeeld wat die verhoudings van die ligte elemente in gaswolke moet wees wat nie deur stervorming besoedel word nie. Metings van die wolke het ons gewys dat daar nie genoeg baroniese materie kan wees nie, dit wil sê materie wat uit normale atome bestaan ​​en om die massa wat ons in die Heelal ken, op te maak. Die gevolgtrekking is dat die grootste deel van die heelal iets anders moet wees as baryoniese materie. Dit is 'n tweede bewysstuk wat dui op die realiteit van Dark Matter. 'N Derde is berekeninge van hoe die struktuur van die vroeë heelal tot vandag moet verander. Hierdie berekeninge kan die algemene verspreiding van materie op groot skale opmerklik goed weergee, maar slegs as ons 'n donker materie-komponent in die berekeninge insluit.

Miskien is die beste bewys vir Dark Matter as ons 'n voorwerp in die heelal kon vind waar die grootste deel van die massa nie was waar die grootste massa was nie. Dit sou 'n rookgeweer wees vir eksotiese donker materie, wat op sigself die bestaan ​​van Dark Matter & # 8217s bevestig, selfs sonder die veelvuldige ander redenasies wat ons daartoe lei om te aanvaar dat dit werklik is. Hierdie rookgeweer het met die Bullet Cluster in 2006 gekom. Twee trosse sterrestelsels het mekaar raakgeloop en deur mekaar geloop. Die meeste van die ligmassa en die massa wat bestaan ​​uit protone, neutrone en elektrone in sterrestelsels, is in die vorm van plasma tussen die sterrestelsels. Toe die twee trosse deur mekaar beweeg, het die plasma in die twee trosse interaksie gehad en in die middel van die stelsel vasgevang. Nie-baryoniese donker materie-deeltjies sal egter net vrylik langs mekaar stroom, soortgelyk aan wat gebeur as u twee handvol sand op mekaar gooi. X-straalwaarnemings van die Bullet Cluster toon die plasma wat in die middel van die cluster vasgevang is. Waarnemings van gravitasielensing van die lig van agtergrondstelsels toon egter aan dat die grootste deel van die massa van die trosse buite die middel is en vrylik deur mekaar geloop het. Wat ons het, is 'n situasie waar die grootste deel van die sterrestelsel nie die plek is waar die grootste massa is nie. Daarom het ons direkte bewyse vir Dark Matter. Dit is 'n eenvoudige voorspelling van die Dark Matter-hipotese wat deur eksperiment bevestig is.

Baie mense is filosofies ongemaklik met die idee dat die grootste deel van die massa in die heelal bestaan ​​uit dinge wat ons nooit direk gesien het nie, dinge waarvan die identiteit vir ons onbekend is. Die wetenskap het egter getoon dat Dark Matter, in teenstelling met die ligter eter, werklik is. Die ligter eter was 'n hipotese wat voorspellings gemaak het wat nie geverifieer is nie. Daar is baie bewyse wat dui op die realiteit van Dark Matter, en vandag weet ons ongetwyfeld dat Dark Matter bestaan.


"Die oerknal verdwyn" & # 8211 Wetenskaplikes betwyfel die bekendste wetenskaplike teorie sedert die relatiwiteit van Einstein

& # 8220Die Big Bang-teorie sê niks oor wat geklop het, waarom dit geklop het of wat gebeur het voordat dit geklop het nie. breukdeel van 'n sekonde na die oerknal.

Carl Sagan & # 8217s vrae

'As die algemene prentjie van 'n uitbreidende heelal en 'n oerknal korrek is,' het Carl Sagan gesê oor die beroemdste wetenskaplike teorie sedert Einstein se relatiwiteit, 'moet ons dan nog moeiliker vrae beantwoord. Hoe was toestande tydens die oerknal? Wat het voor dit gebeur? Was daar 'n klein heelal, sonder materie, en dan het die saak skielik uit niks geskep? Hoe gebeur dit? ”

Die Big Bang-teorie sê dat ons heelal ongeveer 14 miljard jaar gelede met 'n kolossale ontploffing begin het en sedertdien uitgebrei en verkoel het. Sterrekundiges kombineer wiskundige modelle met waarnemings om werkbare teorieë te ontwikkel oor hoe die heelal ontstaan ​​het, insluitend Albert Einstein se algemene relatiwiteitsteorie saam met standaardteorieë van fundamentele deeltjies. NASA-ruimtetuie soos die Hubble-ruimteteleskoop meet vandag steeds die uitbreiding van die heelal.

Gravitasiegolwe & # 8211 Reine data van die oerknal

Die vraag wat inflasie aangedryf het, is steeds onbeantwoord. 'N Probleem om hierdie vraag te beantwoord, sê NASA, is dat inflasie ver was voor rekombinasie, en die ondeursigtigheid van die heelal voor rekombinasie is dus 'n gordyn oor die interessante, baie vroeë gebeure. Gelukkig bied pas opgemerkte swaartekraggolwe deur die LIGO- en VIRGO-sterrewag 'n manier om die heelal waar te neem wat glad nie fotone insluit nie. Hierdie rimpelings in die ruimtetyd is die enigste bekende vorm van inligting wat ons onverstoord kan bereik vanaf die oomblik van die oerknal. Verskeie missies word deur NASA en ESA oorweeg om die swaartekraggolwe uit die tydperk van inflasie te soek.

Verskeie bekende wetenskaplikes meen egter dat die oerknal nooit gebeur het dat dit heeltemal verkeerd is nie en weerspreek word deur bewyse wat gelei het tot wat sommige as 'n 'kosmologiekrisis' beskou.

Betree Fred Hoyle & # 8211 “Die oerknal het nooit gebeur nie”

Die vroegste beroemdste kritikus van die Big Bang-teorie is die ikonoklastiese Britse astrofisikus, Fred Hoyle, wat die wetenskaplike was wat die teorie oor die oorsprong ons heelal en ons bestaan ​​as die "Big Bang" genoem het, wat hy in 1950 geskep het terwyl hy besig was om te doen. 'n reeks BBC-radiolesings oor sterrekunde toe hy gesê het: Een idee was dat die Heelal sy lewe 'n eindige tyd gelede in 'n enkele groot ontploffing begin het, en dat die huidige uitbreiding 'n oorblyfsel is van die geweld van hierdie ontploffing. Hierdie oerknal-idee het vir my onbevredigend gelyk, selfs voordat die uitvoerige ondersoek getoon het dat dit tot ernstige probleme lei. & # 8221

Hoyle, who studied at the University of Cambridge under physicist and Nobel laureate Paul Dirac, who predicted the existence of antimatter, moved rapidly to the forefront of astronomy, showing how nuclear physics could illuminate such celestial phenomena as white dwarfs, red giants, supernovae and the brilliant radio sources that came to be called quasars. Hoyle founded the prestigious Institute of Astronomy at Cambridge in the early 1960’s and served as its first director, yet his stubborn refusal to accept the big bang theory -made him persona non grata in the field he had helped to create.

Hoyle calculated that inside stars carbon would have to exist in a very special “steady state”: the 7.65 MeV state of carbon-12. Without it, nucleosynthesis could not proceed beyond a very simple stage. However, no one had ever observed carbon in this state. If the 7.65 MeV state did not exist, reports The Guardian, Hoyle reasoned, “the universe would contain no carbon. And if there was no carbon, there would be no human beings. Hoyle was saying that the mere fact he was alive and pondering the question of carbon was proof the 7.65 MeV state existed.”

“I began to get the sense that there was something seriously wrong, not only with these new concepts, but with the big bang itself,”
Hoyle said as he watched cosmologists in the 1980’s struggle to explain the formation of galaxies and other puzzles, “I’m a great believer that if you have a correct theory, you show a lot of positive results. It seems to me that they’d gone on for 20 years, by 1985, and there wasn’t much to show for it. And that couldn’t be the case if it was right.”

“Many Little Bangs in Pre-existing Space and Time”

“Rather than one big bang,” Hoyle said in a 2020 interview with John Horgan author of “The End of Science” for Scientific American, “there were many little bangs occurring in pre-existing space and time. These little bangs are responsible for light elements and the red shifts of galaxies. As for the cosmic microwave background, Hoyle’s best guess was that it is radiation emitted by some sort of metallic interstellar dust. Hoyle acknowledged that his “quasi-steady state theory,” which in effect replaces one big miracle with many little ones, is far from perfect. But he insisted that recent versions of the big bang theory, which posit the existence of inflation, dark matter and other exotica, are much more deeply flawed. ‘It’s like medieval theology,’ he exclaimed in a rare flash of anger.”

Will Cosmology Undergo a Paradigm Shift?

“Will cosmology undergo a paradigm shift that leaves the big bang behind?” asks Horgan. “Probably not. The theory rests on three solid pillars of evidence: the red shift of galaxies, the microwave background and the abundance of light elements, which were supposedly synthesized during our universe’s fiery birth. The big bang also does for cosmology what evolution does for biology: it provides cohesion, meaning, a unifying narrative. That is not to say that the big bang can explain everything, any more than evolutionary theory can. The origin of life remains profoundly mysterious, and so does the origin of the universe. Nor can physics tell us why our universe takes its specific form, which allowed for our existence.”

Enter Dark Energy

In the late 1990’s, writes Horgan, “ astrophysicists discovered that the universe is expanding at an increasing rate being driven by enigmatic dark energy. This is the most significant finding in cosmology—and arguably science as a whole—over the last 25 years. But the big bang theory has absorbed this finding, just as evolutionary theory absorbed the discovery of the double helix.”

“Dark energy is incredibly strange, but actually it makes sense to me that it went unnoticed,” said Noble Prize winning physicist Adam Riess about “dark energy,” a force that is real but eludes detection in an interview. “I have absolutely no clue what dark energy is. Dark energy appears strong enough to push the entire universe – yet its source is unknown, its location is unknown and its physics are highly speculative.”

Hoyle’s brilliant skepticism, has been reaffirmed as Eric Lerner, author of “The Big Bang Never Happened” and colleagues continue to publish articles refuting the Big Bang theory.

Famous Scientists –“Open Letter to the Scientific Community”

The “Open Letter to the Scientific Community” published in the May 2004 issue of New Scientist was signed by 35 astrophysicists and physicists –famous scientists who made major contributions to astrophysics and astronomy, such as Hermann Bondi, Thomas Gold and Jayant Narlikar–saying that the Big Bang theory had not been proven and that its predictions were contradicted by astronomical evidence.

“The big bang today relies on a growing number of hypothetical entities,” observes the Open Letter, “things that we have never observed– inflation, dark matter and dark energy are the most prominent examples. Without them, there would be a fatal contradiction between the observations made by astronomers and the predictions of the big bang theory. In no other field of physics would this continual recourse to new hypothetical objects be accepted as a way of bridging the gap between theory and observation. It would, at the least, raise serious questions about the validity of the underlying theory.”

“But the big bang theory can’t survive without these fudge factors. Without the hypothetical inflation field, the big bang does not predict the smooth, isotropic cosmic background radiation that is observed, because there would be no way for parts of the universe that are now more than a few degrees away in the sky to come to the same temperature and thus emit the same amount of microwave radiation.

“Without some kind of dark matter, unlike any that we have observed on Earth despite 20 years of experiments, big-bang theory makes contradictory predictions for the density of matter in the universe. Inflation requires a density 20 times larger than that implied by big bang nucleosynthesis, the theory’s explanation of the origin of the light elements. And without dark energy, the theory predicts that the universe is only about 8 billion years old, which is billions of years younger than the age of many stars in our galaxy.

“What is more, the big bang theory can boast of no quantitative predictions that have subsequently been validated by observation. The successes claimed by the theory’s supporters consist of its ability to retrospectively fit observations with a steadily increasing array of adjustable parameters, just as the old Earth-centered cosmology of Ptolemy needed layer upon layer of epicycles.

“Yet the big bang is not the only framework available for understanding the history of the universe,” the Open Letter concludes,. “Plasma cosmology and the steady-state model both hypothesize an evolving universe without beginning or end. These and other alternative approaches can also explain the basic phenomena of the cosmos, including the abundances of light elements, the generation of large-scale structure, the cosmic background radiation, and how the redshift of far-away galaxies increases with distance. They have even predicted new phenomena that were subsequently observed, something the big bang has failed to do.”

Thomas Gold, one of the signers, believed with Hoyle that there was reason to think that the creation of matter was “done all the time and then none of the problems about fleeting moments arise. It can be just in a steady state with the expansion taking things apart as fast as new matter comes into being and condenses into new galaxies”.

Two papers were published in 1948 discussing the “steady-state theory” as an alternative to the Big Bang: one by Gold and Bondi, the other by Hoyle. In their seminal paper, Gold and Bondi asserted that although the universe is expanding, it nevertheless does not change its look over time it has no beginning and no end. Since then, over 200 additional astronomers and physicists have added their signatures to the Open Letter.

In an Nov 12, 2020 interview with Jonathan Tennenbaum for Asia Times, Eric Lerner says “I’ve just submitted to a peer-reviewed journal, we look at 18 large, independent data sets of observations, and in 17 of these, the predictions of the Big Bang theory are clearly contradicted by the data.

Lerner starts his book “The Big Bang Never Happened” with the “errors” that he thinks invalidate the Big Bang. These are
The existence of superclusters of galaxies and structures like the “Great Wall” which would take too long to form from the “perfectly homogeneous” Big Bang The need for dark matter and observations showing no dark matter the FIRAS CMB spectrum is a “too perfect” blackbody –a physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence.

“For example, the universe contains objects that are 10 times older than when the Big Bang was supposed to have happened. The Big Bang’s predictions of the distribution of the light elements in the Universe are completely wrong – orders of magnitude wrong.
The Big Bang’s predictions of the distribution of the light elements in the Universe are completely wrong – orders of magnitude wrong. The Big Bang theory’s predictions concerning the cosmic microwave background have multiple contradictions, as do the theory’s predictions concerning so-called inflation and dark energy.

“You need – with one exception – gravitation, electromagnetism, nuclear forces and nuclear reactions: things that we have studied here on Earth,” says Tennenbaum . “You can get rid of so-called cosmic inflation, you can get rid of dark energy, you can get rid of the expanding universe. You can get rid of dark matter and just throw them into the dustbin of history. The only exception is the one that Edwin Hubble pointed out one hundred years ago, namely the red shift — the shift of the observed spectrum of light from astronomical objects toward longer wavelengths – that is, lower photon energies – which is conventionally explained in terms of the so-called Doppler effect, by assuming that those objects are moving away from us. The red shift appears to be larger, the more distant the object.

“In 1929, Edwin Hubble discovered that the universe is expanding, with most other galaxies moving away from us. Light from these galaxies is shifted to longer (further away and redder) wavelengths – in other words, it is red-shifted, a result of the expansion of the universe. The Big Bang theorists take the red shift measurements as decisive evidence that distant galaxies are moving away from us, and that the Universe itself is expanding.

:Expansion is only one specific explanation of the red shift relationship. But in science, just to give an explanation for something is not enough. The validity of an explanation of a theory needs to be tested by its predictions – by comparing its predictions with subsequent observations.

The point is, apart from the red shift, says Lerner, the expansion theory makes many other predictions. The key observational data set that I and my colleagues concentrated on over the course of a long period from 2005 to 2018 – and the results were published in peer-reviewed journals, including the Monthly Notices of the Royal Astronomical Society in 2018 – deals with surface brightness. And, as I mentioned, for these and 16 other data sets, the predictions of the Big Bang theory turn out to be all wrong.

“So what I’m saying,” concludes Lerner,” is that the crisis in cosmology has reached a point where the alternative to the Big Bang is, quite simply, no Big Bang – no Bang at all.”


Observations challenge cosmological theories

Recent observations create a puzzle for astrophysicists: since the big bang, fewer galaxy clusters have formed over time than was actually expected. Physicists from the university of Bonn have now confirmed this phenomenon. For the next three years, the researchers will analyze their data in even greater detail. This will put them in a position to confirm whether the theories considered valid today need to be reworked. The study is part of a series of 20 publications which appear in the journal Sterrekunde en astrofisika.

Nearly 13.8 billion years ago, the big bang marked the beginning of our universe. It created space and time, but also all the matter of which our universe consists today. From then on, space expanded at a terrifying rate and so did the diffuse fog in which the matter was nearly evenly distributed.

But not completely: at some places the fog was a little bit denser than in others. As a result, these regions exerted a slightly stronger gravitational pull and slowly attracted material from their surroundings. Over time, matter concentrated more and more within these condensation points. At the same time, the space between them gradually became emptier. Over 13 billion years, this resulted in the formation of a sponge-like structure: big "holes" devoid of matter, separated by small areas within which thousands of galaxies agglomerate -- the galaxy clusters.

Six parameters explain the whole universe

The standard model of cosmology describes this history of the universe, from the first seconds after the big bang to the current day. The beauty of it: the model manages to explain, with only six parameters, everything we know today about the birth and evolution of the Universe. Nonetheless, the model may now have reached its limits. "New observational evidences point to the fact that the matter is distributed today in a different way than the theory predicts," explains Dr. Florian Pacaud from the Argelander-Institut für Astronomie of the University of Bonn.

It all started with the measurements of the Planck satellite, which was launched by the European Space Agency (ESA) to measure the cosmic background radiation. This radiation is, to some extent, an afterglow of the big bang. It conveys crucial information on the matter distribution in the early universe showing the distribution as it was only 380.000 years after the big bang.

According to the Planck measurements, this initial distribution was such that, over cosmic time, more galaxy clusters should have formed than we observe today. "We have measured with an X-ray satellite the number of galaxy clusters at different distances from ourselves," explains Dr. Pacaud. The idea behind it: the light from remote galaxy clusters has traveled for billions of years before reaching us, and so we observe them today as they were when the universe was still young. Nearby clusters, on the contrary, are observed as they appeared much more recently.

"Our measurements confirm that the clusters formed too slowly," said Dr. Pacaud. "We have estimated to which extent this result conflicts with the basic predictions of the standard model." While there is a large discrepancy between the measurements and predictions, the statistical uncertainty in the present study is not yet tight enough to really put into question the theory. However, the researchers expect to obtain substantially more constraining results from the same project within the next three years. This will finally reveal whether the standard model needs to be revised.

The dark energy -- a constant?

The study also supplies a glimpse into the nature of the dark energy. This mysterious constituent of the Universe acts as a kind of interstellar baking powder which cause the cosmic expansion to accelerate. The "amount" of dark energy -- the cosmological constant -- should have stayed the same since the big bang or so assumes the standard model of cosmology. Many observations seem to point in this direction. "Our measurement also supports this thesis," explains Dr. Pacaud. "But here again we shall obtain more precise results in a near future."

The study is a part of a large-scale project with the appropriate name of 'XXL Survey', in which more than 100 scientists all around the globe cooperate. The 20 new publications from the collaboration, gathered in a special issue of Sterrekunde & astrofisika , only provide a taste of the project's full power. The current analysis is based on a sample of 365 clusters, from which (so far) only 200 are used for the statistical analyses. By the end of the project -- planed for 2020 -- this database will double to some 400 to 500 clusters.


Astronomy and particle physics race to replace Standard Model

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Deel hierdie verhaal

If energy issues seem to be attracting the attention of a lot of physicists, the Large Hadron Collider seems to be drawing the attention of many of the rest of them, including people in fields like cosmology, which deals with items on the opposite end of the size scale. In turn, the people working on the LHC and other particle detectors are carefully paying attention to the latest astronomy results, hoping they'll put limits on the properties and identities of the zoo of theoretical particles that need to be considered.

There are two reasons for this newfound unity in physics. If cosmology has become a part of elementary particle physics, as Nobel Laureate George Smoot put it at the Lindau Meeting, it's because we've found that "it's a continuum from quantum mechanics to clumps of matter to galaxies." The properties of the tiniest particles should dictate what the Universe looks like, but all the cosmological data is telling us there must be something in addition to what we know about, dark matter particles that we haven't yet identified.

The second issue is that we know the Standard Model, which describes the properties of these particles, is wrong, but we're not sure what to replace it with yet, and it's entirely possible that astronomy and cosmology will provide key insights into this process.

The Lindau meeting featured an all-star panel that ran through some of the evidence that we could be on the verge of finding something big, in a discussion entitled "Dark Matter, Dark Energy, and the LHC." Smoot and his co-laureate John Mather, who won for the Cosmic Background Explorer, were joined by physicists David Gross, Carlo Rubbia, Gerard t'Hooft, and Martinus Veltman.

From particles to the Universe

The cosmologists kicked things off by discussing the evidence for dark matter. Smoot described how cosmologists can model a universe with dark matter, gas, photons, and neutrinos initially clumped, and observe how they spread. These models provide some specific predictions about things like the cosmic microwave background and other properties we can observe, with an accuracy of about one percent. And they give us a Universe that's only about 27 percent matter, most of it dark, along with lots of dark energy, which is pushing the Universe apart at an expanding pace

Nobody has a clue what dark energy might be, but dark matter is really coming in to its own. Saying, "I'm a measuring kind of guy," Mather discussed some of the ways that astronomers were pinning down the properties of dark matter. These include detailed measurements of some aspects of the cosmic microwave background left over from the Big Bang, and large-scale surveys of gravitational lensing, which will produce data on the quantity and distribution of dark matter. Mather also suggested that we can read the temperatures of X-ray emitting gas clouds, and this will let us weigh the galaxy clusters that hold the gas in place, providing an independent measure.

Initial attempts at most of these have already been done, which is what gives us a lot of our confidence in the existence of dark matter. But Mather also suggested it may be time to try a more exotic search, one for early-generation stars that lived unusually long because dark matter annihilations within the stars have prevented their gravitational collapse.

David Gross highlighted some confusing astronomical data that indicates an excess of gamma rays that may be the product of dark matter annihilations. Some studies haven't seen this, and the ones that have suggest very different dark matter properties. Nevertheless, Gross was optimistic we'd have that sorted out within a decade.

He was also convinced that there's something there to sort out, saying that astronomers had convinced him that not only does it exist, but it takes the form of weakly interacting massive particles, or WIMPs (Weakly Interacting Massive Particles).

The only one who appeared not to be convinced was Veltman, who called dark matter "bullsh*t," and said he thought highly of an alternative called MOND (Modified Newtonian Dynamics). As the rest of the panel tried to find out why, it became clear that Veltman had stopped paying attention to the field about five years ago, and wasn't up on the latest data. At this point, Gross described the bullet cluster as a clear demonstration of dark matter, while Rubbia referred to data related to the production of matter during the Big Bang the panel eventually moved on.

What is this dark stuff, anyway?

So, if almost everyone is convinced that dark matter exists, what is it? The term WIMP could cover a lot of ground. Rubbia mentioned one possible WIMP: sterile neutrinos, a heavy version of the three familiar flavors of this particle. Rubbia said some of the recent results, like strange antineutrino masses and the confirmation of flavor oscillations have gotten a lot of people excited about the prospects of discovering a sterile neutrino.

The biggest problem is that there are no sterile neutrinos in the Standard Model. That in itself isn't so much of a problem evidence has been piling up from these and other experiments that indicate that the Standard Model isn't a complete description of particle physics. But that also means that we've got no clear idea of what to replace it with, all of which makes predicting the precise properties of a sterile neutrino rather challenging. That, in turn, makes creating a detector to pick one up very challenging.

The other big alternative source of dark matter comes via supersymmetry, which postulates another complete set of particles that match the quarks, leptons, etc. that we already know about (it's a bit like having a full set of anti-particles, without the annihilation-upon-contact aspect). The symmetry works for particle identity, but breaks down for mass the supersymmetric particles are much heavier than their regular counterparts, and that heft places the lightest supersymmetric particle right in the range expected for dark matter.

Some forms of supersymmetry could handle a number of other issues with the standard model and observational astronomy, but we'll go over those in more detail once we start our coverage of our visit to the LHC.

Fortunately, these heavy particles (assuming they are WIMPs) are well within the energy reached by the LHC, and they're obviously stable, since they seem to have lasted the lifetime of the Universe. So, if they exist, we should be able to detect them as they carry mass and energy away from collisions.

Taking odds on what we're going to see

With the possibilities laid out, the panel spent some time discussing what they felt were the likely outcomes from the experiments in the works. Gross said that he thinks we'll get a dark matter candidate particle before we know whether it's supersymmetric if we somehow stumble onto supersymmetry first, then we'll have a dark matter candidate by default. t'Hooft mentioned it was possible that all the supersymmetric particles would require higher energies, but suggested the theorists who like the concept will go on quite happily, and wait for the next accelerator.

Veltman suggested the chances of seeing the Higgs boson, another target of the LHC, "are minimal" given the current data. Cryptically, he also suggested that we might see something that looks a lot like a Higgs, but isn't.

Rubbia felt the same way about the quark-gluon plasma that the LHC will produce by colliding lead ions. Scientists at Brookhaven's RHIC have claimed to produce a quark-gluon plasma that behaves as a perfect liquid and, although Rubbia called this work "beautiful," he felt that the material being observed had been misidentified. After RHIC's work, he now thinks that the LHC won't reach sufficient energies to make what he'd consider the real plasma.

Will the LHC spot evidence of extra dimensions required by string theory? Not according to Peter Gross, who termed it "an act of desperation" to need so many possible models before we can get them to spit out something that looks like our Universe, with all the fundamental physical constants having the right values.

A specific constant—Einstein's cosmological one, which could explain dark energy—is also bugging a lot of people. The current estimates for the cosmological constant are all very small, almost (but not quite) zero. t'Hooft (and others) seems to think it would be more satisfying if it were simply zero, or a large enough number that it might be easier to find a relationship between it and some other constants.

In fact, t'Hooft suggested that the LHC will make our current list of fundamental constants much larger, and that it will take theorists many years to start reducing that list to a manageable number. But, he added, the more unexplained constants you have, the more interesting it should be.


Are there predictions of the distribution of matter at the end of time - Astronomy

These various questions fall into the areas of cosmological parameter estimation (Hubble constant, matter density, dark energy density, etc.), dark matter searches, early universe model building (inflationary theory, theories of dark energy, string cosmology).

What are the new frontiers?

  • Struktuurvorming
    What is the (statistical and precise) distribution of structure today and how is it evolving? On large scales, on small scales? Are there simple ways to characterize and understand the emergence of regular structures and regularity from the complexity due to gravitational collapse?
  • Galaxy properties
    Can we extend our understanding of what matter is doing to an understanding of what luminous (more often observed) matter is doing? Dark matter halos can be reliably simulated using numerical simulations of dark matter and gravity only, and galaxies populate these halos often in a many to one manner. How do they do so and what galaxy properties determine the association to the host dark matter halos (collapse time, recent merger activity)?
  • Galaxy formation
    How do galaxies form? What is the role of black hole growth and quasar activity in the history of galaxies? How do objects at high redshift evolve into those we see today what are the progenitors of today's galaxies of different sorts, of clusters? How did the history of galaxies affect their surroundings (injecting metals, for instance)?
  • Reionization
    How and when did the first luminous objects form and how did reionization occur? What is the respective role of stars and quasars in producing ionizing photons? Were there early supermassive stars (PopIII) and if so, when did they stop forming and what happened at the end of their lifetimes?

Measurements addressing these questions also can shed light on cosmological parameters, etc., and vice versa. Different theories (e.g. different types of matter) predict different results for each of the properties above, and different cosmological histories.

    The expansion of the universe can be studied by measuring redshifts of cepheids, just as Hubble did in the 1920's. The cepheids fluctuate in luminosity on a time scale related to their luminosity. Knowing their absolute luminosity allows one to calculate their distance. The Hubble Space Telescope has a Key Project to measure the Hubble Constant H0. An introduction can be found in this Scientific American article by W. Freedman. Also, some recent review articles are at this link, here and here (a recent workshop summary). (Hubble diagram taken from this paper.)


Jill Tarter: Alien tracker

Humans have wondered since the beginning of time whether anyone else is out there. For astronomer Jill Tarter, this question spawned a career. Like Ellie Arroway, the heroine of Carl Sagan’s 1985 novel “Contact,” Tarter devoted decades to scanning the heavens for life in the field known as SETI, the search for extraterrestrial intelligence, including a stint as director of the Center for SETI Research at the SETI Institute. In fact, Jodie Foster consulted with her during filming of the movie version of "Contact.” Now retired, Tarter never made contact with any non-earthlings, but her passion and dedication for using scientific methods and pioneering technology to find them has helped push our search for cosmic neighbors out of the realm of quackery and into the realm of respectability, and even possibility.


Kyk die video: Bongkar pasang bushing racksteer tanpa harus buka roda, penyebab bunyi tak-tak (November 2022).