MAP-prvi rezultati

[zupan]

Satelit MAP je objavil prve rezultate!!!
glej linke:
http://physicsweb.org/article/news/7/2/4

Ancient radiation sheds new light on the universe
11 February 2003

NASA today unveiled the first detailed full-sky map of the cosmic microwave background, the microwave "echo" of the Big Bang. Scientists created the map using data collected by the Wilkinson Microwave Anisotropy Probe satellite (WMAP) over a 12-month period. The results provide further support for the inflationary Big Bang model of the universe and reveal when the first generation of stars was created.

The photons in the cosmic microwave background were created in the Big Bang and then continually scattered by free electrons in the early universe. They were released when the universe had expanded and cooled enough to allow these electrons to combine with protons and form hydrogen atoms. The properties of the photons - which have been stretched to microwave wavelengths by the expansion of the universe -- can therefore be used to study the universe at this "time of last scattering".

A number of experiments have been carried out on the ground and in balloons to study the tiny temperature fluctuations in the microwave background caused by variations in the density of the early universe. WMAP, however, has been able to study these fluctuations in far more detail. And unlike previous experiments, it can record images of the microwave background across the whole sky.

"We've captured the infant universe in sharp focus, and from this portrait we can now describe the universe with unprecedented accuracy," says WMAP Principal Investigator Charles L. Bennett of the Goddard Space Flight Center. "The data are solid, a real gold mine."

The data indicate that the time of last scattering occurred about 380,000 years after the Big Bang and that the Universe is now 13.7 billion years old, give or take 1%. They also reveal that the earliest stars in the universe were created just 200 million years after the Big Bang.

In addition, the results support the idea that the universe underwent a period of rapid expansion when it was very young and that its geometry is flat. The data show that 4% of the universe is ordinary matter, 23% dark matter and 73% dark energy. The NASA researchers say that this dark energy is more likely to resemble Einstein's "cosmological constant" than a negative-pressure energy field called "quintessence", but they do not rule out quintessence.

WMAP is named in honour of David Wilkinson of Princeton University, a project team member who died in September last year. The satellite was launched in June 2001 and now orbits the Lagrange Point, a million miles from Earth. It will continue to observe the cosmic microwave background for another three years.

Author
Edwin Cartlidge is News Editor of Physics World

Ali pa osebne impresije Johna Bahcalla z Advanced Study Institute na Princetonu
http://www.sns.ias.edu/~jnb/

Remarks at the Wilkinson MAP press conference: 02/11/03
by John Bahcall, Institute for Advanced Study, Princeton, NJ

Every astronomer will remember where he or she was when they first heard the WMAP results. I certainly will.
For cosmology, the formal announcement today represents a `rite of passage’ from speculation to precision science.
I am thrilled by the precision of the results we have just heard from Chuck and David.
However, I am astounded by what they mean. Before WMAP, astronomers had assembled an implausible model of the universe with a little bit of ordinary matter; a significant portion of dark matter (whatever that is); and a whole lot of dark energy (another strange beast). I confess; I was skeptical.
But, the WMAP measurements convinced me. The error bars are tiny. There are multiple, redundant checks on the experiment.
The way the world is, is the way WMAP sees the world. We will have to understand this universe. We have no choice.
A natural question, given so many important measurements by WMAP, is: What is the most revolutionary result? In my opinion, the most revolutionary result is that there are no revolutionary results. WMAP has confirmed with exquisite precision the crazy and unlikely scenario that astronomers and physicists cooked up based upon incomplete evidence. Incredibly, everybody got it essentially right.
Lets consider a human analogy to try to appreciate better what WMAP has achieved.
Suppose we equate a 50-year-old man to the current universe, then the analogy is correct if the epoch that is studied by WMAP is a newly born baby, only 12 hours old. . The WMAP scientists have measured for the infant universe the total body weight, the length of the legs, the size of the ears, and the amount of hair
What the WMAP scientists have done is the equivalent of a doctor using the results of an annual physical checkup to infer correctly the detailed physical characteristics of the same individual when he was only 12 hours old.
I have distinguished colleagues, historians, who argue with great erudition about what events occurred a thousand or two thousand years ago. The WMAP results prove that astronomers and physicists know what happened in a broad sense in the universe almost 14 billion years ago.
For me, the bottom line of today’s announcement is that we live in a crazy universe whose defining behavior we know precisely for the last 14 billion years.
The WMAP achievement makes me proud to be an astrophysicist.

Homepage MAP-a je
http://map.gsfc.nasa.gov/

[saso]

V zadnjem času naj bi bil največji dosežek znanosti doslej najboljša in najnatančnejša fotografija začetkov vesolja, ki so jo posneli s sondo WMAP (Wilkinson Microwave Anisotropy Probe). Kdo je organiziral projekt WMAP in za kaj natančno sondo uporabljajo?
Projekt so organizirali v okviru NASE in še nekaterih ameriških univerz. Sonda WMAP kroži po krožnici okoli Zemlje, kjer nabira svetlobo iz vesolja. V vesolje so jo poslali, ker je tam veliko manj motenj pri nabiranju svetlobe oziroma podatkov. Za podatke, ki so jih objavili zdaj, je sonda neprestano nabirala svetlobo eno celo leto, potem pa so podatke znanstveniki še pol leta analizirali. Napovedujejo, da bodo imeli čez eno leto nov paket podatkov, ki bodo še izboljšali rezultate, ki so jih dobili zdaj.

Ali sonda zbira podatke na splošno ali ima specializirane naloge?
Zbira samo svetlobo neke specifične valovne dolžine, ker je ta svetloba najstarejša v vesolju in z njeno pomočjo lahko dobijo znanstveniki veliko informacij o tem, kakšno je bilo vesolje včasih in na splošno o modelu vesolja. Ti podatki so tako pomembni za astronomijo, da se jim je splačalo poslati specializirano sondo in mislim, da ta celo ni edina - poslali so še druge, ki podobno zbirajo svetlobo, da bodo lahko podatke primerjali.

Kaj ta fotografija "začetkov vesolja" prikazuje?
Na splošno bi lahko rekli, da fotografija predstavlja prstni odtis vesolja. Ko gledamo nebo, pravzaprav gledamo svetlobo, ki prihaja iz vesolja in hkrati gledamo nazaj v čas. Svetloba ima namreč zelo veliko hitrost, ki pa ni neskončna, zato že z Lune rabi eno sekundo, da pride do Zemlje, od Sonca potuje svetloba osem minut, od prve zvezde pa do Zemlje svetloba pride šele v štirih letih. Bolj ko gledamo globoko v vesolje, dlje v preteklost gledamo. Obstaja pa neka meja v vesolju, prek katere ne moremo več gledati nazaj v preteklost. Ker se vesolje širi, to pomeni, da je bilo nekoč tudi zelo majhno in tudi zelo vroče. Ko je bilo vesolje v neki točki v preteklosti zelo vroče, ni bilo več prepustno za svetlobo, v vesolju je bila neke vrste megla. Slika, ki jo je posnela sonda WMAP, pa prihaja ravno iz tistega trenutka vesolja, ko je to postalo prosojno, tik za &meglo&.

Potem to pravzaprav ni fotografija začetka vesolja velikega poka?
Slika prikazuje vesolje, staro 380.000 let. Če primerjamo starost današnjega vesolja s starostjo človeka pri petdesetih letih, to pomeni, da ta slika prikazuje vesolje, ko je bilo "staro" dvanajst ur. Zdaj pa ocenjujejo, da je vesolje staro 13.7 milijarde let.

Kaj natančno predstavljajo različne barve na tej fotografiji?
Osrednji rdeči pas je svetloba, ki prihaja iz naše galaksije. Mi smo znotraj galaksije in pogled ven v vesolje je podoben, kot da bi gledali iz krožnika. Male razlike v barvah so male razlike v temperaturi svetlobe, ki prihaja iz preteklosti. Te male razlike nosijo veliko informacij o tem, kakšno je bilo vesolje nekoč. Podobne slike so posneli že prej z nekim drugim satelitom, a je bila ločljivost tako slaba, da znanstveniki niso mogli vedeti, koliko je napaka same meritve in koliko je uporabnih podatkov. Te male razlike v temperaturi so neke vrste prstni odtis vesolja in iz teh meritev lahko teoretiki, ki računajo razne modele vesolja in predvidijo kakšen odtis bi določen model dal, zelo natančno izberejo pravega kandidata za model vesolja - kakšna je njegova sestava, starost in podobne stvari.

Ali je zdaj teorija velikega poka glede teorij o začetku vesolja dokončno uveljavljena v znanstvenih krogih ali se še vedno pojavljajo druge teorije?
Mislim, da je to dokaj splošno sprejeta teorija. Ob objavi teh zadnjih podatkov, so tudi dvomljivci, ki niso verjeli prejšnjim slikam vesolja, sprejeli razne čudne napovedi tega teoretskega modela, ki se sklada z najnovejšo sliko, in pravi, da je v vesolju le štiri odstotke atomov oziroma navadne snovi.

Na podlagi slik WMAP-a so izračunali, da je vsebina vesolja sestavljena le iz 4 odstotkov atomov (navadne snovi), 23 odstotkov neznane temne snovi in 73 odstotkov skrivnostne temne energije. Kakšne so domneve o tej neznani temni snovi in skrivnostni temni energiji?
Skrivnostna je zato, ker ima fizika svoj standardni model osnovnih delcev, ki pojasnjuje, kako se vsa znana snov obnaša. Te temne snovi in energije, ki po zadnjih meritvah predstavljajo več kot 90 odstotkov vsega v vesolju, pa se kot vse kaže ne da spraviti v noben predalček v tem modelu. Tu je težava - imamo zelo natančne podatke o tem, da temna energija in snov obstajata, ne vemo pa prav dobro, kaj bi to lahko bilo. Podatke o obstoju temne snovi in energije so počasi nabirali že kar nekaj let. Ker temna snov sama ne sveti, se jo lahko opazuje samo kot učinek na vidno snov, torej posredno. Ko so na primer opazovali nekatere galaksije, so ugotovili, da se vrtijo veliko hitreje, kot bi se v primeru, če bi bila tam samo tista snov, ki jo lahko vidimo. Sklepali so, da je okoli galaksij še nek halo temne snovi. Veliko vprašanje je seveda, kaj ta temna snov in energija sta. Obstaja veliko teorij, a še nobena ni prevladala. Ravno s pomočjo slik satelita WMAP so zelo natančno izmerili, koliko je v vesolju procentualno določene snovi. Prej je bilo tudi glede tega med kozmologi veliko skepse.

Kam bodo sedaj na podlagi podatkov satelita WMAP peljale astronomske raziskave?
Prihaja obdobje, ko kozmologija postaja zelo natančna znanost. Dolgo so bili kozmologi bolj teoretiki, ki so stvari napovedovali bolj na splošno. Sedaj pa smo dobili konkretne empirične podatke, ki se jih da natančno obdelati in tukaj je zelo velik preskok. Naslednja faza bo zbiranje še več podatkov in še bolj natančno določanje kozmoloških modelov.