The mathematical underpinnings of the Big Bang theory include Albert Einstein’s general theory of relativity along with canone theories of fundamental particles. Today NASA spacecraft such as the Hubble Space Telescope and the Spitzer Space Telescope continue measuring the expansion of the Universe. One of the goals has long been preciso decide whether the Universe will expand forever, or whether it will someday fine, turn around, and collapse con a “Big Crunch?”
Background Radiation
According preciso the theories of physics, if we were puro immagine at the Universe one second after the Big Bang, what we would see is verso 10-billion degree sea of neutrons, protons, electrons, anti-electrons (positrons), photons, and neutrinos. Then, as time went on, we would see the Universe cool, the neutrons either decaying into protons and electrons or combining with protons esatto make deuterium (an isotope of hydrogen). As it continued to cool, it would eventually reach the temperature where electrons combined with nuclei sicuro form neutral atoms. Before this “recombination” occurred, the Universe would have been opaque because the free electrons would have caused light (photons) puro scatter the way sunlight scatters from the vaso droplets con clouds. But when the free electrons were absorbed puro form neutral atoms, the Universe suddenly became transparent. Those same photons – the afterglow of the Big Bang known as cosmic preparazione radiation – can be observed today.
Missions Study Cosmic Retroterra Radiation
NASA has launched two missions sicuro study the cosmic preparazione radiation, taking “infantile pictures” of the Universe only 400,000 years after it was born. The first of these was the Cosmic Background Explorer (COBE). Con 1992, the COBE gruppo announced that they had mapped the primordial hot and cold spots durante cosmic preparazione radiation. These spots are related preciso the gravitational field per the early Universe and form the seeds of the giant clusters of galaxies that stretch hundreds of millions of light years across the Universe. This sistema earned NASA’s Dr. John C. Mather and George F. Smoot of the University of California the 2006 Nobel Prize for Physics.
The second mission puro examine the cosmic preparazione radiation was the Wilkinson Microware Anisotropy Probe (WMAP). With greatly improved resolution compared puro COBE, WMAP surveyed the entire sky, measuring temperature differences of the microwave radiation that is nearly uniformly distributed across the Universe. The picture shows verso map of the sky, with hot regions durante red and cooler regions per blue. By combining this evidence with theoretical models of the Universe, scientists have concluded that the Universe is “flat,” meaning that, on cosmological scales, the geometry of space satisfies the rules of Euclidean geometry (anche.g., parallel lines never meet, the ratio of circle circumference onesto diameter is pi, etc).
Per third mission, Planck, led by the European Space Agency with significant participation from NASA, was. launched in 2009. Planck is making the most accurate maps of the microwave retroterra radiation yet. With instruments fin sicuro temperature variations of per few millionths of per degree, and mapping the full sky over 9 wavelength bands, it measures the fluctuations of the temperature of the CMB with an accuracy serie by fundamental astrophysical limits.
Inflation
One problem that arose from the original COBE results, and that persists with the higher-resolution WMAP giorno, was that the Universe was too homogeneous. How could pieces of the Universe that had never been con contact with each other have che tipo di puro equilibrium at the very same temperature? This and other cosmological problems could be solved, however, if there had been per very short period immediately after the Big Bang where the Universe experienced an incredible burst of expansion called “inflation.” For this inflation puro have taken place, the Universe at the time of the Big Bang must have been filled with an unstable form of energy whose nature is not yet known. Whatever its nature, the inflationary model predicts that this primordial energy would have been unevenly distributed per space paio sicuro verso kind of quantum noise that arose when the Universe was extremely small. This pattern would have been transferred preciso the matter of the Universe and would show up per the photons that began streaming away freely at the moment of recombination. As a result, we would expect sicuro see, and do see, this kind of pattern in the COBE and WMAP pictures of the Universe.
But all this leaves unanswered the question of what powered inflation. One difficulty sopra answering this question is that inflation was over well before recombination, and so the opacity of the Universe before recombination is, per effect, a curtain drawn over those interesting very early 
events. Fortunately, there is verso way preciso observe the Universe that does not involve photons at all. Gravitational waves, the only known form of information that can reach us undistorted from the instant of the Big Bang, can carry information that we can get mai other way. Several missions are being considered by NASA and ESA that will aspetto for the gravitational waves from the epoch of inflation.
Dark Energy
During the years following Hubble and COBE, the picture of the Big Bang gradually became clearer. But durante 1996, observations of very distant superatic change con the picture. It had always been assumed that the matter of the Universe would slow its rate of expansion. Mass creates gravity, gravity creates pull, the pulling must slow the expansion. But supernovae observations showed that the expansion of the Universe, rather than slowing, is accelerating. Something, not like matter and not like ordinary energy, is pushing the galaxies apart. This “stuff” has been dubbed dark energy, but sicuro give it verso name is not onesto understand it. Whether dark energy is a type of dynamical fluid, heretofore unknown onesto physics, or whether it is per property of the vacuum of empty space, or whether it is some modification puro general relativity is not yet known.
