What was the Big Bang?
The Big Bang Theory is the leading explanation for how the universe began. Simply put, it says the universe as we know it started with an infinitely hot and dense single point that inflated and stretched — first at unimaginable speeds, and then at a more measurable rate — over the next 13.8 billion years to the still-expanding cosmos that we know today.
Existing technology doesn't yet allow astronomers to literally peer back at the universe's birth, much of what we understand about the Big Bang comes from mathematical formulas and models. Astronomers can, however, see the "echo" of the expansion through a phenomenon known as the cosmic microwave background.
Around 13.7 billion years ago, everything in the entire universe was condensed in an infinitesimally small singularity, a point of infinite denseness and heat.
Suddenly, an explosive expansion began, ballooning our universe outwards faster than the speed of light. This was a period of cosmic inflation that lasted mere fractions of a second — about 10^-32 of a second, according to physicist Alan Guth’s 1980 theory that changed the way we think about the Big Bang forever.
When cosmic inflation came to a sudden and still-mysterious end, the more classic descriptions of the Big Bang took hold. A flood of matter and radiation, known as “reheating,” began populating our universe with the stuff we know today: particles, atoms, the stuff that would become stars and galaxies and so on.
This all happened within just the first second after the universe began, when the temperature of everything was still insanely hot, at about 10 billion degrees Fahrenheit (5.5 billion Celsius), according to NASA
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. The cosmos now contained a vast array of fundamental particles such as neutrons, electrons and protons — the raw materials that would become the building blocks for everything that exists today.
This early "soup" would have been impossible to actually see because it couldn't hold visible light. "The free electrons would have caused light (photons) to scatter the way sunlight scatters from the water droplets in clouds," NASA stated. Over time, however, these free electrons met up with nuclei and created neutral atoms, or atoms with equal positive and negative electric charges.
This allowed light to finally shine through, about 380,000 years after the Big Bang.
Sometimes called the "afterglow" of the Big Bang, this light is more properly known as the cosmic microwave background (CMB). It was first predicted by Ralph Alpher and other scientists in 1948 but was found only by accident almost 20 years later.
This accidental discovery happened when Arno Penzias and Robert Wilson, both of Bell Telephone Laboratories in New Jersey, were building a radio receiver in 1965 and picked up higher-than-expected temperatures, according to NASA
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. At first, they thought the anomaly was due to pigeons trying to roost inside the antenna and their waste, but they cleaned up the mess and killed the pigeons
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and the anomaly persisted.
Simultaneously, a Princeton University team led by Robert Dicke was trying to find evidence of the CMB and realized that Penzias and Wilson had stumbled upon it with their strange observations. The two groups each published papers in the Astrophysical Journal in 1965.
OBSERVING GRAVITATIONAL WAVES
While astronomers study the universe's beginnings through creative measures and mathematical simulations, they've also been seeking out proof of its rapid inflation. They have done this by studying gravitational waves
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, tiny perturbations in space-time that ripple outwards from great disturbances like, for instance, two black holes colliding, or the birth of the universe.
According to leading theories, in the first second after the universe was born, our cosmos ballooned faster than the speed of light
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. (That, by the way, does not violate Albert Einstein's speed limit. He once said that light speed is the fastest anything can travel within the universe — but that statement did not apply to the inflation of the universe itself.)
As the universe expanded, it created the CMB and a similar "background noise" made up of gravitational waves that, like the CMB, were a sort of static, detectable from all parts of the sky. Those gravitational waves, according to the LIGO Scientific Collaboration
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, produced a theorized barely-detectable polarization, one type of which is called "B-modes."
In 2014, astronomers said they had found evidence of B-modes
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using an Antarctic telescope called "Background Imaging of Cosmic Extragalactic Polarization," or BICEP 2 .
"We're very confident that the signal that we're seeing is real, and it's on the sky," lead researcher John Kovac, of the Harvard-Smithsonian Center for Astrophysics, told Space.com in March 2014.
But by June, the same team said that their findings could have been altered by galactic dust getting in the way of their field of view. That hypothesis was supported by new results from the Planck satellite.
By January 2015, researchers from both teams working together "confirmed that the Bicep signal was mostly, if not all, stardust," the New York Times said.
However, since then gravitational waves have not only been confirmed to exist, they have been observed multiple times.
These waves, which are not B-modes from the birth of the universe but rather from more recent collisions of black holes, have been detected multiple times by the Laser Interferometer Gravitational-Wave Observatory.
(LIGO), with the first-ever gravitational wave detection taking place in 2016. As LIGO becomes more sensitive, it is anticipated that discovering black hole-related gravitational waves will be a fairly frequent event.
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