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A 2013 bản đồ of the background radiation left over from the Big Bang, taken by the ESA"s Planông xã, captured the oldest light in the universe. This information helps astronomers determine the age of the universe.(Image credit: ESA and the Planông xã Collaboration.)
The Big Bang Theory is the leading explanation about how the universe began. At its simplest, it says the universe as we know it started with an infinitely hot, infinitely dense singularity, then inflated — first at unimaginable speed, & then at a more measurable rate — over the next 13.8 billion years lớn the cosmos that we know today.

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Because current instruments don"t allow astronomers khổng lồ literally peer back at the universe"s birth, much of what we understand about the Big Bang Theory comes from mathematical formulas and models. Astronomers can, however, see the "echo" of the expansion through a phenomenon known as the cosmic microwave sầu background.

While the majority of the astronomical community accepts the theory, there are some theorists who have alternative explanations besides the Big Bang — such as eternal inflation or an oscillating universe.

The phrase "Big Bang Theory" has been popular amuốn astrophysicists for decades, but it hit the mainstream in 2007 when a comedy show with the same name premiered on CBS. The show followed the home page and academic life of several researchers, including physicists, an astrophysicist và an engineer, và ended in 2019.

The first second, và the birth of light

Around 13.7 billion years ago, everything we know of was an infinitesimally small singularity, a point of infinite denseness và infinite heat. Then, 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 khổng lồ 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 & radiation, known as “reheating,” began the process of populating our universe with the stuff we know today -- particles, atoms, stars, galaxies và so on.

This was all still within the first second after the universe began, when the temperature of everything was about 10 billion degrees Fahrenheit (5.5 billion Celsius), according khổng lồ NASA. The cosmos now contained a vast array of fundamental particles such as neutrons, electrons and protons -- the eventual building blocks or raw material for everything we see today.

This early soup would have been impossible to lớn look at, because light could not carry inside of it. "The không tính tiền electrons would have sầu caused light (photons) lớn scatter the way sunlight scatters from the water droplets in clouds," NASA stated. Over time, however, the miễn phí electrons met up with nuclei and created neutral atoms. This allowed light to 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 & other scientists in 1948, but was found only by accident almost 20 years later.

Related: Images: Peering baông chồng lớn the Big Bang & early universe

Arno Penzias và Robert Wilson, both of Bell Telephone Laboratories in Murray Hill, New Jersey, were building a radio receiver in 1965 and picking up higher-than-expected temperatures, according lớn NASA. At first, they thought the anomaly was due to pigeons và their dung, but even after they cleaned up the mess and killed the pigeons that tried to roost inside the antenna, the anomaly persisted.

Simultaneously, a Princeton University team (led by Robert Dicke) was trying khổng lồ find evidence of the CMB, & realized that Penzias và Wilson had stumbled upon it. The two groups each published papers in the Astrophysical Journal in 1965.

Reconstructing the universe"s baby pictures

In one case, cosmologists are pressing rewind khổng lồ reach the first instant after the Big Bang by simulating 4,000 versions of the current universe on a massive sầu supercomputer.

"We are trying lớn do something like guessing a baby phokhổng lồ of our universe from the lademo picture," study leader Masakhổng lồ Shirasaki, a cosmologist at the National Astronomical Observatory of nhật bản (NAOJ), wrote in an tin nhắn lớn Live Science.

With information about the universe as we know it today, the researchers on this 2021 study worked khổng lồ compare their understanding of how gravitational forces interacted in the primordial universe with their thousands of computer-modeled universes. If they could successfully predict the starting conditions of their virtual universes, they could have sầu more trust in their ability to predict what our own universe looked lượt thích baông xã at the beginning.

Other researchers choose a different path to lớn interrogate our universe"s beginnings, investigating the split between matter và antimatter. One 20đôi mươi study, not yet peer-reviewed, proposed that the imbalance in amount of matter và antimatter is related to lớn the universe"s vast quantities of dark matter, an unknown substance that exerts influence over gravity & yet doesn"t interact with light. Crucial moments after the Big Bang may have sầu "kicked" the universe inkhổng lồ making more matter than its inverse, antimatter, which then could have sầu led khổng lồ the formation of dark matter.

Read more: What came before the Big Bang?

The age of the universe

Artist"s impression of the European Agency"s Planông xã Planck"s main goal is lớn study the Cosmic Microwave Background — the relic radiation left over from the Big Bang. (Image credit: ESA/C. Carreau)

The cosmic microwave background has been observed on many missions. One of the most famous missions was NASA"s Cosmic Background Explorer (COBE) satellite, which mapped the sky in the 1990s.

Several other missions have sầu followed in COBE"s footsteps, such as the BOOMERanG experiment (Balloon Observations of Millimetric Extragalactic Radiation & Geophysics), NASA"s Wilkinson Microwave Anisotropy Probe (WMAP) and the European Agency"s Planông xã satellite.

Planck"s observations, first released in 2013, mapped the background in unprecedented detail và revealed that the universe was older than previously thought: 13.82 billion years old, rather than 13.7 billion years old. The retìm kiếm observatory"s mission is ongoing & new maps of the CMB are released periodically.

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Related: How old is the universe?

The maps give sầu rise to new mysteries, however, such as why the Southern Hemisphere appears slightly redder (warmer) than the Northern Hemisphere. The Big Bang Theory says that the CMB would be mostly the same, no matter where you look.

Examining the CMB also gives astronomers clues as khổng lồ the composition of the universe. Researchers think most of the cosmos is made up of matter và energy that cannot be "sensed" with our conventional instruments, leading lớn the names "dark matter" & "dark energy." Only 5% of the universe is made up of matter such as planets, stars và galaxies.

Faint signals of the universe"s inflation

While astronomers could see the universe"s beginnings, they"ve also been seeking out proof of its rapid inflation using gravitational waves, tiny perturbations in that ripple outwards from great disturbances like, for instance, two blachồng holes colliding, or the birth of the universe.

Theory says that in the first second after the universe was born, our cosmos ballooned faster than the speed of light. (That, by the way, does not violate Albert Einstein"s tốc độ limit. He once said that light tốc độ is the fasthử nghiệm anything can travel within the universe — but that statement did not apply khổng lồ the inflation of the universe itself.)

As the universe expanded, it created the CMB & a similar "background noise" made up of gravitational waves that, lượt thích the CMB, should be a sort of static detectable from all parts of the sky. Those gravitational waves, according to the LIGO Scientific Collaboration, produced a theorized barely-detectable polarization, one type of which is called "B-modes."

In năm trước, astronomers said they had found evidence of B-modes using an Antarctic telescope called "Background Imaging of Cosmic Extragalactic Polarization," or BICEP2.

"We"re very confident that the signal that we"re seeing is real, & it"s on the sky," lead researcher John Kovac, of the Harvard-Smithsonian Center for Astrophysics, told in March năm trước.

But by June, the same team said that their findings could have sầu 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 năm ngoái, researchers from both teams working together "confirmed that the Bicep signal was mostly, if not all, stardust," the New York Times said.

This graphic shows a timeline of the universe based on the Big Bang theory and inflation models. (Image credit: NASA/WMAP)

Gravitational waves have sầu now been confirmed to exist, however. These waves, which are not B-modes from the birth of the universe but rather from more recent collisions of blaông chồng holes, have sầu been detected multiple times by the laze Interferometer Gravitational-Wave sầu Observatory (LIGO) since 2016. As LIGO becomes more sensitive sầu, it is anticipated that discovering black hole-related gravitational waves will be a fairly frequent event.

Faster inflation, multiverses and charting the start

The universe is not only expanding, but expanding faster. This means that with time, notoàn thân will be able khổng lồ spot other galaxies from Earth, or any other vantage point within our galaxy.

"We will see distant galaxies moving away from us, but their tốc độ is increasing with time," Harvard University astronomer Avi Loeb said in a March 2014 article.

"So, if you wait long enough, eventually, a distant galaxy will reach the tốc độ of light. What that means is that even light won"t be able khổng lồ bridge the gap that"s being opened between that galaxy and us. There"s no way for extraterrestrials on that galaxy to communicate with us, lớn skết thúc any signals that will reach us, once their galaxy is moving faster than light relative to us."

Related: Big Bang Theory: 5 weird facts about seeing the universe"s birth

Some physicists also suggest that the universe we experience is just one of many. In the "multiverse" Mã Sản Phẩm, different universes would coexist with each other like bubbles lying side by side. The theory suggests that in that first big push of inflation, different parts of grew at different rates. This could have sầu carved off different sections — different universes — with potentially different laws of physics.

"It"s hard khổng lồ build models of inflation that don"t lead to lớn a multiverse," Alan Guth, a theoretical physicist at the Massachusetts Institute of Technology, said during a news conference in March 2014 concerning the gravitational waves discovery. (Guth is not affiliated with that study.)

"It"s not impossible, so I think there"s still certainly research that needs to lớn be done. But most models of inflation vị lead to lớn a multiverse, and evidence for inflation will be pushing us in the direction of taking multiverse seriously."

While we can understand how the universe we see came khổng lồ be, it"s possible that the Big Bang was not the first inflationary period the universe experienced. Some scientists believe sầu we live in a cosmos that goes through regular cycles of inflation & deflation, and that we just happen to lớn be living in one of these phases.

The Big Bang Theory: making scientific theory a household phrase

From left, characters Howard, Leonard, Penny, Sheldon và Raj from the CBS show "The Big Bang Theory." (Image credit: CBS)

Running for 279 episodes over 12 seasons, the CBS show "The Big Bang Theory" followed a group of scientists — originally, all physicists, astrophysicists & engineers. The show explores the group"s nerdy friendships, romances and squabbles in Pasadena, California. Its first season premiered on Sept. 24, 2007 and the show officially ended on May 16, 2019.

Although the show itself didn"t delve sầu inkhổng lồ much of the physics behind the big bang theory itself, the showrunners did hire UCLA astrophysicist David Saltzberg as a science consultant for the entire run of the show, according to lớn Science magazine. That meant that science jargon, frequently tossed around in the show"s opening scenes & sprinkled through the characters" lives, was reviewed by an actual scientist. Because the characters are immersed in academia, Saltzberg told Science, that added to lớn the realistic portrayal of their lives.

In addition, thanks to Saltzberg, the whiteboards in the background of labs, offices và apartments throughout the show were filled with a variety of cutting-edge & sometimes newsworthy equations và information. Over the course of the show, Saltzberg said, those whiteboards became coveted as researchers sent hlặng new work that they hoped might be featured there. In one episode, Saltzberg recalled, new evidence of gravitational waves was scrawled across a whiteboard that ostensibly belonged lớn famed physicist Steven Hawking, who also approved the text.


The show took some liberties with making up some new scientific concepts, and with the politics of Nobel prizes & academia, according to Fermilab physicist Don Lincoln. But in the over, Lincoln said, the thing that rang least true khổng lồ hyên ổn was the scene where characters were given plane tickets to visit another lab not in coach seats, where many real-life scientists scrunch up their legs, but in Economy Plus.

Related: How "The Big Bang Theory" sent Howard Wolowitz khổng lồ

Notably, several characters in the series take trips. One episode sees main characters Leonard, Sheldon, Raj và Howard phối out on a retìm kiếm expedition to the Arctic — many physics experiments are best performed at or near the extreme environments of the poles. Another put engineer Howard on a Russian Soyuz &, later, a mã sản phẩm of the the International Station along with real-life astronaut Mike Massimino.

Additional resources

This article was updated on May 17, 2021 by contributor Vicky Stein.

Elizabeth Howell is a contributing writer for who is one of the few Canadian journalists khổng lồ report regularly on exploration. She is the author or co-author of several books on exploration. Elizabeth holds a Ph.D. from the University of North Dakota in Studies, & an M.Sc. from the same department. She also holds a bachelor of journalism degree from Carleton University in Canada, where she began her career in 2004. Besides writing, Elizabeth teaches communications at the university & community college cấp độ, & for government training schools. To see her latest projects, follow Elizabeth on Twitter at

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