When was the big bang

By mass, hydrogen was 75 percent of the early universe's matter, and helium was 25 percent. The abundance of helium is a key prediction of big bang theory, and it's been confirmed by scientific observations.

Despite having atomic nuclei, the young universe was still too hot for electrons to settle in around them to form stable atoms. The universe's matter remained an electrically charged fog that was so dense, light had a hard time bouncing its way through.

It would take another , years or so for the universe to cool down enough for neutral atoms to form—a pivotal moment called recombination. The cooler universe made it transparent for the first time, which let the photons rattling around within it finally zip through unimpeded.

We still see this primordial afterglow today as cosmic microwave background radiation , which is found throughout the universe. The radiation is similar to that used to transmit TV signals via antennae. But it is the oldest radiation known and may hold many secrets about the universe's earliest moments. There wasn't a single star in the universe until about million years after the big bang. It took that long for gravity to gather clouds of hydrogen and forge them into stars.

Many physicists think that vast clouds of dark matter , a still-unknown material that outweighs visible matter by more than five to one, provided a gravitational scaffold for the first galaxies and stars. Once the universe's first stars ignited , the light they unleashed packed enough punch to once again strip electrons from neutral atoms, a key chapter of the universe called reionization. In the billions of years since, stars, galaxies, and clusters of galaxies have formed and re-formed—eventually yielding our home galaxy, the Milky Way, and our cosmic home, the solar system.

Even now the universe is expanding , and to astronomers' surprise, the pace of expansion is accelerating. It's thought that this acceleration is driven by a force that repels gravity called dark energy.

Dark matter makes up another 27 percent. In essence, all the matter you've ever seen—from your first love to the stars overhead—makes up less than five percent of the universe. All rights reserved. Origins of the Universe Aftermath of cosmic inflation As time passed and matter cooled, more diverse kinds of particles began to form, and they eventually condensed into the stars and galaxies of our present universe. Nature - Bowman et al. Share Tweet Email. Why it's so hard to treat pain in infants.

This wild African cat has adapted to life in a big city. Animals Wild Cities This wild African cat has adapted to life in a big city Caracals have learned to hunt around the urban edges of Cape Town, though the predator faces many threats, such as getting hit by cars.

India bets its energy future on solar—in ways both small and big. The two groups each published papers in the Astrophysical Journal in Because we can't see it directly, scientists have been trying to figure out how to "see" the Big Bang through other measures.

In one case, cosmologists are pressing rewind to reach the first instant after the Big Bang by simulating 4, versions of the current universe on a massive supercomputer. With what is known about the universe today, the researchers on this study compared their understanding of how gravitational forces interacted in the primordial universe with their thousands of computer-modeled universes. If they could predict the starting conditions of their virtual universes, they hoped to be able to accurately predict what our own universe may have looked like back at the beginning.

In a study, researchers did so by investigating the split between matter and antimatter. In the study, not yet peer-reviewed, they proposed that the imbalance in the amount of matter and antimatter in the universe is related to the universe's vast quantities of dark matter, an unknown substance that exerts influence over gravity and yet doesn't interact with light.

They suggested that in the crucial moments immediately after the Big Bang, the universe may have been pushed to make more matter than its inverse, antimatter, which then could have led to the formation of dark matter. Read more: What came before the Big Bang?

The CMB has been observed by many researchers now and with many spacecraft missions. Planck's observations, first released in , mapped the CMB in unprecedented detail and revealed that the universe was older than previously thought: The research observatory's mission is ongoing and new maps of the CMB are released periodically.

Related: How old is the universe? The maps give rise to new mysteries, however, such as why the Southern Hemisphere appears slightly redder warmer than the Northern Hemisphere. Examining the CMB also gives astronomers clues as to the composition of the universe. Researchers think most of the cosmos is made up of matter and energy that cannot be "sensed" with our conventional instruments, leading to the names "dark matter" and "dark energy.

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 , 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. 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 , produced a theorized barely-detectable polarization, one type of which is called "B-modes. 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 , 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 As LIGO becomes more sensitive, it is anticipated that discovering black hole-related gravitational waves will be a fairly frequent event.

The universe is not only expanding, but expanding faster. In this idea, prior to the Big Bang, there was another universe, identical to this one but with entropy increasing toward the past instead of toward the future. Increasing entropy, or increasing disorder in a system, is essentially the arrow of time, Carroll said, so in this mirror universe , time would run opposite to time in the modern universe and our universe would be in the past.

Proponents of this theory also suggest that other properties of the universe would be flip-flopped in this mirror universe. For example, physicist David Sloan wrote in the University of Oxford Science Blog , asymmetries in molecules and ions called chiralities would be in opposite orientations to what they are in our universe.

A related theory holds that the Big Bang wasn't the beginning of everything, but rather a moment in time when the universe switched from a period of contraction to a period of expansion. This "Big Bounce" notion suggests that there could be infinite Big Bangs as the universe expands, contracts and expands again.

The problem with these ideas, Carroll said, is that there's no explanation for why or how an expanding universe would contract and return to a low-entropy state. Carroll and his colleague Jennifer Chen have their own pre-Big Bang vision.

In , the physicists suggested that perhaps the universe as we know it is the offspring of a parent universe from which a bit of space-time has ripped off.

It's like a radioactive nucleus decaying, Carroll said: When a nucleus decays, it spits out an alpha or beta particle. The parent universe could do the same thing, except instead of particles, it spits out baby universes, perhaps infinitely. These baby universes are "literally parallel universes ," Carroll said, and don't interact with or influence one another. If that all sounds rather trippy, it is — because scientists don't yet have a way to peer back to even the instant of the Big Bang, much less what came before it.