![]() ![]() The Big Bang is the theory we have constructed for how the universe we see around us came to be. Why is this distinction important? It’s important because, although science has been able to establish a history of the universe right back to when that tiny point suddenly created our entire cosmos, what preceded it, the reason for that tiny point of energy being there in the first place, is unknown, and may forever be unknowable. Rather, it was the event that gave birth to the universe. In that sense, the Big Bang was not the event that caused our universe. Now let’s pause a moment, so that we might draw a distinction between the appearance of all that energy in the Big Bang and its sudden expansion. But it is not without problems as with all scientific theories, the Lambda-CDM model continues to evolve. It makes predictions repeatedly confirmed by observation. The Lambda-CDM model has been spectacularly successful at explaining what we observe in the universe. The Lambda-CDM model further states that the universe is expanding at a rate referred to as Lambda (the Greek letter) and is governed by the principles of Einstein’s General Relativity. the matter that makes up everything we see – galaxies, stars, planets, people), 27% cold dark matter (hence the “CDM” of the theory’s name) and 68% dark energy. has zero curvature) and is made up of 5% baryons (i.e. It postulates that our universe began at a specific instant, expanded to be flat (i.e. How could it be otherwise? The current version of Big Bang theory – the one used most by modern cosmologists – is called the Lambda-CDM model. ![]() The galaxy is ablaze with bright, young, blue stars, but looks red in this image because its light has been stretched to longer spectral wavelengths by the expansion of the universe. Galaxy GN-z11, shown in the inset, is seen as it was 13.4 billion years in the past, just 400 million years after the Big Bang, when the universe was only 3% of its current age. Here’s another exceedingly distant (and therefore old) object, captured by the Hubble Space Telescope in 2016. Image via NASA/ ESA/ Garth Illingworth/ Rychard Bouwens/ the HUDF09 Team/ Wikimedia Commons. This object has a redshift of z~10, meaning that it existed some 480 million years after the Big Bang. The Hubble Space Telescope captured this image of an exceedingly distant galaxy called UDFj-39546284. The first stars sparkled into life, cosmologists believe, about 250 million years after the Big Bang, and the first galaxies shortly after that. Before that, the universe was simply too hot and too energetic to let atomic nuclei capture electrons. The first atoms are thought to have formed when the universe was around 400,000 years old. In the view of modern cosmologists, matter and space and time all began when that microscopic point suddenly expanded violently and exponentially. And it’s not just matter that was born in the Big Bang. It’s hard to fathom that, at the moment of the Big Bang, all of the energy in the universe – some of which would later become galaxies, stars, planets and human beings – was concentrated into a tiny point, smaller than the nucleus of an atom. You might know most cosmologists believe it occurred some 13.8 billion years ago. ![]() You’ve probably heard of the Big Bang as the event that gave rise to our universe. More recently, the expansion has begun to speed up again as the repulsive effects of dark energy have come to dominate the expansion of the universe. For the next several billion years, the expansion of the universe gradually slowed down as the matter in the universe pulled on itself via gravity. The far left depicts the earliest moment we can probe so far, when a period of cosmic inflation produced a burst of exponential growth in the universe. Timeline of the universe, from Big Bang to present day. ![]()
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