Hundreds of thousands of years later, electrons stuck to the nuclei to make complete atoms. About a billion years after the Big Bang, gravity caused these atoms to gather in huge clouds of gas, forming collections of stars known as galaxies. Gravity is the force that pulls any objects with mass towards one another -- the same force, for example, that causes a ball thrown in the air to fall to the earth. Where do planets like earth come from? Over billions of years, stars "cook" hydrogen and helium atoms in their hot cores to make heavier elements like carbon and oxygen. Large stars explode over time, blasting these elements into space.
This matter then condenses into the stars, planets, and satellites that make up solar systems like our own. How do we know the Big Bang happened? Astrophysicists have uncovered a great deal of compelling evidence over the past hundred years to support the Big Bang theory.
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Among this evidence is the observation that the universe is expanding. By looking at light emitted by distant galaxies, scientists have found that these galaxies are rapidly moving away from our galaxy, the Milky Way. An explosion like the Big Bang, which sent matter flying outward from a point, explains this observation.
Did you know that the static on your television is caused by radiation left over from the Big Bang? Another critical discovery was the observation of low levels of microwaves throughout space.
What caused the Big Bang? -- ScienceDaily
Even with all that energy in such a small space, however, we didn't collapse into a black hole. Instead, the Universe expanded at a rapid rate that balanced the energy density so precisely that, for all of our measured cosmic history, we've walked that fine line between expanding and recollapsing. Today, all we can see within the Universe extends for some 46 billion light-years in all directions, and scientists can trace this origin back to a hot, dense, more uniform and more rapidly expanding state. Like many theorists, you might be tempted to extrapolate this back even farther, to an arbitrarily hot and dense state: a singularity.
But that temptation is the root of most of our misunderstandings surrounding the birth of the Universe. The Big Bang wasn't the beginning, after all. Instead, that honor goes to cosmic inflation, and everyone should understand why. The Universe doesn't just expand uniformly, but has tiny density imperfections within it, which Adding density inhomogeneities on top of a homogeneous background is the starting point for understanding what the Universe looks like today.
When we look out at the Universe today, we see a number of observable facts that cry out for an explanation. They include:. Remarkably, one framework is consistent with each and every one of these observations: the Big Bang. Galaxies comparable to the present-day Milky Way are numerous, but younger galaxies that are Milky For the first galaxies of all, this ought to be taken to the extreme, and remains valid as far back as we've ever seen.
It takes cosmic timescales for the structure of the Universe to form and build itself up to what we see today. According to the big idea of the Big Bang, the Universe was hotter, denser, and more uniform in the past, and that it evolved into what it is today by expanding, cooling, and gravitating to form a great cosmic web.
The fabric of space itself expands as time goes on, as the laws of General Relativity demand for a Universe that's filled with roughly equal amounts of matter and energy in all directions and locations, causing the wavelengths of photons to stretch, the kinetic energy of massive particles to decrease, and enabling gravitational imperfections to steadily grow.
According to the original observations of Penzias and Wilson, the galactic plane emitted some The temperature and spectrum of this radiation has now been measured, and the agreement with the Big Bang's predictions are extraordinary. If we could see microwave light with our eyes, the entire night sky would look like the green oval shown. That last discovery pretty much killed every one of the Big Bang's alternatives, and installed the Big Bang as the cosmic origin story for everything within our observable Universe.
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The Universe emerged from this early hot, dense, and uniform state, and over time it expanded and cooled. About 1 second after the Big Bang, neutrinos and antineutrinos "freeze out," meaning their energy-dependent interaction rates drop to such a low frequency that they effectively never interact again. And as we move forward, nuclear reactions occur and then cease; neutral atoms stably form, releasing that primeval radiation; gravitational imperfections grow on progressively larger and larger scales, leading to the formation of the first stars, then galaxies, and then the enormous cosmic web.
The stars and galaxies we see today didn't always exist, and the farther back we go, the closer to However, there is a limit to that extrapolation, as going all the way back to a singularity creates puzzles we cannot answer.
If you extrapolate the expanding and cooling Universe all the way back as far as theoretical physics allows you to go, you'll come to an event in the past known as a singularity. Big-bang model.
What Is The Big Bang?
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